Carb Constant Fault!

[Matt Cole]

Does anyone have a solution to the ever increase carb failures regarding the dribbling of fuel down the venturi which causes irratic idling? I'ts now 4 carbs in total that i have had this problem with, even after a rebuild kit. Am i right in thinking it is the seal (fibre?) that the acc pump jet sits on leaks causing flooding on idle?? The fuel seems to come out of the middle of the carb so i presume this seal does two jobs in sealing?? Any one got a cure once and for all??

[Brigsy]

I used a rubber o-ring instead of the fibre seal to stop the acc pump jet leaking on my carb, seems to be holding out.

Also check the aux venturi hasnt come loose, even though its pressed into the body of the carb one of mine had causing the dribble of fuel on idle.

[Matt Cole]

Brigsy, have you used the fibre seal and its still failed?? I wonder if a stronger spring on the acc pump jet body would help??Bloody annoying when they 'just' fail. I just dont understand why the new seal in the kit doesn't work. Which bit of the venturi do you mean comes loose?? I never noticed any loose internal parts.

[Andrew Cooke]

If it's dribbling in the venturi it's nothing to do with the pump jet.

I could cure mine with a standard main jet.

I never worked it out, I don't think the fuel level in the float chamber was too high, but it could be that. It may have been linked to my near solid engine mounts. I spent a day swapping parts in my carb, I gave up in the end as it wasn't that important to me.

[Maka]

i had a similar problem.
Had to swap the carb body in the end as it was very annoying.

that seemed to work well :agree:

[Matt Cole]

If it's dribbling in the venturi it's nothing to do with the pump jet.

I could cure mine with a standard main jet.

I never worked it out, I don't think the fuel level in the float chamber was too high, but it could be that. It may have been linked to my near solid engine mounts. I spent a day swapping parts in my carb, I gave up in the end as it wasn't that important to me.


Andy, not sure what the main jet has to do with dribbling fuel?? This happens to carbs 'all of a sudden' and they can't be repaired. Changing carb bases is not an option as all 4 have the same fault. I even bought one rebuilt off ebay with the same problem. It needs an answer i think.:(

[V Man]

I had this problem to Matt chew. It would idle fine but every few seconds it dribbled.
The O ring was the culprit and it was sorted pretty quickly. Aldi had some O ring kits for really cheap that I wish I had bought for spares:sad2:


I need a carb base as my mixture screw is welded in......
Let me know if you have a spare. I'm on my old no!

[Matt Cole]

is that roger dodger? Our youth has all the carb bits now, all i do is try and fix em. I'll get him asked!:agree:

[Andrew Cooke]

Andy, not sure what the main jet has to do with dribbling fuel??

if the fuel is coming out of the venturi it's the primary fuel circuit, so maybe the higher idle speed is bringing the main jet in? Either the fuel level in the emulsion tube is high enough to overflow into the venturi tube, vibration is flicking fuel from the emulsion tube into the venturi, or there is enough gas speed in the main venturi to suck the fuel from the emulsion tube.

Have you tried a double washer on the float valve to lower the fuel level? I can't recall all the things I tried, it was almost 5 years ago.

[Brigsy]

The original fibre seal worked ok, the one in the kit didn't. I used a tight fitting o-ring & stretched the spring, seems to work ok.

The aux venturi is the bit in the top half of the throat of the carb, the one i had would move when pressed with fingers, how it has come loose ive no idea as a pressed in pin holds it in place. Fuel was leaking at the joint where it meets the emulsion tube. I binned the body as i didnt see any fix, only bodges i.e chemical metal etc.

Id be checking the faces of the carb top & middle to make sure there still flat, check the gasket is ok that goes between them. Check the float isn't cracked & the needle valve is sealing ok, check fuel pressure is ok.

[Andrew Cooke]

hang on, where is your fuel dribbling from? the seal at the base of the pump jet nozzle, or the centre of the venturi?

[Scoff]

its one of those problems that no one seems to have a definitive answer for, I've seen it a couple of times.

if fuel is comming from the aux venturi then that tells you that the main circuit (rarther than soley the idle/progression circuit) is comming into life. it shouldn't be. have you tried dropping the idle speed ? or it could be that the float level wants dropping, you could try an extra copper washer under the needle jet.

[Scoff]

its one of those problems that no one seems to have a definitive answer for, I've seen it a couple of times.

if fuel is comming from the aux venturi then that tells you that the main circuit (rarther than soley the idle/progression circuit) is comming into life. it shouldn't be. have you tried dropping the idle speed ? or it could be that the float level wants dropping, you could try an extra copper washer under the needle jet.

ah, I should read what others (andy) have posted before I do :)

[Matt Cole]

On all of the carbs it looks like its dribbling from the center. Everybody seems to point to the pump jet nozzle seal.:scratch:

[Mart]

Seen it before; it's usually one of three things (assuming fuel pressure is ok, and idle is circa 1k rpm or less)...

1) Acc pump jet (sticky ball bearing) or pump jet seal leaking (as has been said)
2) Needle valve is partially stuck open/won't fully seal.
3) Enrichment block and/or 1st stage diaphragm(s), or needle, leaking fuel through, causing excess fuel to then be present/sit higher in the emulsion tube.

[Scoff]

On all of the carbs it looks like its dribbling from the center. Everybody seems to point to the pump jet nozzle seal.:scratch:

pretty sure andy's post and my own didn't involve the pump jet ;)

[Scoff]

pretty sure andy's post and my own didn't involve the pump jet ;)

edit: and marts, I didn't see that till now.

see, plenty of things to be trying :cool:

[Matt Cole]

Seen it before; it's usually one of three things (assuming fuel pressure is ok, and idle is circa 1k rpm or less)...

1) Acc pump jet (sticky ball bearing) or pump jet seal leaking (as has been said)

Shook it on all carbs, nice and loose

2) Needle valve is partially stuck open/won't fully seal.

They are all new from the rebuild kits, still a possibility though.

3) Enrichment block and/or 1st stage diaphragm(s), or needle, leaking fuel through, causing excess fuel to then be present/sit higher in the emulsion tube.

1st stage diaphragms replaced. If its a blockage, it must be buried deep as the carbs have been cleaned, 2 sonically. How can the needle leak be repaired?

[Mart]

The float may be new (as part of the kit), but have you checked the spindle it sits on/in is true?

Try swapping the 1st stage spring for a known good one.

Also check the 2nd stage spring (especially if you've previously been tweaking the tension screw ;) ), and that the pressure ref' pipe isn't blocked.

Failing that, swap the complete enrichment block for a known good one.

[Matt Cole]

The float may be new (as part of the kit), but have you checked the spindle it sits on/in is true?

Try swapping the 1st stage spring for a known good one.

Also check the 2nd stage spring (especially if you've previously been tweaking the tension screw ;) ), and that the pressure ref' pipe isn't blocked.

Failing that, swap the complete enrichment block for a known good one.


Mart, ya learn something new every day. Pressure reference pipe?? Up to now, our youth has doubled up the float valve with two washers and replaced the pump nozzle seal with an o ring. No luck as yet.

[CHUNK The Goonies]

yeah ive done the lot.. no change. i can still see fuel dropping in the centre of the carb, anyway i think i will try having another go tommorow, and other things mentioned i will go thru the list, and "IF ALL FAILS THROW IT AWAY":confused: i think ill go fuel injected, cut the middle man out