After any ideas, I've bolted my ST170 head back on having got it back from the machine shop who shimmed all the lifters for my piper 285 cams, but im finding atleast when the car is idling, im getting pulses of air coming back out of the throttle body on cylinder 3. Its definatly not exhaust gas, and the car is idling ok otherwise, no misfire etc.

My only thought so far is to check valve clearance on that cylinder, but if the valve was sitting open then surely it would be exhaust gas coming back out.

The inlet cam still needs timing for peak power, but certainly should of been ok for idling.

 

Have you done a compression test since refitting the head?

 

Due to lack of a compression tester no, i'l go out and buy one tomorrow. The head was skimmed with new headgasket and bolts used.

 

not 100% correct mate , get the valve clearance checked , if its too tight you will have this problem @ idle with just a wee bit too much overlap


john

 

I might loose the overlap when the inlet cam timing is adjusted, but i would of thought this would affect all 4 cylinders. Clearances will be first check before i buy a compression tester.

 

If its just 1 cylinder (you said its on ITB's) then it has to be a valve clearance issure on the inlet side, make sure the valve is closing as should and make sure its sealing correctly etc

 

Clearance is fine. Compression check it is then.