Topic: 79 cb400t

[Draven]

I bought my 1979 Honda CB 400 T a few years ago and when I got it home I started it up and drove around the house, and as soon as I came to a stop a connecting rod broke.
Thankfully the bike came with  few extra parts and I was able to replace it. I put the motor back together popped it back in the bike and tried to start it.....nothing, put it away in my parents shed. It sat there for a few years.
I have just now got back to it, I pulled the motor out, opened it up, and cleaned everything really good and fixed a few things i missed the first time. I put it back in, hooked everything up and was shocked when the first I hit the kick start and it fired up, but then quickly died. I got all excited and pushed it over to my car and hooked up the jumper cables
and hit the start button, again it turned over and fired up, and quickly died.
After some fiddling i managed to get it to stay running, but it still died, even with the throttle wide open. I cleaned the carbs out, same thing. Adjusted the carbs according To my manual, no change. Adjusted the timing, getting it to run for a few second is the best I can get out of it.
I just don't know what to do from here.
Any Ideas?

[grcamna2]

The first thing I'd like to ask you is, do you have a very good Honda factory service manual ? I would take that manual & do the sequence of tests that they recommend...
just go right through the different tests & through the "process of elimination" the problem will definitely be revealed to you.

[Draven]

ok i have a clymers honda 400 - 450 twins 78-81
fuel line is clear, lots of compression, spark is good, has a new head gasket, choke and throttle are working fine.
today i went over every inch of the carbs with q-tips, and even grabbed a small clear tank i could use to make sure my fule is clean. now it only runs while i'm hitting the starter

[grcamna2]

How do your points look ? Are you getting any power to both sets of points when checked w/ a test light ?
I would also check the electrical connections to your coils(black wire w/ a white stripe)
That wire is the one you need to make sure has good connections All the way along it's entire length...you can trace it out;check to make sure that your coils are making a good ground connection to the frame(where they mount onto the alloy bracket & where the alloy bracket mounts to the steel main frame);scrape both surfaces of the coils & the bracket/frame. Make them have nice shiny clean metal to metal contact & after your done coat the bare metal surfaces w/ dielectric grease to prevent further corrosion down the road.I would also determine that your off/run/off kill switch on the right handlebar switch is functioning well...use an Ohm meter to check it for continuity.
The electrical systems are sometimes corroded pretty bad on vintage bikes & they tend to be the weak link.
I have the Honda factory service repair manuals (for dealers only) for All 1978'-81' CB & CM400T,E,C,A models & if you need any specs,please don't hesitate to ask.

[Doggie]

I have the same bike and my problem is that the engine cuts out when the handlebars are turned. My guess is the kill switch.
                             Doug

[grcamna2]

OOPS...I just remembered,your bike doesn't have points,please forgive my goof.

[Draven]

ok lastnight i set the balancer system, turns out it was off a bit. i'll check out all the connections, clean them, and update.

[Draven]

alright good news and bad, put it all back together(kick start is now busted, piece in lower crackcase snapped off)took it over to my car and jumped it. fired right up and ran good for about a min. started it back up and played with the throttle and at about half it started sounding like it was revving up, while i held the throttle in one place. now keep in mind i don't have the exhaust on it yet.

[grcamna2]

They will run smoother if you have the airbox w/ filter installed w/ the exhaust system;
I've had the same experience as you have when trying to run one of those.

[Draven]

alright so i've put the exhaust on, i noticed that if i keep it running as long as i can it refuses to start back up
the sound has me pumped to go for a ride so i hope it's something stupid

[Draven]

i think i got it, found a small piece on the carb that was ready to fall off, and did. I put the JB weld to and i'm crossing my fingers

[KB02]

What was the piece?

[Draven]

on the main body, top, around the edge of the vacuum piston

[grcamna2]

JB weld can work miracles !

[Draven]

ok carbs fixed, i replaced the valve cover gasket. i start it up and it idles nice, but still surges when you start to give it gas.

[Draven]

through looking around i found it may be a leaky carb boot or the auto advance may be stuck. for the carbs i will be putting some gasket maker on between the head and boot, letting it dry for a few days. the auto advance however i'm not sure of, not really sure what i'm looking for. my book has nothing on auto adavance, at least thats not what its called in the book

[grcamna2]

How does your spark advancer look? are the springs in nice tight condition? I hope your carb boots aren't a problem;it's tough to do a repair on that old rubber without having it leak again.