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Fuel Level SU Carbs

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mountainman

mountainman

Jedi Trainee
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I have a tr3 with su carbs.
I have a rebuilt fuel pump and getting a good squirt of fuel
to the float bowls. However the fuel
level in the jet head is about a 1/2 inch down from the top.
I checked the float chamber and needle valve and
adjusted it per Haynes manual. Shouldn't it be close to the top?
Any help would be greatly appreciated.
Thanks
 
Hello:
If the float level is too low, you might experience fuel starvation at full acceleration, or perhaps hard cornering.
If the level is too high, the extra fuel dumps down the carburator bore, causing the engine to flood. This is most noticable at idle.
If you have neither problem(starvation or flooding), the level is just right.
My expierence is that it's better to be low than to be high.
Emmett
 
Thank,s Emmett,
Just wanted to to know I was alright with the fuel level Now, I'll try getting them tued up.
Thanks again
 
Aloha,

I agree with Emmett, that sounds about right. If you followed the proceedure to set the float bowl level correctly it has to be. The air flow through the carburetor will draw the fuel up into the venturi by creqting a low pressure in the jet.
 
And once the needle is in the jet, the fuel will "wick" a bit too.
 
<span style="font-style: italic">Montani Semper Liberi! </span>
 
fuel level su carbs

I got an MGB 76 with SU carbs.
I replaced the floats with new plastic ones without any adjustment. I was told to add or remove washers underneath the needle for fuel adj. The needles are balls instead of a "pointeau". Should I refill the fuel bowls to avoid fuel spills?
Even though get the level steady when the ignition is on, the carbs are still flooding when running.
I'm out of clues.

Thanks

Don
 
1/2" sounds too far to me, but I'll agree that if the engine runs OK, it's not worth worrying about.

One way the level could be wrong even though the measurement is right is if mismatched carb parts were used. Somewhere I've got a pair of H6 carbs that use a stud instead of a bolt for mounting the bowl, and the bowls are taller to compensate for the extra length of the stud.
 
Re: fuel level su carbs

don62 said:
The needles are balls instead of a "pointeau".
Click to expand...
That sounds like a "Grose Jet" float valve. Although some swear by them, others have had all sorts of problems. Seems that they don't hold back fuel pressure as well as the stock float valves do, and on some cars the pressure is enough to force the valve open against all the force that the float can muster. Sometimes it's even intermittant.

If that's your problem, the solution is to either go back to the old style float valves (my preference) or add a fuel pressure regulator to hold the pressure down to 2 psi or so.

Or, if the MGB was still using an SU electric fuel pump in 76; you might be able to trim the spring inside the fuel pump to reduce the maximum pressure a bit.

Another fairly common problem is crud in the fuel getting caught in the valves and blocking them open. This is sometimes caused by 'rubber' fuel lines that fail internally, without showing external cracks or leaks. They shed bits of rubber into the fuel after the filter/screen. If your soft fuel lines are more than 7-10 years old, I'd just change them as a matter of course.
 
Re: fuel level su carbs

While on the subject of "rubber" fuel lines, I'd like to add my 2 cents.
The ordinary fuel lines of old are not alcohol resistant and are more prone to the deterioation that Randall described.
While at a NAPA store I read the specs on fuel lines. It was clearly stated that "fuel injection" lines were alcohol resistant whereas the regular fuel lines did not have this specification.
Something to consider in this age of gasahol.
 
Re: fuel level su carbs

I agree the problem of old lines not being compatible with ethanol is real; but anything sold as "fuel line" in the last 10 years at least should be able to withstand it. MTBE has the same problem, and it's been around for at least 20 years now.
 
Re: fuel level su carbs

Thanks for the hints!

My lady blue is back on the road.
I replaced the rubber fuel lines, filter and did a nice clean up of the fuel bowls. I installed the new floats with the new needles. At first attempts the fuel was going straight out of the jet heads when turning the key on. I finally got it leveled and now she runs like a charm. I still don't know what I was doing wrong at the beginning but it works now. I couldn't check the fuel pressure.

Thanks again

Don
 
Re: fuel level su carbs

A 7/16" drill bit makes an ideal rod for setting the H6 SU float height. Check the two prongs are level, as one prong kicked down will keep the bowl too low.

After rebuilding a fuel pump, it's best to replace both needles and seats in case they are tired, and not sealing off properly when the bowls are full. I too prefer the conventional type with neoprene tipped needle, to Grose jets, especially when an electric fuel pump is fitted.

Regards,

Viv.
 
Re: fuel level su carbs

Well, I'm still at the same point.
She ran fine for 4 days then...flooding again.
As soon as I turn the key on the fuel goes straight out, not even in the carbs, about 6 inch high. This is when the pistons are removed.
 
Re: fuel level su carbs

Do you think that the overflow pipes could be my prolem if its plugged off ? The fact that the fuel squirt 6 inches in the air out of the jet.
Does the carbon canister has to be clean out or replaced after a while?
What are the Grose-Jet float valves?

Thanks

Don
 
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