running problems, stalls at low throttle. carb problem? - Honda Rebel Forum

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Old 04-21-2013, 04:22 PM   #1
 
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running problems, stalls at low throttle. carb problem?

I recently rebuilt the top end of my 82 CM 250 engine and put it back together yesterday. I've been trying to get it running good enough to take it around the block a few times but I'm running into problems and I'm hoping you guys could help me out.

Built the bike back up and adjusted the idle to what sounded to be a good speed but every time I get on the throttle and hold it (as if I were riding) it stalls out. I can crack the throttle and let off and keep doing that and it will keep running until I stop cracking the throttle. Usually when I cut it open its probably >1/2 throttle. So I thought it was a carb issue.

Once I pulled the carbs apart I noticed the float was cracked and what looks to be held together with a zip tie. So I kept cleaning and found one of the jets (i think it was the main jet, it was the longest one that had sets of 3 holes 90 degrees off of each other) were partially plugged so I went at it with carb cleaner and compressed air. I also notice some junk over some of the jets but I just cleaned it out with a screwdriver and carb cleaner. It almost looked like silicon... odd. Also one jet would not come out see picture below, it is highlighted in red. I put it back together and it did the same thing with and without the air box on.

I pulled the plugs and noticed that they are unusually black, too rich. So I cleaned them off, pulled and re-cleaned the carb and ran it for a few minutes at idle and it had the same problem. I have attached a few pictures so you guys know what I'm looking at.

Also as a side note my intake manifold boot is covered in silicon, I'm guessing at one time it leaked and that was their fix??? So I sprayed carb cleaner all around the manifold and carb while it was running to check for leaks. The idle didn't change so I'm going to say its not leaking.

Any tips, tricks or suggestions are welcome.
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Old 04-21-2013, 04:41 PM   #2
 
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If someone used silicon seal as a gasket material, it's hard to say how much of it is still in the internal passages. From the looks of the zip tie repair to the float the PO was a bodge repair artist and it may take you a while to get things sorted out correctly.
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Old 04-21-2013, 04:49 PM   #3
 
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Silicone + gasoline @ carburetor = problem.... I found that out the hard way years ago on my XR185. Took forever it seemed to get all the tiny pieces of silicone out of the carb.
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Old 04-21-2013, 05:22 PM   #4
 
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it's like my doctor said when i told him it hurts when i raise my arm... don't raise your arm

if your bike stalls at low idle... don't low idle - keep it pegged at all times
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Old 04-21-2013, 07:04 PM   #5
 
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yes the previous owner really did a bodge job on the carb. If i can find replacement jets I will probably try to get the stuck jet out with an easy out.
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Old 04-21-2013, 07:23 PM   #6
 
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I'll bet an impact driver will loosen that stuck jet.

Here's a good source for new jets:

Honda Jet Kits :: Honda 250 cc Jet Kits :: Honda CM250C 1982 - Jet kits for Carburetors
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Old 04-21-2013, 08:45 PM   #7
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Yes, invest in an impact driver. Really a must have tool for working on bikes. They don't cost much, and work like a charm on stuck fasteners.

Impact Screwdriver Set with Case
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Old 04-21-2013, 09:47 PM   #8
 
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That jet needs to be removed to get the circuit cleaned properly. Try a little heat from a small torch and heat the area first then try the removal. There is usually an emulsion tube below that jet that may or may not be removable. You will see a slot cut into it for a screwdriver if it is removable. Be careful with that one as it can easily be damaged. That is where I usually use heat and chemicals, if the emulsion tube is stuck in there from old gas and gunk.

If there is no slot and it is just a brass fitting down there then plenty of brake cleaner or carb soak, just make sure you have removed all rubber parts such as the accelerator pump and air cut valve if that carb has one.

You probably need to replace the float assy as that repair isn't acceptable. If you could find a high quality epoxy that is gas resistant and there is only a crack in the arm you could probably just repair with that option. If it was totally broken off I would look for a replacement float assy.
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Old 04-22-2013, 07:36 PM   #9
 
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update:

Not sure if I mentioned this or not last night but my left plug wasn't firing very well so I swapped out the plug and it started to fire well. Still have the problem of it stalling at constant throttle. Also the plugs still looked like it was running rich and it also still smoked out the pipes which, according to the clymer manual, means it is running rich. I pulled the stuck main nozzle out of the carb with an easy out and it looked good with nothing blocking it. What carb adjustments can I make to help decrease the fuel or increase the air flow? Keep in mind I am running this without an air filter right now because the air box is a pain to get on and off when your pulling the carbs as often as I am.
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Old 04-22-2013, 09:14 PM   #10
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The only "adjustments" for the Rebel carb are the air/fuel mixture screw, the idle adjustment, and different size jets. There really isn't much you can adjust that will make a significant difference. If the carb is clean and everything else is working as it should, the bike will run fine.
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