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Discussion Starter #1
I know this topic has been beaten into the ground. But since I have never done this, I need a little specific advice I think. And I appreciate all the criticism I can get.
I started the day with a 600 cfm holley with vac secondaries and other than the next softer spring in the vacc diaphram, it was as delivered. I changed to a 50cc acc pump with a .031" shooter. I switched from 66 jets to 72. And after reading all the other posts about timing, I added a bunch of advance (probably 5 more degrees). The timing took out most of the off idle bog (that was first). I could not detect any pinging with my ear (how else do I check it?) Then I went to the 72 jets. That gave the whole setup more punch. Then I switched from the as delivered .025" shooter to a .031 shooter. So far, it feels great, but I don't know how far to go. With jets should I keep going larger until the performance drops off? With the shooter - it seems that going larger until I can't tell a difference is the way to go (is it?)

Since I get pretty good vacuum (13 or 14) at idle, is there any reason to consider a different power valve?

The only problem (if it is a problem) is that my eyes water when standing behind the car ... does that mean it is too lean, too rich, or nothing at all?

Thanks for any thoughts, advice or ideas! This process is a lot of fun, but I don't know how far to go. At this point, on a hard launch, it feels like the engine is putting out more than the chassis can handle!
 
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I always check the plugs when I do jet changes. Black sooty build up means youre too rich, and lean is clean (really clean). Unless you have the right equiptment, guessing and seat of the pants is the only way I know to tune a carb. A dragstrip or a deserted road is also a handy tool.

-You can never have too much power, just not enough traction.-
 

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You should be more specific about your engine, what size,type of mods. With 13-14 inches of vacuum, you either have a big vacuum leak causing a lot of hesitation and will give the exhaust that sharp punjent odor making your eyes water or you have a big cam. I think your jetting is very rich for a street car if you have a mild motor. I think your jetting should be aroud a #65 mains. also, have you tried playing with the pump cam? get back with more info.

Tom
You can do anything you want to......ONCE!
aka "my 66 coupe"
http://albums.photopoint.com/j/View?u=1575517&a=11977890&p=44194856.jpg

Hale Boppe comet shot off my roof. See you can use 100 iso at night with no flash!
 
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Its a 351C with stock 1970 closed chamber heads. Its got a 2.5" exhaust system and long tube headers. The cam is hydraulic with .494" gross lift, duration is 218 at .050 (both intake and exhaust). The intake is an edlebrock performer. It is using a stock ignition system with a pertronix ignitor and coil. The gears are 3.0:1 with a manual transmission - if that makes any difference in this analysis.

Thanks a lot!
 

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You have a fairly mild combo, you're way rich and you shouldn't really need a 50cc pump. Start looking for vacuum leaks and your cam isn't that hot to have a low vacuum reading.

Tom
You can do anything you want to......ONCE!
aka "my 66 coupe"
http://albums.photopoint.com/j/View?u=1575517&a=11977890&p=44194856.jpg

Hale Boppe comet shot off my roof. See you can use 100 iso at night with no flash!
 

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Discussion Starter #7
I really appreciate the advice from all of you.

I did use the Holley site to get as far as I've gotten. I also used a book on Holley carbs but it was a lot of detail and not a lot of general info. Maybe after a pass at tuning, the tech notes from Holley might become more useful.

How do you test for vacuum leaks? I've sprayed stuff around the edges of the intake, and I re-torqued all the intake manifold bolts, and checked all the vac hoses. I did replace some rotted looking hoses today, so I might have fixed a leak (time to check again ... I thought 14 was good for this setup).

Again - THANKS!
 
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yeah...your pretty rich for that setup. But I had the same eye-burning things goin on for a while too. I have a long duration cam wit a lot of overlap. To get it to idel, the carb was adjusted so far that the transfer slots were completely uncovered. To correct that , I drilled 1/8" holes in each of the front two butterlies to let it get some air. It could be a blown power valve, but I doubt you have a "wrong" one.
 
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The advertised duration of my cam is 268 deg. but that is still pretty mellow. The 4v cleveland heads have such huge ports that they make up for the low lift, but they trash the low rpm air feul mixture flow. After mucking with it some today, the vacuum came up to 15 - 16 ... but the weird part - it was plug wires that made that change - so something wasn't firing at low rpm. Actually at about 700 or 750 rpm the vac comes up to 17 or 18. I also switched back to 68 jets since I re-checked the plugs and they were getting a little too dark. This is my first time tuning a 4 barrel carb. I've done two two barrels on a 4 cylinder - but that is real easy because each carb bore goes straight into one cylinder, and the dial-in is the same for each one. I mean - it is still a lot of work to get it right, but it is a pretty easy iterative process to get there. And there are really good guides to get the jetting in the right ballpark with weber carbs.

Cool trick to fix your problem!
 
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