Hair pulling engine problem

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Johnd103
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Hair pulling engine problem

Postby Johnd103 » Mon Sep 12, 2016 1:50 pm

Having a little problem getting the moggie to stay running I have tried everything I can think of there is new rotor arm points and condenser gone into it and the coil works fine . It won't start with any choke at all only with the throttle either a quarter way down or fully down depending on its humour . When it starts it could run for ten seconds or a minute depending again on its humour but my foot has to rest on the throttle to keep it going . When I try rev it up it feels. Like it's struggling to get power then reaches a certain rpm then will backfire through the carb and die off . I've done the timing 3,decrees before tdc and did a rough tune on the carb . Tighten it up fully and slacken it off 2 turns also the fuel pump is fine it throws fuelbout constantly . Any help would be greatly appreciated on this thanks for readingb

bmcecosse
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Re: Hair pulling engine problem

Postby bmcecosse » Mon Sep 12, 2016 3:07 pm

Increase the idle speed....and look for an air leak. But backfiring could be stuck valve - certainly indicates un-burned fuel in the exhaust. Is the carb piston free to rise and fall ? The idea that it will start without choke suggests flooding - does the fuelpump do a few clicks - and then stop when you switch on the Ign - or does it keep ticking??
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Johnd103
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Re: Hair pulling engine problem

Postby Johnd103 » Mon Sep 12, 2016 4:46 pm

I'll look at that later thanks it clicks 3 or 4 times then stops for about ten seconds or so and might let another click out .. I might have said backfire wrong it pops through the carb a big puff of white smoke / vapour

oliver90owner
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Re: Hair pulling engine problem

Postby oliver90owner » Mon Sep 12, 2016 5:06 pm

Back-firing through the carb tells me something different than the other poster thinks. Could be over advanced timing; could be damaged or stuck inlet valve(s). Culd be a couple other reasons.

Check the plugs when it stops while the engine is cold - are they very wet with fuel? Might mean flooding, or even a stuck float/float valve. If the plugs are completely dry, mixture may be too weak.

Johnd103
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Re: Hair pulling engine problem

Postby Johnd103 » Mon Sep 12, 2016 5:58 pm

May have figured out part of the problem there went to check the tappet clearance again and I was in mm so .12 of a mm is very little so converted it and figured out its .30of a mm now it starts and will stay going on her own but won't idle properly it's like it's getting fuel then not then getting fuel again but doesn't cut out completely I think I may change the spark plugs and rebuild the carb with a refurbished kit and not a quick clean up and get the gunk out of it

bmcecosse
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Re: Hair pulling engine problem

Postby bmcecosse » Mon Sep 12, 2016 8:39 pm

And are all the valves going up and down as they should? Run it without the cover to see. Also test the compressions - even just with the starting handle (Ign OFF) - are they all similar - or do some feel 'easy'? Could be head gasket - in fact - quite likely.... Spitting back indicates an Ignition event while an inlet valve is open - which will happen with a stuck inlet valve or blown headgasket.
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kennatt
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Re: Hair pulling engine problem

Postby kennatt » Tue Sep 13, 2016 7:49 am

you say you turned the nut two turns,I take it you mean the nut under the carb,The correct way is to fully screw it right up then back down 12 flats,it sounds to me that the mixture is too weak,Try it again as above before stripping the carb.Once its running and warm, lift the little pin at the side of the carb,if it speeds up turn the nut back up slightly,if it stops,screw it down a bit more The ideal setting is when the revs go up slightly,then fall back and the engine sort of runs a bit rough.lLift the pin till you feel resistance then just lift it a bit more,don't lift it right up.

bmcecosse
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Re: Hair pulling engine problem

Postby bmcecosse » Tue Sep 13, 2016 12:42 pm

The spitting back indicates more than a 'weak mixture' - and in any case this 'number of flats business' is just a guess. When cold starting with 'choke' pulled it has no relevance whatsoever. Check the compressions...
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