Topic: WOT Lean Condition CB350F

[Owned]

Hello all,

I'm running into a problem I can't quite seem to understand.  I have a CB350F.  Running PODS with 85 Mains, stock needle height.  Bike is running well except when warm at wide open throttle.  Around 7k+, plug chop seems to indicate a lean condition.  Anyone have a suggestion of what to check?

Could I possibly have a fuel height condition?

Valves/timing and synch has been completed.

[kslrr]

85 mains is way big.  I kept the stock mains and raised the needles by 2 notches.  You might be experiencing starvation due to restrictions in your fuel lines, filters or even the passages in the carbs.

[BVCB650]

My 650 would do this at WOT and 55-60 mph with pods. Colder plug and stock air box fixed all of that.

[CBGBs]

We checked the timing Owned's bike and make a slight adjustment to the timing. Things seemed to be good at first and then when it was warm it started acting up at over 8000 rpm WOT. If you finesse the throttle it will run in that range but if you hold WOT it starts to lose speed. I think it may be some kind of ignition problem. What do any of you think?

[mlinder]

The 350's and 400's are far more sensitive to intake and exhaust changes than their larger brothers.
75 is stock.
Let's put that in a bit of (circumstantial) perspective.

cb750's often need to go up to 127.5's or larger when switching to pods. That's from 105's, 110's, 115's and 120's (on the K0's, anyway.)
That's as much as 21.5% larger.
75's to 85's is only 13.33% larger.

You may need to go larger. It just depends on location and the bike itself.
I've seen 95's available for these, somewhere. By that, I assume 90's and 92.5's are available, too, which may do the trick.

[CBGBs]

Its been suggested to me that the pilot jet is too small. That at WOT, and way up the rev range that fuel is pulled through the the pilot jet as well to richen the top end. Very interesting.

[BVCB650]

I don't think the pilot even comes into play at WOT.

[CBGBs]

Yeah, you wouldn't think so, but this guy does really know his stuff. He seemed pretty sure. He gave me an explanation that the pilot jet is essentially helping to direct the fuel. Thats why its referred to as a pilot jet. He said that by adjusting you idle mixture screw it will effect the rpm that this problem is occuring. Just to verify that it is effected by the jet.
Owned, have you tried it yet?

[BVCB650]

It is my understanding that the pilot circuit is nill past 1/4 throttle?

[mmtsquid]

The pilot isn't nil at WOT - it still makes a contribution of fuel, so it's possible that increasing pilot size could help.
Having said that, my money is on needing a larger main.

Just call Z1 and order the next size up, and see if things improve.  Even if they don't have your size listed on their website, they can get it.

Remember - when you're messing with carbs, get the main jet at WOT right first, then worry about the rest.

[CBGBs]

The float hight was found to be set extra high and was lowered 6mm. The bike is said to be doing well. It was dying at stops and this seems to be cured too. Hmmm. Great!

[76supersport750F]

Hello I have a 750F that seems to have the same WOT as you.

Can you explain more about what you did to the floats?

[CBGBs]

The floats were adjusted to spec. They were found to be lower than spec and so the fuel level was high. He said the bike revs very well but still stalls at idle on occasion.