Stumped. What's going on with these carbs? Videos included

[Mightymouse]

Hey all,

I'm really stumped about my bikes lack of acceleration.

It's a 97' v-max with about 66,000 miles on it. It's a California model. I had the carbs cleaned and synced 10 months ago. OEM pilot jets and main jets were replaced (I think it was only the ones for fuel. I don't think they replaced the air jets.)

When I got the bike back it could be cold started without the choke on. It seemed very lively to me after I got it back. I stored it for the winter with seafoam fuel stabilizer, brought it out of storage and rode it around this past summer but not as frequently as I would have liked. There were stretches of time that it would sit in the garage for 2 weeks with no fuel stabilizer. Since it was kind of far away from where I currently live, when I had time, I would take it out and run it for ~20-30 minutes. I think I've put about 2,000 miles on it this season. It can still be cold started without the choke but now the bike is not as lively anymore and struggles to get up to speed.

And It seemed to have happened very suddenly. The bike seemed fine one day and then the next day it wasn't. It couldn't accelerate like it used to.

I rolled on the throttle and the bike seemed really sluggish to accelerate. I suspect something is going on with the carbs but I don't know exactly what's causing the problem.

I replaced the fuel filter (hadn't changed it in about 8,000 miles). That didn't do anything. Sluggish acceleration is still there.

I searched these forums and did a few of the tests that were recommended. Here is what I found:


Test 1: Pilot mixture test: engine should complain if RPMs are held @ 1800 for 1-2 min or when the temp needle touches the first mark (should run lean when cold) After 2 min or needle is 1/2 way between mark and cold mark should not complain from 1500-2000 or popping back through carbs.

I just did this one tonight. Video here. No choke needed at startup. I only gently blipped the throttle to get it going. I think I heard some popping through a carb/carbs around the 14 second mark. It starts around 800-900RPMS. A few seconds after starting it, I roll on the throttle gently to raise the RPMs to 1,800 but it's hard to control. The rpms rev up real fast even if I keep the throttle steady. It takes several minor adjustments to maintain 1800 rpm. This takes about 30 seconds to achieve. After 2 minutes the temp needle hits the cold mark and idles around 1000. Because I could hold the engine at 1800 while cold then this seems to indicate the pilot mixture is too rich. I should either clean or enlarge PAJ2.

Here's another video. The only difference is the engine is warmer. I slowly increase rpms and hold it at 1800 and also rev it a few times towards the end. It was a lot easier to gradually increase rpms from 1000 to 1800 with a warmer engine. I noticed while holding 1800 the rpms increase by ~100-200 while my hand is real steady on the throttle. Is this normal? It'll increase for a few seconds and then drop back to 1800. I moved the camera closer to the needle to showcase this. The engine does not seem to complain when the engine is warm so it can't be a lean condition BUT I do routinely hear popping noises coming from the airbox when accelerating with a warm engine in 1st or 2nd gear. Seems like carb/carbs have symptoms of running too rich and too lean?


Test 2: pilot mixture cruise test: engine should run steady at 5k. If stumbles but ok everywhere else then not enough pilot.

I didn't take a video of this but the bike seems to run steady at 5k in 5th gear and ok everywhere else BUT...

I hear popping noises from the exhaust above 4500 RPM in 1st gear (and 2nd gear too but harder to hear (could be the wind). Seems to pop more in this gear when rolling off the throttle slowly). What could this mean?


Test 3: Slide jump test: cruise @ 4K in 5th gear. Pin it fast. There should be NO hesitation. If there is. Too rich. Needle is too rich

Didn't take a video. There IS hesitation. The needle seems to be too rich.

Test 4: hard WOT pull in 2nd or 3rd gear <3k. Should be smooth pull all the way. If it seems to lag in 4-5k range, too much needle. If sputters then not enough needle. {tests needle richness or leanness}

Didn't take a video. NOT smooth all the way through. Seems to quickly speed up and slow down irregularly through the 4-5k range. Not sure if this is a lag symptom or a sputter symptom.

Final videos: I pulled the spark plugs after the bike had been sitting for about 2 hours and inspected them. I took a video of each one. What do you guys think? Do they look normal or can you see something that might explain the symptoms above?

Here's the video for the spark plug from carb #1.
Here's the video for the spark plug from carb #2.
Here's the video for the spark plug from carb #3.
Here's the video for the spark plug from carb #4.

Many thanks for any insight y'all can lend! I've really been scratching my head on this one. I tried to document as many of the symptoms as I could to help all of you with your thoughts.

If y'all want any additional video or pictures or anything, I'll gladly upload them for you if you think it will help.


Best,
Eli

Oh, and just out of curiosity, I took a video of one of these popping events that I can hear in the air box. I uploaded it here. Is this what you mean when you say "popping back through the carbs"?

 

[user 16790]

maybe not much help but have you checked/tested your ignition system, when did you last change the plugs, plug caps and ht leads

 

[MaxMidnight]

I think it is time to get your hands dirty

Whist it does sound like a fuel issue it would be worthwhile checking that the pressure sensor is working and that the hose is intact.

As it seemed to have come on quickly the original work sounds like it was OK so you are looking for something that has broken or come loose.

The colour of the plugs will indicate the mixture when you 'chopped' the plugs. But as they will have been run at various revs and engine loads I wouldn't rely on what you see too much. You would need to hold the motor at constant revs for several minutes to allow time for the deposits to develop before they give a reasonable indication.
Also as different parts of the fuel system (pilot jet, needle and main) are acting on the air/ fuel ratio (a.f.r.) at different revs you still won't know which is the problem.

Have you checked that the slides all move together and/ or checked that the diaphragms are intact?

If they are OK then the next step would be to strip the carbs and inspect the components.

If all that checks out OK then probably the quickest (and cheapest in the long run) would be to put it on a dyno so you will get factual data of what the a.f.r. is doing and thus know where to look.

Some words of caution, you will get plenty of good advice here but as none of us (as far as I know) have crystal balls our suggestions should not be taken as the fix.

 

[Traumahawk]

Sounds like its time for a shotgun. A shotgun is a method to clean the carbs pilot jets.

https://vmax.lvlhead.com/tips/shotgun.htm

 

[Mightymouse]

maybe not much help but have you checked/tested your ignition system, when did you last change the plugs, plug caps and ht leads

Hey Julian,

Thanks for the response. I have never tested my ignition system.

I replaced the plugs about 10,000 miles ago. Have not replaced the plug caps or HT leads.

I don't know much about how to go about testing the system. I have a Clymer manual and a pdf of the Yamaha VMX12N, NC~K, KC manual. Do you recommend one manual over the other? I see the Yamaha one has 3 tests - a ignition spark gap test, ignition coil resistance test, and a pickup coil resistance test.



The Clymer manual has more tests. On page 53 it lists 16 steps for troubleshooting the ignition system:



Which tests are most important for troubleshooting my lack of acceleration? I'm thinking the 3 Yamaha tests are sufficient?

Thanks!

 

[Mightymouse]

Whist it does sound like a fuel issue it would be worthwhile checking that the pressure sensor is working and that the hose is intact.

Ok, I'll do that. Is this the correct procedure for testing that?

The colour of the plugs will indicate the mixture when you 'chopped' the plugs. But as they will have been run at various revs and engine loads I wouldn't rely on what you see too much. You would need to hold the motor at constant revs for several minutes to allow time for the deposits to develop before they give a reasonable indication.
Also as different parts of the fuel system (pilot jet, needle and main) are acting on the air/ fuel ratio (a.f.r.) at different revs you still won't know which is the problem.

Ah, that makes sense.

Have you checked that the slides all move together and/ or checked that the diaphragms are intact?

No I have not. I will do that as well.

If they are OK then the next step would be to strip the carbs and inspect the components.

I'll do that if I have to! The thought makes me nervous.

If all that checks out OK then probably the quickest (and cheapest in the long run) would be to put it on a dyno so you will get factual data of what the a.f.r. is doing and thus know where to look.

That makes sense.

I have a stupid question. Is it possible to test each carburetor individually while idling? Will I cause any damage if I run the bike with only 1 cap attached to 1 spark plug at a time?

If the acceleration problem is coming from a carburetor, testing 1 at a time could reveal the carb with the problem?


Thanks for all your help.

 

[MaxMidnight]

Ok, I'll do that. Is this the correct procedure for testing that?

View attachment 72550

Yes

I'll do that if I have to! The thought makes me nervous.

The trick is to do one at a time, that way you will also have a reference should you forget what goes where.

I have a stupid question. Is it possible to test each carburetor individually while idling? Will I cause any damage if I run the bike with only 1 cap attached to 1 spark plug at a time?

The only stupid question is the one you should have asked but didn't.
If you could get the bike to run on one cylinder you are better man than I!
It's not recommended to try and run a motor with solid state ignition without grounding the disconnected lead(s). To do so can, in theory, damage the ignition unit. That said I don't ever recall reading of it happening.

If the acceleration problem is coming from a carburetor, testing 1 at a time could reveal the carb with the problem?

I can see where you are coming from but the running would probably be so unstable you might not be any the wiser.


Thanks for all your help.

 

[Mightymouse]

Sounds like its time for a shotgun. A shotgun is a method to clean the carbs pilot jets.

https://vmax.lvlhead.com/tips/shotgun.htm

Thanks for the reply! I've heard of this method but I haven't looked into it too deeply yet.

I made a table below that compares the symptoms between lvlheads bike and my bike. They don't seem to align exactly. Can clogged pilot jet (or jets) create different symptoms even though it's the same root problem?

 

[Mightymouse]

Have you checked that the slides all move together and/ or checked that the diaphragms are intact?

Hey, there's a trick Shane Conley does for quickly testing the integrity of the slide and diaphragms without disassembly. He gently sprays compressed air into 2 holes to lift the slide. I don't know what these holes are called. He does this on a carb that came out of a harley but i can see similar holes on the v-max carbs. (pic below)



Do you think this is a good method for checking the integrity of the slide and the diaphragms for these carbs without disassembly?

He shows how to do it at the 2 minute mark. Video here:




Many thanks.

 

[Screwloose]

Hi, i’m a newby here, but had my Canadian VMAX 1999 Carbon for 7 years. I’ve had trouble with these carbs where at 4-5 k revs the engine backfires, stutters and gets worse as the engine temp increases by the half way mark. The below is brief but hope it helps you out. Before I done all this I checked the electrics on 3 points you already mentioned. Also I have some photos of my set-ups if things are unclear.

1. Changed the leads and caps, this helped with the heat problem. The caps were the originals.
2. Sprayed some oil on the VBoost rubbers and found #4 was leaking, changed them all.
3. Carb to VBoost rubbers I found one of them split and leaking, changed them all.
4. While I had the above stripped I done the shims as the carbs would never set up if these are out.
5. Stripped the carbs and cleaned.
6. Changed the float needle valves and seats. There is a guy on here talking about using a clamp and pushing the seat and cap both out together, this works. Check the difference between the old and new needle valve spring, this I believe was my main problem.
7. When building up there is another guy on here giving a float height, this will give you a good starting point, but float heights need to be done later at running engine temp, it does change slightly.
8. Bench test the float heights individually using a false tank etc, this gives confidence on float heights and float needle valve operating.
9. Build up the carbs on a flat surface.
10, I set the accelerator flaps with a feeler gauge to ensure I at least get the engine started easily. Just a rough setting is needed.
11. Install the carbs with air box.
12. Get the carb synchronising kit on and start up. I got a couple of house fans on the engine as this can be a fiddle around and changes with high temp.
13. Set the pilot a/f screws. I found 2 1/4 turns. I find with older engines these move out of factory spec.
14. For height of floats I marked the diaphragm covers and put a bit of tape across them as a guide. It’s usual to be out 2-3 mm.
15. Remove the carbs For adjusting float heights again. If you use an angled screwdriver there is no need to split the carb banks. A bit fiddly but gives assurance of getting it right this time around. I used a method to adjust the floats from the other end of the float as before using a depth gauge, I can get it bang on this way.
16. Re-assemble and do all the setting up again.

Products used were Loctite 648 and Hylomar Blue.

 

[Fire-medic]

If the float needles come-out I replace 'em, you can buy just the needles from K&L, made in Japan. Parts Unlimited catalog has them, I think CaptainKyle and Sean Morley are both Parts Unlimited dealers. I wouldn't bother replacing float needle seats unless the bike was 50,000+ miles, or after cleaning, if you couldn't get a good needle jet float seal, and the carb was overflowing.

I give a good-look at the overall length of the float needle and the spring, but since I normally replace them once I get the carburetors torn-down to that point, it's more of a forensic exam, since I'm installing new float needles. Sometimes the spring is weak, and the o.a. length of the needle valve is < a stock, new one.

The minimal difference in the lengths of these used needles probably wouldn't affect the fuel delivery, but the frozen pin would, in my experience.

One needle valve source, a decent price, for 5 pieces:
https://www.ebay.com/itm/K-L-Float-...gh&fits=Year:1990|Model:Vmax+1200|Make:Yamaha

 

[Tommybob]

Thanks for the reply! I've heard of this method but I haven't looked into it too deeply yet.

I made a table below that compares the symptoms between lvlheads bike and my bike. They don't seem to align exactly. Can clogged pilot jet (or jets) create different symptoms even though it's the same root problem?

View attachment 72551

Worthless.

Sounds like its time for a shotgun. A shotgun is a method to clean the carbs pilot jets.

https://vmax.lvlhead.com/tips/shotgun.htm

You ever been into a set of carbs?

Sounds like its time for a shotgun. A shotgun is a method to clean the carbs pilot jets.

https://vmax.lvlhead.com/tips/shotgun.htm

Have you even been inside a set of carbs?

 

[Tommybob]

Your problem is coil wires.

 

[Tommybob]

Your problem is spark plug wires.

 

[Traumahawk]

Thanks for the reply! I've heard of this method but I haven't looked into it too deeply yet.

I made a table below that compares the symptoms between lvlheads bike and my bike. They don't seem to align exactly. Can clogged pilot jet (or jets) create different symptoms even though it's the same root problem?

View attachment 72551

Yes. Depending on how many pilot jets are clogged. There are people that I know that do a shotgun everytime they do an oil change just to make certain that the bike runs crisp.

One thing that I do that really makes it easier to do a shotgun is to take out paj#2 to be able to get a full blast of air into the carbs.

 

[Parminio]

The right side plugs look like they're running lean and overheating. Not surprisingly, that pop was coming from your right side as well, or at least it appeared that way. The video wasn't really long enough to tell for sure, but that's what it looked like to me.

Something is definitely up.

 

[Fire-medic]

Dannymax says that you should go with OEM needle valves, they're available with the seats, for about $10 apiece more-than the aftermarket needle valves alone. That's not-much, even-if the seats aren't changed-out, and you just replace the needle valves, and thoroughly-clean the needle valve seats, leaving them in-place. Dannymax recommends a paste-type toothpaste and a Q-tip, to remove any stubborn deposits upon the needle valve seat.

Use a good carburetor cleaning spray solvent, and compressed air, to ensure that the needle valve seat screen is thoroughly-cleaned. You should have a good-volume of discharge from the needle valve seat, placing your rubber-tipped air hose chuck into the brass needle valve seat, from the inside the float-bowl side, and evaluating the gasoline inlet pipe air volume, after cleaning.

 

[dannymax]

Some things to check on your float needles:
-the rubber tips are soft & pliable
-the tiny shock absorbing plungers under the retaining wire are not stuck
-no corrosion on the sides to bind the needle in the seat

 

[Mightymouse]

Hey all, want to update about this mystery.

I finally brought this problem to a shop and talked to them about this lack of power. They disassembled the carbs and found one of them had a loose jet needle. They corrected it and now the bike runs great. Acceleration is smooth through all the gears and WOT.

Also, it seems the "popping" sound has gone away as well. Not sure if this was also a symptom of the loose needle.

 

[Mightymouse]

The right side plugs look like they're running lean and overheating. Not surprisingly, that pop was coming from your right side as well, or at least it appeared that way. The video wasn't really long enough to tell for sure, but that's what it looked like to me.

Something is definitely up.

Hey Parminio, I think you had a great observation. This may have been evidence of a loose jet needle...

A local shop found the problem to be just that - a loose jet needle. He couldn't recall which carb it was but I suspect it was carb #1 or #2 on the right side where that popping was coming from. Looking back at those videos I took of right hand side carb #1 and #2 they do look whiter than carbs #3 and #4 on the left hand side.

If the jet needle was loose and dropped and/or the clip securing the needle moved up a few notches, that carb would most likely have been running lean right?

What confuses me is that both right side spark plugs look like they're running lean instead of only the spark plug in the lean carb. Hmmm.

Geeze, it's like to only way to know is to take the carbs apart and inspect them myself.