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MG TD TF 1500 - SUH2 carb running rich

Hi !
Not a question but a easy trick to locate the problem.

Everything seems ok, the adjusting nut is right on the top and still running rich on one carb.
Then I suspected the upper gland washer or the top bearing copper washer (albeit new).

Principle :
Blowing into the float bowl by the overflow pipe will simulate the vaccum of the running engine.

So I removed the succion chamber and the piston, plugged the jet with rubber material and gently blow.
I could immediately see fuel and bubbles leaking out between the bearing and the carb body.
No leak around the jet so the gland washer should be ok and I have to inspect the top bearing/carb body seal surface.


Laurent.



LC Laurent31

Interesting. Its not something that I had ever considered as a possibility. I imagine the scope for leakage there is small, so likely to be fairly marginal. However, if a turn of the nut by one flat can make a difference, then just maybe this can too, that is under the worst conditions. Makes it all the more important to be sure that all the washers and sealing surfaces are clean and good.
Dave H
Dave Hill

assuming the fuel level in the float bowl is adjusted so that the fuel level at the bridge is correct. Most rich or lean condition in these simple carbs is poor adjustment of the fuel height. Too high gives rich, too low gives lean. simple as that.
S Cole

I milled the surface of the carb body. Even with that, it was still leaking. The copper washer is not soft enough and there is litle pression on it. Only the internal spring pressure. So I made a teflon washer. No more leak now (on the bench).

Information : The fuel level was already too low.
LC Laurent31

It had slipped my mind, but there were kits for the H2's a few years back that came with a too thick jet top (copper) washer. By chance was that an older service kit you used? They would cause rich running no matter how adjusted. I think they were Moss kits, but whoever was selling them continued selling them knowing of the problem, until they sold them all.
S Cole

No leak but still running rich !
I noticed that the piston is higher than the other at idle. So I put the pistons on a scale :
253 g and 250 g. The lighter the higher and the richer too.
I added 3 g to the piston : same thing : higher and richer.

The washers come from Burlen : should be OK.

I 'll order a new jet.


Laurent.
LC Laurent31

I changed the jets and it's ok now. It's amazing because I could not see ant wear-out clue on the jets. No difference either with the new ones. It seems to be very sensitive.Interesting fact for those who believe their jets are OK.

Next step was to adjust the fuel level to 0.07 below the bridge. Not easy because of the meniscus of the fuelin the small jet.
So the idea was to lessen the influence of the meniscus effect by having a greater diameter of this meniscus. Lowering the jet well below the fuel level is very easy and gives good results. Then I measured the fuel level by getting down the tip of a dial caliper at the center of the jet bearing. The reflection of the fuel changes drastically when the tip contacts the fuel, giving exactly the same measurement each time.

Laurent.
LC Laurent31

This thread was discussed between 01/12/2016 and 19/12/2016

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