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Discussion Starter #1
A friend of mine brought me his SC28 900RR As it would not start and although its a long story, I'll give you the bullet point version.

18K Only bike obviously been stored and very nicely for a long time. My mate has ran it for about 600 miles since he bought it and one day he went out and it went onto reserve (or so he thought) so he filled it up.
Shortly after it stopped and was making a funny:hmm: noise.
He brought it to me and it would not start it would fire with some easy start but not run.

Took the airbox off and it was full of corn seeds:eek: at least a couple of cupfulls and the air filter paper had been chewed.
Removed all this but the corn had not penetrated to the engine side.:)

Still it did not start and was puffing smoke out the exhaust and occasionally backfiring once every so often.

Long story short, going through everything i eventually took the head off and replaced the head gasket, checked the valves in the head with it upside down and filled with fuel. (all seemed ok.) Suspected a broken head gasket and replaced it rebuilt it new plugs filters valves set and it all ran fine.

Guy came and picked it up and although it appeared to smoke on the overrrun it ran ok. He took it home and two days later it would not fire again. Similiar backfiring every so often but wont run.
Checked everything again, carbs floats, diaphragms, cam timing , battery compression (175psi),so i replaced the spark plugs with old ones and it fired up and ran. A replacement set of plugs :) fired up ok.

Two days later same problem wouldnt fire.
:evilaugh:
Checked everything again and in desperation replaced the igniter coils and ignition box and still would not run.
Replaced the spark plugs and it fired up.:eek:

Took it for a 40 mile run all seemed ok but it still smokes but only on the overrun.

four days later it wont start again, its pushing greyish smoke through the exhaust whilst turning over but it wont run just backfires every so often.

Checked carbs, all clean checked sparks and timing all seem fine, only common thing is the plugs get black and sooty/wet.
Told to check the float heights again but they are not adjustable anyway.

Any ideas or help appreciated as this one has me scratching my head. (the only thing ever I have had so many problems with is where a zx9 bike had worn out valve seats.)

What do I try next?
:idunno::idunno::idunno::idunno::idunno::idunno::idunno::idunno:

HELP!!!!
 

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Sounds to me that the only common denominator here is the plugs foul awfully quick. Why? Hmmm, good question. Reading your points, did you ever have the carbs out and THOROUGHLY cleaned? All the jets out, slides, needles, etc.? I see you said you've checked floats and such. Usually its a lack of fuel issue when carbs sit and don't get used. But sounds like you're getting too much fuel, and or oil in there too. What led you to remove the head?? That seemed like a drastic measure/guess, no? Do you notice the oil level change, or does it get diluted with A/F? Have you tried running it without the fuel pump? Usually dormancy will kill a fuel pump. Try a drop tank and see how she goes, but I would bet my first course of action would be to have absolutely spotless carbs
 

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A friend of mine brought me his SC28 900RR As it would not start and although its a long story, I'll give you the bullet point version.

18K Only bike obviously been stored and very nicely for a long time. My mate has ran it for about 600 miles since he bought it and one day he went out and it went onto reserve (or so he thought) so he filled it up.
Shortly after it stopped and was making a funny:hmm: noise.
He brought it to me and it would not start it would fire with some easy start but not run.

Took the airbox off and it was full of corn seeds:eek: at least a couple of cupfulls and the air filter paper had been chewed.
Removed all this but the corn had not penetrated to the engine side.:)

Still it did not start and was puffing smoke out the exhaust and occasionally backfiring once every so often.

Long story short, going through everything i eventually took the head off and replaced the head gasket, checked the valves in the head with it upside down and filled with fuel. (all seemed ok.) Suspected a broken head gasket and replaced it rebuilt it new plugs filters valves set and it all ran fine.

Guy came and picked it up and although it appeared to smoke on the overrrun it ran ok. He took it home and two days later it would not fire again. Similiar backfiring every so often but wont run.
Checked everything again, carbs floats, diaphragms, cam timing , battery compression (175psi),so i replaced the spark plugs with old ones and it fired up and ran. A replacement set of plugs :) fired up ok.

Two days later same problem wouldnt fire.
:evilaugh:
Checked everything again and in desperation replaced the igniter coils and ignition box and still would not run.
Replaced the spark plugs and it fired up.:eek:

Took it for a 40 mile run all seemed ok but it still smokes but only on the overrun.

four days later it wont start again, its pushing greyish smoke through the exhaust whilst turning over but it wont run just backfires every so often.

Checked carbs, all clean checked sparks and timing all seem fine, only common thing is the plugs get black and sooty/wet.
Told to check the float heights again but they are not adjustable anyway.

Any ideas or help appreciated as this one has me scratching my head. (the only thing ever I have had so many problems with is where a zx9 bike had worn out valve seats.)

What do I try next?
:idunno::idunno::idunno::idunno::idunno::idunno::idunno::idunno:

HELP!!!!

All that effort but you didn't strip and clean the carbs?
 

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My then ten pence would be as follows....

So when the plugs foul, they short and don't work properly. When you change them the bike starts. Is this correct?

If so...
- need to find the reason the plugs are fouling so quickly..

My view would be mixture too rich (really really too rich to foul the plugs so quickly). This could be for several reasons...
1) mixture screw set incorrectly
2) still some blockage in air intakes somehow..
 

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Discussion Starter #5
Fuel pump and carb strip and clean was one of the first things checked first time around and again recently (I just did not make it clear in my post.:O)

Thanks for the suggestions keep them coming,

Carbs were and are spotless no fuel residue, needles diaphragms ok and all passage ways are clear floats are clean and undamaged.

Also tried to run with a remote fuel supply and replaced the fuel filter and checked the fuel lines.
The weird thing is trying to run it on the bench without the airbox to see what is going on there does not appear to be that much fuel coming through.
I cannot find anything at all obviously wrong with the carbs. I have even hooked the carbs up to the fuel pump off the engine and turned the pump over to see if fuel was being dumped in past the needles and all seems to work fine.

I did think could this by sticky piston rings allowing oil pas the bores and wetting the plugs, is this sort of thing a common blade occurrence.
 

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Fuel pump and carb strip and clean was one of the first things checked first time around and again recently (I just did not make it clear in my post.:O)

Thanks for the suggestions keep them coming,

Carbs were and are spotless no fuel residue, needles diaphragms ok and all passage ways are clear floats are clean and undamaged.

Also tried to run with a remote fuel supply and replaced the fuel filter and checked the fuel lines.
The weird thing is trying to run it on the bench without the airbox to see what is going on there does not appear to be that much fuel coming through.
I cannot find anything at all obviously wrong with the carbs. I have even hooked the carbs up to the fuel pump off the engine and turned the pump over to see if fuel was being dumped in past the needles and all seems to work fine.

I did think could this by sticky piston rings allowing oil pas the bores and wetting the plugs, is this sort of thing a common blade occurrence.

After replacing the plugs she runs and rides just fine?
No gremlins at all?
You are starting her on the choke circuits I assume?
Did you strip the chokes out during the carb clean?
 

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You've sprayed carb cleaner around each intake manifold and she's not sucking from anywhere?
 

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Discussion Starter #8
Chokes stripped out during clean all good.
No leakes, have even replaced one rubber that I suspected but no different.
the thing is if it sucked air on one I would expect it to fire up on the other cyls, and run rough.

A mate suggested float heights but they are fixed on these floats and non adjustable. Going to check them again but not convinced.
 

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Im with everyone on the plugs that are fouling to quickly i could gather that it was running way to rich the second you mentioned grayish smoke coming out of the exhaust on the over run. . .maybe check the petcock valve i mean i have struggled with bikes myself and sometimes its the small things that can give you the biggest problems. Just my 2cents.
 

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Discussion Starter #10
I know what you mean about simple things my brain is tired:mad:!
Thing is the petcock is is eliminated as is the fuel pump when using a remote fuel supply.
 

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Crap i forgot you said you ran it from external fuel source my bad:huh: . . .this is a stupid question i know but does it have the stock jetting in or aftermarket jets?that could also be the reason why its running to rich.
 

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Discussion Starter #12
Standard jets standard pipes.Completely standard.
The thing is its not running rich as such because it does not get to the point where it starts so when spinning it over its only running on the pilot/choke circuits.
 
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