poor running vmax

Robert Kemper · 08-28-2011, 02:34 AM

I would like to know if anyone knows the possible explaination why my 1985 vmax spits back on intake side, and backfires or pops on the exhaust side when its cold during warm up, after warm up it mostly goes away. the slides seem to flutter open the frequency is high barley noticeable. not totally smooth.
also i ohmed the pick up coils and my readings were 234.9, 235.7, 236.4, and 117.9 how much trouble can this cause
new to the vmax thank you fo your time.

RCK Coatings, Martinez, CA.

signit98 · 08-28-2011, 03:17 AM

Robert, you might get a lucky response from someone who knows... but - as a point of reference - this is a BMW forum...

Looks like a bad coil... intermittent/temp related issue...

wswartzwel · 08-28-2011, 04:04 AM

Lots of Vmax experience, I used to work for a dealership.

First off
They don't run well with the lid off the airbox.
How many miles on it?
Is the gasoline good fresh gas?

If the intake or exhaust have been modified without rejetting the carbs the bike could be a bit lean.
if the bike has set without being ridden the idle jets could have a bit of residue in them. First thing I would do is drill out the EPA plugs in the carburetors that hide the idle air/fuel adjustment screws. gently seat them and set them at 3 turns out.

Robert Kemper · 08-28-2011, 05:42 AM

Thanks for your reply,

thebike has 45,000 miles on it but is in very good shape. No modifications to intake or exhaust the fuel is good and fresh. It does have a low preasure automotive fuel pump with preasure shut off and no fuel seems to be going by the needles carbs were carefully cleaned and intake runners were checked for leaks after assembly.

your right about me running it without the airbox and also that it hasn't been run in a few years it starts right up choke on to a high idle and the spiting and poping is minimal under these conditions its when the choke comes off during warm up the problem is worse

I'll reinstall the airbox and check it out, do you have any input on the pickup coils resistance readings?

thanks again obviously II need to do a little more work before i ask more questions the diaphrams are also questionable and shouled be replaced the price is slowing me down. is there any place with a price less than 110.00
Robert RCK Coatings.

wswartzwel · 02:22 PM

K&L supply sells aftermarket slide/diaphragms but you need to be a dealer to get an account with them. I don't have the pulse coil values but when they fail it is when the engine heats up that they give problems. I would bet you still have a bit of blockage in the pilot jets. a #77 drill bit should solve that... if you can get a #77 drill bit, one strand from a bicycle shift or brake cable about 6" long... slide it through the jet, and drag it back and forth a few times.

markjenn · 08-28-2011, 01:11 PM

Quote:

Originally Posted by Robert Kemper

your right about me running it without the airbox and also that it hasn't been run in a few years it starts right up choke on to a high idle and the spiting and poping is minimal under these conditions its when the choke comes off during warm up the problem is worse

Sounds like standard plugged idle jet/jet needle emulsifier problems to me. More or less par for the course after a bike sits long enough. I suspect carbs are no picnic on a V-Max, they certainly are not on Honda V4s.

My most recent experience with clogged carb jets was with a Honda generator. I tried a standard fuel cleaner without luck, but then tried Chevron Techron at about 200% the normal fuel maintenance dosage. It immediately unclogged the idle jets and the thing runs like a top now. Techron is now my first shot at this problem before I pull carbs. YMMV.

I hate carbs.

- Mark

SteelerBike · 09-02-2011, 09:03 AM

Have you tried a vmax forum?