Engine breaking up
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Stage IV
Joined: Jul 2014
Posts: 4
Likes: 0
From: Florida
Engine breaking up
I have been helping a friend who has a 1980 80 ci shovel head. It starts breaking up at 2800 to 3000 rpm but only under a load. It runs past 5,000 in the shop. We have replaced the ignition module , pick up Assy carb, intake, coil, plugs,wires. It has been in 2 shops with no help. We have also adjusted the pushrods correctly they were to tight. This has been a 4 month ordeal and everyone we have talked too is at a loss as well. We really need help on this one.
Novice
Joined: Apr 2014
Posts: 23
Likes: 0
From: Tega Cay, SC
Is it getting enough fuel? If there is no load then in the shop you may not notice it firing on less fuel perhaps? When you get it up under a load (assuming you're the load), it starves for the fuel it needs.
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Stage IV
Joined: Jul 2014
Posts: 4
Likes: 0
From: Florida
A leak down and compression test both done everything was good. A new S + S super E and manifold. This is a stock 1980 80 inch motor. Wondering if a weak valve spring or worn cam could cause this?
Cruiser
Joined: Apr 2012
Posts: 154
Likes: 2
From: Denver Co.
My guess would be exhaust. My Evo did the same thing until I opened up the mufflers. You don't mention much about the bike. Try giving as much info as you can about, the bike, the history, the exact conditions, etc.
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Stage IV
Joined: Jul 2014
Posts: 4
Likes: 0
From: Florida
80 ci shovel head stock except for drag pipes, new electronic ignition and S S super E carb. Bike was setting for a couple of years due to shifter linkage problem and we cleaned everything up and replaced the shifter linkage. Bike ran fine for about 3 months then started breaking up occasionally. 1st shop replaced switch and rebuilt carb. No help. 2 nd shop replaced carb intake manifold ignition system and performed leak down and compression test which were good. They adjusted the valves which they said had been too tight.
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