I Think I Have A Compression Issue, Help Please

[Richie-Van-GTi 70 2 Cars]

Ive got my 205 running but not quite right, spec is below in my sig. Anyway I had issues with it 'coughing' back out the carbs, also seems to have a little pop every now and then from the intake (no flames or anything).

It got me thinking so I ran a quick compression test. Im getting 110, 110, 125, 110.

I repeated the test and got the same, thats in psi on a stone cold engine. No idea why pot 3 is higher but not overly concerned, it may be a case of fuel sat in the bore as the plug from 3 was particularly wet.

But do you think my cam timing could be off somewhere? I know I was expecting closer to 160's minimum as my old 1.9 gave 180's cold.

cam timing marks are bang on in time with lower pulley but not sure if it may be the 1.9 pulley against the 2.0 bottom end thats giving me an issue? Also if its got an inlet slightly open when it shouldnt be allowing it to blow back out the carbs would this be too far advanced or retarded?

 

sorry for the essay, thanks for any advice in advance

 

quick vid here so you can see the fuel coming back out the carbs.

http://www.pgacnortheast.co.uk/cough.3gp

Edited March 26, 2007 by Richie-Van-GTi

[Richie-Van-GTi 70 2 Cars]

should mention, coolant is spot on, oil pressure is perfect and the gasket is new.

[zeolite 0]

Have you tried doing a wet compression test? That will tell you a lot about rings and liners.

[Richie-Van-GTi 70 2 Cars]

the rings and bores are fine (no liners iron block), I just put this engine back together and everything was checked. When it was running before fettling with a 1.9 head it gave 160's cold. I would of expected an increase since the 1.9 head should be giving me more squish.

[Richie-Van-GTi 70 2 Cars]

saga continues, a friend suggested bore wash from the over fueling could be the cause of low compression and to try setting the idle fuel right and allowing it build the carbon and oil back up.

Anyway, I used a colourtune to set the idle fuel and now have a nice bright blue flame with idle at just below 1k but something is 'popping' inside the engine. dont know how else to desribe it. It can be heard out the exhaust but is most definatley inetrnal noise. Also noticed when the pop occurs the flame in pot 1 goes extremely bright like its lean. Could it be getting a big old suck of air from somewhere on pot one every now and then? If so could it be blowing from one pot to another? Im not sure if pot 2 is coming up as pot 1 is igniting and pushing a little burst of air through that didnt register on cold compression test?

[max0 5]

no idea mate but i thought most people used the 2.0 head on a 1.9/1.6 engine as the 2.0 head was better-?

 

You tried reshimming the head? I have no idea if thats it but could explain why one of the pots is out?

[Richie-Van-GTi 70 2 Cars]

Max, the head was rebuilt recently (not been on road since) so all clearnances are set at minimum (well a smallest fraction over to allow for expansion when warm).

Using 2.0 bottom end for strength and torque, 1.9 head to increase CR.

I know 2.0 head flows better on intake but worse on exhaust. But since I had the bike mani for the 1.9 port shape and a good 1.9 head and cam set there it made sense to use it. The increase CR so balance out the intake flow loss anyway I reckon.

[Richie-Van-GTi 70 2 Cars]

here, i video'd from the exhaust and then down the gunson, you can hear it make the noise and see the occasional bright flash down the gunson.

 

 

http://www.pgacnortheast.co.uk/pop.mp4

 

From watching that vid a couple of times it seems it isnt firing every time but not sure if thats just the gunson or not. I know it still does it with a spark plug in.

[Richie-Van-GTi 70 2 Cars]

had another tinker and ran a few checks, theres no valves sticking, all valve clearances are right, cam timing is right, firing order is right and compression is now 179/180/179/176 , battery was starting to die a bit so all in all Id say the engine itself is right and the carbs are at fault. The reason for previous low readings was blatantly obvious. Id left the butterflys closed Embarassed

Also when it pops it definatley pops back out the carbs on pot 1 so Im now left wondering if it is a case of carbs needs setting up right and ignition timing neds fettling.

Edited March 27, 2007 by Richie-Van-GTi