After installing a re-build kit in an SU carburetor (especially an H-series) it is sometimes impossible to achieve a sufficiently lean mixture by manipulation of the mixture adjusting nut alone. Before resorting to the quick and make-shift solution of lowering the needle in the piston, examine the sketch below carefully and compare the actual carburetor to them.
The proper solution may be effected through careful installation and assembly technique. The cork seal, located between the carburetor body and the cupped aluminum washer must be spongy and pliable so that it “cold flows” into the cup of the washer as the securing nut is tightened. When properly assembled, only a thin line of cork (0.5 mm) will be visible between the carburetor body and the top edge of the aluminum cupped washer as shown in the illustration.
Assembly in accordance with the illustration will insure that the mixture adjusting nut will provide enough jet travel to set the fuel/air mixture as lean as required while keeping the needle at its specified position in the piston.
Since the metal of the carburetor body is soft, do not, in your enthusiasm to squish the cork seal to its proper dimension, over-tighten the securing nut! Soak the cork seal in light oil (a day or two if possible) prior to assembly. The oil soak will make the cork seal pliable for easy assembly.
Robert Koval
Westmont, NJ
'SU H-type Rebuild Kits' have 8 comments
January 8, 2013 @ 6:37 am Bob Forsblom
Thank you for this article on rebuilding an H-Type Carbs. At this time I am rebuiding three H2’s for customers. In every case that someone had work on the carbs, and it was easy to see, they were assembled without soaking the cork washers in oil first. Thank you for mentioning the need to oil the cork seals first. Suggestion: Make the note in bold type to make the point.
Thanks again for the article,
Bob
Dogsbody
January 8, 2013 @ 8:13 am Steen
Thanks, very timely since I am in the process of rebuilding a carburetor.
January 8, 2013 @ 9:42 am Ed DeMayo
Thank you to all the “cork soakers” at Moss Motors!
January 8, 2013 @ 2:43 pm Pat Garity
The soak should be done with the jet seals too. It will improve the odds of getting proper alignment with the jet. Assemble the jet body around the centering tool. Push the tool out with jet after the carb top is installed. This will prevent chunks of the jet seals being slice off by the centering tool or the jet.
January 8, 2013 @ 3:04 pm henry mixon
Thanks for the valuable tip. As a longtime owner yet sitll novice i appreciate all the help i can get.
January 15, 2013 @ 3:43 pm John Burton
I replace these cork washers several times a year for my customers. I store my stock of seals in a small zip lock plastic bag filled with oil. About a week before I need them I assemble a complete jet assembly in an old su carb body. Each day I tighten the assembly until the cork washer is compressed. If you do it too fast it will break. This way I can swap out the old assembly for the new without the concern of leaks and split seals.
June 25, 2015 @ 3:24 am Dumont
Hi,
I change many parts (gasket cork and cooper, Jet, Bearring Jet, Needle, spring…) but the carb’s still leak at bearring jet and same if the engine turn it really too riche.
I try with weak needle, it beatter but not totaly good.
If I pull the choke, gasoline flow out of the Jet.
I don’t know what i need to do.
If you have any idea!
I have changed also needle & seat by grose jet and made the level of gasoline…
Thank you
June 30, 2015 @ 8:15 am Dumont
Well I finish to solved my troubles.
I bought kit with bearring jet bottom (part: WZX1593)
Think the leak come from plate parts of bearring by pressing the seal.
Thank