• Don't overlook our Welcome Package, it contains many links to important and helpful information about functions at VHT like posting pictures and sending PMs (private messages), as well as finding the parts you need.

    AD

Questions for 81' CM400C

Jwormy

Well-known Member
Joined
Jun 5, 2020
Total Posts
81
Total likes
1
Location
San Diego, CA
Hi All,

Finally got this old CM400 off of my back patio and out onto the street so I can troubleshoot the engine noise with my neighbor wanting to kill me! I did managed to reduce the engine rattling noise by adjusting the cam chain tension screw and a balancer adjustment but I've discovered a few things maybe you guys can help me with. The first, and most concerning issue is that the right spark plug is completely oil-fouled after only idling for a few minutes and the right side is HOT and smoky, I imagine from burning oil. The left side? Cool as a cucumber. The plug on the left side looked like it hadn't even sparked so I tested for spark and it was very weak, but was indeed firing. I did do a compression test before the bike was running and it was low on the left side, normal on the right although the engine was cold at the time. The next thing I discovered is that the center stand is touching the chain. It doesn't seem warped when the bike is up on it, so I'm not sure if its the spring or what. Can it just be removed? Any help appreciated. I wasn't sure which section to post this in so feel free to re-categorize!

Thanks!, Jess
IMG_2281.jpgIMG_2283.jpgIMG_2284.jpg
 
The plug appears wet to me, more so than oil fouled. I'd suggest running thru the ignition system tests found in the SOHC Electrical section to verify your ignition is good.
One side cold says it isn't getting spark or it isn't getting fuel. This all could be a carb issue.
The center stand is a useful tool to have for maintenance. It normally uses the left muffler for a stop. You can make a stop similar to the CB350
 
Pulled the bike inside tonight to test the ignition and noticed fuel leaking from
The carb pilot jets. Anyone know what would cause this?
d760fa12a7b041a1ea8219416d98d52a.jpg



Sent from my iPhone using Tapatalk
 
They have o-rings that need to be replaced. They are also quite a bit too far unscrewed.


Sent from my iPhone using Tapatalk
 
Thanks! I’ll have to check the o-rings but they are 2 1/2 turns out as called for in the service manual.


Sent from my iPhone using Tapatalk
 
Wait for Jim to comment, but my guess is the float height level is also slightly too low (fuel too high).....besides the missing o-rings....
 
If the mixture screw O-rings are missing or damaged then that would account for the leak. As Steve mentions float level incorrect although that usually shows up with drips from the overflow nipple in the float bowl.
The 2.5 turns out specified in the FSM is purely a starting point for mixtures, enough to get it running fairly well. To set the mixtures correctly first sync the carbs. Then ride it for a few miles to get evenly hot and park on the center stand. Idle speed set at 1200 and adjust one mixture screw to get the highest idle speed. IF that speed is higher than 1300 reset the idle back down and continue. Once you have that carb set move to the other one and repeat. Now go ride it for a few more miles and recheck. You may need to run a cooling fan while doing this if it takes more than 5 minutes.
Note: at idle speeds higher than 1300 the second idle transition port is exposed and negates further mixture adjustments
 
Back
Top Bottom