BS38 Carb leaking fuel into throat.

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LTGTR

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77D - stock BS38 carbs.
I recently removed my carbs and replaced a couple of things like jets and needle and seat and cleaned them with carb cleaner and compressed air. I now have them set up on the bench and hooked up to the fuel tank which is sitting above them on a crate, to check for leaks before fitting them to the bike.
The problem is there is a slight fuel leak into the throat of both carbys that is coming from around the part where the needle jet protrudes into the throat.
I didnt remove the needle jets when cleaning the carbs but I did rotate them so I could get a fine carby jet cleaning wire though all the holes.
I measured the float heights very carefully and cant see how the fuel level could be that high to cause it.
Would like to ask the forum's advice.
Regards Ray.
 
1. When you rotated the NJs you tore up the O rings that seal them. O rings need to be replaced. A search will give you size and sources.
2. Low float height is not the only possible float system defect. Others include leaking float and bad float valve. A couple of quick searches will turn up plenty on inspection and correction, no point in writing it all out again.
 
If your needle jets rotated easily while installed then their o-rings were probably worn out to begin with. They should be a snug, push fit into the carb body. With good o-rings, once installed they shouldn't wiggle around at all or turn easily.

cyGGqbT.jpg


The actual size is a rather oddball 3.1 x 1.1 but the more readily available 4 x 1 size fits and works fine.
 
Thanks for the reply Grizld1 and 5Twins - I have ordered new o rings.
I dont have any leak from the bowl overflow outlet and it doesnt look like the fuel level could be that high to bleed into the throat. Maybe the fuel wicks it way up the needle jet.
I recently bought some grease nipples to make float drain plug takeoffs so I can hook up some tubing and see a "fuel height" to be sure of my float heights. The grease nipples dont have enough shoulder on them to support a copper sealing washer so I will fit a nut first that will act as a platform for the copper washer to sit against. I need to find some 1.0 pitch metric nuts (metric fine).
Regards Ray.
 
5twins said:
If your needle jets rotated easily while installed then their o-rings were probably worn out to begin with. They should be a snug, push fit into the carb body. With good o-rings, once installed they shouldn't wiggle around at all or turn easily.

cyGGqbT.jpg


The actual size is a rather oddball 3.1 x 1.1 but the more readily available 4 x 1 size fits and works fine.
Click to expand...
Carb kits should have this o-ring but most do not. I just had to order a few.
 
5Twins, egggary and bowling - thanks for the ideas suggestions.
5twins - your bowl drain takeoffs are very neat - I have saved the ebay listing for future reference.
I have tapped a 1.25 pitch nut to 1.0 pitch (sounds bodgy but it works in this application) and screwed that onto the grease nipple which gives me a platform for the copper washer - ground the end off the nipple to make it the same length as a bowl drain bolt. It works okay. My fuel height ended up being about 1mm below the main body casting which when you take into account the gasket surface of the main body is about 3mm up from that, it gets me the 4mm the spec called for. So im happy with my fuel height.
 
77D - BS38 Carby.
Can anybody confirm if the mixture screw has an o ring or not.
Mine doesn't have any but Im wondering if they should (I cant see any stuck down the threaded hole where the mixture screw fits).
I found some old threads where 5Twin said the 77D carby has only one o ring and that is fitted to the needle jet. But, I also discovered a table that showed all the orings used on the 650 carbys, and that table lists one for the mixture screw on the 77D.
Can the carby guys on the forum help please.
Regards Ray.
 
LTGTR said:
77D - BS38 Carby.
Can anybody confirm if the mixture screw has an o ring or not.
Mine doesn't have any but Im wondering if they should (I cant see any stuck down the threaded hole where the mixture screw fits).
I found some old threads where 5Twin said the 77D carby has only one o ring and that is fitted to the needle jet. But, I also discovered a table that showed all the orings used on the 650 carbys, and that table lists one for the mixture screw on the 77D.
Can the carby guys on the forum help please.
Regards Ray.
Click to expand...
My BS38 carb does not have an O-ring. The BS34 does.
 
Yes, no o-ring on the '76-'77 carb's mix screw, just the screw and it's little tension spring .....

pt1rxO2.jpg


The only BS38 mix screw that has an o-ring is the one in the '78-'79 set .....

96i404f.jpg


This was also the first E.P.A. mandated type with a stepped end instead of just the taper.
 
Bowling, ggggary and 5twins - thanks a lot for going to the trouble to answer my question. I can put that confusion to rest. I am still waiting for the o rings for the needle jets, so my 77D is still off the road.
I had a bit of luck and picked up another 77D with 6000 Klms and Australian delivered. Its all original. not messed with but wasnt stored very well and is fairly weathered (read rusty). Tins are pretty good. It has an Australian compliance plate on it with 3 ADR's (australian design rules). It has little plastic caps on the mixture screws with a little protusion that limits the adjustment to about 1/2 turn. They come off easily. It has the standard aussie delivered twin discs.
I will put up some photos when I start tidying it up. P.S it has the original tool kit but I have to assume its all there because I dont know what a complete tool kit looks like. I can post photos of it for your verdict.
Many thanks for the advice/help you guys and the forum give.
Regards Ray.
 
Help please with fuel leaking into carby float through the needle jet.
I received 6 new o rings from 650direct. I am having a lot of trouble trying to press the needle jet into position with the new oring on the needle jet. After a lot of pushing, twisting and grunting I sort of got it in but in a bench test it still has petrol coming into the throat.
I took them both out and put a minature chamfer on the edge of the hole in the carby body (the edge of the hole was razor sharp and grabbing the o ring) where the needle jet pushes in. I put new o rings on and used a very fine screwdriver to coax the o ring down the hole as I was pushing on the needle jet. Eventually it did go in but both are still leaking.
5 Twins - can you confirm the Suzuki orings are the correct type for my 77D carbys. I will have to buy some genuine orings and try that. I still dont know how I will get the orings to go in with the needle jet.
I have used rubber grease, vaseline and normal grease with no luck.
I have double checked my float heights.
Regards Ray.
 
The O-rings are indeed a tight fit and a certifiable PITA to install. It might help to freeze the needle jets, with O-rings installed, drain the carbs well, and warm the carb bodies with a heat gun. I'm out of ideas on the fuel seep. The fuel level, as measured by sight tube, is below the bottom of the venturi, which is where you see the fuel. The seep happens with the carbs on the bench, so there's no engine vacuum applied to raise fuel. Is fuel being wicked up by capillary action? If so, correct O-rings should stop it. When you remove the NJs for fresh O-rings, you might do another bench test before you reinstall them.
 
Thanks for the replies 5Twins, Grizld and ggggary.
I have included 2 photos of my fuel height. I have left the taps turned on for 45 minutes and no change in fuel height.
As per advice - I have ordered 8 Suzuki (inexpensive) and 6 Yamaha (expensive) o rings from Partzilla. I figure my best chance of solving this is with genuine parts but Im still concerned how I will get the orings to go in the "hole".
It cost me $102 Aus$ for the orings (ouch) but the freight was combined so I bought a few of each.
If this doesnt work Im rooted and the only other way may be to use a sealant in place of the oring. I dont know if there is a sealant that is petrol resistant.
Thanks for sticking with me on this problem.
Regards Ray.
P1030815.JPG
P1030817.JPG
 

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