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View Full Version : Settting up the Choke on Strombergs?



TR4
03-29-2012, 11:57 AM
I had my 64 Strombergs professionally rebuilt and am in the process of tuning them. I feel that I have the air balanced and fuel set very close to perfect. The motor runs very well and the plugs show good color. I am experiencing difficulty in setting the choke though. When the motor is cold, I pull out the choke and it will start right up but will sputter and chug until the motor warms up and I push the choke back in. Then all is well and it runs great. Can someone tell me how to properly set up the choke? The place that rebuilt the carbs tells me the mixture is too rich and the choke needs to be set up leaner. With Stromberg carbs, I'm not sure how to do that. This is for a TR4 with dual carbs.

sd80mac7204
03-29-2012, 12:04 PM
Phil, Try only pulling your choke out part way and see if you engine responds better.

poolboy
03-29-2012, 12:11 PM
With the engine stone cold and low ambient temp., pulling the choke knob all the way out should start the engine at about 11-1200 rpms.
If it's set in that range, once the engine starts to gradually warm up, gradually push the choke knob into the dash accordingly.
Depending on the ambient temperature you may not need full choke..like sd said

TR4
03-29-2012, 12:22 PM
I have tried to use less choke but still get sputtering and chugging. The RPM's do not rise at all with the choke pulled. The motor barely keeps running but when it warms up, it will run smooth.

DNK
03-29-2012, 12:26 PM
Doesn't sound like the choke is working correctly
Have you observed the choke lever as it has been pulled?
Is there any change when you pull the choke

sd80mac7204
03-29-2012, 12:27 PM
Will the engine start with no choke?

TR4
03-29-2012, 12:36 PM
Engine will not start without pulling the choke out.
When I pull the choke knob, the choke spindles rotate as designed and the throttle is increased.

TR3driver
03-29-2012, 01:52 PM
The RPM's do not rise at all with the choke pulled.
That would be the "fast idle" adjustment. For some reason it's not covered in the workshop manual I have handy; but on the front carb (I think) there should be a screw sticking out of the throttle lever, which rides on a cam when the choke is pulled. Loosen the locknut and turn the screw out to raise the fast idle rpm. IIRC, it should be set to supply around 1200 rpm with the engine warm and the choke pulled only enough to start the fast idle without moving the starter bar in the carb throat (first notch).

It's also normal to need more choke for easy starting, and then back it off in stages as the engine warms up. I prefer to err on the lean side (use the least choke that will keep the engine running), because excess fuel can wash away the oil film in the cylinder and promote rapid piston ring wear.

Also check that both starter bars are moving together. Sometimes those folded metal clamps can slip without being obviously loose. I don't know if the TR4 is the same, but on the TR3 the bolts in those clamps take a BA wrench rather than SAE (or a small crescent wrench will work).

Geo Hahn
03-29-2012, 02:49 PM
...IIRC, it should be set to supply around 1200 rpm with the engine warm and the choke pulled only enough to start the fast idle without moving the starter bar in the carb throat (first notch)...

On mine the starter bar moves first and immediately -- I see no way to avoid this as the shaft of the starter bar has the cam which operate the throttle shaft.

The screw described can be adjusted to slightly delay the butterfly movement though on mine I've got it set to move the throttle almost immediately.

I seem to recall there is a spec for clearance between the screw and cam though with worn parts and vagaries in engines it may be a case of 'whatever seems to work'.

TR4
03-29-2012, 03:24 PM
My starter bar moves first and immediately as well.

Sounds like I should try to depress the gas pedal during start up to see if that will affect the rpms.

If so, then I should be able to simply adjust the screw for the fast idle cam.

DNK
03-29-2012, 03:26 PM
Always helpful to step on the gas slightly as you pull as it takes some tension (for bettor words) off the cable

poolboy
03-29-2012, 03:41 PM
Only when pulling the cable though. I wouldn't use the accelerator pedal again until after the engine actually starts, not during the cranking because you'll be leaning out the starting mixture if you do.
The clearance between the head of the fast idle screw and the fast idle cam is usually about 1/4--5/16 when the choke is off. But make it whatever it takes so that the throttle opens enough to make the engine idle 11-1200 when the choke knob is pulled out all the way on a cold engine..
All this assumes the choke cable is attached to the fast idle cam correctly.

TR3driver
03-29-2012, 03:46 PM
On mine the starter bar moves first and immediately -- I see no way to avoid this as the shaft of the starter bar has the cam which operate the throttle shaft.

Ok, my mistake. I was thinking of the arrangement on the later ZS carbs, which don't even have a starter bar (and lost motion in the linkage so you can get fast idle without changing the mixture).

But the idle should still be coming up.

TR4
03-29-2012, 03:50 PM
I agree, the idle should rise. If I don't have luck with depressing the gas pedal, I believe I will try to screw in the fuel adjustment to see if leaning out the carbs has an affect.

At least I have 2 options to try this evening. Thanks for all the input. It sure helps to get a plan of action.

TR4
03-29-2012, 05:36 PM
Reporting my efforts. I tried to work the gas pedal but that failed to help at all so I turned the fuel adjustment screws in 1 full turn each and presto, the choke works like a champ again. So it appears the carbs may indeed have been set too rich. Now, I think I'll back those adjustment screws back out until I get a balance between the choke working and the fuel flowing like it should.

glemon
03-29-2012, 06:42 PM
I have been going through the same thing setting my TR4 Strombergs, if they all work the same, then in addition to the adjustment to the fast idle screw on the choke cam, there is also a low tension spring that works to pull the choke adjustment as you pull the choke cable, at first I thought this was just a return spring, but I believe, and it appears that the spring tension affects the relationship between throttle opening and choke opening, when I was experiencing the same problem changing from a firmer replacement spring to the old spring I had thought of as worn out helped with the balance between throttle and choke on start up and cold idle.

I also leaned out the mixture a little as you did after reading the plugs, and that helped too.