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I am new to the form and I have a question that I can’t seem to find the answer to anywhere. I have a 1986 Honda rebel 450. When I first got the bike it ran rough but it did run, I took it to a bike mechanic to get the carbs cleaned and ever since then the carbs have been gushing gas when I ride. I’ve taken the carbs and sometimes the whole bike to several shops and no one can figure out what is wrong. Two of the several mechanic I took the bike to said that the float needle housing is warped and that might be the issue. I really want to ride this bike all summer… I am reluctant to sell. So the big question is... are there any carbs (be Specific please) that I can use to replace the originals without compromising the bike to much.
Ps. Please add links and websites if possible
Ps. Yes I’ve tried rebuild kits
 

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Welcome to the forum! Sorry. I don't think anyone has a direct or close enough carb replacement documented. So it would be trial and error. It does sound like your float needles are not seating but can't understand how the housing could get warped. I wonder if the float seat could be polished, lapped, or replaced. I don't think the float seat is a replacement part but one could be made with a small lathe and 0.02 worth of brass. Do you have the carb disassembled to take pics?
 
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Honda has a part # for left and right carbs. Different part #'s have been revised and different part #'s for 1986 and 1987. I believe they are all interchangeable except for left and right are slightly different.

1987 carb part #'s

25CARBURETOR ASSY.
16100-MM2-771 16100-MM2-772
25CARBURETOR ASSY.
16100-MM2-772
26CARBURETOR ASSY., R.
16101-MM2-771 16101-MM2-773
26CARBURETOR ASSY., R.
16101-MM2-772 16101-MM2-773
27CARBURETOR ASSY., L.
16102-MM2-771 16102-MM2-773
27CARBURETOR ASSY., L.
16102-MM2-772 16102-MM2-773

1986 carb part #'s

25CARBURETOR ASSY.
16100-MM2-673
26CARBURETOR ASSY., R.
16101-MM2-672 16101-MM2-673
27CARBURETOR ASSY., L.
16102-MM2-672 16102-MM2-673

There is also a serial number on the carb body like VE###### - that might help better identify the carb with a question to Keihin.
 
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float needle housing is warped?? not sure what they are smoking imho
did any of these experts try polishing the needle seat with a Q-tip and a little rubbing compound? or replace the needle with a new one? Viton (rubber) tip of these float valve needles can become hard and not seal.. the rubber tip can also become deformed and leak..
16155-397-971 cmx450c valve needle has been used by Honda on various bikes and quads since 1982 through 2016..

CMX450c carb specs
109887
 
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if you decide to replace valve needle search the part number online.
I find it listed from less than $6 from a couple of suppliers to over $35
 

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May be the term "float needle housing" was misunderstood ?
Where does the leak occure.?
Is it the overflow tube at the bottom of the float bowl ? then, the needle valve has to be cleaned/replaced. (As far as i know, the floater level can´t be adjusted and is fixed. At least it is that way on my own 450 carbs).

Does the leak occure between the sealing surfaces of float bowl and Carb-body ? If so, the floatbowls can be warped.
This typically happens if "mechanics" torque down the floatbowl in a brute-force way. (for example,. if just one or two of the screws are fastened on one side of the bowl with considerable force and only then, the other bolts are screwed in.......(omg).

If so. the floatbowl is warped.

The screws have to be inserted in their treads and screwed down (in several steps and crosswise,) using the force of of just two ore three fingers on the screwdriver.

To check about warping, dissasemble the Carbs from the motorcycle.Then take the float bowls off the carb-body. Take out the o-ring seals very carefully and soak them in gasoline for a few hours (better replace them with new ones.) Check the inside of the bowls for dirt. even very small residue of dirt can ruin the carbs performance

Put the floatbowls on a horizontal glass-mirror. you can check if the floatbowls wobble a bit on the surface (warped) or if some gap is visible between mirror an sealing surface.(warped too).

If the sealing surface seats flat on the mirror and shows no deformity, look for dirt on all sealing surfaces.. Clean with no abrasive means !!

put in the o-ring seals carefully. (you can glue them in with a bit of bearing grease.) Don´t use any sealing compound (regardless of what the advertisements promise!)

Assemble the floatbowls with the carb-body again.

remember; screw in the bolts into their threads soft. torque them down crosswise in several steps. use only the power of two (max three) fingers on on the grip of the screwdriver

Re-install the Carbs into the motorcycle.

Work in a clean environment. clean the table or workbench you are workin on throughly. Don´t work on a dark surface. You can use a clean, old, white, t-shirt on the surface you work on. So you have good contrast to look for dirt.

Of course, if the bowls have been warped, replace with new or completely checked (see above) parts.

May be this is of some help.

...but not complete.

If the needle valves start leaking just a few moments after starting the engine, almost all the time dirt from the tank and fuel lines are the reason. These and the Carb have to be cleaned again throughly.

If you can´t do the work yourself... choose a mechanic who comprehends this post 🐻
 
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Nice Pete!

You could also send them to Jack's Rebel's. Home | Jack's Motorcycle Shop
He has a guy that is a whiz, specifically with CMX450 carbs. If you are looking to get them to daily, turn-key status, and not get your hands dirty, I would. He has stock of 450 carb parts and can replace damaged parts and get it back to you ready to bolt on and go.

Multiple mechanic's have looked at these to no avail.......hmm.....what kind of petcock are you using, OEM (450) or a 250? The OEM 450 should have a vacuum hose connected to the L cylinder. If you are using a 250, the left cylinder needs to be properly capped, if not, gas will pour. Also, OEM, 30 year fuel and vacuum lines are more likely to crack especially with more handling. Worth it to buy a foot or two of line and update to rule out.

Good luck
 

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Discussion Starter #8
Welcome to the forum! Sorry. I don't think anyone has a direct or close enough carb replacement documented. So it would be trial and error. It does sound like your float needles are not seating but can't understand how the housing could get warped. I wonder if the float seat could be polished, lapped, or replaced. I don't think the float seat is a replacement part but one could be made with a small lathe and 0.02 worth of brass. Do you have the carb disassembled to take pics?
Unfortunately I do not have the carbs apart at the moment they are still on the bike. I’ve done a lot of small repairs to bikes over the years… But I am not a mechanic I can promise you that. I don’t understand how the float seat housing would be messed up either but it seems that might be the issue.
 

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Discussion Starter #9
Honda has a part # for left and right carbs. Different part #'s have been revised and different part #'s for 1986 and 1987. I believe they are all interchangeable except for left and right are slightly different.

1987 carb part #'s

25CARBURETOR ASSY.
16100-MM2-771 16100-MM2-772
25CARBURETOR ASSY.
16100-MM2-772
26CARBURETOR ASSY., R.
16101-MM2-771 16101-MM2-773
26CARBURETOR ASSY., R.
16101-MM2-772 16101-MM2-773
27CARBURETOR ASSY., L.
16102-MM2-771 16102-MM2-773
27CARBURETOR ASSY., L.
16102-MM2-772 16102-MM2-773

1986 carb part #'s

25CARBURETOR ASSY.
16100-MM2-673
26CARBURETOR ASSY., R.
16101-MM2-672 16101-MM2-673
27CARBURETOR ASSY., L.
16102-MM2-672 16102-MM2-673

There is also a serial number on the carb body like VE###### - that might help better identify the carb with a question to Keihin.
I’m looking for whole carburetors… Not pieces
 

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Discussion Starter #10
Nice Pete!

You could also send them to Jack's Rebel's. Home | Jack's Motorcycle Shop
He has a guy that is a whiz, specifically with CMX450 carbs. If you are looking to get them to daily, turn-key status, and not get your hands dirty, I would. He has stock of 450 carb parts and can replace damaged parts and get it back to you ready to bolt on and go.

Multiple mechanic's have looked at these to no avail.......hmm.....what kind of petcock are you using, OEM (450) or a 250? The OEM 450 should have a vacuum hose connected to the L cylinder. If you are using a 250, the left cylinder needs to be properly capped, if not, gas will pour. Also, OEM, 30 year fuel and vacuum lines are more likely to crack especially with more handling. Worth it to buy a foot or two of line and update to rule out.

Good luck
I’ve spoken to Jack in the past… I am considering sending my carbs to him I hear he does great work. As for my rebel the carburetor and petcock are all stock original pieces
 

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I’m looking for whole carburetors… Not pieces
Those part #s are for whole carburetors.. as there is a left and right carb they have different part numbers and are drilled differently to accommodate interconnection.. one would have to order both individually for a complete assembly.

I scoff at warped float needle housing as that part is one of the beefiest parts of the casting.. Brass housing/needle seat is press fit into casting, suppose there could be leakage between aluminum casting and brass..
I've worked on 4bbl auto carburetors where the float bowl housing was warped and leaked at mating seam but they were nearly 4 times the size of any one cmx450 carb and prone to warpage..

You don't indicate where your "gushing gas" exits.. @Panic Pete made good point in that bowl could be warped and I have misunderstood your description if it is leaking past bowl seal..

109890
 
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