Initial adjustments of SU H6 Carburetors

[deadair]

I recently rebuilt my SU H6 carbs for my TR3A. I haven't yet started the car and would appreciate any tips on how to set the initial adjustments.

I recall this being documented somewhere the last time I rebuilt them, but can't seem to find this information in any of my manuals.

 

[beefeater]

Measure down from the bridge to the top edge of each jet. Adjust the jets up or down till both are close to .060 for the initial setting. Adjust each one a flat at a time to get the idle right. The distance I've found that works could be anywhere from .045 to .090, depending on the needle diameter and cam shaft in the engine.

Dick

 

[SpannerMan]

Seem to remember that unscrewing the jets to two full turns out from the body is sometimes recommended as a starting position. Pete

 

[Mickey Richaud]

Or 12 flats (sides of the adjuster nut).

 

[PeterK]

12 flats works for me too. But make sure that the jet needles are mounted flush to the surface.

 

[TR3driver]

The initial settings almost don't matter anyway, since you will be starting the engine using the throttle & choke to control rpm & mixture. After that, it's just a matter of keeping it running while it warms up and you can start iterating towards final settings.

 

[PeterK]

True but it's a lot easier to set 12 flats to begin the iterations while the carbs are on the bench. Mine was just a couple of flats off from initial.

edit: I put a drop of yellow paint on one flat to help keep track of where they are set while dialing in the carbs.

 

[Mark Jones]

You can get the instuctions from Burlen's website.

 

[doughairfield]

I just did mine on my TR4 a few weeks ago and was able to dial it in pretty well.

Make sure you have your timing set properly as well as the air intake of both carbs properly in-sync before trying to get the mixture right.

I started out with a pretty rich mixture to get it started without using the choke and then waited until the engine was up to operating temp. I then shut the motor off and ran the jet screws all the way up making it completely lean and then back out 2 full turns per the manual so for me that was a good starting point.

I started the the engine back up and with the air cleaners off and the jet lever connecting rod detached. There is a small lifting pin under and to the front right of each of your dashpots. I pressed up on this pin to see which way the idle changed. If it goes up and stays up, you're too rich, if the idle goes down, too lean. I then used this method, turning one flat per time I pressed the lifting pin up until the idle went up just a bit and then back down resulting in a nice even exhaust note with minimal black exhaust.

Once you get the mixture dialed in you may need to adjust your idle set screws one more time. After you've driven a bit, check your spark plugs and see if they indicate a rich or lean mixture.

I actually bought a color tune kit, but found that by using the above method I was able to tune my carbs quicker and more balanced than with the color tune, maybe b/c I suffer from a bit of color blindness

Good Luck!!!

 

[deadair]

Thanks very much for all of the advice. I really appreciate your input.