Topic: 78 550k won't idle without throttle

[sweet_baby_james]

I rebuilt the carbs for my 78 550k (PD46C carbs).  The bike has pods and a Mac 4-1 exhaust.  The slow jets are stock #42 and the main jets are #104.  Float heights 12.5mm and IMS 1.5 turns. I have bench synced them and I check all the passages are open, used a guitar string and then tested with carb cleaner.  I’ve set the timing and the gaps on the points. I have a strong (blue) spark. Verified that I have equal compression on all cylinders.

When I start up it will not idle, just dies immediately both with and without choke.  If I give a little bit of throttle then it will run but will then die when I release the throttle. From my limited knowledge this sound like an idle circuit issue?

Any help would be appreciated

James

[flybox1]

how about turning your idle set screw, and adjusting your fast idle cam ....

[Bankerdanny]

What Flybox said. There are 2 idle speed screws, one that works on the fast idle cam when the choke is on and another that works on the whole throttle shaft for when the choke is off. The PD series carbs are the only ones with the fast idle cam.

[sweet_baby_james]

I did notice that the fast idle cam on the choke isn't pushing on that bolt.  It's such a PITA to get to.  Should I adjust the cam then the set screw (the large on one the top, right?), or the other way around?

Thanks

[Bankerdanny]

The fast idle cam is a convenience, not a requirement. You can always keep doing what you are doing and use the throttle to hole the idle while warming up. Thousands of 550F and pre-77 550K owners do it every day. My '77 warmed up very fast so it would have been no big deal if the choke idle speed was too low.

That said, removing the tank to gain access to the adjusting bolt isn't that big of a deal.

[flybox1]

#1  ride your bike and get it to Op Temp.  with NO CHOKE, use the idle set screw to get your bike to idle comfortably.
#2 once your bike is cold, pull your choke all the way out (which engages the fast idle cam) and start your bike.  Note what RPM it holds. +/-2500rpm is good.
If too low or too high idle...go to #3

#3 adjust the fast idle cam bolt at the nut, righty to increase, or lefty to decrease, the rpm held at a cold idle. small adjustments here make a big rpm change.

done.

you'll rarely need to adjust either of these again.

as your bike warms, you'll hear the rpm's climb....depress the choke knob slowly to keep the rpms 2500 or lower, and as you get up to op temps, you'll have that choke knob pressed in all the way.

or...you can start and ride off, with your choke knob out, and by your first stop sign/light, you'll be able to press it in all the way.

[Bankerdanny]

The instructions from the factory manual are as follows:

1. Remove tank
2. Pull choke knob fully out and turn adjusting screw until it touches the stopper
3. Push choke knob fully in and turn the adjusting screw 2 1/2 turns.

Fast choke idle speed 3000-4000 rpms

[sweet_baby_james]

The instructions from the factory manual are as follows:

1. Remove tank
2. Pull choke knob fully out and turn adjusting screw until it touches the stopper
3. Push choke knob fully in and turn the adjusting screw 2 1/2 turns.

Fast choke idle speed 3000-4000 rpms

Forgive my ignorance, but you are referring to the idle set screw, right?

[flybox1]

No. he/we are referring to setting the fast idle cam.
Please refer to my post above. It's pretty straightforward. So is his.

[sweet_baby_james]

Ok. Got it. Makes sense now I read all the posts consecutively.

I'll test tomorrow and report back.

Thanks

[sweet_baby_james]

Good news, she's up and running! Thanks everyone.

[Big Al]

Glad you got it sorted.

I work in Angola and have brought some PD46A carbs with me as part of a rebuild project on a 1978, approx., CB550, not sure of model but engine number is CB550E- 2027851. Like others I found that the Clymers and Haynes manuals do not have any info on these Kei Hin carbs, so I joined this forum seeking guidance and will post progress hopefully to add to the collective PD46A knowledge. I have part dismantled the carbs and found the following, which fits in with other damage found to No 4 cylinder, broken rings, bent valve stem, scored cylinder.
Stamped on carb bodies PD46A □ OCY or could be PD46A □ OCV
Setting      Carb 1    Carb 2   Carb 3   Carb 4
Float height   13.5 mm   10.5 mm   12.0 mm   12.0 mm
Air Screw      1 ½ turns   1 ½ turns   1 ½ turns   1 ½ turns
Main Jet      90   90   90   90
Slow Jet       42   42   42   42
Slide Height   34.2 mm   34.3 mm   34.2 mm   33.0 mm
Slow Jet height   14.4 mm   14.5 mm   14.3 mm   15.2 mm
Normal amount of gunge in the bowls and collected in channels, especially just above the main jet. No 4 especially dirty probably due to blow back through the carb.
Number 1 and 2 needle jet holders (emulsion tubes) were loose and No 3 had unscrewed almost completely, making it at least 5 mm lower. I thought maybe somebody had started to dismantle the carbs but on reflection the bowls were still glued on with gasket goo so the bike must have been running like this. As you can see the float heights are all over the place, I will set them at 14.5 mm (after reading sweet baby james post, thank you).
The slide height on No 4 is significantly higher, maybe because somebody tried to balance the carbs after No 4 cylinder already had other problems. Likewise the tick over is wound up so far that the choke lever does not increase throttle opening when on full choke. I will set all slides the same as No 2 to begin with (thanks lucky for slide height measuring tip) and then balance the vacuum later, and reduce initial tick over setting, set fast idle speed etc.
The slow jets are not pushed fully into the bodies and No 4 slow jet is significantly lower. I haven’t pulled the slow jets out yet but when I fit them I will make sure that they all fully seat and check that they are all the same height, maybe even locktight in place if they seem loose.
I will update with what happens when I have finished the rebuild and start the engine.

Big Al