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> Jensen Healey & Jensen GT Tech > Carburetors > Z-S Carbs - "Choke" and fuel/air adjustment

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marvinm
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Well, purely be accident, I discovered the main problem I was having (see Distributor falling out...) and it is definitely air/fuel mixture.  Apparently enough fuel to idle, but not nearly enough to make any power when trying to drive.

I adjusted the "choke" to about 75%, but backed off the fast idle screw to keep the RPMs normal and was able to drive fairly normally...got it up to 80 mph.

Question 1:  With the single "choke" cable and tube between carbs, is there supposed to be anything on the firewall side of the rear carb? A plate to close holes? The normal choke assembly? Mine appears as though someone removed the fuel enhancement mechanism on the rear carb...or it fell off, causing my troubles to begin with.

Question 2:  Is there a more efficient way to set the fuel/air mixture than...A.  Wait for engine to cool.  B.  Pull float chamber plugs.  C.  Watch gasoline coat starter and oil filter.  D.  Make adjustment to jet.  E.  Replace plugs.  F.  Wait for rest of gasoline to evaporate. G.  Start car and get to temperature to test.  H.  Repeat whole process until correct...   ???

Thanks...MarvinM - 10927

Jensen Healey
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Question 2: Get the ZS carb adjustment tool. It works through the damper on the top of the carb. Delta probably has them.

Brett Gibson JH5 20497
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Marvin,

Never heard of that way of tuning Stromb's, but hey if it works for you ........

As for the choke, there is only one and it's on the front carb as you mention, the rear one should have the molding but no thru holes.

Their is a lot written on how to tune Stromb's and I dont need to repeat most of it, do a search and it should come up, but basic, loosen the collar on the shaft between the carbs so they act independent, get the tool for properly adjusting the needles, screw the needles in till seated, then turn out 2-1/4 turns to get in the ball park, turn the idle screw so they have no effect and look thru the carb body to make sure the butterflys are fully closed, then turn the idles back so you can start the car and it keeps running, (I'm doing this from the top of my head so if I am missing  something here please add in). with the engine running check the draft on each carb with a gauge, adjust the idle screws till both carbs pull the same, then lock the collar on the shaft between the carbs. Now you have both carbs set whats left now is to adjust the needle jets till you get a nice mixture and the plugs show a light brown color. As for the temp compensator and bypass stuff, I made mine inoperable or removed it with no problems, some people like to have it but thats just more adjustments and not to value added for me.

If you dont have a repair manual I would suggest you do or at least Google Stromberg 175CD adjustments and you should get all you need and more, (plus what I'm forgetting), they are a pretty simple carb  that lends themselves to be adjusted by owners without to much going wrong, but basic is make sure the main diaghram and needle jets are in good condition, no tears, wholes, bends or scraps.

Good Luck.  Brett

 

Jensenman
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Something which helps a lot on Z-S carbs:

http://www.autoexpertproducts.com/colortune-14mm.htm


That and the mixture adjustment tool mentioned earlier make life a lot easier.

marvinm
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Apparently the adjustment is mostly the needle and not the jet.  I have too many cars with Z-S's to keep the various setups straight.  Thanks.

Now have to read through to see how to disable the temperature valve on the carbs.  Normal idle (after various playing) until the engine gets fully warm, then my idle doubles or better (still no working tach).  Since the compression on the cylinders is good, cold, I'll hope it the temp valve on the carb(s) that's the issue.

MarvinM - 10927

 

Jensen Healey
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To disable the temprature compensator, open the yellow cover, turn the spring over and close it up.

Brett Gibson JH5 20497
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Ditto,

I spent two days tweeking those stupid things till they were perfect by the book, didn't change a darn thing, blocked the off with no issue.

marvinm
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Apparently, there is more than one adjustment on this version of Z-S's. I thought the only one was the jet "screw" under (above) the float chamber plug. I'll have to review. My vintage Haynes manual doesn't cover the version of Z-S that is on the car. My Spitfire carb was not adjustable at all, jet or needle, other than swapping needles.

On the idle speed increase when the engine gets hot...Unfortunately, flipping the bi-metal springs around didn't help. It's bizarre. When just sitting in garage idling, temp gauge gets to about 75% and idle increases dramatically. No working tach, but it probably goes from 1000 to 2000. Always about the same temp range on the gauge.

Member of local Triumph group gave me the "choke" mechanism to put back on the rear carb. It won't actually do anything, but it is more attractive than the paper tape that currently covers the holes where something used to be.

For running/driving purposes, the car is back to "normal". Starts with little choke, idles fine (a little rough, but it is 37 years old), has power when stepping on gas. Will squeal the tires in 2nd and get to 60 MPH in 3rd. MUCH better than a couple of weeks ago.

MarvinM - 10927

subwoofer
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Sure you don't have a (major) vacuum leak somewhere? Brake servo, heater core vacuum valve, ignition retard? That would cause idle to rise when heating up.

Have you checked the throttle spindles for play? Could be that they leak around the seals, or that they flex so much that what position they land in when you let go the throttle is a bit of a guess?

--
Joachim

Last edited on 06-06-2009 09:18 am by subwoofer



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