Su's Dumping in Gas

[Farmer]

Got the engine started ran for a few second, sputtered, died. Pulled spark plugs and they were saturated with gas. let fuel evap for a day. Went out there today, replaced plugs. Tried starting. it wanted to go for a second. then nothing Checked Sus and there was puddles of fuel right at the beginning next to the slides. So the carbs are flooding the engine bad. And of course Ive never used SU before. Do you think I need to rebuild them?

 

Larry

[zerow]

Yes. The needles are most likely culprits in this equation, but the floats could be sticking as well. As a quick fix, remove the fuel bowl tops, and you will see the needles right below where the fuel inlets are located. CAREFULLY disassemble the needle assembly, and with some fine steel wool, polish up the needle. Take a Q-Tip and carb cleaner and clean the inner surface of where the needle seats inside the assembly. Do the same for the other fuel bowl. To check the floats, yours are probably brass, make sure they are not heavy with fuel. If you find this condition - STOP!. This will be the culprit, and you will need to source new floats. The new ones from the Nissan dealer network are plastic and hold up much better than the brass kind. Part Number = 16061-K1407

[Skib]

which SU's are you using?

 

 

the roadster/SSS ones have free floating brass floats that can get a hole in them and sink

the Z car ones have a black "rubber" (its not rubber but idk what its made out of) float thats attached to the float bowl top.

 

you could have a sunk float or just have the float levels off too

[FoxyRoadster]

I'd check the needles, but also has this carb been adjusted at all? As least with my experience on the SU carbs and floats is the overflow tube will spew fuel out as well.

[Farmer]

 

They are the 38mm sss, I believe.

 

Thanks for the replys. Ill check it out once the rains stop

 

Larry

[datzenmike]

" (its not rubber but idk what its made out of) float thats attached to the float bowl top.

 

Probably phenolic resin. It's light and floats but not hollow and can't sink.

[Unclejesse88]

Mine had brass floats that leaked. I bought some new ones from Ztherapy.

[Skib]

those are Z car domes... do the bodys have a 2 bolt flange to the the intake or a 4 bolt?

[banzai510(hainz)]

nice lookn carbs.

 

If this is a new motor and hasnt been broke in I would run it with a weber downdraft first.

then move on to the SUs

 

personally SU are so old now and worn out I would not get them myself unless I heard them running first.

 

DCOEs or Mikunis are usually not as old and dont have as many miles on them(car is usaully wrecked by them and carbs come off)

[Farmer]

I forgot to mention. the gas build up is happening to both carbs.

 

Hainz, yes, it is on a new engine build. Thats a good idea about starting out on weber. Maybe I should of kept the one I had (sold it for 50)

 

 

Larry

[banzai510(hainz)]

On a rebuild I always run the old stuff like the carb and dizzy first to get the motor running as you know they were good before.

Installing other used iteams can induce a proplem or 2 and youll think you did a bad motor rebuild.different coil,bad matchbox dizzy or a misaligned mount. bad carb.

 

On the motor long as the cam,dizzy, and valve lash is good most like it will start up if the other above mentions are also good.

[Driftastic210]

alright im new to the datsun community and i know ill probably get crap for this but what does SU stand for.....im also new to carb's. I got sick of fuel injection.....

[FoxyRoadster]

alright im new to the datsun community and i know ill probably get crap for this but what does SU stand for.....im also new to carb's. I got sick of fuel injection.....

 

 

 

Skinner's Union, its not really commonly known overall but its nice to know

[Farmer]

On a rebuild I always run the old stuff like the carb and dizzy first to get the motor running as you know they were good before.

Installing other used iteams can induce a proplem or 2 and youll think you did a bad motor rebuild.different coil,bad matchbox dizzy or a misaligned mount. bad carb.

 

On the motor long as the cam,dizzy, and valve lash is good most like it will start up if the other above mentions are also good.

When it did start up the first time, it sounded alright. But wont know until exhaust and carb situation is fixed.

 

Drift, the carb is named after the maker, Skinners Union Here a link Wikipedia - SU

 

Larry

[FoxyRoadster]

just a thing you can do with SU carbs is use them as throttle bodies for fuel injection.

[datzenmike]

The Datsun ones aren't really SU's they are made by Hitachi. Like a lot of Japanese stuff they simply copy something that is good and simply make it better. You can call them SUs and everybody will know what you mean.

[paradoxx]

I just had this problem yesterday, I thought that maybe the float needle was not shutting down properly and changed it from another set I have. Started the car and the carb sprayed my valuable gas thru the tube. My mistake was that I didnt checked the float, even if its floating check it. The result was that the float had a super small crack that filled the interior of the float less that half of it, changed the float and the "pollo" is on the street again. I loooove SU......they are sooo simple and reliable!

[Unclejesse88]

True, you need to physically remove the float and shake it/listen to it. I got burned on mine when I pushed the float down it popped back up. Took it out and shook it, it was half full of fuel.

[Rustina 510]

It the float is good then they might both simply be set way to rich, bolt them on and start the car, let it warm up if possible, take the air filters off and use a skinny flat head screw driver to lift the piston in the carb. if the motor revs up slightly then it's to rich. Adjust them tell the motor doesn't change idle rpm,

 

Do you have the sync tool for the carbs, that is really important to check dual carb air flow.

[datzenmike]

take the air filters off and use a skinny flat head screw driver to lift the piston in the carb. if the motor revs up slightly then it's to rich.

 

 

The throttle plate isn't changed so idle air remains the same but lifting the slide would raise the needle allowing more gas in wouldn't it? Making it richer?

[paradoxx]

The throttle plate isn't changed so idle are remains the same but lifting the slide would raise the needle allowing more gas in wouldn't it? Making it richer?

 

I agree with this. Now what I suggest is when making some changes to adjustments let it idle a couple of minutes, check with the unisyn and make any further changes. What Im trying to say is that changes are not immediately shown.

[datzenmike]

Of idle needle is fully seated and it is still too rich a smaller jet or larger needle?

[Rustina 510]

I have been reading on this all week actually to get familiar with my carbs, we have the same ones actually " I think "

 

These carb will dump gas if the airflow is low and they are adjusted to rich, this is common on most of the stuff I have read, lifting the piston allowes more air and in turn, ifthey are set to rich you will get a small increase to idle rpm, adjust tell idle rpm remains as close to unchanged as possible while lifting the piston. It askes to check the air filters Also. If the filters are not allowing air flow it can dump gas because the air fuel mixture is unbalanced.

 

This is just what i have been reading, I have not been able to apply this to my car as it does not have the l20b motor installed yet, but I have read this info in Many other web pages and most of them address this problem with the same troubl shooting and solutions

[Rustina 510]

It also says when making adjustments, rev the motor slightly and let it get back to idle after every adjustment. When lifting the piston, if it revs up it's rich. If it bogs it's lean.

[paradoxx]

another detail you have to check, is how many turns the nozzle has? I use them with 1 1/2 turns open, but maybe different between altitudes. Both carbs should be the same.