Have a weird problem on a 93 evo 1340, bought it for a project and started it up for the first time today, running like crap. Checked ignition and fuel all OK, checked compression front 100psi and rear 0 psi. Took the rocker cover off to see the movement and seemed ok, checked the compression again 100psi on the rear now, put the cover back 0psi. So with the cover on I get 0psi and when I remove it I get 100psi, what's going on.

 

I would guess you have a rocker hanging up on the inside of the cover.
Is it a stock cam in there?

 

It's a stock cam and I was looking at the top cover to see if there was any markings but I can't see anything.

 

Take the rocker box back off look it over. Set it back on only with a couple fastener loose so it stays in pace but really loose .
Spin engine over plugs out with rear wheel- in high gear, see what you hear and see.
(obviously, you will have to have the back end jacked up a couple inches.)

 

or you could start it and then loosen the cover screw a tad each till you hear a noise. you then could use a mechanic stethoscope to localize the area. if the cover is clamping movement, you probably will not get much marking turning at crank speed or less. another trick is to machinist dye the cover and any contact area will show up.
grins and giggles, swap cover.

 

Had a few after market rocker box's that needed clearencing on evo's or the exhaust spring retainers wound hit. What this sounds like , you have a valve hanging open.

 

Yes ESP if someone stuck a cam in it and checked notin.

 

Has the symptom of a valve collar, in contact with the rocker cover?
Scott

 

Thank's for your help guys, took the cover off and it's an aftermarket drag specialties rocker cover and there is 1 point that is hitting the rocker.

 

That would hold the valve open.
Scott