SU carbs

[davjac889]

I have SU carbs on my TR3A, can they be flooded
if the fuel mixture is too rich?
I'm having trouble starting when car is warmed up
and I've got lots of black smoke.
Thanks.

 

[NutmegCT]

When's the last time you adjusted the carbs per the manual(s)?

Tom

 

[davjac889]

Never.

 

[NutmegCT]

Aha! do you have a copy of the workshop manual, or the Practical Hints manual? If not, we can point you to online versions.

Tom

 

[NutmegCT]

If you haven't already, you should do a complete tune-up. But take a look at page 33 of the Practical Hints manual for H6 carb adjustment:

https://www.triumphtr.com/manual_tr3.pdf

Tom

 

[TR3driver]

Sounds more like percolation to me. With the jets located so close to the exhaust manifold, they get really hot after you shut the engine down. The heat, combined with our modern ethanol blend fuel, causes the fuel to literally boil in the jets. The rising bubbles of fuel vapor carry liquid fuel along with them and you wind up with the intake manifold full of fuel vapor, no air at all. (In other words, way too rich.)

Obviously, don't use the choke when starting hot, and hold the throttle about 1/3 down while cranking. This will help clear the fumes out of the intake.

Paradoxically, this can be aggravated by having the mixture too lean at cruise. That pushes the exhaust gas temperature up, which gets the exhaust manifold hotter. My Dad's TR3A used to literally glow red after a stint at freeway speeds (until I found the problem and replaced the worn carb jets).

On my TR3 I made a big improvement in the hot start problem by installing a heat shield between the carbs & exhaust.


Mine is heavy gauge stainless, from https://the-vintage-racer.com//index.php?main_page=product_info&cPath=3&products_id=32 but you could no doubt fabricate your own from mild or galvanized steel (eg roof flashing) if you want.

 

[TR3driver]

If you haven't already, you should do a complete tune-up. But take a look at page 33 of the Practical Hints manual for H6 carb adjustment:

https://www.triumphtr.com/manual_tr3.pdf

Tom

Although the file is bigger, you might find the version at https://docs.google.com/file/d/0B2H...M2U2LWJhYWUtMjEyZDgxMzUyNzUw/edit?usp=sharing to be easier to work with. It has some bookmarks and comments added; plus is not write- protected so you can add your own if you want.

 

[davjac889]

Yes, I do. And ya' know its funny cause the car, this past summer,
was running hot and after fumbling around with the ignition cause it
was also running lousy, I found the needle had fallen down into the jet.
I reset it and secured it. The car ran great!
But I know somehow the black smoke and the fuel mix have to be straightened
out. My one carb is leaking and I don't know if this might be flooding it.
But parts (cork seals) are on the way. I wonder if I should replace jets and/or needles?

 

[NutmegCT]

Yes, I do. And ya' know its funny cause the car, this past summer,
was running hot and after fumbling around with the ignition cause it
was also running lousy, I found the needle had fallen down into the jet.
I reset it and secured it. The car ran great!
But I know somehow the black smoke and the fuel mix have to be straightened
out. My one carb is leaking and I don't know if this might be flooding it.
But parts (cork seals) are on the way. I wonder if I should replace jets and/or needles?

One step at a time! (but Randall is always the first step, and second, and ...)

Tom

 

[alanjohnturner]

Just by chance I just posted a link that will help you with carb tuning.

See "Minty Lamb"

Al.

 

[jimbooth019]

davjac, make sure when you push the choke in that the jet tubes at the bottom of the carburetors are all the way seated. Over time they will get sticky and hang up in the down position causing rich condition when warmed up. Thats a possible short fix, but it sounds like you should take the carbs off and go through them completely, new seals and gaskets. I always soak the corks in oil for a couple of days. (I keep them stored in a container of oil)