5 replies to this topic

[Prawn]

Hi guys, i've got a crazy problem with my weber 45DCOE, and I'm at a loss to what's causing it.

I had problems with a fuel leak caused by split misab plates, which i fixed today, with new misab platse and thackray washers gapped at 20thou as per weber instructions.

The car's running perfectly, starts on the button and drives wonderfully, and appears to idle fine too for a while.

After 3-4 minutes on idle, the car starts to judder for a few seconds, then stutters badly, backfiring out of the carb once or twice before dying. I watched this happen a few minutes ago, and as it died, seemingly loads of fuel poured out of the carb and dripped down onto the manifold!

It looks like the fuel is coming from the front of the carb, around the choke area, although it's pretty hard to tell. it's definitely not coming from the float chamber top gasket, as that's bone dry still.

When I fitted the air filter earlier and held the carb on end (filter to the sky) it did seem to ooze a tiny bit of petrol from around the front choke area, but I assumed this was due to it being held basicly upside down.

Any suggestions would be great! is there a seal around the choke area that could have perished?

I don't really want to risk driving it again as fuel leaking onto a hot manifold doesn't sound too safe to me!

Cheers

Nick

[ianpettifer]

Hammer?
Bump

[Prawn]

thanks IP, your help is legendary.

Sadly, a wise man once said, If a hammer don't fix it, it's technical.

[Kerrin]

Two things come to mind for you to check.

There is a big hole in the front of the carb near the chokes which is the breather/overflow from the float chamber. If it is leaking from there your float chamber is overflowing, but from your description the fuel is coming from the choke area (lever?) I cant think f anyhing round there which may leak.

Perhaps it is best to start with the basics, sorry if i am teaching you to suck eggs, but if it happens gradually i would suspect the following.

1. What is your fuel pressure, too high pressure will push the needle valve off the seat and flood the carb. if you are using and electric pump then a fuel pressure regulator will be required, it looks like you have a Facet Red or Silver top in the boot, on our avatar pictures.

2. If you fuel pressure is fine, take the top off the carb and check that the float is working correctly, has the correct fuel level, and is not filling up with fuel as this will flood the carb.

3. Check all the jets in the top cap are tight as they will mess up the mixture if they work loose.

[Prawn]

Cheers for the reply Kerrin.

the fuel is coming from 'somewhere' near the front of the carb, I wouldn't be surprised at all if it were comming from an overflow, I wasn't aware this existed!

I am running a facet red top fuel pump, with a facet filter king 72mm glass bowl filter/regulator, which was setup on a rolling road.

I initially thought like you, it may be the pressure has somehow become too high, so today I installed a fuelpro adjustable FPR inline between the filter king and the carb, set at 3psi. this didn't solve the problem though.

I had a look a the floats inside the carb, and although i couldn't see anything obviously wrong, I'm now sure this must be the problem. with two regulators in the line both set at 3psi it CAN'T be the fuel pressure, so the float valve is next in line to check.

Is there any way I can check it other than replacing it?

I'm fairly sure all the jets are OK, they were newly fitted at SRD in Launceston about 500 miles ago, and it's been pretty much problem free until recently. it still drives perfectly, it just won't idle for any length of time!

Thanks for your help, I'll take a look at the float again.

[Kerrin]

I cant remember the exact measurement for the float height but will have a look in my "extensive tuning library" in the back room.

Yes found my DCOE tuning book, (speedpro, Des Hammill) Which has proved usefull on a number of carb problems.

The float height and droop is set by the brass tabs in the middle of the float assembly. The height is measured with the floats held up with the needle and seat just touching, by using a steel rule from the underside of the top cover down to the top of the float should be 8mm.

The Droop should be set at 15mm.

Fuel pressure allegedly should be 1.5 to 2.5psi so maybe you still have it set a touch high!

Depending on how worn the needle jet is is it possibly leaking, as this may over richen the idle.

The breather hole is in the airfilter next to the ram pipe and is about 1/2" dia, but if the carb is at an angle towards the engine it may still leak at the front (manifold) if the fuel level is high.

To check the float, knock out the small brass pin and shake the bass floats to see if there is any fuel inside them. You can check how worn the needle valve is at the same time.

I used to have the same problem with my old Opel Manta rally car. the floats were damaged on one carb and it would get richer and richer till it cut out, once the leaky floats were soldered up it ran great.

Hope this helps.