Carburator bogs down while cornering
 

I am running a Holley 750 cfm double pumper with mechanical secondaries on my 351 crate engine from Ford. My problem is that every time I come to a stop or cornering in my FFR Roadster, the engine stumbles for a few seconds. I have to keep my foot on the accelerator to keep the car running. After the car stops it idles fine and under acceleration it runs great. Anyone having the same problems? I'm open for any suggestions.

You probubly need float bowl vent baffles. They are white plastic rectangular tubes that prevent gas from sloshing out of the float bowl vent during braking or cornering. If the motor seems to be going rich instead of "popping lean" this is your problem. Made by Holley.

I have had this exact problem for years when I stop hard. No problems in turns, just hard braking. I just live with it. The car runs great otherwise.

If it's accompanied by a puff of white smoke, it may be that your pcv is ingesting a bit of oil mist and pushing it into the carb. But, the baffle cure seems the most likely road.

TT

Try this!
 

These symtoms are usually caused by a couple of things:

#1. Fuel is sloshing forward from the rear bowl during braking and dumping into the auxilary venturi in the center of each throttle bore. (There is usually a small stamped metal screen installed on the metering block over the bowl vent hole).This sudden surge of fuel happens when the secondaries are closed and dramatically upsets the air fuel ratio causing a temporary rich condition. Just install the plastic "whistle" and adjust the float level. Parts are cheap and work wonders.


#2. Fuel is being forced to the front of the forward (primary)
bowl during heavy braking uncovering the main jets causing a lean condition (no fuel). This condition would normally only happen if the float level was low on the primary bowl combined with questionable fuel delivery.

I experienced this and even went so far as to add the "Jet Extensions" (drag race stuff) to the both primary and secondary main jets.

.........Rick

I have the same combination and problem on my 351 as you. I have the white plastic whistles and just switched from from a stock brass float in the primary and jet extensions with a clearanced float in the secondary to roadrace floats in both. Tried setting float level high, low, and right on. Nothing changes and car runs great otherwise. My search continues.

I run a Barry Grant Demon carb, and I have a rich stumble on hard braking. I assume it's fuel sloshing forward from the secondary bowl, but I haven't yet tried to correct it, as it's relatively minor, and doesn't seem to affect a heel-toe downshift

Apparantly BG hasn't solved all the little quirks that affect Holleys. Overall, though, I love the Demon.

Good luck,

I had a similar problem when hard cornering on the street or track. My engine and carb are the same as yours.

The soulution was to get a better Holley that had been set up for road racing including floats with tapered ends as opposed to the square ended cylindrical ones that come stock.

I've since tested this setup on a skid pad and on some roadcourses with good results.

Good luck!

I have a 600 vac secondary 1850S Holley and it works great in cornering and braking but I am having a problem at the drag strip. If I start in 1st gear(SD T-5 with 2.95 first gear and 3.73 rear gears) the motor stumbles about 50 to 60 feet out at the drag strip. If I start in second gear the car launches soft but no stumble. This does not seem to be a problem on the street. I am guessing that the car will launch better at the strip due to all the sticky rubber.

I have some theories on this:
1. The fuel is sloshing back in the secondaries causing a lean condition.
2. The fuel in the Carb runs hotter due to the heat rising from the motor while waiting to run. This would be the case even if you push the motor to the staging area because the motor is still hot from the prievious run. On the street the motor has cool air flowing over the carb thru the hood scoop.
3. combo of both

I have consistant fuel pressure of 7psi and the floats are set correct. I did put a lighter spring in the secondary diaphragm but it still does this track stumble. I have tried to duplicate this on a rural road but cannot duplicate it.

Any suggestions

In addition to the baffles (and jet extensions in the secondary to counteract acceleration starvation), there is an old drag racer trick that I might recommend trying.

Take a piece of rubber or pvc fuel hose the correct diameter to slip snugly over the two float bowl vent tubes that rise vertically on each end of the carb opening, creating a mildly curved bridge between them. Carefully notch about five little cuts in the middle of the bridge, maybe a half-inch apart, only deep enough that they open a bit when bent into place.

This allows the bowls to vent as designed, but prevents (minimizes) the tendency for fuel to slosh up through the tubes under G's and slop into your venturis.

Wish I had a pic of this, but I think you get the idea. Some guys even go so far as to carefully bend up a piece of soft copper or alum. tubing to make this bridge, and drill the vent holes into it. A little neater than a hunk of hose.

TimV.

Near Stalling under braking/cornering
 

Check your float levels - sounds like they might be set too high - allowing gas to slosh out into the carb throats. If you do not have the clear float (see through) screws in the sight holes - I recommend them. You can (carefully) adjust the float level while the engine is running. You do need to be very careful when loosening the float level locking screw on the adjustment bolt - but it can be done (if you loosen it too much with engine running the pressurized gas will push past - possibly hit your hot manifold - NOT a good thing). Go to the Holly website for specifics on float level adjustment.

Hope this helps -- been there - done that -- and it worked.

Later, Shark

I would go with Tim's suggestion of using the hose or tube between the vent tubes. I would also add that unless you have a lot of cam and at least 11:1 compression, a 750...especially a double pumber, is a lot of carb for a 351.

Here are a couple of thoughts for you:

1. If cost is not a huge issue, call up the Carb Shop, give them all of your specs. They will want to know all about the engine, the weight of the car, gearing etc. They will then recommend and provide a carb that will work. They built the one on my 427 Side Oiler and it has never given any trouble of any kind. It also has "four corner idle" which you might like for yours. If you have a dual plane manifold, it allows idle fuel to be metered through all four venturis....especially helpful with a bumpy cam.

2. Money or not, it may be that simply buying a 650 propared by Holley will solve the problem. I'm absolutely certain you'll find the engine a lot crisper with quicker throttle response. Ask yourself which do you want most; a car that runs like a raped ape at wide open throttle on the drag strip or one that you can drive on the street and push in the corners on a race track. On a good day, a fairly streetable engine like yours will get about 65-70% VE (volumetric efficiency) You can take that percentage against your intended RPM curve/displacement and it will tell you how much air your engine will flow. Remember....it's just a big pump and opening a bigger hole won't make it pump any more. That is all determined by cylinder head/manifold design, piston dome shape compression ratio and camshaft geometry.

HP Books used to print a great book on Holley carbs and gave a lot of information on airflow.

Hope these thoughts help out.

Al

Guys -I have the same problem (bogging whilst in corner) on my car, 'cept I am using the edelbrock #1412 800cfm carb.

I have tried dropping the fuel levels, and blocking the passage at the rear of the carb which links the two float chambers, but it still persists.

Car runs great otherwise. I don't believe you can get float bowl baffles for the edlebrock, less you can tell me different??