Topic: CB400F Re jetting and carb sync but still running bad. Advise please.

[Jimbo]

Afternoon all

Currently in the final stages of finishing my brat build, i have pods fitted standard four to one exhaust and aftermarket muffler. I have stripped the carbs (best i could as the previous owner has rounded the screws off that connects to the needle) cleaned all and re jetted with 42 pilot jets and 82 main jets. The bike will start and run but idols like crap, when i give it any throttle its struggles to rev and i get white smoke out the back, when i give it more throttle it bogs down massively and i get black smoke out the pipe. The plugs are sooty with no oil on them (fouls really quickly) iv tried different combinations of jets but still getting the same result. Carbs seem mostly in sync and the air screws are 1 1/2 turns out.

Any advice would be greatly appreciated

Cb400f
60,000 miles (she's an old girl)
Top end rebuild
New OEM coils

[Tim2005]

Hi, generally 400s with pods need smaller pilots, 38s are about right. However pods on 400s are usually very hard to get right all through the rev range, many of us have ended up going back to the stock airbox.

[harisuluv]

generally with pods we never change the pilot jet.  what needs to be changed usually is the main jet, needle jet position, and air screw adjustment.

Carbs seem mostly in sync

"seem,"  "mostly" No one is going to be able to take anything away from this type of language.  Did you vacuum sync the carbs or not?  By what observation are you determining the sync is good or close to good?

Once you get to the min post count to post pictures, you're going to want to post pictures so we can have a better understanding of everything.

[flybox1]

bench sync'd?  aftermarket float valves?  what is the bowl fuel level?
aftermarket jets? or Keihins?
can you go back to the stock Keihin 40's? and leave the air screws where they are...
if you can get it to idle here, do a vacuum sync, just enough to get it to idle nice.
Assuming all of the maintenance items are completed?.....

[Jimbo]

Afternoon gents

Thank you very much for the help, iv put an order in for 38 pilot jets so i will get them fitted and let you know. The carbs were accurately vacuum synced at idol speed with the choke slightly open i couldn't sync with the throttle open anymore due to the bike bogging down severely. Everything on the carbs are standard apart from the jets iv replaced (they are aftermarket jets) The float valves are original. The carbs were bench synced then vacuum synced once on the bike. ill be trying it again today with the standard pilot jet 40 and a larger main jet 78

Thanks again ill keep you updated.

[flybox1]

The carbs were accurately vacuum synced at idol speed with the choke slightly open i couldn't sync with the throttle open anymore due to the bike bogging down severely.

I dont understand this statement....a vacuum sync is done at the lowest comfortable idle (with no choke)
Please detail your vacuum sync process.

[Jimbo]

Currently the bike struggles to idol and giving it throttle makes it stall out so in order to keep it running iv had to give it a slight bit of choke. I was also unaware that a sync had to be done when the bike is idling. I'm doing this all for the first time so this is all a learning curve for me. Again i appreciate the help and advise you guys are giving me.

[Don R]

 It sounds like it's not getting enough fuel at idle, too much above idle. I bought one with pods and went back to an airbox.  The jets were already stock. It required choke to run also until I put it back to stock. I considered adapting a bigger cone shaped K&N on the back of the collector airbox but apparently am unwilling to do the work because it never happened.

[Jimbo]

Hi Don

Did you go back to standard air box or did you buy alternative ?

[flybox1]

Currently the bike struggles to idol and giving it throttle makes it stall out so in order to keep it running iv had to give it a slight bit of choke. I was also unaware that a sync had to be done when the bike is idling. I'm doing this all for the first time so this is all a learning curve for me. Again i appreciate the help and advise you guys are giving me.

Have you downloaded the Honda Manual for your bike, and are you following the 3000mi maintenance items?
Completing these usually gets bikes running pretty well.

[Jimbo]

Thanks Flybox1

Iv not been following the 3000mi maintenance items. I will get this downloaded and complete.

Thanks again 

[flybox1]

The 350F-400F is the one you want.
Purple, 3rd from the top.
http://www.honda4fun.com/materiale-documentazione-tecnica/shop-manual

[Jimbo]

Got it.. Thanks

[Jimbo]

generally with pods we never change the pilot jet.  what needs to be changed usually is the main jet, needle jet position, and air screw adjustment.

What needle position would you recommend ?

Thanks

[flybox1]

generally with pods we never change the pilot jet.  what needs to be changed usually is the main jet, needle jet position, and air screw adjustment.

What needle position would you recommend ?

Thanks

you're not there yet...Did you complete the 3k mi maintenance?
If so, how does it run now?
Needle clip position will depends on what your plug color looks like and what your final main jet is.

[Jimbo]

Hey Fly

Thanks for the response, reading some of the other threads im glad your on my case in regards to the issues i'm having, you truly are the Yoda of carbs.

Due to the bike being built from the ground up most of the old parts have been replaced with brand new items there isint much that is standard on the bike, including the electrics which has now been replaced with the M unit. All brake hoses have been replaced, Throttle cables, new coils and plugs. Iv done a service on the bike also (new oil filter and oil change) All things on the 3000mi maintenance apart from the ignition timing have been ticked off whilst the bike was being built. 

When i finally got round to starting the bike for the first time after i completed the work she fired up and idled fine (this was with the pods fitted and standard jets) i could even give her a bit of throttle and she reacted fine until i got over half throttle where she bogged down a lot (i do have a video of this glorious moment).

After seeing how the bike reacted i thought to myself does it even need jetting ? But i proceeded to re jet the carbs anyway  BIG MISTAKE. Ever since then the bike has ran like crap kicking out white smoke followed by black smoke at high revs. The plugs are sooty and get fouled very easily. After taking the carbs off and cleaning them numerous amounts of times and changing jet sizes god knows how many times i finally decided to put a bit more effort into the carbs by taking them apart fully and replacing all the seals, float valve, new standard jets, air flow screws basically all the stuff that comes in a carb rebuild kit. This is where im currently at so that's why i was asking the question about the needle position.

Thanks again Fly 

[flybox1]

All good info.  Thanks for the detail.
Carb kits....what brand jets were in those?  Any brand markings on them or on the kit?
Anything other than OEM Keihins are really difficult to tune for because quality control is an issue. 
Overall length, ID accuracy, emulsion hole size discrepancies....all add up to a &itch of a time tuning.
It doesnt matter what CB you have.  Most go back to Keihins because they are the right equipment for your bike.
Bowl fuel level....The clear tube test should be mandatory for anyone installing aftermarket float valves.
For all the same reasons aftermarket jets give us troubles. 
Measuring/setting floats per the book is all fine, but the only way to PROVE the fuel level in the bowl is right is to test it.
If its high or low in the bowl, it will change supply, which can lead to a lean or rich condition, and the jet has nothing to do with it.
Emulsion tube.....there hiding under the main jet.  This thing has to come out and be spotless.
Main jet - the o-ring around its waist needs to be OEM/viton, and seal well, or fuel can be sucked up past it.
Vacuum sync, get it done.

If all of the above is sorted out, you need to pick up a few sets of new plugs to start dialing in your jet/air screw.
Start and warm up your bike.
Throw in a new set, and start the bike again.  Let it idle(no throttle) for 4-5 minutes.  place a fan of some sort on the engine to keep it cool. Shut it down.
Pull all these new plugs out.  Line them up 1-2-3-4, and snap a closeup picture of the insulator and tip electrode.
Post the picture.  Checking out the insulator color will help direct us how to proceed.

[Jimbo]

No problem

Carb kits https://www.davidsilverspares.co.uk/CB400F-SUPER-SPORT-FOUR/part_28459/ (Keyster is the make)

Emulsion tube They were cleaned a few times so shouldn't be an issue but i will go over again.

Main Jet is keyster again but its a tight fit so its possible no leaks... fingers crossed.

Bowl fuel level I will check this and get back to you. I set the float levels today and they were 22mm.

What plugs would you suggest getting? i went for stock as that what was on the bike when i bought it, changing the plugs did make the bike run well the first time i started with the new plugs.

I will follow all instructions and snap a pic for you.

TBC

[flybox1]

I believe D8EA's are stock for the 400F

Yes, you will need to do the clear tube test and verify fuel levels.  Adjust as necessary.
You should invest in Keihin jets, Keysters really can make things difficult 
www.jetsrus.com

[Jimbo]

Thanks for all the help.

Ill make relevant changes and update in a few days.

 

[Jimbo]

UPDATE

So finally got the Carbs back to stock, OEM parts back installed also, cleaned emulation tubes and carbs again also. Put new o rings on the main jet and a fresh set of plugs.

Turned the bike over and it jumped into life, managed to get it running with a slight bit of choke but annoyingly still won't idol AND kicks out more white smoke then before, lower revs seems better but still bogs down when given any throttle past a quarter turn. Plugs are as follows.

Thanks

Slowly loosing the will to live

[flybox1]

Those plugs are really rich.
Tune out the richness and go from there.
Start with clear tube testing yiur bowl fuel level, and adjust as needed, then do a proper idle plug chop to get your mixture screw set correctly.

[jonda500]

UPDATE

So finally got the Carbs back to stock, OEM parts back installed also, cleaned emulation tubes and carbs again also. Put new o rings on the main jet and a fresh set of plugs.

Turned the bike over and it jumped into life, managed to get it running with a slight bit of choke but annoyingly still won't idol AND kicks out more white smoke then before, lower revs seems better but still bogs down when given any throttle past a quarter turn. Plugs are as follows.

^^^^^^^^^^^^^^^^^^^^^^^^^^^Your video is private so we can't watch it... John

Thanks

Slowly loosing the will to live

[Jimbo]

Hi John

Video is now available to watch..

Thanks 

[jonda500]

Hi Jimbo, I agree with flybox1, the next thing I would do is verify the fuel level in each bowl is roughly 3 - 4mm below the top of the bowl and not higher. -I spent years trying to get my reconditioned by harisuluv carbs to work without running super rich and fouling the plugs. I have it running well now and the turning point where I regained the will to live was when I reset the float levels from 0 - 2mm below the seam (where they were when I checked with a clear tube), to approximately 4mm. I also had to go two sizes smaller pilots (#40>#38>#35) and dropped the needles one notch (raised the clips from #4 to #3 slot).
Wish you luck with it, don't give up on it - if you get so frustrated with it that you're at wits end, consider having a nice long break from it and get back to it at a later date, that's what I had to do, John