Hi guys!

This is just a general question.
Do you think engine pops and back fires when valve adjustment is wrong?
Carbs completely sync'd, plugs and wires are brand new. Engine some how pops in carb on low rpm. Any suggestion or information will be appreciated.

 

If the intake valves leaks or the lash is so small that they don’t close perfectly, I think this will happen as you say. A vacuum test could be in place to start with.

Does the engine run OK at higher rpm and load? Popping under load usually means weak ignition or lean fuel mixture that is harder to ignite.

 

if there is backfiring in the carbs then it means the intake valve is open when the ignition fires in the combustion chamber when both valves should be closed. If the engine runs fine at higher rpm, and only at idle, it sounds like the valve timing is off. Or if your cam chain is stretched, causing the valve timing to be off. If the valve was adjusted too much it should run like a bag of hammers all the time, not just at idle. If you have time, take the valve cover off and have a look at the valvetrain. How many miles on your bike Yas?

 

I'm just wondering if there's a leak in the exhaust manifold gasket/s ? That may account for the problem.....is it backfiring through all the carbs, or just one in particular ?

 

Thanks guys.
Actually, this is not my CBR, but my friend's Suzuki VX800, V-twin. Just like R1000 pointed out, it happens when engine under load and low rpm especially at starting, and high rpm is OK. Probably carb needs to be cleaned.

Thanks again!!

 

Tell him to buy a DECENT bike.....he he
And check the exhaust gaskets........and the pilot and main jets for dirt.......

 

GILL,

As I mentioned above, the bike is not CBR.
I cleaned carb and re-sync'd. Still pops in carb around 1500 - 2000 rpm under load.
I will try to change spark plugs. Bike has 19000 miles. I can hardly think cam chain stretched (actually, this engine runs much quieter than my CBR with CCT noise). Sorry, for this is not a topic of CBR... My buddy is desperate.[/align]

 

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