Topic: CB350F runaway idle (various tuning problems)

[scottly]

It's not the gasoline. Read this thread:
http://forums.sohc4.net/index.php/topic,195127.msg2289664.html#msg2289664

[jpschroeder]

Ok, I took it for another drive today and its getting progressively worse!

It seems that when the engine heats up something goes to crap, it wont come off idle without a battle and it almost feels like the engine is...fighting itself. It rides smooth as butter for the first 2 minutes, and then the sound of the engine changes almost to a harmonic throbbing and I lose significant power. I wonder if that extra advance I threw at it is causing some issues on the non-firing cylinder or something crazy like that (if I understand correctly 1-4 both spark and can cause issues).

This bike is gonna drive me crazy. It gives me these glimpses of beautiful riding but then that last ride crushed my spirit. I rode for like 8 minutes and the bike died on me at least 3 times.

Ill check the TDC mark

[scottly]

It sounds like you have more than just a timing issue? Please post a pic of your advancer.

[jpschroeder]

Ill snap a pic and post it here when I get home.

Poking around old threads to see if any of them could give me a clue and I just thought of something. The bike had a new Delkavic 4-into-1 exhaust when I bought it — it had clearly never really run with that exhaust on (the exhaust was new, and the carbs were old and gummed up). maybe there needs to be some off-stock carb adjustments? The Delkavic site says its not required.

[jpschroeder]

Wow, I’ve probably run this engine less than 30 minutes since I cleaned the plugs and they are super black again, so clearly over rich yeah?

Here is a pic of the advancer plate.

[scottly]

That's the stock advancer. You mentioned in the first post that the issues started after adjusting the timing, but you also had just messed with the carbs. Are all four plugs that fouled? Were they fouled before you cleaned them, and if so, how did you clean them? I've found the best way is to burn the black off the center porcelain with a propane torch.

[jpschroeder]

Yeah they were fouled before i cleaned them, and generally yes they were mostly all fouled (some worse than others, #4 being the most fouled).

Today I set the timing back to the standard timing marks, cleaned the plugs again, and then set the air screws at 2 full turns out. I rode it around for 20 minutes and it was a joy, absolute cream machine. But as I came back I started just notice the hints of the same thing (trouble coming off idle, bogging down). So when I parked I checked the plugs, sure enough, dark fuzzy black. Another piece of evidence is it seems to start up great every time with no choke at all, no matter how cold the engine is.

So, in summary — I think this might be the crux of most of my issues: its just way too rich.

How can I lean this thing out?

- The air screws, as I mentioned, are already 2 full turns out.
- Floats are currently 21mm, should I try 24mm?
- Any other tricks to leaning these out? bonus points if I dont have to take the carbs off 😂

[scottly]

Air screws mostly just affect idle and off-idle throttle positions. Try using the "clear tube" method to check the actual fuel level in the float bowls; it should be about 3mm below the surface where the bowl meets the carb body.

[carnivorous chicken]

Check the condition of your air filter as well. Check the condition of the o-rings for your jets -- if they are old and cracked gas can get by them. Check your jets while you are at it. I can't remember if you posted that they have stock jets, but aftermarket jets are notoriously bad for these things, but even if they are stock jets -- did someone poke them too hard in cleaning them and widen the passages? Or worse -- drill them out? What plugs are you running?

[HondaMan]

Check the condition of the o-rings for your jets -- if they are old and cracked gas can get by them. Check your jets while you are at it. I can't remember if you posted that they have stock jets, but aftermarket jets are notoriously bad for these things, but even if they are stock jets -- did someone poke them too hard in cleaning them and widen the passages? Or worse -- drill them out? What plugs are you running?

What he said...^^
There is also this issue: if these push-in mainjets were pulled out and their Orings replaced, the Orings MUST be the correct thickness or the bike will run uncontrollably rich above 1700 RPM. By chance, did you change the Orings with non-OEM types? In 100% of the aftermarket 'kits' I have seen for these 350F/400F carbs, the Orings for the mainjets are too thin.

There are 2 grooves on the little mainjets: it is [sadly] possible to install the new Oring on the wrong groove and then end up with upside-down mainjets, which don't run correctly because the bevel is on the wrong (upper) side then. The fix for this is just to flip them over with the Oring in the right groove. In the 350 Twins this resulted in rich-running engines that would not rev past 5000 RPM.

[scottly]

The carbs were beautiful and clean. All new o-rings, and well seated ones at that.

[jpschroeder]

Original brass #75/#35. All cleaned up. Yeah, all new orings too. That said I’m sure the main jet is after market and it does look thin, although it seems to have a good fit enough to hold itself in there even without the clips (which are installed too of course). I’m pretty sure they are in the correct orientation (larger groove at the bottom holding the clip in). Floats were all set at 21mm, and they were doing their job fine too.

Air filter is brand new. Stock air box etc

Last night I just took the carbs off again and reseated the floats to 24 to see if that could lean it out some. I haven’t gotten a chance to run it yet. Will report back though.

Last night reminded me that while there are a lot of atrocities in this world, and it’s hard to say one is worse than another….certainly installing the stock air box on a CB350F should be counted among them.

[jpschroeder]

Ok, so update/current status:

- New battery, new air filter, D8EA's with .026" gap, clean fuel (90 octane no ethanol), stock airbox, clean carbs (ultrasonic), new orings (from 4into1), stock brass — #35 and #75 and all have keihin star logo stamps on them, needles c-clips are on at the middle, carburetors are vacuum synced, ignition timed static then dynamic (ever so slightly forward of the marks, seems to run better there).

- New thing: I lowered the floats to 24mm to try and lean it out.

- Update: I rode the bike for about 25 minutes today. Unfortunately (?) it still seems to start right up without the choke (a hint to that it may be too rich still?). It runs smooth as a top, honestly, just incredible...for about 15 minutes. So, FWIW, the floats did help a little perhaps. Then the low rpm starts stuttering and it has a hard time coming off idle. After the ride the plugs are blackened up again — its just too rich...

Maybe when i cleaned the slow jets I enlarged the size of the hole? I dont think so...but not sure why this thing is still so rich. What other wisdom would ya’ll have for getting this thing to lean out? Should I consider moving the needle clips?

[jpschroeder]

(related) HondaMan — where can I get proper o-rings for the main jets?

[HondaMan]

(related) HondaMan — where can I get proper o-rings for the main jets?

PM me your address: I'll send a selection of the sizes I use.

[scottly]

Ok, so update/current status:

- I rode the bike for about 25 minutes today. Unfortunately (?) it still seems to start right up without the choke (a hint to that it may be too rich still?). It runs smooth as a top, honestly, just incredible...for about 15 minutes. So, FWIW, the floats did help a little perhaps. Then the low rpm starts stuttering and it has a hard time coming off idle. After the ride the plugs are blackened up again — its just too rich...

 What other wisdom would ya’ll have for getting this thing to lean out?

When cleaning the carbs, did you remove the emulsion tubes and make sure the holes in the sides were clear? Those holes allow air to be mixed with fuel from the main jet, and if plugged will cause a rich mixture.

[RAFster122s]

If you don't pull the jets before cleaning carbs they often have deposits at the ends of the jets in the carb bodies. There is a white hard deposit that builds up inside the carbs...not sure if it is the zinc reaction to the fuel or something in the gas precipitating out but it is trouble.
Saw it in my CV carbs off my CX500 years ago.

[jpschroeder]

When cleaning the carbs, did you remove the emulsion tubes and make sure the holes in the sides were clear? Those holes allow air to be mixed with fuel from the main jet, and if plugged will cause a rich mixture.

Yes these were removed, ultrasonically cleaned, and blasted with carb cleaner and blown out with an air compressor. They looked good to me.

If you don't pull the jets before cleaning carbs they often have deposits at the ends of the jets in the carb bodies. There is a white hard deposit that builds up inside the carbs...not sure if it is the zinc reaction to the fuel or something in the gas precipitating out but it is trouble.
Saw it in my CV carbs off my CX500 years ago.

Yeah, I pulled the jets ahead of time and cleaned them all seperately, each isolated to its own carb so everything went back where it belonged.

PM me your address: I'll send a selection of the sizes I use.

Wow! thank you. DM on the way.

Update: I set the air screws to 2 1/2 turns out — and honestly — this seems to do the trick! I think its still just a tad rich, but overall running waaaaaay better. So in summary, floats are at 24mm, 2 1/2 turns out on the air screws. I’m still going to do some of the things HondaMan recommended: new o-rings on the inlets, and new fatter o-rings on the main jets to see if that helps the overall condition. I may spring for new OEM slow jets at some point to see if that helps too.

[ts354]

Check the condition of the o-rings for your jets -- if they are old and cracked gas can get by them. Check your jets while you are at it. I can't remember if you posted that they have stock jets, but aftermarket jets are notoriously bad for these things, but even if they are stock jets -- did someone poke them too hard in cleaning them and widen the passages? Or worse -- drill them out? What plugs are you running?

What he said...^^
There is also this issue: if these push-in mainjets were pulled out and their Orings replaced, the Orings MUST be the correct thickness or the bike will run uncontrollably rich above 1700 RPM. By chance, did you change the Orings with non-OEM types? In 100% of the aftermarket 'kits' I have seen for these 350F/400F carbs, the Orings for the mainjets are too thin.

There are 2 grooves on the little mainjets: it is [sadly] possible to install the new Oring on the wrong groove and then end up with upside-down mainjets, which don't run correctly because the bevel is on the wrong (upper) side then. The fix for this is just to flip them over with the Oring in the right groove. In the 350 Twins this resulted in rich-running engines that would not rev past 5000 RPM.

OMG, I have been trying for a long time to figure out why my 1973 cl350 is running rich on the right side and won't rev past 5/6k.  It actually ran better on pods.  I spent a good little chunk on oem type air filters and it got worse.  Ive been running the right side on pods and one side on oem air filters.  I'll have to see if it's the case that the right side is installed upside down.  I bought two NOS jets off ebay and was going to see if they worked better.  I bought two of this part number 99154-286-1050 for the jets, hope that is correct.  I have not installed them yet.