Webber 500 Vaporisation?

tetlow · Post by **tetlow** » Tue May 01, 2007 7:15 am

Had a problem the other day on the MGB. I had been out for some time in traffic and the engine got hot. Enough for the fans to come on but not especially hot. The car had been left in a car park for a couple of hours and when started would not tick over properly. After a short trip and a further 30 mins in B&Q's car park the engine started to back fire and would not tick over hardly at all.
I had previously been playing with the fuel pressure regulator and it was set to approx 5 psi which I believe should be OK for a STD 3.5.
I took the car out the next day (which was hotter) after upping the pressure to 6 psi and found the engine did not overheat even though I was in traffic.
I have never had this problem before and I am assuming it was the carb getting too hot and vaporising the fuel in it?? or could it have been some dirt?? I have regularly had the car running with the fans on and never had this back firing.

Am I correct in my assumptions and would increasing the fuel pressure help a vaporising carb?

I have had the headers Ceramic coated inside and out so the under bonnet temperatures should be lower than normal.

Does any one have experience of fitting bonnet louvers / vents on MGB's and do they work? I would rather not as I would like to keep the original bonnet looking standard.

Any remarks would be appreciated.

Regards

Dave

ihatesissycars · Post by **ihatesissycars** » Tue May 01, 2007 7:35 am

If the fuel were vaporising in the carb causing it to go lean in some way then it would run hotter causing the problems you described. Upping the fuel pressure could well replace the vaporised fuel that bit better and return things to normal.

My theory at least!

Well spotted though on your part! Most people would've bought new massive rad's, replaced a million 'stats, put huge fans in etc etc!

tetlow · Post by **tetlow** » Tue May 01, 2007 8:44 am

Cheers

v8alex · Post by **v8alex** » Tue May 01, 2007 12:09 pm

If you have enough under-bonnet space, you could also fit an insulating spacer plate between the carb and inlet manifold. They're about 10mm thick and apparantly work quite well stopping heat conducting into the base of the carb. I've fitted one, but not started the engine yet, so can't comment further !

Alex

sidecar · Post by **sidecar** » Tue May 01, 2007 1:13 pm

I fiited one and it did make a big difference.

Before it was fitted I took the top off the carb to change the jets whilst the engine was still hot, you could actually see the fuel boiling in the float bowls!

You need longer studs which some kits provide but I needed a longer, longer one as the throttle cable bracket mounts off it. (They are a bit of a pain as the thread is different at either end).

Regards,

Pete

mgbv8 · Post by **mgbv8** » Tue May 01, 2007 5:00 pm

I got my long bolt kit from RS for the 500 carb. They are just long enough for the 1" spacer and the ally cable bracket fits on, but without a washer.

JSF55 · Post by **JSF55** » Tue May 01, 2007 8:23 pm

I fitted one of the v8 tuner ones, did the trick on mine, i think PaulB fitted the thicker type to his, john

tetlow · Post by **tetlow** » Tue May 01, 2007 8:58 pm

Sounds good to me. £13 is a not a lot to gamble.
I have about 10mm clearance so it might fit.
Cheers
Dave

Paul B · Post by **Paul B** » Sat May 05, 2007 3:13 pm

JSF55 wrote:I fitted one of the v8 tuner ones, did the trick on mine, i think PaulB fitted the thicker type to his, john

I bought one John, phenolic, but haven't fitted it yet. I thought it would cure a hot starting problem, but I have find that holding quarter throttle and cranking for a couple of seconds and the motor starts every time.

The spacer, as well as another similar ally all one I bought in the USA, is still sitting on the shelf in the garage. I shall fit it next time I'm home, see if there's a noticeable difference of any sort.

Robrover · Post by **Robrover** » Fri May 11, 2007 4:48 am

Use Edelbrock heat insulator gasket PN#9266 for a ported style manifold (e.g. Edelbrock Performer) or # 9265 for an open style. Keep your fuel cool preventing fuel percolation in high underbonnet temps. Come complete with extended carby studs. Summit sell them.

Paul B · Post by **Paul B** » Fri May 11, 2007 8:51 pm

Robrover wrote:Use Edelbrock heat insulator gasket PN#9266 for a ported style manifold (e.g. Edelbrock Performer) or # 9265 for an open style. Keep your fuel cool preventing fuel percolation in high underbonnet temps. Come complete with extended carby studs. Summit sell them.

Try this out on Ebay: 220104323682

" 1 inch Phenolic Carburettor spacer with open centre" £14 inc postage!

He may have one with the four holes in, a browse of his shop.

sidecar · Post by **sidecar** » Fri May 11, 2007 9:25 pm

If space is an issue then the one that I've got fitted is only about 6-8mm thick but still cured my boiling fuel problem.

I can find the part number if needed.

ppyvabw · Post by **ppyvabw** » Fri May 11, 2007 10:40 pm

i have this problem. I find a reving its nuts off clear it usually.

I don't have space for a spacer and i also have the dual port manifold so have to keep the primaries seperate. I have though about making one out of circuit board material. Could this work, it is insulating or would it be too thin

sidecar · Post by **sidecar** » Sat May 12, 2007 7:20 am

ppyvabw wrote:i have this problem. I find a reving its nuts off clear it usually.

I don't have space for a spacer and i also have the dual port manifold so have to keep the primaries seperate. I have though about making one out of circuit board material. Could this work, it is insulating or would it be too thin

Circuit board would be better than nothing, I'm sure you carb would be coller with it fitted. My carb used to be too hot to touch after a run and now its just warm. The fact that you've got dual ports may not matter if you use a spacer that has one hole per choke.

You would need a gasket on either side as ciruit board has no give in it and therefore may not seal. You could use a small amount of silicone sealant.

Rgds,

Pete

tetlow · Post by **tetlow** » Mon May 14, 2007 3:56 pm

Hi Pete
Would you have the part number for the 6-8 mm spacer please and where you got it?

I think this would help and i will just have to slam the bonnet harder if it won't close.

Regards
Dave