Topic: PD41A Carb confusion

[Sellsme]

I  have a 77 CB750K with pd41 carbs, the book says to set the floats to 12.5mm and the 42's to 14.5mm. All the parts are the same and interchangeable. When I set the floats to 12.5 they seam to not be level and the clear tube test shows the fuel line to be much higher than  the gasket. I now have them set to 14.5 and it seems to be running out of  gas at top end. This problem may not be related to the fuel height but for some reason under heavy acceleration it falls  on its butt. I'm not a good typist so I hope this makes sense

[Trav-i]

I have PD "B"s on my bike and I just had them apart yesterday.  After riding to and from Barber about 190 miles each way 2 up I noted carb 1 and 3 weeping from the overflows when I got home.  I took them all apart yesterday ran some lapping compound in the float needle passage and then gave the needles a quick rub down to eliminate any possible burrs causing friction.  While I was in them I checked the float levels and found several to be off so I adjusted them, I set them to 14.5mm and they are fine 12 or 12.5mm would be alright as well.  The height should be measured from the gasket edge for the float bowl, with the top of the carbs pointing at a downward angle.  The tang should be touching the spring loaded pin, not applying any pressure, measure them at this point.  If they need adjustment bend the tang down to raise the level, and bend the tang up to lower the level.  Recheck with the tube method if you wish.  Sounds like you bike is starving for fuel right now, which may indicate your levels are low.

Hope this helps.

Travis

[flybox1]

14.5mm
Set it there, and check the bowl fuel level using the clear tube method.  Its easy as the fuel drains out the overflow.
Adjust if needed.
If your bike feels like its running out of gas in the top end, its a lean/rich (jetting) issue, most likely.  Not a fuel height issue.

[Sellsme]

Thanks for your reply,  measurement should be on the center of the float while looking at the side of the carb. Or should it be at the tip of the float away from the needle side?

[Sellsme]

More info, main needles up one notch, main jets 120, idle jets 40, 4 into 1 exhaust and pods

[flybox1]

(IMS) fuel screws setting?
Open exhaust or baffled?

Measure the tip of the float opposite its pivot. 
Hint:  OEM Keihin pilot jets are 14.5mm tall, so this is a measurement you can eyeball from the side if its go or no-go.

Stock jetting and needle clip setting make these K's pretty lean. 
The addition of pods and an open exhaust compound the issue.
Your bike will appreciate the time you spend getting your jetting accurate.  Starting with the idle circuit.  Your #40's may not be sufficient.

[Sellsme]

Idles  great, exhaust has a muffler with little baffle, not much. Idle screws 1 1/4 out

[Don R]

 Just to be sure, if you haven't already check the flow from the petcock.

[Sellsme]

I put a brand new Honda part petcock on, flows good. Then I just raised the jetting to 125 mains. Idles perfect, pulls hard under acceleration then at high rpm it starts to stumble. At that point It stems like its running on 2 cylinders still at high rpm. If I then  hold it at a constant rpm say 3500 for awhile it seems to recover, down shift, pulls hard then stumble etc. I am starting to think its ignition. Dayna with Dayna green coils. This bike has been completely redone and I have already went through the stage of replacing most of the new China parts with factory. Please any more ideas?

[Sellsme]

Forgot to add, while it is stumbling it is coughing through one or more of the carbs.

[flybox1]

No more ideas.  time to get your hands dirty.

Your bike will appreciate the time you spend getting your jetting accurate.  Starting with the idle circuit.  Your #40's may not be sufficient.

A bike can idle, and idle well, even with an incorrect mixture.    Plug chops and more plug chops. start with the idle circuit.
I probably went through 6 sets of plugs getting IMS through needle shim just right. 

Ensure timing and advance are spot on.

What brand jets are you using?

[Sellsme]

Dyna timing dead on, unsure of where the jets came from. Just changed the jets from 120 to 125, same problem. I used to think I was a pretty good mechanic, this thing has beat me. If you read this post, it really feels like it is running out of gas. I know it is not, it is not just one cylinder  quitting, it is more. Moral of the story, nothing is wrong so what's the problem?

[flybox1]

Aftermarket jets are crap.
Unless your mains and pilot jets are stamped with the Keihin K, they're trash.
www.jetsrus.com

You changed main jets because your butt dyno told you that was exactly what your bike needed? 
You need to be methodical with carbs.  Start with an accurate idle chop, and go from there.
If you cant/wont, or just continue throw stuff at it without supporting evidence...I/we cant help you 

later....

[Sellsme]

Point well taken, and will do just that as soon as I can find someone to follow me in case it quits completely. This thing is  dropping to 2 or 3 cylinders at high rpm and staying there when rpm is back to 3000 for some time, finally recovering.  Just noticed that the dyna coils I am using are 3 ohm and I have the dyna ignition. Supposed to be 5 ohm?

[flybox1]

Sorry.  I know very little about the electronic ignition systems.
Others will chime in.

[martin99]

Don't know if this will be helpful or not, but my F2 wth pods and 41As was a bugger to get anywhere near right. I had the same problem at WOT, felt like fuel starvation. 125 mains didn't help, but 130s sorted it. No hesitation at a ton plus now, and that's plenty fast enough for me! Still got a stumble at low revs, but that's because I'm too much of a tight-wad to invest in 40 pilots 

[Sellsme]

Thanks, 40 pilots really helped me, idles perfect, no stumble at take off

[Sellsme]

May have an ignition problem, dyna ignition with 3ohm coils. using dyna spark wire with ngk resistor plug ends. Does that work?