TR4 ZS Carb Sync

[Todd]

I just rebuilt the ZS 175 CD carbs, adjusted the floats to 17.5 mm and am having a hard time synchronizing the carbs.  The rear carb remains lean.  I have attached links to two videos.  One at idle.  It seems to run OK at idle, but when I drive it (as the second video shows) it runs rough.   Any help would be appreciated.  Todd

 

 

[ctc77965o]

Todd,

For rough initial setup always adjust mixture in both carbs the same...only  when  tuning once it's already running well should you tweak individual carbs. 

Are you sure there's no vacuum leaks?

Is basic ignition timing set?

Is the idle hiss at both carbs same? 

Do both throttles open together?

If all these are ok, then is the choke operating as it should?  Not stuck half-on when you errrrm push the knob in?

After a short misfiring run what to spark plugs look like??

Edited January 3, 2020 by ctc77965o

[John Morrison]

Ho Todd,

welcome to our forum, and nice car by the way.

John.

[Todd]

On 1/2/2020 at 11:39 PM, John Morrison said:

Ho Todd,

welcome to our forum, and nice car by the way.

John.

 

On 1/2/2020 at 9:41 PM, ctc77965o said:

Todd,

For rough initial setup always adjust mixture in both carbs the same...only  when  tuning once it's already running well should you tweak individual carbs. 

Are you sure there's no vacuum leaks?

Is basic ignition timing set?

Is the idle hiss at both carbs same? 

Do both throttles open together?

If all these are ok, then is the choke operating as it should?  Not stuck half-on when you errrrm push the knob in?

After a short misfiring run what to spark plugs look like??

Thanks for the help. Attached is a photo of the plugs. Number 3 and 4 are fouled - Indicating a rich mixture. I just can’t get enough jet adjustment to lean it out properly. 

I readjusted the float in the rear carb to 17.5 mm (from 18.5) thinking it was starved of fuel. 

Since the car was running okay before I redid the carbs, I don’t want to mess with timing, valves, etc. until this is resolved. 

I have set the new needle shoulder to the base of the damper valve. Is that where you set yours?

I am wondering  why I feel no vacuum at the brass elbow (vacuum) fitting under the front carb? Maybe the passageway inside the front carb is blocked allowing no vacuum advance? 

Could that be why it runs okay at idle and poorly when under load?

BTW, carbs throttle and choke are set the same and I have using floating ball air volume tool to equalize the two carbs. 

[Andy303]

Todd:

Regarding the vacuum advance port not showing any vacuum at idle, that is as it should be as the drilling is blocked when the butterfly is closed. It only comes into operation when the throttle is open.

When you say that you rebuilt the carbs, did this include new throttle shafts and bushings? Your description of the problem is similar to one I experienced on my car where the front carb had a lot of play and wear on the throttle shaft resulting in air leaks and being near impossible to tune at idle. Using the usual technique it demanded more and more lowering of the jet meaning that it was far too rich under running conditions.

Another possibility, assuming you rebuilt the carbs off the car, is that there is an air leak on the manifold gasket(s) on that front carb incurred during re-installation. BTDT.

Edited January 5, 2020 by Andy303

[ctc77965o]

Hi Todd,

certainly seems like there something wrong with the rear carb... does your fuel pump have a manual priming lever? if yes, take the top, spring and piston/diaphragm out of the rear carb and then look at the jet whilst operating the fuel pump....no fuel should come out...you should just see the fuel sitting near the top of the jet. if it flows out then there something wrong with the float or needle valve. I dont know how the choke/enrichment works on a ZS CD, my experience only with the later CDSE2 - but on those its possible to fit the enrichment disk 180 degrees out and that will make it too rich.

Needles level with face of piston is a good starting point.

is the height of the jet relative to the bridge the same in both carbs?

[Todd]

22 hours ago, Andy303 said:

Todd:

Regarding the vacuum advance port not showing any vacuum at idle, that is as it should be as the drilling is blocked when the butterfly is closed. It only comes into operation when the throttle is open.

When you say that you rebuilt the carbs, did this include new throttle shafts and bushings? Your description of the problem is similar to one I experienced on my car where the front carb had a lot of play and wear on the throttle shaft resulting in air leaks and being near impossible to tune at idle. Using the usual technique it demanded more and more lowering of the jet meaning that it was far too rich under running conditions.

Another possibility, assuming you rebuilt the carbs off the car, is that there is an air leak on the manifold gasket(s) on that front carb incurred during re-installation. BTDT.

Thanks for the help. I did a complete carb kit from Moss - including the throttle spindles. They were very worn. I did not replace the bushings as this would require drilling the carbs. The spindle play is better - not perfect. 

I will recheck the intake to carb gasket on the front carb  The gasket is symmetrical except for a negative notch.  I am not sure why that is there. Thoughts? Thanks 

[Todd]

21 hours ago, ctc77965o said:

Hi Todd,

certainly seems like there something wrong with the rear carb... does your fuel pump have a manual priming lever? if yes, take the top, spring and piston/diaphragm out of the rear carb and then look at the jet whilst operating the fuel pump....no fuel should come out...you should just see the fuel sitting near the top of the jet. if it flows out then there something wrong with the float or needle valve. I dont know how the choke/enrichment works on a ZS CD, my experience only with the later CDSE2 - but on those its possible to fit the enrichment disk 180 degrees out and that will make it too rich.

Needles level with face of piston is a good starting point.

is the height of the jet relative to the bridge the same in both carbs?

Thanks for the help. No, my fuel pump does not have the lever. That would be nice. 

I start with the two jet adjusting screws in the same location - at the bone, but I have to back off the rear jet screw until the o-ring starts to leak fuel. That can’t be right.

Should I back off the jet bushing adjuster (the aluminum housing holding the jet adjusting screw) back more first?

Also, I don’t know what you mean by enrichment disk. I could have installed something backward. Is there another name for that? Thanks 

[ctc77965o]

Hi Todd,

Sorry i may be causing confusion, as said i only know a later design (adjustable needle) Stromberg.

This is the enrichment device of a 175CD2, from my jaguar 

 

Have you got some pic or exploded diagram of the parts you are talking about? its an adjustable jet design, and you are saying the jets are at different heights?

 

[Andy303]

Todd:

The 175CD carbs found on our TRs do not have an enrichment disc, but use a simple bar to lift the air valve when the choke is applied.

Attached are extracts from the Owner's Handbook for reference.

You should not touch the jet bushing (Item 12) to adjust the jet height - only the knurled/slotted knob of the jet adjustment screw on the very bottom (Item 13). The starting setting is to run this up until the jet is flush with the bridge (or bone as you called it) and then down 3 full turns. If there is fuel leaking around the jet adjustment screw then the o-ring is damaged and must be replaced.

The bushing you mentioned (Item 12) is only to b disturbed if you have to make an adjustment for centering the needle. This is explained in the attachment. The air valve when lifted should drop back without any binding. Ideally both carbs should have the same drop.

TR4-Stromberg-Adjust.pdf

[stillp]

Todd, you said "The rear carb remains lean" but the photo of the plugs shows the rear plugs sooty, suggesting a rich mixture?

Pete

[Andy303]

Here is another manual that may be helpful.

Regarding the throttle spindles, the bushing in the carb body can also wear to the point that even with new spindles there is still too much air getting by. With the engine running try spraying carb cleaner or WD40 on the bushing and see if the RPMs change. I believe that .005  clearance is the maximum wear. I replaced my old Strombergs with new Burlen SU HS6 and out of curiousity I measured the new ones and found the play to be in the range of .002 to .003 with a dial indicator, which is the factory allowance. Even with this there is small amount there is a slight, detectable "wiggle".

tuning_stromberg_cd_carburetters.pdf

[dingle]

Another culprit could be a split or hole in the diaphragm. It will cause a rich mixture. Also, make sure the jets are centered and that the pistons rise in unison, 

Berry