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Flat and lumpy at 5000 RPM  Rate Topic 
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 Posted: 06-09-2010 02:19 pm
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colinw59
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15851's power flattens off and gets lumpy at about 5000 RPM. Stock engine with 68,000 miles and Petronix. Any ideas?

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 Posted: 06-10-2010 12:58 pm
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Brett Gibson JH5 20497
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if your timing is on then I would look at the carbs, sounds like it's lean at high rpm's.

Brett

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 Posted: 06-11-2010 01:05 pm
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colinw59
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Bret the timing is good so is this a carb adjustment and or worn needles? Thanks,  Colin

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 Posted: 06-12-2010 01:49 pm
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Brett Gibson JH5 20497
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Colin, seeing you mention needles I assume you have Strombergs, if it was me the first thing I would do is look at the color of the plugs after a nice run with choke off for some time, light or dark ??.

Lets go with light because thats what I think your issue is, what condition are the carbs in, like the ignition you need to know that they are setup correctly and the parts in them are good, and they are both pulling the same amount of air thru, then it's a matter of adjustment.

Also look around to make sure there are no vacumn leaks, carbs are secure to manifold, plug wires and coil wires are clean.

If thats all good to go then how I like to setup Strombergs (My preference) I screw down the temp compensator so it no longer functions, put a full gasket with no holes to block of the bypass valve, and cap all vacumn ports on the carbs. Having good needles and seats, set the needle adjustment, turn in till seated and then backout 1-1/4 turns for initail adjustment, you might get lucky or you may have to keep playing with this, but when your close  using a small screw drive and not blocking the air intake lift the carb piston barrel about 1/8", the engine should stumble slightly then increase rpm and smooth out.

The disclaimer here is this is the way I do it and it works for me, other people other methods, just as long as we get to enjoy are cars.

Brett

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 Posted: 10-01-2010 03:52 am
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pbahr
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Colin,

So, what's your spark advance at 5000 rpm?

YELODOG

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