Firing On All Four

[shamandog]

This seems strange:

I have a 74 2.O liter with a single weber carb. (I know, two are better--but if I want to stay married I need to wait a while--I just got the car.) Last week I posted about poor performance when it was in the ninties outside.

I adjusted the valves and the performance improved dramatically. (All of the clearances were tight before I did the adjustment. I don't know the maintainance history)

Now I get a very strong backfire at idle. And this is what I don't understand: If I pull the spark plug wire on the number 2 or 3 cylinder (individually), there is no change in engine rpm, or sound or anything. If I pull the wire on the number 1 or 4 cylinder, the engine dies. There is a spark firing on 2 and 3.

Any thoughts? The car is running good, and seems to have power, and I can't believe it's only running on 2 cylinders, but I don't understand why disconnecting number 2 or 3 doesn't cause any change, and 1 or 4 causes the engine to die?

Thanks for any suggestions

Richard

[Jake Raby]

Some engines do this for no reason at all....and some are getting flat cams, and thats why the two opposing cylinders share the same condition...they share lobes.

do a compression check and see what you get.

[Dave at Pelican Parts]

2 and 3 are diagonal to each other. They don't share any cam lobes.

Compression, spark, and fuel are what are needed to make a cylinder fire. (That, and timing.) Sounds like you're missing one or more of them on two cylinders.

--DD

[shamandog]

I haven't had the chance to do the compression test but:

If I disconnect 2 or 3 (individually) nothing changes at idle, but if I drive the car--it runs terrible--no power, rough, etc.. So they must be firing--correct?

thanks

Richard

[tat2dphreak]

I had a similar problem... I had low compression on 2 cylinders... it was running, but rough! compression test should reveal a lot...