• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

TR2/3/3A Another Carb question.

Share this page

D

DavidApp

Yoda
Country flag
Offline
I have just rebuilt the carbs for the TR3B I am brining back to life.

I got the carb kit from TRF and followed the directions on the cork jet seals soaking them in oil. Left them over night in a dish of oil.

Polished the choke jets and reassembled the carbs. The choke jets move nicely and the jets are centered. The jet centering nuts are tight.

Fired the TR3B up and ran it for a few minutes. This highlighted a hole in the exhaust pipe just below the manifold. Then I noticed that both carbs are leaking at the bottom of the jets.
Did I mess up the cork seals? Are the "O" ring seals better and would Hardware "O" rings work?

David
 
I would think it unlikely they would leak unless they went together wrong ? have you looked at the float levels, with the dashpots and pistons out the fuel level should be below the tops of the main jets.
I don't know about using O rings instead of cork seals sorry can't help.

Graham
 
David,

See Tom Bryant’s March 1 post here:

www.tr-register.co.uk

Su Carb Fuel Leek

Hi My son and I have only been members since last September. We bought a 1969 TR3A last year. Noticing a petrol leek just below the jet nut and spring, I bought service kits from Rimmers. Carefully following instructions in an SU handbook fitted the gaskets. The leak is now worse. What have I don...
www.tr-register.co.uk www.tr-register.co.uk
 
Hi David perhaps the brass cup for the cork is upside-down, the cup needs to cradle the cork to expand for the seal. I have also seen the barrels the cork sits inside have cuts inside from the brass cup and leak that way. The rubber O ring is supposed to last longer and maybe they do, but the cork should work for a while. I have cork in mine.

steve
 
Hello Steve.
I was very careful to get the brass washer the correct way around. Flat side to the spring and cupped side to the cork seal.

Reading Tom Bryants posts he is using/suggesting PTFE "O" rings and Nitrile (Buna-N) o-rings for the top gland nut.
I presume the top gland nut is the jet centering nut with the larger cork washer.
He also mentioned the using anaerobic sealant on the washer between the Jet bearing and sealing nut.

David
 
I do not know about any of those options. I have found that the inside of barrel where the cork sits becomes scared by the spring and the cups rubbing and leaks there. Gas typically dissolves most glues. Perhaps give Joe the carb guy a call. He is gruff but cool.

steve
 
Hey David,

You may have fallen for the same thing I did. The latest carb kits are providing an extra thick cork washer for the jet assembly (the large cork one compressed by the very large nut at the bottom of the carb that is used to center the jet assembly). The seal is so thick that I only tightened the big nut until it felt rather tight...and then stopped. It seemed right, but I kept getting a leak. I pulled the jets 3 or 4 times, reinstalling with the big nut firmly.

Well, I finally realized that the big nut has to fully compress the cork and continue to tighten until the nut hits metal to metal. With the old, thin, gaskets this was obvious. But it isn't so obvious with the thick gaskets. The jet nut must seat metal to metal to lock the jet into place. Of course the usual "centering" of the jet precautions apply.
 
Thank you John

So the "O" ring idea may be better under the big nut.

Those cork seals were very thick.
'
David
 
Yes, so thick that you tighten to a point that "seems" right, but it isn't. Keep going until you feel the solid contact of metal to metal.
 
Thank you John.

I will try that first. Tightening the large nut.

I e mailed Joe in NY and he said t call him on Monday.

David
 
Speaking of “another carb question,” I have this problem. Gasoline flows out of the rear SU carb float bowl overflow pipe. Why is that and what fixes it? I assume the shutoff valve is not closing tightly. The carbs were totally rebuilt just this past spring.
 

Attachments

  • 41AB8FDD-5C23-4A1C-BC3E-369158EC03B9.jpeg
    41AB8FDD-5C23-4A1C-BC3E-369158EC03B9.jpeg
    3.2 MB · Views: 196
The first thing to do is take the top off the float chamber and make sure the float is floating, it may have a hole and has filled up with petrol. Next check the float height adjustment is correct then blow out the needle valve in case there is dirt stoping it from sealing.

Graham
 
The causes for float overflow would be dirt in the float valve, a float with a pinhole that does not float anymore, a float set too high, or to much fuel pressure. American cars use 6 psi to the carbs, but British cars only need 3 psi. Any more and the pressure can overpower the float valve. Most of these, with the exception of high fuel pressure, would only affect one of the two carbs.
 
It is only affecting one carb; the rear one. And it has a replacement TR3 fuel pump, virtually identical to the original. The carbs were newly rebuilt and professionally tuned, so I doubt the float is punctured. Perhaps dirt in the valve.

thank you all.
 
Sometimes new parts can be defective.

Check the float is floating and clean the needle valve. There are solid floats available now which gets away from the brass float springing a leak.

I have a filter mounted before the fuel pump. A filter between the pump and carbs would help trap any crud in the system.

David
 
Hello Graham

Not yet.

I have been distracted by a number of other issues on this car. As parts come in I am getting them sorted out.
The fuel line was cobbled together from 3 pieces of solid line 4 pieces of rubber hose and an electric pump that did not work. A roll of 5/16" Copper Nickle line arrived yesterday. It is a major PITA t fit the line working under the car.
The exhaust had a large hole in it by the manifold and the rear brake lines ran over the bump stops showing evidence of being repeatedly hit as the axle tit the stops.

I did speak to Joe C and he is sending new cork seal.

David
 
Isn't it great to find things done wrong by someone in the past who shouldn't have touched it and really only made it worse than it was.

Graham
 
Having got the fuel line connected I can pump gas to the carbs.

I did manage to get a 1/2 flat n both large nuts. That seemed to stop the leak.

Today I checked both carbs again and operated the coke jets by hand and the rear one drips gas as I lower the jet. I presume that indicates tha cork seals are bad?

I did polish the jet spindles before reassembly.
Also worth noting is the fact the rear carb choke had been disconnected before I got this car. Maybe it has a history of the rear jet leaking.

David
 
Last edited:
Back
Top