1960 Morgan +4 (triumph tr3 engine) with twin SU carbs.

I just tried starting her up today for the first time in a few months. Starter clicked for a while, I tried various positions of the choke and then finally she turned over and immediatley died. I had been pumping the gas a little while I tried to start it. After the engine died I smelled gas really bad so I checked the engine and found that one of the carbs was soaked in gas and gas was running out of its overflow onto the floor. Gas was also dripping out of the bottom of the carb. Does anyone know what this might be? (did I flood it?). Thanks for the help...prolly needs the carbs rebuilt. We're taking it to be painted in a few weeks and I want it to run well when it gets back.

5/29/2006 3:34:41 PM

As far as SU carbs go...

1. They don't have a real choke.
2. They have no accelerator pump.


If there's a lot of fuel flooding the barrel and all over the carb, including coming out of the vent tube, then you've got a float stuck. You might try rapping on the float bowl with a wrench or something.

You can't pump the gas pedal to introduce fuel into the barrel on SU's, as they have no accelerator pump. So forget about even doing that; it does nothing.

The "choke" on most SU's is actually a linkage that lowers the jet tubes in the carb body. The SU carb is a constant-velocity, or what the fucking Brits term a "constant depression" (depression being vacuum) carburetor. As air velocity remains more or less constant through the venturi and across the jet, a form of metering has to take place to vary fuel depending on engine load/demand. That's what the vacuum piston and needle do. To richen the mixture for cold starts, instead of incorporating a conventional butterfly, the jet tube that the needle slides up and down in is lowered somewhat, increasing the jet-to-needle cross-sectional area ratio (basically giving you a bigger jet cross sectional area).

Later Skinner's Union carbs do have accelerator pumps and stuff for smog and emissions, but yours don't fall into that league. If they do, then they've been swapped, and I don't know who in their right mind would do such a thing.

5/29/2006 3:50:39 PM

Thanks for the help!

just to illustrate, here is a picture I just took. The carb in the background is doing just dandy, the one in the foreground you can see wetness on.

5/29/2006 4:03:10 PM

didn't the early Z's use twin SU carbs? shit i don't know anything about carbs... bit too ancient for my tastes

5/29/2006 4:38:13 PM

Yeah...they were actually Hitachi clones of the SU carbs. They had three major iterations.

Ten dolla says stuck float. Fuel pump will slam fill one up with gas if you have a stuck float.

5/29/2006 4:55:09 PM

damn this threads way different than what i thought it was gonna be about

5/29/2006 4:55:41 PM

Alrighty, the back carb has stopped doing it and now the front carb is shooting gas out of the overflow. Um so that could be bad. The floats don't seem stuck and the butterfly valve is turning. In all honesty I know zip about carbs, I just know mine are messing up.

5/29/2006 5:36:06 PM

If the float ain't stuck then there ain't no way to gas is gonna come out of the carb in that kinda volume.

5/29/2006 5:38:31 PM

Alrighty...I have the service manual so I think I'm gonna take apart / clean everything tommorow

5/29/2006 6:21:20 PM

i always try to cheat by taking off the fuel hose at the carb, filling it up with carb cleaner, and tap on it till the float comes unstuck, you better make sure you have a rebuild kit or gaskets for that before you take it apart otherwise, thats not your standard parts store item

5/29/2006 9:08:33 PM