Hesitation on acceleration - Team Camaro Tech
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post #1 of 9 (permalink) Old Sep 22nd, 00, 03:22 PM Thread Starter
 
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I have ben attempting to track down a hesitation in acceleration when I accelerate hard. Somebody told me one time to check the timing. It is a 68 Camaro with a 350 bored .060 HEI ignition with an Accel. 9.5:1 compression S/R Torquer heads 67cc, RPM Airgap intake, 600 cfm Edlebrock carb, and a Comp Cams 268H cam with 218/218 and .454/.454 lift. The current timing is 12 degrees, and when I rev it up it stops at 20 degrees at 2500. I have never played with timing so I am really unsure as to what I should have. Thanks for any help.
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post #2 of 9 (permalink) Old Sep 22nd, 00, 06:31 PM
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600 cfm dosen't seem to be big enough, would think that 750-850 cfm would be better, sounds like it's fuel and air starved.
is the excelerator pump set right?
try setting timing at 8 deg.

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post #3 of 9 (permalink) Old Sep 22nd, 00, 08:20 PM Thread Starter
 
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I am looking into replacing the carb. Does 20 degrees sound correct??
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post #4 of 9 (permalink) Old Sep 23rd, 00, 06:25 AM
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Your total timing should be around 34 to 36 degrees. If you only have 20 total that is not enough. Does the timing go any higher as the revs go up? Most performance engines like all advance in by 3000 rpm.

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post #5 of 9 (permalink) Old Sep 23rd, 00, 02:16 PM Thread Starter
 
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Maybe I am reading the tape wrong. At idle the tdc mark on the timing tab points to 12 degrees. It moves gradually to 20 on the timing tape and stops at 2500 rpm. It did not move again up to 3300. I did not rev the motor any higher to see if it would go any higher. Is this read as 20degrees total?? If so, what should I do to correct it??
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post #6 of 9 (permalink) Old Sep 23rd, 00, 10:09 PM
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Sounds like the dist needs some work. It only has 8deg mechanical built in and it should be more like 24. Then when you set the inital to 12 your total would be 36. You didn't mention any vac advance for the street the equation isn't complete without it... An adjustable canister is prefered...

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post #7 of 9 (permalink) Old Sep 24th, 00, 02:44 PM Thread Starter
 
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The distributor has vacuum advance, but I don't know if it is adjustable. I guess my question should be, since I only have 8 degrees mechanical advance at the crankshaft and I should have around 24, how do I get there? Am I correct that if I am 16 degrees low in mechanical advance at the crankshaft that I need to add 8 degrees to the distributor??
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post #8 of 9 (permalink) Old Sep 25th, 00, 06:33 AM
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From what I have read, it sounds like you have enough carb for your car. Your distributor is not advancing enough. Can you replace the vacuum unit? I just did this on a car this week and the rubber diaphram inside the unit was shot. It made an amazing difference! And is relatively cheap. The advance on the distributor is similiar to watching a track team run a relay race. The guy getting the handoff has to get up to full speed to make the transition smooth, if he doesn't, he gets run over. If the distributor does not advance, the engine will "runover" the spark and go nowhere. I would start there. I have never worked on an Edelbrock carb, but if similiar to the Holleys, you can swap out the nozzles that shoot the gas down the throat of the carb for a little larger size, I have also done this to correct hesitation on acceleration with good results. But fix the distributor first, it's not right.

[This message has been edited by denverRS/SS (edited 09-25-2000).]
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post #9 of 9 (permalink) Old Sep 25th, 00, 09:00 AM
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First off, stop thinking about the vacuum advance. I can disconnect mine and rip 4 gears of rubber. The point is, when you go WOT, vacuum drops and the vacuum advnace is supposed to go away.

Do you check again and rev the motor up beyond 2500. Go to 4000 and see if you have any more advance.

Take the cap off, remove the rotor. Now, turn the rotor arms, you'll see exactly how the mechanical advnce works. You should see pins engaging in the top base which limit the travel of the whole assembly. Are there bushings on those pins.? If so remove them. At the same time, you'll want to put a heavier set of springs in there. The springs should be readily apparent. You really want to spread the curve out a bit and have it ciontinue to advnace until approx 2800 with cruising gears or 300o-3200 with 3.73 or greater gears.

It might be good for you to find out who the distributor guru is in your area. Ask the racers. Take the HEI in and have them recurve ir properly.

Not-for-nothing, but I have found, more than once, that a stumble or hesitiation on acceleration is caused by faulty ignition wires.

But u need to resolve your lack of advance first.

EDIT: Dont do ANY carb tuning until you are getting a full 34-40 degrees of MECHANICAL ONLY advance. ( Your initial with mechanical curve in distributor).

[This message has been edited by 427TRI (edited 09-25-2000).]
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