Carb question

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Mar 28, 2008 | 02:50 PM

WeGoOn3

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Carb question

My truck has a new motor (302), less than 5k miles, with a 650 Holley 4barrel carb. The truck runs great on the road, but from a dead stop (pulling out into traffic) when you step on the gas it seems to stumble then take off.

Also, when crusing on the interstate, stomp on the gas, it hesitates then takes off. Runs great if you just barely ease into the gas.

I think the problem is in the carb. I finally got the choke figured out, but I think I'm missing someting somewhere. Its very frustrating.

Mar 28, 2008 | 02:54 PM

RCrawler

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From: Southern Oregon USA

Its possible that the accel pump is bad.

Jason

Mar 28, 2008 | 03:26 PM

pdqford

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From: Central NYS

Quote:

Originally Posted by WeGoOn3

As someone mentioned, check that your accelerator pump is set up correctly. You might want to change the hole for a slightly bigger shot of fuel when you move the throttle.

Quote:

Originally Posted by WeGoOn3

Also, when crusing on the interstate, stomp on the gas, it hesitates then takes off. Runs great if you just barely ease into the gas.

For my money, 650 CFM is too much carb for a stock 302 (just my opinion). You didn't mention what tranny you have (an auto is more forgiving becuase the torque converter will slip and let the rpms come up a little when you mash the gas, which helps it pull more air), or if that carb is a vacuum secondary carb (won't allow the secondaries to open until there is sufficeint air flow in the main booster area). When you mash the gas, if the carb opens too wide for the amount of air the engine can injest (especially if its got mechanical secondaries) the little 302 can't gulp enough air to maintain vacuum under all four main boosters and it ends up getting air but barely any fuel. Presto, you get a lean bog. Sometimes you can compensate for that by having the accelerator squirt in some extra fuel until the main boosters can catch up.

If you want instant throttle response, see what carb Pony Carbs recommends for a 302.

Mar 28, 2008 | 03:52 PM

WeGoOn3

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Thanks.

It is an automatic and it does have vaccum secondaries. The motor is not stock (motorsports b303 cam, gt40p heads, etc.)

So I should start with replacing the accelerator pump?

Mar 28, 2008 | 05:51 PM

78f-150Supercab

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From: San Antonio, TX

Heck, I got a 650 Eddy on a nicely built 351w and it hesitates if I mash the pedal. (everything is brand new so I don't know about it being a faulty accel pump)

Mar 28, 2008 | 07:24 PM

RCrawler

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From: Southern Oregon USA

Quote:

Originally Posted by 78f-150Supercab

Heck, I got a 650 Eddy on a nicely built 351w and it hesitates if I mash the pedal. (everything is brand new so I don't know about it being a faulty accel pump)

There is some adjustment in the Holley and Edelbrock accel pumps. You may need to do a bit of fine tuning to dial in the hesitation issue.

Jason

Mar 28, 2008 | 07:43 PM

fastfarmer

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From: southwest Wisconsin

The Holley accelerator pump can be adjusted by canging the cam that engages it-different color cams have a different rate of engagement- and by changing the squirter- they are avalable with different size nozzles and are numbered; larger number squirter = bigger shot of fuel.

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Mar 29, 2008 | 05:52 AM

fastfarmer

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Joined: Mar 2007

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From: southwest Wisconsin

On the Edelbrock carb that is the only accelerator pump ajustment as I recall. A bogging problem can be addressed with this carb by adjusting or changing (I cant remember which) the spring on the secondary air valve.