Topic: My first bike. 1980 CM400A Restoration project

[TommysCM400]

Before I knew this forum existed I made a long thread over at ADVrider.com

http://advrider.com/forums/showthread.php?t=451619
I've gotten a lot of help, but there's really not a whole lot of specific Honda knowledge over there.

Basically to summarize:

I got the bike for $200, came with a parts bike too.





The bike ran, but pretty rough.

Rebuilt the carbs (all new gaskets/Diaphragms), adjusted the valves. Also put in new fork seals.

The bike runs pretty good. Rode it around the driveway a couple times.

I sync'd the carbs yesterday. The vacuum needles were very bouncy. But I adjusted the sync screw until the bounce on both cylinders were even.

The engine idle also seems to high..and it hangs sometimes. The throttle cables are loose, so its not that. And the idle screw is turned out so far that it isnt touching the controls.

Part of the problem is the return spring on the carbs. Its not strong enough. I kinda noticed it when I had the carbs off the bike, but I just lubed the heck out of it - that helped, but didnt solve it. So I'm probably going to have to add another return spring since it doesnt look like theres any way to adjust this one.
I also lubed the throttle shafts when the carbs were off. Everything seemed fine.


I guess its kind of acting like theres a vacuum leak. I sprayed starter fluid all around the carbs/boots, etc.. Engine never surged. I may try carb cleaner.

The air/mix screws are at the factory setting of 2 1/4 turns out.



In addition to that little issue Im trying to iron out, the front forks feel soft.

The previous owner told me of this. He was going to swap the forks from the blue bike. But I figured, why bother they probably just need new seals/oil. Plus the blue bike has air assist forks, which would be different.

So I put in new seals, cleaned everything up, put in the right amount of ATF fluid..They still seem pretty soft. If you press down on them, they dont just bounce right back on their own 100%.

I should have measured the springs when I had them out, but they were both the same length and they go in tight.

But, for all I know this is totally normal, since Ive never been on a motorcycle before.



Anyways, sorry for the babbling and annoying questions. Just anxious to get the bike on the road soon!

Thanks for any advice.

[tbpmusic]

The air/mix screws are at the factory setting of 2 1/4 turns out.

[TommysCM400]

Thanks, I actually have the Clymer book.

Unfortunately I do not have a tachometer, so theres no way for me to further tune the air/mix screws. I assume a better tune would only result in a higher idle.

I played with the screws a little and was just kinda making the engine run rougher, so I set them back to the fac specs.

I went to auto parts stores and looked at tachs..but they had nothing for a 2cylinder.


I went out and fired up the bike this morning. It actually ran at a lower RPM today. But still, I would expect that if you back out the idle speed screw all the way, the engine should die. It seems like the engine should run a little smoother too.

I also took my propane tank and sprayed it all over the carb/boots, etc..No difference at all. So maybe theres is no vacuum leak..


Edit: Hmm. I found some laser tachometers on eBay. I guess you put a piece of tape on the flywheel, put the laser at it while the engine runs and that tells you the RPM. Guess I would just have to take the flywheel cover off.

I guess the engine could just be running so rich that its idling higher. It does smell pretty gassy while running.

So maybe this all relates back to getting the air mix screws in tune.

[tbpmusic]

Looks to me like it says 7/8 of a turn on those pilot screws, not 2-1/2.

That could be a lot of your problem right there.......
Coould be causing it to run pretty rich at idle.

Never heard of any old Honda with pilot screw settings of 2-1/2 turns.

[TommysCM400]

Looks to me like it says 7/8 of a turn on those pilot screws, not 2-1/2.

That could be a lot of your problem right there.......
Coould be causing it to run pretty rich at idle.

Never heard of any old Honda with pilot screw settings of 2-1/2 turns.

No, they put a limiter cap on the screws from the factory. The limiter cap only allows 7/8s of a turn to a leaner mixture only.

When I rebuilt the carbs I got rid of the limiter caps. (so thats not a factor now)

The article says to seat the screws and then back out the number of times listed in the table - which is 2 1/4.

Yea, Im definitely going to get these tuned right before doing anything else.

[tbpmusic]

The article says to seat the screws and then back out the number of times listed in the table - which is 2 1/4.

Well, I guess if the Clymer says so, it must be true, right?? 

(Best Dr. Phil voice) - so, how's that been working out for you???

[TommysCM400]

The article says to seat the screws and then back out the number of times listed in the table - which is 2 1/4.

Well, I guess if the Clymer says so, it must be true, right?? 

(Best Dr. Phil voice) - so, how's that been working out for you???

 

Well, I'm gonna run off to Harbor Freight and buy one of those laser tachometers. Although I should probably just get one on ebay..Only $25. $50 at HF.

[TommysCM400]

Well, I bought a laser tachometer and tuned the air mix screws. The factory spec is actually pretty close.

I also sprayed propane all over the carbs. No vacuum leaks..

I also noticed on the throttle twist on the carbs, a piece is broken off. I noticed it from comparing this carb with the ones on the blue bike. Thats keeping the butterflies from fully closing. If you push on it with a screwdriver it idles down more. Still not enough to kill the engine, but below the 1200RPM factory idle suggestion.

Adding a return spring would pretty much fix this. But Im having trouble finding a way to mount one. The throttle twists so far around, its going to be tough to mount one that wont interfer with the controls at full throttle.

Otherwise Ill have to pull the carbs and steal the part from the blue bike. Not something I really want to do..but eh, maybe thats the way to go.

[TommysCM400]

Well, I swapped the carbs and that took care of it. Can idle as low as I need.

The butterfly on the other carb set was screwed up..Someone had it apart before and screwed it up.

[Peterbylt]

I have a 79 CM400A. Its a nice little bike, one of the slowest things I have ridden but very comfortable and it get fantastic Gas mileage. I use it to commute back and forth to work the automatic is great when I get stuck in traffic. I have never had any issues with the carbs, in fact I have never had any issues with this bike at all except replacing the battery when I first got it 3 or four years ago, very dependable. Good luck with it. 



Peter

[TommysCM400]

Nice bike.. Is there a band clamp holding your luggage rack to the grab bar?

I just bought an NOS luggage rack but don't have the band clamp (instructions say it should have one)

I'd love to have those saddlebags.. They go for quite a bit on eBay. Hard to find.


Been riding the bike for the last few weeks for nice day trips and quick trips to town. Put close to 200 miles on it so far.

Been a complete blast. I love riding it..

The fastest I've had it was 65mph..and that scared the crap out of me. It feels like going over 100ph in a car.
It's pretty smooth though at that speed. I was surprised.

Overall its a slow bike, which works out just fine for me.

I dropped it once in the driveway practicing circles. Fortunately the bike didn't even hit the ground. I was able to hold it up. Had it been any heavier, I wouldn't have.

I should probably post some updated pictures..but I still need to polish things up and redo the paint job.

[Johnie]

I rebuilt and sold 4 400's the past 4 years.  Kept my first one which is in the picture below.  It is a 1980 CM400E that my son and I worked on together.  I have had offers, but sentimental value to me...plus it is a blast to ride around in the city and slow country roads.  I also have a 1981 CM400A parts bike but all that is left is the motor, frame and some small parts.  Click the pic...