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TR6 TR6 carbs lean

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TR6oldtimer

TR6oldtimer

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Well, I am have real problems getting my rebuilt carbs adjusted. The are running very lean. The needles are out as far as they can go. I suspect I have a vacuum leak or source of additional air entering the system. For example, I can block the hose to the valve cover and RPMS go up significantly.

All the connections to the carbon canister are blocked, so I suspect that the new by-pass valves are the culprit.

When I replaced the diaphragm, I did not adjust the valve setting. So what I plan to do later today, is force the valves closed by turning in the adjustment screw.

Any thoughts or warnings?
 
Ray, you don't have the float chamber vent capped off, do you ? I'm talking about the ones that are pointing toward the cockpit.
The Throttle Bypass Valve remaining open when it's supposed to be closed is just letting some of whatever the mixture is in the carb's mixing chamber bypass the throttle disc and enter the intake manifold directly. That usually raises the idle speed by about 200 but it really doesn't change the mixture, just more of it.
 
If all else fails adjust the float so the fuel level is higher. Don't go more than 2mm at a time.
 
TR6oldtimer said:
Well, I am have real problems getting my rebuilt carbs adjusted. The are running very lean. The needles are out as far as they can go.
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Needles out as far as they will go will, ISTR, cause a lean condition due to the largest diameter of the needle sitting in the jet. Reset the needles correctly in the pistons and that will give a smaller dia of the needle in the jet, allowing more fuel to flow past the needle, creating a richer mixture.
 
Jim, I think we are talking about the same thing. My reference to out is in relation to the venturi, I believe your reference is to the piston.

Thanks for comment, I had to think about it a bit.
 
I remember now reading about fat needles, easy enough to check or even put the old ones back in.

Thanks for the memory jog.
 
Well, here is an update. I put the original needles back in the carb, still lean, I cannot make them go rich. Vacuum at 15-18 lbs, and I did the "cover the carb" thing, no indication of a leak, so I guess it is not a vacuum leak problem.

The engine still misses. So I did a compression test, all cylinders 140lbs. I then pulled plug wires, one at a time, still misses. New points, no change. Checked the fuel flow, it was ok.

So this brings me back to the carbs. I did replace the ventures, carefully measured the original depth and installed the new ones to the same +-.005". I am thinking they may be set to high into the body, but I am loath to the thought of having to re-position them.

My worst nightmare is that I did not properly degree the cam.
 
So, just for clarity here Ray, you've turned the mixture adjustment screw (in the center of the dashpot shaft) clockwise as far as it will go, correct?

And you realize that the bowl vent lines from the sides of the carbs have to be open (not capped off) ?

You've capped off the vacuum to the brake booster. And have the restrictors installed in the lines that should go to both the rocker cover and the canister.

What did you do with the "temperature compensators" during the rebuild?

While I won't say it's impossible, my experience has been that wrong cam timing causes rich mixture (by increasing reversion). But it's not that hard to check with a factory cam, so if you're worried about it ...

It's also worth noting that these engines were supposed to run a little on the lean side. "Best idle" produces about 5% CO, but your engine is supposed to be set to 1.5% (+/- 1%) for reduced emissions. The factory deliberately limited the adjustment range, so it's impossible to make them go rich with the adjustment screw.
 
Time to raise the fuel level in the float chamber.
 
Well, I had a miss. I thought it was a lean carb. It turned out to be a bum coil.

Whew! It could have been worse.
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]It turned out to be a bum coil. [/QUOTE]

Once again, proof that 90% of all carb problems are electrical.
 
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