[Richard_Pitman]

Here in the UK, I'm 55 metres above sea level.

My CB175 was imported from Colorado, USA, average height 2000 metres above sea level.

Could it be that simple, my weak mixture is due to bike being set up to run at Colorado air pressure ? And if so, what changes from original spec would have been made ? As I mentioned in my project thread, I'm pretty sure it has the standard 98 main jets.

( For some reason, John Denver signing about Colorado Rocky Mountain High came to mind )

 

[Simo]

Plug chop?

 

[Richard_Pitman]

From my project thread:

 

[steve9e]

hi Richard,

Have a look at LDR sticky on plug signs. With modern fuels you do not get such a definate sign unless something is very wrong. I would think they look OK to me except they could do with a clean? How long did you run the bike before you took them out ,and was it at running temperature after a road run? Just make sure your jets are correct for the UK/Europe and that the carb is clean etc. Like Simo said do a plug chop, but really there is not a lot to do with the standard carb other than tweek the pilot screw.
cheers

 

[Richard_Pitman]

They are new plugs, probably done a couple of actual road miles, some time idling in the shed before that. Engine fully up to temp when those pics were taken.

No, I don't really see much information to be gained from those plugs, apart from clearly not over rich, or burning oil.

Pilot screw adjustment won't have significant effect on WOT, in any case it idles nicely, suggesting to me that pilot screws are adjusted correctly.

My next experiment will be to raise the carb needles to richen the mixture. From memory, they are in the middle notch at the moment. If that fails, I'll try some different main jets.

 

[Richard_Pitman]

Got it sorted !

First off, I tried raising the carb needles, clip moved from centre (third) notch to bottom notch. This improved things a bit, would now rev to 7500-8000 rpm, but still not right.

So I took out the main jets and emulsion tubes, to confirm that they were correct 98 size. When I first cleaned the carbs, I don't think that I actually unscrewed the jets from the emulsion tubes. I did this time, and there was some dirt in both sides, although the actual jet passages appeared clear when held up to the light. I gave everything a good soak in carb cleaner, then ran some multistranded copper wire through both jets. Refitted and went for a test ride, much better, would rev to the redline now.

Plugs were now quite black, so I put the needle clips back into the standard centre position, then took a final test ride before darkness fell. And it now runs nicely, ticks over correctly, picks up on the throttle without flat spots, and revs out as it should.

Just goes to show that apparently spotless carbs weren't. And I do go to Specsavers !

 

[J-T]

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