Back fire into the airbox

[Franklin]

Hi everyone, this is my first VMAX. Today when I started it at a friends house I noticed it back fire into the airbox. I tought nothing of it at first but when I put it into gear it back fired in to the airbox again. It did this about every two min and continued untill I got the bike home. To top it all off the last 50 miles home I start to hear dif noise when I would get out of it. Made it home checked the diff and oil is good. Im wondering if this might be normal for this bike? Thanks for any help!

 

[poppop]

Not normal for mine,They will be a whole lot of guys on here that will be more help than me.Plugs old,mabye dirty?spark jumping anywhere?When were the valves adjusted?Best of luck.poppop.

 

[Rusty McNeil]

If it does it when you just barely crack the throttle from off idle position, and is worse cold and gets better or goes away as it warms up, I've heard that can be cured by richening inch up the idle mixture screws.

If it does it all the time I don't know.

 

[Franklin]

It does it all the time. I'm checking things now.

 

[[email protected]]

Backfiring is typically caused by a lean condition.

Plugged pilot jets
Fuel/Air screws set too lean (turn counter clockwise to richen up the circuit)
Air box not completely seated or sealed.
Any of the rubber boots could be leaking or have small cracks which can be hard to ID. Boots between carbs and airbox, carbs and intake manifolds, v boost and intake manifolds.

Another possible issue could be poor spark. Check that all plugs are firing strong. Check that none of the wires are arcing to the head. (Easily done in a dark environment)

These differentials do make some noise. If you are hearing excessive noise it seems the most common culprit is a loose nut on the pinion gear which is easily accessible after removing the diff from the swingarm. Just about anything beyond that requires differential dissasembly.

 

[jagco1]

Plus 1 - Mike, carbs could need cleaning to.

 

[tugla]

Also a sync check would help.

 

[The Beekeeper]

My Max runs great, but even I will get a pop into the airbox once in a while, especially just off idle, I would do the Shotgun like mentioned over at the V-4 forum and then sync the carbs and see how it runs......................Tom.

 

[texas-ss-tornado]

Hey Frank, anytime you want to do a Shotgun treatment and sync, bring your bike down and we'll getter' done!!!! unk:

 

[The Beekeeper]

If Michigan is closer I can give ya a hand too!....................................Tom.

 

[Franklin]

Thanks guys, I have got the pop figured out. The tube that runs from the airbox to the case was off plugged it in and it works fine. I did go trough the carbs last night and have everything 100% after I found that the hose needs connected LMAO! Now to the Dif. I know everyone runs synthetic oil in there dif but I have always used Lucas oil stabilizer with dino. Is there anyone that uses this and will it be ok? Im going to change the oil later if this will not hurt anything or I might add some Lucas to what is there to see if it helps. If that dont cure it the looks like a possible pull apart and have a look. Have to give a bigh thanks to you John for the parts to!!!!

 

[texas-ss-tornado]

Glad I could help you out! Feel free to call me anytime if you need parts or advice on your Max! unk:

 

[[email protected]]

Dino gear oil is fine. Hypoid GL4 or better. 80W is what is listed in the manual.

 

[Franklin]

Would 80w-90 GL5 be ok? I would do half of the 80 and half Lucas oil treatment. I have never worked on difs on motorcycles. I normaly build Cafe bikes.

 

[Franklin]

Ok now after a 20 mile run I have a gear noise in the tranny when I'm off the gas plus the temp is running hot in the city. There is so much heat coming off the gear box by the pegs it makes my feet hot. I hope this is not a normal thing with the heat at the foot peg location.

 

[texas-ss-tornado]

That doesn't sound normal to me. What concerns me is that we know this bike was wrecked at one time and may have spent some time "on it's side". I would have thought you would have already come across any tranny issues, but this would really concern me. I don't know what to tell you at this point, maybe some of the more experienced guys can chime in!

 

[Franklin]

Yes that is true. There seems to be more and more coming to light with this bike. What I find that is strange is it sounds like it is low on oil but its not also second gear is good. I'm wondering if the issue with the rear diff could cause this noise. What I'm thinking is get the issue with the diff fixed and see if the noise in the tranny is still there. So anyone with ideas on what to do to the diff since I have never worked on one.

 

[m-cman]

If the problem is in the differential itself, the easiest and probably the cheapest way to fix is replace. There are used ones popping up on eBay all the time. I actually replaced mine with a used Venture off eBay to lower the rpm at cruising and get better mileage on trips. Have no idea what causes one to go bad as they are very reliable. Maybe serious drag racing?

 

[naughtyG]

Ok now after a 20 mile run I have a gear noise in the tranny when I'm off the gas plus the temp is running hot in the city. There is so much heat coming off the gear box by the pegs it makes my feet hot. I hope this is not a normal thing with the heat at the foot peg location.

Do take off your rear wheel, then unbolt and pull off the differential.

I've seen/heard that very loud gear whine only when off the gas, and often it simply is the nut in the diff that's come loose.

 

[Franklin]

Ok I have the diff off and everything is to factory spec. The diff oil was dirty, there were no shavings on the drain plug mag and I also ran the fluid trough a coffie filter and no particals. I have no idea could it be coming from the tranny and it transfers the noise trough the shaft to the diff. Its a stab in the dark or could it be the oil im useing? Valvoline 10W-40 for wet clutch. I have ran this in every bike i've built with no problems. Could i possibly not have enough oil in the motor? I drained the oil change filter and it took 4.25qt. to bring to the top line. I did fill the filter before instalation. Should I have ran the motor to bring the heat up and have oil in the upper part of the motor then top off. Could I have some air in the clutch causing this. I did change the res out and flushed complete.