67 lemans low on power and hard to start. - Pontiac GTO Forum
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post #1 of 12 (permalink) Old 10-02-2012, 07:26 PM Thread Starter
 
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67 lemans low on power and hard to start.

i got my 67 lemans up and going but it is extremely low on power. it is a stock 326 with a th350. 500cfm 4bbl edelbrock carb. i can't seem to get it adjusted where it is happy. i have the timing at about 12 degrees and the idle screws about 1 & 1/2 turns out. it has about 15"hg. when i bump the gas it shoots this puf of something out the top of the carb but no bog. it has no vacuum leaks and the plugs are slightly black but nothing terrible. just wondering if this carb might be too small. does anybody have a similar setup to mine? if so what is it setup like? thanks for your help
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post #2 of 12 (permalink) Old 10-02-2012, 09:23 PM
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Nothing you've said sounds horrible. Folks sometimes struggle for a long time to get rid of a bog, which you don't have so be thankful for that. Its hard to understand what exactly "down on power" means though. That carb should be more than enough on a 326. Can you be more specific?

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post #3 of 12 (permalink) Old 10-02-2012, 10:19 PM
 
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You might need to put an inline fuel pressure reducer in as the edelbrocks do not like more than 5 psi pressure and will blow fuel past the idle circuit giving you a rich condition from the word go. Getting ready to dump the Edelbrock and put dual holleys on mine.

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post #4 of 12 (permalink) Old 10-03-2012, 12:40 AM
 
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I just read an article / post about timing. This is where you you will want to begin. Do a search on "setting timing" or "total advance"... ect.... Basically what you will find is you want to start with 34 - 36 total advance and work back from there. Once you are POSITIVE the timing is correct and you still feel you should have more power then you can explore the carb. Another thing to look for is a vacuum leak.
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post #5 of 12 (permalink) Old 10-03-2012, 06:30 AM Thread Starter
 
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i know these engines aren't known for having a lot of power but on this one it seems that it is challenging to get onto the freeway. i have to hold the gas to the floor for quite a long time to get up to 70.
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post #6 of 12 (permalink) Old 10-03-2012, 09:12 AM
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Which transmission do you have and what's your rear axle gear ratio?

Check the insides of your tailpipe(s) where they exit. Are they dark black and very "sooty" like there's lots of loose carbon powder there, or do they have some other appearance?
Does it run smooth? Have a "miss"? With it sitting still and out of gear, does the engine rev freely?

Has the car "always" behaved the way it does now or has it gotten worse?

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post #7 of 12 (permalink) Old 10-03-2012, 09:19 AM
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15" of vacuum is too low for a stock 326 at idle. It should be 17" or more. Check your distributor position and static timing..the dist may be mis-installed (clocked wrong). If a stock dist, make SURE you set the points dwell first (30degrees) and then set the timing. My bet is retarded ignition..either due to dist issues or a very stretched timing chain. 326's are good strong runners with a bunch of torque. They are not dogs...and a 500cfm sounds about right for one.
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post #8 of 12 (permalink) Old 10-03-2012, 10:02 AM
 
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In addition to the timing recommendations stated, make sure you're getting vacuum and mechanical advance. It almost sounds like the advance is not coming up. You're going to want to start at 12-16 degrees initial and with the light on it, make sure the timing advances as you begin to rev it. If it doesn't jump, you may have a stuck vacuum and/or mechanical advance plate.

Also, you don't say what manifold you have. If stock (or aftermarket spreadbore), I'd sure look at putting the Quadrajet back on it! Those small primaries will give you more velocity and low end torque, than the 500 CFM you're running now. It'll also give you better fuel economy and performance. The Q-jet is hard to beat in my book.

Start with sorting out any/all timing issue first, though.

When the only tool in your toolbox is a hammer, you tend to see every problem as a nail.
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post #9 of 12 (permalink) Old 10-05-2012, 09:40 PM Thread Starter
 
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i have an aftermarket edelbrock spreadbore intake. it is hard to test the full advance cuz the timing mark only goes to 12 degrees. i might have to buy a different timing light to check the full advance. the rear gear is stock 2:80 or close to that. tried to get a reference on how "low on power" this thing is. so i put the front tires at the end of a speed bump and stoped. held the gas to the floor and it couldn't get it's self over the speed bump!! it has a TH350 trans. It has always been like this ever since i had the thing (8 years)!! it seems to rev up freely and smoothly just no power. it has new points, and all the basic tune up stuff. new fuel pump ect......
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post #10 of 12 (permalink) Old 10-05-2012, 10:12 PM
 
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When you rev it in neutral with the timing light on it, does the timing jump? Does it move slowly? Does it move at all? If it doesn't jump by several degrees, I'd go after the breaker plate and make sure it's not gummed up.

When the only tool in your toolbox is a hammer, you tend to see every problem as a nail.
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