SU choke question

[foster461]

It has been many years since I had a car with SU carbs and my understanding was that the cold start mechanism works by pulling the jets down. My TR3 is a pig to start when cold. It starts instantly if I give it a quick shot from a can of instant start and once warmed up it starts at the press of the starter button.

 

While the choke cable seems to be moving the levers under the carbs I'm not seeing any movement of the jet and I wonder if this is the cause of my cold start issues. Should I see any movement of the choke assembly under the carbs when I operate the choke or is there some internal thing going on that cant be seen ?

 

Stan

[John McIver]

Hi Stan,

You should certainly see movement of the jets when the cable is pulled. The cable should be adjusted so that there is just enough end play for the jets to return fully, about 1/16" to 1/8" is sufficient. Three clicks of the knob shaft pulls the jets down enough for a quick start from cold if the bowls are full.

Regards,

John

[TS528L]

Yes, pulling the choke cable should first increase idle speed, and then lower the jets to increase fuel mixture for cold start. If the holes in the brass levers are worn (a lot), they will not lower the jets sufficiently to enrich the fuel mixture for cold start. Maybe the jets are stuck in brass jet bearing.

 

Gunnar

[stuart]

Usual problem is wear in the eyes of the levers and the clevis pins and as has already been mentioned the jets sticking in the sleeves. Freeing up the jets will probably result in the gland seals leaking though,

Stuart.

PS Dont keep using the easystart spray as they get addicted to it!!

[Alec Pringle]

"Dont keep using the easystart spray as they get addicted to it!!"

 

So do the owners . . . . . faaaaar out, man . . .

 

Cheers,

 

Alec

[foster461]

ok, thanks guys. Armed with this information I can now report that:

 

1. The cable was adjusted such that its entire travel was taken up by the linkage.

2. With the cable and connecting bar disconnected I can operate the cold start but boy those springs are stiff. I do observe the jets lowering though.

3. The jet on the rear carb does not return voluntarily despite the spring, possible a condition exacerbated by...

4. ...The pivot holes are about twice the diameter of the pins so in addition to creating more slop the geometry may be off.

 

I'll mess with it some more and if I am still puzzled I'll post some pictures to get further clarification. I'm pretty sure this is the root of my cold starting issues but I'll have to wean it off the spray can.

 

Stan

[foster461]

Here is a shot of the choke linkage from the rear carb. The front is pretty much the same. This lever pivots around the large hole. There is a pin (also shown) that goes through it that is a little worn but is sized correctly for the linkage that is attached to this lever. The hole is three times the diameter of the pin but the hole looks too round to have been worn to this diameter so I am assuming this large hole is by design unless someone tells me otherwise...

 

[nickthepedal]

Stan

My 3A was a bit of a pain to start from cold.

 

However after my carb refurb exercise she starts first press of the button now.

 

Prior to my replacing all the internal seals and giving everything a damn good clean the jets really did not move a deal when operating the choke. They now both pull down in a smooth fashion much further than they ever did and return in the same way. I reckon they were sticking in the bearing due to being a bit on the mucky side.

 

Replacing the seals etc was not too tricky, even I managed it.

 

Cheers.

 

Nick.

[Don Elliott]

Stan - Did you know that with the gear in neutral, the handbrake on and the key turned on, that you can start a TR3A standing looking at the carbs, merely by pressing the rubber plunger button on the rear of your starter solenoid ?

 

This way, you can manually try pushing the choke bars rearward to see if it might tell you something.

[foster461]

Stan - Did you know that with the gear in neutral, the handbrake on and the key turned on, that you can start a TR3A standing looking at the carbs, merely by pressing the rubber plunger button on the rear of your starter solenoid ?

 

This way, you can manually try pushing the choke bars rearward to see if it might tell you something.

 

 

Hi Don, yes I'm familiar with the solenoid and its many handy uses. I made use of it last night in fact as I was trying to locate the timing hole in the pulley.

After all the great info I went back and reconfigured the cold start mechanism. Since the jet on the rear carb was still sticking I chose to enable the cold start on the front carb only and this morning it started instantly from cold despite the below freezing temperature. I also checked the timing and balanced the carbs (a lot easier than the 3xdcoe's on my TR6..) and it starts and runs very nicely although it does sound like a tractor idling in the driveway.

 

Stan

[pfenlon]

Hi Don, yes I'm familiar with the solenoid and its many handy uses. I made use of it last night in fact as I was trying to locate the timing hole in the pulley.

After all the great info I went back and reconfigured the cold start mechanism. Since the jet on the rear carb was still sticking I chose to enable the cold start on the front carb only and this morning it started instantly from cold despite the below freezing temperature. I also checked the timing and balanced the carbs (a lot easier than the 3xdcoe's on my TR6..) and it starts and runs very nicely although it does sound like a tractor idling in the driveway.

 

Stan

 

 

Stan, I dissconnected the linkage between both carbs on my TR3A, and the cable then only had to work on 1 carb only, started first time every time just with Choke on 1 carb, less strain on the whole system, worked for me.

[Don Elliott]

Peter - I've heard that too but have never needed to resort to that as I didn't have a problem with both chokes connected.

 

Stan - I looked at your photo and then I checked the same part under my rear carb. I didn't remove the pin but just pushing backwards on the lower end of the brass part you show, I would estimate that the hole in mine is about the same diameter. It's original and I have not drilled it any larger so I consider it to be "as original" - for all the times I had to use the choke in more than 52 years. I would guess that I pulled the choke cable and moved that part somewhere between 3,000 to 10,000 times. I can't believe that it would wear by pulling. If you could see wear, it would have made a slot or an oval hole, not perfectly round.

 

Edit - I forgot to mention that the temperature in the early afternoon here (Montreal) for the last week or so has been about 10 deg. C (50 deg.F) and I have been out and about with the top down almost every afternoon. It normally should be a daily high of 2 deg. C (36 deg. F) at this time of the year. Thank you for global warming or whatever is doing this. Makes life more pleasant.

Edited November 14, 2010 by Don Elliott

[foster461]

Peter - I've heard that too but have never needed to resort to that as I didn't have a problem with both chokes connected.

 

Stan - I looked at your photo and then I checked the same part under my rear carb. I didn't remove the pin but just pushing backwards on the lower end of the brass part you show, I would estimate that the hole in mine is about the same diameter. It's original and I have not drilled it any larger so I consider it to be "as original" - for all the times I had to use the choke in more than 52 years. I would guess that I pulled the choke cable and moved that part somewhere between 3,000 to 10,000 times. I can't believe that it would wear by pulling. If you could see wear, it would have made a slot or an oval hole, not perfectly round.

 

Edit - I forgot to mention that the temperature in the early afternoon here (Montreal) for the last week or so has been about 10 deg. C (50 deg.F) and I have been out and about with the top down almost every afternoon. It normally should be a daily high of 2 deg. C (36 deg. F) at this time of the year. Thank you for global warming or whatever is doing this. Makes life more pleasant.

 

 

Thanks for the confirmation of the lever hole Don. I will rebuild the carbs this winter when I pull the motor and get both cold start mechanisms to work properly. I wouldn't get too confident re the weather, it will be winter conditions eventually and usually sooner rather than later.

 

Stan

[whiteone]

I have heard it said before that cars become addicted to Easy Start!

I have three questions:

(1) Why ?

(2) How ?

(3) Could it just be that the engine will only start using Easy Start until an underlying fault (or faults) is corrected ?

Here's a good topic for discussion !