Carburetor Problems? Bogging off the line.

Schober Motorsports · May 23, 2015

Hey guys,

Had the car out for the first time this year getting some test n tune done, and had a hard time trying to figure out why it wasn't running as good as planned... It would bog off the starting line and I KNOW thats gotta be killing my ET. Attached is the video from my helmet cam, tell me what you guys think of the take off... Maybe its just me? Or does it seem like it hesitates taking off?

440 cid, Hughes Whiplash Cam, Edelbrock TM7 Intake, Iron Heads, 750 Holley Double Pumper (That started to pour gas out of the venturi's, maybe the issue??? ) Headers, 2500 stall converter, 4.11's out back

Right now I got my timing set to Initial 12 with it being all in @ 2500 rpm for a total timing of 34 degrees.

Maybe timing isn't correct? Ran a 8.86 (1/8 mile) as a best time today with my typical times being 8.40's.

Any ideas?

https://youtu.be/5BWzh2xluTg

Endangered Species · May 23, 2015

I would start with you floats and Needle and Seat.

Pull the bowls off and spray them out then hit them with some air. Pull the needle and seats out and make sure they are clean and free from debris.
Screw the needle and seat back in as you are doing this turn the bowl upside down so the float is hanging, screw the needle and seat until the float is level. It will be on the top side (bottom when the bowl is upside down) of the sight plug... that's ok.

While you have the carb apart, spray down the metering block and blow them out. If you left fuel in it over the winter you may have some corrosion.

Then put the bowls back on, fire the car up and see if the venturi's are still dripping.
The go from there.

Cranky · May 23, 2015

First off, what's your compression test at? If it's low but even, you might could use some more timing. Quick check and easy to try just to see how it responds. If it ain't pinging, give it some more. I bet it'll perk up. 440s are generally pretty perky with 750's on them...

bigmanjbmopar · May 23, 2015

I would suspect the carb has issues, Try an 850 DP or rebuild that 750 and down size the secondary jets. As far as your timing goes assuming its a mech only distributor? bump it up to 38 total mech + initial. 12 is a good spot. Also on the carb, is the float levels good? is the accelerator pump good? are you getting enough fuel? I'm no racer and my car is set up for the street but I am fresh off tuning this weekend since I got my A/F ratio gauge installed and everything pretty dialed in.

Badvert65 · May 24, 2015

You need to stop the fuel gushing from the venturis before you can do any troubleshooting at all. You can use carb cleaner to clean off the needle and seat in the carb. Just hold the adjusting nut and remove the screw on top, spray cleaner directly down the hole. You can even use the end of the spray tube to push down on the needle, if there is fuel in the bowl, you should hear the float clank un and down when you push the spray tube down the hole. Once that has been remedied, you can address the bog. I would start by making certain that there is absolutely NO play in the accelerator pump linkage. Any slack, no matter how small, will be felt as hesitation. I was running a near identical engine/trans/rear combo in a 65 Sport Fury and my best 60 foot time was somewhere in the 1.8 sec range. I had a 750 Vac secondary carb and was using 31 or 35 pump squirters and the 'pink' pump cam (only one with three screw holes) on the second or third screw hole (I don't remember exactly). It's a place to start. Don't worry about jets for now as they have the most effect on mid and upper range power. You are just tuning the 60 footer for now.

Schober Motorsports · May 24, 2015

Right now I'm getting 2.16 - 2.18 60', I will start messing with that carb soon, thinking that its a main problem right now. I bought it used and threw a rebuild kit in it, but I've had problems with it since I got ahold of it.

Shorthorse · May 24, 2015

Carbs can be a real pain. What KD & badvert65 said. You've got to stop the gushing (bad needles & seats, float adjustment or stuck float, etc.). Other things to consider. Check you power valve. Make sure you don't have a slight vacuum leak around the gasket base. Unless you know its history, a used carb is always a crap shoot and should be thoroughly gone through.

Cranky · May 24, 2015

Yup, carb has to be right. What kind of fuel are you running through it? E-10, E-85? Holleys hate ethanol unless the gaskets are made and it's tuned on it. Still would like to know what your cranking PSI is......

TekHousE · May 24, 2015

I know the problem.

I have that exact cam and a 750 DP on my 383.

The power valve is wrong out of the box on the Holley for our low (under 9.8) compression motors.

This might help:

http://forums.holley.com/entry.php?430-Holley-Power-Valve-Tuning

[video=youtube;mE_xTUXQJQ8]https://www.youtube.com/watch?v=mE_xTUXQJQ8[/video]

My 750 came with a power valve twice the compression rating that I have. SO we went with the #35 Since I am getting about 7.5 inches of vacuum at idle.

We also rejetted the secondaries from #80 to #84

Mike Gaines · May 24, 2015

If you are getting a bog...make sure you do everything the guys have told you about making sure the carb is working right...needles, seats, power valves, etc....but then when it is all done you must have set the throttle butterflys not to be opening to much at idle. You have a rectangular "slit" in your throtle bore. when the carb is at rest the butterfly on the carb should expose just enuf of that "slit" to make a minature "square" . Hard to explain, but read up on this....it has to be correct or you will get a bog.I had the same problem and this fixed it.

petieg383 · May 24, 2015

Check your floats for sure. I just replaced mine, it had a tiny hole in it and was 3/4 full of gas. Made gas pour out the vent tube and everywhere else. The needle and seats don't usually go bad but can get stuck too.

Gas sucks today. Totally ruining everything that actually uses gas.

Meep-Meep · May 28, 2015

The emulsion circuit will not work properly unless the float level (really fuel level) is correct. Fix that first. Also, Holleys have an issue with the needle and seat o-ring going flat and allowing fuel to bypass the needle. Pull the needle and seat assys out and replace the o-rings. Then start with jets and PV.

Carburetor Problems? Bogging off the line.

Schober Motorsports

Well-Known Member

Endangered Species

Well-Known Member

Cranky

Banned Henchman #27

bigmanjbmopar

Newb with a view

Badvert65

Well-Known Member

Schober Motorsports

Well-Known Member

Shorthorse

Well-Known Member

Cranky

Banned Henchman #27

TekHousE

Well-Known Member

Mike Gaines

Well-Known Member

petieg383

Well-Known Member

Meep-Meep

дворянин

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