HEI Vacuum increases idle speed. - JeepForum.com

 
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post #1 of 10 Old 05-20-2016, 04:42 PM Thread Starter
NHcjfan
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HEI Vacuum increases idle speed.

Hello all. I recently upgraded to a motorcraft 2150 after battling fuel leakage for a year in my YF. I decided to order a CRT Performance HEI distributor that I thought would compliment the upgrade. Got it all timed up 6 BTDC, runs great idles great.... until I hook up the vacuum line from the carb to the distributor. It immediately advances the timing and increases the RPM. It has an adjustable vacuum advance so I turned it counterclockwise all the way thinking it would fix the problem. No dice. I'm almost ready to put the Prestolite back in her.

Is my carb creating to much vacuum at idle or issue with the distributor?

Any advice would be appreciated or anyone with a similar set up.

1977 cj5 258 motorcraft 2150.

BTW Jeep runs great cruising down the road. Could I run it just on mechanical advance?

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post #2 of 10 Old 05-20-2016, 05:16 PM
Matt1981CJ7
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Sounds like you have the vac advance hooked to manifold vacuum.

If so, the increase in timing and RPMs at idle is perfectly normal and desirable.

Matt


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post #3 of 10 Old 05-20-2016, 05:28 PM Thread Starter
NHcjfan
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I have it hooked up to ported vac on the carb. so maybe my throttle plates aren't closing all the way?

Maybe I will use manifold vac and adjust idle after I hook the vacuum line back up.

Should have some time to work on it tomorrow. Just looking for a few ideas to get started.
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post #4 of 10 Old 05-20-2016, 05:59 PM
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Yes, ported vac at idle indicates the throttle plates are open too far. The idle circuit may be under- jetted.

I prefer manifold vac advance for the stronger, cooler, more efficient idle.

Matt


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post #5 of 10 Old 05-20-2016, 06:22 PM Thread Starter
NHcjfan
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I think I will run it off manifold vac and adjust the idle to spec.

Should I address the other issue? Is there a way to adjust the throttle plates?

I really want to dial this thing in properly. I may have to pull the carb back off to see.
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post #6 of 10 Old 05-20-2016, 06:29 PM
Matt1981CJ7
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Where did your lean/best idle mixture screw adjustment end up?

Matt


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post #7 of 10 Old 05-20-2016, 07:20 PM Thread Starter
NHcjfan
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About 1 1/4 out. I need to get a vacuum gauge. Just did it by ear.
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post #8 of 10 Old 05-20-2016, 08:09 PM
Matt1981CJ7
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Yeah, you need a vacuum gauge. Ear-tuning only goes so far.

Matt


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post #9 of 10 Old 05-23-2016, 04:48 PM Thread Starter
NHcjfan
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Thanks for the advice Matt. I simply adjusted the idle after setting the timing and hooking up the vac advance. Silly mistake on my part as I was setting idle first. Anyway Jeep is running better than ever. Just picked up a T18 so now on to that project.
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post #10 of 10 Old 05-23-2016, 05:33 PM
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Great to hear!

Good luck with the trams swap.

Matt


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