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TR4/4A TR4 Stromberg Carb. adjustment


Jedi Warrior
Country flag
My TR4 runs and starts beautfully with the choke on, but the moment the choke is pushed in (even after the engine is warm) the car stutters and dies. I bought a Color Tune plug to help me adjust the carbs, but if I can't get the engine to idle without the choke were do I begin? The carbs. have been professionally rebuilt.


Jedi Trainee
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OK, try turning the jet adjustment knob one or two turns down (rich) and see what happens. You have synchronised the butterflies and the choke right? You might also have the idle speed too low, mine likes to idle at 800 to 9oo RPM indicated. /bcforum/images/%%GRAEMLIN_URL%%/savewave.gif


Jedi Knight
As stated above, you should try to set the idle up first. Your carbs being professionally rebuilt would likely have been bench tested and the adjustment screws set close to what is needed. For adjusting the fuel mix, counter clockwise on the adjustment screw will enrich the carbs. Clockwise will make them leaner.


Country flag
Hi Larry, sounds like she is too lean.

Are you running SU or ZS carbs?

ZS would have been original. What model ZS?

Depending upon which ZS carb you have the mixture adjusted via a special mixture tool through the top where the damper screws into the top.

Here are a good link for the ZS carbs,



Jedi Hopeful
Hi Larry, If the car is idling ok with the choke you have two things to check, the mixture and idle adjustment. When the choke is on, the mixture is made richer and the fast idle assembly is opening the throttle discs more. I would adjust both carbs idle adjustment screws a quarter turn at a time, until you get the idle RPM's you want. The jet adjustment for mixture should be close as the carbs were just rebuilt. The colortune will tell you what you need to do to set the correct mixture. Remember that your idle mixture is a combination of jet position and throttle opening so you may have to adjust both to get it correct.


Luke Skywalker
Hi Larry,

Check for air leaks, too. A small one or two might lean out the mixture radically, beyond the adjustment range of the carbs, yet still allow the car to run when enriched by the choke.

Must be nice hearing it run, even if not for very long! I'm jealous!


Jedi Trainee
Country flag
"By jet adjustment knob, do you mean the mixture adjusting screw on the bottom of the carbs? and to richen the mixture do I screw in (clockwise) is this what you mean by down?"

Yes that is the screw/knob I mean. Looking up at the botton of the carb, if you turn the screw/knob clockwise you will lean out the mixture, In your case you will want to turn the screw/knob counterclockwise to richen up the mixture.

But first make sure your idle speed setting isn't too low. When the choke is on, there is a fast idle cam that speeds up the idle. See if reseting the idle speed doesn't solve your problem. To speed up the idle you will turn each idle screw an equal amount in a clockwise direction.

Then if that doesn't help, set your mixture by the book, in other words lifting the piston a small amount and seeing what the engine does. You do have a manual right? or do you need further help?. /bcforum/images/%%GRAEMLIN_URL%%/smile.gif


Jedi Warrior
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I backed out the fuel mixture screws two turn (richer), adjusted the idle, rechecked the flow and used my Colortune. Its running and idling great! I took it up the street and got into second gear. /bcforum/images/%%GRAEMLIN_URL%%/smile.gif

I'm not sure if its perfect, but I know I'm really close if not. This was the first time that I've tried Colortune. The best I could get the color was blue with an occasional flash of white. I didn't use the copper washer that was suppied with Colortune and suspect that this might have been an issue.


Jedi Hopeful
Larry, Blue with an occasional flash of white is pretty darn close.


Luke Skywalker
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TDSkip, thanks for posting this site. I haven't dived into my carbs yet on my '74, but this will be most helpful... many thanks!
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