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Discussion Starter · #1 ·
Hi guys,

I just stripped and cleaned the carb on my bike. Inside was a lot of grime and varnish. Before I did this the bike wouldn't fire up at all.

Now I'm finding that it idles happily, but when I touch the throttle it dies.

A few things I've noticed:
i) If I increase the idle speed using the adjuster, then the engine speed increases without stalling. If I twist the grip it dies.

ii) The choke seems to be working. Engine speed increases when I open the choke.

iii) Even when the bike is cold I don't need any choke to start the engine - maybe already running too rich? There's a fairly strong exhaust smell that makes me think it may be.

iv) The pilot screw to adjust air/fuel (mine has no limiting tab on it and is missing the internal spring and washers) doesn't seem to do anything when I turn it.

I'm wondering about a few different things that might be causing this:
1) The pilot screw needs replaced. It's missing washers, and doesn't appear to be doing anything. Is there any internal part that this should be pushing against that may be stuck or leaking?

2) The main seal around the float bowl on the carb looks old. It's pretty dried up. I would have replaced it when I put the carb back together but it seems to cost about $30. Could the carb be leaking here? Would that even cause the problem that I'm seeing? I did leave this on when chem-dipping the float bowl. I know I shouldn't have, but the seal was so old I could see it would be destroyed if I removed it. I kept the chem-dip of the float bowl to 15mins only and the seal looked the same when I took it back out.

3) The tiny holes in the carb body could still be dirty. Some are quite inaccessible and I could have dipped the carb for longer. I'm pretty certain the jets are clean. Certainly the main ones, which are big enough to see through easily. Even the side holes on the jet holders are definitely clean. The slow jet has a tiny opening - I can see through it but it might still be a little clogged, it's hard to tell. I could pull the carb again and chem-dip this for longer (I only did 30mins)

4) Perhaps I screwed up the jets while cleaning them? I noticed afterwards that Haynes says not to use anything to poke through the jets in case you enlarge the holes. I did use a piece of light gauge wire to check they were clear, but I'm 100% certain that it couldn't have enlarged them. Maybe if I'd used a coat hanger it could have, but not some really thin electrical wire.

5) The accelerator pump. The rubber on it looked okay, and I didn't dip clean this. I mean the rubber is clearly a little old and stiff, but it didn't look cracked or damaged. The long pin part of it had some surface rust that I took off using fine emery cloth because it was causing it to stick. When I put it back together I checked that the pin was sliding okay in the body. Again I could replace this, but it's really pricey ($69).

So my question is - do any of these seem likely candidates? What's my best approach now the carb is back on the bike? Is there a way to check whether any of these parts are functioning correctly (for example the accelerator pump)?

Thanks for your help!
 

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The carb is still clogged inside I bet. Sometimes it take more than one cleaning to get it actually clean when they are really dirty. You should use ChemDip and remove anything that isn't metal and soak it over night, then rinse everything with water and then use an air compressor to blow out all the passage ways in the carb body, accelerator pump bowl, and float bowl. Make sure the emulsion tubes on the jets are clean also.
 

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Discussion Starter · #3 ·
Okay, I stripped the carb down again and soaked it over night. This morning I used compressed air to blow through all the passageways. There are a couple where I can't guarantee they're clean just because they're so hard to get to:
a) the part of the body where the slow jet screws in doesn't seem to have a hole at the bottom - is it on the side of the hole?
b) the part of the body where the accelerator pump goes - seems to have a hole at the bottom but I'm not sure the air is blowing through it.

For the other holes it's obvious when you blow air in that it's coming out somewhere else, and that everything is clear.

I've ordered the gasket kit so I can replace the float bowl gasket. That should arrive today or tomorrow.

I noticed in one rebuild video that the cap that goes over the vacuum piston ( part 15 here ) is shown to have a notch inside that needs to be lined up. Does anyone know whether the older 1985 style carb has this same notch? I certainly hadn't noticed it, and now I'm wondering if I didn't get this lined up right. Perhaps the piston wasn't getting vacuum on the top side of it?

I'd love to know if there's any way to test individual parts of the carb once it's rebuilt. I'd like to know whether the CV vacuum piston is moving up and down the way it should. I'd also like to know the accelerator pump is doing it's job properly.
 

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Discussion Starter · #4 ·
Does anyone know what the o-ring is that's shown just below the floats here and numbered 1?

I've ordered the gasket kit, which comes with o-rings for the float-bowl drain and for the pilot screw. But I can't figure out what the third o-ring is for?
 

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Discussion Starter · #6 ·
I just put my carb back together for the test shown above - it works! The piston does move up and down with the throttle when there's a vacuum on the engine side of the carb. So I'm fairly happy that this part of the carb is working.

I've noticed that the gasket that was on the float bowl is missing the extra loop at one side. This seals a connection between the carb body and the accelerator pump. So the carb is probably leaking there.

I rechecked all the connecting holes and I believe they're all clean. First time I cleaned it I didn't blow air down these holes, so they may still have been blocked.
 

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Discussion Starter · #7 ·
Well I put the whole thing back together with the new gasket. It's running much nicer now. There is no stalling on throttle like before.

The pilot screw still doesn't seem to have much effect - I need to spend longer measuring with the tachometer I think.

I still seem to be getting a little gas coming out of the bottom drain. The float definitely isn't stuck. Perhaps it's coming up too high before cutting off the fuel from the tank? I don't see any way to adjust this. Haynes says that the float has a metal tang that you can bend a little to adjust the float height, but mine seems to be made entirely from plastic.
 

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Maybe the float valve isn't sealing completely. Could be the rubber tip is bad or the valve seat.
 

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Discussion Starter · #9 ·
Yes I was afraid of that. I guess I'm going to have to pull the carb again - third time lucky.

I'd have to guess that after 24 in chem dip the valve seat must be clean, but I can take a look at it while the carb is out. The rubber tip was certainly still soft, but maybe it's not making a good seal.

I'm also a bit concerned that perhaps the plastic of the float may have warped a little causing the float height to be off.

The float is about $36 and the float valve is about $26, so I think I'll just need to guess which one to buy first and test it out. I could replace both while I have the carb out, but $60 is a bit expensive.
 

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Hi guys,

I just stripped and cleaned the carb on my bike. Inside was a lot of grime and varnish. Before I did this the bike wouldn't fire up at all.

Now I'm finding that it idles happily, but when I touch the throttle it dies.

A few things I've noticed:
i) If I increase the idle speed using the adjuster, then the engine speed increases without stalling. If I twist the grip it dies.

ii) The choke seems to be working. Engine speed increases when I open the choke.

iii) Even when the bike is cold I don't need any choke to start the engine - maybe already running too rich? There's a fairly strong exhaust smell that makes me think it may be.

iv) The pilot screw to adjust air/fuel (mine has no limiting tab on it and is missing the internal spring and washers) doesn't seem to do anything when I turn it.

I'm wondering about a few different things that might be causing this:
1) The pilot screw needs replaced. It's missing washers, and doesn't appear to be doing anything. Is there any internal part that this should be pushing against that may be stuck or leaking?

2) The main seal around the float bowl on the carb looks old. It's pretty dried up. I would have replaced it when I put the carb back together but it seems to cost about $30. Could the carb be leaking here? Would that even cause the problem that I'm seeing? I did leave this on when chem-dipping the float bowl. I know I shouldn't have, but the seal was so old I could see it would be destroyed if I removed it. I kept the chem-dip of the float bowl to 15mins only and the seal looked the same when I took it back out.

3) The tiny holes in the carb body could still be dirty. Some are quite inaccessible and I could have dipped the carb for longer. I'm pretty certain the jets are clean. Certainly the main ones, which are big enough to see through easily. Even the side holes on the jet holders are definitely clean. The slow jet has a tiny opening - I can see through it but it might still be a little clogged, it's hard to tell. I could pull the carb again and chem-dip this for longer (I only did 30mins)

4) Perhaps I screwed up the jets while cleaning them? I noticed afterwards that Haynes says not to use anything to poke through the jets in case you enlarge the holes. I did use a piece of light gauge wire to check they were clear, but I'm 100% certain that it couldn't have enlarged them. Maybe if I'd used a coat hanger it could have, but not some really thin electrical wire.

5) The accelerator pump. The rubber on it looked okay, and I didn't dip clean this. I mean the rubber is clearly a little old and stiff, but it didn't look cracked or damaged. The long pin part of it had some surface rust that I took off using fine emery cloth because it was causing it to stick. When I put it back together I checked that the pin was sliding okay in the body. Again I could replace this, but it's really pricey ($69).

So my question is - do any of these seem likely candidates? What's my best approach now the carb is back on the bike? Is there a way to check whether any of these parts are functioning correctly (for example the accelerator pump)?

Thanks for your help!
Clean out the slow jet....and I mean really clean it!!!!!!!!!
Too many members are having the same problems with their carbs because of the same problem over and over.
The slow jet orifices have so much impact on off-idle, and too many members don't realize that.
Get it clean, and make sure everything is clean(not just clean, but sparkling clean) and you should have no problems.
The slow jet orifices are so small that the tiniest of particles whether seen or unseen will clog and give you more grief than you would imagine.
Clean, clean, clean. That is the key.
 

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Discussion Starter · #12 ·
Thanks for the suggestions.

I think this evening I'll try to check the height the float is sitting at. If I use a rubber hose on the drain pipe and open the drain screw with the hose held up high, I should be able to work out what height the fuel is sitting at in the carb.

It's just possible that the float valve wasn't seated right when I first put it back together. I'm not seeing it letting any fuel through now. I'd much rather be able to measure the fuel height in the carb though because I'm not happy riding around with it if the fuel is sitting really close to coming out of the overflow. Perhaps it might help seat the valve better if I drain and refill the carb a couple of times?

I have another question - the pipe on the carb drain was missing on my bike. I'd like to replace it now (mainly because otherwise any overflow gas ends up landing on the hot engine). Can I just use gas tubing like I used to connect the gas tank to the carb? What is the correct routing for this tube? Does it go down behind the gearbox and exit at the bottom of the bike?
 

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Yes, yes, and almost.

The clear tube on the drain is a good way to gauge float height.
Fuel line will work well to route the drain/overflow away.
It would route to the bundle where the puke tube and airbox drain go on the right side near the passenger peg mount.
 

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Discussion Starter · #14 ·
If I use clear hose on the drain to measure the fuel height in the carb, can anyone give me a value for how high it should be?

I think I will measure the fuel height relative to the line where the float bowl joins the top part of the carb.

If I can't get a value for this height then I'll need to take the float bowl off again and measure the height from the lip of the bowl to the top of the overflow pipe.
 

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Discussion Starter · #15 ·
I tried the draining and filling the carb a couple of times, but I was still finding that if I tilted the bike over a bit there were a few drips of fuel coming out.

I measured the fuel height with the makeshift manometer, and it was 7-8mm above the lip of the float bowl.

I then stripped the carb off again. The carb overflow pipe is 5mm above the lip of the float bowl. I'd attribute the extra 2mm height I measured as being due to the bike being on its side stand, at an angle when I measured the fuel height.

Anyway it's clear the fuel level was extremely close to the top of overflow.

Hmmm, seems like it's time to replace some parts.
 

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Discussion Starter · #16 ·
I've ordered the float valve....$33 from Honda. Let's hope I don't need to go back for the float as well.
 

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Discussion Starter · #17 ·
I installed the new float valve last night and it seems to have solved the problem. I'm not seeing any fuel coming out of the overflow, and if I measure the height relative to the line where the float bowl joins the carb body, it is only about 1-2mm above the line now. So the fuel level in the carb should be at least a few mm below the overflow.

It's amazing that the new float valve fixed this. The old one has absolutely no signs of wear on it, the rubber feels okay, and the spring in the top still moves. So I guess the interesting info here is that an old float valve can leak without any obvious visual signs of wear.
 
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