Runs for a second the stops. Help

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electrajohnt
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Runs for a second the stops. Help

Post by electrajohnt »

This is about a 1960 G12 coil ignition but put the question in general because I doubt if the issue is specific.
Trying to get it running after refurb, not much done in the engine except clean the head up and grinding valves.
I flood the carburettor, switch on the ignition and it fires up readily. Just as readily it will then cut out. Choke on or off makes no difference. Flood the carburettor again it repeats the above.
If I juggle the throttle it makes a slight difference for 1/2 second then it spits back and cuts out.
Screwed the pilot mixture screw in, no different.
I have made sure the carb orifices are clear using aerosol carb cleaner.
Just raised the needle to richest position, it was previously in the mid position, but can't try it because it's just started to snow heavily.
I do wonder if I set it just a bit to far advanced such that when it fires the automatic advance and retard over advances it to a point where it spits back and cuts out. To save me stripping it down to a point where I can fit a timing disc does anyone know a measurement of the piston position before tdc I can check the timing too..
Or, has anyone got a suggestion I can try that will resolve the issue.
Hopefully yours
John T
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dave16mct
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Re: Runs for a second the stops. Help

Post by dave16mct »

This is usually caused by a blocked pilot jet.
Dave.
Mick D
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Re: Runs for a second the stops. Help

Post by Mick D »

Hi

First thing I'd check would be the valve clearances, if they're OK it smacks of pilot jet or bypass blockage, (too low revs for it to be the needle, put it back to #3 notch). May also be worth confirming the correct fuel level in the float chamber.

Don't subscribe to the timing theory unless you're getting significant and frequent kick backs when trying to start.

Regards Mick
electrajohnt
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Re: Runs for a second the stops. Help

Post by electrajohnt »

Hello Gents.
I have had the carburettor apart three times, the pilot jet is clear. But, as you are so positive and unanimous I will take it out again, quite confident it will be clear. I will also check the valve clearances. although it has goo compression.
Thanks for the interest shown.
Regards
JohnT
Last edited by electrajohnt on Sat Jan 02, 2021 5:12 pm, edited 1 time in total.
JohnT
SPRIDDLER
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Re: Runs for a second the stops. Help

Post by SPRIDDLER »

Sounds like an obstructed pilot jet to me too.
Force aerosol carb cleaner or WD40 through these drillings
Monobloc pilot drillings (511x640).jpg
Remove the actual pilot jet and check it's clear and make sure as best you can that the tiny drillings 7, 8, 9 and 10 are clear as when petrol evaporates over time a gummy residue is left behind. (More so nowadays with the added ethanol)
Mononloc left side (530x556).jpg
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Mick D
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Re: Runs for a second the stops. Help

Post by Mick D »

The pilot by pass is item 8 in Sprid's illustration, this supplements the pilot jet as the throttle slide is initially opened - make sure this is clear.

Regards Mick
electrajohnt
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Re: Runs for a second the stops. Help

Post by electrajohnt »

Thanks Spriddler,
I have checked them all except the 7 & 8, I will do the check tomorrow.
JohnT
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electrajohnt
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Re: Runs for a second the stops. Help

Post by electrajohnt »

Mick D wrote:The pilot by pass is item 8 in Sprid's illustration, this supplements the pilot jet as the throttle slide is initially opened - make sure this is clear.

Regards Mick
Mick,
That may the issue, excuse the manner of description - it just goes Brrrrrrrrm then cuts out, if I catch it on the throttle it will do half a Brrrrm, spit back and cutout. So, sounds like a possibility No8 could be the culprit, I will report back tomorrow.
Regards
JohnT
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bitza
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Re: Runs for a second the stops. Help

Post by bitza »

Might be worth trying brake disc cleaner spray when dry does'nt leave a residue ,
Plugsnpoints
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Re: Runs for a second the stops. Help

Post by Plugsnpoints »

I had similar symptoms with mine.

I know it's different to what others have said, but I'd check the ignition advance/retard is free and working ok, and double check the timing. That worked for me. The next thing I'd have a look at is the flange gasket/o-rings on the inlet. Mine had a hole that was sucking enough air to cause major upset.

Andy
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