mattsclean90

I just bought a 90 lx with a fresh 306 in it. The car was running perfect and had the following upgrades already done to the engine:

Trick flow intake
Trick flow stage 1 cam (499,510 lift)
1.6 fms roller rockers
stock heads

So after driving it like this for a few weeks I decided to put a set of edelbrock performer rpm heads on it. They are the ones with the small 1.90 intake valve. I tore the engine down myself and put felpro 1011-2 head gaskets on. Put felpro 1250 intake gaskets on and made sure everything was in perfect shape. I added the heads with a set of comp cams pro magnum 1.6 ratio roller rockers and stock length pushrods. Well I adjusted the valves the same way I always do by bumping the engine over and adjusting the intake valve when the exhaust starts to open and adjusting the exhaust when the intake valve starts to close. Well it was time to fire it up and it fired right up but the rockers sounded way too loose. They were clacking and the engine didn't want to rev up at all. Studdering and not much vacuum unless you revved it up around 5,000 or so. So I readjusted them again and the same thing happened.

So I ended up changing the roller rockers to harland sharp 1.6's today and readjusted them the same way again. This time they seemed too tight and the engine would do nothing below 5,000rpms again. So I went back and loosened them all 1/2 turn and now the engine will rev from around 2,500rpms and up perfect. But below that and it won't run at all basically. Missing and studdering real bad. But as soon as the rpms hit around 2,500 then the engine revs up perfect and nice and quick like it should. So I loosened them up again and now they are too loose and the engine still only runs at around 2,500 and up. I'm completely stumped as to what is wrong unless I have the wrong length pushrods. I ordered a set of FMS stock length hardened pushrods because that's what I was told to use. Where did I go wrong guys? I have went over the whole engine and everything is fine. The distributor is on the right tooth. The timing is set at 10* initial. No leaks of any sort. No loose vacuum connections. 35psi oil pressure at around idle and 42lbs of fuel pressure at idle. The engine is beyond sluggish and doesn't want to rev until around 2,500rpms......Please help!!![/align][/align]Do I have the wrong length pushrods??[/align]

92hatchLX

How does you valve train Geometry on the tip of your valve stem look? Checking your valve train geometry will tell you if you've got the correct length push rod or not.

mattdel

so you upgraded your heads and didn't touch the fuel system....

mattsclean90

I haven't checked the wear pattern because I don't have an adjustable pushrod to check it with. I noticed that on some of the rockers they looked turned to the side a tad bit. I have done over 5 top ends of 302's and never once had this problem. I remember once I put too much preload on a set of rockers and the engine did the same thing as this one is doing. But all I had to do is back them all off about 1/2 turn and it fixed the problem. I tried that today and it didn't fix it. I even backed them off to 0 lash and it still acted like some valves were either not opening on time or staying open for too long. Does anyone have a trick flow stage 1 cam with performer rpm heads on here that knows what length pushrod they used?

mattsclean90

The fuel system has been upgraded. Here is the list:

Trick flow track heat upper and lower
Trick flow stage 1 cam
Aeromotive adj. fpr
FMS 24lb injectors
190lph fuel pump
bbk 70mm throttle body and egr spacer
C&L 76mm mass air calibrated for 24lb injectors
Edelbrock Performer rpm heads with 1.90 intake and 1.60 exhaust valves
Harland sharp 1.6 ratio stud mount roller rockers
FMS hardened pushrods in stock length
BBK long tubes with matching off road x pipe
And of course a K&N......lol

92hatchLX

You don't need and adjustable pushrod to check and see if you areusing the correct size push rod length. Pull one of your valve covers off, remove a rocker arm, clean off valve stem tip, color it with black permanent, place rocker arm back on the head, set the tightness and turn the motor over by handa few times and look at the wear pattern. Have you ever used that method before? That'll tell you if your pushrods are too short, long or perfect. That would be my next step if I were you.

mattdel

+1

92hatchLX

mattsclean90

So if my pushrod length is too short or too long the engine will act the way I described? It acts just like the valves aren't opening and closing at the right times. But then when I rev it up as soon as the rpms get close to 2,500-3,000 the engine revs fast and normal like it should.

92hatchLX

It could be a possibility, it's really hard to tell over the internet and I'd be willing to bet that is what it is, but who knows. Try checking your valvetrain geometry firstlike I had describedand see what the out come is. How long are the current pushrods? Stock?