This is driving me crazy, does anyone else have this problem, and have they cured it ? At low rpm's between 1000 - 2000 occassionally one of my carbs backfires through it, usually when the bike is running on the hotter side, seems to be intermitent, but its annoyong - i have cleaned and synced the carbs 1000 times , and they are perfect - i'm pulling my hair out - please help
Help Support VMAX Forum:
How do your plugs look? Mixture screws? Sounds like you're running lean in at least one of your carbs.
Check for leak in air box, vboost or carb boots. What did you do to clean the idle circuits?
[email protected]
Well-Known Member
I kinda thought this normal for the vmax?:confused2: I know my bike has done it since I got it with 2K miles on it. Mostly when its warmed up, and I let off the throttle like when coming up to a stop sign. I would describe it as a carb fart. Same scenario, only while down very low in the RPM's. Is this not normal?? Still stock... But not for long
unk:
unk:
This is a lean mixture/air-leak symptom.
How old is the bike? Rubber ages and seals start to leak.
1) Check to see that the rubber boots and clamps are sealing on the carbs, v-boost and inlet manifold joints. Make sure the inlet manifolds are tight and not leaking between the manifold and the head. Liberally, spray water on these joints. If the engine RPM goes down, you have a leak.
2) Incorrect idle mixture setting or blocked air-jets. Adjust idle screws and do shotgun clean on jets.
3) Hole in one of the coasting enrichment diaphragms or perished (flabby and stretched) diaphragms. The coasting enrichment diaphragm moves a brass fitting through a tube in the carb housing to restrict or enhance off idle/on idle fuel mixture. This can bind if dirty or corroded. Remove, inspect, clean and replace as necessary.
4) Hole in carb slide diaphragm or perished (flabby and stretched) diaphragms. Remove, inspect, clean and replace as necessary. Make sure slide diagram covers are correctly installed and not leaking.
5) Long Shot. Incorrectly installed slide springs where the spring does not seat around the prongs on the underside of the carb side covers does also cause this.
6) Air leak from the rubber caps that cover the vacuum inlet tubes on the lower manifold. These are the ones you fit your carb synch tool tubes to.
How old is the bike? Rubber ages and seals start to leak.
1) Check to see that the rubber boots and clamps are sealing on the carbs, v-boost and inlet manifold joints. Make sure the inlet manifolds are tight and not leaking between the manifold and the head. Liberally, spray water on these joints. If the engine RPM goes down, you have a leak.
2) Incorrect idle mixture setting or blocked air-jets. Adjust idle screws and do shotgun clean on jets.
3) Hole in one of the coasting enrichment diaphragms or perished (flabby and stretched) diaphragms. The coasting enrichment diaphragm moves a brass fitting through a tube in the carb housing to restrict or enhance off idle/on idle fuel mixture. This can bind if dirty or corroded. Remove, inspect, clean and replace as necessary.
4) Hole in carb slide diaphragm or perished (flabby and stretched) diaphragms. Remove, inspect, clean and replace as necessary. Make sure slide diagram covers are correctly installed and not leaking.
5) Long Shot. Incorrectly installed slide springs where the spring does not seat around the prongs on the underside of the carb side covers does also cause this.
6) Air leak from the rubber caps that cover the vacuum inlet tubes on the lower manifold. These are the ones you fit your carb synch tool tubes to.
Mine did this since it was new. went through the carbs, checked everything, cleaned rejet, ran on dyno.
it did it more when it was lean, then we fattened it up a little and it did it less but continued to do it, then i switched to flatslides 10,000 miles later
this is a common problem for the max, even when tuned to perfect A/F ratio. but wiil tend to do it more so when lean
it did it more when it was lean, then we fattened it up a little and it did it less but continued to do it, then i switched to flatslides 10,000 miles later
this is a common problem for the max, even when tuned to perfect A/F ratio. but wiil tend to do it more so when lean
4gasem
Well-Known Member
Mines backfired since new. Not badly but a little.
Remember that back fire is through the induction system and after fire is through the exhaust system.
Remember that back fire is through the induction system and after fire is through the exhaust system.
Popping is more likely to occur at low rpms due to higher vacuum. Check boots, boots, vboost is closed and manfolds are tight. Check condition of o-ring on the underneath side of each manifold. When's the last time you adjusted the valves?
MONTREALMAX
Well-Known Member
leak in the airbox? do you mean all screws are tight and boots clamped firmly on carbs? or is there something else to check in the box?
Exactly. Make sure clamps are straight and firmly try to pull up on air box around each boot. Should be tight. Also, make sure velocity stacks are tight where they go into air box. I took mine out and put a bit of Permatex black around the mating edge.
MONTREALMAX
Well-Known Member
PATMAX
Well-Known Member
I get absolutely no burp or backfire or pop but I am running a little rich and I am at sea level. Stage 1 , K&N with "Y" removed and Kerker 4-2-1. Oh, and I have newer boots on my carbs, boost manifolds.
MONTREALMAX
Well-Known Member
permatex.....smart did not think of that area for a leak replaced those stacks last year but just put them straight in eh?
I had the same issue but mine is due to my fuel switch on the handle bar or relay. I switch it to reserve and it goes away, I put it back to normal and around 2500 to 3000 I get a pop change it back to res and it runs like a champ :bang head:. From what I was told I need to check my relay or res switch. I have not been able to have anyone look at it yet to determine if its the relay or bad switch.
forgiven
New Member
I just got this issue after changing air filters to a K&N. I wasn't sure if it was a lean condition via more air flow or leaking by the new filter. I think it is just a lean condition though because the previous air filter ran fine and it was quite dirty.
