Hey guys I have all stock vmax besides slip ons, every time I turn on bike I hear the vrrrrt, vrrrrrt from the vboost cycling, and when I slowly roll on the throttle in lower gears the vboost usually comes on. But if I hammer the throttle at about 7k rpm the bike stutters for second and usually goes into vboost and then stutters again... it’s like it doesn’t know what to do... sputter, boost, sputter? Also the right slip on pushes out at least twice the amount of exhaust as the left pipe?? Bike starts right up and idles great... Please help!
Vboost cuttin in/out
- Thread starter MotoLife
- Start date
Help Support VMAX Forum:
A few quick things to check.
How-clean is the air filter? How-about the gas filter? Either of these can cause issues if not operating optimally (a clean air filter, unobstructed gas flow in the gas filter).
If you have a K&N-style filter, try cleaning it, don't use too-much oil to re-charge it. A stock pleated paper air filter, try blowing it out from the inside-out with an air hose, or replace it if it's showing dirt.
The gas filter, remove it, and try blowing it out, see if there's any restriction. Replace it if there is, take yours to the auto parts store and you should be able to find something very similar for probably 1/3 the OEM pricing. Try "advanced-searching" function on the forum to show part #'s for common name-brand gas filters.
Into a clear receptacle, one at a time, drain the contents of each float bowl and see if you have contaminants or water in the gas. If you find contaminants, check the interior of the gas tank, a stock tank should be shiny metal inside, dark deposits or rust are needing to be removed. If someone previously tried lining the gas tank, you might see that. There are many ways to clean a gas tank, again, 'advanced-search' is your friend on the forum.
About the air exhaust volume, you might want to use a stick or a rod to probe the exhaust to see if a critter nested inside there.
How-clean is the air filter? How-about the gas filter? Either of these can cause issues if not operating optimally (a clean air filter, unobstructed gas flow in the gas filter).
If you have a K&N-style filter, try cleaning it, don't use too-much oil to re-charge it. A stock pleated paper air filter, try blowing it out from the inside-out with an air hose, or replace it if it's showing dirt.
The gas filter, remove it, and try blowing it out, see if there's any restriction. Replace it if there is, take yours to the auto parts store and you should be able to find something very similar for probably 1/3 the OEM pricing. Try "advanced-searching" function on the forum to show part #'s for common name-brand gas filters.
Into a clear receptacle, one at a time, drain the contents of each float bowl and see if you have contaminants or water in the gas. If you find contaminants, check the interior of the gas tank, a stock tank should be shiny metal inside, dark deposits or rust are needing to be removed. If someone previously tried lining the gas tank, you might see that. There are many ways to clean a gas tank, again, 'advanced-search' is your friend on the forum.
About the air exhaust volume, you might want to use a stick or a rod to probe the exhaust to see if a critter nested inside there.
desert_max
Well-Known Member
Exhaust pressure imbalance? Sync the carbs.
MaxMidnight
Well-Known Member
When you say 'hammer the throttle' does this mean going from a steady state to wide open in one quick movement?
If so then perhaps you are expecting too much?
It takes time for the carburetors to react to the throttle and meet the demand that the throttle is asking of them. I suspect that what you are feeling is a temporary leaning off of the mixture which causes the stutter.
My TDMR's have accelerator pumps that push some extra fuel into the system to compensate for this.
If once you have made sure that the basics are correct as suggested by messrs Medic and Dessert the condition remains the I think what you are experiencing is normal.
The 'fix' is stop wrenching the throttle open and do so more progressively.
Air filter is super clean, I have never checked the fuel filter, Could the fuel filter really make it run bad at high rpms, but not low rpms?
I get what your saying but for at least 2 seconds sometimes the bike just bogs, at around 7k to 8k rpm, then hits vboost for a second and then cuts back off and bogs again....Ill try to make a video today but I doubt you guys will hear it...But maybe
That orange colour is rust and filter replacement is well overdue.
Grab a torch and see what is the state of the tank.
Also you can disconnect the vboost and see what happens (remove connector when ignition is off and vboost is off as when it has completed its cycle after ignition was turned on)
I would expect that should rule out vboost but not if it is losing the ignition signal - when you are testing, does the rpm needle remain steady?
Grab a torch and see what is the state of the tank.
Also you can disconnect the vboost and see what happens (remove connector when ignition is off and vboost is off as when it has completed its cycle after ignition was turned on)
I would expect that should rule out vboost but not if it is losing the ignition signal - when you are testing, does the rpm needle remain steady?
desert_max
Well-Known Member
I doubt the exhaust imbalance is the cause of your bog. (Although it should be addressed and will likely improve with the suggested carb sync).
The bog could certainly be a fuel delivery issue. At higher RPM, the demand is obviously greater and if there's a flow restriction, it's show up there first. Based on the look of that filter, you may be on the right track!
For sure, the suggestion to inspect the tank is a good one. Just be aware that the British term "torch" refers to a flashlight. Probably not a good idea sticking what we Yanks call a torch into your gas tank.
Just sayin'...
The bog could certainly be a fuel delivery issue. At higher RPM, the demand is obviously greater and if there's a flow restriction, it's show up there first. Based on the look of that filter, you may be on the right track!
For sure, the suggestion to inspect the tank is a good one. Just be aware that the British term "torch" refers to a flashlight. Probably not a good idea sticking what we Yanks call a torch into your gas tank.
Just sayin'...
Gas tank looked great! I think I could see all the way down the to fuel pump? Put a new fuel filter in and it still stutters at high rpm...
Yes sir, the rpm needle stutters when the bike does!
When you say disconnect vboost, you mean round connector under the left scoop? Are you saying unplug it before I start it or a after the vboost noise?
desert_max
Well-Known Member
That’s a dang good answer/clue to a dang good question. Starting to sound like an intermittency in the primary ignition circuit. Wonder if it’s a Vboost mod gone rotten?
Take a close look for any monkey business in the wires feeding the rear coils - likely the left one. The tach and Vboost are fed from there. (Vboost might actually be the front left. I forget). But if somebody was dinking with the Vboost to make it come in quicker, they would’ve tied in on the left rear coil probably.
Take a close look for any monkey business in the wires feeding the rear coils - likely the left one. The tach and Vboost are fed from there. (Vboost might actually be the front left. I forget). But if somebody was dinking with the Vboost to make it come in quicker, they would’ve tied in on the left rear coil probably.
Last edited:
One is broken-off? No it appears you have OEM wires. Just look at the wire center, and see if it's green and cruddy-looking. If it is, trim it back about 1/4" to find good shiny wire strands, and when you seat the wire into the ignition coil tower, give 'em a twist, to ensure they are well-seated, then screw-down the plastic circumferential nut. That compression ring is just there for a water-resistant seal. Push it backwards away from the end of the wire, insert the wire into the coil tower, w/that twist to ensure it's fully-seated. When you move the circular nut to engage the ignition coil tower threads, that compression ring just slides-along into the tapered end of the coil tower.
I don't see anything not stock around the under the seat ignition coils. An add-on for the VBoost is usually crammed-into the space above the front engine cyl head, behind the steering head, with wires tapping into the round plastic wire disconnect and its wires behind the left scoop which is the power source for the VBoost. A way to leave your VBoost open for the small-block Chevy lopey idle, is to wait for the VBoost to cycle open, when you turn-on the ignition, and then unplugging the round plug. This will leave the VBoost open. To close it, re-plug the electrical connector, and turn-on the ignition key.
Last edited:
desert_max
Well-Known Member
Yes, your secondaries look good. But I was referring to the wiring in the circuit feeding the coils which are the primary circuits. That would be the yellow connectors and any aftermarket splices into that wiring. As Mr. medic notes, it looks pretty clean in there. You’re just going to need to scrutinize very carefully. It definitely sounds electrical (ignition) in nature if the tach is going wonky at the same time the bike misbehaves.
My Westfalia does the same thing, but usually on a trip out of The Hills early in the morning if it has rained and the ignition has gotten damp. The tach goes nuts, the van starts bucking and I know I’m in for a little trouble. Missing an NLA distributor grommet. Considering it’s Arizona, I can mostly get away with it. If I lived east of the Mississippi it would be fixed already.
My Westfalia does the same thing, but usually on a trip out of The Hills early in the morning if it has rained and the ignition has gotten damp. The tach goes nuts, the van starts bucking and I know I’m in for a little trouble. Missing an NLA distributor grommet. Considering it’s Arizona, I can mostly get away with it. If I lived east of the Mississippi it would be fixed already.
Following on from FM. The HT leads push into the coils and are held in place by the rubber grommet then the cover is screwed down. The left lead in the photo looks shorter but that is only due to the position of the rubber grommet - you should be able to feed the lead through the grommet.
The way I would do it is to push the grommet back a bit, push the lead into the coil as far as it will go then move the grommet so it butts against the coil, then screw the cover down. The cover is shaped to clamp on the grommet when it is screwed down holding the lead securely.
Following on from DM. The lead that feeds the tacho also feeds the Vboost, the fuel pump relay module as well as to trigger one of the coils; it comes from the ignition module. Check the conection at the ignition module seeing as it seems 2 circuits (tacho and vboost) are being affected.
The way I would do it is to push the grommet back a bit, push the lead into the coil as far as it will go then move the grommet so it butts against the coil, then screw the cover down. The cover is shaped to clamp on the grommet when it is screwed down holding the lead securely.
Following on from DM. The lead that feeds the tacho also feeds the Vboost, the fuel pump relay module as well as to trigger one of the coils; it comes from the ignition module. Check the conection at the ignition module seeing as it seems 2 circuits (tacho and vboost) are being affected.
If I remember correct im pretty sure the left lead is a bit shorter because i broke a piece off inside the tower when i first got the bike, gonna try to fish it out today and then ill take a look under left scoop again, I think PO was messing with something because when I took Vboost control box out, the epoxy was already seperated from the black box... Do you think a broken piece inside the ignition coil tower would cause any issues? thanks guys !
Last edited:
Most-assuredly! The primary ignition wire needs to be in good shape, and continuous! Any break in it, and your spark plug's ability to fire is compromised. Use a pick or a small pair of needle-nose pliers to remove that broken-off piece! Even-if by some fortunate connectivity/continuity path of electrical energy, the spark plug for that cylinder was able to-fire, it definitely is not optimal!
In automobiles, before COP's were ubiquitous and you still had distributors and spark plug wires, one of the ways to eliminate/lessen RF noise (a continuous 'crackle' heard from your radio speakers, with the engine running) that automakers used, was carbon-impregnated stranded nylon primary ignition circuit wire conductors (for spark plug wires). The stranded pure-copper (Cu) wire caused all-sorts of radio problems. Spark plug caps ran resistors in them to stop the RF interference 'noise,' and the caps could and did 'blow,' and you would 'drop a cylinder' in normal spark plug firing.
Last edited:
desert_max
Well-Known Member
Just to make sure we disseminate accurate guidance including terminology: in automotive (and motorcycle of course) ignition circuits, the high voltage lines out to the spark plugs are actually the secondary wires. Seems odd, but it's actually true. The primary circuits and wiring are the small 12'ish AWG lines from the ignition box.
However, to FM's point, if your coil-to-plug wire broke off inside the tower, that very likely is your problem.
However, to FM's point, if your coil-to-plug wire broke off inside the tower, that very likely is your problem.
