Jet Assembly sticking

[doughairfield]

I'm having a bit of a problem with one of my SU H6 carburetors on my TR4.

When i pull the choke out, it articulates the jet lever arm, pulling the jet assembly down, enriching the mixture I assume. Everything starts up fine. But when the engine warms up and I push the choke back in, the jet assembly doesn't move back up into the carb for normal running. I then have to pop the hood and push the jet assembly back up, resulting in smooth running.

I had the carbs rebuilt recently, but they were in pretty bad prior shape so I don't really know what the proper operation of the jet assembly is supposed to be.

 

[NutmegCT]

Doug - just my two cents:

I had the same problem with the H6s on my 1959 TR3.

Removed the jets, polished them with steel wool and toothpaste (!). And found that one of them was actually slightly bent, so it would "stick" in the jet assembly. Got two new jets.

Also made sure the cork gaskets were lubed inside the jet assembly. You may have rubber o-rings, but I'm pretty sure they need some lubrication so the jets will move through them.

Hope this helps.
Tom

 

[Moseso]

In my case (same problem) a mere application of a little silicone grease to the jet solved it. Polishing the jets surely won't hurt -- and then a little silicone grease too...

 

[TR3driver]

I would also replace both the return springs, and the springs that hold pressure on the jet seals. These springs are not included in rebuild kits and hence not always replaced during rebuilds, but should be, IMO. It's quite common for folks to stretch the jet seal spring out to put more pressure on the seals (in an attempt to stop them from leaking), which can also cause the jets to bind. And the return springs just get weak with age soemtimes (even if someone hasn't modified them as well).

Original jets came in a high state of polish, but modern replacements don't. They need to be polished before installation. I also coated mine with a very thin layer of silicone grease.

 

[doughairfield]

Great advice, thanks. I've already replaced the return spring and put some lithium grease on the jet, although, just on the lower end near the coupler in my attempt to solve this problem.

Guess I'll pull it apart and give a good going over and check that jet to make sure it's true.

 

[TR3driver]

Lithium grease won't help much, as it will get washed away by the fuel. The pure silicone stuff should offer some lubrication longer.

 

[JohnnyMead]

Doug,
Have you disconnected the linkages and tried moving each jet/spring assembly by hand? You may be able to isolate the roughness or binding to a specific part of the system (one carb, part of the link, etc.).
John