Topic: Carb Issue, makes NO sense.

[fletcha221]

Hey guys, did a search, and everything I've read is not lining up with what I'm experiencing.

Bike: K5, k8 Carbs, Rebuilt motor to stock specs, 10 Degree advance, 35 slows, 120 mains, pods, 4:1 to 1.5 inch exhaust pipe , no baffle.

She is running way rich. Stumbles at idle, and have ZERO top end. The plugs are black, and I'm getting black smoke out of the exhaust.

I have the air screws 4 TURNS OUT!!!!!!  If I go any further, the damn things are going to fall out.

I guessing, I need to move down to 110's. I'm think the math is too far off for the bike to run correctly.

Thoughts?

-Fletch

[iron_worker]

The mains have nearly nothing to do with how it will idle.

Are you sure 4 turns out is leaner? I'm not familiar with PD carbs.

Are you sure it's firing on all 4 cylinders?

Are you running velocity stacks or uni filters? These will drastically change your tuning requirements.

IW

[Lars]

Not familiar with those carbs, but on the original ones the air screw should be 1 turn out. Guess your filters are giving you an issue.

[flybox1]

hey fletcha....mixture screws turned OUT makes it richer on the PD carbs. (check my sig.)
turn your screws back to 1.5 turns out, and go from there.  it should be pretty close.

[fletcha221]

Running K&N filters. Out is leaner in on these carbs. She is firing on all 4. Throttle is nice and "Blippy" in the low RPM, but as you wind it up, she bogs.

I know the slows are what dictates fuel at idle, but my research shows that #35's should be perfect.

It just does not make sense, you would think that with a free flowing exhaust and pods, you would need bigger mains for high end.......

Here she is, take a LOOK!!!!!!!!!

http://750brat.blogspot.com/

[flybox1]

IIWY:
mixture screws at 1.5 turns out - stock is 1 turn.  you have pods, you need a little more fuel - go to 1.5.
pilot #35 - this still should be ok as you can tune with your mixture screw.
needles shimmed 1mm - you'll need more fuel mid-range because of your pods and open exhaust.
mains #130 - 110's are stock, 120's might still be to lean with your pods.  id start right with 130's and do a plug chop.

[iron_worker]

I thought the early non-PD carbs idle screws (sometimes referred to as air screws) regulated the air coming into the pilot circuit... thus the farther out you turn the screw the more air comes in and the richer it gets.

I believe the reverse is true for PD carbs. They regulate fuel flow and so turning the screws out is richer.

Hopefully someone can confirm this!

IW

[flybox1]

^YES!
for PD's you richen the circuit when you turn the mixture screw out. 
he's added to his overly rich condition.

[brewsky]

Changed intake, changed exhaust, changed carbs, changed advance......=?? starting from scratch....

Is your accel pump functioning?...."Stumbles at idle"

"air screws" are actually "mix screws" on PD's......IN=leaner, OUT=richer.

I would go to 110 or 112.5's, 38's, 1 needle shim, 1 1/2 out on screws and start plug chopping (or dyno sniffing) from there.

Here's my exercise  results, .......(still in progress):

[flybox1]

^ yes! he's on 120's now.  might work if he can get a good plug chop, but with his pods AND open exhaust, i'd bet 130s will be closer.
the jump back down in size will be way to lean for his intake and exhaust. 
im on 120s now with a stock airbox and a lightly baffled kerker.

[fletcha221]

Hey guys, there is a chance these are PD42A carbs......is the mixture still the same?

I read that screwing clockwise was richer, and likewise. The bike seemed to respond according to these adjustments.

I completely rebuilt the carbs, all stock settings, cleaned the pump, she works like a charm.

Take a look, maybe I'm missing something.

http://750brat.blogspot.com/

[flybox1]

clockwise is LEAN (for PD's a or b)

[fletcha221]

Also,

Read this on another post:

"I would suggest while they are still off the bike that you set up or check your full bowl levels with the clear tube to 2-3mm below the bowl gasket and set the gap on the accel. pump rod to allmost zero. Don't forget the choke idle cam adj. It is so much easier to do this off the bike on a test stand."

Is there a chance I have the Accel pump gaped wrong? Perhaps causing an "Always on" effect?

What the hell is the Choke idle cab adjustment!??

[brewsky]

Hey guys, there is a chance these are PD42A carbs......is the mixture still the same?

Here's the comparo sheet:
The type should be stamped on the carb body
http://www.motorcycleproject.com/motorcycle/text/specs.html

[flybox1]

ok....
Fast Idle Cam (not the Choke idle cab)  .  this cam actuates when you pull your choke cable.   it is hidden down in between #2 and #3 carbs .    the cam 'lifts' your carb slides ever so slightly to allow the bike to idle high(2500, but adjustable) until it warms up.  when you push your cable back in, the cam disengages and the slides lower to the level you set with your idle adjustment screw.

[iron_worker]

The accel pump can't be "always on". I believe it's just a plunger than pushes forward as you twist the throttle. Only the fuel that is in the plunger body can be pushed out... The throttle must then be backed off to refill the plunger body so the fuel can be pushed out once again when the throttle is again twisted.

I'm not too familiar with PD carbs but I suspect that the choke idle cam adjustment is a cam that bumps up your idle speed when your choke is applied. The older non-PD carb bikes didn't have this and when cold starting they would not idle unless you manually raised the idle setpoint with the thumbscrew or held the throttle slightly open until the engine warmed up a bit.

There is likely a procedure in the manual or or here somewhere for adjusting this cam properly. I would imagine it adjusts how much the idle is bumped up when choke is applied.

*edit* FLybox is one fast typing mofo. *edit* lol

IW

[brewsky]

^ yes! he's on 120's now.  might work if he can get a good plug chop, but with his pods AND open exhaust, i'd bet 130s will be closer.
the jump back down in size will be way to lean for his intake and exhaust. 
im on 120s now with a stock airbox and a lightly baffled kerker.

That's what I thought with mine till I put a meter on it.
With completely open 4/1 exhaust, stock airbox opened up with 4 additional holes and K/N, I was still rich with 112.5's.

[flybox1]

dont worry about the 'gap' on your accel pump. 
to verify your accel pump system is working properly, i would slide your pods off, and while looking into the carb intakes, you see fuel shoot out of each of the brass standpipes when you actuate the throttle....
if they do not, you need to clean this system.

[flybox1]

^ yes! he's on 120's now.  might work if he can get a good plug chop, but with his pods AND open exhaust, i'd bet 130s will be closer.
the jump back down in size will be way to lean for his intake and exhaust. 
im on 120s now with a stock airbox and a lightly baffled kerker.

That's what I thought with mine till I put a meter on it.
With completely open 4/1 exhaust, stock airbox opened up with 4 additional holes and K/N, I was still rich with 112.5's.

with #42 pilots(assumption ), I dont doubt it! 

[fletcha221]

Lots of fuel coming out of the pump. That pump works just fine.

I think I may have a plane crash comedy of errors going on here. I don't know why, but I'm guessing I'm getting some false indicators.

I'll adjust the mixture screw back to 1.5 turns out and see what happens. If the issues continues......

I think I need to check the slow jets to be sure they ARE the correct ones, If they are 42's or something like that, might be too much for the low end, and maybe something crazy like the float level is too low.....causing a lag in fuel for the high end?? UGHHHHHHHHHHHHHHHH

The idiot who "rebuilt" the carbs before me but the slides in backwards, so maybe there is something I missed when completely taking these apart, cleaning, and reassembling them.

[crazypj]

Why don't you post a close up pic of one carb showing the fuel/air screw your referring to so we don't have to guess what your doing?

[flybox1]

trick - put a straight edge across the top of your pilot jets to gauge float height 

[fletcha221]

OK................SO I'm the idiot.

I got to thinking that when I got the carbs, the slow jets were missing. I remembered I ordered them from Sirius Consolidated. I went back and checked what I ordered. Guess who picked the #42's instead of the #35 by accident.

No wonder the goddamed thing won't idle correctly.

SO, Off comes the carbs.

D'oh.

So, a really rich condition CAN cause the bike to bog under load at higher RPM? I've had bikes run rich and not get much out of the top end, but never bog the way this does.

[fletcha221]

Hey PJ, there is only one screw on the carb, sooooooo, I'm not sure what you are talking about.

[flybox1]

just get your IMS back down around 1, first, and start from there. if you still cant adjust out the rich low end, you'll need to swap them for 40/38/35s.