So a couple years ago I decided to pull my mom's old motorcycle out of the barn and get it running. I'm a noob at working on stuff, so I gave it to a friend to work on. We cleaned and reconditioned the gas tank (including replacing the pitcock), and I know he rebuilt the carbs and replaced the throttle cable. He ran out of time, so a couple months ago I decided I'd finish it up myself. I got it to start up fine, but it is idling really really high (like 6000 rpms). Adjusting the idle screw doesn't seem to be helping. There seemed to be a lot of pressure on the throttle cable, so i disconnected it to let it fall slack and make sure that wasn't the issue. It wasn't. I had to replace the float in one carb, and was not having fun adjusting it. I tried the float measurements per the service manual and couldn't get enough gas. So I measured the old one, and the other side and installed it based on what was in there already. I guess I should mention I did install the little stopper on the float and it seems to be filling up correctly. Does anyone have any suggestions as to what I can try to get the idle speed down? I suppose it's possible my friend rebuilt the carbs incorrectly. It's very possible I need to adjust the float level (though logically, that doesn't really seem like it would affect idle speed). It is somewhat possible I have the wrong throttle cable. Any other suggestions?
CB175 High Idle
- Thread starter bilwaukee
- Start date
how far in is the thottle level screw?
back it out some so its not accelerated.
are you sure you adjusted the idle screw the right way?
to the right is lower idle, left is higher.
also, if your throttle grip/mechanism is not put on right on your bars, it can cause it to accelerate and appear to no have tension on the cable.
also, cable positioning can affect it and also appear to not have tension.
the floats will most of the time not be like the book says, it will differ by a mm or two..
and sync your carbs. check all that then get back to us, pm me if needed.
back it out some so its not accelerated.
are you sure you adjusted the idle screw the right way?
to the right is lower idle, left is higher.
also, if your throttle grip/mechanism is not put on right on your bars, it can cause it to accelerate and appear to no have tension on the cable.
also, cable positioning can affect it and also appear to not have tension.
the floats will most of the time not be like the book says, it will differ by a mm or two..
and sync your carbs. check all that then get back to us, pm me if needed.
well, the throttle cable i completely disconnected (disconnected from the hand grips and from the handle bars). it's more or less hanging off the bike. i thought there was a chance it was installed backwards into the carbs (as it seems like that is actually possible), but compared to the factory manual it seems right. i'll try the throttle screw again. per the factory manual it says it should be like 2 turns out. i basically started with it two turns out, and it was way off. again, we're talking like 6000 rpms instead of the 800 (or whatever) it should be. as for the carb rebuild kit, i'd really hate to have to buy a second one, but i'm willing to if there are no other things to try.
i have to ask, what do you mean by "sync your carbs?" is it possible the float issue plays into this? as an engineer, it seems like it wouldn't matter since the float just lets gas in faster or slower and higher or lower. the throttle should really control flow rate, so the float can't cause this issue.... maybe i'm wrong.
i have to ask, what do you mean by "sync your carbs?" is it possible the float issue plays into this? as an engineer, it seems like it wouldn't matter since the float just lets gas in faster or slower and higher or lower. the throttle should really control flow rate, so the float can't cause this issue.... maybe i'm wrong.
Sometimes the manual is wrong. Close the idle screws and turn them out 1/8 turn at a time. And see if tha works. Sometimes you have to run idle higher. No biggie.
Also do you check that your choke Is not on?
Floats will either make you run rich, good, or lean. Or not run.
Sync'ing your carbs means getting a sync gauge and check to adjust your carbs so that they are all working the same.
Here's a link I found on google that explains
http://m.motorcyclistonline.com/howto/motorcycle_carb_sync/
Also do you check that your choke Is not on?
Floats will either make you run rich, good, or lean. Or not run.
Sync'ing your carbs means getting a sync gauge and check to adjust your carbs so that they are all working the same.
Here's a link I found on google that explains
http://m.motorcyclistonline.com/howto/motorcycle_carb_sync/
Back up a little bit. First off it's easy to put the slides in back to front on some carbs - can't remember if it's possible on yours but check that teh cutaway is facing the filter and not the engine.
Next, there are two screws on your cabs. One adjusts the amount of air that mixes in with fuel through the pilot jest. The other raises teh slide when you screw it in. Peer down the carbs from the filter side and adjust the slide screws so that they just touch the slides and then turn them in say another 1/2 turn to start with.
The screw that's mounted horizontally close to the filter end is the air/mixture screw. The screw in the middle (where the slide runs up and down) raises the slides. Try to grab two manuals form on line. First a shop amnual and secondly copy of a Carburetor manual. You can grab a VM Mikuni manual for general information on how carbs work.
Next, there are two screws on your cabs. One adjusts the amount of air that mixes in with fuel through the pilot jest. The other raises teh slide when you screw it in. Peer down the carbs from the filter side and adjust the slide screws so that they just touch the slides and then turn them in say another 1/2 turn to start with.
The screw that's mounted horizontally close to the filter end is the air/mixture screw. The screw in the middle (where the slide runs up and down) raises the slides. Try to grab two manuals form on line. First a shop amnual and secondly copy of a Carburetor manual. You can grab a VM Mikuni manual for general information on how carbs work.
Foxriderar77
New Member
I am having the exact same issues with my CB 175, The floats can be real finicky.
Teazer- I thought that the larger cutouts had to face the engine, not the filters, guess I found the answer to my problem haha
Teazer- I thought that the larger cutouts had to face the engine, not the filters, guess I found the answer to my problem haha
You could also check to see if you have a vacuum problem at the carb boots. Turn the engine on and squirt some starter fluid, or propane, around the carb boot. If the fluid or gas fires off in the engine block, then you have a leak and need to fix or replace the boots. I had to do that with my girlfriend's xs400. Between that and changing out the old messed up throttle cable, the high idle problem went away.
