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Author Topic: Cb400t carb issues which jet is the main?  (Read 1874 times)

Offline devon

  • Posts: 150
Cb400t carb issues which jet is the main?
« on: May 26, 2012, 02:13:47 »
I've got a couple things acting funky with my 78 cb400t. I've removed the airbox, replaced with UNI pods. Removed the factory installed exhaust crossover and attached two slip on mufflers.

When I rebuilt the carbs I mixed up the main and secondary jets. They are literally IDENTICAL in size so they can be installed in either place. One is a 78 the other a 105. I assumed the 105 was the main and went ahead with that.

I read that the 105 is actualy the secondary so I took the carbs apart and swapped em. The bike would barely start and when it did it would sputter and die with even a slight turn of the throttle.

So, back apart they came and switched the jets back. It's currently running extremely rich and actually stalled a couple times while I was out test driving it. I guess that I just need to know which jet is which so I can either start doing some jetting as is or diagnose a strange starting symptom.

Thanks,
Devon 8)

Offline HerrDeacon

  • DTT SUPPORTER
  • *
  • Posts: 3617
Re: Cb400t carb issues which jet is the main?
« Reply #1 on: May 26, 2012, 07:56:57 »
Your primary is the 78 and the secondary is the 105, with the secondary jet being the one closest to the float. Did you put the rubber slow jet plug back in?
Perry

1972 Honda CB350 K4 / 1978 Honda XL250S /1982 Honda MB5 / 2014 Honda CB500X

Offline devon

  • Posts: 150
Cb400t carb issues which jet is the main?
« Reply #2 on: May 26, 2012, 11:37:01 »
Yes sir, I double checked those plugs were there. Any suggestions on where to start to diagnose this starting/idling problem?

I can't remember where the idle screw is right now so I'm gonna reset that to 1.5 turns, but that's the only idea I've got unless the carbs werent seated properly against the rubber last time..

I'll switch the jets back tonight, reset the idle screw and update then.

Thanks for the reply!
Devon

Offline devon

  • Posts: 150
Re: Cb400t carb issues which jet is the main?
« Reply #3 on: May 27, 2012, 17:37:06 »
Alright, swapped the 78 and 105 jets, set the idle screw 1.5 turns out and reinstalled the carbs. The bike does start now - but it doesn't run well.
Today I set the valve clearances, they were slightly off (too tight on one intake and too tight on one exhaust) The next step I believe is a carb sync.

Since I'm dealing with a crappy idle (600ish) what should I be doing before a carb sync? The manual suggests setting the idle to 1200 rpm, should I just be cranking up the throttle stop screw??

Thanks again,
Devon

Offline crazypj

  • Posts: 12487
  • Split personality, I fake being smart
Re: Cb400t carb issues which jet is the main?
« Reply #4 on: Jun 03, 2012, 11:58:09 »
It will never run right with stock jetting and pods.
It's also real difficult to get it running better than mediocre with pods without doing a lot of carb work.
The mid range (around 4~5K) will be real rich when jetted properly for 7~10K
I know I could improve things but not sure I could 'fix' problem completely without a lot of experimenting

'you can take my word for it or argue until you find out I'm right'
I gave my girlfriend an orgasm the other night, but, she spat it back at me
 Some humans would do anything to see if it was possible to do it. If you put a large switch in some cave somewhere, with a sign on it saying 'End-of-the-World Switch. PLEASE DO NOT TOUCH', the paint wouldn't even have time to dry
 Itís not worth doing something unless someone, somewhere, would much rather you werenít doing it  (Terry Pratchett)
CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline devon

  • Posts: 150
Cb400t carb issues which jet is the main?
« Reply #5 on: Jun 03, 2012, 12:31:48 »
You're right, I'm gettin absolutely nothin from 1/4-3/4 throttle.

I'm ready to do a carb swap but have no idea where to start. I'm thinking about ordering some vm30s from
Dime city.

The only barrier for me right now is jetting. the few hundred I'll spend on the carbs is in my budget but i don't have another few hundred
to drop on the five bajillion jetting options for those carbs just to find out which setup I require.

Thanks again!
Devon 8)

Offline Fredflame

  • Posts: 1
Re: Cb400t carb issues which jet is the main?
« Reply #6 on: Jun 30, 2017, 19:02:00 »
Hey Devon! Could you let me know what is the solution you found for your CB400T jet issue please? I actually have the same problem and want to change jets or carbs but don't know what to buy...

Let me know!

Cheers

Fred

Offline crazypj

  • Posts: 12487
  • Split personality, I fake being smart
Re: Cb400t carb issues which jet is the main?
« Reply #7 on: Jun 30, 2017, 23:20:26 »
5 yr old thread  ::)
The 3 jet didn't get any better so either put stock airbox back on or swap to Mikuni's
'you can take my word for it or argue until you find out I'm right'
I gave my girlfriend an orgasm the other night, but, she spat it back at me
 Some humans would do anything to see if it was possible to do it. If you put a large switch in some cave somewhere, with a sign on it saying 'End-of-the-World Switch. PLEASE DO NOT TOUCH', the paint wouldn't even have time to dry
 Itís not worth doing something unless someone, somewhere, would much rather you werenít doing it  (Terry Pratchett)
CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0