Hi all, i am currntly running a stock a15 engine with stock gx head and put 2 1200 gx flat top su's on it, it is running very rich, both carbs are now completly closed at the bottom screw and i have set the float level more down and still not luck, both needles are flush with the piston and are both m83 gx needles. anyone have any ideas?

what dashpot oil you use?

3 in 1 machine oil, think it's a 10w something, the only things not changed yet is the needle and seats but carbs not running over whith feul, funny as i have used the same jets in my gx a14 and my 73 ute with a15

Funnily enough I just bought a pair of SU's and was warned about this problem by one of the old mechanics at work. Try ATF, or a slightly higher viscosity oil (15W) in your pots.

using heavier oil will make the mixture richer. i suspect your float is not fuel tight anymore. if you take out the brass float, shake it. if there's anything in it, the float is kaput. you shouldn't hear/feel anything when you shake the float. after years, cracked float is normal. cheapest substitute for float (not available in malaysia) is pingpong/table tennis ball. you don't even have to re set the float level LOL

i bought new floats, found a place that still had a few in stock, so not the problem.

Sure they aren't L series needles in there?

are the spacers in there? Something not right. Too much fuel pressure pushing past the needles?

took the needles out, definitely m83 needles. running standard mech feul pump. thinking it might be needle & seats that's causing the problem.

I'm assuming they are 1 1/4 SUs or maybe 1 1/2?? Reason I ask is they run a smaller diameter 'jet' - I've never tried to put a 1 3/4 SU jet onto a 1 1/2 but it might be possible. If that is the case, it'd cause the situation you are now experiencing.

I had a needle and seat problem, and in hit weather the fuel tank pressurised one summer due to faulty fuel vent and weak point was the stuck needle.
Flooded the bore and filled sump with petrol.

Extreme situation but needle and seat would cause richness that float etc won't fix