loud backfiring and gas smell

[chuck55]

Hi all

I am having a problem I can't figure out. My briggs V twin with the nikki 6 carburetor has been backfiring and smelling like gas. I replaced the carburetor, changed the gaskets on everything, set the valve clearances, replaced the fuel filter and air filter, and the problem got worse with much louder backfiring. I couldn't find anything wrong with the old carburetor. I'm stumped. Tonight I put gasket compound all around the tube to the gas pump thinking maybe there is a leak and it doesn't get enough gas. When I disassembled it previously, there was cork OHV gasket material and leaking oil from the OHV cover.

Any ideas? The backfiring is really loud, but becomes less frequent when the motor is under load

 

[Rivets]

Please supply us with all engine numbers so we have an idea what you are talking about. Model, type and code. Two things come to mind immediately, as we know backfiring is caused by excess fuel. Bad carbs or wrong valve clearance. Your valve clearances may be off, what did you set them to and how did you set them? Is it backfiring through the carb or muffler? Did you use an OEM carb or cheaper aftermarket one? What was the part number for the replacement carb. Sounds like a fuel or timing problem, if it does it under all conditions, but I wouldn’t rule out ignition until you answer these questions.

 

[Fish]

Could have just dropped an exhaust pushrod, or have a bad cam.
Yeah, post all of the numbers so we know what you have.

 

[bertsmobile1]

I do not see any mention of checking the timing key in the flywheel
Same story, if the timing is wrong it could be too late to fire ON TDC and firing when the exhaust valve is open.

 

[hlw49]

Hi all

I am having a problem I can't figure out. My briggs V twin with the nikki 6 carburetor has been backfiring and smelling like gas. I replaced the carburetor, changed the gaskets on everything, set the valve clearances, replaced the fuel filter and air filter, and the problem got worse with much louder backfiring. I couldn't find anything wrong with the old carburetor. I'm stumped. Tonight I put gasket compound all around the tube to the gas pump thinking maybe there is a leak and it doesn't get enough gas. When I disassembled it previously, there was cork OHV gasket material and leaking oil from the OHV cover.

Any ideas? The backfiring is really loud, but becomes less frequent when the motor is under load

Post model type and code no.

 

[chuck55]

Please supply us with all engine numbers so we have an idea what you are talking about. Model, type and code. Two things come to mind immediately, as we know backfiring is caused by excess fuel. Bad carbs or wrong valve clearance. Your valve clearances may be off, what did you set them to and how did you set them? Is it backfiring through the carb or muffler? Did you use an OEM carb or cheaper aftermarket one? What was the part number for the replacement carb. Sounds like a fuel or timing problem, if it does it under all conditions, but I wouldn’t rule out ignition until you answer these questions.

It is a 44R677 0021G1. The valve clearance is .004 to .006. I checked the valve clearances last night and they were in spec at TDC on the compression stroke. I used feeler gages. I used a cheaper aftermarket carburetor, but I was getting this problem with the old one and I replaced it and am still getting it. The carburetor is a nikki-6 796227, and I understand there is no way to adjust the jets due to environmental rules. The backfiring is through the muffler

 

[chuck55]

Could have just dropped an exhaust pushrod, or have a bad cam.
Yeah, post all of the numbers so we know what you have.

please see my response to rivets above. It is a 44R677 0021G1. The valve clearance is .004 to .006. The carburetor is a nikki-6 796227. The backfiring is through the muffler

 

[bertsmobile1]

Once again I will ask about the timing key
Being a V twin is it quite feasable to be firing on one cylinder and not on the other so when the unburned fuel hits the hot muffler it ignites.
So two things to do
Remove the nut / olt that retains the flywheel & check the key slots line up to make a perfect square.
If they are just the slightest bit off then the key has split & the timing of the sparks will be a poofteenth wrong .
2) remove the kill wires form the coils and do a test mow , carefully .
Problem goes away = bad diodes in the kill wires

 

[chuck55]

I pulled the flywheel and don't see anything wrong with the key - not split or deformed. I tried replacing the diodes a year ago, but will try again when I get it back together

 

[chuck55]

Are there any specs on the nikki carburetor so I can check the oriface diameters? Does anyone know where I could find them?