Cafe Racer Forum banner

1978 Honda CB400T no spark!

1K views 13 replies 3 participants last post by  BriOpal 
#1 ·
I’ve been trying to diagnose this issue for the past couple weeks. It’s my first motorcycle, and I’m trying to fix it up on my own. Bike was sitting for 3 months, during the winter. It did start in January but as I was warming it up, it shit off on its own. So far I’ve charged up the battery, replaced spark plugs and checked compression (was 122 when it’s supposed to be between 177-191), still nothin. Now I’m thinking to move into pulling the carbs cleaning them OR rebuilding. Am I goin about this the right way?
 
#2 ·
Yes, if it has carbs learn to clean and service them, good news is almost 100% of the problems will be in the very bottom parts of the carburetor, where the fuel lives.

but you say it has no spark? that is a serious problem, see if it relates to a bad battery by using jumper cables and connecting it to a car battery you know is good, that will trouble-shoot the battery question.
 
#4 ·
No use all the original parts if you possibly can,
rubber bits that you find might be the only thing that needs replacing. (you might not even encounter any)
Take pictures of everything as you take it apart so you know how it goes back together right.
Make sure your tools all fit the screws nice, expect some fuel mess and the need to use solvents.

... it is infinitely easier if you watch somebody skilled do it the first time out :|
 
#7 ·
Almost 100% it is yuck in the carbs and it is an easy enough fix, just be advised it might take more then one attempt so don't become too disheartened if it still has issues, if you can watch for indication of water droplets rolling around in the bottom of the float bowls, would not surprise me. Also would not surprise me if they are totally gross inside.
 
#10 ·
Dirty carbs is the likely culprit. Here is a post by one of the internet's Honda 400 Gurus on rebuilding vb carbs. Follow exactly what he says and they will work properly. Rebuilding VB Carbs
I would recheck the compression it's unlikely to have both cylinders the same low figure. The 400 motors are pretty much bullet proof so unless it has excessive miles it should show better than that.
Did you clean the tank and petcock?
 
#11 ·
Dirty carbs is the likely culprit. Here is a post by one of the internet's Honda 400 Gurus on rebuilding vb carbs. Follow exactly what he says and they will work properly. Rebuilding VB Carbs
I would recheck the compression it's unlikely to have both cylinders the same low figure. The 400 motors are pretty much bullet proof so unless it has excessive miles it should show better than that.
Did you clean the tank and petcock?
Oh perfect, I’ll definitely give that a look when I get to cleaning the carbs. I haven’t thought to clean out the tank and petcock. You have some pointers for that, once I get to it?
 
#13 ·
The previous owner was riding somewhat regularly, here there taking it to the shop. Slowly fixing it up. It was a project bike for him and he got too busy to pay attention to it. I bought, the bike rode like a champ. I have all the shop paperwork, all the work that’s been done. And I saw that the last time carbs were worked on, was 2017. And there’s no rust from what I can tell, but I will see for sure when I clean it out
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top