Engine stumbles powering thru corners

[SlapHeadDiver]

Hi
I've a MGB Roadster 3.9 V8 230bhp with Edelbrock 1404. Goes really well on the road and on a track day [not racing] very well in a straight line but as soon as we enter a corner and until we [son and I] begin to straighten up the engine stumbles/stutters.

Facet fuel pump via a King fuel regulator, currently set to 5.5 psi has been 6

We've recently fitted the innovate DLG-1 with twin lambdas and we can now see on the level both reading 12/13 range but thru the corners can drop to 10 and as high as 22. If it's a left hander the left bank is high and vice versa on a right hander.

Spoken to a number of people and tried things but to no avail, really frustating. Now we know it's going rich and lean thru the bends my son thinks we should add a fuel feed to the lefthand side of the carb and split the fuel feed from the regulator in the engine bay so it feed both sides of the carb together as he thinks it's the G force causing one side to go rich the other lean.

Looking at the carb it looks like there is a blanking plate/plug that can be removed and an inlet fitting [8089] fitted, is that correct? If so any reason why I shouldn't do that and have dual feeds?

We've been trying to resolve this for ages, we only do a handful of track days each year and there is nowhere round here where we could test it on the road, we need to be doing 70+ thru a corner to make it happen.

Thanks
Mark

[DaveEFI]

I assume you've double-checked the fuel level is correct? If it is and surging is causing it to run weak, I'd guess you wouldn't be the first to experience this. Is a baffle kit available to help control it?

[SlapHeadDiver]

Hi Dave
Fuel level - I've checked the floats are correctly set and the king filter regulator is showing fuel well up towards the top if that is what you mean

Baffles - These are already fitted
Thanks
Mark

[DaveEFI]

It must be fuel surge within the carb, I'd say, assuming plenty fuel in the tank? Rather than a regulator problem?

[SlapHeadDiver]

Fuel level in the tank? It does it even with a full tank otherwise we were considering a swirl pot

If we can fit a 2nd fuel feed into the carb as I think might be possible just looking the unit and without dismantling as yet, do you think it would help or make it worse?

Cheers
Mark

[DaveEFI]

Not an expert on Edelbrock carbs - if I wasn't happy with SUs I'd go for injection. But they are a common mod for the RV8, so I'd be looking for something basic? Unless twin feeds to a carb come into that category?

[SlapHeadDiver]

The previous owner did the V8 conversion and fitted the Edelbrock 1404 carb. It's only when really pushing it thru corner that the 'stumble' shows itself i.e. on a track day. On the road it's never pushed quite that hard
I'll keep looking for a solution
Cheers
Mark

[DaveEFI]

Can't really see a B GT reaching cornering forces other cars with the same carb couldn't? And if it has baffling known to work, it then must be the supply failing to keep up (as the float chamber would soon empty when racing)? But no idea why. And no idea why it should go rich either. Weak I can understand.

[Ian Anderson]

Presume Facet red top? If so it is marginal at your horse power.
These can draw fuel but do not really suck so hopefully you have the pump near the tank!
Clean the pre filter on the pump.

What orientation is the pump? Up down, north south or east west un the chassis? They should be fitted up down with inlet at bottom.

Worst would be East West as cornering could cause the pup innards to not move due to centrifugal force.

Just some things to chew over!

Ian

[SlapHeadDiver]

Hi Ian
Facet redtop, correct
Near tank, virtuall underneath it
Orientation of pump and feed, I'll check in the morning. When you say north south do you mean front to back of car or roof to floor ie vertical? Latter might be tricky
Clean pre filter, will do but fitting the red top was one thing we tried as a possible fix but didn't so doubt the filter is the issue but orientation or feed might be.
Thanks
Mark
Ps: just reread you message, best is up down ie roof to floor. It's definitely not up down, I'll see if I can rotate it

[SlapHeadDiver]

Hi Ian
Pump runs North/SOuth [front to back with the Inlet/outlet at the back. Inlet is at the bottom
So overall could be worse but there is room with mods to the fixing plate to turn 90deg so it's up/down with the inlet/outlet at the bottom

I'll clean the pre filter on the pump and the inline one between tank and pump as well as king filter regular in the engine bay while at it although it's unlikely to make an difference to the stumble as it has done it from day 1 of fitting them

Next track day, Angelsey Aug 8th, fingers crossed it at least improves it if not resolves it

Thanks
Mark

[Ian Anderson]

Hope it all works. Sometimes it is the easy and basic bits that cause all the problems.

Ian

[GDCobra]

Disclaimer - I haven't dealt with carb's for some time so may be talking total garbage but just thought I'd try to clarify something.

I've read and re-read the original post and it seems that you are getting one bank rich and the other lean for a given corner direction and these reverse when cornering the other way?
This makes is sound like one side is getting (plenty of) fuel and the other being starved. From what I remember this seems strange as the float bowls are mounted fore and aft, odd that centrifugal force should affect them in opposite ways.
Is there any chance you have the carb' mounted with the float chambers on the sides? Possibly a different carb' to the one I had.
The only other way I could see centrifugal force affecting the float chambers in an opposite manner is if the float pivot is reversed in each (quite possible if the float chambes are the same and simply rotated 180° front to rear) so the force is acting to close one (reducing fuel level - lean) and open the other (increasing level-rich)


You mention adding a second feed to the opposite side of each float bowl but (if I thinking of the same thing) these connections simply feed to the same point on the float bowl where it encounters the float valve so would this really help?

Mind you I'm with DaveEFi, any problem with carb' and it's replaced with EFi. In fact I don't even need a problem!

Edit - Just re-read the OP again, realise it is an Edelbrock (Don't know why but I though a Holley) so float chambers are on sides, probably makes most of my post pointless. Sorry!

[SlapHeadDiver]

Hi GD
Thanks for your reply, I'll check the floats but I don't there's a problem as they sit left and right. I did change the floats for off roaders and ensured the pivot range was correct but that didn't change anything.

Maybe changing the pump so it is up/down improves/solves it as per Ian, can but hope
Thanks
Mark

[SlapHeadDiver]

Fact pump rotated, now up/down with feed in/out at the bottom

Filters - Between tank and pump, facet filter and king filter reg in the engine bay checked and are all clean

Angelsey track day on the 8th, fingers crossed it has at least made a difference if not resolved it completely. I'll let you know either way

Thanks for all the feedback
Mark