Bad miss, stumble on acceleration? please help? - Team Camaro Tech
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post #1 of 15 (permalink) Old Nov 14th, 09, 12:58 PM Thread Starter
Greg
 
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Bad miss, stumble on acceleration? please help?

67 camaro 373 posi 4spd 350 edelbrock 425hp kit, roller valvetrain. Holley 650. I have a bad stumble when pulling out to the point it feels as if im in 3rd gear until the rpms build up and then it kicks in. There is still a miss through driving speed but nothing like the intial pull out. It seems that at low rpm it is lugging horrible. Once the car is warmed up it is still a problem, but not as bad. I pulled a couple plugs on each side and they are wet, the distributor cap looks good.The car starts easily and does not smoke, not sure it its running to rich or if maybe the advance in the distributor is not working properly. Any help is appreciated.
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post #2 of 15 (permalink) Old Nov 14th, 09, 03:21 PM
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Re: bad miss, stumble on acceleration? please help?

Did this suddenly occur? Was anything done to the car/engine before the symptoms developed?

If no. and the plugs are wet with gas, sounds like carb needle and float possibly sticking causing a flood condition or a blown power valve? Pull the inspection port covers off of the bowls and if fuel gushes out, you have probably found your problem.

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post #3 of 15 (permalink) Old Nov 14th, 09, 04:56 PM
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Re: bad miss, stumble on acceleration? please help?

Firing order 18436572. Check it.

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post #4 of 15 (permalink) Old Nov 14th, 09, 05:40 PM
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Re: bad miss, stumble on acceleration? please help?

dont' know if this helps, but just had an issue similar to this, and it would miss especially down low...kind of like breaking up and then it would be fine. well, I checked the carb base gaskets and the one right on the carb had a fairly decent size on the side that wasn't making contact and created a nice size vac. leak. I tried reusing the old gaskets and modifying them, but made it worse to the point I could hear hissing, and I couldn't even free rev the motor without it stumbling. So, the new gaskets went in and blamo, the off idle hesitation is gone! how about that! something to consider.
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post #5 of 15 (permalink) Old Dec 5th, 09, 05:50 PM
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Re: bad miss, stumble on acceleration? please help?

look. the problem here is this : HOLLEY i had the same carb. they get very finicky especially if it sat for a while. u can rebuild it, but just get a friggin elderbrock. saves u time, hassle and money

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post #6 of 15 (permalink) Old Dec 5th, 09, 06:54 PM
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Re: bad miss, stumble on acceleration? please help?

Dont buy the Edelbrock.
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post #7 of 15 (permalink) Old Dec 5th, 09, 07:36 PM
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Re: bad miss, stumble on acceleration? please help?

Quote:
Originally Posted by jeremycam View Post
look. the problem here is this : HOLLEY i had the same carb. they get very finicky especially if it sat for a while. u can rebuild it, but just get a friggin elderbrock. saves u time, hassle and money
Quote:
Originally Posted by Jeremiah View Post
Dont buy the Edelbrock.
Come on guys, only opinions please. If you have something to say, give us a story or an example...no theory's. ...lmao...

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post #8 of 15 (permalink) Old Dec 6th, 09, 11:50 AM
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Re: bad miss, stumble on acceleration? please help?

Just two notes that helped me with my new Holley 600dp. I had to put two washers under the accelerator pump spring so it wouldn't compress before pushing on the pump arm. I changed the primary shooter from a 28 to a 35. What a difference. Bam....stumble gone.

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post #9 of 15 (permalink) Old Dec 10th, 09, 09:58 PM
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Re: bad miss, stumble on acceleration? please help?

Quote:
Originally Posted by jeremycam View Post
look. the problem here is this : HOLLEY i had the same carb. they get very finicky especially if it sat for a while. u can rebuild it, but just get a friggin elderbrock. saves u time, hassle and money
Eddy carb? Screw that ill take a demon without cleaning the fuel bowls before installing it. Check for a cracked spark plug maybe but if your plugs are wet check your float and work your way around. Check out holleys site man they have a checklist for problems to troubleshoot.

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post #10 of 15 (permalink) Old Dec 11th, 09, 07:36 PM
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Ryan
 
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Re: bad miss, stumble on acceleration? please help?

does it stumble when you shift and just start pressing the gas pedal?

If so...several things to check
1. secondary spring correct for vacuum at idle or low throttle
2. there is a spec for the butterfly position relative to the transfer slot
3. Vacuum distributor or timing...I have chased many stubles through the carb when it turned out to be timing.

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post #11 of 15 (permalink) Old Dec 12th, 09, 10:40 AM
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Re: bad miss, stumble on acceleration? please help?

1st check havnt a couple HT leads wrong, or a lead leaking
2nd check is the gap under the accerator pump at WOT 15 to 18/1000
3rd check flaot levels and there is no crap in the shut off valve
4th with vac gauge in car check u have the right power valve or its not defective

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post #12 of 15 (permalink) Old Dec 12th, 09, 10:11 PM
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Re: bad miss, stumble on acceleration? please help?

Don't feel bad. Many of us have suffered the exact same symptoms. There are two basic things that contribute - timing and carb setup.

I see this is your first post - welcome aboard. Search the archives for topics like "vacuum advance", "carb(erator) too big", "stumble","bog", and "3456" (factor in a square bore carb sizing formula). You should find lots of basic info to get you started. There are lots of little details.

Here are my thoughts which are likely to coincide with one another:
* The cam may be a bit too radical for the torque convertor on your car.
* The 650 carb is a perfect fit for a 350 street motor. Make sure it's at factory baseline specs for starters. Consult the Holley web site for jet sizes and other baseline calibration details.
* If the carb is a mechanical secondary type, and you have an automatic transmission, you'll need to refrain from mashing the gas to avoid the bog - unless you have a high stall convertor.
* If you have a vacuum secondary carb (best for auto-trans), perhaps the secondaries are coming open too soon.
* Vacuum leaks are a prime culpret. Anything that allows air to get past the butterflies without affecting fuel metering will cause a lean out that often creates a back-fire throught the carb. My Holley's front accellerator pump lever was hitting the number 1 runner on my Edelbrock Performer RPM intake creating a huge leak at the base gasket.
* Base timing isn't set correctly. Base timing should be between 10* and 15* BTDC in most cases. Engine / cam specs vary the optimum setting widely. Cut and try is needed to find the optimum.
* For all but the most radical motors, vacuum advance is a huge benefit. It will improve idle speed, raise idle vacuum, and make for better street manners. If you have anything other than a stock cam, an adjustable VA unit is a good idea. It allows you to set the vacuum level for full advance as well as limiting the total amount of VA advance.

Be patient, don't tweak too many things at once. You're fine tuning your setup and it takes a few carefully thought-out passes to get it right. Use your plugs to help you determine if the fuel mixture is right, but beware reading a cold plug that been in an idling motor will always be black. Get the plugs good and hot by driving the car if possible, and read them immediately after.

Dave
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post #13 of 15 (permalink) Old Dec 13th, 09, 08:45 AM
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Re: bad miss, stumble on acceleration? please help?

dont ya just love it when ya spend time to help someone and they never reply back?
is it fixed????
I guess we will never know?
Its only common courtesy to reply good or bad if the ideas fixed the problem or not.
I know in the future im gonna keep a record of the people i helped that never reply back that way im not wasting time and effort to help someone who wont give us an idea if the problems are fixed!


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post #14 of 15 (permalink) Old Dec 15th, 09, 08:00 AM
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Re: Bad miss, stumble on acceleration? please help?

yeah just as i thought!!!!!


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post #15 of 15 (permalink) Old Jan 5th, 10, 09:25 PM Thread Starter
Greg
 
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Re: bad miss, stumble on acceleration? please help?

Pulled several plugs all were wet thought i would try a different carb setup a friend had and changed to an edelbrock until i can get the carb worked on and problem solved, runs like new. thanks for the help been on an 8 week assignment and have just been able to tinker again.

Last edited by caleb530; Jan 5th, 10 at 09:46 PM.
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