TR2/3/3A Technical Assistance Needed - TR3B Carb Adjustment

[mxp01]

All:

I have apart my carbs on my TR3B. The car had been running way too rich. I watched a video on carb adjustment that showed I needed to bring the jets up to a baseline before backing them off 12 "flats" or two complete revolutions. Does this hold true for the SU H6 carbs? If no, can anyone tell me the right adjustment?

Also: One of the needles is slightly bent. I'm not in a position today to address that today, but what adjustments should i make today to get it operational?

Next: Are there idle adjustment screws on these? I can't see them.

Please let me know ASAP if you can.

Thanks,

Mike

 

[TR3driver]

A bent needle means you'll never get it to run right. The clearance between the jet & needle is very close at idle, and any binding means the mixture will be either too rich or too lean, depending on which way the piston tried to move the last time. It will alternate running like the choke is on (piston lower than it would otherwise be) to not getting any fuel at all (piston higher than it otherwise would be).

For your questions: Yes, 2 turns down is a reasonable starting point. But it's only a starting point, to get the engine running. You'll have to make adjustments from there.

There is no separate idle mixture adjustment; the relationship between load and idle mixture is fixed by the needle shape (and spring inside the dome). The idle rpm adjustment I hope is obvious.

 

[mxp01]

Thanks you. That was very helpful. I got the carbs running much better than before, but will need a new needle to really approach this correctly.

Thanks again,

Mike

 

[DonP]

Get a couple of extra needles. They can be very "fragile" and even a small bend that you can't even see, from accidentally letting the piston and needle slip and land on the ground can do it in. Cheap insurance to stay on the road. (Now, don't ask how I know how easy it is to drop and bend one.)

 

[mxp01]

Thanks for the advice. I will say this: This was the first time I ever worked on SU cabs, my only experience being with Webers. Even with a bent needle, the car newly adjusted carbs are running much, much better. Here's an interesting factoid: The carbs were dumping so much fuel into the engine that the car was really shaking/vibrating - to the point nuts, bolts, and screws were shaking loose. Now it runs so much smoother that it is a really noticeable improvement. Also, I ordered new needles and plan to take another run at it this weekend. The current improvement, though, is really noticeable.

 

[poolboy]

You might want to change the motor oil and filter if the carbs were dumping that much fuel.. Smell the oil on your dipstick.