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that honda XL again.

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siMcfixit
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Joined: 01 Mar 2021
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PostPosted: 17:50 - 29 Apr 2023    Post subject: that honda XL again. Reply with quote

googlidge of engine number came back as an 85 cb 125. but others say same engine.
its in a dirt frame at the moment. no battery. just basic wire from engine to coil condensor. points. basic setup.
was getting nowhere fast with the origional carb.. a 26. seen better days. so wound up with a pz27 carb.
bike starts... but badly "bogs"?
open. and a 98 jet. so been down through all the sizes I have and its sitting with a 90 in it now.
still same. starts. can make it sound nice at idle,mix needle ect. but still bogs.
discovered valve clearances at zero. sorted that.
bit better but still bog.
checked cam timing and counter wieghts behind the points.
new spark plug. just because. obviously the more I go down the range of jets ect the less black.
but she is still being a bogger... anyone any ideas. ?
also. new points.condensor and coil. timing and gap done. and redone. and agian. is an old 6v system.
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Nobby the Bastard
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PostPosted: 18:18 - 29 Apr 2023    Post subject: Reply with quote

Can you get Dave001 to translate for you?
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WD Forte
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PostPosted: 19:32 - 29 Apr 2023    Post subject: Reply with quote

lux lyk txt spk m8
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stinkwheel
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PostPosted: 21:44 - 29 Apr 2023    Post subject: Reply with quote

Airbox on, air filter in good order? Exhaust system fitted and functioning? Ignition timing and points gap correct?
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jeffyjeff
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PostPosted: 22:01 - 29 Apr 2023    Post subject: Reply with quote

The symptoms you describe suggest the carburetor is too large for your engine. In such a case, the carb won't provide a combustible mixture over the rev range. Idles OK, but when you open up the throttle, the air entering the cylinder moves at a lower velocity (because the diameter is too large) insufficient to draw fuel into the venturi. Air Fuel ratio leans out and the engine stalls. You say it is "bogging down", and you are probably feathering the throttle in order to keep the engine running. It doesn't take much, if the carburetor size is over by just a few mm, it can affect performance at critical points in the rev range.
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MCN
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PostPosted: 08:34 - 30 Apr 2023    Post subject: Reply with quote

Nobby the Bastard wrote:
Can you get Dave001 to translate for you?



BCF Gliff-Mastir Dave001.

Laughing
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siMcfixit
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PostPosted: 10:50 - 01 May 2023    Post subject: Reply with quote

jeffyjeff wrote:
The symptoms you describe suggest the carburetor is too large for your engine. In such a case, the carb won't provide a combustible mixture over the rev range. Idles OK, but when you open up the throttle, the air entering the cylinder moves at a lower velocity (because the diameter is too large) insufficient to draw fuel into the venturi. Air Fuel ratio leans out and the engine stalls. You say it is "bogging down", and you are probably feathering the throttle in order to keep the engine running. It doesn't take much, if the carburetor size is over by just a few mm, it can affect performance at critical points in the rev range.

logic. it had crossed my mind. when I purchased it said suitable for 125 ect. up to 200cc
will go try with a new 26mm
many thanks
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siMcfixit
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PostPosted: 11:20 - 01 May 2023    Post subject: that bike agian Reply with quote

The points situation bugs me, I would of thought to set the gap at the TDC as marked on side of engine. but that is not the high point of the cam where the points live. if anything the points are open to their max after TDC.
I thought ok. so is the camshaft out of sync. stripped and checked it, nope its where it should be. and cam chain not sloppy, so not heaps of play.
As for exhaust/airbox situation, a cone filter and home brew exhaust. I can understand on some bikes that would upset things. but on a small 4stroke motor?
keeping at it. if nothing else then others might be able to learn something from all this.
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P.
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Joined: 14 Feb 2008
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PostPosted: 11:28 - 01 May 2023    Post subject: Re: that bike agian Reply with quote

siMcfixit wrote:
As for exhaust/airbox situation, a cone filter and home brew exhaust. I can understand on some bikes that would upset things. but on a small 4stroke motor?


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MCN
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PostPosted: 15:24 - 01 May 2023    Post subject: Reply with quote

Have you tried switching it off, then switching it on again?
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Nobby the Bastard
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PostPosted: 15:30 - 01 May 2023    Post subject: Reply with quote

The measurement is quoted at TDC is because TDC is easy to find and the gap quoted at TDC ensures the points open sufficiently to break the circuit to create the spark at the correct time before TDC.

The fact that the points open more after TDC is irrelevant.
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