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MG TD TF 1500 - Tight, Leaky Jets w/New Parts & Teflon

Part of the preparation for Lazarus' 4,000 mile trip in May is a full rehab of the carburetors. They hadn't really been touched for about 15,000 miles. Took them apart and went through the Moss rebuild kit parts list, eliminating parts that wouldn't be necessary (or are already in my goodie bag) and ordered the rest to take advantage of their latest sale prices. Also had a set of teflon 'O' rings and old-style GroseJets.
Assembled them with new jets, needles, jet bearings, o-rings and seals. First observation was that the jets were very stiff in the bearing. (Yes, I oiled the pieces, sanded the corners of the jet holes and centered the needles.). Shrugged it off put the system back on the car. Set all of the adjustments as prescribed (6 flats down, throttle screws one turn from holding paper, choke linkage disconnected). Key on - float chambers filled nicely. Fired up within a couple of seconds of spinning the starter, revved happily with either carb. Dug out the old rubber tubing and got them to balance very nicely. With that I called it a day.
Went in yesterday and connected the choke linkage and discovered that I could just barely pull the jets down at all, and it wasn't a cable issue. Did a bit of oiling and tried again. No relief. Then noticed that there was fuel dripping from the jets.

Where to start!!! Probably should have followed the 'if it ain't broke, don't fix it addage'. Bud
(Sorry for the verbosity)
Bud Krueger

Interesting. Where did you get the Teflon O-rings? On both cars I have installed them on, the choke pull was vastly easier, and have had no leaks several years later. I got mine from the guy in Bath, Maine I think. Did you really check for some old cork stuck in the jet bearings? I have left old seals in a time or two and it leaks and is a mess. George
George Butz

I went through the same thing trying to fix Barbara Day's survivor winning TD at North Conway last summer. Her rear carb was leaking badly when she arrived. The jet pickings were shot. Several people donated parts from there goodie bags buried in their tool boxes. Some cork packings broke when touched, others were so hard I could not get the jets to slide easily, others just leaked. I was finally able to get some fairly fresh cork packings. Her distributer was also not advancing properally, causing overheating. Rick Smith and I set it at 24' advance at 3,200 rpm just to get her home. Jeff at advance distributers rebuilt it and Barbara says it runs like a dream now. I'll be following this thread to hear answers on the jet packings.
-David
D. Sander

Teflon came from Tom Bryant. Jet bearings are new, ergo, no old seals. I may start by going back to the old jets. It'll be awhile before I can try -- we're still battling Storm Hercules and Lazarus' garage is behind a 3' snow drift with temps heading toward -5F tonight. Bud
Bud Krueger

Bud,

Try Thomas Bryant email thosbryant at gmail dot com

He sent me 8 O-ring for the jets and two big ones for the jet nut.

Two of the small O-rings at each location - top and bottom on the jets.

Rod.



R D Jones

Hang in there Bud... you guys down there got the "jackpot" in regards to snow accumulation as Barry Burbank WBZ weatherman likes to say.
Frank Cronin

bud, i thought viton seals are the hot set up. regards, tom
tm peterson

"i thought viton seals are the hot set up."

Viton 'O' rings swell just a bit slower than nitrile. Teflon 'O' rings are the ones to use.

Bud, try disconnecting the linkages from the jet levers and then move each jet individually to see if one of them is jamming somehow, or if possibly it is the linkage that is causing the problem.

Regarding the new Gross jets - unless they are new old stock, you may find that they will fail in a short period of time. Seems that the new manufacture of Gross jets are not trouble free like the ones of old.
Cheers - Dave
David DuBois

tom, the Viton seals don't have a good reputation.

Dave, I've tried each separately. They're both very tight. The GroseJets are from when they were made about 30 miles from here. I've had them for quite a long time. I've contacted Tom Bryant about getting fresh set of O-rings. I'll go back to step one and work around the old jets. Bud
Bud Krueger

Bud,

The jets are on the order of .2495 in diameter. Your Teflon seals may be too tight. If they are it wouldn't hurt to run a .2500 reamer through them. I do prefer the cork seals, oiled overnight, as they will adjust to accept the exact diameter necessary.

It is also possible to assemble the jets slightly out of alignment with the result being exactly as you describe. Try removing the jet assemblies, and carefully reassembling them to see if that is the case. Make sure you can move the Teflon seals on the jets, and make sure the jets move up and down in the assemblies before you start tightening things up. Centering the jet, if one bearing moves and the other doesn't can contribute to the misalignment.

Hope this helps,
dave

Dave Braun

The carburetors are once again back in the basement workshop. Managed to get through the drift enough to get the door open. I'll be going through a series of tests and measurements to see if I can identify the culprit(s). What's a good petrol substitute for bench testing? Thanks for your input Dave. Bud
Bud Krueger

Stoddard Solvent is a good substitute for gasoline for flow testing purposes. Its specific gravity is close to gasoline, and it is much less flammable.

Warmly,
dave
Dave Braun

Thanks, Dave. I may just have a can of mineral spirits in the basement. Bud
Bud Krueger

Okay, pulled everything apart and dug out the verniers. Within the resolution of my digital vernier there is no more than .001 inch difference in the old jets or the new ones. No measurable differences found in any of the components. Assembling with the old jets and bearings using the teflon o-rings and rubber o-ring for the jet nut gasket resulted in leakage. Problem was solved by using a new set of old-fashioned cork jet seal washers and new cork jet seal gaskets. Reinstalled them today and now I can pull the choke knob out again. Case closed. Bud
Bud Krueger

BTW, Dave. My readings on the four jets, 2 new and 2 about 10-12 years old ranged from .247 to .248. Bud
Bud Krueger

I should have used a micrometer. I was verifying that my stock was indeed under a 1/4. Glad you found a solution, I do think the cork gland seals can be made to work reliably.
Dave Braun

Bud,
Glad you got it resolved.
Tom Bryant did mention to me that he doubted I would ever need new jets when I redid my carbs, Since they don't really wear that much, if at all, when correctly installed, (centered) and with the small mileage I do.
I only replaced the STD cork graphite seals as the jets were a little stiff and I was not too sure what the 10% ethanol was doing to them. I did have to replace the armored hose's as the ones I brought over from Europe failed with the ethanol and sprayed petrol everywhere. Fortunately there are some holes in my firewall that tell you things like that, long before they become a real problem. :)

So far all of the seals obtained from Tom Bryant are working well. The only other mod I am considering is the replacement of the Bowden cable on the choke for solid piano wire. I have tinned the last 5 ins of the Bowden cable and it helps to push the jets back to the normal - no choke position. Just don't know how long it will remain stiff enough.

I wonder if polishing the jets where the seals contact would make them a little easier to push back up when the choke goes in?

Rod.
R D Jones

I thought the return springs reset the jets. Regards, Tom
tm peterson

Tom, that's theoretical. There are also some laws of physics about friction, etc. Bud
Bud Krueger

This thread was discussed between 03/01/2014 and 15/01/2014

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