TR2/3/3A Carb Idle Question

Rebuilt my SU's about six months ago on my '58 TR3A. The rebuild included new throttle shafts. Having an issue after using the throttle. The engine will idle at about 500 rpm or more higher. So does not return back to the 900 RPM level. I disconnected the throttle linkage to the carbs, disconnected the link between carbs, and still have the high RPM problem. I can "lift" or pull back the the throttle shaft arm on the right carb and the idle will return to 900 RPM which is what I am looking for.

My plan is to pull off the carbs and check the fitting and placement of the butterfly valve. I am thinking the issue is with the fit being off. Please note the throttle shaft on the carb body was not reamed. My understanding is that if there is a gap, the idle will vary. This is not the issue I am dealing with. The issue is with a higher RPM. The RPM does stay constant. Just does not return back to the 900 RPM but rather stays at about 1400 RPM or slightly higher.

Any recommendations on what to look for to resolve is much appreciated.

The TR3 throttle linkage pulls down pretty hard on the front shaft, which causes it to wear the most at that point. When the shaft deflects down, the throttle plate drags on the bore, causing it to stick open a bit.

Might not be your problem, but something to look for. It's happened to me several times.

When I go the 2 back on the road I was a bit bummed that I had the same issue. I could set the idle to a perfect 750 when tinkering, but driving it would tend to remain over 1000 unless I pulled the pedal up with my toe. This is with new carb shafts, new throttle bushings, and the entire throttle geometry set spot on. My point being nothing was worn out or binding at all.

I decided to loosen the clamp for the axial spring on the front of the front carb shaft and increase the spring tension. An extra 180 degrees of tension is all it took. Now the idle is a rock solid 750, no matter how I come off the gas. So- just a thought. If everything else checks out, the axial spring is really easy to tighten until you get a solid idle.

I am thinking this is the issue. If I want to fix, do I need to have the carb body reamed and a bushing inserted?

TR3driver said:

The TR3 throttle linkage pulls down pretty hard on the front shaft, which causes it to wear the most at that point. When the shaft deflects down, the throttle plate drags on the bore, causing it to stick open a bit.

Might not be your problem, but something to look for. It's happened to me several times.

Click to expand...

Nice set up John. You did all the updates. I tried to get by with just new throttle shafts. I think I will need new throttle bushings on the front or right carb. Can I ask who you used to get this done?

Thanks,

CJD said:

When I go the 2 back on the road I was a bit bummed that I had the same issue. I could set the idle to a perfect 750 when tinkering, but driving it would tend to remain over 1000 unless I pulled the pedal up with my toe. This is with new carb shafts, new throttle bushings, and the entire throttle geometry set spot on. My point being nothing was worn out or binding at all.

I decided to loosen the clamp for the axial spring on the front of the front carb shaft and increase the spring tension. An extra 180 degrees of tension is all it took. Now the idle is a rock solid 750, no matter how I come off the gas. So- just a thought. If everything else checks out, the axial spring is really easy to tighten until you get a solid idle.

Click to expand...

FWIW, I did my own using the same basic technique outlined at https://www.chicagolandmgclub.com/driveline00/1001/jasw.html

ENCO is no more (bought out by MSC), so you may have to do a little research to find the required reamer; but it shouldn't be too hard. This one looks like it might work, but double-check dimensions with the vendor before ordering. It's important that the shank be 5/16" all the way.
https://www.fastenal.com/products/details/360112-131588

I didn't use a nut to drive it, though, just mounted the other end in my drill press, locked the quill and pulled down against the blade part of the reamer.

Randall,

Thanks for the research and the helpful tip for reaming and using a bushing.

TR3driver said:

FWIW, I did my own using the same basic technique outlined at https://www.chicagolandmgclub.com/driveline00/1001/jasw.html

ENCO is no more (bought out by MSC), so you may have to do a little research to find the required reamer; but it shouldn't be too hard. This one looks like it might work, but double-check dimensions with the vendor before ordering. It's important that the shank be 5/16" all the way.
https://www.fastenal.com/products/details/360112-131588

I didn't use a nut to drive it, though, just mounted the other end in my drill press, locked the quill and pulled down against the blade part of the reamer.

Click to expand...