Spark but not firing

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pin
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Spark but not firing

Post by pin »

Hi all
A friend has just brought a 750b and has been tinkering with it ,
He said that when he picked it up it was running ok now the centre pots not firing ,
Changed the plug and had a look at the points he said that it’s now sparking but still not firing ,
Tried running on choke still not joy Took the air filter out and sprayed some wd 40 In to the carb still not joy ,
Checked the plug which looked dry but when it’s running there is some smoke coming out of the centre pot exhaust ,
Don’t know where to look next apart from checking the compression,
Any help would be welcome
Thanks
Pin
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Alan H
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Location: Wombwell, Republic of South Yorkshire

Re: Spark but not firing

Post by Alan H »

If the centre pot isn't firing, there can't be any smoke coming out of the centre silencers. Is the downpipe warm? Sort out the ignition side.
New plug, cut 1/4" off the ht lead, replace the plug cap for starters. Then get Baz to do your carbs.
Use easy start, not wd40.
Proof that four strokes are over complicated
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pin
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Re: Spark but not firing

Post by pin »

The centre pipe gets warm but not hot enough so you can’t hold the pipe ,
There is smoke coming out of the centre pipe exhaust but not a lot , I did hold my hand Over the end the exhaust , the exhaust gas is cold and has a lot of oil enough to make my hand wet ,
I did put a new plug in which I did check that it sparks but when I looked at the plug after trying to start the bike it was or looked dry ,
I’m probably overlooking something but will put a new plug in and get some easy start
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pin
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Re: Spark but not firing

Post by pin »

I can’t work this one out new plug good spark sprayed easy start into the carb still does not fire
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canaletto5
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Re: Spark but not firing

Post by canaletto5 »

Did you have the throttle wide open when you sprayed in ther easy start? It sounds like a pilot circuit problem so you could need to have the carbs properly serviced. Kev
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pin
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Re: Spark but not firing

Post by pin »

It all started to play up after he striped and cleaned the carbs he doing them again now ,
I still don’t understand with spark and fuel sprayed into the carb it should fire / back fire or do something but nothing
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canaletto5
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Re: Spark but not firing

Post by canaletto5 »

Have you checked that the pipes and baffles aren't clogged with carbon? Kev
barney01
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Re: Spark but not firing

Post by barney01 »

So check the timing. If the piston pushes all the mixture/easystart out before the spark it wont fire. Would also account for no heat in pipe if no combustion.
NO SMOKE .......NO POKE
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BAZ
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Re: Spark but not firing

Post by BAZ »

Remove the carbs and check for suction on the intake...
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pin
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Re: Spark but not firing

Post by pin »

Carbs removed it is sucking on all pots about the same , pipes and baffles checked and look ok ,going to clean the carbs again to see if anything blocked ,
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