Vmax running on 3 (or 2??) cylinders

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propwash

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Hello friends.

Before I describe my issue I will add disclaimer I am extremely non-tech so pardon my rather layman (and lame) attempt of an explanation here…

So I’ve got a 99 vmax in pristine condition, about 2 months ago. (Many thanks to a local member who gave the bike a once-over and the thumbs up to take the plunge)

Overall runs well…except in one aspect. When starting up, it will run on 2-3 cylinders. It will run very sluggishly, acceleration reminding me of my old Honda 125, even with aggressive throttling. Then after about 5m, the other cylinder kicks in and it will run normally after that (I assume effect of warming up…or caffeine kicking in) There’s no “pattern” to this, some days I’m blessed with a normally running motor, other days it will act up and take a few mins to run smoothly. This evening however, it would not smoothen out from my ride from work to home - I was on the road for over 10m…and nothing. :bang head:

In addition, when under this condition, idle is very very slow. Maybe 1/2 RPM as standard idle. It takes careful acceleration for it not to die when giving it gas (floods out)

It’s quite clear it’s got some carb or jetting gremlins. I will be taking it to a shop - no chance in hell I’m doing anything myself (no tools or knowhow), but I figure if someone here knows the symptoms it will be easier to describe to the tech. After all, by the time I get to the shop it will probably be running on all 4. I regularly add SeaFoam to the fuel but it appears to have no effect here.

Finally, I recorded a quick vid - mostly to show the low RPM at idle. I gave her some acceleration but without benchmarking this video with one where it runs normally, it’s hard to compare. Still, figured this video would help back up my case.

https://youtu.be/SpI4ulkTMGs
 

vwaxxed

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Sounds like it is probably time to yank the carbs off and go through them. Be careful where you take them, a lot of people miss the setup on these. I just had a guy pay $400 to a shop that "specialized in vintage motorcycles" and they were way off. He shipped them to me to go through and i couldn't believe how bad they were lol.
 

93max

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Sounds like it is probably time to yank the carbs off and go through them. Be careful where you take them, a lot of people miss the setup on these. I just had a guy pay $400 to a shop that "specialized in vintage motorcycles" and they were way off. He shipped them to me to go through and i couldn't believe how bad they were lol.
This is true!
My son brought his cb750 thats having issues with one cylinder.
I guess he "missed" the needle jet was MISSING on the cylinder in question.
We don't know for sure yet if that was the issue as it hasn't arrived yet but sure would explain the black plug!
Left pic missing rt pic what's SUPPOSED to be there!
 

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93max

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Sounds like it is probably time to yank the carbs off and go through them. Be careful where you take them, a lot of people miss the setup on these. I just had a guy pay $400 to a shop that "specialized in vintage motorcycles" and they were way off. He shipped them to me to go through and i couldn't believe how bad they were lol.
This is true!
My son brought his cb750 thats having issues with one cylinder to a "guy".
I guess he "missed" the needle jet was MISSING on the cylinder in question.
We don't know for sure yet if that was the issue as it hasn't arrived yet but sure would explain the black plug!
Left pic missing rt pic what's SUPPOSED to be there!
 

Joe Planter

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Hello friends.

Before I describe my issue I will add disclaimer I am extremely non-tech so pardon my rather layman (and lame) attempt of an explanation here…

So I’ve got a 99 vmax in pristine condition, about 2 months ago. (Many thanks to a local member who gave the bike a once-over and the thumbs up to take the plunge)

Overall runs well…except in one aspect. When starting up, it will run on 2-3 cylinders. It will run very sluggishly, acceleration reminding me of my old Honda 125, even with aggressive throttling. Then after about 5m, the other cylinder kicks in and it will run normally after that (I assume effect of warming up…or caffeine kicking in) There’s no “pattern” to this, some days I’m blessed with a normally running motor, other days it will act up and take a few mins to run smoothly. This evening however, it would not smoothen out from my ride from work to home - I was on the road for over 10m…and nothing. :bang head:

In addition, when under this condition, idle is very very slow. Maybe 1/2 RPM as standard idle. It takes careful acceleration for it not to die when giving it gas (floods out)

It’s quite clear it’s got some carb or jetting gremlins. I will be taking it to a shop - no chance in hell I’m doing anything myself (no tools or knowhow), but I figure if someone here knows the symptoms it will be easier to describe to the tech. After all, by the time I get to the shop it will probably be running on all 4. I regularly add SeaFoam to the fuel but it appears to have no effect here.

Finally, I recorded a quick vid - mostly to show the low RPM at idle. I gave her some acceleration but without benchmarking this video with one where it runs normally, it’s hard to compare. Still, figured this video would help back up my case.

Hey man so I watched your YouTube video I’ve been having the exact same issue with mine. I’ve taken my carbs apart countless times, cleaned them, rebuilt them, synced them. Nothing seems to work. I’m thinking it may be my battery of all things but I don’t know. What did you end up finding out? My bike literally does the EXACT same things in the video. Even sounds the same because I have cobras as well. Please help
 

Fire-medic

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If you put your location under your screen name, you may-be able to get assistance from someone local to you. What year is your bike?

I am the person to whom this member turned for a look at the bike he was considering to purchase. He was buying it at the shop owned by someone I've known for a long time. The bike sat in their inventory for months. The shop mechanic had-to rebuild the carbs twice before it sold.

I took the bike for a test-ride before the purchase. It exhibited the Cobra 4-into-4 malady, the VBoost wasn't kicking-in like it does on a stock-exhaust bike, and it just wasn't representative of the breed, when using an OEM exhaust; it was representative of the Cobra-equipped bikes: less HP, less VBoost effect, but "them-pipes shore-are purty!"

In the end, he told me that he was "more-of a Honda Shadow guy," and he bought one, and was selling the VMax. I haven't had any contact with him in years, I assume that he sold his bike.

Something to consider is, "what engine and electrical system do you have?" Since these bikes can use any engine in any frame, you could have a 1985-1989 engine & electrical system in a 1990+ frame. The early bikes use a different, two pick-up coil system for firing the ignition, while the 1990+ bikes use a single pick-up. Conceivably you could have one pick-up coil go-out, on an early system, and it would spark intermittently. That's a bit of a long-shot, but it could happen.

There are any-number of other maladies which can befall an ignition system, or cause cyl cut-out issues:
1] bad ignition coil. Swap the coil on the non-firing cyl to another cyl & see if the problem 'follows' the switch
2] bad battery. CDI ignitions like 12+ volts to run properly. Load test the battery, it may have a weak cell or cells. Clean the battery terminals, check them for condition, replace any having detached wires in the bundle for each terminal.
3] bad spark plug cap. See #1. Remove the cap & wire, if you have green discoloration on the end of the spark plug wire, trim it back to shiny wire, usually a 1/4" trim is sufficient. many guys like to run COP's (coil-over-plug) instead of the stock coils. Read under those threads by using the search engine. Briefly, some members report CDI problems with the early systems if they are not using resistors with the COP's. Denso COP's seem to be preferred over the Mitsubishi. Contact Sean Morley one2dmax@aol.com for sets of COP's using resistors.
4] a pinhole in your fuel delivery system, check it carefully. The molded hose from the tank to the fuel filter can be replaced with a ~8" or 9" gentle loop of reinforced fuel hose. Don't forget to inspect the hose from the fuel filter to the gas delivery manifold. The molded 'T'-hose in the carbs is one which can tear when you're trying to disassemble the carbs. It's best to bite the bullet and to buy the OEM one, here.
5] a clogged fuel filter, I open mine to inspect what's been collected. If you find rust, what does the inside of the gas tank look-like? Time for a cleaning, and perhaps a fuel tank liner treatment. The experienced guys here will admonish you, "follow the directions, exactly!" If you don't, you will have-to strip the failed coating and do it again.
6] the pilot jets in the carburetor jet blocks clog very-easily. Any rust in the tank will cause problems here.
7] holes in or poorly-installed CV diaphragms. They need to be perfect, and properly-installed to work on the airflow, as-designed. If you remove the slide needle, ensure that you index it properly to tighten-down the screw holding it in-place. There is a nipple which needs to go into its hole to tighten the slide screw.

There are many-other things that can affect your operation, those are some of the ones others have reported having to-overcome.
 
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Joe Planter

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If you put your location under your screen name, you may-be able to get assistance from someone local to you. What year is your bike?

I am the person to whom this member turned for a look at the bike he was considering to purchase. He was buying it at the shop owned by someone I've known for a long time. The bike sat in their inventory for months. The shop mechanic had-to rebuild the carbs twice before it sold.

I took the bike for a test-ride before the purchase. It exhibited the Cobra 4-into-4 malady, the VBoost wasn't kicking-in like it does on a stock-exhaust bike, and it just wasn't representative of the breed, when using an OEM exhaust; it was representative of the Cobra-equipped bikes: less HP, less VBoost effect, but "them-pipes shore-are purty!"

In the end, he told me that he was "more-of a Honda Shadow guy," and he bought one, and was selling the VMax. I haven't had any contact with him in years, I assume that he sold his bike.

Something to consider is, "what engine and electrical system do you have?" Since these bikes can use any engine in any frame, you could have a 1985-1989 engine & electrical system in a 1990+ frame. The early bikes use a different, two pick-up coil system for firing the ignition, while the 1990+ bikes use a single pick-up. Conceivably you could have one pick-up coil go-out, on an early system, and it would spark intermittently. That's a bit of a long-shot, but it could happen.

There are any-number of other maladies which can befall an ignition system, or cause cyl cut-out issues:
1] bad ignition coil. Swap the coil on the non-firing cyl to another cyl & see if the problem 'follows' the switch
2] bad battery. CDI ignitions like 12+ volts to run properly. Load test the battery, it may have a weak cell or cells. Clean the battery terminals, check them for condition, replace any having detached wires in the bundle for each terminal.
3] bad spark plug cap. See #1. Remove the cap & wire, if you have green discoloration on the end of the spark plug wire, trim it back to shiny wire, usually a 1/4" trim is sufficient. many guys like to run COP's (coil-over-plug) instead of the stock coils. Read under those threads by using the search engine. Briefly, some members report CDI problems with the early systems if they are not using resistors with the COP's. Denso COP's seem to be preferred over the Mitsubishi. Contact Sean Morley one2dmax@aol.com for sets of COP's using resistors.
4] a pinhole in your fuel delivery system, check it carefully. The molded hose from the tank to the fuel filter can be replaced with a ~8" or 9" gentle loop of reinforced fuel hose. Don't forget to inspect the hose from the fuel filter to the gas delivery manifold. The molded 'T'-hose in the carbs is one which can tear when you're trying to disassemble the carbs. It's best to bite the bullet and to buy the OEM one, here.
5] a clogged fuel filter, I open mine to inspect what's been collected. If you find rust, what does the inside of the gas tank look-like? Time for a cleaning, and perhaps a fuel tank liner treatment. The experienced guys here will admonish you, "follow the directions, exactly!" If you don't, you will have-to strip the failed coating and do it again.
6] the pilot jets in the carburetor jet blocks clog very-easily. Any rust in the tank will cause problems here.
7] holes in or poorly-installed CV diaphragms. They need to be perfect, and properly-installed to work on the airflow, as-designed. If you remove the slide needle, ensure that you index it properly to tighten-down the screw holding it in-place. There is a nipple which needs to go into its hole to tighten the slide screw.

There are many-other things that can affect your operation, those are some of the ones others have reported having to-overcome.
Thank you so much this helps a bunch. I see that you saw my post that I just made regarding my issue. In that case I have to know, knowing that it was running good on all 4 cylinders when I first put the carbs on, does that narrow down the issue or could it still be any one of these problems?
 

Joe Planter

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Thank you so much this helps a bunch. I see that you saw my post that I just made regarding my issue. In that case I have to know, knowing that it was running good on all 4 cylinders when I first put the carbs on, does that narrow down the issue or could it still be any one of these problems?
If you put your location under your screen name, you may-be able to get assistance from someone local to you. What year is your bike?

I am the person to whom this member turned for a look at the bike he was considering to purchase. He was buying it at the shop owned by someone I've known for a long time. The bike sat in their inventory for months. The shop mechanic had-to rebuild the carbs twice before it sold.

I took the bike for a test-ride before the purchase. It exhibited the Cobra 4-into-4 malady, the VBoost wasn't kicking-in like it does on a stock-exhaust bike, and it just wasn't representative of the breed, when using an OEM exhaust; it was representative of the Cobra-equipped bikes: less HP, less VBoost effect, but "them-pipes shore-are purty!"

In the end, he told me that he was "more-of a Honda Shadow guy," and he bought one, and was selling the VMax. I haven't had any contact with him in years, I assume that he sold his bike.

Something to consider is, "what engine and electrical system do you have?" Since these bikes can use any engine in any frame, you could have a 1985-1989 engine & electrical system in a 1990+ frame. The early bikes use a different, two pick-up coil system for firing the ignition, while the 1990+ bikes use a single pick-up. Conceivably you could have one pick-up coil go-out, on an early system, and it would spark intermittently. That's a bit of a long-shot, but it could happen.

There are any-number of other maladies which can befall an ignition system, or cause cyl cut-out issues:
1] bad ignition coil. Swap the coil on the non-firing cyl to another cyl & see if the problem 'follows' the switch
2] bad battery. CDI ignitions like 12+ volts to run properly. Load test the battery, it may have a weak cell or cells. Clean the battery terminals, check them for condition, replace any having detached wires in the bundle for each terminal.
3] bad spark plug cap. See #1. Remove the cap & wire, if you have green discoloration on the end of the spark plug wire, trim it back to shiny wire, usually a 1/4" trim is sufficient. many guys like to run COP's (coil-over-plug) instead of the stock coils. Read under those threads by using the search engine. Briefly, some members report CDI problems with the early systems if they are not using resistors with the COP's. Denso COP's seem to be preferred over the Mitsubishi. Contact Sean Morley one2dmax@aol.com for sets of COP's using resistors.
4] a pinhole in your fuel delivery system, check it carefully. The molded hose from the tank to the fuel filter can be replaced with a ~8" or 9" gentle loop of reinforced fuel hose. Don't forget to inspect the hose from the fuel filter to the gas delivery manifold. The molded 'T'-hose in the carbs is one which can tear when you're trying to disassemble the carbs. It's best to bite the bullet and to buy the OEM one, here.
5] a clogged fuel filter, I open mine to inspect what's been collected. If you find rust, what does the inside of the gas tank look-like? Time for a cleaning, and perhaps a fuel tank liner treatment. The experienced guys here will admonish you, "follow the directions, exactly!" If you don't, you will have-to strip the failed coating and do it again.
6] the pilot jets in the carburetor jet blocks clog very-easily. Any rust in the tank will cause problems here.
7] holes in or poorly-installed CV diaphragms. They need to be perfect, and properly-installed to work on the airflow, as-designed. If you remove the slide needle, ensure that you index it properly to tighten-down the screw holding it in-place. There is a nipple which needs to go into its hole to tighten the slide screw.

There are many-other things that can affect your operation, those are some of the ones others have reported having to-overcome.
Also my bike is a 1994 model
 

Fire-medic

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I suggest a systemic 'rule-out' or 'check and correct found faults' approach, same as any good mechanic would do. You determine the symptoms in as-much detail as you can, and then investigate any possible causes for them, correcting the ones you discover. Remember that more-than one thing may be affecting your ride.
 

Joe Planter

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I suggest a systemic 'rule-out' or 'check and correct found faults' approach, same as any good mechanic would do. You determine the symptoms in as-much detail as you can, and then investigate any possible causes for them, correcting the ones you discover. Remember that more-than one thing may be affecting your ride.
Thank you, I will try and rule out what the problem is.
 

Joe Planter

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I suggest a systemic 'rule-out' or 'check and correct found faults' approach, same as any good mechanic would do. You determine the symptoms in as-much detail as you can, and then investigate any possible causes for them, correcting the ones you discover. Remember that more-than one thing may be affecting your ride.
Okay so I have new info. Checked my spark by taking out the spark plugs and reattaching them to the coil wires and turning the bike over. What I found out was the front right plug was the only one that had really good spark. Rear right had little to none, and the entire left side had no spark at all. Oh and by the way, when I pulled out the front 2 plugs, they were black. When I first got the bike 1.5 month ago, the plugs were all brand new, so I think my carb issues along with me riding it like that made the plugs turn black. My next guess is to try and throw new plugs in it, check for spark the same way, and see what I find. Let me know what you think
 

MaxMidnight

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Whilst that may get it running again it won't fix the problem.
Are the plugs a sooty black or oily?
If the former then you need to establish why it is running rich, if the latter then (ideally) do a cylinder leak-down test or compression test (I'm assuming you haven't over filled the oil).
 

Joe Planter

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Whilst that may get it running again it won't fix the problem.
Are the plugs a sooty black or oily?
If the former then you need to establish why it is running rich, if the latter then (ideally) do a cylinder leak-down test or compression test (I'm assuming you haven't over filled the oil).
They were a sooty black, with UN-Burnt gasoline, no oil on the plugs whatsoever. But only 2 of them were black, the front 2 plugs. Other ones were fine. Maybe I’ll switch the plug that I know has good spark to the other coils and see what I get. I don’t know that it was running rich, just it’s running on 2 cylinders therefore I would assume it was only running extremely rich in the 2 that weren’t firing, because they weren’t firing... I’m not an expert though.
 

Fire-medic

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I'm no pro mechanic, but your list of poorly-igniting primary ignition components says to-me, you have some fundamental issues. Here 's what I'd suggest to check your coils' function: get a pair of clips like you'd use on a battery for charging at the terminals, any auto parts store should have 'em in the electrical supplies section. Not the big, 400 amps or-whatever they are ones, the smaller ones, like you'd find on a battery charger. Make up a jumper wire 2 ft long using some stranded 12 ga. wire & the clips, Use that to ground the spark plug threads to a good location where you have a bare ground available. Given the length of the wire, you should be able to go directly to the battery ground. Now, try the plugs you already-have, each in-turn on the high tension (primary) leads for each cyl. What kind of spark do you get? Now, try a brand-new spark plug on each high-tension lead (your spark plug wires) and see what you get. That's pretty-much what you were gonna do, just with the addition of the known good ground jumper wire I suggest you use.

Obviously, there's something fundamentally-wrong here. You have a later model ignition, w/only one pick-up coil, (1990-2007) so it's not that on the early pick-up coils, where you have a pair of pick-ups, you could have one coil go-out, and two cylinders would drop their spark. It almost seems like you have some issue with the CDI, where it's intermittently cutting in and out, which is possible, but not something I've seen. My experience is that the CDI either works, or it doesn't. Sean Morley may be able to shed some light on this as to whether or not that is a common thing.

One thing that sometimes happens is that the circuit board in the CDI has joints which benefit from being re-soldered. The point where that may-work is where the plug into the CDI box is, the leads off that sometimes have been found to not conduct electricity properly after years of use. Some say it's cold joints, breaks in the wires, whatever, it costs nothing but time to remove the CDI box, and to re-solder the plug leads at the circuit board. I'm not-saying, "that's it," but given your description of symptoms, I'd say it's worth investigating, and trying.

The other thing to consider is the CDI box-swap. "Replace with one of known good operating condition," as the manuals say. Sean Morley has a box of electrical components he sends you, you try them one at a time, to discover the bad component. If you replace several at the same time, you don't know which component was 'the bad-one.' Sean charges you for the one(s) you keep.
 

Joe Planter

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I'm no pro mechanic, but your list of poorly-igniting primary ignition components says to-me, you have some fundamental issues. Here 's what I'd suggest to check your coils' function: get a pair of clips like you'd use on a battery for charging at the terminals, any auto parts store should have 'em in the electrical supplies section. Not the big, 400 amps or-whatever they are ones, the smaller ones, like you'd find on a battery charger. Make up a jumper wire 2 ft long using some stranded 12 ga. wire & the clips, Use that to ground the spark plug threads to a good location where you have a bare ground available. Given the length of the wire, you should be able to go directly to the battery ground. Now, try the plugs you already-have, each in-turn on the high tension (primary) leads for each cyl. What kind of spark do you get? Now, try a brand-new spark plug on each high-tension lead (your spark plug wires) and see what you get. That's pretty-much what you were gonna do, just with the addition of the known good ground jumper wire I suggest you use.

Obviously, there's something fundamentally-wrong here. You have a later model ignition, w/only one pick-up coil, (1990-2007) so it's not that on the early pick-up coils, where you have a pair of pick-ups, you could have one coil go-out, and two cylinders would drop their spark. It almost seems like you have some issue with the CDI, where it's intermittently cutting in and out, which is possible, but not something I've seen. My experience is that the CDI either works, or it doesn't. Sean Morley may be able to shed some light on this as to whether or not that is a common thing.

One thing that sometimes happens is that the circuit board in the CDI has joints which benefit from being re-soldered. The point where that may-work is where the plug into the CDI box is, the leads off that sometimes have been found to not conduct electricity properly after years of use. Some say it's cold joints, breaks in the wires, whatever, it costs nothing but time to remove the CDI box, and to re-solder the plug leads at the circuit board. I'm not-saying, "that's it," but given your description of symptoms, I'd say it's worth investigating, and trying.

The other thing to consider is the CDI box-swap. "Replace with one of known good operating condition," as the manuals say. Sean Morley has a box of electrical components he sends you, you try them one at a time, to discover the bad component. If you replace several at the same time, you don't know which component was 'the bad-one.' Sean charges you for the one(s) you keep.
Thank you this helps me a lot, I will do what you suggested and get back to you. And just so I know, the CDI is essentially the ignition system?
 

Joe Planter

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Yes, it's behind the steering head.
So checked my spark today, basically got a flat head screwdriver and put it on the end of each plug. All of the plugs are putting out good spark, so no issues there. I’m honestly at a loss here. I’ve never seen anything like this before, this seems to be a VMAX from hell. Like I know you need 3 things to make an engine run properly, air, fuel, spark. I had an issue with fuel (carbs) but resolved that, spark isn’t an issue, air though? I mean it starts, so it has to be getting air, I have good compression too. I mean I’m a pretty good backyard mechanic but this is just going right over my head, it’s driving me nuts!!!! Like I have so much going through my head right now like “should I take it to a shop and throw some money at them to figure it out?” Or “should I just sell this thing?” or “should I just keep dumping money into it and replacing parts until things are fixed?” I don’t know what to do at this point
 

desert_max

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How did you "resolve" the issue with the carburetors? During one of those countless disassembly sequences, did you take the jet block apart and pull the pilot jets out of all four? And confirm you cleared them?

The reason I ask is because it sounds like you have an issue with your carburetors.
 

Fire-medic

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How did you "resolve" the issue with the carburetors? During one of those countless disassembly sequences, did you take the jet block apart and pull the pilot jets out of all four? And confirm you cleared them?

The reason I ask is because it sounds like you have an issue with your carburetors.
VMax pilot jet.jpg VMax pilot jet lighted.jpg

Pilot jet, clean and cleared.

I don't recall you saying that you suspected an air leak, but spraying your entire set of carbs, from the air boots to the VBoost to cyl head point, to see if your rpm's rise, indicating an air leak, is what I think you should try. You use starting fluid. Some people use propane, but a liquid is easier to see where it goes, compared to a gas (not 'gasoline' but one of the states of matter: solid, liquid, gas). Remember that you may-locate one leak, but you have-to keep going because there may-be another, or even-more than that. I had an idle difficulty on a bike I was working on recently, and the air leak was the o-ring between the VBoost manifold and the cyl head on the #2 cyl. My suggestion is, if you find a result like that, you replace all four of the o-rings! Why have-to re-do all your work, because in the disassembly, one of the fragile o-rings also became incapable of making a good seal? Replace all-four.
 
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