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Twin HS4 Su's leaking fuel

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George P

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I need some help here,
My twin HS4's were recently overhauled and refitted to my 79 Midget1500
Ever since then I get fuel coming out of the front Carb overflow
I contacted the company that did my carbs and the sent me a new float bowl top with needle valve and float, I fitted this and I still have a fuel overflow.
I cleaned out the float bowl and checked the needle valve was free to move. Still fuel was leaking.
I fitted a nice fuel filter in the line. Still I get fuel leaking.
I then resorted to violence and shimmed up the needle valve seat 1/8" and I still have fuel leaking.
I have the original mechanical fuel pump fitted
What's happening here ?? What else can I do ??
I'd be grateful for any help.
And just on the side I have a screw inserted into the chrome cap of my rocker cover, is this correct ??

IMG_2610.JPG
 
George, I am not sure that this picture can really help. The rocker cover is lovely and I see the vent for the engine but, can you post a pic of the carbs themselves?

thanks
 
JPSmit said:
George, I am not sure that this picture can really help. The rocker cover is lovely and I see the vent for the engine but, can you post a pic of the carbs themselves?

thanks
Click to expand...
Thanks JP, hopefully you can see fuel leaking from the front float bowl top. Also I'm showing the carbs and the new filter.
 

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JPSmit said:
George, I am not sure that this picture can really help. The rocker cover is lovely and I see the vent for the engine but, can you post a pic of the carbs themselves?

thanks
Click to expand...
This may show the fuel leak better.
 

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Does the float actually float?

Also, I just noticed you have no clamps on your fuel lines. That could be what's leaking. In my opinion you need some clamps, no matter how tight the lines feel when you push them on the tube. 😁
 
Thanks Rick, yep no clamps, that line was put on as a temp measure. The real line has clamps indeed.
I tried two floats and two needle valves and two float bowl tops, all do the same Leak!!!
 
George -
See my post regarding setting float level over on the MG side. May be your issue.

Mickey
 
RickF said:
Next thing to check is fuel pump pressure. SU's like 2.5 psi.
Click to expand...
Thanks Rick, I watched the video. My float bowl top is No2277 and does not have the bendy adjuster, I have just ordered an earlier 2276 with the spring arm (Picture) in the hope that it might cure my problem. Not sure how to check the fuel pressure

Float.jpg
 
Harbor Freight sells a fuel/vacuum tester (around $14.00) which can be tee'd into the fuel line before the carbs. My only other thought is possibly using a Viton float (Joe Curto and Moss sell these) as I have found the ethanol blended gasoline will deteriorate the original type float.
 
George P said:
Thanks Rick, I watched the video. My float bowl top is No2277 and does not have the bendy adjuster, I have just ordered an earlier 2276 with the spring arm (Picture) in the hope that it might cure my problem. Not sure how to check the fuel pressure

View attachment 71630
Click to expand...




Meanwhile I glued in place a wee packer here on my spare float here to see if that would help!



Inkedfloat3_LI.jpg
 
Well that did not work seems like it shut the fuel of altogether so back to square one. I'm still losing fuel even after switch fron and rear floats and needle valve.

Need help before I catch fire!!!!
 
Are you certain the float actually floats? Could it be a leaky gasket? If none of these then I think you are down to checking the pump pressure although if a real SU pump I don't think that is likely.
 
is it actually leaking out the overflow vent[which is behind the small metal plate where your fuel line goes on] or is it leaking out of the gasket area? as that gasket looks a bit dodgy to me, sorta home made
Russ
 
I ran into this several weeks ago. I installed new Ethanol Resistant Floats and upgraded to the "Superior" Gross Jets with the Ball Valve. Adjusted Float Height correctly. Started Engine Gas leak from Front Carb. Changed back to old Vitron Tipped valves on front carb, leak stopped and moved now to rear carb, crap, Changed back to Vitron Tipped Valve on rear, reinstalled old valves and leak went away. Problem solved.Order new Vitron Tipped Float Valve and issue will be solved.
 
Jim_Gruber said:
I ran into this several weeks ago. I installed new Ethanol Resistant Floats and upgraded to the "Superior" Gross Jets with the Ball Valve. Adjusted Float Height correctly. Started Engine Gas leak from Front Carb. Changed back to old Vitron Tipped valves on front carb, leak stopped and moved now to rear carb, crap, Changed back to Vitron Tipped Valve on rear, reinstalled old valves and leak went away. Problem solved.Order new Vitron Tipped Float Valve and issue will be solved.
Click to expand...
Front HS4 carb leaks through at 4000 rpm, it’s the vent not the gasket, put in new vitron, still leaks, submerged float in jar of gas overnight with no leaks floats fine, adjusted float way high to ensure closure of vitron valve, still leaks at 4K.
 
hmmmmm...... years ago I had a similar problem... .. in the end it turned out to be a fuel pump that put out 7 pounds of pressure instead of 3.. the problem didn't show up until I had the carbs rebuilt... I've since installed a pressure regulator (NOT those ROUND CHEAP ONES from MO#$) but a good Holley...
 
George P said:
I need some help here,
My twin HS4's were recently overhauled and refitted to my 79 Midget1500
Ever since then I get fuel coming out of the front Carb overflow
I contacted the company that did my carbs and the sent me a new float bowl top with needle valve and float, I fitted this and I still have a fuel overflow.
I cleaned out the float bowl and checked the needle valve was free to move. Still fuel was leaking.
I fitted a nice fuel filter in the line. Still I get fuel leaking.
I then resorted to violence and shimmed up the needle valve seat 1/8" and I still have fuel leaking.
I have the original mechanical fuel pump fitted
What's happening here ?? What else can I do ??
I'd be grateful for any help.
And just on the side I have a screw inserted into the chrome cap of my rocker cover, is this correct ??

View attachment 71587
Click to expand...
2 years later, did you ever get to the bottom of it?
 
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