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Discussion Starter #1
Hello again,

So the bike is up and running, which is a fantastic step forward, but when I push the starter button the engine is very, very loud and will usually stall after 10-20 seconds. Sometimes I'll even hit the kill switch since I don't want something to break. After a second or two the engine will settle down a bit (my ear is not good enough to approximate the RPMs, but even this sounds dangerously high) and then rev again as if I were opening the throttle (I'm not) before stalling.

First off, I got this carb professionally cleaned before putting it back on the bike (the only professional work done so far). I didn't like doing it, but I bought it used from my local dealer, and after a month of wrestling with a broken pilot screw in the original carburetor I thought it was safest to have them clean and reassemble with a rebuild kit first time around in case anything was wrong from the outset. So, in sum, I do not think the problem is a dirty carb.

I started fiddling around with the idle screw to see if that would help, and a few days ago did hear the RPMs drop pretty low (after a loud start), which I was excited to see, but of course after 15ish seconds it sounded as if I were throttling (I wasn't) and the bike stalled out again.

I have read through many of the threads and (think I) have narrowed the issue down to a few different possibilities, but of course would love help in this particular situation since I haven't found anything exactly like this problem, at least so far as my untrained eye can tell.

Since the RPMS seem so loud by just pushing the starter button, I was wondering if my throttle were somehow not closing all the way. But the mechanism seems to click back into place as it should, and after adjusting the tension of the cables I do not notice any difference in the problem. The free play seems just enough at around that 2-3mm mark.

I tried spraying penetrating oil into the intake where I thought a leak might be occurring, but there was no perceptible changes in the RPM then either. (It seems to be running lean, though to be honest can't say for sure what that symptom sounds like-- can anyone define for me?)

And even though the mechanic told me that he had adjusted the pilot screw to spec (2 1/4 turns out) I tried for myself to make sure; still nothing.

I realize the problem could be as simple as the fact that I haven't fine tuned the pilot and the idle, but since the engine stalls so quickly and runs so loudly I don't want to make the problem worse before admitting ignorance and asking for help. A huge thank you, as always.
 

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Discussion Starter #2
quick update: I actually think the engine is running rich. The farther I bring the choke down the louder the already dangerously loud engine becomes. Bike seems most stable when there is no choke. Also, there is a faint smell of gas after it stalls.
 

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If the engine will start with no choke, don't use any. Listen to this Rebel engine running to hear how one sounds compared to yours.

Sent you a PM.
 

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I have an 86' and had the opposite issue, my engine was running too lean and was idling too low. If you adjust your fuel/air mixture screw you should be able to resolve the issue.
 

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I wouldn't start adjusting anything until you find the problem. Your description is a classic lean condition, all the adjustments could be ok it sounds like it is running out of fuel and just moments before the fuel is consumed the revs will go up until the last of the fuel is consumed and then it will die. When operating a chain saw all is well when there is adequate fuel at the moment when the fuel is depleted the revs will increase very high then it will die. Your fuel could be low in your tank or the supply could be restricted. Some times the fuel indicator is on run, however the reserve valve assembly may be leaking and letting just enough fuel through to start but not enough to maintain operation. Check your supply pull the fuel line off the carb and open the fuel valve and confirm the flow. Yes it may be lean but it may not the carb or adjustments. Also make sure the "O" rings are in the intake manifold.
 

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Discussion Starter #6
Thanks guys. Interesting stuff.

I ended up reinstalling the carb today into the intake boots just in case there was an air leak I had missed and the engine actually seemed to stabilize some. I didn't get the same up and down revving as the day before but the RPMs were still dangerously high. No stalling, no invisible throttling, but I did hit the cut off switch after 20 seconds because the bike was shaking and white smoke was being expelled from the exhaust. I then pulled the choke and found destroyed plastic threads I'm worried some of which may have gotten into the carb. See below. If you look closely you can even see a bit of plastic stuck between the spring. With flite's advice, I did my best to clean the choke hole and am now waiting on a new choke nut from 01, who manufactures and sells them on eBay (100% rating).

109439


Do these symptoms seems as if plastic might be clogging the pilot jet, and to DN's point restricting the fuel supply? DN, your comments are insightful because although it stopped today my petcock WAS leaking yesterday, which-- while obviously a problem that needs to be fixed before I ride the bike-- I had thought it low on list of priorities when it came to dealing with the idle issue. But why would the leak (which only occurred when the fuel switch was turned on) indicate a restricted fuel supply? The tank definitely has gas. My hunch is that if the leak persists the culprit lies with the new o-ring I put around the fuel screen that fits into the petcock for first generation bikes. It didn't fit tightly the way I expected. And since we're on the subject of o-rings, I didn't know the intake manifold needed one. Is that true for '85s?

Now, all that being said, what's interesting is that the bike idles way better off of choke, and if this were a lean condition wouldn't the opposite be the case? From what I've read online the high revs do seem to indicate a lean condition. Furthermore, with flite's advice I started the bike both with and without the air filter to see how that would affect idling and it ran better with air filter on, further indicating lean condition.

I'm sure there's something I'm missing...
 

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I was referring to these O rings they are sometimes damaged or missed and not installed. On an earlier post a chap had a running and idle issue with a cleaned, rebuilt and assured was adjusted correctly carb but had forgotten the very important O rings.
DSC05559.JPG
DSC05560.JPG
 

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Did you check that the TINY parts of idle mixture screw are in correctly and in the right sequence? Very easy to mess that up. There is a miniature spring, tiny flat washer, and super tiny o-ring that should be installed on that mixture screw. Also, good to check that part of the old o-ring is not stuck down in the threaded hole of the carb by the shop guy.
 

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Discussion Starter #10
Thanks Ron. I did. Just finished a 72 hour parts cleaner dump, reassembled the carb and installed without the throttle cables attached and the engine revving just as loud and fast. Maybe worse. Within 5 seconds there was gray smoke escaping from the fins at the engine cover.
 

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Discussion Starter #12
Plugs.
109454


Bike couldn't have been on for more than a total of 3 minutes put together. Seems like oil in combustion chamber. Want to do a compression test but don't want to harm the engine.
 

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The choke on the Rebel carb is an enricher type, it does not control air ... it controls extra gas flow. When the choke lever is pulled all the way toward the rider, raw gas is dumped into the airstream on the engine side of the carburetor. When the choke lever is pushed forward toward the headlight, the extra enricher raw gas is shut off.
You mentioned you replaced the plastic cable fitting connection at the carb, are you sure that cable is routed properly and the cutoff valve is installed properly?
 

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Discussion Starter #14
Right. I was confused (and maybe still am). I had assumed that when the plunger was pulled back (and the choke lever pulled toward the rider) more air entered the carb, which changed the air pressure of the float bowl, allowing more fuel to flow into the compression chamber per second. But I think that is how a choke works versus the Kiehin's enrichment system, and in 2018 duckster said that "the plunger is actually a plug type valve that flows raw fuel into the carb throat when it is pulled away from the seat. Something has to seal off the enrichener passageway if the plunger is not there." So, in sum, with the "choke" lever pulled down, another hole in the carb opens that allows more gas to flow into the system? Thank you for bearing with me.

Ron, when you say cutoff valve do you mean the brass plunger at the end of the choke cable? I am not sure that was installed correctly at all, especially because of the plastic that had been stuck in the spring. I'm beginning to wonder whether even when the choke looked like it was closed it actually wasn't because the plastic somehow prevented it from doing so. In fact, the new choke nut has not arrived yet. Today I tested the bike with my thumb over the opening of the choke. But I assumed that was equivalent to "full choke." Is it? I hope that's the problem. Any possibility that valves/pistons are to blame? Was planning on running a compression test tomorrow.
 

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Yes, that brass plunger on the end of your choke cable controls the amount of RAW GAS that is dumped into the carb throat on the engine side of the carb (does not control air). The brass plunger MUST be in place. Fully open a lot of fuel is dumped in and is why the idle speed goes so high when the enricher choke is activated.
 

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Ron may be onto something. Does the brass plunger move in and out when moving the enricher lever?
 

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Discussion Starter #17
Yes. But unclear whether it was moving enough, or if it was ever able to fully retract due to the plastic refuse caught in the spring. Or whether the cable had long enough reach down the carb in the first place to function properly! I measured the .41 inch spec between the nut and the plunger required before installing, but, again, maybe with the plastic things got out of wack. The lever definitely wasn't moving back and forth as it should have...

The reason these questions have more weight is because as I was trying to install the new choke nut I realized that for whatever reason the .41 inches required at the end of the cable for the choke to function properly had disappeared. Not sure if you can see because it's was dark outside and I've been kicked out of the garage at this point but when I investigated choke at the handle bar I found something that looks like yarn snagging the cable.
109455


I picked it out and am now in process of reinstalling the choke cable at the lever but it was tricky in the dark so will have to wait until tomorrow. I'm still hesitant to start the engine again after the smoking at the fins, and not sure why improper choke function would be responsible for that.
 

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Discussion Starter #18
update: removed choke cable from housing and there seems to be a kink in the braids-- they're unwinding near top. Reinstalled anyway just to see what would happen and I can see now that it is definitely not retracting when i lift the lever up to close the choke (and push the cable downward, closing enrichment system). I have to pull the cable down at the other end in order for it to reach its full length. Even then it is not long enough, for whatever reason, for me to reinstall choke nut, spring, and plunger.

So I have a few questions:

1. When reinstalling choke cable, do you all put the plunger system on first before winding through housing at top or the other way around? Why does my cable seem so short? Well aware I could be making a mistake. Have noticed that when wrenching that doing things first time around can take (no exaggeration) 5 times longer than the second time, at least for me.

2. I have noticed on the forum that others have replaced the cable with a manual plunger, and have also noted flite's drawback, which is that there is no finesse with the plunger, since you can only go full on or full off. That being said, I can see the advantage of a cable, but on ebay I only find them for bikes '96 onward. Are those compatible with first generation rebels? honda rebel choke cable in Throttle & Choke Cables | eBay. For this bike especially can see the advantage of cable mechanism.

3. Regarding the high RPMs and gray smoking fins 5 seconds after the bike has been started, I'm hopeful that these problems have had to do with the enrichment system. According to the below chart, oil fouled plugs, which I had-- there is is a picture above-- can be caused by excessive choking! (Though option number 3 is far less heartening: worn piston rings and valve guides.)


When the smoking happened my thumb was over the enrichment hole rather than filled with the plunger and choke nut. I am thinking of screwing in choke nut with plunger and with my arm manually moving the plunger up and down to see how that would affect the idling, but do not want to damage the engine. Given the symptoms my bike has been experiencing, do people think I should proceed?

4. A compression test would be helpful to narrow down the culprit. Can I run it with the engine cold?
 

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1. Don't put the brass plunger, spring and plastic nut on until the cable has been routed and attached at the handlebars. Those parts slide onto the cable end and once attached to the carb cannot come off. The easiest way to route the cable (assuming the existing cable is routed correctly) is to tie a long piece of string to one end of the old cable and pull it out the other end. To install new cable, tie string to the appropriate end and pull into place.

2. The choke cable is the same for all model years of the CMX250.

3. I'd order a new cable and install it. I'm beginning to suspect it may be causing the high revs.
 

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Discussion Starter #20
3. Unfortunately I don't think so. I ordered the new cable, and in the mean time ended up putting the nut back in the carb with spring and plunger attached to the cable at .41 inch spec; I wanted to test how the bike would run with choke off versus thumb over hole/choke on and found the very high revs again. But at least there wasn't smoke. Tells us that the extra gas was making things worse. In fact, this time the tip of the right spark plug was slightly white. Think I ran the bike for about 20 seconds or so. Sprayed carb cleaner on the intakes but can't tell if I heard a change in the revs because it was running so fast and loud. Bike still shaking. When I turned it off the exhaust pipe was very very hot; the engine was only warm.

I have yet to turn the pilot screw from the 2.25 spec. Could the problem be as simple as adjusting the mixture, like skeletor suggested? Or are the current symptoms too extreme for such a simple solution? Last week when I first turned the bike on(!!) and the RPMs were erratic, fiddling with the idle screw brought the revs down to below the 1,400 recommendation. I felt relieved until a few seconds later the idle whipped up really high and stalled, but still. Is there a certain number of turns the idle is supposed to be out? At the moment it is turned in as tightly as possible (counterclockwise), because I thought that might help the extra gas problem.
 
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