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Four stroke experts needed.

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Hi all, long time lurker, first time poster. As the title states, I am in need of advice from a thumper expert as my area of expertise is in 2 strokes.

I have a street bike with a 200cc air cooled XR200 clone. I am hoping one of you experts can help me with a problem as I am at my wits end with this bike.

The bike is a Dragon ¾ chopper with the Lifan 200cc air cooled motor and Keihin carb. Recently it developed running problems. It starts fine, idles fine, and goes up to about ¼ throttle fine. Over ¼ throttle it bogs out and dies. I originally suspected main jet in the carb due to the symptoms but apparently that wasn’t the issue.

Here’s what I’ve done so far:

1) Cleaned the carb and jets 6 times so far.

2) New fuel with techron concentrate.

3) New fuel filter

4) New NGK plug

5) Checked battery, ground, and electrical connections

6) Tried adjusting needle jet, no change in performance

7) Cleaned air vent on gas cap

8) Verified good fuel flow thru petcock

9) “ “ “ “ good airflow

10) And probably several other things I’m forgetting.

My only ideas at this point are possible valve issues as it has about 800 miles on it. But can’t get valve specs anywhere, and even if I could, I think that it would affect performance across the board and not just at ¼ throttle or above. Second idea was a possible bad CDI. But once again can’t get ohm specs/readings so I can’t really test it. Third idea was I noticed light surface cracking on the rubber intake boot from carb to cylinder and thought it could be sucking air in there and causing a lean condition. I am having a problem locating that part so I tried wrapping it in duct tape which I think would have affected it and still had no change in performance.

So, anybody have any ideas?

Thank you in advance for your time, any help would be greatly appreciated. And I apologize for the length of the post but I wanted to make sure I gave as much info as possible.

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Dying under quarter throttle is not the main jet.

Pull the pilot jet and blow some air through it.

I would look for water but given the number of times the carb has been apart, that isn't likely.

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Dying under quarter throttle is not the main jet.

Pull the pilot jet and blow some air through it.

I would look for water but given the number of times the carb has been apart, that isn't likely.

It doesn't die under quarter throttle, as I mentioned, that's the only time it runs right. It dies OVER quarter throttle, which would be main jet.

I agree with the idea of water but not only has the carb been apart, the fuel was all drained, replaced, and is free of water.

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I would check the fuel lines from petcock to carb for any resistance...it sounds like it is starving for fuel or it could easily be a problem with ignition timing.

Although the ignition module is not testable without a known good part, I would check the key for the flywheel and make sure it isnt bent or have any freeplay.

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I would check the fuel lines from petcock to carb for any resistance...it sounds like it is starving for fuel or it could easily be a problem with ignition timing.

Although the ignition module is not testable without a known good part, I would check the key for the flywheel and make sure it isnt bent or have any freeplay.

Thanks for the suggestion on the flywheel woodruf key, that's one of the few things I haven't checked. I'll give that a shot tonight.

Fuel lines seem to be flowing freely, but it certainly exhibits the conditions of starving for fuel.

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Well it wasn't the flywheel key either, anyone have any other ideas? I'm about ready to ghost ride this bike off a cliff?!foul:

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The needle & needle jet, start taking over as you're passing 1/4 throttle it, but it sounds like you've checked that. Have you checked float height? What color is your plug?

JM

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I apologize, I thought I had updated this. I finally figured it out. Turned out while I had checked that the connections on the coil were tight, one of the female connections where it was crimped turned out to be corroded. Stripped the wire, new female, and it was good to go.

Thanks for the replies.

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