VM29 carbs help

[razooki]

OK, I messed around some more today trying to fine tune the carbs. The bike idles just fine but I have a couple of issues:

1. #4 exhaust is colder than the rest. I definetly have spark and I'm quite sure I get gas because when I pull the plug it's black and shiny.
2. even though it idles fine I tried the highest idle method but the
adjustment screws seem to have no effect on the idle.
3. Do I need to absolutely do an idle adjustment using the highest rpm method before I do a carb sync?

Thanks,

Raz

 

[49er]

OK, I messed around some more today trying to fine tune the carbs. The bike idles just fine but I have a couple of issues:

1. #4 exhaust is colder than the rest. I definetly have spark and I'm quite sure I get gas because when I pull the plug it's black and shiny.
2. even though it idles fine I tried the highest idle method but the
adjustment screws seem to have no effect on the idle.
3. Do I need to absolutely do an idle adjustment using the highest rpm method before I do a carb sync?

Thanks,

Raz

Your #4 plug being black and shiny, indicates either a very rich condition, a bad HT connection at your coil or plug boot ,or oil is being burnt on that cylinder. This is in contradiction to your symptoms when you say that it idles good, but the pipe is colder than the others. A colder pipe at idle usually indicates problems in the idle circuit, due to partially blocked pilot jet passages. How well did the PO really clean your carbs??

If oil burning is occurring in #4, that plug could be suffering as a result.
Probably time for a compression test to confirm that the rings aren't letting oil past them.

 

[razooki]

I solved the #4 exhaust problem - bad plug. I changed all of them and now it REALLY idles. So on to my other questions.

If it's idling so well do I still need to do adjust the idle using the highest rev method or can I just do a sync?

 

[KEITH KRAUSE]

You should adjust the air screws for best idle before vacuum synching. That's what any book or person would tell you. You want the correct air/fuel ratio. Assuming the bike is operating correctly, it will tell you by reaching the best idle/highest rpm when the screws are set just right. If too little air, the fuel isn't atomized properly.
If you can't reach best idle and the screws seem to have no effect that tells you something isn't right. The air screws wouldn't be there if they had no effect.
Many owners say they can't hear a difference in the idle speed or claim the screws do nothing. Sometimes the owner just can't hear a difference because of their own hearing. Other times it's because they've set the idle too high to begin with and/or the bike isn't at full operating temperature and the screws aren't designed for that condition. Factory idle, fully warmed up, is approx' 1,000 rpm or what your FACTORY manual states...not 1,150 or 1,200, etc.
Other causes are dirty/plugged carbs/passages, incorrect jets, worn/incorrect parts, poor vacuum/intake leaks, poor valve clearances, etc.

 

[razooki]

I think I may be missing something regarding this setting the idle. Do I start with the engine at normal idle and then adjust each carb individually and then use the idle screw to back it down to normal idle? For some reason I thought the engine needed to be at about 2000RPM and then mess with the screws until I heard the idle going up and then back down the idle screw to normal.

 

[Guest]

I think I may be missing something regarding this setting the idle. Do I start with the engine at normal idle and then adjust each carb individually and then use the idle screw to back it down to normal idle? For some reason I thought the engine needed to be at about 2000RPM and then mess with the screws until I heard the idle going up and then back down the idle screw to normal.

I adjust mine at normal idle.

 

[razooki]

That may be my problem then. I'll try it this way then.

 

[KEITH KRAUSE]

Assuming the carbs are clean, floats adjusted, bench synched carefully, etc...
Set the side air screws to an initial uniform setting. I can't say what's the best starting point for the 29's. A typical 750/1000 with factory carbs and the pilot circuit operating correctly usually likes them about 1 1/2 to 2 turns out at the most with 1 1/2 to 1 3/4 a common final setting. If you've got it idling half way decent then you can use the current settings you have to start I suppose.
Warm up the bike to full operating temp.
Place on centerstand is best.
Set idle to factory setting, 1,000 rpm or something very close to that by using the idle adjuster knob.
Start at any carb.
Slowly turn a screw in either direction until you hear the rpm's max. Find the sweet spot and stop.
Return the idle to the base 1,000 setting by using the idle adjuster knob.
Repeat this cycle to the other 3 carbs.
Now you're ready to vacuum synch and test the jetting/performance.

 

[razooki]

I tried exactly that a couple of days ago and maybe I'm hard of hearing but I could not discern any change in RPM when I messed with any of the screws. I've also never done this before so maybe I'm not listening well enough. At any rate I bit the bullet and ordered a Colortune. I figured for a novice like me it can't hurt. I'll report back when I'm done with it.