I've never had so much trouble with SUs before, please help! - Page 5

Derek UK · Jul 28th, 2022, 23:19

I don't know if the .90 jet is physically the same as the .100 one as far as it fitting the carb. As it has a smaller bore I guess it could run out of gas at full throttle and top out at 4k revs. You could probably get it to idle OK. Proper SU jets have a coloured ID band on them. Yellow for front carb and red for rear carb. Don't know what the physical difference is as far as fitting them incorrectly. Pity you have ditched the bad ones, I'm sure Ron would have liked to get his hands on them. Maybe a pair of .90 tubes were incorrectly fitted to .100 fittings?

Othen · Jul 29th, 2022, 06:17

Quote:

Originally Posted by Bork Volvo

I want to give everyone a sincere thank you for your ideas and thoughtful replies. Just to let you know, I have successfully resolved the issue with my SU HS6 carburetors and the 4,000RPM limit!

I had a bit of a meltdown this morning where I turned to my helper and said, "I hate this car." I was feeling so terribly defeated that I dismissed him for the day and started putting away my tools.

In my SU drawer, I found another set of authentic SU jets still in the box. A lightbulb went off; at this point, the jets were the only things that I hadn't revisited or switched during my entire campaign. The jets fitted to my car were purchased from a local British car specialist. Even though the jets were new and supposedly for SU HS6 carburetors, something in my gut told me to get rid of them.

I swapped them out for the SU jets from my inventory and my car suddenly would rev to the moon! An absolute night and day difference.

Again, thank you for your thoughtful replies and creative problem solving. Hopefully this saga can help somebody else with a similar issue!

Curiouser and curiouser.

:-)

Ron Kwas · Jul 29th, 2022, 13:45

Indeed...!

It's a stretch to imagine what on a set of jets could have been wrong...they had to be 0.100"! (with 0.090"s, the Metering Needles would have jammed)...the only other thing I might suggest is a flow restriction in the Jet Supply Tubes...either at the Jet crimp end, or at the slightly tricky compression fitting at the Bowl end (perhaps the anti-compression sleeve "Fuel Line Insert" inside the tube was not in place which allowed the tube to be crushed, restricting flow... Ref: https://www.sw-em.com/SU_HS6_Jet_Supply_Line_Seal.htm ).

Too bad...I would have liked to root cause the issue...we'll simply have to let it stand as a fuel flow restriction of unknown specific cause.

Cheers

Jul 29th, 2022, 13:45	#43
Ron Kwas Premier Member Last Online: Today 00:07 Join Date: Jul 2007 Location: Connecticut, USA	Indeed...! It's a stretch to imagine what on a set of jets could have been wrong...they had to be 0.100"! (with 0.090"s, the Metering Needles would have jammed)...the only other thing I might suggest is a flow restriction in the Jet Supply Tubes...either at the Jet crimp end, or at the slightly tricky compression fitting at the Bowl end (perhaps the anti-compression sleeve "Fuel Line Insert" inside the tube was not in place which allowed the tube to be crushed, restricting flow... Ref: https://www.sw-em.com/SU_HS6_Jet_Supply_Line_Seal.htm ). Too bad...I would have liked to root cause the issue...we'll simply have to let it stand as a fuel flow restriction of unknown specific cause. Cheers Last edited by Ron Kwas; Jul 29th, 2022 at 13:48.

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Jul 28th, 2022, 23:19	#41
Derek UK VOC Member Last Online: Yesterday 13:53 Join Date: Jul 2006 Location: Chatham	I don't know if the .90 jet is physically the same as the .100 one as far as it fitting the carb. As it has a smaller bore I guess it could run out of gas at full throttle and top out at 4k revs. You could probably get it to idle OK. Proper SU jets have a coloured ID band on them. Yellow for front carb and red for rear carb. Don't know what the physical difference is as far as fitting them incorrectly. Pity you have ditched the bad ones, I'm sure Ron would have liked to get his hands on them. Maybe a pair of .90 tubes were incorrectly fitted to .100 fittings?

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