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MGB Properly starting a warmed-up or hot MGB

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Gas flows to the front carb first. Seems strange to set them up separately due to their interdependence even when all connections are disconnected for this procedure, but ok.

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???

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Don't they kind of work together even when they're not linked together? What I meant was that you have to undo the linkage on the throttle and choke shafts so the two carbs can be adjusted separately.
 
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Could I suggest opening each carb about one flat from what you think is correct and checking that for hot starting? Pay close attention and let us know of any change.

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Ok, I did that. This was just after 5pm. The car had last been run at around 1:30pm. I opened the carbs one flat apiece, and cranked the starter. No choke, no foot on the gas. It fired off quickly and was around idle speed after a few seconds. The temp gauge was at the low end.

It carb backfired at a couple of stop signs, but drove pretty well.

Then, after reaching NOT, I stopped to get gas. After filling the tank, I tried to start it again without choke or foot, and it wouldn't quite do it. It was trying, but not hard enough. My foot on the gas got it going, but it had some trouble getting up to idle. Drove fine the rest of the way.

Oh, and there was the slightest bit of run-on when I stopped for gas, and when I got home. Not much, but enough to notice. The car doesn't have any of the anti-run on stuff installed, and hasn't done it since I installed the Pertronix.

Thank you,
 
One more half flat guy. You just almost there.
 
Now about the run on. Run it a few days then look at the timeing. Advance one degree at a time. If it gets worse back off one degree at a time.
 
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One more half flat guy. You just almost there.

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I made this adjustment this morning, but haven't had a chance to try it out yet. We'll see...

Thank you,
-Bill
 
Crosses fingers.
 
Finally had the chance to try this new carb setting this morning. On the way to work, I decided to stop and get some breakfast. By the time I stopped, it was at NOT. I was in the store no more than 10 minutes. When I came out, the car wouldn't start until I put my foot on the gas.

Thank you,
-Bill
 
What is your idle set at? Should be about 7 to 9 hundred. Faster idle will make it start easier.
However, I think you are fine. Choke when cold. throtle when warm. Enjoy it for awile and see where it goes. Too many vairables on an old engine and parts.
 
My experience has only been with SUs on a midget, but I beleive your carbs are set too rich. As a previous poster replied, the first small amount of choke movement on my midget opens the trottle without moving the jets down. This should lean the mixture slightly and would be the same as slightly pressing the accelerator. If your choke acts the same, then I would try leaning the carbs a bit. I understand what you mean when you say that adjusting the carbs does not work exactly like the books say. On mine, I could lean them and then lift the piston and have the engine stumble and die. I could enrichen them and lift the piston and have the engine speed up. I could never find that elusive spot where the engine speed should increase slightly and then settle to an even speed as indicated in the instructions I had. I finally adjusted mine to the point where the engine would just start to slow down and stumble when the piston was lifted, and then turned the jets two flats richer.

Thanks,
Jeff
 
I think that changing the charcoal in the adsorption canister might help. I know some gas got sucked in there during the float bowl trouble where the floats stuck and let too much gas through, which can cause breathing problems.
 
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My experience has only been with SUs on a midget, but I beleive your carbs are set too rich. As a previous poster replied, the first small amount of choke movement on my midget opens the trottle without moving the jets down. This should lean the mixture slightly and would be the same as slightly pressing the accelerator. If your choke acts the same, then I would try leaning the carbs a bit. I understand what you mean when you say that adjusting the carbs does not work exactly like the books say. On mine, I could lean them and then lift the piston and have the engine stumble and die. I could enrichen them and lift the piston and have the engine speed up. I could never find that elusive spot where the engine speed should increase slightly and then settle to an even speed as indicated in the instructions I had. I finally adjusted mine to the point where the engine would just start to slow down and stumble when the piston was lifted, and then turned the jets two flats richer.

Thanks,
Jeff

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The SU's on a B work pretty much the same way. I might have gotten a bit overeager with enrichening, as I went at least 1/2 flat beyond what was recommended here. As it is, the rear carb seems to need one extra flat of richness over the front carb.

I was beginning to think that I was too thick to do this correctly, and that all the signs of proper adjustment were going right past me. Odd that it can be so problematic. I'll be able to relax a bit when I get it through my head that it doesn't have to be spot-on to work.
 
Something is causing them (or 1 of them) to want whatever a little more air...maybe the cannister is blocked but they don't feed into it..so, its possibly to rich.

Here's another question, though I don't know if its answer would cause your problem...are your butterfly's centered?
 
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Something is causing them (or 1 of them) to want whatever a little more air...maybe the cannister is blocked but they don't feed into it..so, its possibly to rich.

Here's another question, though I don't know if its answer would cause your problem...are your butterfly's centered?

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Does this mean are the butterflys in the same place on the throttle shafts? I'm not sure, to be truthful. Seems like having them otherwise would interfere with their opening and closing.
 
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Does this mean are the butterflys in the same place on the throttle shafts? I'm not sure, to be truthful. Seems like having them otherwise would interfere with their opening and closing.

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Not necessarily, I think I know where Tonys coming from. The butterflys or butterfly can be off just a small amount and still not bind up, but it won't close like it should. If it's a two carb engine and one is not closing as tight as the other one, then you'll never get the carbs to act the same at idle. Maybe through the full cycle, I don't know. You have to loosen the butterfly screws,(only loosen them enough so the disc can move! Don't take them out!), back off the idle screw and move the throttle shaft open and closed to center the disc in the throat. You want a tight fit all way around. Holding it tight, tighten up the screws. Not saying this is your problem, but who knows? /ubbthreads/images/graemlins/cheers.gif PJ
 
Well said, Paul!
 
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