CB466f

[MarkCR750]

Are you running a standard air box and filter?, it could be a little lean if not, that would give poor pick up on acceleration, are the float heights correct?, do you carbs have an accelerator pump like the CB750, maybe not but if they do check that it's delivering jets of fuel when the throttle is twisted quickly, what's it like on hills? Oh hang on you're in Holland you wouldn't know would you 😄.

[Erwin83]

Hi mark,

Yes carb settings are all standard, carbs newly built with new jets and needles, etc.. I'm also running a standard filter and airbox. Only thing different from a standard cb400f is the exhaust (open 4-2, see pics).
A cb350/400 does not have an acceleration pump btw.

After synchronising, i haven't played around with the airscrews at all. They be a bit far out.
Is a bad pick-up from idle "typical" for a lean idle?
If so, which way is leaner, which way is richer (clockwise, anti-clockwise)?
I would say, clockwise is close, so less air, so richer. But i can't really find this info.

Thanks for the advice.

Erwin

[kevski]

Screw should be around 7/8 of a turn out + or - 3/8 of a turn my own 350 are 1 turn out.

[Erwin83]

Screw should be around 7/8 of a turn out + or - 3/8 of a turn my own 350 are 1 turn out.

Thanks. But i'm running a 400cc engine with the 400 carbs etc.
For the 400, screws should be 2 +/- 0,5 turn out, if i remember correctly.
But those are numbers from the book. Not sure how strict that is.

[kevski]

I just see you are running open pipes, this can affect the running as no back pressure, you may need to increase the size of the pilot jets to compensate, the information for the air screws is correct and turning them in will increase the fuel at low engine speeds but may not be enough.

[Erwin83]

I just see you are running open pipes, this can affect the running as no back pressure, you may need to increase the size of the pilot jets to compensate, the information for the air screws is correct and turning them in will increase the fuel at low engine speeds but may not be enough.

Thanks Kevski! Quite helpful.
I think i have the screws all leaned out now at 2,5 out.
So let me first try to make idle somewhat richer by turning everything in again. After syncing, i have not played with the air screws at all.

With regards to the lack of back pressure, isn't that something that especially plays a role at higher revs?
I'm actually quite happy with how she runs higher up.

[kevski]

The air screws are what the pilot circuit is metered by with them maxed out and open exhaust you are leaned right out giving you the poor running at low revs take them in a bit at a time and see what it gives you, you need some back pressure even at low revs to run smoothly.

[Erwin83]

Changed the float level to 24mm now..... And we've got reliable idle!
Also a nice coffee brown color on the plug.

Turns out i also had a broken coil lead on pot 2. Did a bush-fix with a small screw, will order new replacement coils with new leads as all are very rigid and old.

Still with a hot engine (seriously hot), it drowns on pick up from idle to any throttle.
Will look into the air screws a bit see what that does.

With my friend's 500 four, out playing together:

[Erwin83]

Last week I installed a new set of (aftermarket) coils, after I broke a lead, just after selling my spare coils. Ah well...

The settings of my little 400 is juuuuuuuuust about perfect now.
I don't have any hick-ups while riding, and both constant speeds as full throttle I'm getting a healthy response and good sounds.
Even the dreaded camchain noise has reduced significantly since I pushed the rod down according to known methods...

The only thing is still the idle at warm / hot engine.
Since I synced the carbs, she runs idle very well and sounds sweet but a few seconds in and she drops below 1000 rpm and ends up stalling, unless I blip the throttle again.

In order to avoid endless carb setting tinkering, could this be related to another setting or a defective components?
Points setting, ignition timing, condensors, advancer?

[andut]

Good to hear that you're getting some progress Erwin !

Does the idle speed increase before it dies and do you still have the air screws at 2.5 turns ?  If it isn't increasing in speed before stalling, it could be overfuelling slightly, so you may want to try running it a little weaker via the air screw adjustment and see if it improves - do the plugs look wet immediately after it stalls ?

You'd expect to wind the air screws out to weaken it - more air = leaner mix, but I read an equally plausible description of the 400's Keihin idle circuit as posted by Hondaman on the US site that makes some sense and suggests winding the mixture screw out will actually richen the mixture as it's the air bleed that draws the fuel into the idle jet, and the greater flow or air would draw more fuel.  Regardless of the theory, it's an easy experiment to do, so it would be worth trying an adjustment in small steps in either direction to see how the bike reacts. - and then let us know how you get on !

It's also worth thinking about plugs - have a look at Julie's recent 400 idle issues thread that appear to have been improved by a change in plugs.

Andy

[Erwin83]

Good to hear that you're getting some progress Erwin !

Does the idle speed increase before it dies and do you still have the air screws at 2.5 turns ?  If it isn't increasing in speed before stalling, it could be overfuelling slightly, so you may want to try running it a little weaker via the air screw adjustment and see if it improves - do the plugs look wet immediately after it stalls ?

You'd expect to wind the air screws out to weaken it - more air = leaner mix, but I read an equally plausible description of the 400's Keihin idle circuit as posted by Hondaman on the US site that makes some sense and suggests winding the mixture screw out will actually richen the mixture as it's the air bleed that draws the fuel into the idle jet, and the greater flow or air would draw more fuel.  Regardless of the theory, it's an easy experiment to do, so it would be worth trying an adjustment in small steps in either direction to see how the bike reacts. - and then let us know how you get on !

It's also worth thinking about plugs - have a look at Julie's recent 400 idle issues thread that appear to have been improved by a change in plugs.

Andy

Hi Andy

thanks a lot for the feedback.
I've been playing with the airscrews and first went from 2,5 to 2. Now I'm at 2,25 turn out, because I also thought I needed some more air to prevent the stalling.
Also tried to give the carb some more idle by giving the base throttle position a bit more, but that only make the return to idle worse, and finally still the bike stalls.

The idle certainly does not go up before it dies. It runs nicely around the 1200 rpm mark first and then slowly goes to 1000, 900 and below 800 rpm it won't run anymore obviously.

My plugs remain black carbon (so seems rich). I have 4 new D8 plugs ready for install.

I'm actually considering lowering the float level another 1 mm, because I feel the bike runs slightly rich all over the revs, but this has not bee scientifically proven.

I'll look for the other thread, I remember replying in there too.

[Erwin83]

[Erwin83]

[Erwin83]

Movie with sound:

https://youtu.be/ztPY2APeSJI

[Erwin83]

It's been a while since my last update.

After losing 2 cylinders (capacitor blew up) during the last few km's of the Distinguished Gentleman's Ride in 2018, I added one more mod to the CB350 (with 400 engine): Electronic ignition unit.
Ever since, the bike has been running great, though starting to leak more and more oil from valve cover seals and head gasket (O-rings). Up to the point that it wasn't just a drop anymore, and my left shoe got wet.
So, I decided to make the CB my winter project again for season 19-20. Last winter I restored and customized a 1978 Guzzi V35 to a Scrambler, so was in need of new work anyways.

Coming up:
- New cylinder base gasket, new head gasket, new valvecover gasket, etc..
- And whilst everything needs to be taken apart anyways: I ordered a 466 big bore kit from Australia . I've been wanting to do such a job for a while and took the chance now.

- Also (already done): new stem bearings and new wheel bearings are installed.
- New throttle cables have been ordered (I was riding with just a pull-cable for the last decade or so)
- New instrument cables have been order. Shorter ones to match better with my set-up: 60cm rpm (of a Honda CB360 G5) and 80cm speedo (of a Honda CB50-J)

I'm just about ready to start pulling the engine apart and will post update every so often.