Idle drops when hot

[DocDoom]

Just sanity checking here.
So a few days ago I took maybe a two hour ride in 90 degrees or so. After getting back I noticed the idle went from 1100 to about six. Moreover, if I touched the choke about a millimeter it would kill it at that time. Fired right back up several times while I was testing this. Doesn't stall yet on it's own but it's close.

Ethanol free gas, carbs rebuilt<1k less than a year ago. Synced as well, also replaced battery like six months ago with this MotoBatt 12 Volt 20.5 Ah MB16AU Sealed Maintenance Free AGM Battery https://a.co/d/ewjq68f

So.... I'm thinking I'll read the voltage off, under load and after warm under these conditions. Is it possible it's just running super rich? I haven't messed with AF much because I'm not experienced with it and don't want to run it lean on accident. The mechanic I asked to do that after rebuilding the carbs said to live with the mileage "cause it's running good" but I do only get about 68 miles pre fuel light. Checked the choke circuit everything slides freely. Dash dims when things like the turn signal are on but that's been every bike I've owned. Dunno if helpful.
I guess my question is:

1. Check battery voltage of course, and charging voltage. Go through that to make sure everything is in spec.
2. Check plugs after that.
3. Test stator, replace if defective or if charging is crappy, if it is that's a decision tree unto itself.
4. Move to cops if coils are cracked, and because they [Yamaha coils] are like 140 dollars each. Lower voltage draw on the battery too.
5. Maybe mess with the A/F, though I don't know of an empirical way to know if it is too lean. Smells quite gassy at lights, but that isn't actionable or empirical. CV carbs probably run richer when hot for awhile but .. the issue now persists. It could well be a rich condition messing up the plugs. Afaik everything is stock, I don't recall the jet sizes but my bet is they are stock.

Are these sane first steps? Would you change the order of them? Am I missing any?

Thanks fellow riders.

 

[MaxMidnight]

Obviously fuel consumption depends on how hard you ride the bike but I would expect that 90 miles to a tankful would be about the norm?

Does this only happen in high temperatures or does it do it at a lower ambient?
Mine will exhibit a similar issue when ambients are high and I'm in slow traffic. Once back on the move or when it is cooler the bike runs fine.
One thing I would check is that the rubber rain/ heat shield is in place.

Always start with the basics: are the carbs still in synch. and is the air filter clean; are the float levels correct and do you have the correct jets installed?

If you suspect a charging issue then you need to work through the system in a logical manner; don't just 'dip in' and hope you have found the issue.
See attached.
If not done ensure all earth points are clean.

Just because you see signs of cracking on the coils it doesn't mean they are unserviceable. If the checks show they are in spec. and there is no electrical leakage then save your money.
There was a video posted a while ago that dissected cracked coils. It showed that the cracks were confined to the outer plastic and that the inner insulation was OK. Someone recall the post?

My standard answer for carb set-up is to get it on a dyno so you can measure what the a.f.r. is doing throughout the rev range. You will then be working with factual data and again remove the guess work. It will probably work out cheaper in the long run in terms of time spent and money by trying to best guess the issue.
An alternative would be to do a plug chop at the revs where you have the problem. That will give you an indication if you have a rich or lean condition but unless you are adept at plug reading not tell you by how much.

The only 'messing' you can do with the carbs is via the idle mixture screws. This will have some effect but I suspect not sufficient to correct an excessively rich or lean mixture. Beyond that you are into swapping to different size jets which you will need to buy (thus my comments in the previous paragraph)

Bottom line is 'Don't guess, base you diagnosis on facts not intuition'.

 

[DocDoom]

Obviously fuel consumption depends on how hard you ride the bike but I would expect that 90 miles to a tankful would be about the norm?

Does this only happen in high temperatures or does it do it at a lower ambient?
Mine will exhibit a similar issue when ambients are high and I'm in slow traffic. Once back on the move or when it is cooler the bike runs fine.
One thing I would check is that the rubber rain/ heat shield is in place.

Always start with the basics: are the carbs still in synch. and is the air filter clean; are the float levels correct and do you have the correct jets installed?

If you suspect a charging issue then you need to work through the system in a logical manner; don't just 'dip in' and hope you have found the issue.
See attached.
If not done ensure all earth points are clean.

Just because you see signs of cracking on the coils it doesn't mean they are unserviceable. If the checks show they are in spec. and there is no electrical leakage then save your money.
There was a video posted a while ago that dissected cracked coils. It showed that the cracks were confined to the outer plastic and that the inner insulation was OK. Someone recall the post?

My standard answer for carb set-up is to get it on a dyno so you can measure what the a.f.r. is doing throughout the rev range. You will then be working with factual data and again remove the guess work. It will probably work out cheaper in the long run in terms of time spent and money by trying to best guess the issue.
An alternative would be to do a plug chop at the revs where you have the problem. That will give you an indication if you have a rich or lean condition but unless you are adept at plug reading not tell you by how much.

The only 'messing' you can do with the carbs is via the idle mixture screws. This will have some effect but I suspect not sufficient to correct an excessively rich or lean mixture. Beyond that you are into swapping to different size jets which you will need to buy (thus my comments in the previous paragraph)

Bottom line is 'Don't guess, base you diagnosis on facts not intuition'.

I really appreciate the answer on short notice.
Ambient temps here are high, South Florida is dipping into the summer season. I can say it wasn't an issue a few weeks ago, onset was very sudden. I will clean the grounds. I'm pretty confident with electrics, so I was hoping a good dig through might unearth something. Idle is just universally lower, 1k at startup a drop of 100 and 4-5 once at temp. This is a new thing. I agree with the dyno idea. Making sure the plugs aren't black and getting resistances on the components and battery output felt like a decent first step, after which the possible offenders kind of sprawl depending. I can resync the carbs. Jets I can check also.

It's good advice. I'll call around to some dynos and see what that situation is like. From an engineering standpoint the cops idea mostly appeals because it eliminated guesswork and possible wire breakdown when hot.

I don't know what a default rubber shield looks like but there is one over the front cylinders. Today I took it out on 35 mph roads, no traffic no stop and go to check if findings were consistent. They were. Idle dropped to 400 by the time I was home just after up to temp, longer ride not correlated, likely confounding.
Get carb sync tool, sync, check plugs and battery, check charging and components, resync, investigate Dyno. I'm confused as to why one day to the next a rich condition would cause this other than fouling. The rich condition should be addressed on it's own merit on a Dyno I'm sure but it would seem another culprit is afoot.
Thank you sir, truly.

 

[Parminio]

I do only get about 68 miles pre fuel light

That is simply horrific on a grand scale.

A colder engine uses more gas, a hot one uses less. When you're running as rich as you are, and you must be running GOD AWFUL rich, the hotter it gets the worse your engine will suffer.

I wouldn't be the least bit surprised that what's actually happening is you're flooding out when it gets that hot and losing an entire cylinder because of it.

 

[DocDoom]

That is simply horrific on a grand scale.

A colder engine uses more gas, a hot one uses less. When you're running as rich as you are, and you must be running GOD AWFUL rich, the hotter it gets the worse your engine will suffer.

I wouldn't be the least bit surprised that what's actually happening is you're flooding out when it gets that hot and losing an entire cylinder because of it.

Okay, but were that the case why would this be a sudden artifact after around 800 miles post "professional" tune?
The spark plugs were changed about 3 days before I brought it in for that, so that will probably be the first order of business to check.
Can you clarify? Other than the use of the choke why does an engine after running for 2 minutes for example before getting up to temp at 2+x minutes use more fuel? I'm asking because it's relevant.

 

[Gbianchi]

Okay, but were that the case why would this be a sudden artifact after around 800 miles post "professional" tune?
The spark plugs were changed about 3 days before I brought it in for that, so that will probably be the first order of business to check.
Can you clarify? Other than the use of the choke why does an engine after running for 2 minutes for example before getting up to temp at 2+x minutes use more fuel? I'm asking because it's relevant.

Is your cooling fan working and could it be requiring more than its share of voltage, just a thought.

 

[DocDoom]

Is your cooling fan working and could it be requiring more than its share of voltage, just a thought.

It is working, and that's a good idea to check. Part of the plan is going to be to get voltage off, at idle, at 2500 rpm cold and when up to temp with fan running. It may be weak spark at idle with overdraw on the fan. I may pop the top off and double check the work on the tune/recent carb rebuild to make sure the enrichener circuit isn't partially open on one or more cylinders causing a mechanically and not jet induced rich condition. Also maybe vacuum leaks, not sure a lot of it will be troubleshooting at the first steps. Thank you for the suggestion though, I'll add it to the what to check list.

 

[MaxMidnight]

Okay, but were that the case why would this be a sudden artifact after around 800 miles post "professional" tune?
The spark plugs were changed about 3 days before I brought it in for that, so that will probably be the first order of business to check.
Can you clarify? Other than the use of the choke why does an engine after running for 2 minutes for example before getting up to temp at 2+x minutes use more fuel?

Not sure what a 'professional tune' is as there is little that can be tuned other than the idle mixture and carb synch.
Can you confirm that the air filter is clean?

Assuming the plugs are the correct grade and are working then that is unlikely to be the issue but you do need to confirm all cylinders are firing.

An engine does not get up to temperature after 2+x minutes (not sure how long that is) and it will take 10 miles or so of riding before it is. The temperature 'indicator' is only showing that of the coolant and not the whole engine i.e. the oil and all of the metal components.
When an engine is up to temperature the heat will aid the atomisation of the fuel and the better this is the more efficient the engine is.
Therefore, assuming the engine is less efficient during warm up it will require more fuel to achieve a given performance.
How much more I have no idea, it may be insignificant...or not.

 

[DocDoom]

Not sure what a 'professional tune' is as there is little that can be tuned other than the idle mixture and carb synch.
Can you confirm that the air filter is clean?

Assuming the plugs are the correct grade and are working then that is unlikely to be the issue but you do need to confirm all cylinders are firing.

An engine does not get up to temperature after 2+x minutes (not sure how long that is) and it will take 10 miles or so of riding before it is. The temperature 'indicator' is only showing that of the coolant and not the whole engine i.e. the oil and all of the metal components.
When an engine is up to temperature the heat will aid the atomisation of the fuel and the better this is the more efficient the engine is.
Therefore, assuming the engine is less efficient during warm up it will require more fuel to achieve a given performance.
How much more I have no idea, it may be insignificant...or not.

Fair enough.
The nomenclature I used is ambiguous, I apologize. I meant to say: the last time I asked someone with a shop of many years experience to go through and rebuild the carbs, with OEM kit, and set the mixture screws and sync etc. It was new to me at the time, 2 carb set up were the most I've ever rebuilt , and I generally wanted a known good starting point.

I will check the air filter and ensure all cylinders are firing.

My question on the fuel was simply that: if I suppose incorrectly worded. If at two minutes of riding from cold it is using more fuel and at some interval in the future when up to temp it is using less, what causes this and to what extent. If this extent were extremely dramatic in magnitude it may explain the symptoms. I also generally didn't understand why, so thank you.

I plan shortly to get the electrics measured, as well as what has been included, eg with fan. Then test and replace plugs. I will then be able to test I am getting spark on all cylinders as well as see if any have fouled causing me to drop one. Or at the very least if one isn't giving spark for a reason among which could be fouling. The starter can be run with plugs out and boots on against the engine or a ground of some sort to check for spark right? This won't fix the fueling issue, but it will pick an initial path between electric breakdown and battery/stator to an extent, I think.

Also, thank you.

 

[Parminio]

post "professional" tune?

You're getting 68 miles per tank. You are literally draining nearly a gallon of gas either onto the pavement, which you would no doubt see, or into your engine. Whoever did the "professional" tune has more than one bat in his belfry if that's the result you're actually getting.

 

[DocDoom]

You're getting 68 miles per tank. You are literally draining nearly a gallon of gas either onto the pavement, which you would no doubt see, or into your engine. Whoever did the "professional" tune has more than one bat in his belfry if that's the result you're actually getting.

68, 65, and 72 were the last 3 prior to red light. The work was warrantied, but apparently "it's running good and you should live with the gas mileage." I've elsewhere posted a few YouTube videos on replacing various parts of the bike, none of which have interplay with that system.

At this point, there is the very real question of should you let someone who substantially overcharges because they're the only folks in the area specializing in not efi/American reenter the bike given it'll be acrimonious at least, and if the error was genuine or a VMAX nuance it likely won't be fixed second time around. It may be looking for more obvious things first, measuring float heights/jets etc will give me more actionable Intel. If it ran rich for IDK 8 tanks in between me fixing it (the other issues) bad enough to foul a plug, that's pretty actionable. In any event, the mechanic is innocent until demonstrable otherwise, it's not as if these are simple machines. I won't fault the guy until I find a pilot stuck in a main or something.

 

[Parminio]

Anybody that told you "just live with the mileage" when you're reeking of gas as you sit there idling and lost nearly a gallon per tank compared to every other gen 1 Vmax on the road has absolutely ZERO credibility of any kind. You could have done the job yourself blindfolded and been better off.

Pal, I had a HOLE in my gas tank and got better mileage than you.

 

[MaxMidnight]

I plan shortly to get the electrics measured, as well as what has been included, eg with fan.

A good starting point but if the output is below what is expected then urge you to work through the test procedure previously posted.

The starter can be run with plugs out and boots on against the engine or a ground of some sort to check for spark right?

You can but for a modest sum it would be better to fork out for a spark plug tester.

This won't fix the fueling issue, but it will pick an initial path between electric breakdown and battery/stator to an extent.

I would be inclined to diagnose them separately. If the output or battery voltage drops too low then you would be experiencing starting issues and you would lose all sparks.
Even with good output from the alternator a dodgy HT system will still cause issues.

I hope you find this post helpful (unlike some of the other posts on this thread )

 

[VMAXXIMUM]

I

68, 65, and 72 were the last 3 prior to red light. The work was warrantied, but apparently "it's running good and you should live with the gas mileage." I've elsewhere posted a few YouTube videos on replacing various parts of the bike, none of which have interplay with that system.

At this point, there is the very real question of should you let someone who substantially overcharges because they're the only folks in the area specializing in not efi/American reenter the bike given it'll be acrimonious at least, and if the error was genuine or a VMAX nuance it likely won't be fixed second time around. It may be looking for more obvious things first, measuring float heights/jets etc will give me more actionable Intel. If it ran rich for IDK 8 tanks in between me fixing it (the other issues) bad enough to foul a plug, that's pretty actionable. In any event, the mechanic is innocent until demonstrable otherwise, it's not as if these are simple machines. I won't fault the guy until I find a pilot stuck in a main or something.

If your not comfortable working on your carbs yourself and the shop isn't doing the job(which seems to be the case) take them off and send them to Dannymax or Sean or Capt. Kyle. Now you'll have a known starting point from experts who take pride in their work.

 

[DocDoom]

A good starting point but if the output is below what is expected then urge you to work through the test procedure previously posted.

You can but for a modest sum it would be better to fork out for a spark plug tester.

I would be inclined to diagnose them separately. If the output or battery voltage drops too low then you would be experiencing starting issues and you would lose all sparks.
Even with good output from the alternator a dodgy HT system will still cause issues.

I hope you find this post helpful (unlike some of the other posts on this thread )

That's a very good idea, I've ordered an inline tester and a screw it in and play with frequency on the bench kit.
Caveman eyeball watching spark against ground probably isn't optimal, plus if someone suggests more tools...
In terms of electrical diagnosis you can bet I'll be following the flowcharts. Non-newtonian (mostly) and confusing world that stuff is. I appreciate it as always.

I think I have a reasonable initial prodding order worked out.

 

[Tom Determan]

You might want to check the oil in case the crankcase found all that lost gas, and others can chime in here, maybe there's something going on with a CV plunger, turning it into a "choke". Maybe you have a torn or mis-seated diaphragm or debris causing it to hang up ? I'm sure others here are more familiar with the nuances of the CV plunger's failure modes.

 

[DocDoom]

You might want to check the oil in case the crankcase found all that lost gas, and others can chime in here, maybe there's something going on with a CV plunger, turning it into a "choke". Maybe you have a torn or mis-seated diaphragm or debris causing it to hang up ? I'm sure others here are more familiar with the nuances of the CV plunger's failure modes.

Good point.

 

[willibauer]

68, 65, and 72 were the last 3 prior to red light. The work was warrantied, but apparently "it's running good and you should live with the gas mileage." I've elsewhere posted a few YouTube videos on replacing various parts of the bike, none of which have interplay with that system.

At this point, there is the very real question of should you let someone who substantially overcharges because they're the only folks in the area specializing in not efi/American reenter the bike given it'll be acrimonious at least, and if the error was genuine or a VMAX nuance it likely won't be fixed second time around. It may be looking for more obvious things first, measuring float heights/jets etc will give me more actionable Intel. If it ran rich for IDK 8 tanks in between me fixing it (the other issues) bad enough to foul a plug, that's pretty actionable. In any event, the mechanic is innocent until demonstrable otherwise, it's not as if these are simple machines. I won't fault the guy until I find a pilot stuck in a main or something.

actually, in our loose vmax community here in germany many riders tend to have a similar mileage. I've had the red light on after less than 100 clicks some times. Depends on how hard you ride it, I guess.
But if the guys in the US normally have higher mileages, better listen to them ;-)

Dropping idle is known here, too, but there seem to be too many possible reasons to list them.
From leaky rubber hoses on the gassers over bad valve plugs or coils or whatever. Could be a pain to find the problem I'm afraid.