CB350F Carb Tuning

[imseamless]

I have found my bike doesn't want to get past 4-5k in all gears. I'm running un-oiled K&N pod filters, size 85 main jets and a 2-1 exhaust on both sides with mufflers. When I was able to get to the top part of the gears earlier, it sang like a bird. Now I can't seem to get out of the low end. Also, when I was in the top end of the gear before, I rode 30 miles at freeway speeds fine. As I came off the freeway, it started backfiring and died as I slowed down.

Would this mean I'm getting too much gas with that 85 and should go down to an 80? Or maybe I need to adjust the mixture screws?

 

[imseamless]

So I'm guessing I'm getting too much gas. When the weather gets unshitty I will do the "Ride, shut off the engine and pull the plug" thing. Was hoping someone would be able to suggest a starting point from the above information.

 

[Big R]

Hmmmmm. How are you trying it now? Surely not just revving the engine?

One of the things that drove me nuts when tuning was my fuel filter was slightly clogged. So be sure to check EVERYTHING else first- valves, timing, tank vent, battery power, etc.

 

[imseamless]

Hmmmmm. How are you trying it now? Surely not just revving the engine?

One of the things that drove me nuts when tuning was my fuel filter was slightly clogged. So be sure to check EVERYTHING else first- valves, timing, tank vent, battery power, etc.

I tested it by riding around the suburbs for about 25 minutes, which worked out great. Since that went so well, I thought I'd ride it back to the city, where I live, which is 30 miles away at freeway speeds. As I was getting off the freeway 30 miles later, she started back firing and ended up dying.

I have not checked the valves or timing, but I have ensured my battery, tank vent, fuel filters, coils and plugs are good. So that leads me to believe its either my mix or what you suggested valves or timing. Excuse me for my lack of knowledge (I'm new to building bikes), but I check my valves by measuring their spacing? As for the timing, I am unfamiliar with that. I just found a youtube video of a dude adjusting it on a twin... I am guessing it would be similar for my four. Here is the video: setting ignition timing on a honda cb350 part 2

 

[Big R]

Ya, I can't help with the timing on a F- except follow the manual. For a quick reference check of your mixture, you can try making a high speed run with no air filters. If the carbs were rich, then the added air will help. Likewise, try running with the choke shut to see if too much air is the problem.

I can't remember, are they cv carbs?

 

[imseamless]

Ya, I can't help with the timing on a F- except follow the manual. For a quick reference check of your mixture, you can try making a high speed run with no air filters. If the carbs were rich, then the added air will help. Likewise, try running with the choke shut to see if too much air is the problem.

I can't remember, are they cv carbs?

Thanks for the suggestions, I will try both. And no, I believe they are linkert carbs.

 

[imseamless]

So no tools handy tonight but I was with my bike. It's all snowy outside so I can't ride, but I wanted to make some kind of progress. Went out to the bike and started it up. Held the revs around 7k, freeway speeds, and noticed it missing and popping a bit.

Any thoughts? Didn't pull off the pods cause I dont even have a screw driver!

 

[Swapmeet Louie]

So no tools handy tonight but I was with my bike. It's all snowy outside so I can't ride, but I wanted to make some kind of progress. Went out to the bike and started it up. Held the revs around 7k, freeway speeds, and noticed it missing and popping a bit.

Any thoughts? Didn't pull off the pods cause I dont even have a screw driver!

Actually sounds lean to me...?

I would not suggest holding your bike @ those rpm's without a load on the motor though.


Edit: You need to check your valves as stated earlier

 

[imseamless]

Actually sounds lean to me...?

I would not suggest holding your bike @ those rpm's without a load on the motor though.


Edit: You need to check your valves as stated earlier

Louie, thanks for the note about not holding the revs- I didn't know that. I will check the valves this weekend!

 

[imseamless]

Re: CB350F Carb Tuning (Pictures of plugs - Opinions!?)

Finally have proper tools on-hand, so I ran some tests. I read in the thread called "Motorcycle Carburetor Theory 101" to run at full throttle, pull the clutch, kill the engine and pull the plug. Upon doing so (actually ran at 7k, but that is pretty full thottle- didn't wanna push it too hard) I found the plug is pretty black. See below:

The Carb Theory document says "If it's black or dark brown, the air/fuel mixture is too rich and a smaller main jet will have to be installed"

Does anyone have any other ideas before I take the main jet from an 85 to an 80?

 

[imseamless]

Re: CB350F Carb Tuning (More photos and troubleshooting)

Ok. The above photos were running pod air filters. Since I am guessing I'm running rich, I pulled off the air filters and ran the same test with open carbs. I was expecting to find my spark plugs a lot more tan. Unfortunately, they look about the same:

Kinda weird. I'll check my valve spacing now and hopefully someone can chime in with any ideas on the plugs?

 

[Big R]

Were those plugs new when you put them in for the chop? They don't have to be factory fresh, but try giving them a scrubdown with some cleaner and a tough nylon brush.

I can't tell on my phone, but what color is the entire porcelain under the electrode? If it's completely white, you are running lean.

 

[imseamless]

Were those plugs new when you put them in for the chop? They don't have to be factory fresh, but try giving them a scrubdown with some cleaner and a tough nylon brush.

I can't tell on my phone, but what color is the entire porcelain under the electrode? If it's completely white, you are running lean.

Hey Big Rich,

You're correct, brand new plugs. I've ridden them maybe 70 miles total. The porcelain under the electrode is whiteish-tan. Definitely far from a dark color, but is not clean white. Would you suggest going up to a 90 main jet then? Is it the porcelain I am concerned with, not the top?

 

[imseamless]

Also just remembered something. When I got on the throttle without the pods on, it didn't pull as hard as it did before. I think this further proves I'm running lean as more air seems to have made it worst.

 

[Big R]

I would try 90's. Better to be on the rich side, ya know?

Also, scrub those plugs. Check and see what they look like before and after you try chopping. Have you checked the valves and timing yet? I may have missed it if you did......

 

[imseamless]

I would try 90's. Better to be on the rich side, ya know?

Also, scrub those plugs. Check and see what they look like before and after you try chopping. Have you checked the valves and timing yet? I may have missed it if you did......

Cool, I'll go throw 90's on after I type this. I'll scrub the plugs after I rejet. I haven't checked the valves or timing yet. I don't have the manual for this bike, but I have one for a 750 so I've been going off that an an italian copy of the 350 manual. I'm a little apprehensive to get into the valves/timing at this time because I don't have experience or a wing man. I'm hoping tomorrow I can have a buddy give me a hand and check out the valves.

 

[bobjohnson]

Yeah those dont look rich to me, maybe a little bit lean, maybe.


Get a box of plus, like 20 or more, and do plug chops with fresh plugs. You will be able to tell a lot more than you can from used plugs.


If i had to guess, id say if there is anything wrong with the carbs, you can dial it out without swapping jets. But what i would do is:


Get new plugs and put them in
Put in the 90 mains
Plug chop


If its really rich, go back to the 85s, swap plugs for fresh ones again, raise needle one clip and try again.


Im going to assume since you had the carbs all apart and have been swapping jets and stuff that youve synced them? If theyre not really close, the bikes not gonna pull well at high rpms under load.