no compression in cylinders 1 and 3???

[jrentz13]

I have an 1835cc motor with dual empi pic34 carbs. I recently replaced the carbs, from 32 s to 34 s. I started to run hot and I pulled over to check the plugs by pulling the plugs off the distributor one at a time and 1 and 3 had no change in idle. I then replaced the plugs with no change. the plugs from 1 and 3 were sooty but not burned white or grey. I decided to do a compression check on the cylinders and had no compression in 1 and 3. What could be my problem???

[JSR-69]

You'll need to run through the standard checks starting with valve clearances. Odd that it's cylinders on opposite sides, if you'd lost compression in both on the same side, I'd suspect a loose head.

If you valve clearances are OK, then you've either got burnt valves or a broken piston ring ... but that is unlikely to give you zero compression, just lower than normal.

I take it you haven't heard any unusual "noises" from the engine bay recently?

Judi

[Editor]

I can't see how you were able to decide to pull over as it was running hot if only two cylinders were firing! That would have been a more obvious reason for stopping. Do those plugs/plug caps get warm? That's a good check that something is firing when running at normal rpm. If something is marginal it can happen that a plug doesn't fire.

Two camshaft lobes are common to both 1 and 3 cyls - a bad cam would affect both 1 and 3, but it would not tend to lose compression - the valves just wouldn't open correctly.

How did you check the compression with a gauge or by feel by turning over the engine? Try turning the engine over by hand and listening for wheezing sounds as it compresses (or not). Check the valve clearances - a tight valve or even two isn't unusual. Watch out for the valve stem lengthening (valve clearances keep disappearing) and the valve is about to lose its head.

[jrentz13]

I found out it was running hot after i pulled over i pulled over because it felt like i had half throttle. I figured the linkage rattled loose on one side. which happened a few days earlier after i put the new carbs on. As for the compression i thought it was strange to have no compression on opposite sides, at the very least low compression. I did a valve adjustment and the valves were on point at .006 nothing dramatic.

[Editor]

I suggest you check the compression again, just to be sure - if you confirm there is none in those two, I can't see what alternative you have other than pulling the heads off and seeing what's wrong.