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SU HS4 carbs only run on full choke

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markrobbins Mark Robbins
Vancouver, BC, Canada   CAN
1974 Triumph 1500 "Spitty"
Hi all, I've been through a bit of an epic repair and replace Journey with my 1974 1500 Spitfire. I've managed to get it running again since I've replace the head gasket, but she only runs on full choke. Even if I let her warm up for a bit she still won't run unless the choke is fully out.

Before changing the head gasket I had on the stock single Stromberg carb. I wonder what could be missing in this puzzle? Anyone else have a similar problem? Thank you for all replies.

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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
How have the jets been adjusted? Have you tried a richer setting?

jimgt6 Jim E
Seekonk, MA, USA   USA
Get the Haynes SU carb book. A wealth of knowledge. Has a chapter devoted to HS carb.

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markrobbins Mark Robbins
Vancouver, BC, Canada   CAN
1974 Triumph 1500 "Spitty"
I have them set at the recommended initial setting of: jet level with bridge then two full turns richer (down or anticlockwise).

carChips Avatar
carChips Victor Harnish
Kelowna, BC, Canada   CAN
1933 MG Magnette
1973 Triumph Spitfire 1500 "Chip"
1989 GMC Sierra 1500 "Bush Truck"
When you set up your SUs, pull the dash pot and piston and measure the depth of the jet from the bridge with the tail of a caliper. That measurement should be 2mm, that is your base setting. Sounds like your jet is flush with the top of the bridge if you need that much choke.



'S all for now
Vic

carChips Avatar
carChips Victor Harnish
Kelowna, BC, Canada   CAN
1933 MG Magnette
1973 Triumph Spitfire 1500 "Chip"
1989 GMC Sierra 1500 "Bush Truck"
We were posting at the same time, sorry. If that's the case then check the float in the float bowl, you should be able to roll a 3/16" drill bit between the float and cap (turned upside down of course) with a slight amount of interference. Maybe the drill bit moves the float a hair.



'S all for now
Vic

markrobbins Mark Robbins
Vancouver, BC, Canada   CAN
1974 Triumph 1500 "Spitty"
Hi Vic,

I checked the float heights a while back, and also I can see the fuel level in the jets is where I've read its supposed to be, but I'll have another look.

Ill also put my Medtronic back in, check the timing and readjust idle screws

Cheers!



Edited 2 time(s). Last edit at 2018-02-06 11:12 PM by markrobbins.

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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
Seems like you have checked the jet level and fuel level in the float bowls, so how about vacuum leaks?

Leaks at the manifold and carb flanges, also wear at the throttle shafts?

Will the engine run at higher rpm 'on the throttle' without choke?

grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
What needles are in the carbs? Were the carbs originally fitted to a Spit 1500, or something else? You haven't by any chance got a pair of carbs from an MGB, which have the wrong float chambers for horizontal carbs? Do you have the correct engine breather pipework for a Spit 1500 with twin HS4s?

Sorry for all the questions, but without knowing exactly what the setup is (and maybe seeing a couple of images) it's really just guesswork from this distance!

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markrobbins Mark Robbins
Vancouver, BC, Canada   CAN
1974 Triumph 1500 "Spitty"
Hi Grumpicus,

The carbs have the right float bowls, new floats, new needles and set with 1/8 bit as per the manual.

The needles are ADN. I also have a pair of AAR handy.

The carb breathers go into a T then into the rocket cover.

I'm going to enriched the jets a few turns and screw in the idle screws a turn or two.

carChips Avatar
carChips Victor Harnish
Kelowna, BC, Canada   CAN
1933 MG Magnette
1973 Triumph Spitfire 1500 "Chip"
1989 GMC Sierra 1500 "Bush Truck"
Can you post a picture with the airfilter off?



'S all for now
Vic

markrobbins Mark Robbins
Vancouver, BC, Canada   CAN
1974 Triumph 1500 "Spitty"
I'll do that on Friday evening.
I'm away from home for a couple of days.

Thanks

grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
In reply to # 1511943 by markrobbins Hi Grumpicus,

The carbs have the right float bowls, new floats, new needles and set with 1/8 bit as per the manual.

The needles are ADN. I also have a pair of AAR handy.

The carb breathers go into a T then into the rocket cover.

I'm going to enriched the jets a few turns and screw in the idle screws a turn or two.

Hi Mark - sounds good! The idle screws will need to be be screwed in slightly, or the throttle butterflies will be completely closed - pulling out the choke will open them slightly to increase the idle speed, and then start to lower the jets to richen the mixture. With HS4s fitted, the engine breather is as you describe, all other engine vents are sealed or blanked off.

Lizzard d id
san jose, CA, USA   USA
In reply to # 1511943 by markrobbins The carb breathers go into a T then into the rocket cover.
Good news is it runs !!!
Try clamping of the carb breather . Don't let air into the carbs via the breather . Does it run any better that way ?

markrobbins Mark Robbins
Vancouver, BC, Canada   CAN
1974 Triumph 1500 "Spitty"
Hi Lizzard, I'll try clamping it off.

Carb question: is it possible I set the needles too far out of the slides?

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