Thread: cam timing

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I have a rebuilt 1970 350. Has 1967 "camel hump" heads. Runs good until I get into the 4-barrel, which is a Edelbrock
#1405. 600CFM. When you floor it it tries to get to about 3000rpm's and that's it. It then bogs out and looses power. I put a new carb on, put a new fuel pump on, changed filters, re-adjusted valves, I have tried everything I can think of. Rebuilt the distributor, completely. Everything on the engine is new. The cam
is a EPWI cam int. .280, lift exh .295. Could the machine shop got the cam timing wrong?

It sure sounds like a carb problem.

Is the throttle linkage fully opening the throttle blades on the carb?

Is the choke operating normaly?

Do you have a vacuum leak?

When you put the dizzy back together, were the advance weights backwards???

I'ves taken them apart, found them backwards, not checked on proper "twist", and reassembled them as they came.

Nearly the same problem, instead of advancing with RPM, you get all retarded.

Thanks for the input guys. Sorry for the delay in responding. I only get online on the weekends. The carb is ok. Old carb does the exact same thing. I will check the advance this weekend. I ran into a guy on the web with similar probs. His was cam timing. Hate to think a machine shop would get the timing off. I'll keep trying before I get into the timing cover.

Well I checked the mech adv and decided to replace it. It was installed correct. When I hit about 3000 RPM it is blowing air and fuel out of the carb. Sure has me baffled. I still think I either got a bad grind on the cam or it is set too retarded. Sure could use some input on things I have not thought of.

You've got gasses going the wrong direction (getting to basics here). What that means is you've probably got a valve theat's open at the wrong time. Since, based on your rpm qualifier being correct, it seems to be "rpm based", it's either a timing or mechanical problem. If you had a "bad grind" I would think you'd have trouble across the entire range. Could be you have a bad or broken valve spring. Since it's coming through carb it would have to be intake. Could still be the dist. Based on the way you phrased the original post it sound like it did this before you rebuilt the distributor. Yes? Might also examine the timing chain/gears.

Run a Compression test across all the cylinders, if you’re getting a wide variance in the different cylinders, the timing will be off. If there all are reasonably close, I would check your valve adjustments next. (my hunch is it’s in the later)

I rebuilt the dist while the engine was at the mach shop. Wasn't really nothing wrong with it. Just thought it would be good to have mostly new parts in it. But I do believe you are on to something about the springs. Mach shop said old ones were still ok. I guess I should have insisted on new ones.It could be weak springs. Seems like the timing is off because it kinda runs as if the dist is retarded. Sure do appreciate the steer towards springs. I had totally forgot the mach shop said he shimmed them up. I'll check that next. Thanks a lot Bob

Thanks Streets I honostly didn't know the reason behind the shims. Machinist said the springs were a little weak so he shimmed it up and then they were ok. Do you think if the springs are weak the valves could actually be floating?

Bind or float.

Well guys I was right on the money. The cam was too retarded. Causing the engine to be constantly in a bind. Reset cam timing and now I have power for days. What happens is an intake valve stays open too long. Causes you to loose power on the compression stroke. It was close enough to allow the engine to run until high rpm's then it leaks out the intake valve.
So I guess jr. might actually know a little something after all. Though I must admit Uncle Bob did mention timing and so did blackcadillac. I was hounding on the idea of cam timing the whole time was just looking for an easier way out. But thanks for the many ideas. Later dudes