Strange symptoms...

[lethal dose]

Been an obnoxious spat of vmax ownership this time around. Started off with carb issues... cleaned X3 then sent to Danny. Came bike (DANG he does good work!), hooked them up, bike seemed to have a demon (cracking and banging through right exhaust) left over. Recleaned carbs... no dice. Replaced all boots and checked for vacuum leaks... none. Bike seemed slightly better except the newly acquired stumble from 5-7k rpm. Talked to Sean, he is sending a full test kit (fuel, electrical, etc.). On a whim, I decided I'd drain my fuel, put a new fuel filter on, and run two gallons of fresh (half sunoco 112 leaded and half 87 ethanol free pump) fuel through while waiting for the test kit. The bike runs great... usually. It seems like if I let it idle for a while then try to rip it through the gears hard, it stumbles from 6k-7.5k rpm but ONLY in 1st gear- no others. Again... it only seems to do this after it's idled for a bit (but not always). I took it back to the garage and set the mixture screws to 2.5 instead of 3 thinking it may have just been loading up at idle. Maybe some improvement... not sure. Eventually, I got it up to the stumble point and held it there for a bit, then it started banging and popping through the exhaust. It did this for over a mile at all RPMs until I pulled the clutch in and revved the daylights out of it which seemed to clear it out.

Settings: airbox "T" removed, 155 mains, mix screws 2.5, full holeshot header.

Thoughts?

Remember... bike always ran a-1 until the initial carb problems.

 

[Traumahawk]

Since your still running the airbox, I'm assuming that your still running the stock needles? I think your too rich thru the mid range, but with stock needles there isnt really a way to tune that out. With a full exhaust....it will flow more air, and there fore PULL more air into the carbs...and with it more fuel. Most "stock" Vmax with a full exhaust, and airbox will need to go down 1 jet size to 150's from the stock 152's.

So my opinion....drop atleast 1 jet size.....if not two. That should lean you out thru the midrange....and a Vmax makes its best HP lean uptop.

Also.....make certain that your plugs are gapped at .035.

Even though it ran A-1, before the initial carb problems.....what were your floats set at? After the carb rebuild the floats are set perfect now (Danny does GREAT work) so the jetting requirements might have changed.

 

[Dragmaxster]

Put the "t" back on-set the rear a/f 's to 3 turns out-give us a plug reading after that (what are they gapped at now?)

 

[lethal dose]

Stock needles with one shim. Plugs gapped at .35. I hear what you're saying, but the bike ran perfectly... for years.

 

[lethal dose]

Don't have the "T"- never have. Keep in mind... this is ONLY happening in first gear and it seems like ONLY after it's been idling.

 

[lethal dose]

Plugs look like a sandy brown.

 

[Dragmaxster]

Stock needles with one shim. Plugs gapped at .35. I hear what you're saying, but the bike ran perfectly... for years.

Best way to read an engine is the plugs- I'm kinda thinking a valve out of adjustment.You can still get the carbs to sync up but a valve being out will create an off balanced vacuum.

 

[Dragmaxster]

Plugs look like a sandy brown.

That sounds good.

 

[Traumahawk]

Take the shim out of the needles. Your running rich enough with the 155's that it shouldnt be needed.

 

[lethal dose]

Will try, Trauma. Sean said it could be fuel bleeding past a needle, too. It's just weird that it ONLY happens in first gear USUALLY after prolonged idle.

 

[lethal dose]

To add... bike has 12,000 miles.

 

[Traumahawk]

I think it only happens in first gear.....because AFTER that, youve blown out the excess fuel.

 

[Dragmaxster]

TB99 had this same problem and i can't remember the saint that sent him the "T" for free but it helped. I rebuilt his carbs and he had a leaking valve cover gasket he is kicking himself for not replacing while carbs were off and i believe we will be adjusting valves soon (20,000 miles). He had a very similiar problem at 6500 rpm. I sent him some coils and suggested he unplug the vboost when open to see if it is his module is dying out.
When is the last time you did a valve adjustment and what is the mileage?

 

[Traumahawk]

With the mileage at 12000, he's probably never had the valves adjusted. I believe the manual doesnt call for it until 26000.

 

[Dragmaxster]

With the mileage at 12000, he's probably never had the valves adjusted. I believe the manual doesnt call for it until 26000.

I hear what your sayin traumahawk but a hard run motor is gonna need it sooner.

 

[lethal dose]

Never adjusted that I know of.

 

[Traumahawk]

I hear what your sayin traumahawk but a hard run motor is gonna need it sooner.

True.....but even with dyno time....I didnt do mine until about 32000. I will do it again this winter at around 48000 just due to sheer convenience. There are people on this forum that have never had the valves adjusted. The vmax is just a stout engine.

 

[Dragmaxster]

True.....but even with dyno time....I didnt do mine until about 32000. I will do it again this winter at around 48000 just due to sheer convenience. There are people on this forum that have never had the valves adjusted. The vmax is just a stout engine.

I always adjust them after going to a track and especially if i miss a gear and over rev it. Floating a valve will usually loosen it. I run megatrons on most of my motors so not too many carb problems. When i have a problem with backfiring i go to valves before electronics.

 

[lethal dose]

I hear ya... but REALLY dread checking the valves. I haven't a clue and am horrible at online tutorials.

 

[Dragmaxster]

Well after you try seans "gifts of gold" hopefully one will solve it --- if not get back to us. Hang in there.