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Old 08-17-2005, 10:10 PM
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Engine Stumbles when Brakes Applied

I have a newly rebuilt 302 Ford HO motor with only about 30 miles on it in my '27 Model T Ford Roadster Pickup. Carb is a Holley 600 Double Pumper with mechanical secondaries and manual choke. Trans is a 4-speed manual.

Motor idles fine but wants to stumble and die when brakes are applied. (Nope, does not have power brakes). I have adjusted float levels but this didn't seem to make a difference.

It also has a Ford Motorsport Cam M-6250-F303, 226 int/exh @ 0.050 lift, yet the motor has very little lope to it. This is a "factory" roller cam motor of '87 vintage with '83 Ford aluminum intake that cam from the factory with a Holley carb.

Not a motor guru, looking for advice. Any suggestions?

Thanks for your help.

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Old 08-17-2005, 10:15 PM
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So you are saying when you slow down using the brakes and not just sitting still right?

Does it happen immediatly when you jab the brakes or is there a delay?

Rich
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Old 08-17-2005, 10:19 PM
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Correct. When the car is moving forward and the brakes are applied it stumbles and wants to die. Slight delay.
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Old 08-17-2005, 11:51 PM
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Brake lights

Doc here,

I would first check to see battery is full charge, and alternator is putting out 14.4 volts at Idle...

Then , Next I'd look for a massive load from the brake light circuits drawing power away from the Ignition..AND possibly almost rotor locking the alternator trying to keep up under the load..causing the engine to load and stumble..

quick test...just pull the fan belt and try it..if it works OK then, your alternators is seeing a very heavy load during braking..

If ALL that checks out good,then I'd start looking at float levels in the Carb..(sloshing on brake..)

Doc
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Last edited by docvette; 08-17-2005 at 11:53 PM. Reason: added info
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Old 08-20-2005, 09:37 PM
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Problem is definitely not related to brake lights or wiring. Stumbles the same when I use the hand brake (emergency brake).

I have adjusted the float level so it is just barely below the inspection plug on the side of the bowl.

Any more ideas?
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Old 08-20-2005, 09:48 PM
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What does it do when you are sitting still idling and mash the brakes? If it does nothing then I would say that rules out what Docvette is refering to about the alternator etc. It would then have to be carb related. Is your engine positioned in the car to let the carb sit level at ride height? Just thinking......If not that could be it.
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Old 08-20-2005, 09:56 PM
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interesting problem,

Seems to be a real stumper of a problem, having never owneda street rod I would just hazard a long shot and ask, is the carb sitting level??,
Short of borrowing another carb just to rule out the possibility of demonic possesion of your holley, I would also check for a heavy float that may have fuel in it.
please keep us posted!! after all , 30 miles is waay to short for a rod run!! lol!!
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Old 08-20-2005, 10:14 PM
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Good comments in ref. to if the carb. setting level.

It does set level. I built the car myself and know how important this is. before I welded in the motor mounts I put a level on the top of the carb.

Brand new Holley, heck brand new Hot Rod for that matter. This is my second complete Hot Rod build. The only bummer about building one yourself from the ground up is since everything is untested, there are usually a few bugs to work out.

This is my first mechanical secondary carb. Anything special I should know about setting it up that I may have missed?
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