carberator

I just finished putting kits in both carberators. When I started to make the initial adjustments I found that Bentley does not address my model. It looks as if the early carbs do not use the adjustment tool and they do not have the deceleration adjustment.

What is the proper way to adjust the mixture etc.? The only adjustments that I see are for the fast idle, choke and what Bentley calls the trim screw. I assume that the trim screw adjusts the mixture?

BTW the commission number is CC25632L

Thanks, Pete

Pete, sounds like you may have the early CD with an adjustable jet as opposed to the adjustable needle. If it is LUCKY YOU! The jet is adjustable by a "screw" at the very bottom of the float chamber.And this is the best part, you will be able to adjust mixture with the engine running, like the SU carbs.
Turning the screw into the carb will raise the jet and lean the mixture.
If you have temperature compensators, the idle trim screw taps into the air coming into that port. And it's actual effect on mixture is minimal and just about undetectable without a C/O meter.
Here's the thing, though; I believe that the jet adjustable carbs did not have the temp. comp's.
So I am somewhat puzzled.
Any chance you could post a picture or 2 ?

Is that the large screw at the bottom of the float chamber?
I think I have them turned all the way in. I do not think my car has the temp. compensator.

I do not have a picture.

Thanks, Pete

BTW my car is green now.

Yes, that's the adjustment. 1 1/2 turns down from full up (lean) may prove to be a good starting point.

Don't want to rain on anyone's parade ... but I believe TR250 and early TR6 had NO main mixture adjustment. Fixed needle plus fixed jet. The "trim" screw has only a minor effect, and only at idle. The "large screw" in the float chamber is just a plug.

Many folk upgrade to the later adjustable needle configuration, though.

I guess the way to tell for sure without my seeing the carb would be for you to examine at the object in question.
If the screw appears to be just below and screwed into a "nut like" object then it is an adjustable jet carb.

According to the Bentley Manual and the owners manual that I have the carbs are Stromberg 175CDSE. The screw at the bottom of the float bowl is about 1/2 to 5/8 diameter and screws directly in to the float bowl.

I talked to tech help at TRF and was told that these are factory set and should not be adjusted. To bad!! I have had them out to replace the 'O' ring.

When it warms up so that I can open the garage door I will try adjusting these screws.

Thanks, Pete

TR3driver said:

Don't want to rain on anyone's parade ... but I believe TR250 and early TR6 had NO main mixture adjustment. Fixed needle plus fixed jet. The "trim" screw has only a minor effect, and only at idle. The "large screw" in the float chamber is just a plug.

Many folk upgrade to the later adjustable needle configuration, though.

Click to expand...

TR3driver is quite correct - there is no adjustment on the TR250/Early TR6 ZS carbs. Adjusting the lower nut will just cause the carb to leak. There is an idle mixture trim screw on the right side of the carb (I think), but this is supposed to be used for "running in" only, and should be screwed down. And there is the bi-metal temp compensator behind the plastic cover on the same side - but probably best to leave that alone.

One thing that can affect how the carbs run is the damper fluid you use. Try experimenting with different viscosities and see what works best. I use 20W50 in the TR, and auto transmission fluid in the Lotus (about 20W I think?), which also has ZSs. But depending on how your engine is set up, you may get better results from something else.

Also - I'm sure you've done this - but they need to be balanced too. I have one of those plastic "velocemeter" gauges which work great. Much better than the silly "floating pea" setup.

Hope that helps,

Rob

I got the car warmed up yesterday and balanced the carbs using the low idle screws. I have it idling about 1000rpm but it is not smooth at all.

I have Pertronix ignition and I have adjusted the valves. I have tried adjusting the ignition timing to get the idle smoothed out. I don't know exactly what the timing is on now because my timing light died. I found earlier that the timing light did not help much anyway. I just adjusted the timing so that it ran well and did not ping.

Any more suggestions appreciated, Pete

With the aircleaner removed. Engine off. take your finger and lift up the piston in the carburetor appx. 1/2 inch.

compare resistances between the two carbs. How much pressure difference was felt? They should be the same. If not a problem.

Another recommendation is to remove the top, pull out the piston and with a bright light and magnifying glass search the diaphragm for cracks, tears, etc. This is an often overlooked problem that occurs with rubber diaphragms as they get old.

Have you hunted around for vacuum leaks ? A leaking brake booster can spoil your idle quality. So can a leaking vacuum retard module.

You can momentarily alter the mixture by pushing up or down on the carb piston. Just removing and inserting the damper plunger should make it run rich for a second (while it's going in).

It should NOT be necessary, but here's a link to an article on how to convert to adjustable needles :
https://www.buckeyetriumphs.org/technical/Carbs/AdjNeedle/AdjNeedle.htm
But IMO it would be easier (and likely just as cost-effective) to pick up a pair of decrepit later carbs on eBay and use the pistons, needles & adjusters from them (after changing the O-ring of course).