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HS6 idle setting

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T

TexasKnucklehead

Jedi Knight
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If you've looked at my unisyn post, you know I'm adjusting HS6s on a TR3. I noticed as I reworked the linkage to center pull, that the butterflies on both carbs did not exactly align the same way to the adjustment/stop mechanism (throttle return lever). When balancing, I found the front carb idle adjustment screw ended up so high that it doesn't contact the lever (butterfly completely closed). The rear carb idle screw was used to synchronize to the front carb, then the linkage synced. (And checked at a throttle activated position.) So, basically, the idle cannot be dropped below 900RPMs. Is this a problem? And if so, how could I possibly drop the idle speed?

After fiddling with the jet adjusting nut, I used "color tune" and think I have it running pretty well. Both jets are set 17 flats from the top. It starts quickly and idles smooth with a nice blue color on the tuning plug. As soon as I get the tub finished and put back on, I'll take it for a ride to see how well it performs, but for now, I'm happy.
 
If the carbies have been rebushed, during re-assembly each butterfly has to be centred very accurately in the carby body to achieve a low idle speed. The 2 x screw holes in the butterfly (where it goes through the spindle slot) are oversize to accomodate the movement needed to centre them.

When refitting, the butterflies have to be held really hard closed against the carby body while the spindle fixing screws are tightened.

After centring the butterflies, you should be able to look through the carby body with the throttle held closed, and see virtually no daylight.

If this process is not followed, the butterflies, or often just one butterfly, will allow too much mixture through for a low idle to be set.

Viv.
 
Viv, thanks for the response. I removed both carbs, and held them up to the sun as a back light and here's pictures of each. I noticed the front carb had a small amount of slack between the bush and arm, so the whole butterfly could move a little right and left. I loosened the screws, held the shaft toward the center of the carb, and the butterfly against the housing and re-tightened. The idle is slightly lower, but much more stable (before, I had to occasionally blip the throttle for it to settle). This is hard to photograph (with my skills) but the light comes around each butterfly at different places. Either the butterflies are not perfectly round or the carb throat is distorted.

The shafts have been re-bushed. I think I'm OK, but is it common for this happen?
 

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That's often as good as you can get them. If the butterfly has been running out of centre for any time, it will rub away the carby body. Renewal of the body (and butterfly) is about the only fix.

Re-set the idle for each carby with one throttle rod connector loosened, so they are independant of each other. Tighten the connector when the idle is as good as possible.

All the linkage rod joints need to be free and well lubed, or friction hinders the return springs. Many cars have found the need for an additional throttle return spring from the bell crank to the slotted generator tightening bar.

Viv.
 
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