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Discussion Starter · #1 ·
'81 CM400T Possible Cafe project

Update April 13th:
So I think I'm going to turn this into a Cafe racer project but with my own style. I really like the low handebars but I need to be able to carry a passenger if needed so I'm not a huge fan of the seats.

I finally was able to register here. I've had a thread going on sohc4.net since March 23rd and have fixed a few of the problems with help from them. I'm a complete noob with motorcycles but have tinkered with cars my whole life so I know some things. I have a clymer which is very helpful.

I bought the bike with a couple problems. The PO did a real nice job fixing it up (heavy sarcasm) and neglected to include numerous important parts. No airbox to carb boots, air filter, dead battery and more.

March 23rd.
Got the bike home. Bogged at 3-4k. High Idle around 6k. I was told this is because it is running lean.
Fixed the bog with airbox to carb boots. Brought the idle down to 5k.

April 1st
High idle around 5k
Ran seafoam. Brought idle down just a tad. New battery.

April 4th
Idle continues to lower and is less sporadic. About 4k now. Backfire into the left carb
Emptied the tank. Cleaned the filter.

April 5th
Took the carbs apart. They were very clean with just a little sediment in the bottom of the float bowls. Noticed the pilot screw cap on the left carb is broken off and the right carb was filed down so it can rotate completely.
New fuel line. More seafoam

April 7th
High idle is less frequent. Usually right after pulling in the clutch. I can get it to lower if I fiddle with the idle adjustment screw. Muffler leaks bad in the crossover. Comes out the left side.
Seafoam in the oil. Rode for about 20 minutes then changed the oil. Hard to shift at first. Much better now.


So now I'm contemplating getting a new set of carbs as the PO really seemed to screw these up. Someone suggested syncing the carbs which could get rid of the backfire but I can't find where to do it in the clymer? I was going to make my own sync out of tubing and some wood. I don't know where to attach the tubes to or the adapter I would need.



 

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Re: Another CM400T First Bike - Lots of problems

Here's the Page from the Honda Shop Manual.

Hope this helps.
 

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Re: Another CM400T First Bike - Lots of problems

Welcome aboard! :D

First off we'd appreciate it if you updated your profile to include your location, sometimes help is nearby. It also helps to include the year and model of your bike in your signature, helps to keep folks on the right track.

AND WE LOVE PICTURES! ;)

It sounds like you do have a fuel system problem. Could be an air leak or something in the carbs. Just because the bowls looked clean doesn't mean all the passages are. Do a search of the forum for good discussions on cleaning them.

Here's a source I used for carb kits.

http://www.crc2onlinecatalog.com/Index_Main_Frame.htm

Recently carb kits specifically for the 400 have become available but they're a bit pricey. There's also somebody selling kits on e-bay for about $45 a pair, best price I've seen. Have to check the jets that come with them though as these bikes use several different sizes in different years and models.

Good luck and let us know how it goes.
 

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Discussion Starter · #4 ·
Re: Another CM400T First Bike - Lots of problems

J-T said:
Welcome aboard! :D

First off we'd appreciate it if you updated your profile to include your location, sometimes help is nearby. It also helps to include the year and model of your bike in your signature, helps to keep folks on the right track.

AND WE LOVE PICTURES! ;)

It sounds like you do have a fuel system problem. Could be an air leak or something in the carbs. Just because the bowls looked clean doesn't mean all the passages are. Do a search of the forum for good discussions on cleaning them.

Here's a source I used for carb kits.

http://www.crc2onlinecatalog.com/Index_Main_Frame.htm

Recently carb kits specifically for the 400 have become available but they're a bit pricey. There's also somebody selling kits on e-bay for about $45 a pair, best price I've seen. Have to check the jets that come with them though as these bikes use several different sizes in different years and models.

Good luck and let us know how it goes.
Profile updated.

There is no air leak that I could find. I sprayed wd-40 around the airbox boots and there were no spikes in the revs.

The jets were clean, as many passages as I could see were clean. I'll take them completely off and dissemble them and soak them in some carb cleaner.
 

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Re: Another CM400T First Bike - Lots of problems

Love all the CM400's that are popping up! Welcome!
I should post up a project log on my CM400 one of these days but I'm terrible at tracking and documenting progress when I get enmeshed in a project. ;)
Peace
 

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Discussion Starter · #6 ·
Re: Another CM400T First Bike - Lots of problems

Thanks for the picture. It's still very difficult to see though.

I took the carbs completely off and apart to clean them thoroughly. I took lots of my own pictures this time.

- Changed the 2 adjusting arms. Both were way off.
- The right carb bowl was dry
- Both floats had a little orangish, tannish substance caked around the top. Bad gas?
- The air valve (I think is what it is. On the side of the left carb) is very, very dirty.
- Everything is relatively clean. The dirt from the pictures is mostly from the outside.
- What do the "nozzles" circled below do? Fuel came out of them.





























 

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Re: Another CM400T First Bike - Lots of problems

Your carbs are a tad different than mine. I don't see the vacuum holes that our 79 has. It also appears that you have an accelerator pump on yours as well. That changes a bit of what I said in the e-mail earlier as I haven't dealt with that style.
 

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Discussion Starter · #8 ·
Re: Another CM400T First Bike - Lots of problems

Well after taking the carbs apart and cleaning everything it runs much smoother now. The idle got stuck once at 3k. I only took it down the road and back but I noticed that it has less hesitation but also seems like less power. Maybe it's a smoother power band. I have no complaints though. It didn't backfire either. Now I just need to figure out that random high idle.
 

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Re: Another CM400T First Bike - Lots of problems

Boy, we can start our our CM400 subgroup. They seem to be cropping up everywhere!
 

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Re: Another CM400T First Bike - Lots of problems

those circled tubes are the float bowl air vents (lets air into the bowls) follow the passages from the slow speed jets you can see where they go they need to be clear to idle properly [attachment=0:1u9jji15]cm400t027.jpg[/attachment:1u9jji15]ooops think arrow should go straight up to the air/idle
 

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Re: Another CM400T First Bike - Lots of problems

Do the carbs have a stamping on the side of them?

Reason i ask is they look nearly identical to that of whats on my '82 CX500. And i mean down to the accel pump.

I'm sure they are different but see if they say like VB26A or something like that.
 

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Discussion Starter · #13 ·
Re: Another CM400T First Bike - Lots of problems

sakibomb said:
Do the carbs have a stamping on the side of them?

Reason i ask is they look nearly identical to that of whats on my '82 CX500. And i mean down to the accel pump.

I'm sure they are different but see if they say like VB26A or something like that.
VB 22EASE
 

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Discussion Starter · #14 ·
Re: Another CM400T First Bike - Lots of problems

It's hard to tell with a cell phone but there's a significant difference.

Before cleaning and adjusting. Notice how high the RPMS are when I push in the choke.
[youtube:1uxxq38c]9JqBlvuSkwY[/youtube:1uxxq38c]

After. Sorry for the night time shot
[youtube:1uxxq38c]YyfmC5vQhdg[/youtube:1uxxq38c]
 

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Re: Another CM400T First Bike - Lots of problems

In my experiences, the rubber "caps' on the synchronization tubes leaking
is often the culprit for the high-idle syndrome....
Replace with new ones from an auto parts store carb section....
Cheap, it may solve the problem, and it can't hurt...
 

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Discussion Starter · #16 ·
Re: Another CM400T First Bike - Lots of problems

Not sure what you mean? As far as I know there are no sync tubes on the 81. I still haven't figured out how you're supposed to sync them.
 

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Sensei
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Re: Another CM400T First Bike - Lots of problems

On the 81's, there are screws in the head casting you remove to sync....Top of the intake ports just ahead/above the "boots".... Screw could be loose, or have a bad sealing washer....
 

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Re: Another CM400T First Bike - Lots of problems

Yeah, there's no rubber caps on the 400T, they are screws directly into the head. Worth checking to make sure they are screwed in though, they are on top of each intake port.
 

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Discussion Starter · #19 ·
Re: Another CM400T First Bike - Lots of problems

Ah finally. I noticed those. Didn't know what they were for though. Thanks!
 

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Discussion Starter · #20 ·
Re: Another CM400T First Bike - Lots of problems

Checked them and they're not loose. I was contemplating boiling the carbs in lemon juice and see if that helps the high idle.

Anyone have any recommendations on cleaning the outside of engine and carbs? I don't really want to take it out at the moment. It's still my main method of transportation.

I'm also haveing trouble with it idling in gear. The clutch is grabbing but no matter what I do to adjust either end it doesn't help.
 
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