Put the SU on today - she starts instantly but is very very anemic. I touch the gas and she stalls.

Was trying to make it work and it seems like a lot of gas in the carb and gas was spitting out the overflow line.

Other than the carb I had to put in a smaller fuel line (3/8" to 1/4") but same fuel pump as always.

Float? or something I haven't thought of.

if float, how should it be adjusted?

BTW - is an HS4 off a MGB

Not that I have any answers and I apologize in advance, but I could not help but quote my favorite automotive author, Peter Egan, when he was rebuilding his MGB, tried the Weber, and couldn't get it to run well, "it must need more cam!"
Cheers, good luck!

Seems pretty obvious that the float valve isn't doing its job. This is not unusual--just unstick it, and if the tip is obviously bunged up or it happens again, replace it. Make sure that the float height is OK, while you're at it.

As an aside since I had the tops of the carbs apart yesterday. How can you adjust the float level if you can't see the float in relation to gas level in the carb. Is there a technique to measure float level height?

I THINK that I understand what you are asking-
Here is how I do a final check on my float level:
1/ take the dashpot(s)and piston(s) off of the carb(s)
2/ turn on the electric fuel pump
#/ if the fuel level comes up to about 1/8" below overflowing over the saddle then it is good. If the fuel level is too low then adjust the float, if it is running over the saddle(s) then adjust the float.
Works for me.
Bill

Look at page 85 of Haynes.

H1 and H2 carbs are set at 1/8 in under the lever to body and HS2s 1/8 from body to float.

The top of the float chanmber is held upside down to do this.

There is a real spec, for almost all the stuff on our cars guys.

thanks Jack - set the float last night - no change. I'm a little stumped.

One question though - with the jet on an SU - if you take the float off, do the "guts" slide out? or is a piece missing? Doesn't seem to affect the function but it doesn't seem right either

Is your ignition timing OK? EAsy cold starting and weak power is often an indication of retarded igniton timing.

And, did you adjust the jet-nut? You should wind it all the way "up" (so it is screwed in all the way) and then unwind it down 2 full turns (or as the book says, "12 flats"). This should get your close.

Are you referring to the jet or the float needle? I think you mean the needle.

Not sure about HS2s, but on H1s and other SUs I've seen, you can remove the float and the needle falls out. There is a housing, if I can call it that, for the float needle that screws into the body. This is all pretty straightforward and covered in shop manuals. It's a good idea to have a manual at hand when you pull apart a carb, or for that matter, anything on the car. There are several good books about SUs, in particular, that you can get.

Nial,

Timing should be fine from before.

thanks for the jet nut setting was looking but could not find.

Steve, thanks for explaining the float needle - you're spot on about the manual, my challenge is that it's an MGB carb and all my books are ZS (though I'll go back to Haynes which covers previous years)

did adjust the float but gas is still coming out of the overflow (I walked away to scratch my head awhile)

The car will run terrible if there's too much fuel pressure. And it will force past the float needle and pour out the overflow.
Do you have a stock fuel pump or did you add an electric one?
If you have an aftermarket pump, you *need* a fuel pressure regulator unless you're sure you don't have too much pressure (2 lbs of fuel pressure is plenty for your setup).

I know you said the timing *should* be OK, but it never hurts to check.

You don't have two plug wires mixed up, do you? (it happens to the best of us)

Did you have the camshaft out? If so, are you sure cam timing is correct (it's tricky on these)

Old stock fuel pump

timing and cam dialed in before - which is to say that it was running smoothly before - the ZS was just a PITA around running rich. Hence the SU - but nothing else as been changed

Took the carb apart on the car and there was a little puddle of gas around the needle hole - seemed like that shouldn't be

Ah hah! It seems that you are having the same issue you where having with the ZS. Time to examine your fuel pump!

Fire up the car and let it idle for a sec. This will fill up your fuel bowl. Then disconnect your fuel pump. Fire the car up again. It will run for a minute on the fuel remaining in the bowl. If there is an improvement... then you know something funky is going on with the fuel pump.

There are several pumps available for the 1500. It's feasible that you have a pump mismatched for your application.

or buy a 20 dollar inline fuel pressure regulator & dial it down to 2 or 4 psi... I know my car (allthough a 1275cc) ran exactly like yours when I put a new fuel pump in, thought it might be able to handle 7 psi... it could not :-) very similiar symtoms.

so close ....


had some time today

1. replaced the plugs - helped some.

2. got it running (just) big backfire and she quit - but I saw the flame - hmmm - air leak - yup, different gasket, tightened her up and Bob's yer uncle (because we all know float problems are related to air leaks in LBC's)

3. she starts like nobody's business

4. Idles perfectly

5. dies every time I open the throttle

6. did spray WD40 around joints - nothing changed

7. thoughts?

Very very rich me thinks.

What is this $20 regulator thou speakst of? Sounds like something I could use with my rattlecube pump...I think it may be taxing my Weber, but I don't want to lay out long green to find out.

Did you fix the problem with fuel coming out the overflow? No point in doing anything else until that is fixed.

If the float needle isn't shutting off the fuel, the level will be too high no matter how you've set the float. Then raw fuel will spill into the intake.

So, if fuel is getting past the needle when it should be shut off, there are two possibilities: (1) bad needle valve, (2) too much pressure. Both should be easy to check. I had this problem and couldn't fix it by replacing the needle valves. I had to add a pressure regulator and set it to about 2 psi. (I use a Facet pump, which put out 3.5 psi, almost exactly the same as the mechanical pump, but still too much.)

By the way, it's possible to have a small leak past the needle, not enough to cause overflow, but enough so that the fuel level is too high, even if the float height is OK. If you're seeing raw fuel in the intake, the fuel level is almost certainly too high.

~Here~ is a decent, low-cost fuel pressure regulator (although JP probably doesn't need this if he has a stock, mechancial pump).

The factory electric SU pump put out about 2.5 psi, by the way.

I wonder if you have very weak spark (sometimes, if it "won't take the gas", it's because the spark is being snuffed out by the extra fuel/air).

And I'm still wondering about ignition timing.

The carb damper pistons move up and down easily, right?

"Choke" mechanism (really,the fuel enrichment device) is "off", right?

Valve adjustment is correct?