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Old 08-23-2013, 12:56   #1 (permalink)
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Trouble running

[I] have 1972 Mercury cougar with 351 Cobra Jet, Holley 650 carb, MSD ignition, Edelbrock performer intake. [I] recently built the engine, 1st one in over 25 years. The timing is set at 10 degrees [B]TDC, all unused vacuum ports are plugged, [I] have the idle fuel mixture screws set at 1-1/2 turns out. The car runs ok at an idle but as soon as [I] put it in gear forward or reverse it sputter and dies. [I]t will only run in drive if [I] keep my foot on the gas. Any idea's on what [I] am missing???????
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Old 08-23-2013, 17:00   #2 (permalink)
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Re: Trouble running

If you're running a stock cam, then you're a little over sized with the carb. Since it's a CJ, you're probably closer than if it was a stock 351. However, I'd think your timing would be more advanced. I'll confess, I stole this from another forum, but this was the recommended way to check\set the time: "To properly set the timing on a Cleveland it is roughly the same as any other small block from ford.
Disconnect the vacuum adance and plug it so it doesn't leak.
Start the engine and run it at 3000 rpm.
Set the timing to 36 - 38 degrees (use a timing light with a built-in advance)
Return the engine to idle an check the timing - that is the maximum timing you can safely set at idle unless you recurve the distributor.
Reconnect the vacuum advance."
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Old 08-24-2013, 08:44   #3 (permalink)
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Re: Trouble running

As you know, Holly's are infinitely tunable, but horrible if not set up right. I have tuned a few Holly's and am currently running a 670 Holly Avenger 4150 in a '73 Nova with a 350 HO engine, 700R4 automatic, and 3:73 gears. The car is a 3800 pound, stock appearing, air conditioned, street driven sleeper and the carburation is right on.

It sounds like you have the pilot screws set about right, but also make sure the float levels and metering block jets are in the ball park (you can fine tune later). Once those circuits are close to right, you can move on to your most likely problem.

Now to the problem. If you have an off idle stumble, make sure your accelerator pump is squirting fuel and make sure to start with the middle length pump arm (again, you can fine tune later). Replace the diaphragm if a steady fuel stream is not observed.

You didn't say which model you have, but if it's a vacuum secondary carb, check the secondary throttle plate spring. Your problem is often caused by the secondary throttle plates opening too soon. Try replacing the secondary spring with the next step heavier spring. Buy the secondary spring tuning kit at a speed shop because you will need to try different springs to get it right. (They are color coded)

Assuming that your cam and ignition timing are correct, and your carb is clean with no leaks, a 650 will perform well on your engine, but depending on your tune, rear gears, and torque converter stall speed, you are close to over carbureting a mild 351 with a 650.
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Old 08-24-2013, 12:40   #4 (permalink)
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Re: Trouble running

No idea about the Holly's but on carbs over in Europe/UK , the carb accelerator pump or the timing were favorites when a flatspot like that was present .Good to learn something new from Bajarider 's post
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Old 08-27-2013, 06:52   #5 (permalink)
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Re: Trouble running

Hi RS:
Works the same in the US too, but SUs and Amals still confound me.
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Old 08-27-2013, 10:46   #6 (permalink)
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Re: Trouble running

Quote:
Originally Posted by Bajarider View Post
Hi RS:
Works the same in the US too, but SUs and Amals still confound me.
I wish I had a pound for every SU I've tuned or overhauled , Webers and Strombergs were also popular .I left the bike carbs to my wise old mentor and foreman who was a genius at setting them up .
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