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Old 10-08-2007, 11:41 PM   #1
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Air Leak or Tune?

Having a problem with my new Kyosho CRF .12, didnt seem to get much response in that thread so thought i'd start this

The engine has the somewhat common problem of not retuning to idle immediately after being gassed. When I bring the engine up to temp and tune it on the box, the only way I can get it to return to idle after being gassed is to bring the idle right down. This seems to work, but at the end of the heat when it's up to racing temperature (only 105-110 degrees C) the idle hovers again before dropping back down. I should mention the drop back down isn't gradual, it more hangs up and then drops back to idle, rather than staying up and then gradually returning down.

I tried both leaning and richening the bottom end without much success, and if I turn the idle up even slightly the problem is much worse. I'm not sure if this is relevant, but the engine also flamed out twice in racing after 2 crashes, one was a rollover and the other the car ended up on a bit of an angle... both times I didnt gas it when it was sitting in the grass so i figured that was due to the low idle

OK, so I know a lot of people with this engine have problems with the glue seperating from the carb insulator, but my carb hasn't moved and when i pulled it out last night the insulator was tightly fixed (still could have had cracked glue i guess). I also tested for a leak using the soapy water technique and I got no bubbles from around the carb, but admittedly this was the first time I've ever tested for an air leak

Also my Fuel is not the issue, neither is shimming or plugs. Hope someone can help, I really want to avoid cutting the insulator off and attaching a new one if that isn't the problem
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Old 10-19-2007, 11:02 AM   #2
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Just a thought here, but have u tested ur fuel lines and tank to make sure they have no pinholes that u cant see that might be causing this surging idle headache??
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Old 10-20-2007, 12:49 AM   #3
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dude the symptoms sound like it is lean.

could be your fuel man. i'll see if i remember to bring some runenrtime tomorow and we can try another fuel
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Old 10-20-2007, 06:09 AM   #4
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I had a similar problem. Reduce the idle speed till the engine will just stay alive. Only then will you be able to adjust the low speed mixture.

Quote:
Originally Posted by CraigM View Post
Having a problem with my new Kyosho CRF .12, didnt seem to get much response in that thread so thought i'd start this

The engine has the somewhat common problem of not retuning to idle immediately after being gassed. When I bring the engine up to temp and tune it on the box, the only way I can get it to return to idle after being gassed is to bring the idle right down. This seems to work, but at the end of the heat when it's up to racing temperature (only 105-110 degrees C) the idle hovers again before dropping back down. I should mention the drop back down isn't gradual, it more hangs up and then drops back to idle, rather than staying up and then gradually returning down.

I tried both leaning and richening the bottom end without much success, and if I turn the idle up even slightly the problem is much worse. I'm not sure if this is relevant, but the engine also flamed out twice in racing after 2 crashes, one was a rollover and the other the car ended up on a bit of an angle... both times I didnt gas it when it was sitting in the grass so i figured that was due to the low idle

OK, so I know a lot of people with this engine have problems with the glue seperating from the carb insulator, but my carb hasn't moved and when i pulled it out last night the insulator was tightly fixed (still could have had cracked glue i guess). I also tested for a leak using the soapy water technique and I got no bubbles from around the carb, but admittedly this was the first time I've ever tested for an air leak

Also my Fuel is not the issue, neither is shimming or plugs. Hope someone can help, I really want to avoid cutting the insulator off and attaching a new one if that isn't the problem
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Old 10-21-2007, 02:55 AM   #5
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I took the carb out to replace the insulator and noticed a decent amount of fuel had leaked through the front bearing, does this mean the bearing is gone or is this normal?
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Old 10-21-2007, 04:05 AM   #6
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Quote:
Originally Posted by CraigM View Post
I took the carb out to replace the insulator and noticed a decent amount of fuel had leaked through the front bearing, does this mean the bearing is gone or is this normal?
I would be surprised if the bearing was gone. If you already have the engine out replace both bearings any way it's certainly cheaper than replacing the engine later because you thought it would be ok.
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Old 10-22-2007, 04:10 AM   #7
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Craig, I've been running the original CRF for almost a year now. The problem you are experiencing is definitely a lean condition. The CRF is definately not your standard run of the mill motors. I'd bet that you dont get that high idles untill you run a few laps, thus heating up the motor, then bring it in, and its like gurgling high idle, and when you blip the throttle, your idle stabilizes. You need to richen the bottom end, and most likely you'll need to open up idle screw, otherwise the motor will die.
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Old 10-24-2007, 11:44 PM   #8
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Craig, I've been running the original CRF for almost a year now. The problem you are experiencing is definitely a lean condition. The CRF is definately not your standard run of the mill motors. I'd bet that you dont get that high idles untill you run a few laps, thus heating up the motor, then bring it in, and its like gurgling high idle, and when you blip the throttle, your idle stabilizes. You need to richen the bottom end, and most likely you'll need to open up idle screw, otherwise the motor will die.
nah the idle doesnt stabalise when its reved, but generally the problem worsens after a few laps. assuming it's the insulator, the air leak would worsen as the block expands. richening bottom helps a bit but then it's super rich duper and doesnt get anywhere near temperature

I've replaced the insulator and glued it with cold weld and sealed the carby with rtv. I didn't bother replacing the bearings because they're so new. I'll run it this weekend to see if the fix works
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