Hey there, i got a Yukon 150 YXL and it was all in bits, wiring harnes, egine, body, the lot, So buying the thing was a gamble and the bigger question would be why the bloke took it apart then sold it. Regardless i assembled it and the only problem i am having is with the engine, as i got it it ran terrable, ran extreamy rich to the point it would barly runa nd when it did it would only work at 1/2 throutle. So i took apart the top end and found out the timeing was to retarded so i redone it but now it barly startes and when it does it realy resists anything i do, also befor i did the timing i was getting good compresion of around 170 PSI but after i got around 140-150 PSi, i also did the tappets to ensure nothing can go wronge. The engine no longer runs rich but now it barly runs and does not behave well. For christmas i am getting a top end rebuild kit, would this fix the problem since i think it may be the valve seatings or something valve related.

Sorry if this is long but i would realy apretiat any input on this, thank you!

 

are you sure you got the timing right? did it bog down like the carb was not feeding the cylinder or was it not idling correctly and missing? i'm not understanding the "resists everything i do" statement. .
barely starts? barely cranks/turns over or finally starts after cranking it awhile? could be just valve adjustments could fix it.

 

Yeh im sure the timing was done correctly as the cam shaft was alined with the tdc mark on the flywheel. As for how it behaves i only have a idle air/fuel mixture adjuster so there is not much to do there as it is a brand new carby, it doesnt like to start, it cranks over fine with the starter motor but it barly fires and when it does it only workes on half throutle and is realy boggy and mis-firing. The spark is good and plug has been regaped and cleaned. Thanks

 

IMO, somehing is not correct in the valve train. Going from 170 to 140 tells me so.
Do you have a manual to tell you the exact alignment of the valves?

 

Yep, and also due to the unknown history i have got a top end rebuild kit with piston and rings purely to ensure there are no futur problems, would this also fix the current problem

 

I doubt it. Blowing a comp of 170 is mighty fine IMO. Your statement of it comming down to 140 leads me to believe there is another problem.
So your manual says you have the timing correct?
Valves adjusted correct (usually about .004 I think)?

 

Following the manual the timing is 100% correct and double cheaked. The rocker arm clearance has also been ajusted to the 0.08mm standered valve clearance stated in manual. Cam lobes are also within service limits. Which leaves me to beleive a valve seating issue, maybe weak spring, bent shaft or damaged seat maybe?

 

You've indeed done your homework!
Does this machine have a compression release mechanism?

I'm no 4 stroke wizard but I'm not beyond trying.

 

Cheers, not bad for a 15 year old And no it doesnt have a compression release mechanism just a normal 4 stroke.

 

I you by chance checked the vacuum fuel shut off? They are known to leak past the diaphragm and dump fuel straight into the engine. Causing it to flood.