Author Topic: CB400F Idle/Charging (Read 7970 times)

rk · « **on:** May 18, 2013, 01:10:58 PM »

Hi Guys - Made some serious progress on the bike this week. Valves are set, timing is set, carbs are synced... it idles really nicely when it's cold but starts to stall once it's warm unless I bump up the idle screw to around 3000RPM. Otherwise it runs really well.

I'm thinking it's running rich...?

Would switching to a smaller main jet fix this? I put a standard carb kit in the bike when I bought it.

Pods, aftermarker exhaust (no idea what kind) and the engine's been bored to 473cc (I think).

Also - I've been looking at a cafe-type seat and would like to reposition the battery, fuse block (planning to change it to the newer style flat fuses) and the regulator and rectifier to in the seat hump. I've read a few threads about using a Dodge or Ford regulator in place of the Honda parts... is there a concise 'how-to' guide somewhere I haven't been able to find?

Thanks Guys!

Rodger · « **Reply #1 on:** May 19, 2013, 05:37:56 AM »

Pods, bore, and after market exhaust, it's not too rich! It's too lean, with out a dyno or a dozen spark plugs to do chop tests it's going to be hard to get the jetting right. The stock jets are for stock air filter and stock exhaust, pods and after market exhaust breathe more air into the engine thus needing more fuel. Plus it's not like the engine is bored one over its almost 20% increase in CC's. Once again more air and still stock jets feeding too little gas.

Some of the other guy who hop these up maybe able help with jetting, mine is all OEM.

phil71 · « **Reply #2 on:** May 19, 2013, 03:48:46 PM »

that rectifier retrofit is a bit of a pain, and pretty tech-y. Unless you're out of work, it's more worth your time to just order a one-piece solution.. roughly $115 from many suppliers. It's a HUGE time saver.

Psychonaut · « **Reply #3 on:** May 19, 2013, 04:43:42 PM »

There are air bleed screws to adjust AFR from idle to 1/8 throttle. If it runs good everywhere else I would not rejet.

Does it start cold with or with out choke? How soon can you turn the choke off when cold?

rk · « **Reply #4 on:** June 02, 2013, 06:35:24 PM »

It starts cold with choke, it takes about a minute (at around +20C OAT) before I can nix the choke and it idles on it's own.

The AFR is adjusted with the use of a manometer or colourtune... correct?

Psychonaut · « **Reply #5 on:** June 02, 2013, 06:49:02 PM »

This is dead on exact.

http://www.ebay.com/itm/AEM-UEGO-Digital-Wideband-O2-Air-Fuel-Ratio-AFR-Gauge-6-in-1-WBO2-Kit-30-4100-/271214175268?pt=Motors_Car_Truck_Parts_Accessories&hash=item3f259fe424&vxp=mtr

Some to try to read plugs.

If it starts cold without choke you are probably too rich at least on your idle circuit.

rk · « **Reply #6 on:** June 02, 2013, 07:08:35 PM »

Is this better than a carb synchronizer or colour-tune? Or is this an entirely different adjustment?

I'm looking at building my own carb synchronizer... where does one get the brass stems that screw into the carbs?

rk · « **Reply #7 on:** June 02, 2013, 07:11:48 PM »

I'm 100% the bike is running too rich, I can smell it/see the soot in the exhaust... this would mean I'd need to back the air/fuel screws off (counter-clockwise) right?

Psychonaut · « **Reply #8 on:** June 03, 2013, 05:40:00 AM »

This is how I made a sync tool

http://forums.sohc4.net/index.php?topic=107357.0

Wideband

http://forums.sohc4.net/index.php?topic=107406.msg1202240#msg1202240

HondanutRider · « **Reply #9 on:** June 03, 2013, 06:00:06 AM »

Quote from: Ryan Kurtz on June 02, 2013, 07:08:35 PM

I'm looking at building my own carb synchronizer... where does one get the brass stems that screw into the carbs?

I used some small diameter brake line that I threaded the end to the same pitch, and just finger tighten them into the carbs, bottoming out the bit of thread on the ends to seal. They work fine for me.

rk · « **Reply #10 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.

Also - has anyone replaced the oil gallery plug seal (behind the AC generator)? Mine is still leaking, I've tried a few different solutions but I can't find a good match for the stock seal.

rk · « **Reply #11 on:** June 12, 2013, 09:04:08 PM »

Also - stock pilot jets, 90 mains.

Psychonaut · « **Reply #12 on:** June 13, 2013, 05:56:13 AM »

Did you leave a little slack in the cable? Could be tight. Is your linkage on the right side of the bike, idle stop touching the adjustment screw?

rk · « **Reply #13 on:** June 13, 2013, 07:42:09 AM »

Yep, that's all set up as per the manual.

Psychonaut · « **Reply #14 on:** June 13, 2013, 12:59:20 PM »

Quote from: rk on June 13, 2013, 07:42:09 AM

Yep, that's all set up as per the manual.

What happens when you turn the idle adjustment screw? Does it raise the idle higher? If you turn it counter clock wise, does it lower the idle?

rk · « **Reply #15 on:** June 17, 2013, 03:47:42 PM »

Yes, when I turn the idle screw in the RPMs go up, and vice versa... except it doesn't really hold an idle well below 3000RPM.

Today I pulled the carbs off again:
- Cleaned them
- reset the carb height to 22mm (the manual calls for 21 stock... I thought with all the mods I'd be better off at 22mm - does this make sense?)
- charged the battery

Everything is nice and airtight from the intake side, no air leaks or anything. It still doesn't start really nicely... once it's running anything about 4000RPM is great.

I've been playing the air/mix screws... started at 2.5 turns out, then to 2, then to 3... 3 seems to be about the best so far, it idles decently at 2000 RPM however it still stalls out anywhere below that. Should I back off the screws another .25 or .5 of a turn?

#90 mains, #40 pilots, needles are in the centre slot... it seems to be getting closer.

Psychonaut · « **Reply #16 on:** June 17, 2013, 04:55:14 PM »

You said you benched sync these. Have you vacuum synced since then?

90 mains is pretty big. I have 80 mains and floats at 21mm. With a wide band my air fuel is very rich everywhere. It doesn't lean bog when I wack anymore it but it is very rich, mid t0 high 11's at cruise and WOT. With 22mm you might be ok. If I had 90's I think I would trail black smoke if it didn't miss first. Why did you jump from 75 to 90?

rk · « **Reply #17 on:** June 17, 2013, 07:11:39 PM »

Long story short, the original owner loved the bike. It was stolen in 85' and the cops found it years later (in less than stellar shape I'm guessing). So the guy tore it apart and sent the engine away to be rebuilt in Edmonton. They did some head work, bored it out (to what I'm not 100% sure), installed the Yoshima pipe, new fender, seat, etc. I'm guessing the #90 mains were installed somewhere along the way.

It runs really well above 3000 RPM, lots of power, sounds awesome. It's just the idle that's driving me nuts. That a mild oil leak.

I haven't vaccuum sync'd them yet. I've been asking around if anyone has a manometer... I'm still trying to source parts to build one. I found some 6mm bolts to drill the centres out... however I'm pretty sure they're made out of some pretty serious steel, 3 drill bits later I gave up and am on the look out for alternatives.

HondanutRider · « **Reply #18 on:** June 18, 2013, 06:16:02 AM »

A better alternative to using 6mm bolts that are drilled out, is to thread a section of small-diameter brake line. It fits just correct and you can slip some hose on the other end for your gauges. I don't have a sealing problem screwing them into the carbs, as I don't thread the ends very much and can therefore bottom them in the carb body. Otherwise, use a nut and sealing washer.

iron_worker · « **Reply #19 on:** June 18, 2013, 07:53:55 AM »

If it starts with the choke OFF then it's way rich. Engines need more fuel when they are cold since there is not much latent heat in the engine to atomize the fuel. Once the engine is warmed up, the fuel begins to atomize nicely in the intake tracts, and thus less fuel is needed --> turn off the choke.

Your bike is so rich at idle that you are already rich enough to stat it when cold. Then as it warms up, you have no way to lean out the mixture to the proper running temperature mixture.

Your evidence that screwing the IMS out to 3 turns out seems to help supports this. These are air bleed screws and allow more air into the pilot circuit as you screw them out ... IE leaner. However, they have a limited range and are only really effective between 3/4 - 2 turns out or so.

The reason it won't idle below 2-3k is because once you open it up a bit then the bike starts to run on the mid range circuit ... IE the needle clip position starts to become dominant. Your idle circuit is just too rich for it run but your mid range is close enough.

You need smaller idle jets. 38s ... possibly 35s.

IW

rk · « **Reply #20 on:** June 22, 2013, 09:30:23 AM »

Anyone have a favourite place to buy jets?

I'm in Canada... so somewhere with reasonable shipping would be handy.

Vinhead1957 · « **Reply #21 on:** June 22, 2013, 05:09:25 PM »

You knew this was coming ! My favorite place is Lear, but in a pinch I go to Boeing

Psychonaut · « **Reply #22 on:** June 22, 2013, 09:41:13 PM »

I bought mine from Dime City Cycles. There maybe someone cheaper in Canada though.

bbi · « **Reply #23 on:** June 23, 2013, 12:19:24 AM »

OK I will throw my 2 cents in, I just finished a 400f build and the idle was crappy like yours, bench sync then vac sync would start easy and off choke in about 10 seconds, its warm here would idle good till it warmed up adjusted idle screws and would either be to lean no return to idle or to rich by exhaust smell with a 40 pilot. I have a stock airbox stock header with a big open muffler all else is stock...... I went up to a 42 on the pilot and it idles awesome now and purchased pilot jets from Honda, I haven found a source for jets outside them and don't use aftermarket. my take is with too small a pilot when you get the airscrew in a decent place for mixture theres not enough airflow to emulsify the fuel in the pilot circuit so you get a poorly atomized fuel, I have a lot of jetting experience but majority is 2 stroke these are a little different animal. some things to remember
idle=pilot (the slide cutaway handles transition but rarely mess with it)
off idle to 3/4=needle and clip position
3/4 to WOT=main jet (main does have a small influence on off idle to 3/4)
and they all build upon each other IE richer pilot adds to mid range, don't think of jetting as RPM specific but throttle position specific, a great tool I have used for years is to put a pin in your grip then with tape mark your throttle housing in 5 increments like idle, half, full, and in between those as well that way when your riding you have a quick visual reference for what circuit your on.
jetting is an art with lots of trial and error as you learn, keep notes

Psychonaut · « **Reply #24 on:** June 23, 2013, 05:22:07 AM »

I ran a wide band on my bike for a while. The main jets change the AFR everywhere not just 3/4 to WOT. It will increase the AFR at 4500 rpm cruise with just as much as WOT at 9k.

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Author Topic: CB400F Idle/Charging (Read 7970 times)