1972 solex carburetors , mid range hesitation

[BRok13]

I just rebuilt a set of 72 bs38 solex carbs , idle is great , under a load is great but mid range and take off there is a stumble and hesitation. I have a short exhaust and running filters. stock jets are 130 main and 42.5 pilot with the needle at slot 4 . After running stock and still having hesitation I changed the jets to a 45 pilot and 132.5 main and put the clip on slot 3 .. still having hesitation ( oh yeah 1.25 turns out on the mixture screw) any suggestions ?

 

[gggGary]

What needle and needle jet are you running? Rebuild kits are notorious for supplying the wrong brass.
from 5T's most excellent and helpful chart;
Stock is 4JN19 slot 4 and Z6 (long)
Needle slots are numbered top down, higher number (lower on the needle) is richer.

What air filters, how short are the pipes.
Valves set, chain adjusted, compression checked?

Oh what ignition are you running?

 

[BRok13]

Im running stock needle and needle jet as you listed. My pipes go down a little past the oil bolts and Im running pod filters and a pamco ignition . Everything ran good when I was running the linked late 70's carbs the only thing I have changed recently is the carbs. Compression , valves and chain are fine .It's hesitating like Im not getting enough fuel

 

[gggGary]

#1` try foam filters (Uni) bunch of reports on here with poor running as the slide opens with "pleated" oiled pod filters.

 

[5twins]

The carbs on these bikes got better and better as the years went on. Some of the early sets can be troublesome, some are actually just plain worn out. The fact that a later set worked fine and these earlier ones don't could be indicating something like that. I would carefully examine the butterfly shafts for play in the body and the needles and needle jets. If you look in the top of a needle jet, you will see a small step about 1/8" or 1/4" down. That is the metering orifice and yes, it is quite large by carb passageway standards. That step should be equal all around and form a perfectly round hole through the jet. If it's worn away on one side, making the hole egg shaped, that jet is worn and won't flow correctly (it will be too rich). There's also an o-ring on the outside of the jet that makes it fit snugly and seals it into the carb body. That needs to be good.

 

[BRok13]

Ok changed to fresh plugs because fouled out from tuning trial and error put new ones in still hesitation I took the left plug out and its wet , like oil ...

 

[BRok13]

ok so Im running short exhaust just at the oil bolts , pod filters, stock 130 mains and 42.5 pilots 1 full turn out on the mixture screw . Idle is great , high speed is great although take off is blurping at slow speed .. Thought it was my diaphram , has a slit in it , replaced. Still having the same issue . These carbs have been fully rebuilt but Im scratching my head on this one. sounds like it's spitting out of the left carb when it has the blurp , anyone HELP! hahaah

 

[DogBunny]

http://www.xs650.com/forum/showthread.php?t=43
You need to read the carb guide, first link above. You need to re-jet. I would try one up on pilot to 45, four up on main to 140, and drop the slide needle one clip position.
Read the carb guide. After you re-jet, you need to sync the carbs and check for intake leaks.

You also need to put at least a small baffle or an anti-reversion bolt, or lollipop, or thumbscrew in the end of your pipes. Google "anti-reversion".

 

[BRok13]

float height... grrrr hahaha thanks everyone for your replies.