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Hello, I recently picked up a 1966 mustang with a 1968 302 with edelbrock alum heads with roller rockers, pretty aggressive cam, edlelbrock performer intake, MSD 6 box, MSD blaster coil, MSD billet dissy. I am still playing detective with most of the modifications and upgrades made, so hopefully I can provide enough info. The carb is a Holley 650 cfm 4150 HP with mechanical secondaries. It looks almost brand new. The idle Hg is 11, So I have 6.5 power valves in the primary and secondary. Adjusted the floats, and idle mixture. It runs fine at idle and just cruising but when I try to accelerate quickly (to pass) it bogs at first but then takes off. If I really get on it, then let off the gas and push the clutch in the engine will die and smokes really bad and doesnt want to start right back up. Giving it throttle does not make any difference, the only thing I can do is keep it under slight throttle (the engine is running really rough at this point) untill the engine recovers. Sometimes also does this while going up a long hill. Any tips or ideas on what to check? Any help will be great.

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Mike
 

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"...........The carb is a Holley 650 cfm 4150 HP with mechanical secondaries. It looks almost brand new. The idle Hg is 11, So I have 6.5 power valves in the primary and secondary. Adjusted the floats, and idle mixture. It runs fine at idle and just cruising but when I try to accelerate quickly ............"

Thanks
Mike
when you "really get on it" are you opening the throttle enough to open the secondaries ? If so then the problem might just be you are giving it more gas than the engine can burn. Thats the whole rationale behind the need for vacuum secondary carbs.

Z.
 

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when you "really get on it" are you opening the throttle enough to open the secondaries ? If so then the problem might just be you are giving it more gas than the engine can burn. Thats the whole rationale behind the need for vacuum secondary carbs.

Z.
I had someone work the pedal while I watched the carb and the secondaries are opening/operating correctly. The problem with the carb only seems to occur while operating in the secondary's range.

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Mike
 

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I had someone work the pedal while I watched the carb and the secondaries are opening/operating correctly. The problem with the carb only seems to occur while operating in the secondary's range.

Thanks
Mike
I think you missed my point. It sounds like you are opening the secondaries before the engine can handle the additional intake of gas and air. If you going to run a mechanical secondary carb you have exercise some judgement on when to give the engine all 4 barrels.

your situation is additionally aggravated by you having an aggressive cam. with such a cam your power band will be narrow and higher up the rpm scale. Giving the engine full throttle before you are in the power band will not result in acceleration.

Z.
 

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Definitely sounds like you're dumping way too much fuel in the motor. Zray is right, your secondaries are opening before your engine needs it, and causing it to bog down on you. The other problem, when you get on it, then drop out of it and it dies and smokes is probably because there is a bunch of unspent fuel setting in the cylinder. So essentially you're flooding it. Again, because your carb is dumping way too much fuel because the secondaries are opening before they are needed.
 

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for street driving a milder cam would help, but the cam isn't opening the secondaries, it's your foot. Keep your foot out of the secondary range until you have build up the rpm to the power band of the cam and you will be happier. A milder cam will lower the power band down the rpm scale and you will be able to give it more throttle sooner.

someone else please chime in if I'm not stating this clearly.

Z.
 

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No one has mentioned timing, do you know what your base and total advance is? The MSD billets come in several forms. Adjustment of the advance depends on which one you have of course. Just a simple idea to eliminate first, if you're not getting any or enough advance it will run rich as well. It does sound like the secondaries are opening too early though.
 

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You just need to keep trying diff combinations and see what your motor likes.

Your first issue was with the initial bog when you get on it. Check your squirter size in your secondaries. The only thing the squirter does (in the secondaries) is give that initial burst of fuel when you go into the secondaries, then the tubes do the rest. Check and see if you are getting that initial squirt of fuel when the secondaries are opened.

After you have one of those episodes where the car seems to obviously be loading up on fuel, have you checked the plugs afterwards? Your plugs will tell you a lot..

I would def change the cam on your carb at the secondary linkage. Switch to a cam that is not so abrupt... more of a conservative onset. I would guess that the one you have on there now is almost a 90 deg angle (prob red in color)... switch to one that has an easy curve to it.

Disconnect the secondary linkage all together and drive it for 10 miles or so. Get on it as well. You will obviously be down on horsepower, but if the car runs fine and your plugs are clear.... at least you know the primary's are good.

I just spent the weekend doing this myself. Removed the carb at least 7 or 8 times.... But I was dealing with changing jets, pump diagrams, etc.
 

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Thanks for your help. Do you think getting a cam kit and switching to a cam that shoots the fuel later will help?
reading your post again, I see that you probably talking about accelerator pump cams. In my opinion that is fine tuning fix, and your issue is not going to be fixed by any fine tuning. I have the accerator pump cam assortment, and it is interesting to experiment with them.

I still think keeping your foot out of the secondaries until your rpm is in the power band of your camshaft will solve most of your problems. Other than that I would think about going to a more street friendly camshaft.

Another thing, what is your rear end gear ratio?

Z.
 

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Sell the Holley and get one with vacuum secondaries. IMO you have too much carb. Especially if you are running something like 3.00 rear gears.
 

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Maybe you need a 50cc accelerator pump on the secondaries to go with larger squirters? You could be getting a lot more air than fuel when they open up.
 

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Maybe you need a 50cc accelerator pump on the secondaries to go with larger squirters? You could be getting a lot more air than fuel when they open up.

his problem is already too much fuel. That's why he has a cloud of black smoke coming out the exhaust when he gets on it.

Z.
 

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his problem is already too much fuel. That's why he has a cloud of black smoke coming out the exhaust when he gets on it.

Z.
Didn't catch the black cloud mentioned. But when does the cloud start? Oh well, went back and reread. Sell DP and get vacuum secondary carb!
Posts like this make me feel good about dropping $2K on a FI system.
 
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