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M21 starting issues
#809980 05/23/20 7:19 am
Joined: Dec 2014
Posts: 214
Howley Offline OP
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Hi all,

I'm having intermittent starting issues with my m21.
The procedure is:
- Fuel on
- choke fully closed
- ignition half advanced
- tickle carb until fuel comes out the top hole of the float chamber.
- use decompression lever to get piston just through compression.
- Kick

Normally the bike will start first kick, but every now and then it won't. I'll kick it ten times then pull the plug to find it shiny black (fuel and soot).
I'll clean and replace the plug and try again, and after pulling the plug again it will be wet with fuel and not sparking. An alternative plug produces a good spark so the mag is fine.

I'm at a bit of a loss as to why this happens. It seems like the plug gets saturated at the first attempt, and the soot it leftover from the previous run's idle (I'm not yet able to ride it on the open road).

Can anyone offer any advice or suggestions? Could the previous shut-down be fouling the plug?

Thanks,

Luke

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Re: M21 starting issues
Howley #809981 05/23/20 8:21 am
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Modern fuels in Aus seem to be able to set up a conduction path along the insulator if the motor won't start after a few kicks. I had this problem with the Firebird a few years back. Swapped the plugs and it started first kick.
This seems to be more prevalent with fuel which has been left for a while, and the volatiles have evaporated.

If the bike is going to be left for any length of time before starting again, it's a good idea to turn the fuel tap off and let the float bowl run dry.


I've found with the B44 that if it won't start after a couple of kicks with the throttle closed, turning the fuel off and giving it full throttle will usually get it to start.
As Brian said to the multitude outside his house, "you are all different, you are all individuals", so this might not work for you M21. It's worth trying, though.

Re: M21 starting issues
Howley #809986 05/23/20 9:05 am
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On all my carbed engines after a lay up I pour in some paint thinners into the tank 15 mins before I open the fuel tap, this adds some volatiles and I have said goodbye to sore legs and arms from kickstarts and rope pulls.

Re: M21 starting issues
Howley #809988 05/23/20 9:48 am
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The plug shouldn't be black and sooty from the previous run if the carburettor is set correctly


BSA B31 500 "Stargazer"
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Suzuki GSX1100 EFE "Sorcerers Apprentice"
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Re: M21 starting issues
Howley #810025 05/23/20 6:50 pm
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I dont understand why you are "fully closing the choke" that will sure help to flood it ........try it with the choke open ....i never use the choke on my M20 and it starts just fine


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
Re: M21 starting issues
Howley #810075 05/24/20 3:40 am
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So when it does start, why aren't you taking it for a run on the road ?
This will often burn off any deposits on the plug, and leave it nice and clean for the next time.

Also, tickling it and choking it are near the same thing.
Maybe try just tickling it and see how it goes ?
It may then need a trace of choke to keep it running, until it warms up a shade.

Re: M21 starting issues
Howley #810101 05/24/20 1:00 pm
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I find with my M20 that if I will be restarting hot, like at a fuel stop then I just kill the spark or lift the decompressor to stop the engine & it will fire up no problems.
If I am not going to restart hot, like the end or a run or at a lunch stop then it is turn the fuel off & starve the engine off.
The final few strokes the carb fuel level will be very so so the mix will be very lean.
This burns all the crud off your plug insulator so you have a nice clen plug to start next time.
AsShane has already mentioned , modern fuels are conductive at compression pressure.
This is even worse if ou are using E10 or premium fuel.
Bog std 91 unleaded for an M series engine.
And as already mentioned, flooding or choke but not both.


Bike Beesa
Trevor
Re: M21 starting issues
Howley #810649 05/28/20 8:17 pm
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Magneto. intermittent starting problems, worse when hot, plug might fire out of the cylinder but not strong enough to run the bike.

Re: M21 starting issues
Howley #810667 05/28/20 10:41 pm
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Thanks for all your replies.
You make good points about choke and tickling. I'll stick to one only from now.
I'm also suspecting my plug. It only sparks with a very strong kick, where an old oily dusty one from the shelf sparks strongly with anything.
I'll replace the plug then try your suggestions.

Re: M21 starting issues
Howley #810683 05/29/20 12:46 am
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Originally Posted by Howley
I'm also suspecting my plug. It only sparks with a very strong kick, where an old oily dusty one from the shelf sparks strongly with anything.
I have been told that older spark plugs had glazed porcelain insulators and the new ones are unglazed. If that is correct, it would lead to much more rapid contamination.

Re: M21 starting issues
Howley #810713 05/29/20 9:05 am
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Hi Luke,
I find that starting my M21 from cold needs the coke on full, ignition half retarded and a mild carb tickle (say 2-3 seconds) if fuel come out the over flow at the float chamber cap it's flooded.

Re: M21 starting issues
Howley #810716 05/29/20 11:03 am
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Thanks Matt.
I'll try that too.

Re: M21 starting issues
Shane in Oz #810719 05/29/20 11:44 am
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As I have said in other threads, an old sage once told me " 90% of carb problems are the spark plug"

Re: M21 starting issues
Howley #810737 05/29/20 2:57 pm
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I agree with the previous comments about modern fuel and spark plugs especially if the fuel isn't fresh. What I have found in these situations when my bikes wont start easily is that the carb pilot jet is gummed up and the float bowl has some water accumulation. I would rebuild the carb using the guide Here and change the plug for a new one. This usually becomes an annual ritual in the UK after over wintering unless you use a fuel additive as Kommando suggests. I haven't tried paint thinners but Briggs & Stratton sell an additive to keep fuel fresh which seems to work.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: M21 starting issues
Howley #810808 Yesterday at 05:22 AM
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"90% of carb problems are the spark plug"

It was the spark plug. It idles better now too!


Moderated by  Allan G, Jon W. Whitley 

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