I figured out that the choke on my stock Keihin has stopped working. Pull the **** and all I get is fast idle, the choke butterfly is free but not moving with the cable. I can't see that it's even connected to the linkage in anyway. It's like it's missing a spring, lever or clip. Maybe I'm not holding my mouth right or got my hat turned around the wrong way or something but I can't figure out what it needs to work. It used to work right, I have no clue what happened to it.
Does anyone have a good close up pic of the right side of a Keihin carb preferable around a 1983 model that I could compare mine too?

 

Can you post a pic of what you have? There is a spring on the front facing side of the carb that is part of the choke mechanism. This and some plastic parts are not very strong.

If you have a round air cleaner with a bolt in the middle, if the bolt is too long it will interfere with the choke plate and cause it to break and perform as you describe. I have seen this on two ironheads.

I got lucky with mine - when i came back from a ride the parts that fell off were sitting on a lifter block.

 

I don't know how much help this pic will be, I can't seem to get a close up that is in focus. It's blurry but you can see that the choke cable is pulled out all the way but the choke butterfly is wide open. There is nothing connected to the choke butterfly shaft to pull it closed when you pull the choke **** out. The choke butterfly is free and flips back and forth easily from open to closed. I can't see that anything is broken off or where anything is missing. At first I thought that the lever or tab on the end of the choke butterfly shaft was on the wrong side of the fast idle cam. When I took the butterfly and shaft out to move it to the other side I couldn't get everything back together again because the screw holes in the butterfly wouldn't line up well enough. The butterfly also was in a bind in the carb throat and wouldn't move so I figured that it wasn't supposed to go together that way. There is a weak little spring on the end of the shaft that doesn't seem to be doing anything, I don't know what that's all about.

 

Here are three pics of a mid 80's big twin Keihin carb, follower by three pics of a 1978 Keihin carb. Note that the choke mechanism is different between the two carbs.

 

Okay, the big twin carb is the same or nearly the same as mine. What pulls the choke plate closed when you pull the choke ****/cable out? There is no tension on mine at all, it just flops around on it's own. What does the spring on the end of the choke plate shaft do? The spring on mine is weak and loose and I can't see that it does much of anything. Is that spring somehow supposed to keep tension on the choke plate and force it closed? Then the when you push the cable back in to turn the choke off, it actually pushes the choke open?
By the pics, mine looks to be assembled right but it won't close unless you close and hold it closed with your finger.
Btw, thanks for the good pics. Maybe one of these days I'll figure out how to use the GF's camera correctly.....

 

There is a 90` hook on each end of the spring. In the 3rd pic you can see one hooked over one prong of the 3-prong thingy. The 3 prongs set different tension on the spring depending on which one is used.

If the hook is broken off then probably the whole carb is good just for spare parts. Often tho it just comes off the prong, and you can carefully re-attach it - using a pair of tweezers or very light needle nose pliers [the kind used for small electrical work, not the typical workshop ones].

Pulling the choke **** out closes the choke plate; pushing it back in opens it.

It is a choke because it chokes off air from going into the carb in order to richen the mixture. More modern bikes have an enrichener which adds extra fuel into to make it more rich.

 

Ah ok, the spring on mine only has a hook on one end of it and that is just like what is in pic #3. That is what was throwing me off because there was nothing to hold the spring in tension against anything. I can't see junking the carb just because the spring is broken or am I missing something here? You suppose that spring is available anywhere? I know it doesn't come in the rebuild kit because I got that today.

I replaced the accelerator pump diaphram today. The old one looked terrible, dried out, shriveled and cracked all around the center. With the new one in.....hardly any difference in the way it runs. The hesitation is still there and just as bad as before.

The more aggravated I get with this the more I'm thinking of making the switch to a newer CV carb but I'm getting tired (and broke) of throwing money at this thing trying to get it to run right.

 

The other end of the spring does not show in the pic. On your carb it is probably broken off. Directly behind the 3-prong thingy there is a boss - you can see it clearly if you look down from the top. That boss has a thin line cut into it. This is where the other end of the spring mates. The other end is round to match the boss.

This is assuming yours is the same as this one.

In any case it will work if you can find a way to secure that other end of the spring.

What is happening is that while you are riding the choke is constantly flopping open and closed. So you get really bad performance. To temporarily eliminate this problem you could find a way to keep the choke open without blocking air flow thru the opening.

The choke only needs to be closed for cold starting.

 

Yep my spring only has a hook on one end, the other end is just round. The boss is there on the carb. I don't know about the line for the spring though, something to look at tomorrow.
The fast idle cam, I think that is what it is called, holds the choke open while the **** is pushed in or in the off position. The only time that the choke can flop around is when the ****/cable is pulled out so that is not a factor in how it runs once the choke is off.

I did notice that with the air cleaner off, I'm getting a spray or mist of gas out of the carb while revving the engine. A couple of times it has tried to roast me by shooting foot long flames out of the carb when it pops back through the carb. Would a bad or out of adjustment intake valve cause that?

I'm waiting for the mailman to deliver my new intake boots and then I'm going to take the carb off, put the rebuild kit in it and reinstall with the new boots. I tried spraying around the boots checking for leaks and found one spot where the engine perked up but I couldn't tell for sure if it was a leak or simply getting some overspray past the boots and close enough that it was sucked into the carb.

As close as I can tell the idle mixture screw? The one of top that used to be capped off was out about 2 turns. It's really hard to tell when it seats. It just doesn't have a good feel to it at all. Turning that screw in will definitely slow the idle down and finally kill the engine. Turning it out will speed the engine up and smooth the idle out but I went as far as 4 full turns out and it never slowed down again, idled rough or died so I quit and set it back at 2 turns out where it was when I started.

 

So the spring is broken. As long as it does not flop when open it is ok. Even a small amount of flopping can interfere with air flow. Back in the day it was common to remove the choke plate all together just to get better air flow. You only need it for cold starting.

When you twist the throttle there should be a squirt of gas from the accelerator pump nozzel, bottom front right of the carb opening; as the engine rev's fuel will be drawn in thru the tiny ports at the top middle back of the venturi. If any of this fuel sprays out thru the front then [1] is the accelerator pump aimed wrong so the fuel stream bounces back? unlikely but worth checking. [2] air is rushing out the carb rather than in - perhaps a cam timing or ignition timing problem.

Have you had the cams out and back in again? Have you had the cam cover off? Do you know about lining up the cam timing marks? What year is the bike? is it electronic ignition or points?

When you have the carb off you will want to do a thorough cleaning, including the pilot screw passage ...

Cleaning a Carb

1. Removing it from the bike should be straight forward. First thing when it is out is to check the pilot screw setting. Turn it all the way in until gently seated counting the number of 1/4 turns; then write this number down; then reset it.

2. I put mine in a vice to remove the screws, and for much of the following work. Wrap in a shop towel; close the vice gently taking extra care with the choke and throttle linkages. The vice is a needed extra pair of hands.

3. You must be very careful handling the float so as to not change the level. You must have the official specs for setting the level as in the FM, and check it, every time you dismantle the carb, as the last thing before putting it back together.

4. The jets are made of brass, a soft metal that is easily damaged. Use an exact correct size screwdriver. I ground a medium flat blade screwdriver down to exact size on my bench grinder to access the slow jet.

5. The general appearance of the inside of the carb is not necessarily a good indication of its condition. It can look spotless and have clogged jets, or look cruddy and have clear jets.

6. Ignore any advice that says to soak or boil the whole carb in carb cleaner. Rather, clean each individual part. Do not allow any solvents to contact any rubber parts [tip of needle, o-ring seal for bowl]

7. Make a list of all of the jets and passages for your carb using the carb manual or the FM for the bike. Then ensure that you can blow either compressed air or carb cleaner thru each one.

8. Remove the pilot screw and clean the parts and the passage. The passage contains in this sequence: pilot screw, spring, washer, o-ring. These are very small parts, especially the washer and o-ring. Usually the spring will easily fall out. One time i thought the spring was not in there because it would not fall out; i obtained a new spring and could not get it in! The technique for removing the washer and o-ring is to use a pipe cleaner: stick it in the hole, twist it around, remove it - you should see the washer and o-ring on the end of the pipe cleaner.

EDIT: the washer and o-ring are part of the pilot screw assembly for 1979 on. They are not in the 1978 and earlier Keihin carbs.

Remember that the purpose of the washer is to protect the o-ring from the spring and you will always get them back in in the correct sequence.

9. Dismantle the accelerator pump assembly noting carefully the sequence and orientation of the parts. Clean and inspect the parts. Replace the diaphragm if it is cracked.

10. Check the float level then carefully put it back together. I personally find it very confusing trying to decide which way to bend the tang if it is not correct. If the fuel level is low is the float high or low? Do i need to bend the tang up or down? On the bench the carb is usually upside down, adding to the confusion. Sort all this out before making an adjustment.

Best to replace the original Phillips screws for the bowl with stainless steel socket head screws.