1981 Honda CM400 Build

[Drey6]

Hello all,
Picked up this bike for $500 dollars in rural-ish Ohio. It's a 1981 Honda CM400E with 34,000 miles and it runs fairly well. So today I started tearing her down. Here's some pics of what I did today and also when I first got her.

 

[Drey6]

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[Drey6]

After about 2 hours of alone time with the bike today.

 

[Drey6]

I bought a whole engine gasket set and I am going to most likely need help with what's what while replacing them. Also, while taking out the airbox today there were two fuel overflow lines coming from carbs(?) and I don't know what to do with once I switch over to the K & N air filters. Would I not need them anymore? Removal. Some info on this would be awesome.

 

[fresh_c]

Unless you are replacing the carbs DO NOT, and I repeat DO NOT, remove the stock air box for K&Ns, Uni pods, v stacks, eBay pods, or anything else. Learn from our mistakes! Trust me, your bike will not run over 6k rpm without the magical powers of the stock air box.

In regards to the engine gaskets, there is an online version of the factory service manual for CB/CM400 bikes floating around. I think I even have a link to it in my build. The shop manual has a step-by-step guide to tearing down the engine and thus replacing the gaskets. Read through the guide a couple times before deciding you are up to the challenge.

 

[Drey6]

Glad you said that fresh_c. Last night pondering it I was still weighing the option (heavily) to just leave it. So I guess there's my answer. I have scoured your build thread a few times and want to see how you feel on clubmans vs. clip ons in regards to tank clearance.

 

[fresh_c]

I went with clip-ons because you can set them up to your personal geometry much easier than clubmans, and the fact that they look a lot more pro. As far as tank clearance goes, you can move both around to make them fit but it may not be comfortable.

 

[Drey6]

Thanks for the info. This is my first bike and obviously first build. So I assume more questions are to come.

 

[kraptastic k]

+1 on carb swap... If you're going to put individual air filters on your carbs, you'll need aftermarket carbs. The 79-82 Honda carbs are not really capable of functioning properly with individual filters (professional builders aside, such as Steel Bent Customs).

Just trust us on this one

1981 CB750K (getting there now)

 

[Drey6]

I'm sold on leaving the airbox then. I took the carbs off today and will be cleaning those soon along with replacing those gaskets. Still feel pretty comfortable so far with how its all going. The rubber tubes between the carbs and engine that are clamped on are all dry-rotted and majorly fucked. Anyone know the official name for what those are so I can find replacements? Having trouble tracking those down. Thanks!

 

[kraptastic k]

Carb boots. I think you may and should spend about $60 or less on OE replacements. They are critical in preventing vacuum leaks, I absolutely recommend getting them.

1981 CB750K (getting there now)

 

[kraptastic k]

See Dime City Cycles, I know they have the replacement. Looks like its $40 a part there... Shop around >.>

1981 CB750K (getting there now)

 

[Drey6]

That's the name! I couldn't really search much cause my description sucked, but with the name I can find them for sure. Definitely want to do this as clean as possible.

 

[Drey6]

Here is how she stands up to today.

 

[Drey6]

Does anyone know the exact size I would need for the clip ons?

 

[oldskool]

Unless you are replacing the carbs DO NOT, and I repeat DO NOT, remove the stock air box for K&Ns, Uni pods, v stacks, eBay pods, or anything else. Learn from our mistakes! Trust me, your bike will not run over 6k rpm without the magical powers of the stock air box.

In regards to the engine gaskets, there is an online version of the factory service manual for CB/CM400 bikes floating around. I think I even have a link to it in my build. The shop manual has a step-by-step guide to tearing down the engine and thus replacing the gaskets. Read through the guide a couple times before deciding you are up to the challenge.

If anyone would like to know how to tune the stock cv carbs let me know. I run a 82'450 in a 81 frame. its been ported and polised,open exhaust, and pods. Runs awesome n have no prob keeping up with bigger bikes.it even pulls wheelies wit a 3
' extended swingarm. the 400's really come alive when they are ran with pods and a more open exhausts. Its as simple as jet changes and needle shims. Hit me up and I don't mind walking you through it. You'll be glad you did.

 

[kraptastic k]

Trust this guy ^^^

He will lead you to a functioning CM if anyone will.

1981 CB750K (getting there now)

 

[fresh_c]

If anyone would like to know how to tune the stock cv carbs let me know. I run a 82'450 in a 81 frame. its been ported and polised,open exhaust, and pods. Runs awesome n have no prob keeping up with bigger bikes.it even pulls wheelies wit a 3
' extended swingarm. the 400's really come alive when they are ran with pods and a more open exhausts. Its as simple as jet changes and needle shims. Hit me up and I don't mind walking you through it. You'll be glad you did.

How about to post up specifically what to change rather than making everyone come to you?

 

[Not_a_sunbeam]

Always enjoy viewing the builds. Weird, your bike has two gauges but an E only is supposed to have a speedo since the motor has no tach drive. Is this bike like mine, a CM400T frame with an E engine? I plan to just ditch my tach since it's useless weight. I'm also very interested in some info on tuning the stock carbs for pods.

 

[oldskool]

How about to post up specifically what to change rather than making everyone come to you?

If I get some extra time I'll start a thread on tuning the carbs for these bikes. I've noticed there is a theory on the carbs being untuneable. The E has idiot lights next to the speedo,and there is no difference in the motors. The difference is options like the wheels,tach,and the T had a windshield option if i remember correctly.