CM 400C Repair Thread

Friday_Z

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Joined
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Location
Texas
Hello gentlemen,

I recently got the aforementioned bike, but it’s been sitting for 15 years. There is a long list of repairs I have to dive into:

- freeing the engine
- drain the old fuel and any other liquids that might have gone bad
- fresh oil filter
- carburetor rebuild
- new rubber components for fuel lines
-new battery
- petcock rebuild

Honestly, I’d like to get her running by the end of the month. Ambitious, I know, but any help here would be very much appreciated or any pointers as to where I can find video guides to do it myself. Feel free to mention anything I might have missed in the above list.

Thank you all!
 
Friday_Z said:
Hello gentlemen,

I recently got the aforementioned bike, but it’s been sitting for 15 years. There is a long list of repairs I have to dive into:

- freeing the engine
- drain the old fuel and any other liquids that might have gone bad
- fresh oil filter
- carburetor rebuild
- new rubber components for fuel lines
-new battery
- petcock rebuild

Honestly, I’d like to get her running by the end of the month. Ambitious, I know, but any help here would be very much appreciated or any pointers as to where I can find video guides to do it myself. Feel free to mention anything I might have missed in the above list.

Thank you all!
Click to expand...
Moved to Projects and Builds section.

Honestly, the bike will tell you what else is needed as you go along. Those are good places to start, but when you begin with unsticking the engine you never know what that might bring.
 
Friday_Z said:
Hello gentlemen,

I recently got the aforementioned bike, but it’s been sitting for 15 years. There is a long list of repairs I have to dive into:

- freeing the engine
- drain the old fuel and any other liquids that might have gone bad
- fresh oil filter
- carburetor rebuild
- new rubber components for fuel lines
-new battery
- petcock rebuild

Honestly, I’d like to get her running by the end of the month. Ambitious, I know, but any help here would be very much appreciated or any pointers as to where I can find video guides to do it myself. Feel free to mention anything I might have missed in the above list.

Thank you all!
Click to expand...
Firs thing you'll need is this: CM400 FSM

To be frank, 90% of the videos out there are detrimental to your goal of actually getting the bike running properly, and the 10% that do actually do something just follow the steps outlined in that manual - along with the litany of threads on this forum for these bikes. Like this one here, that'll be critical to properly cleaning and servicing those carbs:

How to Rebuild the VB Carburetors

This is dealing with the VB22J carbs in particular but most of it applies to the VB21 and VB24 carbs. As everyone knows that has done these they are problematic to get right the first time at best so hopefully this will help you get there. In this case I'm dealing with VB22J carbs that have had...
www.vintagehondatwins.com www.vintagehondatwins.com

Resist the urge to just fire up the parts cannon and start chucking chinese junk at the bike. Right now, just start with Air and Oil filters, a 5 qt jug of T4 Rotella 15W-40 from Autozone, a decent AGM-style battery and a fresh set of plugs.

Something like this is a good start: https://4into1.com/tune-up-kit-hond...Ndw2hxhLlIIerSjLoXmbG3H8WBVNTuOA_eRV3yOvypFg6

Do not buy one of the "carb rebuild kits" that are out there. All you're going to need are new gaskets and orings. Those can be purchased separately and won't waste your time or money.

Buy real 5.5mm fuel line. Try your local Honda auto dealer first. If they have it in stock in Bulk hose, it's around $1/ft.

In your intro, you said the motor does NOT appear to be seized, so please clarify what you mean by "freeing" the engine. If it is seized, don't buy a single thing for the bike right now. That's an engine-out, top end teardown at a minimum and you'll want to open it up before deciding if you're going to pursue this.

What part of Texas are you in?
 
EzPete said:
Firs thing you'll need is this: CM400 FSM

To be frank, 90% of the videos out there are detrimental to your goal of actually getting the bike running properly, and the 10% that do actually do something just follow the steps outlined in that manual - along with the litany of threads on this forum for these bikes. Like this one here, that'll be critical to properly cleaning and servicing those carbs:

How to Rebuild the VB Carburetors

This is dealing with the VB22J carbs in particular but most of it applies to the VB21 and VB24 carbs. As everyone knows that has done these they are problematic to get right the first time at best so hopefully this will help you get there. In this case I'm dealing with VB22J carbs that have had...
www.vintagehondatwins.com www.vintagehondatwins.com

Resist the urge to just fire up the parts cannon and start chucking chinese junk at the bike. Right now, just start with Air and Oil filters, a 5 qt jug of T4 Rotella 15W-40 from Autozone, a decent AGM-style battery and a fresh set of plugs.

Something like this is a good start: https://4into1.com/tune-up-kit-hond...Ndw2hxhLlIIerSjLoXmbG3H8WBVNTuOA_eRV3yOvypFg6

Do not buy one of the "carb rebuild kits" that are out there. All you're going to need are new gaskets and orings. Those can be purchased separately and won't waste your time or money.

Buy real 5.5mm fuel line. Try your local Honda auto dealer first. If they have it in stock in Bulk hose, it's around $1/ft.

In your intro, you said the motor does NOT appear to be seized, so please clarify what you mean by "freeing" the engine. If it is seized, don't buy a single thing for the bike right now. That's an engine-out, top end teardown at a minimum and you'll want to open it up before deciding if you're going to pursue this.

What part of Texas are you in?
Click to expand...
Thanks for the tips, right now I’m just taking this thing apart and assessing the damage and what I’m willing to do to try and fix it. I live west of Houston.
 
Okay, small update I found water in the alternator cover. Good news is that the engine still turns over freely and the oil is good, so there isn’t contamination into the engine. How do I go forward with this?
 
Friday_Z said:
Okay, small update I found water in the alternator cover. Good news is that the engine still turns over freely and the oil is good, so there isn’t contamination into the engine. How do I go forward with this?
Click to expand...
Pictures will help here, but that is the absolute worst place to have water in this engine - you're going to need a clear picture of what kind of corrosion mess you might have on your hands and there's some key components to the ignition system housed there.

The fact that water got in there means the engine was left open for some time as well, which sucks but isn't insurmountable.

Couple of paths forward here:
1. Commit to the rebuild. Go ahead and pull the engine now, get it up on a bench and pull the side covers off, heads off and start inspecting to get the list of stuff that'll need to be replaced.
2. Cautiously optimistic. Get the rotor off, get some pictures of the components and let's see what's salvageable. Might be worth doing a quick compression check using the kickstarter.
 
EzPete said:
Pictures will help here, but that is the absolute worst place to have water in this engine - you're going to need a clear picture of what kind of corrosion mess you might have on your hands and there's some key components to the ignition system housed there.

The fact that water got in there means the engine was left open for some time as well, which sucks but isn't insurmountable.

Couple of paths forward here:
1. Commit to the rebuild. Go ahead and pull the engine now, get it up on a bench and pull the side covers off, heads off and start inspecting to get the list of stuff that'll need to be replaced.
2. Cautiously optimistic. Get the rotor off, get some pictures of the components and let's see what's salvageable. Might be worth doing a quick compression check using the kickstarter.
Click to expand...
image.jpgimage.jpg
 
How much Water in the Stator/Alternator area? You may want to pull the Rotor/Flywheel to get a look at the Stator. Mine was rusted to the rotor which is what was locking up my motor, sounds like your is not that bad, but may be worth a look. you will need a removal bolt and flywheel holder and possibly an impact screw driver with JIS bit to remove the stator bolts.

Sorry you added a photo while i was typing, I can see the water line on the rotor!
 
That is less than ideal. Get some PB blaster and soak that rotor retaining bolt and let it sit for a while. You're going to need to pop that off to see what the stator looks like behind it. It's salvageable - doesn't bode well for the carbs. While you're waiting for the PB to soak in on that bolt, now would be a good time to remove the carb rack and get a look at the internals there. It's a PITA on the CM's hopefully @LongDistanceRider or @Maraakate have some tips there.
 
EzPete said:
That is less than ideal. Get some PB blaster and soak that rotor retaining bolt and let it sit for a while. You're going to need to pop that off to see what the stator looks like behind it. It's salvageable - doesn't bode well for the carbs. While you're waiting for the PB to soak in on that bolt, now would be a good time to remove the carb rack and get a look at the internals there. It's a PITA on the CM's hopefully @LongDistanceRider or @Maraakate have some tips there.
Click to expand...
Is there any way to do this without removing the engine or should I bite the bullet and pull it out right now?
 
Here is an example of what I bought, and it worked for me, and price is not too bad knowing you may only use it once. The JIS screws you will want to take your time, soak them with penetrating oil and don't rush those, rent or buy an impact screwdriver and get some JIS bits that fit it.

Removal Bolt

Flywheel holder

Cleaning instruction for the Carburetors is here:....
Rebuilding VB Carburetors
 
Friday_Z said:
Is there any way to do this without removing the engine or should I bite the bullet and pull it out right now?
Click to expand...
No you can pull the rotor and stator in the frame, here is a link to my build. look at post #9 to see all the pieces laid out so you have an idea what you will be looking at.

Go to post # 9 for picture
 
Last edited by a moderator:
esmith250624 said:
No you can pull the rotor and stator in the frame, here is a link to my build. look at post #9 to see all the pieces laid out so you have an idea what you will be looking at.

Go to post # 9 for picture
Click to expand...
Fixed the link to go right to the post. You can do it by clicking on the post number to the upper right of the post first, then copying the URL above afterward - takes you right to it.

1780939482073.png
 
Friday_Z said:
Is there any way to do this without removing the engine or should I bite the bullet and pull it out right now?
Click to expand...
No need to pull it just yet. Plus it’s easier to pull with this stuff removed anyway - and way easier to get the stator and rotor off while it’s still in the frame. You'll definitely need a JIS impact driver with JIS 2 and JIS 3 bits - a regular Phillips will strip immediately and then it's a world of pain getting them out. I know Northern Tool sells Vessel brand stuff that is very reasonably priced, or you can go the Bezos route, but that'll be a tool that will save you hours of time down the road.

Take a lot of photos as you go, and bag everything together - camera, gallon ziplocks and a sharpie are your friend here.
 
EzPete said:
No need to pull it just yet. Plus it’s easier to pull with this stuff removed anyway - and way easier to get the stator and rotor off while it’s still in the frame. You'll definitely need a JIS impact driver with JIS 2 and JIS 3 bits - a regular Phillips will strip immediately and then it's a world of pain getting them out. I know Northern Tool sells Vessel brand stuff that is very reasonably priced, or you can go the Bezos route, but that'll be a tool that will save you hours of time down the road.

Take a lot of photos as you go, and bag everything together - camera, gallon ziplocks and a sharpie are your friend here.
Click to expand...
image.jpg
Got the carb this far out
 
Engine turns over, that's a plus.
Water in the stator area? fairly normal as the thin gasket there really doesn't keep it out. No concerns for water inside the engine as that area is sealed by the crankshaft seal.
Carbs normally come out the left side of the bike but so far it's good. Plus for waiting to remove the cables until the carbs were free.
I see no need for engine removal at this time even though with the mufflers off it'll drop right out.
 
LongDistanceRider said:
Engine turns over, that's a plus.
Water in the stator area? fairly normal as the thin gasket there really doesn't keep it out. No concerns for water inside the engine as that area is sealed by the crankshaft seal.
Carbs normally come out the left side of the bike but so far it's good. Plus for waiting to remove the cables until the carbs were free.
I see no need for engine removal at this time even though with the mufflers off it'll drop right out.
Click to expand...
I moved it to the left side, the cables seem to be interconnected with the carb, so how would I be able to remove the carb and take a look at it ? image.jpg
 
You have 3 cables. I find it easier for access if I remove the left upper engine mount, that triangle piece, so the cables have more room to move.
Be careful of the throttle cables, the pull cable is the toughest and the cam eccentric is easy to break which mean carb replacement since there are no parts.
 
remove all the slack you can from the cables, then it’s find the loosest one and slide the barrel end out of the cam it’s riding on. The push/pull combo can take some finagling - just don’t try and force anything, but you have to do a combination of rotating the cam with your thumb, while working the barrel end free.

It’s one of those “slow is smooth, smooth is fast” things.

I usually start with the choke (closest to you) it’s the easiest and gets it out of the way.
 
Nice! OK - while you soak the screws holding the bowls on in PB Blaster (along with every other fastener on that rack), now's a great time to read through that carb rebuild thread and then remove the bowls to see what those internals look like. IMO, that'll be more indicative of the future of this project (well, that and the ignition testing with that series - you'll get there down the road). You'll notice some of the screws are already totally ham-fisted. You'll be replacing some - if not all of those.
 
Watch out for this little spring later, when you get to the part about taking them off the rack. It'll go flying.

1780952534563.jpeg
 
EzPete said:
Nice! OK - while you soak the screws holding the bowls on in PB Blaster (along with every other fastener on that rack), now's a great time to read through that carb rebuild thread and then remove the bowls to see what those internals look like. IMO, that'll be more indicative of the future of this project (well, that and the ignition testing with that series - you'll get there down the road). You'll notice some of the screws are already totally ham-fisted. You'll be replacing some - if not all of those.
Click to expand...
image.jpgimage.jpgimage.jpg
Internals look pretty clean imo, is there anything I should be worried abt?
 
Those are the vacuum chambers/tops. The other side is the bowl and where all the jets/floats are - that’s the side that can get ugly if fuel was just left sitting in there for years.

Make absolutely certain that you are not mixing parts from one side to the other.
 
Not too shabby looking. Little bit of varnish but not bad at all.

The next part is removing the jets and floats - this is where the instructions in that thread are key. Follow those steps. Those jets are made of some really soft brass so a screwdriver that fits the slotted heads exactly with no slop is critical.

The main jet you’ll have to remove is that idle jet buried under there. Once you get there, try to get a clear look to see if it’s slotted or the press in version. 81, there’s a good chance it’ll be the slotted/threaded jet that is easy to remove with a 4mm wide, 1MM thick driver. There’s a full description of how to make one in that thread.
 
Thanks for all the help! I think I’m about done for the night, I’ve been working on this thing all day😂.
I’m getting a new gasket kit for the carb, is there any specific one that you would recommend?
 
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