CB400F Jetting issues and running rich (solved)

Re: CB400F Jetting issues and running rich

What happens if you take her to mid throttle? Are all cylinders firing at mid throttle?
If yes then check pilot jet for blockage primary air for blockage and mix screws for broken tip. Make sure you can see through the jets and holes and corresponding orifices look the same size. I guess you have no idea what the POs have done before you!

Sent from my GT-I9506 using Tapatalk
 
Re: CB400F Jetting issues and running rich

IronJim said:
The coils operate as follows 1,4 - 2,3.

Iv currently got 2,3 running perfect but 1,4 are my issues currently, Took them both off to see if they have a spark and they DO have a spark so no issues with firing. my next idea is to have a look at possible blocked pilots.
Click to expand...

Iron Jim, he was asking if you mistakenly had a coil hooked up such as left coil on 1/2 and right coil on 3/4 (as it wouldn't be the first time a PO has done this) Glad you have them hooked up properly from your answer though :)
 
Re: CB400F Jetting issues and running rich

No the coils are set up properly 1,4 2,3

Managed to get the bike idling nicely now and can even throttle all they way through without any hiccups, Cylinder 1,4 seem to kick in once the bike has warmed up. I cleaned the carbs thoroughly and replaced the main jet to a #82 instead of the original #75 bike seems to run much better this way. Still getting some smoke mid rev range but im wondering if this will go away with time as the bike hasn't been run properly for a least 7 years. Or it needs a bigger main jet

Im going to get the bike out tomorrow for a run so ill see what the plugs are saying
XS750AU said:
What happens if you take her to mid throttle? Are all cylinders firing at mid throttle?
Click to expand...

1,2,3, Cylinders are all firing fine 4 is still an issue and struggles to get hot. All carbs have been stripped and gone through with wire so no issues should occur, i also have new air screws in place.
 
Re: CB400F Jetting issues and running rich

Hi
Sounds like good progress. If it is rich in mid range, try lowering the needle 1 position.
Is no4 high tension leed ok?

Sent from my GT-I9506 using Tapatalk
 
Re: CB400F Jetting issues and running rich

IronJim said:
No the coils are set up properly 1,4 2,3

Managed to get the bike idling nicely now and can even throttle all they way through without any hiccups, Cylinder 1,4 seem to kick in once the bike has warmed up. I cleaned the carbs thoroughly and replaced the main jet to a #82 instead of the original #75 bike seems to run much better this way. Still getting some smoke mid rev range but im wondering if this will go away with time as the bike hasn't been run properly for a least 7 years. Or it needs a bigger main jet

Im going to get the bike out tomorrow for a run so ill see what the plugs are saying
1,2,3, Cylinders are all firing fine 4 is still an issue and struggles to get hot. All carbs have been stripped and gone through with wire so no issues should occur, i also have new air screws in place.
Click to expand...

Well, #4 struggling to get hot is your issue now. No sense doing much else until that's sorted out. If #1 is warms up the others, and #4 has spark, then it's got to be clogged idle jet (still) mixture screw broken/tip broken or setting way off, or back to the float height. When you have the carbs off, you should be able to take the pilot jet out and see light through it. Not dim light, BRIGHT light (so long as you are actually staring at a light ;) ) IF that's ok, take your carb cleaner spray, hold the slide if you had mechanical slides and there is one hole that it sprays through near the back of the slide, or hold the butterfly open if you have diaphragm slides and you should see a jet of fuel come up through 3 or 4 holes and then some fuel should also come through a hole that is 3/8" or so further forward towards the engine side (which is your mixture port typically) In your case, there's 2 ports in the rear of the carb. A large brass tube which goes to the main jet, and a small hole diagonally up in the carb body. With the jet in place you should see fuel come out of the pilot jet (if it's clean) when you spray through it. I added a couple of pics just in case :)
 

Attachments

  • 20160613_155150.jpg
    20160613_155150.jpg
    388.9 KB · Views: 318
  • 20160613_155235.jpg
    20160613_155235.jpg
    333.1 KB · Views: 320
Re: CB400F Jetting issues and running rich

Thanks Bruno

Really appreciate the pictures and directions, I'm taking the carbs home with me this weekend so i get to work on them all weekend, Ill update you of my progress when i,m back.

Thanks for all the advice guys i really appreciate every message
 
Re: CB400F Jetting issues and running rich

IronJim said:
Thanks Bruno

Really appreciate the pictures and directions, I'm taking the carbs home with me this weekend so i get to work on them all weekend, Ill update you of my progress when i,m back.

Thanks for all the advice guys i really appreciate every message
Click to expand...

Yep, Pictures always help! Check that each mixture screw is set about the same (technically they don't have to be all the same , but that's a whole nother' story.) Could be as simple as that. One thing to verify is that the screw is "bottoming out" and isn't FEELING like it's bottomed out due to crud/varnish/dirt or whatever in there :) Best way is to take apart and clean/verify. Don't lose the spring!
 
Re: CB400F Jetting issues and running rich

MotorbikeBruno said:
. One thing to verify is that the screw is "bottoming out" and isn't FEELING like it's bottomed out due to crud/varnish/dirt or whatever in there :) Best way is to take apart and clean/verify. Don't lose the spring!
Click to expand...

The screws are new, they came with the rebuild kit (probably the only thing used i used were the screws and the seals)
 
Re: CB400F Jetting issues and running rich

IronJim said:
I cant verify that for sure !! lol
Click to expand...

Ha! We've all had those moments. Just clean them, then walk away. Come back and clean them again (but better) and have a beer...then clean them one more time and you should be good. :eek: :eek: ;)
 
Re: CB400F Jetting issues and running rich

Update

So I finally got her fired up and running. Did a vacuume sync today and will be giving her a run over the weekend. Thanks for all the help and advise you have given me it has taught me so much.https://vimeo.com/172025084

If you've never owned one you'll never understand

CB400F
 
You must log in or register to reply here.

DTT Light or Dark

  • DTT Light
    • www.jadusmotorcycleparts.com
    www.lostapostle.ca/
    www.sparckmoto.com

    Spread the Love

    Back
    Top Bottom