TR2/3/3A More TR3 SU Rebuild Questions.

[karls59tr]

I soaked the cork jet gland seals in oil for 24 hours as directed. They seem to be twice the thickness of the old ones but I guess they get compressed when installed? I seem to remember installing rubber o rings in place of the cork seals the last time I did a rebuild on a different set. Anyone heard of that? The rebuild kit I got was from the UK. They supplied a float bowl needle and seat unit. The needle has fluted sides, a small plunger on one end and a Viton tip on the other. When installed in the seat the needle immediately jams and can only be tapped out with great difficulty. I don't need that diaster waiting to happen so I'm looking for some Grose jets but Moss and Joe Curto dont seem to supply them. Anybody know who does? I have a set on my TR3 and they have been trouble free.

 

[MGTF1250Dave]

Aloha Karl,

An answer to one of your questions, Moss has the grose-jet, part # 386-390. I just check on line at their website. it is not illustrated but listed.

Regarding the use of o-rings to replace various cork seals it can be done. Two common places are the seal between the carburetor body and the aluminum ring that holds the jet bearing assembly and as jet seals. IMHO the cork seals work well if the are not allowed to dry out for extended periods of time. Soaking them in oil softens them and allows them to conform to the metal retainers and makes a better seal.

The advantage of o-rings is that they won't dry out and crack or break. A possible problem is that jet seals might stick to the jet and make using the choke to stick. Another is that you might not be able to crush an o-ring thin enough between the carburetor body and the aluminum ring. There should be .5 mm of the seal showing to get the jet bearing assembly properly positioned. This jet assembly positioning is critical if the mixture adjusting nut is to effect full mixture control from rich to lean. You will also insure that the mixture adjusting nut will provide enough jet travel to set the fuel/air mixture as lean as required while keeping the needle at its specified position in the piston.

 

[TR3driver]

Moss also sells the O-ring jet seals (365-420). I like them, because they last a lot longer than the cork ones ever did for me.

Never had any trouble with the cork under the locknut, so I'd leave it alone. IMO it is important that the nut clamp the jet housing firmly against the carb body, regardless of how much cork is showing.

Strange about the Viton float valves, they always work well for me. Grose Jets seem to be more sensitive to fuel pressure, I've "fixed" several cars now by throwing them away and reinstalling the stock-type valves.

 

[karls59tr]

Interesting about the .5mm cork showing. I've never seen that mentioned in other SU reading. I soaked that cork seal in oil and later found out that it should have been soaked in water but I dont think it will make that much difference.
Do either of you know what the colour marking on the piston return spring should be for a TR3?
I understand that SU springs are colour coded. I have a set of carb springs that are marked red ( RF mistakenly sent them as master cylinder springs years ago!)but they don't have the cone shaped ends that the old springs do.

 

[NeilRogers]

I used O-ring jet seals on my TR3 carbs and will be changing them back to cork this spring. They cause the jet to stick when the choke is puhed in. The jets do not go back in fully so I have to push them back by hand.

Seemed like a good idea at the time.

Neil
TS80748LO

 

[TR3driver]

Do either of you know what the colour marking on the piston return spring should be for a TR3?

My Haynes carb manual says red. I've also got a couple of NORS spares that show traces of red at one end, and lack the cone-shaped section as well. Still in bags with SU part numbers, so I'm guessing that they quit bothering with necking down one end.

 

[karls59tr]

Neil. As a result of the jet sticking would your carbs be running rich? Maybe this is why my 3 was running rich and fouling the plugs? :-(

 

[TR3driver]

As a result of the jet sticking would your carbs be running rich?

Yup, that's exactly what happens.

Something I've found to help considerably is to polish the surface of the jet until it shines. Originals were apparently supplied shiny, but the replacements I got were dull. A little quality time with some toothpaste was all it took to stop the sticking.

Replacing both the jet return springs, and the springs inside the jet housings seems like a good idea, too.

 

[Brinkerhoff]

If the outside of the jet is not perfect ( I polish with 600 and light oil) fuel can leak around the outside of the jet past the small seals (I prefer o rings)into the carb preventing you from leaning out the carb enough even with the adjusting nut up all the way . A very common problem with this type of SU . T series MG , MGA , TR3. I've had great results assembling with light oil too. The spring should snap the jet up when the lever is released and all is good. Kevin

 

[karls59tr]

In Bob Shaller's book he suggests polishing the jet with "jeweller's rouge"but nobody seems to have heard it so I did mine with Mother's Mag and Aluminum polish. They seemed to shine up nicely. 600 not too abrasive?For oil do you mean "3 in 1" oil? Whether using cork or o rings the issue seems to be that sticking problems occur when the oil film wears off the o ring or the cork seals eventually dry out. There dosn't seem to any easy way to lubricate the jet once its installed but one would think a thin layer of oil would last a few months though??? While we're on the subject of jets....did the original TR3 jets have the .100 marked on the stainless part? The jets I got in my rebuild kit are unmarked. Do you know if the jets that Moss supplies have the marking?

 

[Brinkerhoff]

I'm sure polishing like you did is better but the first time I used 600 grit was 25 yrs ago in a pinch to remove scoring caused by grit in fuel . Wet the jet with Marvel Mystery oil and wrap 600 grit around jet applying light pressure with a twisting motion to put a nice hone pattern the full length of the jet. Clean the jet well and assemble with MM oil which will wash off soon in gas of course but the gas will lube the seals. I've just used std neoprene orings found at Hardware stores. There are different ways to skin a cat ! I usually find myself needing to fix something on a friday night when I want to drive to a show the next day, so I've learned to improvise and I never throw anything away. I've also found that the hole can have a burr on it and cut the bottom seal when you go to install it . Any dirt or grit in these small seals whether cork or neoprene is not acceptable and will impede proper movement of the jet. Kevin

 

[TR3driver]

Stock jets didn't even have a stainless part! And no marking for .100" that I've ever seen. But the only other jet is .090" and they obviously don't fit (the needle won't go all the way into the jet).

Scoring that bad would be grounds for replacing the jet, IMO. But of course sometimes you have to work with what you have. I polish mine to a shine, no honing pattern visible. And no oil (since as noted it will get washed away by fuel the first time you pull the choke).

Another cause of not being able to lean out the mixture is having jets that are worn internally, which can happen if they aren't centered perfectly.