Topic: Missfire / 'bogging down' under load

[Robbbiee]

Hi all,
New to this forum so bear with me.
CB400F - 1975, blue.
Owned the bike for 12 years now and decided this year to tart it up a bit.
In any event, looking great after some replacements and cometics but recently developed misfire? or maybe fuel delivery problem.
So, to hunt this down I have replaced plugs, points, coils and set the timing dead on, and yes, the advance works.
Starts first time and idles well at 1500. I can rev it through the range and quite smooth, no misfire or 'bogging down'. As soon as I hop on and ride, she bogs down at anything over 4000rpm when I demand a chunk of throttle. A little better when warmed up but not much. I can tootle around all day at 30 - 35mph and 3000rpm, but as soon as give her a bit of wellie, bog down, no response and then maybe she'll pick up and get going maybe not. I have tried carb cleaner but no change.
Any thoughts / help greatly appreciated,
Rob

[harisuluv]

How long have you had the pods?  What changes did you make to the carbs for the pods?

Also, that looks like a hand bent yosh.  Where did you get that, and for a 400f too.

[Robbbiee]

Not the pods - does same with or without.
Yoshi was recent install - had it shipped from dealer in UK

[harisuluv]

How long have you had the pods?  What changes did you make to the carbs for the pods?

[Bodi]

Please explain "does it with or without the pods": did you reinstall the stock snorkels, airbox, and filter for "without"?
Just pulling the pods off is pretty much the same as having them on, to the carbs. The stock setup is quite different and provides the airflow characteristics that the carbs were originally tuned for. Running pods on a 400 and getting very good performance is possible... but it takes a LOT of tuning effort.
I would check ignition timing first. If it's set too far retarded you get what you describe. If the advancer is not working you get what you describe.
If timing is OK, do a few plug chops to see what the carbs are actually giving the engine.
It's also possible that the cam sprocket is a tooth off, that sucks power output.
The engine needs roughly no power to rev freely in neutral, power required for moving the bike is a different story.

[Robbbiee]

Re the pods: It runs poorly with or without the pods. The original air box set up has been removed - as you say, perhaps that is the problem.
The timing couldn't be more perfect and the advance is working so I don't think its in the ignition.
I replaced condensers this weekend - purchased from 4into1. One of the new ones was already bad and it ran terribly - I'll send that one back. Replaced that with one of the the old ones, so now one new condenser, one old. So, there is nothing more to switch on the ignition side as far as I know.
I do appreciate your help and advice. I was wondering if I shouldn't just replace the carb set with the racing set they sell on 4into1 - expensive but obviously tuned to run w/o the air box configuration.
Best,
Rob

[flybox1]

those carbs will work fine, but did you re-jet them to compensate for your increased airflow and decreased back pressure?

[Robbbiee]

No, I didn't re-jet them at all. My guess is running too lean now (and it does run better with some choke) and so prolly will have to re-jet.
Do you know if the racing carbs from 4into1 work pretty much plug and play or is there a ton of tuning to do also?
Best,
Rob

[harisuluv]

Why is it so hard to answer some simple questions?

1.  The pods on and the pods off (without anything else) are going to run about the same.  Is this what you're talking about?  The airflow on pods is pretty comparable to velocity stacks (no filter at all!).  The real comparison would be if you said the bike works the same with the pods or stock airbox.
2.  What jetting changes/adjustments did you make to the carbs? 
3.  You say you've made some upgrades/changes to the bike, do these coincide in time with when you started having problems?

If you want to run new CR carbs, and you just have your heart set on them, buy them.  If you think they are going to be bolt on and go, think again.  You can expect as much tuning problems or more getting them running right on a stock engine. 

[harisuluv]

No, I didn't re-jet them at all. My guess is running too lean now (and it does run better with some choke) and so prolly will have to re-jet.
Do you know if the racing carbs from 4into1 work pretty much plug and play or is there a ton of tuning to do also?
Best,
Rob

They are not plug and play at all.  I know the idea of brand new carbs is appealing and the idea of bolt and go new carbs is nice, but that's just not the case.  They are meant more for racing applications. 

Yes if you made the proper adjustments, your bike would probably run fine.  You are not the first to put pods and a 4-1 on that bike.  There are plenty of people who have done it.  This will get you there or at least be very close:

Main:  85 or 90
Slow:  (40) leave stock
Needle jet:  4th slot from top (it should be in 3rd slot now which is stock)
Airscrew:  Start with 1.5 and adjust if needed.

[Robbbiee]

The bike ran about the same with pods or the stock airbox arrangement and no filter - and it ran very well.
Ya know, I bet its the Yoshi - Problems really started when I put that on, but for the life of me I can't see why (or refuse to believe why) that would make a difference unless there is less (or more) back pressure versus the stock 4 into 1, and the airflow / mixture gets all screwed up because of that.

[calj737]

The Yoshi is a very free-breathing exhaust and it will effect your fuel ratios quite a bit. Stepping up the mains is almost guaranteed required, as well as other minor adjustments.

[harisuluv]

The problem is he has modifications (the pods mainly) and has stock carb settings.  That is the problem. 

He even cites his issue in the range where the needle jet would cause bogging down. 

He said it quite well:  "I can't see why (or refuse to believe why)". 

Good luck.

[calj737]

Not disputing you, James, only specifically answering his last question 

[flybox1]

No, its not just the exhaust.
its the combination of the exhaust AND the PODS, and yes, re-jetting will most certainly be required with that setup.
It wont run well, if at all, with stock jetting.  You can get it to run well with the stock carbs.
Jet it like Harisuluv posted.  His suggestion is a good one.

[harisuluv]

Not disputing you, James, only specifically answering his last question 

no worries, i didn't take it that way  

[Robbbiee]

Thanks all - I shall try the re-jetting ad suggested. Most helpful!
Best,
Rob

[Robbbiee]

Update.

Thanks all for your help and advice. The re-jetting worked like a charm. I have never had those carbs off since owning the bike and to be honest they were a bit of a mess inside.
Cleaned up, new parts and some TLC worked wonders.
The bike sounds awesome with the Yoshi and pulls like a train.

BTW - does anyone know of Honda 4 bike clubs in the Chicago / Milwaukee area?

Many thanks again,

Rob