Engine issue!
 

Hello,
I have a 73 with a 1.7 that I put a 1.8 big bore kit on with web cam and lifters and 44 webbers. It just started running like it’s missing on 1 cylinder. I thought it was a bad plug wire but that check good. I noticed that on that barrel of the carb there is a lot of black soot on the butterfly. I then notice when it’s running there is a lot of turbulence in that barrel, it spitting fuel and air out the top of the barrel. I talk to some of my 914 buds and we all thought it had to be a bad valve or cracked head. Well so far everything looks good. I turn the head upside down a filled that side with solvent, nothing is leaking through on the valves or anywhere else. My next thought is to find someone to do a Dye Penetrant inspection on the head.

Any thoughts?

So you've removed the cylinder head already?

I would have suggested a compression check first; possibly a leak-down test to see what that found. It might be something as simple as the ring gaps lined up incorrectly.

Did the engine run well for a while, then started doing this? Or has it done this since you upgraded it? Which upgrade did you perform, installing 93mm cylinders from a 1.8 or installing 96es to get 1911cc? If the latter, was any machining done to the heads, or were these "slip-ins"?

The 96mm cylinders that fit the 1.7 heads are notoriously thin.

Is there any sign (black soot, etc.) of leakage on the cylinder seating surface?

What else was done to the engine when the larger P&Cs were installed?

--DD

Did you happen to check the valve lash before you removed the rockers? You might have had a tight intake valve. Had you recently adjusted valves?

Had the carbs been balanced recently? If they are way out of balance sometimes it will run like it has a dead cylinder. Could also explain the turbulence if that carb was the one hanging open.

The engine ran great before this. It has maybe 10K since it was re done. I install a NPR of America 96mm kit I got from Brad Mayeur. I had the new valves put in the 1.8 heads when kit was installed. The valve lash was perfect. The carbs had been synced up just a week before. There is no soot except in the one carb.

OK, so no changes to the engine or fuel system or ignition at all, and it suddenly started to do this one day out of the blue?

Did you check for leaks in the intake system, particularly under or in that carb?

What other troubleshooting besides checking the plug wire did you do before tearing the head off?

--DD

Yes was working fine parked it got in it a few days later then started with what i have already stated.

I check the plug wire, tired a new plug wire, tried a new plug, checked for leaks at the carb and intake, checked lash on valves.

it seems to be pushing air out of the carb not in