missing at high rpms
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New User
Joined: Oct 2004
Posts: 21
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From: Wabeno WI
missing at high rpms
I recently installed 410 gears front and rear in my bronco. It is lifted and has 33 inch tires. The original 302 with about 100,000 miles,edelbrock four barrell intake, edelbrock 500 cfm carb and a c4 tranny that is rebuilt with a good shift kit. When I drive it after the new gears it runs pretty high rpms at highway speeds. It started to cough and miss on the highway. I had a mechanic adjust the carb and he found the timing was off so he adjusted it. The next day I toke it for a ride and held it to the boards, when it shifts into second gear it barks the tires. After this it staarted missing even worse and I bearly made it home. I checked the timing and it was off again. I tried to set it and it ran worse than before. After replacing the timing chain it still misses and coughs at 60mph and above and sometimes aven slower. Is the fuel pump not pumping enough fuel, or maybe valves bad? It runs perfect around town or in the woods and if it is parked it reves up fine.
Elder User
Joined: Sep 2004
Posts: 500
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From: midwest
if your timing is all correct it sounds like a carb problem. check the float level and choke operation. if you remove the top of the carb maybe jet it 1 -2 sizes up if you think it maybe lean at high rpm. if it does it after its up in the rpms it sounds like it maybe running low on fuel, my 460 did this. is your timing still set right with the new chain? check it out and let us now.
Elder User
Joined: Mar 2004
Posts: 660
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Check your plug gap. Too much plug gap can cause a higher RPM miss, but provide good power response at lower RPMs. I'm not saying I know that's your specific problem for sure. However, I do know this could be the problem. It takes a lot more electrical power to jump the gap in time, during higher rpms, or during higher cylinder pressure situations. Old style ignition systems usually can run no more than .035", if high rpm, or high compression is encountered. The stock Duraspark II system calls for .044", and can run up to .055, with something like the Jacobs coil, up to about 6,000 rpms. The post 86 ignition systems on EFI Ford V8's call for .052".
Thread Starter
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New User
Joined: Oct 2004
Posts: 21
Likes: 0
From: Wabeno WI
my timing is set right, the fuel pump is only a year old, but it might not be getting enough fuel. I have a clear fuel filter and sometimes it is full sometimes it is only three quarters to half full.
Hotshot
Joined: Jul 2002
Posts: 14,285
Likes: 12
From: Bend,OR
isnt there another filter besides that clear one you have. it would either screw into the front of the carb or be on the fuel line under the truck. but i agree it sounds like fuel starvation . you may also have a bad coil.
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