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Discussion Starter · #1 ·
I built a 302 and put it in my wife's 66 mustang. Mild build, 11:1, 500 lift cam, 2.02 intake valves, Eldelbrock intake 670 Street Avenger carb, headers and Pertronixs III distributor and coil.

No matter how I adjust the carb, ( float, idle mix, accelerator pump...) no vacuum leaks, checked the squirters, played with timing... I still have a stumble when taking off easily. When I nail it there's no issue. If I try to cruse steady in 3rd gear at 2500 rpm or so I can feel it also. I have not replaced the power valve ( this is a brand new carb ) but maybe I need to-to rule it out.

The car overall runs super strong, no complaints about power or hard acceleration.
I'm open for suggestions. Thanks, Tim
 

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Hi Tim,
Is the Pertronix distributor the same one that was on the engine before? Is it both vacuum and mechanical advance or just mechanical? From what you said about the carb seeming to be OK, timing and advance/retard are jumping out at me. Running 11:1 (how much if at all did you shave the heads) are you running a bit more retard to avoid detonation with the gas that's available. I'm a believer in the keep advancing the timing until it detonates and then back it off a couple degrees. Just my humble opinion.
 

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Pull a Plug I bet she is lean..............also will it go rich with the idle adjust screws or does it just quit going up in idle speed.......here again lean and last when you are in 3rd and cruizn if you back off the gas very slowly does pick up speed or smooth out...then its lean
 

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Discussion Starter · #4 ·
The Pertronix is new and is vacuum or mechanical. I have the same method on timing as you Steve. The distributor is set up as mechanical . As far as being lean, I richened it up this last week and that made a slight improvement. Thanks for the feedback guys. I don't think I like this carb much. A 670 cfm should be about right for this engine I would think.
 

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Hi Tim,
You didn't mention if the car was stick or automatic. It's been my experience that if you're running a stick, the all mechanical advance is much more forgiving but with an automatic you really need the vacuum/mechanical advance working together. If you're running an automatic try hooking up the vacuum too. With my running a Vertex mag on my motor there is no retard mechanism in a mag so even with my 4:56 gears if I'm in high gear and below 3 grand and want to nail it I have to down shift or the motor stumbles because of no retard. The curve on a mag is done with the internal magnets and is very limited, mine is set up for all in at 2800 so you can see why I have to down shift. Is your Pertronix set up where you can curve it without having to use a distributor machine? I know a lot of the newer electronic distributors are very consumer friendly because they're not dealing with springs and weights.

Again, just my humble opinion.
 

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Tim do you have a jet and metering rod kit for the carb??? and your right the cfm is a good match dont give up.........in the fuel world there is no bolt on and it runs perfect......no intake leaks from milling the heads to much and not matching the intake.....just a thought.... leak would be inside the engine, usually will suck oil .........Lash
 

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Jets wont have any affect on off idle mixture. Holleys don't use metering rods like Edelbrock and Q jet carbs do. Jets take over when at cruising, and steady speeds. I'd try going about 4 sizes larger (to start with) on the nozzles. I agree that it sounds like a lean stumble, and larger nozzle will allow much better squirt on initial easing into the throttle. If you go 4 sizes larger and it's better, but doesn't quite fix it, then going a bit larger might be needed.
 

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Discussion Starter · #8 ·
Going to try some bigger squirters. One gentleman suggested bumping up my stall converter to 2900. I might do this no matter what. Can't seem to run the vacuum advance with pump gas no matter what. And yes the Pertronix III is very user friendly. I highly recommend it for a driver. Never thought about an internal vacuum leak since I seem to have plenty. ( running a C4 by the way ) To bad my wife won't let me chop up her Mustang, it would appeal to me more. Thanks guys. Tim
 

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Vall I thought he was running a edlebrock carb I see its the manifold when I read his post again , does the holly have a stroke adjustment or a cam that can be changed out for the squiters, I dont know what model he has, that would be for off idle, the jets for cruze, and yes I do know about what carb circuit does what, but thanks for the reminder.............Lash
 

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Discussion Starter · #10 ·
Lash, you are correct, there is an adjustment on the cam that I didn't mention. I have played with that also to no avail.
 

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Then if it has a cam then there should be one available that has a different profile to make it squirt early with more fuel.... a different profile...also be sure the secondaries are closed all the way I have seen ones that the stop screw was not set correctly....this can cause stumble, I dont use holly carbs my self unless its for wide open throttle use racing, street I like a carb like a AFB only one of the many newer versions
 

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Lash,
That's what's great about a Holley. There are a multitude of accelerator pump cams available with different profiles and most have 2 holes available for positioning and the accelerator pump arms are completely adjustable. There are many, many different size accelerator pump shooters and nozzles available. There are also 2 different size accelerator pumps available, an assortment of vacuum secondary springs and a bizillion different power valves.
 

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True but it cost money and time ......do the idle adjust screws stop making a difference after 3 turns or so out
 

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Vall I thought he was running a edlebrock carb I see its the manifold when I read his post again , does the holly have a stroke adjustment or a cam that can be changed out for the squiters, I dont know what model he has, that would be for off idle, the jets for cruze, and yes I do know about what carb circuit does what, but thanks for the reminder.............Lash
He mentioned he has the 670 Avenger carb. A Holley vacuum secondary carb, with just a primary accelerator pump.
The "cams" on the throttle linkage will adjust the accelerator pump stroke. Changing cams will give different profiles on the stroke to get either slightly longer stroke, or more off idle stroke. I've never had much luck getting any significant changes by swapping cams. I have found big changes going to the 50cc accelerator pumps, instead of the stock 30cc pumps though! But those are rarely needed on the street.
I put dual 450's on my Austin's SBC, and because of Holley's stupid idea to delete secondary accelerator pumps on these mechanical secondary carbs, I had huge stumbles off idle, or cruise speeds. Had to go to 50cc pumps, and also go up about 6-8 sizes on the nozzles to finally get rid of the stumble. Played with timing also, to finally get them right.
 

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Do they still make the after market secondary squirt kits, I have not played with carbs for years since the intro of more efficient fuel injection... witch I love...Yea I went hi-tec
 

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Hi Lash,
Are you talking about the kit to convert vacuum secondaries to mechanical that consisted of some linkage that attached to the secondaries to open and close them and also a replacement primary squirter that had long nozzles facing towards the secondaries along with the smaller ones facing the primaries. If you had a choke you had to remove the butterfly because of having to drill two holes through the choke air horn for the retro fit squirters to pass through. You also had to replace the smaller 30cc accelerator pump with the larger 50 cc reo pump. I used one and it really didn't work all that badly. The main problem was it was only available in one size; not real tuneable. If that's the kit you're talking about I used to see some at swap meets but haven't in years.
 

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Discussion Starter · #17 ·
Just thought I'd give a follow up on this sense you guys were nice enough to make suggestions. I fattened up the idle and slightly cracked opened the secondary butterflies. It's running pretty dang good. I'm still going to put a higher stall in but I've been more concerned about working on my car lately.
 

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Opening up the throttle plates, or bringing the idle up will help the problem, but usually is a fix that just masks the real issue. Today's fuel is terrible on accelerator pump diaphragms, and it could be that your diaphragm is stiff from the mixed gas we have, and not giving a full squirt. I've had to replace the diaphragms in several of my Holley carbs, just because of this junk gas we have hardening them.
You might consider changing to the ethanol diaphragm to eliminate the hardening, and pump issues.
http://www.ebay.com/itm/like/291593899356?ul_noapp=true&chn=ps&lpid=82
 
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