150GTL looks good, doesn't run good, help! - MVAgusta.net
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post #1 of 4 (permalink) Old 11-04-2017, 01:11 PM Thread Starter
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150GTL looks good, doesn't run good, help!

Had a few requests for a photo so (hopefully) have attached a couple, I think everybody will agree this is a 1971 GTL. Missing a centre stand and the tinwear if anyone can help with these I would be gratefull. If the throttle adjusting screw is set to a fast tickover the revs will quickly die back and engine will stall, the slightest touch of either the adjusting screw or the throttle will however set the revs racing to about 4000, they will then die back and stall, the dellorto MB22B carb has been carefully cleaned, no adjustment seems to make any difference. Anybody got any ideas?
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post #2 of 4 (permalink) Old 11-05-2017, 12:46 PM
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Hi Colin, Nice looking bike!
Sounds to me like you bike is not running on the pilot fueling circuit.
I have a 175 CS57 and it wouldn't idle when I bought it. The problem in my case, was the pilot jet was too small at 35 when it should be a 45. Check that the pilot circuit airways are clear as they can block with corrosion if the bike has been stood. To get a good idle and pick-up you have to finely balance the idle speed adjusting screw (slide stop) and the idle mixture screw - remember that the screw adjusts the air flow on the MB22, so screwing in richens the mixture and screwing out weakens it. My screw is around 1 1/4 turns out.
I've uploaded some useful Dellorto docs to my Dropbox on the following link.
https://www.dropbox.com/sh/ip7epicpt...bHn_YnMda?dl=0
Page 12 on the pdf has a good explanation of the pilot circuit.
Hope this helps,
Rpn
esq'z me and esq'z me like this.
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post #3 of 4 (permalink) Old 11-06-2017, 03:03 AM Thread Starter
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Thanks for the info Mondello I think you are correct when you say the bike is simply not running on the pilot circuit, I also had not realised that the idle mixture screw adjusted the airflow, I had thought it was a fuel adjustment. I will have another go at it thanks again.
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post #4 of 4 (permalink) Old 11-06-2017, 02:44 PM
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Thanks, I'm pleased if I can help.
To set my CS57, I warmed it up then set a fast tickover by screwing up the throttle stop. Then I slowly lowered the throttle stop adjusting the idle mixture each time to get the best running. As you lower the throttle stop you increase the suction on the pilot jet and it should start to feed fuel into the engine.
If you can't get the pilot circuit to give an even, fairly low, tick-over then it's blocked (or you have the wrong size jet as I did).
One test you can do with the carb off the bike, is to spray carb cleaner into the pilot circuit air inlet point (see pdf doc). Then check it comes out of the outlet point that is just downstream of the front edge of the throttle slide.
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