Vmax Carb Problems

[BrianK]

We cured the same issue "rpm hanging" while dropping slowly back to idle, by re-doing the sync. For what ever the reason, this solved our problems with two different Vmax.

The carb set had already been removed, cleaned, re-built and synced, but for some reason it required another run through with the Sync Tool to get it running as it should be.

FWIW -
Mercury Filled Sync Tools do not need to be calibrated as they are already calibrated at the factory.

Manometer Fluid Sync Tools do need to be calibrated before each use and the rpm during the "sync process" should be very similar to when calibrated. (this is directly from Motion Pro)


Hope that helps.

BrianK
Houston
bdk2272-5125

85' Vmax

 

[naughtyG]

When I do my sync I always set my idle a little higher (around 1250rpm) by turning in the idle screw. Once I'm happy with the sync I turn it back out to get the wanted 1000 rpm idle.

You say you set your A/F screws at 2 1/4 turns. Any reason why? Was that where they were set before? I would try 2 1/2 turns as a start, and then try a 1/4 to 1/2 turn either way to check which runs best.

Some people say you can adjust each A/F screw individually, by screwing them in all the way (or until rpm really suffers) then slowly backing them out looking for the highest rpm idle. This did not work for me - when I tried I could not detect any noticeable changes in idle while adjusting any single A/F screw.

Also, to check your lean/rich condition, one good way is to run your bike til it's nicely warmed up, then ride it at least 5-10 miles, and bring it to a stop from 50/60mph by pulling the clutch and hitting the kill switch. Then remove and inspect each plug - that should give you a good indication of the mixture's status on each one.

 

[atVMAX99]

Went back at it today and went a new approach, I was questioning my Pilot Mixture screw settings of 2 1/4 turns because I noticed I had the Idle Speed screw wound higher than normal and I was starting to think this is the real source of the hanging idle. I wound down the Idle Speed to a spot that looked like it used to be at, I set the Mixture screws to 2 1/2 turns out and started the bike cold with 3/4 choke, as the bike warmed and rpm's started to climb I knocked the choke down accordingly holding 4k rpm's. The temp guage got to the "dot" and I took the choke off, the idle held at 1000 and while revving NO HANGING IDLE. Excellent! I'm onto something here so I took it for a spin down the street, bike was running great and again no hanging idle. Now it was cool today about 55 degrees, as that cold air was hitting that rad I noticed the temp guage dropped on me maybe a 1/4 inch below dot, the bike started not holding it's idle so back to the garage. I increased the mixture screws to 2 3/4 turns out and restarted, the idle was barely holding on at 500rpms so I started to tweak up the Idle speed, bike held 1000rpms, revved the motor and still no hanging idle so I took it down the street again. It was running good but sometimes jumping right off of idle I got a couple of coughs, so I went to 3 turns. It seemed to like this, I brought it back to the garage and let it run in there holding a 1000rpm idle, goosing the throttle and still no hanging! I let it idle somemore, by this time the bike was hot enough for the fan to start coming on, still held 1000 and still no hanging. I shut it down and restarted immediatety and no issues right back to 1000rpms and held. I'm planning a several hundred mile ride with my brother on Saturday and the forecast is calling for highs around 88 degrees so I'm a little concerned 3 turns maybe too rich for those temps, I'll definately have my small screwdriver with me.
So it looks like the hanging idle was caused by setting the idle speed too high to keep it idling at 1000 with the mixture screws set too lean, I used 2 1/4 turns as a starting point because the screws were originally only 2 to 2 1/4 across all 4 carbs before I tore them apart and I never ventured as rich as I am now because I thought this is the range they were supposed to be at.

Update:

The ride was excellent, bike performed beautifully! We went to Gettysburg, from my house is 90 miles, overall miles on outing was 247 and even in 90 degree temps it ran and restarted fine!