TR2/3/3A Centering The Jet

[frankfast]

Recently having trouble with RPMs settling down to idle and plugs being rich and am suspicious things are sticking so I ordered an SU tool kit from Moss. I followed the centering jet instructions by using the centering pin in place of the needle. I backed off the jet as far as it would go and slackened off the lock nut. The centering pin fit into the bearing and the piston moved up and down freely. But every time I tightened the lock nut the centering pin would ride up and when the lock nut was tight the piston wouldn't move. I did this multiple times with the same result. After loosening the lock nut the centering pin would then bottom out again and the piston would move freely. Not sure if I'm doing some thing wrong here or if there is a trick involved using this kit. Instructions are minimal.

 

[Rhodyspit75]

Are these instructions any help? https://mossmotors.com/media/instructions/386-500_INST.pdf

 

[Snowkilts]

Tom Bryant has a series of blog posts covering all aspects of SU carb rebuilding. I've found them very helpful.

https://thosbryant.wordpress.com/2014/01/02/su-carburetor-rebuilding-hs-6/

 

[frankfast]

Anybody familiar with this kit?

 

[Snowkilts]

From Tom Bryant's blog:

"There are special tools for this job, but don’t bother to buy one; they don’t work. You can’t get a better centering tool than the actual jet and needle pair to be mated to one another. Commercial centering tools can only introduce another layer of inaccuracy into the equation, resulting in alignment that can never be better than using the actual parts, and is often a lot worse."

 

[Sarastro]

Centering that jet can be a real pain. I think the problem is this: as you tighten it, especially in an old carb, the parts tend to slide into old wear areas. One thing I've found that helps--move the jet around a bit so the old wear areas are no longer matched, and often that will help. Then tighten the jet GENTLY and check repeatedly as you do it. If it starts to bind, back off a bit, move the jet, and start again.

I agree, you really don't need any special tooling, and in fact it might make the job harder.

 

[frankfast]

Yea, I gave up with the centering tool that came with the kit and went back to the instructions in the manual. It looks like I got it it pretty good. The slide doesn't bind and bottoms out with a good thud. Haven't started it yet. Have to get some oil for the pots and sync the carbs but I think I've solved the centering issue. Don't think this kit is worth the money.

 

[titanic]

I have always had success by starting with the adj. nut all the way up, loosen gland nut, slowly tighten gland nut while lifting&dropping piston. If piston doesn't hit bridge with audible click, loosen glad nut and lightly tap jet assembly from the side&tighten. Repeat procedure until click is heard. It takes far less time to do the procedure than describe it.
Berry

 

[frankfast]

That's exactly what I did.

 

[CJD]

Also...don’t try to crank the nut down. Just past snugg is enough if your seals are serviceable.

 

[titanic]

Also...don’t try to crank the nut down. Just past snugg is enough if your seals are serviceable.

I found out (the hard way) that unless the big cork seal is fully compressed, it will be impossible to get the jet high enough to get the mixture lean enough.
Berry

 

[CJD]

I found out (the hard way) that unless the big cork seal is fully compressed, it will be impossible to get the jet high enough to get the mixture lean enough.
Berry

That may be due to a less than optimum rebuild kit. So many of our repro parts/kits are despicably horrible.

 

[sp53]

Some of the reasons for that idle not returning and carbon build up I have dealt with over the years are for the carbon: weak spark, a poor grade of fuel, a distributor that does not advance and return correctly, and a choke that does not return-- sometime because the inner spring on the glad washer assembly is too long and holds the jet out not letting the choke back.

And for the higher idle are: air coming in from a secondary source, not enough dwell on the points, and too much wear on the carb domes.

I am sure there are more, but some of the things I have done over the years to fix the problems are: I use a high voltage coil and metal plug wires. Have a new distributor with the timing about 6 and the dwell close to 60 degrees, make sure the jet fully returns, and make sure there are no vacuum leaks around the carbs and intake manifold. And really probably the most important is I only use the high grade Chevron fuel.

When these cars were new Chevron white pump was 101 octane. I actually put some Union 76 in the other day and the idle went up to 1300 from 850 and the car would start to miss when I would wide open the throttle, but it started right up with either fuel brand. Anyways Went back to Chevron paid 30 cents more a gallon and the idle came down and the miss went away.

 

[frankfast]

I'm sure there are many reasons that keep these motors from running at their optimum. I have one bad stud on the back carb that keeps me from torquing it down properly and I'm not sure if it is leaking air. The car runs hot when the temp goes up and there is an aluminum radiator in its future. I've replaced the points with an electronic Pertronic distributor and coil and replaced the wires and love that improvement. I've been messing with the carbs for a while now and finally think I'm getting to know how they work. The motor has good compression and doesn't miss at high speed. The car looked great when I got it but ran like crap but now it is running reasonably well. It's definitely the type of car you have to keep after but then again it is almost sixty years old.There are plenty of things that still bug me and plenty of things to keep me occupied but that's why I got it.

 

[TR3driver]

I have always had success by starting with the adj. nut all the way up, loosen gland nut, slowly tighten gland nut while lifting&dropping piston. If piston doesn't hit bridge with audible click, loosen glad nut and lightly tap jet assembly from the side&tighten. Repeat procedure until click is heard. It takes far less time to do the procedure than describe it.
Berry