Edelbrock 500cfm problems- more of...

[topcatcustom]

My carb has seemed to work ok, but all of a sudden today the pressure gauge fitted just before the carb was reading about 1psi instead of 5psi, and the carb bubbled over with petrol.

Turn on fuel pump and does the same every time now- not attempted to start engine!!!

Any ideas?!?! So much for my MOT

[sidecar]

My carb has seemed to work ok, but all of a sudden today the pressure gauge fitted just before the carb was reading about 1psi instead of 5psi, and the carb bubbled over with petrol.

Turn on fuel pump and does the same every time now- not attempted to start engine!!!

Any ideas?!?! So much for my MOT

Its got to be a float or float valve issue!

Crap in the carb! (i.e. there is dirt in it, I don't mean take a dump in your carb!)

Also take the petrol pipe of the carb and block the end of the pipe with a bolt, turn on the pump then check the pressure on the gauge, I bet it will show 5 PSI.

[mgbv8]

This means I posted a load of crap on the MX5 thread then??
I thought it was a Holley you were using.

As you had a backfire I'm wondering if the pressure wave has actually bent the float arm so its trying to overfill.

[topcatcustom]

last night I stripped the top off the carb, took the floats out etc and blew them all through, found a bit of crap in the float chambers which I cleaned right out, back together and held good pressure on the gauge again.

Today, was ok, then during a drive I noticed the pressure was low again and when I stopped there was fuel splashes over the bonnet

Drove it a little with the fuel pump off and then switched it back on for a few seconds, off again etc etc, after a couple of attempts it held pressure again on the gauge. This says to me that there was crud stuck in the float valve- but not sure how it can keep happening when I blew all the pipes out, and have a filter right before the regulator?!

Car conked out today and wouldn't start again (battery's not great so didnt have a lot of attempts) but as it just happened I'm assuming it is the carb again as it showed low pressure before it happened again and has flooded or similar.

[sidecar]

last night I stripped the top off the carb, took the floats out etc and blew them all through, found a bit of crap in the float chambers which I cleaned right out, back together and held good pressure on the gauge again.

Today, was ok, then during a drive I noticed the pressure was low again and when I stopped there was fuel splashes over the bonnet

Drove it a little with the fuel pump off and then switched it back on for a few seconds, off again etc etc, after a couple of attempts it held pressure again on the gauge. This says to me that there was crud stuck in the float valve- but not sure how it can keep happening when I blew all the pipes out, and have a filter right before the regulator?!

Car conked out today and wouldn't start again (battery's not great so didnt have a lot of attempts) but as it just happened I'm assuming it is the carb again as it showed low pressure before it happened again and has flooded or similar.

Maybe the crud is actually coming from the regulator, you could fit a paper filter between the regulator and the carb. One word of warning, several Cobra owners have watched their cars go up in flames because they fitted a glass or plastic filter in the engine bay which has then broken allowing fuel to go everywhere.

Personally I hate regulators and would always fit a low pressure pump so that a regulator was not needed.

[topcatcustom]

I dont like the regulator, but the holley red pump is slightly too high pressure I believe, it also acts as a splitter for my twin carb feed. Maybe I'll fit a filter king regulator in line and take the guts out of the holley reg?

The filter is one of those billet ally sort of ones with a removable element.

[sidecar]

I dont like the regulator, but the holley red pump is slightly too high pressure I believe, it also acts as a splitter for my twin carb feed. Maybe I'll fit a filter king regulator in line and take the guts out of the holley reg?

The filter is one of those billet ally sort of ones with a removable element.

I'm sure you will suss it out, after all the carb does not ask for much, just clean fuel.

BTW just seen the picture of your car on the other thread, your F-in nuts! (In a good way)

[topcatcustom]

Lol cheers!

Right guys- not driven it enough to be of much help diagnosing this prob- not even 100% sure it is the carb, but when I got home (a couple of hours after it broke down and wouldnt start) I got in it, fuel pressure was good again (maybe crud pushed through float valve??) and it fired up and ran again. Took it down the road and stalled it whilst under a very small amount of throttle (i.e. not idling) and it wouldnt start again for about 3 mins.

It seems it will happily start from cold, but not from hot? Though I thought this was only a problem when the carb was under the bonnet and surrounded by heat? The carb is always pretty cool as the blower doesnt get that hot and it has loads of cold air around it.

Really want to get this sorted as want to use it over the weekend!!!

[kiwicar]

Hi Tom,
you may be getting icing in the carb (it was very humid around here yesterday)? if not you may have crud in the carb passages that are blocking up, then when you stop it slowly settles out and off you go again.
Best regards
Mike

[unstable load]

Could also be that you have some crud in the needle and seat that is keeping it open against the floats.

[topcatcustom]

I'm getting a new battery today (90 bloody quid- yes I'm a tight ass) which will help keep the cranking speed up but I will also take the carb off again today and give it a good flush through. I did the top half including the floats etc and cleaned out the float bowls the other day but I'll do the whole thing after lunch, then I'm going back onto the road

[bigaldart]

I would go with Kiwi, icing is a distinct possibility. Another possible is vapour lock in the pipes under the bonnet. As methodical as you are I would be surprised at dirt in the needle and seat being an issue but it never hurts to check. Is the fuel tank clean and flushed? Just go through step by step and see what happens. You will get there.

Alan

[topcatcustom]

Well- had a great weekend with the car and didn't let me down, though the fuel pressure is still playing up. It will bang straight up to 5psi ish when flick the fuel pump on, then after driving for a while it will tend to drop down to about 2-3psi, and sometimes even lower to only just picking up off the needle seat!

If it were the float valves then it would be pumping fuel into the engine and would be massively rich- which is not happening as the AFR is perfect and runs great. Which could mean the gauge is faulty (which I would think highly unlikely as brand new and good one, plus too simple to go wrong!)

I think it either has to be the Holley regulator is going all over the place but seems unlikely, or it's the Holley fuel pump? I think I am right in remembering that they have a pressure relief valve built in? If so then due to the nature of the pressure shown on the gauge it seems most likely that the fuel pump is playing up- either not working properly or the relief valve is not working correctly.

Any thoughts?

p.s. it also has a full tank of juice.

[sidecar]

OK then, if your carb is not flooding but the pressure is dropping then you do have an issue. (Assuming that the gauge is not duff)

My money would be on the pump or regulator being faulty. You could disconnect the fuel pipe from the carb and run it into a large container, run the pump for 5 minutes and watch the flow rate to see if it drops off. A bloke on the Cobra forum had all sorts of issues like your having, it was a duff regulator in the end.

Another test would be to run the pump for 30 seconds into a container, (use a 2 litre plastic milk container). Then run the pump for 5 minutes into a large container, then run the 30 second test again and compare the results.

Finally measure the amount of fuel that was delivered in 30 seconds, double it so that you get the CC of fuel per minute. You can use the formula below to work out whether you pump is man enough for your engine:-

BHP that the fuel can make = CC per minute x 4.7

So if you think that you engine should make 285 BHP it will need 1.339 litres of fuel per minute to do it. (You would want the pump to be able to deliver more than this)

I did not have a decent way of measuring the CC of fuel directly so I marked the milk container then replaced the petrol with water, I then weighed the water using my wife’s kitchen scales, each gram is more or less one CC.

My pump can deliver 2 litres of fuel per minute, my lump makes 285 BHP.

[bones]

I had a problem last year with the pressure moving around alot, took the regulator off and it was fine after that so maybe you could try another reg. Although ive got to put a return pipe in the nos side of it as pressure drops ?? rich