Honda Twins banner

1 - 17 of 17 Posts

·
Registered
Joined
·
266 Posts
Discussion Starter #1
Hi people.
First post (other than in the new member introduction). Just bought a 1980 CM400E. First bike I've owned in more than 30 years. Was an Auto Mechanic most of my life. Specialized in Carbs. Those days are long gone ! The 400 runs great. Idles good, accelerates and decelerates good. The problem is when it's parked on the kickstand. In the morning I'll have a small puddle of gas on the floor. Seems ok on the center stand but that's a pain for me ! Looks like the overflow tube from the left carb. Working on Auto Carbs, I'm guessing the needle isn't shutting the gas off completely. Do these float bowls come off without removing one or both carbs ? The thought of Synchronization makes me a little nervous. Only had one Carb per vehicle back in the day. I know.......I need a manual. I'll get one. Just wondering if I'm one the right track. Would be nice if it could be fixed right on the bike. And where does everyone get Carb parts ? Right from Honda if they're still made ? I see a few posts saying to stay away from aftermarket floats and needles.......
 

·
Registered
Joined
·
69 Posts
Hello.
The dripping fuel could be leaking needle/seat. It could also be a crack in the brass overflow tube inside the bowl. It could also be the drain plug/gasket.
Maybe turn off the petcock and see if it still happens. If it doesn't leak, blame the needle/seat. If it does, blame something else.

The consensus is to use Honda parts. They are mostly available, but expensive. I used partzilla.com and delivery was quick.

Good luck.
 

·
Registered
Joined
·
78 Posts
Hi,
it depends on the type of carburator if you have to remove them to take of the bowl or not. On some carbs (like on my CB200) the bowl is simply fixed by a clamp, it can be opened while the carb is still on the bike. But it is a bit tinkering and fiddling because you don't see much. For the same reason (one carb leaking) last weekend, I had to remove the carbs on a friends Kawasaki LTD 450. These bowls were fixed by 4 small screws each, so I had to take both carbs off together, as they were joined by a common fuel tube and choke mechanism. Removed the tank, parts of the air filter, then loosened the intake manifolds, and finally got the carbs out after removing the cables. I replaced the bowl gasket plus the float needle on both, put some sealant on the bowls top, reassembled it and it was leak-tight again.
The reasons for "small" leaking are mainly: worn needle tip, or debris sticking inside the needle or needle valve seat, so that it can not get tight closed.
If your carburetor is removed, also check the float (remove it and shake it). If you hear some liquid inside the float glugging, the floater is leaky and needs to be replaced by a new one.
Just my 2 cents...
BTW: Do you have a name? :confused: Its much nicer to talk/write to people with a name;)
 

·
Registered
Joined
·
266 Posts
Discussion Starter #8
I'm Pete. Gotta decide now if I wanna remove the Carbs or try fiddling with the leaking one on the bike. I don't have a Synchronizer so not sure if I'm ready to do the job either way. Checking to see what the floats are made of. I'm used to Automotive Carbs, mostly GM. They had a Phenolic float that actually sucked up gas and caused it to flood over. Gotta check into it more before I do anything. Thanks for the reply !
 

·
Registered
Joined
·
78 Posts
Hi Pete,
I think if you remove the carbs and only remove the bowl, check or fix the float and needle, you can just put it together again and you'll be fine!
No need to sync them again. Apart from that, sync is at least to some extent easy when the carbs allow you to look at the throttle flap or piston through the air filter side. Just make sure both open exactly at the same moment when you twist the throttle, and that the both are fully open at WOT. Again adjusting depends on the type of carbs, some have a split cable, each end entering one carburator, each one adjustable via a cable adjuster screwing. Other carbs are mechanically connected with a common axle and some joints. These have an adjustment screw to turn the linkage vice versa, so you can also synchronize throttle positions quite easy.
The sync of the mixture screw however is best done with an exhaust co-tester. But as long as you don't tinker with that, everything stays the same as it was. I hope my explanations are understandable, english is not my mothers tongue...
BR
Klaus
 

·
Registered
Joined
·
266 Posts
Discussion Starter #10
I understand you fine. Everyone I've talked to around here tries to tell me synchronizing 2 Carbs is Rocket Science. Having rebuilt Carbs all my life I know better. I will get some gauges though. When I DO feel the need to rebuild them I'll go through all the motions.
Left the bike on the center stand all night with the fuel valve off. It still leaks but it's never a huge puddle. I'm sure there's enough fuel in the bowls to make it look major. Bike started up in a second without the choke and ran fine. Got a can of Carb cleaner and lightly sprayed the Carbs while it was running. Wanted to clean them a little. Not much crud there though. Looking for any vacuum leaks also. When I sprayed near the Air Cutoff Valve on the left side the bike stalled. Started right back up. Gotta read up on these VB's and see what that could mean.
All I see is Clymer Manuals. Are they any good ?
 

·
Registered
Joined
·
266 Posts
Discussion Starter #11
201_4642.JPG

Got this pic from a link to a post longdistancerider provided. Air Cutoff Valve I guess. Bike will stall when I spray Carb cleaner at it. Gotta read up more on it !
 

·
Super Moderator
Joined
·
24,208 Posts
View attachment 289630

Got this pic from a link to a post longdistancerider provided. Air Cutoff Valve I guess. Bike will stall when I spray Carb cleaner at it. Gotta read up more on it !
I'll guess that the small O-ring is missing. Other choice is the cover is warped which can be correct by sanding it flat.
 

·
Registered
Joined
·
280 Posts
on my 82 450 nighthawk, I had carbs rebuilt by jacks rebels, as soon as I turned the petcock on the first time fuel flowing out of left carb, bounced the bike up and down a few times and it stopped. anyway moving ahead, road it a few miles and leaking again. took out the 3 screws holding the bowl on, and sprayed the piss out of the float valve with carb cleaner, put it back together and no more problems, figure a little piece of dirt got in the way.
 

·
Registered
Joined
·
71 Posts
Think I'll order that valve then see if the cover is warped !
I would order 2 of them, not just the one as there is one on each carb. I would rebuild them personally... My guess is varnish? Or maybe rust from inside the Tank? As for the gas leak, either the rubber tip on the needle is hard or its full of varnish. I rebuilt my cm400t carbs about a month ago using everything from eBay. The kit I got came with both air cutoffs and the floats ($65). I also bought the accelerator pump ($15). $80.00 and runs like a top... They come out as a pair with 3 cables. 1 choke cable and 2 throttle cables - one push and one pull cable. Any other questions, feel free to message me. Robert
 
1 - 17 of 17 Posts
Top