Spitting Weber and over-fuelling

[Charles73]

I’m experiencing an issue on cylinders 3 & 4, but mostly no.4.

I’m getting lots of fuel coming out of the trumpet, and it seems to flood very easily. Once cleared it runs ok, but the engine oil is black and smells very fuelly! Suggesting fuel is not getting burnt.

I’ve checked the floats for holes, I’ve weighed them, checked heights and valves. All of which seem fine.

I’ve also checked ignition with strobe and is set to 12 degrees.

I also have done a compression test and all cylinders give the exact same reading.

It’s getting very frustrating and I’m getting rather tired of changing the oil….

Anything else I should be looking at to solve this?


Many thanks
Charles

[mbell]

Either fuel level or fuel pressure is too high.

What fuel pump are you running and what/how have you checked the fuel level?

Can you pull a main jet stack and measure fuel level with engine running or fuel pump running? Or confirm fuel level is below the passage to the carb throat.

[Charles73]

Either fuel level or fuel pressure is too high.

What fuel pump are you running and what/how have you checked the fuel level?

Can you pull a main jet stack and measure fuel level with engine running or fuel pump running? Or confirm fuel level is below the passage to the carb throat.

I’m running and electric pump (facet cylinder type) with a Malpassi pressure regulator next to the carbs.
Maybe I’ll wind the pressure down slightly, but I’m only getting the issue in the rear carb, so I thought it would be more a carb problem that an overall pressure problem.

I’m not too knowledgeable on carbs so I will do what you’ve suggested and report back!

Thankyou

[EPA]

The float might not be moving freely in the bowl for some reason, I would swap the carb lids around, complete with the floats to see if the problem moves.
If the float is not hanging properly it might not be operating the valve when the correct fuel level is reached
Ed

[mbell]

I would swap the carb lids around, complete with the floats to see if the problem moves.

That is a good suggestion.

I’m only getting the issue in the rear carb, so I thought it would be more a carb problem that an overall pressure problem.

It could still be a pressure problem, just one carb is over come sooner than the other.

Might also be worth checking the float valve operation and limit adjustment. If allowed to drop too far the valve can jam up a bit or drop out.

[h20hamelan]

Colourtune is neat for viewing events, did you say you had spark at #4?

[Charles73]

Colourtune is neat for viewing events, did you say you had spark at #4?

Yes definitely have a spark as once cleared it runs quite well considering!

[Charles73]

I have reduced fuel pressure (no gauge to hand unfortunately, but went half a turn for now) and she seems a lot happier. After a road test there was still a very small amount of fuel coming from the air box, but nothing like before. This makes sense as fuel gets to rear carb last, so I guess this will see the effects of too higher pressure more than the front carb.

I also checked fuel level by removing main jet a measuring with a vernier. From the top of the carb to level it measures around 40mm….quite hard to do accurately, unless there’s a better way? Also, should a be measuring with the engine running? (I did so).

I’m yet to check float isn’t fouling etc but I will.


Thanks for your suggestions so far. Much appreciated

[ericbushby]

Hi Charles,
You do not need the engine to be running so long as fuel pump has just been pumping.
At 40mm the fuel mixture was too rich especially on the idle circuit on my Weber 40 151 carburettors, although I did not get any spitting.
Mine runs better at 44mm to 45mm from the rim of the jet cover.
Try measuring it with your vernier and a small torch. As you extent the probe you should see the surface of the petrol shiver as the probe touches it so you can measure it quite accurately. we are not bothered about a millimetre.
Good luck,
Eric in Burnley
!967 S3SE DHC

[Charles73]

Hi Charles,
You do not need the engine to be running so long as fuel pump has just been pumping.
At 40mm the fuel mixture was too rich especially on the idle circuit on my Weber 40 151 carburettors, although I did not get any spitting.
Mine runs better at 44mm to 45mm from the rim of the jet cover.
Try measuring it with your vernier and a small torch. As you extent the probe you should see the surface of the petrol shiver as the probe touches it so you can measure it quite accurately. we are not bothered about a millimetre.
Good luck,
Eric in Burnley
!967 S3SE DHC

Hi Eric, thanks for the instructions…

I’ve just measured the level on both carbs. I’m getting 43mm from the rim of the jet cover on both.

I think I’ll try what was suggested earlier and swap covers/floats over and see if the problem moves. I have a feeling the issue is pressure related now though.

Many thanks

Charles

[ericbushby]

That seems OK then.
If the pressure was too high that might cause the petrol to be forced past the float valve and raise the level of the fuel too high. As the level appears to be correct then that does not appear to be happening.
Eric in Burnley.

[gjz30075]

What exactly is the fuel pressure?

[Charles73]

What exactly is the fuel pressure?

I haven’t been able to check yet. I will put a gauge on it tomorrow. From memory it was set to 2.5psi but I remember the tuner found power was dropping off at higher revs due to lack of fuel pressure so he increased it (I don’t know by how much).

By decreasing it by a turn I have noticed an improvement.

[alan.barker]

Charles,
Replace the Facet and Regulator by a "Huco Pump". Designed for Webers low pressure.
Alan

[elans3]

Set it between 2.5 and 3.5 psi, no more than that.