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SU HS4 carbs only run on full choke

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Lizzard d id
san jose, CA, USA   USA
In reply to # 1512174 by grumpicus OK, so you believe that the '12 flats down' position is completely random - fine, that's your opinion.
This all started because you said , and I quote ,
"If you're having to turn the adjusting nut through a turn or two to make a difference, there's something else wrong...."
If they were adjusted to level , all the way up , lean as can be , a turn down is still rich . It will take more than a turn just to get to 12 flats down . You indicated that there would be another problem other than just the need to dial in the carbs . I object to telling him to look elsewhere when he is doing an initial dial in of the carbs he has just installed . I think he should adjust the carbs to suit the motor he has just installed them on .

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grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
In reply to # 1512209 by Lizzard
In reply to # 1512174 by grumpicus OK, so you believe that the '12 flats down' position is completely random - fine, that's your opinion.
This all started because you said , and I quote ,
"If you're having to turn the adjusting nut through a turn or two to make a difference, there's something else wrong...."
If they were adjusted to level , all the way up , lean as can be , a turn down is still rich . It will take more than a turn just to get to 12 flats down . You indicated that there would be another problem other than just the need to dial in the carbs . I object to telling him to look elsewhere when he is doing an initial dial in of the carbs he has just installed . I think he should adjust the carbs to suit the motor he has just installed them on .

Sure, I did write that in post #19, based on the OP's statement in post #4 that he had already set the jets two turns (12 flats) down from being level with the bridge - as his starting point. I have not stated, nor have I implied, that anyone should attempt to adjust the mixture with the jet level with the bridge. As you highlighted, that position would give a mixture which would be far too weak. If the jet is already two full turns down as the starting point, my experience is that it should not be necessary to turn the adjusting nut very far from that to effect a mixture change - certainly not as much as a further 2 or 3 full turns down.

aebreard Armand Breard
Monroe, LA, USA   USA
On my HS4's on the '74 B, I think I used 6 flats down for the jets as an original or starting position. Sounds like you need to lower the jets, and you are getting
plenty of good advice. In order to close up the suction around the throttle shaft, I used some very small o-rings, which worked. I also use on all SU's Ford
ATF in the dashpots, which has performed well. Armand

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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
Personally I have found the initial setting (12 flats) to be 'close enough' to get the car running.

I (personally ) would be surprised if, good carbs, installed properly, with close to correct needles etc.
would need FULL choke in order to run.

I (personally ) suspect there may be a vacuum leak at the manifold or even at the carb throttle spindals.

It would be easy to add a drop or two of heavy oil (STP) to the throttle shafts, just to see.

carChips Avatar
carChips Victor Harnish
Kelowna, BC, Canada   CAN
1933 MG Magnette
1973 Triumph Spitfire 1500 "Chip"
1989 GMC Sierra 1500 "Bush Truck"
I set my SUs down 2 mm or 12 flats or to turns to get it to start. I have a lumpy cam and now the jets sit at 2.1 mm. I never count flats because there may be a variant in threads.

I'm with Tony, check for a vacuum leak.



'S all for now
Vic

Wolfcreek Steve Steve P
Central, WI, USA   USA
Stop the pissing match about 2 turns down (12 flats) and suggest to the OP that he double check for vacuum leaks, that's what a real mechanic would do!

carChips Avatar
carChips Victor Harnish
Kelowna, BC, Canada   CAN
1933 MG Magnette
1973 Triumph Spitfire 1500 "Chip"
1989 GMC Sierra 1500 "Bush Truck"
Which also equals 2 mm or .079".


In reply to # 1512262 by Wolfcreek Steve Stop the pissing match about 2 turns down (12 flats) and suggest to the OP that he double check for vacuum leaks, that's what a real mechanic would do!



'S all for now
Vic

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Lizzard d id
san jose, CA, USA   USA
Four hours after the end he says stop .

markrobbins Mark Robbins
Vancouver, BC, Canada   CAN
1974 Triumph 1500 "Spitty"
Now, now gentlemen. Can we please shake hands? Or at least mumble a "lets agree to disagree, eh?"

Anyway, I went to fiddle again, and this time when I go to start it with the choke out, it's revving up then dying.

Jets are now 4 turns (not flats) rich.

Even though I've had the manifold off a couple of times, I'm inclined to agree there's a leak somewhere. What's the consensus on the best gasket? I have high heat gasket card, so is it worth a try making my own?

Please see photos attached. Note the fuel connecting pipe is just temporary.



Edited 1 time(s). Last edit at 2018-02-08 10:29 PM by markrobbins.

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jimgt6 Jim E
Seekonk, MA, USA   USA
One possibility is that the mating surface of the intake manifold to head is warped. This happened to me with my GT6. I had the manifold trued and the problem was solved. It was not out very much. You could not detect it by eye.

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
Job to tell from the photo, but you seem to have a heat shield between the carbs and manifold?

Did you use sealant on this? (both sides)

markrobbins Mark Robbins
Vancouver, BC, Canada   CAN
1974 Triumph 1500 "Spitty"
I wouldn't put it together without something, Tony.

There is a gasket, each side of the heat shield. Both gaskets were soaked in oil before assembly.

I'm going to remove the heat shield and try again.

Thanks all!

Lizzard d id
san jose, CA, USA   USA
If it starts and runs you can do the old spray in with something and see if the rpms change . Some people use an unlit propane torch , some wd40 , some starter fluid , etc . Test it that way to find if there is a leak before pulling it apart . Pinpoint the problem and then work on the problem if one is found .

markrobbins Mark Robbins
Vancouver, BC, Canada   CAN
1974 Triumph 1500 "Spitty"
I've got it apart again, which is accomplished in about 15 minutes now. The manifold gasket is one of those laminated silver jobbies, with the dimples. It looks like a piece of crap tbh, and is already delaminating. So. I've made my own with some high temp gasket card. I'll put it back together in a couple of days and report any results.

BTW I've also shelved the heat shield for now.

grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
Removing the heat shield for test purposes is fine, but it's needed in warmer weather, especially if the carbs have the Waxstat jets. On a warm day, without the heatshield, heat from the exhaust manifold/header heats up the Waxstat capsules, and can lean out the mixture to the point that the engine needs some choke just to keep it running in slow traffic. I've never had a problem with air leaks at the heatshield, but I use gaskets on both sides of the shield. The Waxstat jets can sometimes go rogue - when/if that happens, the heatshield doesn't make much difference.....

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