andy_h Posted May 24, 2014 Share Posted May 24, 2014 While on track my carbs leak fuel onto the inlet manifold, but I can't replicate in the pits. I've established it's not coming out of the carb top but I can't find where it is coming from. Any ideas? Does the void/space behind the choke cover fill with fuel? I don't have a gasket between the choke cover and the carb body, and all the exploded diagrams don't show any so it isn't supposed to have one. If this mating surface isn't perfect could it be this? Thanks, Andy Link to comment Share on other sites More sharing options...
oldbutnotslow Posted May 25, 2014 Share Posted May 25, 2014 Check the needle valve size/ float height. From memory it should be 175 and 10mm. If its too large or the float is set too high you can get fuel sloshing about It may be worth having or doing yourself a full rebuild. They dont go on forever There are various kits on e-bay but watch out as some dont contain the correct size valves and or there are bits missing I use a local Webber stockest when I rebuild them for customers. they are a little more expensive but I know that I am getting genuine parts and all the bits are there Link to comment Share on other sites More sharing options...
zetec Posted May 25, 2014 Share Posted May 25, 2014 Or buy my lovely 45's mate ! . ( they are used but new!) They are still in the for sale section & haven't been sold yet Link to comment Share on other sites More sharing options...
john g Posted May 25, 2014 Share Posted May 25, 2014 Have a look at the sides of each carb and check the locking screws that hold the venturies in place have not become loose. Link to comment Share on other sites More sharing options...
andy_h Posted May 25, 2014 Author Share Posted May 25, 2014 Thanks OBNS, The needle should be 200 for my engine and I did the floats a few time while in the pits so I don't think its either of these. I've already bought genuine refurb gasket kits but I need to establish where its leaking from first. Do you know if the choke void should fill with fuel? I've read up that choke mechs are a problem which it why they are not used, but it doesn't stop them leaking if it is this? Thanks for the offer Craig Johng, I'll check thoses Link to comment Share on other sites More sharing options...
andy_h Posted May 25, 2014 Author Share Posted May 25, 2014 Johng, They are ok and wire locked so its not these. Link to comment Share on other sites More sharing options...
elie boone Posted May 25, 2014 Share Posted May 25, 2014 The float level with plastic floats should be 13mm measured with the gasket in place. Link to comment Share on other sites More sharing options...
Klunk Posted May 25, 2014 Share Posted May 25, 2014 Hi Andy, What state are the o-rings under the pump jet cover screws. If these are poor (or the wrong size) fuel will spray out of here when accelerating. Guess how I know The choke opening with the gauze is an air intake and does not have a gasket. This shouldn't be the problem... Regards, Giles Link to comment Share on other sites More sharing options...
andy_h Posted May 25, 2014 Author Share Posted May 25, 2014 Hi Giles, I have fitted new o rings today as part of rebuild. The originals ones look ok, if a little cracking. Ok, I won't make a gasket for the choke cover. Link to comment Share on other sites More sharing options...
oldbutnotslow Posted May 25, 2014 Share Posted May 25, 2014 One other thing. Check the fuel pressure. Its not unknown for too high a fuel pressure to overcome worn float needle valves Do you know if the choke void should fill with fuel? No they shouldn't but you can get excess fuel flowing from the gauze underneath the choke mechanism. The mechanism isn't usually the issue. The problem usually lies elsewhere Have a look at this here add THIS Edited by - oldbutnotslow on 25 May 2014 22:36:22 Link to comment Share on other sites More sharing options...
andy_h Posted May 25, 2014 Author Share Posted May 25, 2014 Thanks all. Both carbs rebuilt today using genuine refurb kits. Changed all gaskets and needle valves, reset float levels, and droop levels. Need to finish off and refit to car and test. Link to comment Share on other sites More sharing options...
andy_h Posted May 25, 2014 Author Share Posted May 25, 2014 From the rebuilds I rekon it was the o-rings under the pump jet cover screws. They were cracking and have to assume under pressure they were letting fuel by. Link to comment Share on other sites More sharing options...
BBL Posted May 26, 2014 Share Posted May 26, 2014 I recently read about a similar problem of carbs leaking fuel in a Seven, which turned out to be caused by a worn motor mount (the rubber/steel puck ones on the lower frame rail, not the brackets to the engine). The rubber would compress too much under load, causing the carbs to contact the upper frame rail and weep fuel at the carb/head interface. Something to check. Link to comment Share on other sites More sharing options...
OliverSedlacek Posted May 26, 2014 Share Posted May 26, 2014 If there's a problem with the float valves, then the excess will find it's way out through the cold start circuit and come p155ing out through the gauze under the actuating mechanism (guess how I know). If you were finding fuel on your inlet manifold, that looks like the obvious suspect. As mentioned, worn float valves and excess fuel pressure may be the root problem. I first found it to be an issue just on right hand corners, and it didn't show under gentle driving. Link to comment Share on other sites More sharing options...
andy_h Posted May 26, 2014 Author Share Posted May 26, 2014 Thanks. When I removed the float valves and compared to the new ones the original ones did look a little warn (points slightly less pointy than the new ones, and a slight change in colour) so I think these we're warn enough not to fully close and with too much fuel in the chamber it came out via the cold start circuit. Sound plausible enough for me anyway. Not refitted to car yet as I've managed to lose a carb to inlet manifold stud. Link to comment Share on other sites More sharing options...
andy_h Posted June 5, 2014 Author Share Posted June 5, 2014 Need some more advice please. I've fitted the carbs to the manifold but the book says to set the carbs so 5mm gap between the face of the carb and face of the manifold (misab's are between these obviously) at each nylock. I've done this but the space appears too big as some metal caps are flapping around as no pressure from the nylocks 🤔 Took an hour last night just trying to get each of the 8 nylock gaps right 😳 I'm measuring using a digital caliper. The book is rebuilding and power tuning carbs, I can't remember the author, he can't be wrong? Link to comment Share on other sites More sharing options...
Molecular--Bob Posted June 5, 2014 Share Posted June 5, 2014 Chris at the 7 workshop told me that if you were using the rubber bungs and cup washers, then you should aim for around 1-1.5mm exposed rubber between the two washers on each mount. This has worked fine for me on the zetec with 40's. About like this here Edited by - Molecular--Bob on 5 Jun 2014 18:24:57 Link to comment Share on other sites More sharing options...
andy_h Posted June 5, 2014 Author Share Posted June 5, 2014 Thanks, but the rubber mounts and cup washers are not exactly made to a tolerance (I am being polite). The space between manifold and carb faces all need to all the same. Unless someone comes up with more science I'll have to play it by ear. Link to comment Share on other sites More sharing options...
OliverSedlacek Posted June 5, 2014 Share Posted June 5, 2014 I've never checked or adjusted the carb-to-manifold spacing, and can't see the point. You want a nice even pressure on the misab spacer washers and you need some compliance to provide vibration isolation. About 1-1.5mm of rubber showing between the cup washers works for me. Link to comment Share on other sites More sharing options...
andy_h Posted June 5, 2014 Author Share Posted June 5, 2014 Thanks. The reason the space needs to be done and checked regularly according to the book is to maintain the correct pressure on the misab rubbers and to prevent air leaks. When I took mine off I had marks showing leaking, for some time as I never checked them 😳 Link to comment Share on other sites More sharing options...
andy_h Posted June 8, 2014 Author Share Posted June 8, 2014 Update- Carbs rebuilt and refitted. I used 4.5mm between carbs and inlet manifold at all eight mounting points. Seems to work as has a little flex on the mounts and the induction growl I had has gone ☹️ It sounded great but obviously not good for performance. Balanced the carbs and after a road test all feels good except for a bit of hesitation on pickup, which I'll need to tune out. Did a 'spirited' test drive and no fuel leak so hopefully that's resolved now too Link to comment Share on other sites More sharing options...
OliverSedlacek Posted June 8, 2014 Share Posted June 8, 2014 Hope it's sorted Link to comment Share on other sites More sharing options...
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