Engine loses power around 5000RPM

[73EStroker]

I didn't read all 9 pages of this thread but here are a couple of simple things to look at. I had a GM product once (EXXXXCCCCUUUUSSSSEEE ME) and it had similar problem as yours at around 4000RPM. It was the little ground bonding strap in the distributor that bonds the advance/retard movable plate to the body of the distributor. It was broken and I guess the oil or grease in the bearings at high speed caused a high resistance joint which caused the miss. Changed the little flexible wire and voila away she went to 5800RPM and no miss.
BTW - 99% sure that if the tach needle is jumping all over the place then it is electrical. If it is mechanical and the ignition is working properly then the tach will still read steady as it is driven from the speed the electrical pulses are received. It shouldn't care if the fuel delivery or the valve springs are weak. Also try running it without the tach. It may be faulty and pulling the ignition down at high RPM. you need a much more solid ignition at high RPM compared to lower RPM - that is why most of these multispark ignitions stop firing multiple times as the RPM goes up. Need more power.

[Jacksboys]

Thanks for the info.

Once my schedule settles down a little I will try a few more things.   

[Harts56]

I had similar problems a couple years ago.  Wss looking at changing all sorts of parts at BIG dollars.  Ended up being  the reluctor gap in the distributor.  Takes only a couple minutes to check.

Good luck!

John

[Jacksboys]

Thanks for the info.   


My schedule should be getting lighter soon, so I will have a little more time to figure it out.   

[nivvy]

Spitting/sputtering/cracking is an indication of being too LEAN. Now, what RPMs that it's doing this tells you which jet you need to change! 2000 RPMs and lower, and you need to richen up your idle jet (go bigger). 2500-4000 RPMs and you need to richen up your main jet!

[Jacksboys]

Spitting/sputtering/cracking is an indication of being too LEAN. Now, what RPMs that it's doing this tells you which jet you need to change! 2000 RPMs and lower, and you need to richen up your idle jet (go bigger). 2500-4000 RPMs and you need to richen up your main jet!

Thanks for the info, but I am running an O2 sensor, so I am not too worried about it running lean.  Once I try a few ignition tests first, I will give it a try since it won't cost me anything.