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Zenith Stromberg CD 175 Too rich

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houleyh

Senior Member
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My carbs are allways too rich (CD 175 - TR?). Is the Jet adjustables on thoses. They are recessed about 0.100" into the carb housing and getting them higher whould help leaning the mixture?

Your toughts

Thanks

Yvan Houle
 
As Paul says above, you adjust the mixture using a special allen wrench through the top of the damper (remove the plastic nut and damper piston first.
Turning the wrench (clockwise I think) serves to lower the needle (connected to the air valve) further into the fixed jet thereby leaning out the mixture for all speed/throttle ranges.
 
Tanks guys. That goes foe the needle. What about the jet? Can it be adjusted upward? The needle does'nt seem to go low enough and disengage.

Thanks
 
No, I don't believe you can adjust the main jet in a ZS carb. All the adjustment is with the needle. If I remember correctly, the jet is machined into the body of the carb so it's not even replaceable if damaged.
 
Not all ZS carbs are adjustable though - some have a fixed needle and you need to swap the needle to adjust the mixture. You might want to check this before ordering the adjustment tool. Perhaps the easiest way is to pop the top cover off (4 screws) and lift out the spring/damper/diaphram (sounds like you may have already done this) and use a regular allen key of the correct size down in to the piston/damper shaft to adjust the needle up and down.

A note of caution - if the carb is of the adjustable type, and you adjust the needle to far lean (i.e. down out of the damper body) it will disengage from the adjusting screw, and you cannot adjust it back up. If this happens, just gently push the needle back while turning the adjusting screw clockwise (rich).

I've found a good starting point is to have the shilder of the needle flush with the body (this is about 1-turn down from max. rich, and about half the two-turns of full adjustment on these carbs)

Also check the diaphram for tears and make sure the damper moves freely when reassembled etc.

Rob.
 
Although not intended to be adjustable, the jet will move if you put enough force on it. IMO it shouldn't be necessary though, unless there is something else wrong.

I once fought overheating problems on a TR3A for a long time that eventually turned out to be worn jets. Had SU carbs so not the same as your ZS; but similar. With both carbs, the mixture adjustment actually affects the entire range. So, if some other factor is making it idle rich; and you lean out the jet/needle to correct the idle; the cruise mixture will now be too lean and potentially cause problems. On my Dad's TR3A, it cost him an engine rebuild when the lean mixture finally eroded a valve stem enough to break.
 
Yvan, let me jump in hear and maybe give you another thing to look at. When replaceing the choke cable in past years, someone may not have done it right. Undo the small bolt at the end of the cables on the carb and pull down on the choke body and see if it moves lower. I have found this problem in many a rich running car. Hope it works that easy.

Wayne
 
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