The photo of the plug was after a 4km Idle home when the bike stopped I checked the plug and it was light grey. I read a 220 page book about two stroke performance tuneing by grayham bell. I thing the problem is thst the shop hasnt machined tge head properly for the correct squish tolerances and didnt cut away the centre section which in turn has raised the compression ratio far too much and the engine is getting too hot and and suffering from detonation from overheating and causing a vapour lock in the cylinder wich is preventing the fuel from enttering the combustion chamber and starving the engine. I no expert but could this be the case BIG ???
250 what could be wrong 97 kx250
- Thread starter jimsowen
- Start date
Oh heck that guy was into PHONES. Somehow I thought you were showing the plug as it was when it gave the symptom known as "dieing". Now I see you just wanted us to see it as it was when you rode it home slow.
Ok. I can believe your engine has a squish band that isn't optimum. I have seen it over and over and over. If it was done right your rig should have been happier with leaner jetting than was optimum on the stock bore. It may now require richer jetting to save it from detonation. But unless it is causing your bike to seize as I do believe I stated, I don't think that a lean condition is causing the die out unless you are getting said lean condition from a bad float level. If you set it EXACTLY like Andrew said to it should be fine. Reread that instructional and if you have any doubts do over.
Somewhere in that 220 pages I hope they covered how a motor requires leaner jetting as it gets warmer.
Ok. I can believe your engine has a squish band that isn't optimum. I have seen it over and over and over. If it was done right your rig should have been happier with leaner jetting than was optimum on the stock bore. It may now require richer jetting to save it from detonation. But unless it is causing your bike to seize as I do believe I stated, I don't think that a lean condition is causing the die out unless you are getting said lean condition from a bad float level. If you set it EXACTLY like Andrew said to it should be fine. Reread that instructional and if you have any doubts do over.
Somewhere in that 220 pages I hope they covered how a motor requires leaner jetting as it gets warmer.
Alexander grahym bell was the person who invented the phone lol. And yes the book goes in to highly detailed jetting discriptions taking barometric pressure, humidity, altitude, temperature and even different octane levels, avgas, ethanol and methanol jetting heat ranges to plug heat and combustion temperatures to obtain correct compression ratioes and burn rates so as not to cook the engine and retain maximum horsepower levels.
No they didnt say about that but it discribed how detonation is caused by incorrect squish and how port timing hight and shape can have a massive effect on how the engine will function. With what was explaind about corrected squish chamber tolerances I assumed that my compression ratio was too high thats why I blew a head gasket the first time I rode it for 5 mins slowly and with such pressure in the crank area and cylinder that couldnt escape through the expansion chamber quickly enough it created a no suction of the fuel through the carby. Im not exactly sure if its called vapour lock but thats the word that came to mind when I was trying to explain it.
Ok. There is no such thing as vapor lock within an engines cylinder. It is a condition of the fuel delivery system with the carburetor involved sometimes.
Detonation can damage a piston, and if it results in preignition the head can get what looks like chicken pox. A head gasket being damaged if the surfaces are right and the torque correct is pretty much out of the question.
Your compression ratio has not gone up so much as to cause concern as much as the shape and diameter of the squish area. Was the shape of the piston crown changed.
In light of what you told me about how the shop built this one so far I think I would be checking for piston seizure and port height just so I could know what was and wasn't done.
Detonation can damage a piston, and if it results in preignition the head can get what looks like chicken pox. A head gasket being damaged if the surfaces are right and the torque correct is pretty much out of the question.
Your compression ratio has not gone up so much as to cause concern as much as the shape and diameter of the squish area. Was the shape of the piston crown changed.
In light of what you told me about how the shop built this one so far I think I would be checking for piston seizure and port height just so I could know what was and wasn't done.
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Measure the outer extreme of the squish and the piston or use some clay. Simply raising the head up will reduce compression two ways but does not change the shape.
I am sure in the 220 pages they covered the fact that you can have a squish area that is too spacious and contribute to detonation too. Ask if you aren't familiar with how it works if bell didn't.
I am sure in the 220 pages they covered the fact that you can have a squish area that is too spacious and contribute to detonation too. Ask if you aren't familiar with how it works if bell didn't.
Yeah it did explain that the smaller the squishband the better unless its too small tge tgd piston will hit the head deck. I measured it and they havnt machined the extra.75mm around theouter edge to accomodate the bore diametre being rebored. So theyve dodged tge f6655k out of Iit. Not happy.