Carb problems

[badhuis]

At least - that is what I think.

From cold, choke needed to start but has to pressed in at least half because otherwise the engine hunts / runs irregularly.

Then, engine cold, it runs terrific. Good acceleration, no smoke, beautiful even running.

When the engine is hot it sometimes splutters but still runs OK. The spluttering gets a bit worse. In the end the engine nearly always splutters.

 

So I thought the carbs are running rich. However when I try to adjust the big nut even one flat the engine protest.

When I lift the air valve 3 mm as specified in the WSM (using a 3mm drill), the rpm does not go up or down much so it seems good?

 

Carbs have new needles and housings, new O rings instead of the cork rings. Before, I found the cork rings would bind the choke mechanisms, now with the O rings it does not.

Another strange thing is that the idle rpm is too high (1000 rpm lowest) and I cannot lower it. The carb stops are fully retracted.

BUT when I lift the throttle pedal a little the rpm goes down 200 rpm. Wear in the front carb butterfly spindle?

 

I have a electronic points system (magnetic pickup) with a new coil.

 

1963 TR4 with standard SU H4 carbs.

 

Any suggestions much appreciated!

 

Dion.

[ctc77965o]

Hey Dion,

 

The fact that you can't get the idle down sounds like air leak...maybe a manifold gasket problem...

 

At idle when you do you piston lift you get an OK result because carb is set rich to fight the airleak...when you drive at higher throttle openings the air leak is only a small proportion of total airflow and so the carbs run rich, foul plugs and bad running.

 

Use a plastic tube to listen for air leaks when idling..around manifold to carb or mainfold to head joints.

[RogerH]

Hi Dion,

I had something very similar.

Remove the return springs from the carb linkage and wiggle the ends of the spindle (in closed position and fully open position)

It sounds like the spindles are worn, Mine were quite bad but the holes in the body were good.

A rebuild kit worked wonders.

 

When you fitted new needles and jets did you centralise the needle - very important.

 

Check the colour of the spark plugs - run the engine for 30 seconds at 2500rpm and without lifting off kill the ignition - check the plugs

 

My rear carb was chocolate brown, the front carb was black.

 

When try to start the back needed choke the front was already over choked so it refused to start easily.

 

Also get the butterflies balanced

 

Roger

[mike ellis]

Hi Dion,

 

If you can reduce the revs by lifting the pedal make sure you have the strong pedal return spring fitted and also the spring on the end of the throttle shaft can be adjusted.