Engine tech

[jasper1252]

I have always thought that this engine is not perfect. So i pulled o compression test with the throttle open (cold) and pull 100psi. Now it does have the 750 big bore kit and also has only around 500 miles on it. I havent found definate specs but it sounds low to me. I'm wondering if i maybe got the cam off one tooth because their both the same? Is that compression right?

 

[KevC]

Hi jasper
The carb slides and the throttle butterflys must be held open. (just opening the throttle dont work on CV carbs)
Readings are best taken on a warm engine and should be around 140 to 145 psi and should be within 10% of each other.
make sure your valve clearances are set correct also
Cheers Kev

 

[KevC]

Also refer to the excellent thread by inxs here
http://www.xs650.com/forum/showthread.php?p=4375#post4375

 

[650Skull]

Jasper, here is a graph i came across, you will have to finish it up to your CR as it only goes up to CR of 8.0 and it is only a guide to answer your question about weather 100psi is right
http://www.type2.com/library/engineg/comrat.htm

 

[BigJimmyW13]

On inxs - He's one of the guys on the forums that is VERY knowledgeable and I most certainly respect him when it comes to XS650's. I only say I respect him with regards to XS's only because I don't know him in any other realm, but I'm sure he's a great guy. Or maybe he's a no good rotten scoundrel, but he still has my xs respect.

 

[inxs]

- dude, my wife says im an asshole bullshitter with too much time on my hands ...the main thing is, my kids still like me, so does my dog , still, thanx for the thought

- in truth i like to contribute and say my bit but prefer to stay in the background

 

[angus67]

- dude, my wife says im an asshole bullshitter with too much time on my hands ...the main thing is, my kids still like me, so does my dog , still, thanx for the thought

- in truth i like to contribute and say my bit but prefer to stay in the background

Your still ahead, 3:1!! as long as the 'like yous' out weigh the 'dont like yous' , your golden!!

 

[XSLeo]

Head gasket bad between cylinders can cause a low even reading. Jasper are you using points or TCI ignition. With points and the cam was off one tooth your breaker plate will be need to turn one way or the other way too far to time up. Filing the slot on the breaker slot plate to get the timing would indicate if the cam was off by one tooth. I'm not sure about the TCI ignition, never had one.

 

[inxs]

- 1 tooth off on the cam chain equals round 10° timing...