44s leaking from progression ports after shutdown !?

[Brown-nose]

New motor to me, regular 2276, came with HPMX 44s...10 mins or so after shutdown i see one carb barrel (number 4 cyl) starrting to fill up with fuel. Not the regular IDF drip or from the squirters but from the progression holes onto the butterfly. Only 1 carb and number 4..

So carb off, compressed air through idle passages, jets, check valve in float bowl. Check float level, was approx 13mm closed so changed it to 10mm and 32mm, though there seems to be differing opinions on this subject. Seat and needle look good. Fuel pressure checks at 3.2 ish psi (CB pump)fuel tank was low at the time so gave carb a good check over and clean.

I'm aware of the tuning problems you can have with these when you have the idle screw too far in and the ports uncovered so i'm sure that's not an issue.

I felt confident I had covered all bases, put some fuel in the tank and ran the car for 15 mins or so, waited agood while and didn't see any leaking...so today I went out for a good drive, came home, shut it down and 10 mins later..it's leaking !

It's summer temps here in the UK but would fuel boiling only affect one barrel ?! Manifolds are warm but not hot. Valve lash is checked. I try and use decent fuel whenever possible but this is a realky mild 2276, low comp and small cam etc And car does not run hot or pink, I'm 100% on that...Fuel tank breather (stock) is a little pinched...doubt this would be the cause..

Help ! Any ideas ?

Thanks

[j-dub]

Brown Nose,
Did you ever make any progress on this? Sometimes what happens is after you shut your car off the heat from the engine rises and will heat up the carbs and eventually the fuel in the float bowl. This heat causes the fuel to expand and the fuel pressure to rise, can even cause the fuel to run up the bowl and down down the progression wells. Some fuel pumps or regulators act like one way valves and will not allow the raised fuel pressure to bleed back to the tank.

Typical solutions are to run all fuel lines further from the exhaust, use phenolic spacers between the manifolds and carbs and use a fuel pump that lets excess fuel pressure bleed back. A good example of a fuel pump that will allow pressure to bleed back is the carter pump that CB sells. The factory style pump typically will not.  What type of pump are you running?

[Brown-nose]

Hi j-dub, thanks for your reply. Since my post I switched the LH carb top (the leaky  side) to the RH carb to see if the problem followed. I also fiited new float gaskets from eurocarb as I had caught one on the stud. Drove it for an hour and no flooding on either side. I then set the other float to 10/32 as it seemed safe now. I tested the fuel pressure, in-line, before both carbs with sytec gauge. 3 -3.2 PSI. It's a CB or carter pump by the way.

I have done a few miles now and no flooding though I will say the whole pin/float and needle valve fit and quality in these HPMX need to be carefully inspected. I can't say exactly what was the cause of my problems though I did read if the idle air bushing is blocked or cannot breathe fuel can make it's way through the progression holes. The new gaskets I fitted were slightly different shape and cutout around the float assembly (you can now see the float bowl fuel level from the top of the carb) so maybe this has helped ?

I agree with your comment on the perculating heat rising from the manifolds into the carb and heating the fuel after shutdown. This is something I have battled before with IDAs and tried most fixes. As a result I have moved some fuel lines in this car which were touching the fan shroud. The car has tall manifolds which probably does transfer more heat ? I also have a switch to the pump so can run the carbs a little "empty" before putting it away. I used the insulating spacers before with IDAs, they didn't help me much then but if I still think it is an issue with this car I can try them.

On the pressure after shutdown I did notice the gauge still read 1psi or so for quite a while. I assume this is residual. I still think a bigger (than stock) tank breather may help all round with fuel pressure (assuming you use bigger than stock fuel lines) but welding a fitting to the tank neck is a pain. Perhaps drilling a the top of a 67 flat cap for a fitting might work ? Just a thought..

[Martin S.]

That residual pressure contributes to the problem and makes any small leak after shutdown into a place where that pressure goes.
If you loosen one of your lines right after shutdown, there could easily be a gush of fuel pushed out. At least that's what I found with the stock pumps without the relief valve. I was having a drip problem after shutdown which disappeared after I changed to the generator style of fuel pump with the build in shut off valve.
VW used an external shut off valve in the later dual port engines which is no longer available. This is the pump I'm using now which has the valve and worked. I did have to adjust the rod length to get a nice low pressure but it fits with an alt as well as a generator which is cool.

http://www.cip1.ca/ProductDetails.asp?ProductCode=VWC%2D113%2D127%2D025%2DDOE

[Brown-nose]

Well, I thought I had the problem licked but after an hour drive today in hot weather, sure enough still leaking one carb, number 4 bubbling up through the holes onto the butterfly. When I take the fuel line off or remove the tank cap it carries on. With the carb off I can see it isn't losing a huge amount of fuel but obviously I'm not happy to drive it like this. I might order the heat isloation gaskets next, I see there are a few variations, any recommendations ? I can't see them making much difference, also both carbs have shaft/bearing wobble so might as well replace these whilst they are off (again)

[Brown-nose]

I see CSP do a spacer, anyone run these

https://www.csp-shop.com/en/brand-shops/heat-insulation-flanges-for-weber-129-707-040p-14457b.html

Also this company in the US, probably who supply aircooled.net as they offer two different thickness

https://www.thegansmann.com/collections/isulators/products/weber-idf-ida-phenolic-insulator-kit?variant=46222759048

[j-dub]

Did you verify that your carbs, especially on the 3-4 side are hot to the touch when this is happening?

[Brown-nose]

Yes, carbs and manifolds are hot to the touch...it's 5-10 mins after shutdown. Summer temps here now. I'm pretty much 100% on the cause being heat soak in the bowl finding it's way out..

I'm not switching off the fuel pump before shutoff yet, I realise this will help (V8 guys do this) but you can't always rely on this if you aren't sure when you have to stop !

[j-dub]

I have a set of the heavy paper gaskets sold as insulator gaskets but have never tried the Phenolic gaskets myself. I think they are the logical next step for you. Which height are you going to go with, do your air cleaners have enough clearance?

[Brown-nose]

Thanks, I think I will go with the CSP ones and see..

[Brown-nose]

so I tried the CSP phenolic spacers...same sort of driving conditions. They do help, the leak is not so bad with them installed, still leaks but not as much volume. Interestingly number 3 barrel seemed to join the party now and leaks a little from the ports and the squirters. Number 4 also leaks a touch from the nozzles when it didn't before.

Knowing nothing about thermodynamics I wonder if the bigger 9mm spacers would help even more ? Or maybe double up on the CSP

As an experiment I ran the float bowls dry before switching off and this stops any issues 100% but isn't always practical.

I guess lowering the float settings may help a little, I may try that.

Incidentally I changed the shaft bearing, I managed to remove 3 of them just with a strong magnet, didn't even need to remove the butterflies !

[Greg Ward]

The biggest cause for this that I have personally come across is after I put a "kit" through my carbs.

48IDF's on a 1915cc engine, never had the problem before, ran the car hard on the street, come back to the garage, shut it off and get out.

Can hear some "perculating" in the engine bay, check it, take the top off 3 and 4 side carb and see fuel literally pooling in.

Took me 3 months to fix this back then, and it was all due to the gaskets from the carb main body to top body. The one that is most prominent in the redo kits you buy, it didn't have the holes in the gasket that allow the idle jet circuit to work properly, they were closed shut.

Didn't get new gaskets, just a small hole punch in the gaskets where there should be holes for the idle jet circuit and Voila! problem solved.

Have always checked this on every set of carbs since.

Cheers,

Greg

[Brown-nose]

Thanks Greg, are you referring to the idle air bushing that I mentioned near the top of the thread ? The bronze holes for air into the idle circuit from the carb top ?

I did check the gaskets and they seemed ok. The holes are there, in both sets (EMPI and Eurocarb) of gaskets I tried.

I'll double check again as I have to get the carbs off again this week.

Cheers

[Greg Ward]

Yes, I am , those are the ones.

I was actually hoping for a problem there.

Please let me (us) know what happens.

Cheers,

Greg

[Brown-nose]

Hi Greg, I had the carbs off today as I bought some more phenoilic spacers to try, this time 6mm so with the CSP ones as well that makes 9mm. I haven't had a chance to drive it yet as I've yet to fix a rear hub seal for the 2nd time. I did run it up and sync the carbs etc and it was hot today so 180 ish on the gauge and no leaking after shutdown today. Not a fair test but a start, anyway I checked the gaskets, no constriction to the air circuit, holes are there....

I'm wondering if this is a breathing issue then would the CB Jet Doctor help ?

[Greg Ward]

That's a good thing then, you've tested and proved it can't be then what I experienced.

My only other suggestion would be to make sure that your fuel tank breather is working, not holding pressure in there?

I've had one of them that was blocked before, but it also caused driving problems, so anyway, one more thing to check, but all I can think of at the moment.

Cheers,

Greg