Author Topic: Scared of being lean...CB350F airscrew direction (Read 7318 times)

Blackhole · « **on:** April 11, 2012, 05:46:52 PM »

I just got my bike back together and took it for a small, very cold ride. It ran great and starts right up but I just want to make sure that the bike is not running lean. I have a fear of doing damage to the motor because of it being on the lean side. It didn't back fire once and had good acceleration through all the gears, but my new Mac 4-1 header has a slight gold color to it now with only thirty miles on it. I have the stock airbox on the bike and everything else is stock except for the exhaust. I set the airscrews at 1 1/2 turns out when I set the carbs up but then read this in the FAQ "
What happens when I turn the airscrew out - richer or leaner?
If your airscrew is on airbox side of carb, turning out will lean mixture; opposite if airscrew is on engine side of carb. "
My airscrew is on the airbox side so I turned it in 1/2 turn to have it run a little richer because of the header. So on my bike...a 74 CB350F...you turn the airscrew in to make it richer? I also think it would be nice to have another gear....but I can live without that.
Thanks in advance from a guy that HATES adjusting carbs.

tomkimberly · « **Reply #1 on:** April 11, 2012, 06:48:08 PM »

The air screw should be 7/8 turns out (+/- 18 turn). 1 1/2 turns out is to much.

Tom

jessezm · « **Reply #2 on:** April 11, 2012, 06:49:59 PM »

You've got that right. Stock setting is 7/8 turns out, 1/2 turn in from there would be richer. If you want another gear just slap a 400f engine in there!

Just on a side note, you should diagnose a "lean" condition by reading the plugs at specific throttle settings. Your pipes might be more likely to turn colors if they are single vs. dual walled, or you may be lean, but need larger main jets, change needle position, or pilot jets, rather than enriching with the air screw... Just food for thought.

Blackhole · « **Reply #3 on:** April 11, 2012, 07:08:33 PM »

Thank you. I will give it another 1/2 turn in and see how it rides. That should put me at 1/2 turn out for the screws. I don't mind working on other parts of the bike but when it comes to carbs I just hate the fact that it is not an exact thing like "tighten it down to 14 ft lbs and your good" type of thing. Once again thank you.

Rob69 · « **Reply #4 on:** April 11, 2012, 07:38:37 PM »

Quote from: Blackhole on April 11, 2012, 05:46:52 PM

I just got my bike back together and took it for a small, very cold ride. It ran great and starts right up but I just want to make sure that the bike is not running lean. I have a fear of doing damage to the motor because of it being on the lean side. It didn't back fire once and had good acceleration through all the gears, but my new Mac 4-1 header has a slight gold color to it now with only thirty miles on it. I have the stock airbox on the bike and everything else is stock except for the exhaust. I set the airscrews at 1 1/2 turns out when I set the carbs up but then read this in the FAQ "
What happens when I turn the airscrew out - richer or leaner?
If your airscrew is on airbox side of carb, turning out will lean mixture; opposite if airscrew is on engine side of carb. "
My airscrew is on the airbox side so I turned it in 1/2 turn to have it run a little richer because of the header. So on my bike...a 74 CB350F...you turn the airscrew in to make it richer?

It's important to bear in mind that Mac pipes are of single wall construction, whereas the stock pipes are double wall construction. Single wall constructed pipes are prone to discoloration. What you're looking for is uniformity. If there's no uniformity, you may have a problem worth investigating. I'm assuming that the valve clearances, point gaps and ignition timing is all correct, as well as having properly synchronized carburetors.

Quote from: Blackhole on April 11, 2012, 05:46:52 PM

I also think it would be nice to have another gear....but I can live without that.
Thanks in advance from a guy that HATES adjusting carbs.

You could check into gearing it taller. I don't know if there's much in the way of sprocket choices for your bike.

flybox1 · « **Reply #5 on:** April 12, 2012, 07:46:39 AM »

have you completed a vacuum sync of your carbs. if not, set your AF screws to 7/8 out, and then do your sync. then check your plugs after a short idle. they will tell you if you are lean.
did you increase your main jets to 78 or 80's because of your MAC exhaust, or are you still running 75's?

Blackhole · « **Reply #6 on:** April 12, 2012, 05:27:21 PM »

I did a bench sync and have not done a vacuum one yet. Plugs, and points are new and the timing and valves have been set. I guess I will buy a sync tool and work on that. I rode the bike again today after work and it runs real well. I didn't switch the main jets when I cleaned the carbs. Is switching the mains something that is a must when using a header? The only reason I went with the Mac was because the bike came without an exhaust when I pulled it from the guys barn. Thanks for the help...I will look into getting that vacuum tool. The bike has nice pep, but it is around 6 grand a 60 mph. I guess I will just have to stay off the interstates

Hablo · « **Reply #7 on:** April 12, 2012, 08:20:47 PM »

Where are you guys getting the 7/8 turns out from?
I just looked at my Clymers manual and it says 1 1/2 - 2 turns out.

Rob69 · « **Reply #8 on:** April 12, 2012, 11:02:07 PM »

Quote from: Hablo on April 12, 2012, 08:20:47 PM

Where are you guys getting the 7/8 turns out from?
I just looked at my Clymers manual and it says 1 1/2 - 2 turns out.

Both the Honda service manual and my Honda spec manual call for 7/8 of a turn.

tomkimberly · « **Reply #9 on:** April 12, 2012, 11:37:57 PM »

Quote from: Hablo on April 12, 2012, 08:20:47 PM

Where are you guys getting the 7/8 turns out from?
I just looked at my Clymers manual and it says 1 1/2 - 2 turns out.

The Clymers manual is wrong, never trust aftermarket manuals for specs.

Tom

tomkimberly · « **Reply #10 on:** April 12, 2012, 11:41:12 PM »

Quote from: Blackhole on April 12, 2012, 05:27:21 PM

I did a bench sync and have not done a vacuum one yet. Plugs, and points are new and the timing and valves have been set. I guess I will buy a sync tool and work on that. I rode the bike again today after work and it runs real well. I didn't switch the main jets when I cleaned the carbs. Is switching the mains something that is a must when using a header? The only reason I went with the Mac was because the bike came without an exhaust when I pulled it from the guys barn. Thanks for the help...I will look into getting that vacuum tool. The bike has nice pep, but it is around 6 grand a 60 mph. I guess I will just have to stay off the interstates

Don't baby that motor, it likes to run 9 - 10k rpms. Oh and BTW, there is more than likely no need to rejet for this little four.

Tom

Trevor from Warragul · « **Reply #11 on:** April 21, 2012, 12:30:46 AM »

On my CB350/F I have the air screws set to 1 5/8 turns out. I tried 7/8 & it ran like crap. When quoting the Honda specs you have to bear in mind that these were devised when the petrol (gas) was wonderful high-quality leaded. It has been my experience that the horrible modern unleaded (in Australia at least) tends to make older bikes run rich. Mine ran really well on the old leaded, to make it run equally as well on modern unleaded I had to go down one size on the main jets (4-1 exhaust, standard airbox), sidegap the plugs & use Lucas petrol treatment.

My $0.02

Trevor

faux fiddy · « **Reply #12 on:** April 21, 2012, 04:21:54 AM »

Quote from: morini on April 21, 2012, 12:30:46 AM

sidegap the plugs My $0.02

Trevor

Not sure what that is. Prolly a stupid question(?)

Trevor from Warragul · « **Reply #13 on:** April 21, 2012, 09:21:27 PM »

http://performanceunlimited.com/documents/plugsidegapping.html

crazypj · « **Reply #14 on:** April 22, 2012, 12:25:52 AM »

Just took a look at 350F carbs, I had forgotten how tiny they are

They have AIR screws not FUEL screws.
OUT=LEAN
IN=Rich
If someone is using 1-5/8 turns out, the pilot jets are either not stock or have been drilled out oversize?

Trevor from Warragul · « **Reply #15 on:** April 22, 2012, 02:24:06 AM »

Quote

If someone is using 1-5/8 turns out, the pilot jets are either not stock or have been drilled out oversize?

Standard 35 pilots. Like I said, modern Australian unleaded seems to make older bikes run rich. I also went down one size on the mains as well...

bking · « **Reply #16 on:** April 25, 2012, 06:39:54 PM »

My experience with my sons CB350F that we are just getting on the road. New Mac 4 into one header and carbs just rebuilt but not synced yet. (Can any body direct me to a link for syncing his carbs?, I have the gauges) I had the air screws out at 2turns each. The bike did not idle very well but run down the road good. Just read tonight that they are air screws and fuel screws and should be 7/8 a turn out. I readjusted. It idled much better but the the power off idle up to about 5500 rpms was not good, it felt rich and a little miss. After 5500 she started to rip and really liked it on top to 10,000 rpms. It pulled harder than at 2 turns out. I will lean it out a little tomorrow and give it another try.

Does the air screw effect the idle circuit? It did seem to run better after turning in the air screws.

lucky · « **Reply #17 on:** April 25, 2012, 09:21:59 PM »

Quote from: bking on April 25, 2012, 06:39:54 PM

My experience with my sons CB350F that we are just getting on the road. New Mac 4 into one header and carbs just rebuilt but not synced yet. (Can any body direct me to a link for syncing his carbs?, I have the gauges) I had the air screws out at 2turns each. The bike did not idle very well but run down the road good. Just read tonight that they are air screws and fuel screws and should be 7/8 a turn out. I readjusted. It idled much better but the the power off idle up to about 5500 rpms was not good, it felt rich and a little miss. After 5500 she started to rip and really liked it on top to 10,000 rpms. It pulled harder than at 2 turns out. I will lean it out a little tomorrow and give it another try.

Does the air screw effect the idle circuit? It did seem to run better after turning in the air screws.

When adjusting the mixture look at the tachometer and watch it. Try to get the rpm as high as it will go and then richen it 1/8 turn.

If you have a diagnostic type tack/dwell meter it works much better.

Trevor from Warragul · « **Reply #18 on:** April 26, 2012, 12:45:40 AM »

Quote

Does the air screw effect the idle circuit? It did seem to run better after turning in the air screws.

In = richer
Out = leaner

I'd say your looking for a point somewhere between 7/8 & 2 turns out...

jstfkndi · « **Reply #19 on:** February 01, 2013, 08:14:52 AM »

I know this is old, but what are the concerns of the bike running lean? The damage that occurs? I have on that has an exhaust that is probably aftermarket and I am running stock jetting and airbox.

crazypj · « **Reply #20 on:** February 02, 2013, 06:41:10 PM »

Little bit lean, little bit over advanced timing and you get this

Or, this

jstfkndi · « **Reply #21 on:** February 04, 2013, 05:34:54 AM »

Ouch!! Thanks for the lesson my friend! Turned my screws in a bit and seems like it is doing good when it's warm. When cold, it doesn't want to idle worth a sh*t. Oh well. It rolls and seems like the mix is good, so I won't complain.

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Author Topic: Scared of being lean...CB350F airscrew direction (Read 7318 times)