Topic: Can a cone or baffle fix this lean-ing exhaust issue?

[Autoground]

CB650c with Keihin carbs.

I'm currently having to run with my air-fuel mixture screws at 3 1/4 turns out, but my plugs say I'm lean.

I'd toyed with the idea of calibrating the accelerator pump rod, but my mechanic (who I'm miffed at) pointed out that I have an aftermarket exhaust that might be leaning out the mixture in the chamber.

The issue is almost completely resolved by having the screws so far out and I don't want to get into rejetting. I'm hoping a baffle or cone would restrict air flow enough to find a nice compromise on

A pic of my exhaust is attached. Is there a cone-cap with db killer that would fit this?

I'm open to all thoughts. Thanks for intput!

[Scott S]

 That exhaust really shouldn't cause a lean condition.
 It looks like the baffle was removable at one time. IF you can get it out, you can try wrapping the baffle with some packing.

 Refresh my memory: on your carbs, is the mixture screw on the air box side or the engine side?

[HondaMan]

The CB650 SOHC4 often runs with white plugs. It is a lean-burn engine! I have seen very few of them with carbon-fouled plugs. My brother, used to his CB500-4 using a set of plugs every 4k-8k miles (blackened) oft remarked that once a year (10k-12k miles) was too often to change his 650's plugs.

[Autoground]

I've never had such a lean-burning engine. Maybe I'm being overly cautious, too fearful of melting my plugs.

The screws are on the engine side. They are screwed 3 1/4 turns out, so that should be making it rich.

[Scott S]

 Yes, if they are on the engine side they are fuel screws, so turning them out adds more gas. Try going in and see if it's better (I think 1.5 was stock).

[Flyin900]

You don't show or say if your running a stock air box/filter or pods, as that will also affect it, if you actually have a lean condition. There is no adjustment to the accelerator pump that I am aware, beyond the factory clearance spec on the rod to the actuator tab .

[Autoground]

Correct, there's no adjustment, but the rod has been ever-so-slightly bent, and that prescribed gap from the rod to the actuator tab is mighty small. I've wondered if slipping out the rod and trying to true it in a vise would solve some low-gear stumbling.

I'm going to go a half turn every day or two and keep acquiring data. Sounds like there's no baffle small enough to go into the current exhaust hole.

[Alan F.]

I'm humbled in current company, but to me the simple important factors are #1 if you're running pods or stock airbox, and #2 what does that exhaust baffle look like? Is it just an end cap with the rest of the baffle rotted or cut away? Wrapping the baffle has been mentioned, and it's a good idea. Replacement baffles are available (diameter at end of your muffler is the important factor) or mods can be done to your existing baffle to reduce flow and noise if needed.

Not to say the lean nature of a CB650 or fuel screw positions are unimportant, just asking about the simple stuff as it would apply to all bikes.

[Flyin900]

You don't show or say if your running a stock air box/filter or pods, as that will also affect it, if you actually have a lean condition.

Very key part of the potential issue as noted above.

If the carbs are the CV style with the larger heavier aluminum slides, I am pretty familiar with that style. They definitely don't like a pod filter, or even a modified air filter or box.

[Autoground]

Whoops, sorry I missed this answer.

Yes, stock airbox and stock carbs. To my knowledge, after repeated cleaning the carbs, everything is at stock setting except for the air-fuel mixture screws.

My plugs are white, but the RPMs are slightly slow to return to baseline when let go of the throttle. And I do have those screws way out. So I've got symptoms of rich and lean.

However, there is cause to celebrate, because all of these little things don't stop her from running well enough to hit the highway! This is the first week that I've had this thing running and I've been workign on her for a year-- so I'm very delighted! But there's always something....

[Alan F.]

Congrats on a runner! How's your fuel mileage compared to what other cb650s are getting?