# ???? 08 750 rear cylinder not firing ????



## drewski1126 (Jan 4, 2018)

OK so here’s what I’ve got. 


My engine will run on Mischel start up but starts to after fire in the rear cylinder throttlebody throat while running. I can let it run for 15 to 20 minutes and with the infrared thermo check the head pipes and about 8 inches down on the front it’s around 500°, but on the rear I check it little bit down the pipe and it’s only 180. Fuel is getting both cylinders equally, compression is 50 on the front, 70 on the rear. spark looks good on both, just installed new at radium plugs, and swapped the coils to check those too. 

After taking the rear spark plug out it’s super fouled, while the front looks slightly brown on the anode. 
I can cover the intake on the rear and it just try’s to suck my hand in. I do that to the front and it kills the engine. 

Also, I can squeeze off the fuel to the rear injector or spray additional fuel into the throat, and nothing changes. 


Could it be 180 our on the timing. ??? Only thing I can think of. 

Thanks in advanced 


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## NMKawierider (Apr 11, 2009)

Well, with the plug fouled it won't fire. The question is-what is it fouled what? Gas.. or oil? Also, it might fire outside the cylinder but under compression it may not if it's too wet or the plug has a problem or the coil voltage is too low. Does this machine have a battery or charging issue? Could it have s stuck injector? And how about valve timing? Could that cam chain have jumped a tooth? Might check these things.


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## drewski1126 (Jan 4, 2018)

No charging issues on the bike that I can see. Rectifier and magneto all check good. 

Will do a test on the coil voltage when I get home later tonight. 

It runs pretty decent at the moment. I just can’t get over the temperature difference in the two header pipes. Just wondering if that is normal maybe or not. 


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## NMKawierider (Apr 11, 2009)

drewski1126 said:


> No charging issues on the bike that I can see. Rectifier and magneto all check good.
> 
> Will do a test on the coil voltage when I get home later tonight.
> 
> ...


 That much temp difference is not normal. Indicates a dead cylinder.


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## drewski1126 (Jan 4, 2018)

Had a friend mention to me maybe the valve lift is not adequate enough on the rear cylinder. Gonna check that tonight too


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## NMKawierider (Apr 11, 2009)

drewski1126 said:


> Had a friend mention to me maybe the valve lift is not adequate enough on the rear cylinder. Gonna check that tonight too
> 
> 
> Sent from my iPhone using Tapatalk


That's possible too. Check that the top end is getting the lube it needs.


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## drewski1126 (Jan 4, 2018)

Checked the lobes on the canes and they all look good. Oil is getting to em too. 

Took the throttle body back off and checked the butterfly’s, looked like someone had jacked with the adjustment on the rear one. Seems to be running better but the temps are still off. 

Wondering if a bad fuel pump could be the cause of it running lean. Got a pressure coming to check that. Already did the flow test and it passed.
View attachment 19586
View attachment 19594



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## drewski1126 (Jan 4, 2018)

Turns out the rear cam was 180 out. Went through the timing process again and had to flip the cam to get it to Line up. 

Runs great now


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## Tacomaholic14 (Aug 14, 2021)

drewski1126 said:


> Turns out the rear cam was 180 out. Went through the timing process again and had to flip the cam to get it to Line up.
> 
> Runs great now
> 
> ...


I'm rebuilding my 08 750 and just did the timing and I belive mine is doing the same as yours. It will fire and run but just in 1 cylinder the front. I took the plug wire off the front and tried firing it off the rear cylinder and it only fries for like 2 revolutions then spats flame out threw the throttle body and while both plug wires are connecting and it's running on the front cylinder. It flame outs threw the rear throttle neck. It ran fine before I tore it down just had a blown gasket and now I'm pretty sure the rear cylinder isn't timed 100% how exactly is the timing done of these motors ?


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