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1980 CM400, Hard to start, won't idle

6K views 9 replies 6 participants last post by  dtsmjr8dan 
#1 ·
Hi all, first post here so if this is a repost please move to the right place.

I have a 1980 Honda CM400, was running beautifully, then I parked it for ~6days and when I started it again it refuses to idle. It is also has trouble turning over (electric start) it struggles, then turns over easy for a few strokes, struggles turns easy, and eventually starts. At full choke it idles for a little bit, and it will run if I give it enough throttle to keep it at 3000RPM. Both pipes get hot, but the left definitely heats up a lot slower then the right. If I rev it up to 5-7k RPM I get what sounds like a little backfire.

My first thought was plugged idle jet, so I took both jets out of both carbs, cleaned them (could see clearly through each), also replaced the inline fuel filter (hadn't been done in awhile so figured I should). Choke appears to be functioning fine, value timing is good, battery is good. Fairly new to working on a bike so really just not sure what steps to take next, any help/advice is greatly appreciated!!

Cheers,

Rob.
 
#2 · (Edited by Moderator)
What do your plugs look like? Are they the proper plugs? D8EA?

Edited the plug number
 
#3 ·
New plugs would be a good step. Another possibility is a plugged/restricted passage in the carb which a quick cleaning won't fix. If you check the Fuel supply and carburetion section you can find lots of information on that.

Welcome to the group.

Got pictures?:p
 
#6 ·
These models only depend on the alternator for power to the ignition, tools1. They will run just fine with no battery at all. So, new plugs and then carbs.
 
#9 ·
So correct plus are in there D8EA, both have good spark. The left plug was black and wet with fuel, and the right is just black (looks like it was running rich, this may be from running it with full choke while diagnosing the problem).

from your suggestions this leads me to think left carb issue of some sort? any body have a good link on how to begin looking at that?
 
#10 ·
You'll want to get some clean/new plugs in there. There is a sticky in the fuel section for the carbs.
 
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