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Discussion Starter #1
Hi guys,

Just to preface, I barely know the basics when it comes to bikes. So with that said, I rebuilt both carbs on a cb175. During the build, I increased the main jet and also lowered the retaining link on the needle to account for pod filters being added on. I installed them back on my cb175 the bike started up but shot right to redline. First time it happened, it scared the living crap out of me. I thought the bike was possessed. So, I humble myself and ask for your help. Something tells me it is as simple as turning a screw.

Oh yeah, while I'm at it, is it normal for me to start the bike cold without having to choke it? The bike seems to only want to start with the choke wide open. I thought rebuilding the carbs and cleaning it up would fix that but it didn't.

Thanks. I've been thinking I may start a thread for my project. This bike is supposed to be for my daughters when they get older. They've already named it "bullet speed". I guess it is contingent on me getting the bike to run first.


Ken
 

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Ken..... It is more likely you "developed" an air leak that is causing the revving spike.
I cut and add paper gaskets to the intake manifold joints to overcome this...(that's the "usual" culprits)...
 

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Discussion Starter #3
Would it help if I tighten the carbs more? I didn't crank down on the bolts that join the carb to the engine block. Is this typically pretty tight?
 

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Sensei
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could help, but that o-ring is already deformed, and you may crack the aluminum manifolds... A decent "snug" is usually sufficient.....


...... paper gaskets take about 15 minutes work, and usually fixes this.....
 

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Discussion Starter #5
I forgot to mention, all the o- rings were replaced. Does this point to the adjustment in the needle valve?
 

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Sensei
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OK....ASSUMING your manifold joints are airtight, you could simply be getting too much fuel/air mix in.....
Are the slides in correctly (cut-aways towards the air cleaner?)
Are the needles in with the circlips (e-clips) in the center slot?
Do the slides drop to the almost fully closed idle position (back off the idle screw ajustment)
Are the throttle cables too tight? (there should be slack at idle in all three cables, and refer to previous question)
Are the rubber gaskets on the carb tops? (air can leak in there as well)
 

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Discussion Starter #7
Well I went through the checklist and it worked! The little cb175 has a lot of pickup now with the new larger main jets. Looks like the project can continue.
 

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I'd like to know more about these paper gaskets. Here's what I envision from your description...

A strip of paper about .5" wide and with a length to cover the circumference of the carb/inside of intake boot. Am I on the right track? How heavy of paper do you use?

Thanks!
 

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Basically, what I think Steve was getting at was this: Pick up a sheet of gasket paper and lay your intake "manifolds" on them and trace the outside and the bolt holes onto it. Cut it out. Then trace and cut the hole in the middle for the air/fuel to actually pass through, and trim further if necessary to eliminate any gasket even slightly blocking the passage. Then bolt between the intake "manifolds" and the head...


GB :mrgreen:
 

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Re: Rebuild carbs and now bike spikes up in RPM after starti

I am having the same trouble. i rebuild and cleaned my carbs and its just spiked up the rpms like crazy!Did the gasket paper end up solving your problem?
 

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Sensei
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Re: Rebuild carbs and now bike spikes up in RPM after starti

This topic is very specific to the 175's with all aluminum manifolds.....
However, bikes that have rubber "boots' may have a leak at the "boot" to head joint as well .....
 

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Discussion Starter #14
Re: Rebuild carbs and now bike spikes up in RPM after starti

I did solve my problem. I had installed the slide backwards. I believe a previous post mentioned making sure the cutout portion of the slide is pointing towards the air filter and that the slide seats all the way. Let me know if this works.....
 

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Re: Rebuild carbs and now bike spikes up in RPM after starti

I had this same problem too. In my case the 'O' ring was to big causing the carb body to distort as the screws were tightened. I measured the groove in the carb body and ordered an O ring from an engineer store, use the measured inside dia and for cross section dia I added 1mm to the depth of the groove, built it up with a smear of Hylomar to the mating faces, perfect seal and perfect throttle response.
 
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