Author Topic: CB400F Idle/Charging (Read 7968 times)

rk · « **Reply #25 on:** June 26, 2013, 09:07:46 PM »

Thanks for all the input guys!

Today I picked up some #38 pilots from the Honda dealership in town... $16 for all 4, pretty decent I'd say. However it's not fixing the problem. I had it out for about an hour (after I put the new seat on, but immediately went home once I realized I forgot to put the license plate back on!) and it didn't really idle much better.

It would hold an idle at around 2000RPM now, however occasionally it would rev up to 3000RPM or so on it's own and then back down again, and then sometimes it would just die. I'm trying to find the sweet spot with the idle screw and the air/mix screws... but to no avail yet.

I checked for air leaks with starting fluid and it seems to be all air tight. Any other tips or ideas before I try bbi's idea and get #42s or even #45s? It is over-bored, podded, Yoshima exhaust...

rk · « **Reply #26 on:** June 26, 2013, 09:16:55 PM »

Also - new seat!

Psychonaut · « **Reply #27 on:** June 27, 2013, 05:43:46 AM »

I was reading back through this. If it idled good at one point I would think that what you have is good, maybe something comes out of adjustment. Did you vacuum sync or just bench sync? I do know that every cb400 idles fine with 40's. I would not try a 42 or 45 especially with a 90 main. Do you have a propane torch? You can check for air leaks with that too, it's easier to work with in my opinion.

Quote from: rk on June 12, 2013, 09:02:40 PM

Snapped the throttle cable last week so I've haven't been doing much. I had the bike running like a top a week or so ago, started right up with choke... after about 2-3 minutes the choke came off and it idled at 1200RPM no problem.

I have literally touched nothing, aside from replacing the throttle cables and now the bike runs like #$%* again! It will only start with the choke OFF, and won't hold an idle lower than 3000 RPM without dying. The top end is fine, no backfiring or anything like that. I've been trying to fiddle with the air screws... started at 2.5 turns out, then 2, then 2.75, then 3, then 3.5 and nothing seems to really be working all that well.

Any ideas guys? I had the carbs off and bench sync'd last week, cleaned as clean as I could possibly get them... fuel filter is brand new, going to put the battery on the charger again tonight to see if that helps. I'm scratching my head.

rk · « **Reply #28 on:** June 27, 2013, 10:00:57 AM »

Negative on the propane torch.

Just bench synced, I'm thinking a proper vac sync will help (hopefully) a lot. However I'm still trying to find the parts to put it all together, having a hell of a time finding adapters to fit to the bike. I've tried a few different welding tips, tried drilling the centres out of some bolts... nothings working for me yet.

I don't have a really comprehensive garage, so I'm limited by space at $$. I have all the basics, but don't have a propane torch... yet!

crazypj · « **Reply #29 on:** June 27, 2013, 10:07:57 AM »

Vacuum adapters for a 400f are just about the easiest thing to find, all over eBay for about $20.00 a set (5x0.8mm)
Main jet has no effect on idle
'Big bore kit' (probably 466) makes carbs work more efficiently usually need to stay stock or even go down on pilot size

HondanutRider · « **Reply #30 on:** June 27, 2013, 10:28:23 AM »

Quote from: rk on June 27, 2013, 10:00:57 AM

--------- having a hell of a time finding adapters to fit to the bike. I've tried a few different welding tips, tried drilling the centres out of some bolts... nothings working for me yet.

???Maybe you you didn't see my recommendations in posts #9 and #18...

rk · « **Reply #31 on:** June 27, 2013, 02:10:44 PM »

Sorry - Wasn't ignoring your brake line suggestion. However I don't have access to a tap/die/threader kit.

rk · « **Reply #32 on:** June 27, 2013, 02:12:11 PM »

The problem with ordering them off Ebay or Amazon is they're $10 for the set... and $25 for shipping... for something that realistically costs about $1 to produce. Hence why I'm trying to come up with a more cost-friendly alternative... otherwise I'll just save a little cash and buy the motion pro unit.

HondanutRider · « **Reply #33 on:** June 27, 2013, 02:28:36 PM »

Quote from: rk on June 27, 2013, 02:10:44 PM

Sorry - Wasn't ignoring your brake line suggestion. However I don't have access to a tap/die/threader kit.

How much does a thread die cost and a few inches of brake line? Maybe even a local shop or garage would be able to fab the four pieces up for little.

Psychonaut · « **Reply #34 on:** June 27, 2013, 02:33:41 PM »

You are chasing a tail you may never catch if you just bench synced them.

If you don't want to spend the coin on a tool and want to make one.
http://forums.sohc4.net/index.php?topic=107357.0

Carb adapters for $9 or do what Hondarutrider suggested.

http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-carburetor-intake-parts-5mm-vacuum-intake-tuning-port-adapters-08-0013.html

rk · « **Reply #35 on:** June 27, 2013, 02:58:43 PM »

Ordered some from a Canadian distributer - should be here in a few days.

I've been tallying up my shipping/customs costs to get stuff shipped up here for this bike... I probably shouldn't have because we really get screwed as soon as we buy something from the US. My total cost for parts and my total cost for shipping and customs are almost equal at this point... I'd say my reluctancy to purchase is justified.

Anyways - I'll get the rest of the parts sourced here and hopefully make some headway with the idle as soon as I can vac sync it.

Thanks again for all the input guys, I really appreciate everyone's advice and suggestions.

crazypj · « **Reply #36 on:** June 27, 2013, 05:04:30 PM »

If your that cheap, just give up NOW
Sell the damn thing before it costs any more and steal a bicycle
http://www.ebay.com/itm/Motion-Pro-5mm-Brass-Carb-Sync-Syncpro-Adapters-Carburetor-Synchronizer-08-0013-/300717866065?hash=item46042e7c51&vxp=mtr

Even cheaper

http://www.ebay.com/itm/NEW-MOTION-PRO-CARBURETOR-CARB-5-MM-ADAPTER-TUNER-SYNCHRONIZER-SYNC-/400517774119?pt=Motorcycles_Parts_Accessories&hash=item5d40b83b27&vxp=mtr

rk · « **Reply #37 on:** July 03, 2013, 03:07:26 PM »

Had the carbs off the bike again today, tried the 'light behind the slide' and 'guitar string' method of bench syncing... cleaned everything out again (although it was totally clean anyways) and put it all back together. I noticed that the slides don't quite come right to the floor of the intake, even with the screws all the way up... on all 4 carbs there is a very very small bit of light that gets through to the other side. Is this normal, or are my slides screwed up?

The bike immediately idled at 1200RPM - EUREKA!... not. After a few minutes I revved the bike up to around 5k, it never did come back to 1200... it bounced around 3k the entire time. It's also spitting a bit of fuel out of the carb intake on the #4 and maybe the #2.

Took it out for a ride, sometimes it idles at 2k, sometimes is just dies. Other times is fluctuates back and forth between 2500 and 3200 RPM.

The gas is good and clean, and so is the tank. I've tried looking for vacuum leaks multiple times with starter fluid. The ignition is working fine. I have no idea what the I should be doing at this point... The stuff to build a manometer is in the mail... however by reading on here... the bike should at least half-assed idle without a vac sync. I'm trying everything I can figure out how to do to this thing and none of it seems to be working. Help!

rk · « **Reply #38 on:** July 03, 2013, 03:59:06 PM »

Dumb Question... but when you drill bit guys bench sync your carbs:

After all is said and done with the throttle at idle are your slides still going to be an 1/8" (or whatever drill bit you use) open? Is it possible my guitar wire is too narrow and the slides are closed too much? Obviously I can open the slides more with the idle screw... what do you guys think?

And for finding vacuum leaks, is there a different or better way than starter fluid? I run the bike and spray is around every point which could leak and the idle stays the same... meaning no leaks... correct?

rk · « **Reply #39 on:** July 03, 2013, 08:43:11 PM »

Picked up a timing light... way easier than jerry-rigging a light bulb with some alligator clips!

It appears as though the timing was slightly retarded (the light was coming on before the mark met with the 'F') on all 4 cylinders (I checked all 4 because the Dyna-S system on mine allows you to move not only the plate, but each pickup... does that make sense?). So I fixed that.

I tried setting the screws one turn out, and it seems to be better. However... and this is sorta what it's been doing all along... as soon as I rev it up it never comes back down to idle. It always hangs up around 3000 RPM until I back off the idle screw and then as soon as it drops to around 1200-1500 I have to turn it up again so it holds the 1200. It does this every time.

I also found that with the air/mix screws turned out to around 2.5 turns that when I do rev it up, it sits at around 5000RPM until I back off the idle screw and turn it back once the idle drops again.

What would cause this? The gas is good, no vac leaks, timing is good, valves are good... What gives?

kghost · « **Reply #40 on:** July 03, 2013, 10:40:14 PM »

SYNC the carbs.

Period. Full stop.

I have a 350f and a 400. They do exactly as you describe without a vacuum synchronisation.

rk · « **Reply #41 on:** July 09, 2013, 02:38:50 PM »

So the parts showed up to build a manometer - So I built one, used 90W gear oil in it. Hooked it up to the bike after it was warmed up... worked for a little bit but then the oil started to foam/bubble... rendering the whole damn thing useless. Tried it again today, after a spent a few hours coaxing the bubbles out... same thing.

- Is there a better way to remove the bubbles?
- Why is it foaming?

The bike idles fine (1200 RPM) with a bench sync until I rev it up, then it won't come down below 3000 RPM. The #4 carb also spits gas out of the intake... what gives? Is a vac sync really the answer here?

Psychonaut · « **Reply #42 on:** July 09, 2013, 03:29:07 PM »

I've never seen gear oil foam.
If one carb is pulling a lot more than the other the oil will get sucked out pretty fast. To avoid that, if you see a carb that is way off, shut it off and slow that one down then restart the bike. If they are pretty close (bench synced) you should have enough time to adjust them with out worry.
If you do have one tube get too low it will take a few minutes for the oil to level. Thick oil is slow to move but that is what makes it safer to use. Using thinner oil is a nightmare.

Psychonaut · « **Reply #43 on:** July 09, 2013, 03:32:34 PM »

If you hook the sync up, the oil level should be pretty cloe to the same height before starting the engine. Once the engine is started a tube might go up, a tube might go down. You need to keep the tubes from moving. If one is slowly moving that is not too bad, If one is climbing or falling fast, that is a problem. I would not rev with it connected.

rk · « **Reply #44 on:** July 10, 2013, 06:22:32 AM »

Yeah I haven't read anything else about gear oil foaming on someone... had to happen to someone I guess! I had it pretty damn close with the bench sync, the #4 went up really quick so I adjusted it a little to far... and then it all went downhill from there.

I bench synced it again but it's not the same as I had it before.

Side note - I've noticed on all but the #2 (pretty sure its the #2) I can't push the slides right to the floor of the carbs with the air screws. There's always the smallest bit of light that will show through... Less that the diameter of a small 'E' string on a guitar. Is that normal? Or is this what's causing my headache?

Psychonaut · « **Reply #45 on:** July 10, 2013, 10:06:35 AM »

Quote from: rk on July 10, 2013, 06:22:32 AM

Yeah I haven't read anything else about gear oil foaming on someone... had to happen to someone I guess! I had it pretty damn close with the bench sync, the #4 went up really quick so I adjusted it a little to far... and then it all went downhill from there.

I bench synced it again but it's not the same as I had it before.

You tried to bench sync it again after a vac sync?

rk · « **Reply #46 on:** August 01, 2013, 04:12:13 PM »

No - I wouldn't try a bench sync if I was successful at vac syncing it... because that wouldn't make any sense. I ended up trying to play musical carbs trying to balance them without all the oil getting sucked into one carb or another until it was completely screwed up and had to start again. However, thanks to IronWorker I (we) were able to vac sync my carbs.

I put #38 pilots in, in an attempt to reduce the idle speed. However it was too lean then and didn't have the throttle response when transitioning for the idle circuit. So I put the 40s back in, and now I'm stuck with a hanging idle (around 3000RPM). Right now it's sitting at 90mains, 40 pilots, and air/mix screws backed out to 2.5. I don't know where to go from here...

Also - I'm having a charging problem... there's a lot of info on this forum about it that's been very helpful. However... is it normal for the battery (system) to read 11.4 volts at all engine RPMs? Has anyone had this happen? It seems like a simple fix by adjusting the regulator, but before I try to 'improve' the thing... I thought I'd see if anyone has run into this scenario before.

Psychonaut · « **Reply #47 on:** August 01, 2013, 04:39:20 PM »

Quote from: rk on August 01, 2013, 04:12:13 PM

I put #38 pilots in, in an attempt to reduce the idle speed. However it was too lean then and didn't have the throttle response when transitioning for the idle circuit. So I put the 40s back in, and now I'm stuck with a hanging idle (around 3000RPM). Right now it's sitting at 90mains, 40 pilots, and air/mix screws backed out to 2.5. I don't know where to go from here...

Mains don't just control fuel at WOT. I used a wideband on my 400 with stock jets and with 80 mains. 80's are on the rich side and not just at WOT. They are rich everywhere ut they do take out the quick twist flat spot. This isn't guessing by looking at the color of plugs. This is reading a gauge that tells the exact AFR every time I look at it. With 80's I am 11-low 12's at cruise, 11's at WOT. It might have hit low 12's above 9k. You can keep your 90's but it will never run right regardless of what has been done to the engine. To much fuel puts the fire out. Just trying to help by giving first hand, learned knowledge.

rk · « **Reply #48 on:** August 01, 2013, 07:22:21 PM »

I have no idea what 'using a wideband' means. Sorry man. I'm not doubting your experience, I just don't know what you are getting at.

So you would suggest using a smaller main? like a 78 or 80? What would/do you have for a pilot jet then?

I do appreciate your help Psychonaut!

Psychonaut · « **Reply #49 on:** August 02, 2013, 06:02:44 AM »

A wideband O2 sensor accurately measures across a wide range (up to 10:1-20:1 AFR) with 0-5 volt ourput unlike narrow band that will just be accurate around stoich (14.7:1) with a 0-1v output. They are very accurate.

Stock 40 pilot.

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Author Topic: CB400F Idle/Charging (Read 7968 times)