Topic: 400F sputtering/rich at idle

[minimo]

I'm struggling to resurrect a 1975 CB400F. Ultrasonically cleaned carbs have been taken off and on more than a few dozen times over just the last few days. Anyway, the bike is giving me a lot a grief as I can't seem to chase the issue of getting it to idle in any decent way.

Throttle at low rpm's bogs down like it's running rich, and lo and behold, when pulling the spark plugs I see all soot and some wetness in others... It's actually never really consistent. Not all cylinders fire either.  In between one of the on again off again episodes with the carbs though I did manage to get all cylinders to fire in which case I took the bike out for a stuttering ride - sputters at low rpm's (if I don't rev the bike would die) but seems to run fine at higher rpm's. The bike is pretty much stock - airbox, new air filter, even new points and condensers. Back to the carbs, I'm reusing the stock float valves and seats (new o-rings with a nice snappy fit). The 75 mains and 40 slows are aftermarket from 4into1. Air mix screw is backed out twice from fully closed (stock). Does this sound like I need to downsize the slows? Is it a bad idea to mix/match the stock float valves with these aftermarket mains/slows?

What is a good systematic approach to this craziness? Thanks!

[minimo]

And I left out a few things:

I did perform a clear tube float height test and all measured consistently about 1/4" below the mating surface. I also performed a vacuum carb sync test and was able to achieve even lines across all four.

I did not get around to inspecting the needle in the throttle body. I actually struggled to find any screwdriver to fit/reach to remove the two screws so I left it. Any tricks to getting to those tiny phillips screws? Such a pain.

[Deltarider]

Good you didn't force your way in there. The secret is using the right JIS screwdriver. With a 'normal' screwdriver you run the risk damaging the screws. But if you have no indication someone has opened them before to change the needle positions (I know, hard to tell maybe), I would leave them alone. I don't no why Honda in the Parts List for your model lists no less than three different size slow jets (and three different size main jets) but maybe the smallest slow jet listed (#38) is worth trying. Cf. at the bottom (right) of p. 16 in http://www.honda4fun.com/pdf_parts_list/pdf_spac400/CB400F-F1-F2/CB400F-F1-F2.pdf. Have you tried with the airscrews 2¹/₂ turn out?

[minimo]

Thanks, deltarider. Yes, I’m looking into smaller sized pilot jets. jetsrus.com seems to be a good resource for bonafide Keihin parts.

Cool in the JIS screwdriver. It’d have to be a really skinny one to fit. Thanks for the heads up on that.


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[minimo]

More on the needles, it was TwoTired who mentioned that the aftermarket brass parts don’t conform to Honda dimensions and that the needle taper profile might be different also.

Man, so many things to consider here. Where to begin again...


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[PeWe]

- Ignition properly set at idle?
- All jets are in the carbs?
- Air jets are not clogged? (The small hole you'll see when removing air filter/pods. Here usually a brass jet.

- Not possible to adjust with air screws? Or if carbs have fuel screws. 
- You blew this circuit clean with compressed air? Possible to remove air screws and blew carb cleaner inside and hopefully clean dirty circuit.
    (There is a spring inside. Some carbs have a washer and o-ring too.)
Screw between throttle and filter - air screw (open give more air that can bring more fuel with the flow in the pilot circuit, like a spray gun)
Screw between throttle and inlet - fuel screw (open give more fuel)

[Deltarider]

Cool in the JIS screwdriver. It’d have to be a really skinny one to fit.

It's my experience with crossheads that it usually takes a one size bigger than you had expected...

[DaveBarbier]

What brand of new points/condensers are you using? Do they have a logo that looks like 3 petals? Says Daichii anywhere? I would shoot an ignition strobe light on the plate and see what cylinders aren't firing. Use new plugs, please.

We're assuming your ignition timing and gap is properly set.

If one pair of cylinders aren't firing properly (1/4 are tied together and 2/3 are tied together regarding ignition) try swapping around the condensers to see if the issue moves to the other pair of cylinders.

Also measure the resistance of each plug cap and post ohm readings. Should be around 5k ohms. Are the coils original?

[minimo]

Thanks, PeWe! My answers in green.

- Ignition properly set at idle?
Yes. However, after posting about this I changed the points/condensers (yes, Daiichi) and finding it a challenge to adjust static gap/timing. Great.

- All jets are in the carbs?
Yes

- Air jets are not clogged? (The small hole you'll see when removing air filter/pods. Here usually a brass jet.
I ran all the carb parts and their components in an ultrasonic bath (distilled water and some Pine Sol) a count of six times, picked and poked at all the holes as best I could with tiny musical wire and blew out all of the passages with compressed air. Thanks, PeWe!

- Not possible to adjust with air screws? Or if carbs have fuel screws. 
The bike is running the stock air box and air filter - not air pods. It does have an aftermarket exhaust... I can try playing with the air mix screws - they're turned 2x out from fully seated. I can turn them out maybe another half turn to lean it?

- You blew this circuit clean with compressed air? Possible to remove air screws and blew carb cleaner inside and hopefully clean dirty circuit.
I did blow into it with compressed air but didn't think to spray inside. I will try that. Thanks.


(There is a spring inside. Some carbs have a washer and o-ring too.)
Screw between throttle and filter - air screw (open give more air that can bring more fuel with the flow in the pilot circuit, like a spray gun)
Screw between throttle and inlet - fuel screw (open give more fuel)
Yeah, I'm definitely going to try playing with the air mix screw. I will try to be systematic about it, turning maybe 1/4 at a time across all. In this case, on the 400f it's turn it in to enrichen the mixture; turn it out to lean it

[minimo]

Hi, Dave. Just before my initial posting I replaced the points/condensers with some Daiichi's. I'm still finding it fidgety and difficult to get a good handle on gap and static timing... And as far as strobing is concerned, I wish that the bike would idle steadily for me to maintain the appropriate rpm to take any valid measurement or reading.
I would have to give it throttle or else the bike would shut off. I would try to maintain the rpm using the idle stop screw but I would get instances where the rpm would spike up to gradually fall again and eventually shut down...

Use new plugs. OK.

Funny thing is, between all the carb pulling off and on and float height adjusting, I was at one point able to get ALL the cylinders to fire - and this was on the previous points/condensers before swapping those out with the new Daiichi ones.

I will look into finding ohm resistance on the plugs. I've never done that before.
Yes, the coils are original. I did the spark test placing the plug against the engine to get a spark, and they all did.

Thank you, DaveB!

What brand of new points/condensers are you using? Do they have a logo that looks like 3 petals? Says Daichii anywhere? I would shoot an ignition strobe light on the plate and see what cylinders aren't firing. Use new plugs, please.

We're assuming your ignition timing and gap is properly set.

If one pair of cylinders aren't firing properly (1/4 are tied together and 2/3 are tied together regarding ignition) try swapping around the condensers to see if the issue moves to the other pair of cylinders.

Also measure the resistance of each plug cap and post ohm readings. Should be around 5k ohms. Are the coils original?

[minimo]

To eliminate the possibility, I'm going to pull the carbs again and give them another round of ultrasonic bathing (maybe even a chem dip) just to be sure I haven't introduced anything like potato chip crumbs which very well my be lodged up in those darn passages.

[Tim2005]

As Dave alluded to, try getting rid of the Daichi stuff & refit your originals, there's a general consensus that Daichi is not a good brand at all. 

Also, what state are your HT leads/coils/caps? I'd focus on getting the ignition right first.

[DaveBarbier]

Hi, Dave. Just before my initial posting I replaced the points/condensers with some Daiichi's. I'm still finding it fidgety and difficult to get a good handle on gap and static timing... And as far as strobing is concerned, I wish that the bike would idle steadily for me to maintain the appropriate rpm to take any valid measurement or reading.
I would have to give it throttle or else the bike would shut off. I would try to maintain the rpm using the idle stop screw but I would get instances where the rpm would spike up to gradually fall again and eventually shut down...

Use new plugs. OK.

Funny thing is, between all the carb pulling off and on and float height adjusting, I was at one point able to get ALL the cylinders to fire - and this was on the previous points/condensers before swapping those out with the new Daiichi ones.

I will look into finding ohm resistance on the plugs. I've never done that before.
Yes, the coils are original. I did the spark test placing the plug against the engine to get a spark, and they all did.

Thank you, DaveB!

What brand of new points/condensers are you using? Do they have a logo that looks like 3 petals? Says Daichii anywhere? I would shoot an ignition strobe light on the plate and see what cylinders aren't firing. Use new plugs, please.

We're assuming your ignition timing and gap is properly set.

If one pair of cylinders aren't firing properly (1/4 are tied together and 2/3 are tied together regarding ignition) try swapping around the condensers to see if the issue moves to the other pair of cylinders.

Also measure the resistance of each plug cap and post ohm readings. Should be around 5k ohms. Are the coils original?

There's a saying that goes, "90% of carb problems are actually ignition problems." Maybe it's 75%...but you get my point. First you need to get your ignition down and the other 3k mile maintenance stuff which is laid out in the manual. Cam chain tension, rapper clearance, etc.

With new plugs you should be able to idle for a bit to test with a strobe. If you have to hold the throttle that's fine. I'm looking for no firing or intermittent firing on one set or both sets of cylinders. I'm not really looking for exact idle and advance timing settings. That can come later. And as I said before, if one is misfiring, swap the condenser and see if the issue follows it.

Is there a reason you switch out the points and condensers? If the original weren't causing issue I'd pop them back in. I once had a problem of misfire with a brand new Daichii condensers right out of the box. New TEC or ND (Nippon Denso) are good replacements.

Test the plug caps for resistance, not the plugs. It's easy. Pop the plug cap off and unscrew it from the plug wire, one lead of your meter (set to ohms) on one end and one on the other.

If your carbs are in the realm of correct jetting you'll be able to hold an idle. I'm leaning towards ignition right now. Also might be good to make sure your battery is charged and you have newish gas in the tank.

[minimo]

Thanks for that, Dave.
I’ll try to hone in on the points/condensers soon. Although I was gunning to beat my timing on the last carb removal off the bike :-) Definitely going to put the original set of points/condensers back on as many of you have suggested.

There was no real reason other than the idea that if I’d swap out the old and place a fresh new set and set that all up good, I could eliminate that as a possible culprit. Perhaps I’m doing the opposite of what I intended?

I’m 99% clear on the ohm test. I had to dig into a bit more instruction and found this:

I have a feeling I’ll be going through quite a number of spark plugs to sort this out. Is that normal? Good thing Pep Boys had these for relatively cheap $2.85 each - but this will soon add up.

Thanks, DB!

Hi, Dave. Just before my initial posting I replaced the points/condensers with some Daiichi's. I'm still finding it fidgety and difficult to get a good handle on gap and static timing... And as far as strobing is concerned, I wish that the bike would idle steadily for me to maintain the appropriate rpm to take any valid measurement or reading.
I would have to give it throttle or else the bike would shut off. I would try to maintain the rpm using the idle stop screw but I would get instances where the rpm would spike up to gradually fall again and eventually shut down...

Use new plugs. OK.

Funny thing is, between all the carb pulling off and on and float height adjusting, I was at one point able to get ALL the cylinders to fire - and this was on the previous points/condensers before swapping those out with the new Daiichi ones.

I will look into finding ohm resistance on the plugs. I've never done that before.
Yes, the coils are original. I did the spark test placing the plug against the engine to get a spark, and they all did.

Thank you, DaveB!

What brand of new points/condensers are you using? Do they have a logo that looks like 3 petals? Says Daichii anywhere? I would shoot an ignition strobe light on the plate and see what cylinders aren't firing. Use new plugs, please.

We're assuming your ignition timing and gap is properly set.

If one pair of cylinders aren't firing properly (1/4 are tied together and 2/3 are tied together regarding ignition) try swapping around the condensers to see if the issue moves to the other pair of cylinders.

Also measure the resistance of each plug cap and post ohm readings. Should be around 5k ohms. Are the coils original?

There's a saying that goes, "90% of carb problems are actually ignition problems." Maybe it's 75%...but you get my point. First you need to get your ignition down and the other 3k mile maintenance stuff which is laid out in the manual. Cam chain tension, rapper clearance, etc.

With new plugs you should be able to idle for a bit to test with a strobe. If you have to hold the throttle that's fine. I'm looking for no firing or intermittent firing on one set or both sets of cylinders. I'm not really looking for exact idle and advance timing settings. That can come later. And as I said before, if one is misfiring, swap the condenser and see if the issue follows it.

Is there a reason you switch out the points and condensers? If the original weren't causing issue I'd pop them back in. I once had a problem of misfire with a brand new Daichii condensers right out of the box. New TEC or ND (Nippon Denso) are good replacements.

Test the plug caps for resistance, not the plugs. It's easy. Pop the plug cap off and unscrew it from the plug wire, one lead of your meter (set to ohms) on one end and one on the other.

If your carbs are in the realm of correct jetting you'll be able to hold an idle. I'm leaning towards ignition right now. Also might be good to make sure your battery is charged and you have newish gas in the tank.

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[minimo]

As Dave alluded to, try getting rid of the Daichi stuff & refit your originals, there's a general consensus that Daichi is not a good brand at all. 

Also, what state are your HT leads/coils/caps? I'd focus on getting the ignition right first.

Thanks for that, Tim.
Good to hear another confirmation to look into the direction of getting my spark correct first. I will get some data to ya fellas soon. Thanks for your inputs.


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[minimo]

I’m eager to get in the garage and have some alone time with these slutty coils and give you fellas all the nasty and juicy details about them. Yeah.

Meanwhile, I wanted to draw your attention briefly to the points/condensers and show you how they were wired when I received the bike (and pretty much how I left it to run since the PO said the bike was running fine before she decided to store it for over a year outdoors).

Notice how on 1-4 at left, the blue and green wires are set apart on opposite sides of the plate tab. Does it matter that the wire connectors are not touching? I noticed that on my other CB’s, the wires on 1-4 and 2-3 touch respectively.

Just curious.


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[strynboen]

the clips on the kondensatore can almost toutch the metal plate..so try to turn the clip a half turn..and refit it

[Deltarider]

the clips on the kondensatore can almost toutch the metal plate..so try to turn the clip a half turn..and refit it

Strynboen is right. Check that the 'elbow' of those connectors does not accidentely (intermittent) make ground. The order of the wires doesn't matter as long as they contact that little center bolt and do not make ground. Did you say your bike runs well at higher rpms?

[DaveBarbier]

Thanks for that, Dave.
I’ll try to hone in on the points/condensers soon. Although I was gunning to beat my timing on the last carb removal off the bike :-) Definitely going to put the original set of points/condensers back on as many of you have suggested.

There was no real reason other than the idea that if I’d swap out the old and place a fresh new set and set that all up good, I could eliminate that as a possible culprit. Perhaps I’m doing the opposite of what I intended?

I’m 99% clear on the ohm test. I had to dig into a bit more instruction and found this:

I have a feeling I’ll be going through quite a number of spark plugs to sort this out. Is that normal? Good thing Pep Boys had these for relatively cheap $2.85 each - but this will soon add up.

Thanks, DB!

Hi, Dave. Just before my initial posting I replaced the points/condensers with some Daiichi's. I'm still finding it fidgety and difficult to get a good handle on gap and static timing... And as far as strobing is concerned, I wish that the bike would idle steadily for me to maintain the appropriate rpm to take any valid measurement or reading.
I would have to give it throttle or else the bike would shut off. I would try to maintain the rpm using the idle stop screw but I would get instances where the rpm would spike up to gradually fall again and eventually shut down...

Use new plugs. OK.

Funny thing is, between all the carb pulling off and on and float height adjusting, I was at one point able to get ALL the cylinders to fire - and this was on the previous points/condensers before swapping those out with the new Daiichi ones.

I will look into finding ohm resistance on the plugs. I've never done that before.
Yes, the coils are original. I did the spark test placing the plug against the engine to get a spark, and they all did.

Thank you, DaveB!

What brand of new points/condensers are you using? Do they have a logo that looks like 3 petals? Says Daichii anywhere? I would shoot an ignition strobe light on the plate and see what cylinders aren't firing. Use new plugs, please.

We're assuming your ignition timing and gap is properly set.

If one pair of cylinders aren't firing properly (1/4 are tied together and 2/3 are tied together regarding ignition) try swapping around the condensers to see if the issue moves to the other pair of cylinders.

Also measure the resistance of each plug cap and post ohm readings. Should be around 5k ohms. Are the coils original?

There's a saying that goes, "90% of carb problems are actually ignition problems." Maybe it's 75%...but you get my point. First you need to get your ignition down and the other 3k mile maintenance stuff which is laid out in the manual. Cam chain tension, rapper clearance, etc.

With new plugs you should be able to idle for a bit to test with a strobe. If you have to hold the throttle that's fine. I'm looking for no firing or intermittent firing on one set or both sets of cylinders. I'm not really looking for exact idle and advance timing settings. That can come later. And as I said before, if one is misfiring, swap the condenser and see if the issue follows it.

Is there a reason you switch out the points and condensers? If the original weren't causing issue I'd pop them back in. I once had a problem of misfire with a brand new Daichii condensers right out of the box. New TEC or ND (Nippon Denso) are good replacements.

Test the plug caps for resistance, not the plugs. It's easy. Pop the plug cap off and unscrew it from the plug wire, one lead of your meter (set to ohms) on one end and one on the other.

If your carbs are in the realm of correct jetting you'll be able to hold an idle. I'm leaning towards ignition right now. Also might be good to make sure your battery is charged and you have newish gas in the tank.

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Just to be overly clear, the plug caps are the elbows at the end of each plug wire. They screw into the plug wire with what looks like a wood screw. Pop them off the spark plug and unscrew from the plug wire. Set your meter to ohms and measure the plug cap thusly:



After this, you can also use some wire cutters and snip off about 1/8" or maybe 3/16" of the plug wire. That will get you to better copper that the plug cap can screw into.

Here's a link on testing coils. Your YouTube video seems good but our coils are a bit different. http://forums.sohc4.net/index.php/topic,5752.msg8383.html#msg8383

Here are some more pictures of my coils when I tested them. These are good numbers.






Notice I'm testing the 1/4 coil and the 2/3 coil by sticking the leads in the plug wire. The other pictures show the test of the coils which is essentially the same test the guy in the video does first.

Hope that's clearer!

[minimo]

Thanks, strynboen! I’ll make sure those connectors don’t ground to the plate. Thanks for the warning. Great to see you here!

Deltarider, yes, when I was able to get the bike going at one point it did operate well at higher speed/rpm. However, the bike struggled to remain idle as I’d give it throttle or else the bike would shut off.


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[minimo]

All very clear! Thanks so much for that, DaveB!


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[minimo]

I have some coil data for you:

SPARK PLUG CAPS
#1 = 8.88
#4 = 11.23
#2 = 9.08
#3 = 9.53

COILS TEST
1-4 = 14.14 drops to 14.06
2-3 = 14.08 drops to 13.99

PRIMARY @ 200 ohm
1-4 = 5.0
2-3 = 5.2

Maybe my MM setting is incorrect but I could not get any reading for the SECONDARY on either 1-4 nor 2-3. I tried getting the secondary on #4, is this how to do it? MM set to 20k, one meter connects to black/white the other connects to plug wire:





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[minimo]

 Also, I’m not getting continuity between the “gazouta” 1-4 & 2-3. These are the spark plug wires with boots off.


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[Deltarider]

Also, I’m not getting continuity between the “gazouta” 1-4 & 2-3. These are the spark plug wires with boots off.


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Then select higher scale, knowing 200kΩ. What plugs do you run, the "R" type or the nonresistor type?

[DaveBarbier]

Unless smarter people disagree I would replace the plug caps. They should be around 5k ohms. Parts stores should have them for under $4 each.

The coils test from plug wire to plug wire seem fine to me.

When you say "primary" you mean testing the black/white stripe wire and the blue (or yellow depending on the coil) right? That also looks good to me. The 550 uses 5 ohm coils and I believe the 400f is the same.

Unsure about the other tests. Maybe someone else can chime in? Seems to me your coils are fine.

What spark plugs are you using?