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Discussion Starter #1
Hey, I was on here a while ago asking about bikes and I just picked up a CB750. It's in good shape but didn't quite run so I took off the carbs and sure enough the slow jets were clogged. Other than that everything looked pretty clean. The only problem I have now which can't find in the factory or clymer manual is the choke valve on the number 1 carb is loose an doesn't move with the other three. It stays down when I turn the choke off and I can wiggle it around with my finger. I'm pretty sure I can be riding this as soon as this is fixed so I would definitely apprecate any and all information that might help.
 

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you didn't do a crap job so much as I am not sure how to help you.

Honestly I am not sure Honda makes that part seperatly for your carbs and whether it is still available. Replacement also requires a full teardown of the carbs to the basic components.

Your best bet is to get another set of used carbs off ebay and from the two sets make one really good set.
 

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And if everything else is OK with those carbs, use them. You only use the choke when starting, and having a working choke on the other three cylinders should be enough to start the bike.

I'd at least try them before spending money on other carbs.
 

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The early CB 750 SOHC Carbs have a link type of thing that goes from the choke rod mount to the choke plate (inside the carb, next to the slide). They are linked together with a link that goes from the lever to a recess in the choke plate and it controlls its up and down movement.
You will need to remove your carbs from the bike and seperate them from the mounting plate to get access to the choke plate. They can be a bugger to get lined up correctly.
After you have removed the carbs and seperated them from the mounting plate, you will need to remove the nut that holds the choke lever on the carbs. Remove the lever and hold the carb upside down to get the parts out(the choke plate and lever will fall out of a cavity next to the slides, you'll need to remove the tops of your carbs). You should have a choke plate and link come out of the hole. The link has a small button on it that goes in the recess of the choke plate and raises it up and down with the lever. Getting the button/recess AND the choke lever lined up at the same time can be frustrating.

Not so much a crappy question, but a crappy answer (Pull them carbs again!!<img src=icon_smile_big.gif border=0 align=middle> )

You might be able to get to the link thing with out pulling the carbs from the mount, but I find it easier to pull them apart.( or the link may be missing, or mounted backwards)

DG
 

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unga - it isn't that the choke is stuck in the off position in the one cylinder, it is in the down position and won't retract so the choke is always on for #1 cylinder. honda chokes are a trap door style which means the airflow is constantly blocked and the cylindy will run rich no matter what.

Honda does not sell the choke individually nor any of its parts. If the choke trap door is just free wheeling in the carb there is a good chance it broke off the choke linkage and can't be reconnected. Maybe you got lucky and it just wasn't put back right, but if it is fucked then you are going to need another set of carbs to pirate parts from. I had this happen to my 74 cb550 a while ago and the only solution was to get another carb bank with working choke and pirate it for parts.
 

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My reply above was for the early style CB 750 Carbs on the top in this picture. The early style carbs do not have an accelerator pump. The later (F) style carbs are pictured on the bottom. They have an accelerator pump.
The choke mechanisms are completely different on the 2 styles of carbs.
DG





Edited by - dgfischer on Sep 23 2007 8:36:33 PM
 

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Wow,

for once I totally forgot to be my usual hard-on self....must be slipping in my old age.

For future reference - When posting a Tech Question you must include:

Year of Bike
make of bike
model of bike
relevent modifications (e.g. don't ask a timing question and forget to mention you have an aftermarket cam)
 

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Discussion Starter #10
Thanks for all the advice. I'll be pulling everything apart tonight or tomorrow and hopefully I'll be able to put everything back together without pirating parts. To clarify I have a 1974 Honda CB750 (K5 according to the serial number) with no relevant mods. My carbs look like the top picture from dgfischer's post. If the little button that the choke plate is supposed to fit on is indeed broken off, will leaving the choke plate out cause any problems? I know UngaWunga said the other three should be enough to start it which makes sense, but I'm not sure if that's assuming the other is stuck in the off position as opposed to being totally gone.
 

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If it is a 1974 it is a K4, if it is a 1975 it is a K5. If the build date on the neck tag says 74 then unless it is like january of 1974 it is most likely a 1975. Does this make a difference? slightly as there were a number of subtle changes on the 1975s. For example does your petcock use two screws and a flange to attach or is it a screw on?

In the warmer weather I usually use the choke for all about 2 seconds to start it when cold: pull it, up start, shut it off just like that. cb750s don't really idle when cold anyway. When it is cold weather I will have the choke on for up to 2 minutes while she warms up. running it without choke in #1 should be ok for starting and running, the only problems being that it may make your kick starter a little harder to use (when #1 is the cylinder to start off of) and that you'll probably have a little bit of a surge when it is warming up.
 

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quote:
If the little button that the choke plate is supposed to fit on is indeed broken off, will leaving the choke plate out cause any problems?
The little button would take alot of abuse to get broken off. If you push the choke plate up with your finger and then work the choke lever does it feel like something is happening in there? If so you probably just need to put the button in the recess, if not the link may have been left out (GASP!).
There shouldnt be a problem with just having the choke plate in just 3 carbs(by removing the choke plate in the 1 carb), but if it were me I would replace the link to have the carbs perform like they were meant to. I probably have an extra link if you need it, PM me.
If you can feel that the link is still present, you may be able to slightly loosen the nut on the choke lever (not remove the lever) to give you the play in the link that you would need put the button in the recess. The lever is indexed to the link and you may be able to get it in place by just giving it (the link) enough play to "slide" over the choke plate to get the button in to the recess.
Good Luck!
DG
 

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Discussion Starter #13
I got it all put back together last night. For whatever reason the choke linkage just wasn't connected to the plate. I loosened the nut and reconnected it. After I pt everything back together I was able to start my bike for the first time since I owned it. It was awesome. Next step, brakes... going doesn't do me much good if I can't stop. Thanks for all the help.
 
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