# Backfire after top end rebuild



## kim.m.anthony (5 mo ago)

Hi All,

I’ve just reconditioned the heads and put them back on. 

I have a backfire with low power. 

Is this a symptom of perhaps my timing chain being out? Maybe slipped a tooth? I was thinking I’d do a compression test to check. 

Or perhaps a sensor? 

Any thoughts would help. 


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## kim.m.anthony (5 mo ago)

Can anyone confirm that a good compression test would confirm no issues with the timing?? 


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## VStar650CL (Nov 12, 2020)

kim.m.anthony said:


> Is this a symptom of perhaps my timing chain being out? Maybe slipped a tooth? I was thinking I’d do a compression test to check.


Could be.



kim.m.anthony said:


> Or perhaps a sensor?


The MAF perhaps, but doubtful.



kim.m.anthony said:


> Can anyone confirm that a good compression test would confirm no issues with the timing??


If it's only out 1~2 teeth on the big chain then compression might not show up very much. If it's out more than that then you'll definitely get an abnormally low reading on all cylinders. If it's a jumped cam chain, you'll definitely show up comparatively lower on the affected bank. I don't know if you dry-cranked it with the fuel cut off before starting it, to pressurize the tensioners. If not, then there's a good chance the bank1 cam chain is jumped..


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## rogoman (Dec 16, 2004)

VStar650CL said:


> Could be.
> 
> 
> The MAF perhaps, but doubtful.
> ...


If everything checks out good with the mechanical synchronization setup of the chain assembly and good readings from a compression test as per @VStar650CL's recommendation, then when your engine back-fires it can do so in one of two ways. First and the most common way is when the engine is running a small explosion of un-burnt fuel is ignited inside of the intake manifold creating a loud bang which is the backfire sound you hear. This explosion can bend the throttle actuator plate, push intake gaskets outward creating a vacuum leak and even blown apart a plastic intake manifold. This occurrence can happen once or a few times when the engine is under load. The second kind of problem will occur at the tail pipe which is a rich fuel mixture problem that can happen when fuel delivery parts fail such as an injector, fuel pressure regulator or intermittent ignition system failures.

Anytime you have an engine that is backfiring the first thing to look for is a check engine light. If the "check engine" or the "service engine soon" light is on, scan the computer for trouble codes. This will help locate the system that is having a problem and needs repair.


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