TR2/3/3A Choking the TR3

[Jim Lee]

Hope all are well at the start of the holiday season.

I am looking very closely at the choke linkage and beginning to think that much of what I thought were hard starting problems were actually due to the 50+ year old choke linkage not working as planned. I have my choke working right now, as far as I can tell, but I am just wondering if others with more choking experience than I might have suggestions for me, conventional or otherwise.

The part on my buggy that is most obviously in need of attention is right at the meeting of the cable with the bottom of the forward carb. Right now it is attached with a jury rigged deal that I hope to show you below. It involves alot of washers and a cotter pin using a version of a bolt that I believe is either to small for the linkage opening or I am missing some Anglican hardware that went down in my, or a previous owners, Davy Jones Driveway Locker years ago.

I think that what was happening was the I was not getting enough 'pull' on that very bottom of the carb linkage up front. I was just outside messing around with it and it appears that you really need to pull firmly against the spring that holds it back. I believe that my setup was pulling but not pulling far enough to actually lower the jet, assuming I am correct in that this is what needs to be done to start a rock cold engine (in the almost winter that we have here in North Carolina). You folks up North probably have a wealth of information on starting very, very cold. In any case here is a picture of what the bottom of my forward carb looks like, first without the choke pulled and then with the choke pulled fully. I don't expect anyone to run out and examine the same scene on yours but if I could get your opinions on whether it looks like my cable is pulling enough I would really appreciate it. I will also try to include the ridiculous attachment of the cable to the linkage that I currently have and am open to any suggestions on that.

Thanks very much,
Jim Lee

 

[Banjo]

Doesn't look too bad from here. Making sure all pins and pivots are present and in good shape is important. Also adjust the connector rod to give equal "activation" of the jets. the best way to tell if it's moving far enough is to try and start it in the cold. In my experience, well trimmed SUs on a well sorted and adjusted motor, will start an engine remarkably easily in even the coldest conditions. They may be cold blooded, and like the choke left on for a bit while things come up to temp, but it should start fairly easily.

 

[Perrymip]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]The choke link between the carbs is NOT supposed to straddle the levers. Instead, both legs of the link go behind the levers. I know this sound strange, but it really does work better that way.[/QUOTE]

This description above is from <span style="font-style: italic">TR3driver</span> and is located with an image here.

 

[Geo Hahn]

If I'm looking at that last pic right it looks like quite a bit of slack between the clamp and the arm. I think this should be more or less taut, maybe even a touch of pre-load on the linkage to the rear carb to take up some of the inevitable slop in the connections.

The arrangement of the yokes on the arms is counter-intuitive (and not like you have it). Prior posts have shown a pic taken from the Practical Hints manual. OTOH, I'm not convinced that the official TR way is always the best here and you may want to experiment with the combination of yoke positions that give you best movement w/o binding. This will be clearer when you have seen the picture.

 

[TR3driver]

Looks to me like you are getting plenty of movement at the jet, Jim. As long as you can pull it that far with the knob, and both jets return to their full up position when you release the knob, then I would say that the remainder of the linkage is probably "close enough".

That said, mine is arranged so that the main lever will pull back to parallel with the cable support, and yours isn't coming back that far. As Geo says, maybe you need to tighten up the cable a bit.

However, I would double-check that the rear jet is coming down by the same amount.

Also, if you think that not enough choke is your starting problem, it is easy enough to experiment by unclipping the spring from the lever. Then you can set both jets to wherever you want them, and they will stay there. Obviously you don't want to run the engine that way for more than a few seconds, it's only a test.

 

[bigjones]

The way I got the choke to finally work is as follows:

1. Under the hood, undo the <span style="font-weight: bold">screw </span>that holds the inner choke wire to the carb linkage.
2. From the cockpit, pull out the choke to the 2nd notch (or equivalent)
3. Under the hood, push the linkage until you see the jets fully extended.
4. Tighten the <span style="font-weight: bold">screw</span>.
5. From the cockpit, set the choke to the 1st notch (or equivalent)
6. With the cold engine running, and the idle screw totally backed off, adjust the fast idle screw to give say 1000 rpm.
7. With the engine fully warmed up (takes a while!) adjust the idle screw to say 600 rpm.

I'm just a few miles north of you (getting cold isn't it!) but the beast fired up first thing this morning. Don't settle for anything less. There is nothing worse than cranking and cranking. Nothing better than an instant response. Keep at it!

Good luck!

 

[Jim Lee]

Between steps 6 and 7 I am returning the choke to its full forward (normal) position right?

Thanks,
Jim Lee

 

[bigjones]

Quite right, Jim. Sorry for confusion.

 

[Mkutz]

Yes, make sure the fast idle is properly set up.

Also, check the float bowl level to make sure this is correct too. The way the enrichment of the choke works is that the top of the jet tube is pulled down which allows the area to pool with raw gasoline. If the float level is too low, then you might not have enough pooling, thus creating too lean a condition at start up.

Lastly, see how far the top of the jet tubes drop down, when looking in the venturi area of the carb, while the choke is engaged. You'll have to lift the piston up to get a clear view. The reason I bring this up is that my carbs were rebuilt last year and the rebuilder used two different length jet tubes when he did so. So, the tube on the front was 1/16" shorter than the tube on the back carb. The effect of this was that the front carb was running excessivley rich, and could not be leaned out to an appropriate degree. So, if you carbs have been the recipients of jim crack repairs over the years, and have a hodge podge assembly of wrong parts, then this might be worth a look. The remedy would be to use genuine SU jet tubes, period. You might just want to replace the tubes and the jet bearing kit to make sure everything is properly spaced as it should be.