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SU HS4 head jets adjustment

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don62

don62

Senior Member
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I just want to confirm the right adjustment.
I read to adjust the adjusting nut 12 flats from the carb bridge. What is the bridge? If I screw it all the way in(clockwise)until the spring is the tightest and then unscrew
12 flats or 2 turns, is it the same?
Correct me if I'm wrong, underclockwise would give a richer mixture?

Thanks

Don
 
Carb "bridge" refers to the high flat area in the throat of the carb, running across the inside. The method is: start out with the jet end flush with the bridge by looking in the throat as you raise the jet to be so. THEN lower it the 12 flats.
 
Thanks again for your help.

I had a hard time to find the perfect setting because the gap of my points was a bit off. I reajusted to .014in and retuned the carbs, now it runs like a charm.
How much mileage per gallon should I expect for a 1.8L, SU HS4 carbs type? I heard 33(hwy only), is it possible?

Thanks

Don
 
I've heard people report that they get up to that much in economy with their cars. I believe it's possible if everything is well sorted out. I think it may even be possible to do a little better.

I have a '76 that up until very recently was running on the stock ZS carb. With it, I've never gotten better than 25MPG (HWY only). Most of the time I average between 17MPG and 20MPG. Then again, most of my driving is 'city driving', and I like to use the loud pedal. /bcforum/images/%%GRAEMLIN_URL%%/smirk.gif

I recently switched over to a single HS6 carburetor. I have not yet gone through a full tank of gas with it. I'm dieing to find out what it's done to my fuel economy.
 
Thanks for the reply!

I'm out of ideas now.
Eventhough she was running great yesterday, again today
she's misfiring. I replaced the points, the gap is still ok.
We adjusted the valves at .013in. The jetheads were replaced last summer. It seems as if something get untuned after driving a while on the hwy. The spark plugs were replaced. I went to see a pro in a british garage, he resync
the carbs and readjusted the jetheads. She ran fine when I left the place but after 20 min on the hwy again she was misfiring and dying on me I had to reset the jetheads to make it home. Any clues.......

Don
 
Yep. has to be the jets. Think I would replace them. One has a crack, bad o ring or such. When your guy set and balanced em he wiggled them just a bit and closed the problem till vibration opened em again

Reach under the carbs and wiggle each one just a bit with your fingers while the engine is running poorly and see what you get.
 
don62 said:
Thanks again for your help.

I had a hard time to find the perfect setting because the gap of my points was a bit off. I reajusted to .014in and retuned the carbs, now it runs like a charm.
How much mileage per gallon should I expect for a 1.8L, SU HS4 carbs type? I heard 33(hwy only), is it possible?

Thanks

Don
Click to expand...


Condensor been changed?

mark
 
Affirmative the condenser was replaced.
The jet heads look fine but their control arms are screwed from the outside instead of the inside.
This seems to put some tension on the jet heads itself.
I'll see if I can reverse them as per the maintenance manual.

Thanks

Don
 
Does the size of the jet heads from my su hs4 the same for any model? i.e. .090in.? If not is there a model number written somewhere on the carbs to get the right size?

Thanks again

Don
 
Jet I.D. is a constant, the needle profile is the mixture determinant at any given demand.
 
The bottom of the jet heads are getting wet of fuel.
Is this normal or they should be dry at all time?

Thanks

Don
 
By "bottom" do you mean the black plastic part on the outside, underneath the carbs? That would be a problem. The exhaust manifold is beneath them, they should be dry.
 
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