TR2/3/3A SU carb. Acts like an expansion valve !

Went from 83mm to 87mm, did the break in run and proceeded to re-tune the carbs. In the process, I touched the rear carb and it was ice cold. also that half of the intake manifold was also cold. Had tried to degree the valve timing when the engine was torn down. Was this the error? Plugs 3&4 were wet. 1&2 ok. Plug wires all ok. Advice please.

1960 TR3A

Double check that the choke is not still holding the jet down. Or that the jet is not fully up. If okay there then retune the rear carb. It is running rich.

Yes choke

Is the piston sticking up on the rear carb?

David

A lot on my plate right now, but the choke is not even hooked up, the jet is fully home, the adjuster nut was at 12 flats and piston is not real smooth. Thanks all for the input. With time, I am about to remove carb and inspect. The float valve etc. looked ok.

LeT

The problem might be the link that holds and connects the 2 carbs together. Like Goe stated these cars will run kinda ok on one carb.
steve

How are you balancing the airflow between the carbs? That is always step one to tuning the SU's.

The other early step is to make sure the jet depth is the same on both carbs:

Numerous tuners advocate using the tail of a dial caliper to measure the depth of the jet from the bridge. Des Hammill suggests .050"/1.25mm as a starting setting for 1-3/4" SUs. Then make adjustments from there for correct running.

When it runs properly, per APT in Riverside CA (Triumph dyno tuners), average the jet depth. For instance, if one carb is .060" and the other is .050", set them both to .055".

Steve, I like that--- always like new smart ideas. I am not sure if I am interpretation correct. Are you proposing to pull the piston and needle out and off and then look into the jet orifice and see if the jet is down from the top .050?
steve

sp53 said:

Steve, I like that--- always like new smart ideas. I am not sure if I am interpretation correct. Are you proposing to pull the piston and needle out and off and then look into the jet orifice and see if the jet is down from the top .050?
steve

Click to expand...

Steve,
Apologies for not being clear. Yes - pull the dome, piston and spring and measure straight down from the bridge to the jet surface. Be sure to keep each piston with the same dome, as they're a matched pair.

This whole issue started over 1 year ago when it would not start. About a year ago, I started the rebuild (I found 2 exhaust valves that were pocketed). After I installed a genuine SU rebuild kit, was now running at about 1 gallon per 10 minutes.

Now, with both jets turned to Zero flats, almost right. Re-examines the carbs, only to find the rear carb has a .125" jet! (factory supplied). The front carb has std .100" jet. Now I can tune a well behaved engine.

By the way, the rear carb was at about 55 degrees F. with the front at like mid 80s Now at about equal temp. Question: can temperature be used as a tuning tool?

Thanks to all who helped with the problem. LeT