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Discussion Starter #1
Hi everyone,

I've got this problem with my 1998 Quadrunner LTF250, and I'm hoping there are some experts here that might be able to help me get on the right track again.
The problem is that the quad seems to be eating spark plugs like candy. If I put a brand new plug in, it will start great, and run fine, but after a few short rides it gets harder and harder to start it again, until the plug is completely stuffed and I need to replace it. When I take the plug out (even after a few minutes of idling), it is pitch black.
I've been doing a lot of reading, and people say it can be either oil in the combustion chamber, or it's running extremely rich.
Before I start spending $$$ on parts, I'd like to know which of the two is most likely the problem.

So far, I have cleaned out the carby and the airfilter. I don't think there is any issues there. There is not much I can regulate on the carby, as there is no mixture screw or something like that. I have checked the diaphragm in the carby and it seems to be in tact. Don't think it has ever been replaced, but this is an expensive part for a 98 model, so I don't just want to replace it without a good reason. The rubber seems to be quite thin and flexible. Not sure what a new one feels like.

When I rebuilt the quad a few years ago, I put new piston rings in. The cylinder wall looked good to me, but I was told recently that I should have honed it before putting the piston+rings back in (which I didn't), and that this could possibly be my problem because oil might get in the combustion chamber that way. Is this true ?
Is there a way to check this without taking the whole cylinder off ? Would a compression test be sufficient for that ?

I also put two new values in. (I actually took the head into a shop and have some professionals do that bit)
The only thing at this stage is that it looks like I have a small leak between the cylinder head and the valve cover, but this should not matter right ?

Has anyone dealt with this before, and What would you advise on doing next ?
Any help is appreciated. Thanks heaps guys !
 

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I dont know a lot about these motors...But I would think if your burning oil enough to foul a plug, you'd see blue smoke in the exhaust. Maybe getting a weak coil ??
When my KQ gets hard to start..I have the valves adjusted.
 

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Discussion Starter #3
That is what I thought as well Tigmonster. That is why I want to make sure I have checked everything I can before I pull the cylinder off and realise nothing is wrong... Even if I did not hone the cylinder when I put new rings in, that should not cause a plug to foul that quick right ?
I'm going to check the valves this weekend.

Which coil are you talking about ? Ignition coil ?
 

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Ignition coil..... I dont have the specs on it...I do believe there is a page on here to check the ohms on it ...some on Youtube also
 

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Discussion Starter #6
I just checked the ignition coil, and it seems to be ok.
The primary is between 1 and 2 Ohm, and the secondary is 9800 Ohm.
 

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Discussion Starter #7
Just lifted the valve/cam cover to check if the valves were stuck, but it doesn't look like anything is wrong there.
 

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Discussion Starter #8
Looks like I might have found what the problem is. After TubbyTubb pointed me to the 'metering' rod in the carby under the diaphragm, I opened it up again, and compared it to the carby diagram. Turns out that I'm missing a ring that is keeping the needle down under the large spring ! I'm very confident that this might be my issue. It will obviously cause the needle to go open way too far and will flood everything...
Now I need to find out how I can get this special ring. If I have to get it from the US it will take a bit of time to get here :-(
https://www.dropbox.com/s/lmck0ff6eyl9dow/carburator.jpg?dl=0
 

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Hi everyone,

I've got this problem with my 1998 Quadrunner LTF250, and I'm hoping there are some experts here that might be able to help me get on the right track again.
The problem is that the quad seems to be eating spark plugs like candy. If I put a brand new plug in, it will start great, and run fine, but after a few short rides it gets harder and harder to start it again, until the plug is completely stuffed and I need to replace it. When I take the plug out (even after a few minutes of idling), it is pitch black.
I've been doing a lot of reading, and people say it can be either oil in the combustion chamber, or it's running extremely rich.
Before I start spending $$$ on parts, I'd like to know which of the two is most likely the problem.

So far, I have cleaned out the carby and the airfilter. I don't think there is any issues there. There is not much I can regulate on the carby, as there is no mixture screw or something like that. I have checked the diaphragm in the carby and it seems to be in tact. Don't think it has ever been replaced, but this is an expensive part for a 98 model, so I don't just want to replace it without a good reason. The rubber seems to be quite thin and flexible. Not sure what a new one feels like.

When I rebuilt the quad a few years ago, I put new piston rings in. The cylinder wall looked good to me, but I was told recently that I should have honed it before putting the piston+rings back in (which I didn't), and that this could possibly be my problem because oil might get in the combustion chamber that way. Is this true ?
Is there a way to check this without taking the whole cylinder off ? Would a compression test be sufficient for that ?

I also put two new values in. (I actually took the head into a shop and have some professionals do that bit)
The only thing at this stage is that it looks like I have a small leak between the cylinder head and the valve cover, but this should not matter right ?

Has anyone dealt with this before, and What would you advise on doing next ?
Any help is appreciated. Thanks heaps guys !
You will have to get a hotter spark plug. My lt185 has the same problem
 
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