67 Mustang 4bbl conversion

Yoruai@hotmail. · May 2, 2005

67 Mustang
289 engine
4bbl Edelbrock Performer

Got the old parts off(intake manifold & carb), got the new stuff on, rerouted some hoses and lines to fit the new configuration, changed the oil and it fired right up. The distributer matched up with marks I made so the timeing should be pretty close.

However it idles at 3000 rpm and measures 8 on the vacum scale no matter how a adjust the mixing screws. I realize adjusting carburators is an artform I'm not proficient at and will glady take my car to a shop for it but I'm afraid to take it out of park. Even opening the throttle a quarter way emits a deafening roar and rocks the front end.

Also there is an odd rattling sound in the engine that was not there before the converstion. A freind who knows more than me but not much thinks it may be the rocker arms hitting hard. He used the description "hammering" when refering to the sound. There are also small poping backfires through the carb.

I'm going to continue twisting screws and turning the distributer until it sounds driveable. Hopefuly one of you will be able to help this amature before he backs into the cross street neighbors house.

ForceFed70 · May 2, 2005

Sounds like fun.

Have you played with the idle speed screw? 3000rpm is the lowest you can get it? If so... check your choke settings. Once the engine has been running for a couple of minutes, the choke should be fully open. If it's not, then that's probably why your ideling so high... the choke needs to be adjusted.

86T-Top · May 2, 2005

Stop randomly turning screws!

You need to adjust your idle speed screw on your card to lower the idle, not your idle mixture screw. Read the instructions that came with the carb, they will tell you where the screw is. If you don't have the book tell us what type of carb you installed and we can tell you which screw you need to adjust.

As for vaccum, you only have 8 on the vaccum guage is because the car is idling at 3k rpm, lower the rpm and the vaccum will increase.

Mario

Yoruai@hotmail. · May 2, 2005

The carb is an Edelbrock performer #1406, the screw I've been adjusting as the idle screw is on the right side near the throttle linkage. I don't have a manual and the one online at the Edelbrock site tells you what each screw does but not where it's located. All of ther manuals and direction sheets I've gotten are crap.

With the idle screw all the way out, not putting pressure on anything and the choke open the rpms drop to 2600. When I held the choke open however the car began to squeal and then died.

PoliceInterceptor · May 2, 2005

If it won't idle below 3000, my first guess is massive vac leak.

As for the noise,

STSFCTN67 · May 2, 2005

Do you have a return spring? If so disconnect the linkage to the pedal and see if the idle goes down. Sometimes after a carb swap you may have to tweak your linkage.That happened to me once.

If that does not work check for vacuum leaks by spraying aroung the intake and the base of the carb with starter fluid. If idle goes up while spraying - then there is the leak.

86T-Top · May 2, 2005

Ok, you are turning the right screw. This happened to me when I installed my E-bock 1406 carb. I found that the high idle screw from the factory was set to make my car idle around 3000 rpm. Have you blip the throttle to knock it off of high idle? Try that. If it knocks the idle down you need to adjust the high idle screw.

If that does not work, and your base idle truley is around 3000 RPM, then I would check to see if the throttle plates are fully closed. I have found that E-bock carbs need to use HEAVY return springs to get the throttle plates to close fully. Also check what STSSFCTN67 said, your throttle linkage may be too tight, causing the throttle plates not to close fully.

After that if the idle is still high, then it is time to look for a vac leak.

Mario

Yoruai@hotmail. · May 2, 2005

Sorry, I was tinkering. It idled that high before I even reconnected the linkage. I'll try the carb starter to check for a leak. No one has given that method yet. Thanks.

ron67fb · May 3, 2005

so the timeing should be pretty close.

Something tells me it isn't close and it's advanced, a lot, which would cause a really high idle. That hammering sound is most likely detonation.

84convertablegt · May 3, 2005

ron67fb said:
Something tells me it isn't close and it's advanced, a lot, which would cause a really high idle. That hammering sound is most likely detonation.

good call

67 Mustang 4bbl conversion

Yoruai@hotmail.

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That's why they call it "dope"

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67 Mustang 4bbl conversion

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