Edelbrock carb leaking fuel under braking

[jefferybond]

Hi folks,

I took my Rover V8 powered kit car around Llandow circuit this weekend, and I have a problem with fuel leaking from my Edelbrock 500 carb under heavy braking.

First of all, the top of my carb pokes out of a hole in my bonnet, and is topped with a hilborn scoop. I noticed that under heavy braking, I had a strong smell of petrol, and a oily film would appear on the passenger side windscreen.No other problems though, running fine, and it didn't catch fire. The film on the screen is definitely petrol residue, not coolant or oil.

I think it's coming from the accelerator pump rod, which is near the front of the carb on the passenger side. Would heavy braking cause fuel to slop to the front enough to leak out here? If so, how can I fix it?

One contributing factor might be that my carb is tilted forward slightly. The engine is mounted level and I have not used a carb leveling plate. I figured that the small tilt of the carb is minor compared to normal cornering/accelerating/braking forces, but who knows?

Cheers,
Jeff

[kiwicar]

Hi
As a general rule 4 barrel carbs don't like being anything other than horizontal and with no accelerating forces on them (ie static would be nice) so what you describe is quite in keeping for one. being level would help, and I think (though I don't have my book on carbs at the moment) that you can get a kit to reduce this habbit of chucking petrol everywhere.
Best regards
Mike

[jefferybond]

Is that a carb levelling kit you refer to, or some other kit specific to the edelbrock carb?

Jeff

[katanaman]

dont know if it will help your problem but there is an edelbrock off road kit available. You can of course get levelling plates as well if your carb is at an angle.

[kiwicar]

Hi
There are leveling plates, which would help and be worth fitting, there are also kits to stabalise the floats/ float bowl inlet valve (off road kits) which was what I was intending to say but failed. The off road kit should also help under acceleration. Holly and some others partially solve this by fitting two float chambers and feeding the primarys and secondarys from different float chambers and a Kit for the holly is available that puts a plastic plate thing in the top of the float chamber to reduce the sloshing of petrol in there.
Is this on a Circute car? just you could try turning the carb through 90 degrees so it only floods in, say, left hand corners with the car only turning right as you go round the track the problem should be reduced? It obviously would only work on an open plenum manifold.
Best regards
Mike

[Eliot]

Many people experience problems like this - especially the Ultima GTR. On my dakar it would slosh when going round corners.
Suffice to say, along with mallory distributors it was all binned for electronics.

[ChrisJC]

Suffice to say, along with mallory distributors it was all binned for electronics.

Amen to that.

Chris.

[mgbv8]

Hi folks,

I took my Rover V8 powered kit car around Llandow circuit this weekend, and I have a problem with fuel leaking from my Edelbrock 500 carb under heavy braking.

First of all, the top of my carb pokes out of a hole in my bonnet, and is topped with a hilborn scoop. I noticed that under heavy braking, I had a strong smell of petrol, and a oily film would appear on the passenger side windscreen.No other problems though, running fine, and it didn't catch fire. The film on the screen is definitely petrol residue, not coolant or oil.

I think it's coming from the accelerator pump rod, which is near the front of the carb on the passenger side. Would heavy braking cause fuel to slop to the front enough to leak out here? If so, how can I fix it?
Thats exactly where it is coming from mate! Mine use to do it all the time on the drasg strip when braking. The worst bit was it left streaks up my Hillborn Scoop
As the lads say. You can get bits to address this issue.

One contributing factor might be that my carb is tilted forward slightly. The engine is mounted level and I have not used a carb leveling plate. I figured that the small tilt of the carb is minor compared to normal cornering/accelerating/braking forces, but who knows?

Cheers,
Jeff

[jefferybond]

I've had the top of the carb for a look, and there is nothing obvious amiss. The float heights are correct etc.

One thing that puzzled me is the passageway at the rear of the carb that links the left and right float chambers. Llandow circuit is mostly right handers, and would surely cause the fuel to run from the right hand bowl into the left (overfilling it, also the side that feeds the accelerator pump), and therefore be another cause of the problem?

I've temporarily blocked this passageway now, to see if that helps.Anyone know what the purpose of this passageway is?

I've also thought of mounting the carb backwards, would that have any adverse effects?

This is a road car by the way, only very occasional track use, so it's not a major issue, just an annoyance!

Cheers,
Jeff

[topcatcustom]

The passage between float chambers is what feeds the one on the opposite side from the fuel pipe inlet. Edelbrocks seem to only use 1 side, and the gallery to top up the other side, as mine will be very thirsty at WOT I drilled and tapped the other side and have put duel feeds in, holley style. Probably not necessary but done it anyway.

[mgbv8]

You should not notice any real problem with mounting the carb ther opposite way round. A lot of folk do this if its easier to connect the throttle etc.

[kiwicar]

A seperate feeds and needle valves with the ballance passage blocked up should help, putting petrol tank foam into the carb around the float (but not stopping it moving) would also help, I can send you some if you want to try it. Fit 2" SUs?
Best regards
Mike

[jefferybond]

The passage between float chambers is what feeds the one on the opposite side from the fuel pipe inlet. Edelbrocks seem to only use 1 side, and the gallery to top up the other side, as mine will be very thirsty at WOT I drilled and tapped the other side and have put duel feeds in, holley style. Probably not necessary but done it anyway.

Not sure about that! There is one fuel inlet, but the passage to the other side is within the top cover. There are two needle valves (obviously), one on each side.

The passage I'm referring to is in the main body of the carb, ie. after fuel has passed through the needle valves. It's normally above the normal fuel level, so does nothing, but when cornering it lets fuel from one float chamber to flow across to the other side and flood it (as far as I can tell). What could be the real purpose of it?

Cheers,
Jeff

[kiwicar]

How many ovrflow drillings does it have? one for each float chamber, or just one for both, it clearly is to allow fuel from one float chamber to the other, just need to sort out why, I still think blocking it up would be good for avoiding flooding when in a corner.
Best regards
Mike

[sidecar]

The passage between float chambers is what feeds the one on the opposite side from the fuel pipe inlet. Edelbrocks seem to only use 1 side, and the gallery to top up the other side, as mine will be very thirsty at WOT I drilled and tapped the other side and have put duel feeds in, holley style. Probably not necessary but done it anyway.

That's not quite right, the passage way in question directly connects each float chamber. There is another passage way in the top half of the carb that feeds both float valves, this top passage is the one that can be fed with two inputs by drilling and tapping a new inlet.

The "trench" like passage way in the lower half of the carb may be there just to equalize the fuel in each chamber or as some sort of vent but I also came up with the same theory that it will allow most of the fuel in one chamber to spill into the other chamber when cornering...I spent ages making a little filler out of aluminum to block mine. Whether this has made any difference is hard to say.

All I can say to Jeff is great minds think alike!

Pete