rough idle after running at temp

vmaxxx98 · May 18, 2013

i have a 1998 that iv'e owned since new...so far i have flushed the coolant and made sure there were no bubbles in the system, changed the oil to mobil 1 synthetic, checked the thermostat and changed the plugs....basically what happens is, the bike starts without a problem, usually no choke, it runs like a monster pulling very hard...the temp gauge rarely gets past halfway...BUT, after 20 minutes or so of riding, the idle gets real rough and wants to die out at stoplight, i have to rev it to keep it going.....a little extra info: the bike was out of commision for the past 4 years and this was never a problem before...stage 1 jetkit and cobra slashcuts with 8 holes drilled in the back of each pipe (sounds GREAT too)

44boyd · May 18, 2013

Battery new? Might be losing power when the fan kicks on. Check wires for corrosion.

alorio1 · May 18, 2013

Check voltage across battery with fan on, you should have around 13.8 volts. If not 13.8 your charging system has problems. A Vmax does not run well when the voltage is low.

Rollie · May 18, 2013

Check spark plugs , wires & all connections especially to coils .

MaxMidnight · May 19, 2013

If it is starting without choke then I would lean off the idle mixture screws - with the motor at operating temp turn each one back until the engine note drops the back out a bit.

It may also be worthwhile checking float heights.

dwarf717 · May 19, 2013

If the bike sat for four years, and was put back into use without having cleaned the carbs properly, then they need to be cleaned now. No way you can get away without doing it. If you can start that bike from cold without choke,it is because it is running way too rich, possibly from a dirty choke system which is not allowing it to close fully. The choke being partially opened would account for the poor idle when the bike is warm after 20 min., and it would also mask a poorly working , and dirty condition of the idle, and pilot circuits

alorio1 · May 19, 2013

alorio1 said:
Check voltage across battery with fan on, you should have around 13.8 volts. If not 13.8 your charging system has problems. A Vmax does not run well when the voltage is low.

My thoughts are you have low voltage to the battery, to prove or disprove my theory do this; If you have a car battery charger that puts out 4 to 6 amps charge rate, ride the bike untill it starts to act up and return home and connect the battery charger to the battery, on the 6 amp rate if available, while bike is running. You should see your bike start to run normal again within a minute or so. If it doen't respond then you can kick this theory to the curb and move on to other suggestions.......

RaWarrior · May 19, 2013

My vote was for electrical maladies as well. Electrical components have a habit of working OK when cold, and malfunctioning when they get hot (i.e stator or rectifier). Low voltage makes the Vmax's ignition act up. Once it's acting up, check the voltage across the battery with the engine running. If it's less than about 13 something's wrong. The fan draws a good bit of current, so if the charging system is just marginal normally, once it kicks on it can pull the voltage down pretty quickly.

My bike never really needed much choke unless it was a chilly morning, and even then 1/2 choke or less, and it would idle no choke pretty much instantly, albeit slowly until it warmed up a bit.

naughtyG · May 20, 2013

I also reckon that if it sat for four years, the carbs need going through. The Shotgun may help, but there's a good chance it'll start acting up again quickly and there's no alternative but to go through the carbs properly to clean up the idle circuits..

tugla · May 20, 2013

draining carbs into clear container to look for contaminants also checking fuel filter.....but as mentioned i think getting into the carbs wont be a waste of time.....

vmaxxx98 · May 20, 2013

update, the battery is brand new as are the plugs (gapped at 9) i checked the idle screws and the back left was 5 1/2 turns out hence the reason that plug was darker than the rest, did slight adjustments with the rest of the screws...i did the pea shooter deal, checked the coils and plug wires, all good...took it for a ride and it was a little better but still wanted to die out, just not as bad as before...ALSO, i forgot to mention in my original post, I GET ABOUT 70 miles to the tank....i do have a tendency to ride it hard, but thats why i got a vmax...for the power and speed...

Traumahawk · May 20, 2013

vmaxxx98 said:
update, the battery is brand new as are the plugs (gapped at 9) i checked the idle screws and the back left was 5 1/2 turns out hence the reason that plug was darker than the rest, did slight adjustments with the rest of the screws...i did the pea shooter deal, checked the coils and plug wires, all good...took it for a ride and it was a little better but still wanted to die out, just not as bad as before...ALSO, i forgot to mention in my original post, I GET ABOUT 70 miles to the tank....i do have a tendency to ride it hard, but thats why i got a vmax...for the power and speed...

So what are the idle screws at now? The reason why I ask is that a rich condition will get worse as the engine warms up. As a general rule, the A/F screws should be 2 1/2 turns out.

vmaxxx98 · May 20, 2013

here is a vid (if it works) of what my bike sounds like after its up to temp.... the idle screws were put at 2 1/2 turns out, 1/4 turn adjustments when needed

vmaxxx98 · May 20, 2013

https://www.dropbox.com/s/5ak5cko7oprpsr2/VIDEO0011.mp4

Traumahawk · May 20, 2013

I too wonder what the voltage is on the battery with it idling and the fan running. It could be that the voltage is falling off after it gets hot.

I ask this cause when it finally dies...its hot enough that the fan is running.

vmaxxx98 · May 20, 2013

the thing is, the temp gauge can be below halfway and the fan is NOT on and it still acts this way...i was just letting it run to take the vid, i had already riden 15 minutes or so....but i certainly will check the voltage tomorrow

Traumahawk · May 21, 2013

Ok...thanks....and if its not the voltage..then thats one more thing that can be checked off the list as a possible cause.

dwarf717 · May 21, 2013

You did the pee shooter, and it got a little better....what does that tell you? Being the pee shooter is a lazy mans, hope Im lucky and it works attempt at cleaning carbs, I'm going to say it once again. Take the carbs off, pull them apart, and clean them thoroughly, and properly. Maybe the running voltage is possibly down a bit...But if it were low enough that the bike runs poorly to the point of wanting to die, then it would not fire up again. The battery would be dead.

vmaxxx98 · May 21, 2013

dwarf, it's not as much as a lazy man's way, but a poor man without the knowledge of the carb system, also i do not have a garage where i can disassemble them in a clean environment, i do not have the tools to sync them either....i haven't worked in a year so i don't have the funds to have someone do the work....this whole problem started years ago when i took it to the dealership to get it to get it tuned up for the riding season....the mechanic put the bike to "spec" even though i have a stage one jet kit and aftermarket pipes.....dissatisfied with the performance, i took it to another mechanic to set it right which he did...some time later on a run, one of my spark plug wires partially came off the the coil just enough for water to somehow get in start to corrode said wire....after that there was an obstruction in the back left carb and it didn't fire at all....so, i made an attempt to disassemble that carb and find the obstruction, which i did..i kept all the pieces in an exploded position so it would be easy to reassemble it, the next day i went to work on it and everything was on the ground, seems a cat and a squirrel had a tussle on my workbench..discouraged, everything went into a box where it sat for years until 3 months or so ago someone offered to put it back together for me.....which leads me here

Traumahawk · May 21, 2013

I will say one thing...there are some INCREDIBLY sharp people on this forum...it might take a bit...but they will get to the root cause of your problems.

Something that you posted above...the carbs on the Vmax are a bit touchy..and the manual I believe says that the carbs have to be sync'd every 8000 miles...or anytime that adjustments are made to the carbs.

The good news...with the right tool, it takes about 5 minutes to sync the carbs.

rough idle after running at temp

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