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Discussion Starter · #1 ·
Hi all, first time posting on the board. New to restoration, but have a few contemporary bikes.

I've been working on my '72 CB175 and just today ran into a new problem. The last few times I rode it, everything was working fine - carbs were reasonably synced, good power, no major issues.

Today, though, I was having more trouble than usual getting it to start up, and then finally when it did, it would rev up to about 9k RPM and continue to idle that fast. Obviously, with a cold engine, I don't want to damage anything, so I shut it down, tried to check the idle adjustment (seemed fine), etc.

I had recently taken out the slides from the carbs, then reinserted, but it didn't seem like they had any trouble going back in. Re-check the slides? Pull carbs entirely and try to troubleshoot?

Any help is greatly appreciated. Thanks!
 

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Sounds like the spark advance could be stuck open, behind the points plate. Secondly is the throttle cable bound up. That seems really high revs for either of these situations, but couldn't hurt to check.
 

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Discussion Starter · #3 ·
Thanks. When I put the slide back in, the throttle cable did seem like it was binding a bit, but tinkered with it a bit to make sure it wasn't getting stuck. Bike revs fast even with throttle fully closed, so I'll check the spark advance next. Tempted to pull the carbs and try to clean them fully, as well.

Any thoughts on why it's hard to start at first, as well? That seems like it may be a separate issue, but I spent about 10 min trying to get it to fire up...related?
 

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You throttle may seem closed on the bars, but look inside and see if the slide is up. check to see if the slide is up with the bike off. I believe those carbs are center pull kiehns, not diaphram type.
 

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Sensei
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27,183 Posts
It is possible you reversed the slides when re-installing (backwards or swapped carbs they go in)...... Cut-away goes to air cleaner side, and shorter (ramped notch) goes to idle screw side.... An air leak in the intake can also cause run-away revving.....
 

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Discussion Starter · #6 ·
Thanks all, got it fixed finally. Slide was backwards, but all set now.

Now to take the whole bike apart to repaint and restore.

Thanks again.
 
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