Topic: Help needed for Pd42b's

[kerryb]

I'm waking up a '78k bike after a very long nap (10 yrs or more).  Compression is within 2 lbs on all cylinders , timing is static correct.  Carbs are very clean ( 3 times) jets are stock, 35 & 110.  Mixture screws set a 1 turn out.  Accel pump nozzles squirt great.  Carbs are bench sync'ed.  No airbox yet, just the intake rubbers so far, will be stock airbox soon,  4 into 4 exhaust in fair condition.
Here's my problem, starts easy with one squirt from the accel pump, will idle at 1100 rpm after repeated starts, but choke is ineffective, and pipe 3 gets very hot very fast and I'm afraid of doing damage to it by running long enough to do a vacuum synch.  Pipe 4 also gets hot quick too but not quite as bad as #3.  Pipes 1 and 2 seem to act at normal temps.
Checked float heights with clear tube method...#'s 3 & 4 are right at the bowl seam , #2 is 2mm below the seam, and #1 is 4mm below the seam on  float bowl.
I think my next step is to adjust the floats, but I'm not sure which way to go, where should the level be?  Do I need to turn the mixture screws out 1/2 turn or more?   My initial goal is to keep from burning something up while trying to make it run better,  yes I have a box fan blowing air over the cylinders while running.  all evidence points to fact that this indeed is a motor with only 23k miles on it.
Any help or links would be appreciated.

all part of the adventure

[colvinry]

Pop off the carbs. Adjust the float settings per the manual see attached. Perform a bench sync with a 1/8 drill bit Shaft or smaller

It's going to be impossible to tune those for an idle without the air filter on. The idle is very finicky and you need to set them up to exact riding setup. Pop out the jets and give them a cleaning and make sure all your orafices are free and passin gas. Lol.

That should get you running. Then vac sync and you should be able to walk it right down to a good idle. Vac really helps.

Also look over your boots and make sure they are not leaking. Test them by spraying with wd or brake clean and if it revs it means there are cracks in the boots. This will make it really hard to put a good tune on the carbs.

The pages attached are out of the shop manual. Set everything to stock and go from there. Don't forget to bench sync. Start at 2 and set the rest to that.

Ryan

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[Paintedseat]

Set floats to 12.5 mm, Install airbox, idle screws 1.5 out. Bow far of the accelerator rod is the arm?

[kerryb]

OK...I set all floats to 14.5, mix screws to 1.5, stock airbox on.  I ran it just enough to see the choke works now, but not enough to get it warmed up properly.  Idle is improved but not great yet. Also cleaned/checked all passages one more time. Haven't done a vac Synch  yet, hope to have enough time tonight for that and do thorough check for leaky boots.
p.s.  have copy of factory service manual and couldn't locate the passage for float measuring!!!
Used 14.5 'cause that's what I could see in the previous post.  Is 12.5mm used in special cases?
I know I've read the explanation of air vs fuel at the mixture screws but couldn't find it again in search to verify,  when I turn the screw out, am I adding more fuel or more air to the mix? ( in Pd42's)

Thanks for the help.

[kerryb]

Note to self;  always remember to tighten the boot clamps after reinstalling them!  Hanging idle solved, low idle solved, bench synch was so good vacuum synch right on for all four.  Swapped coils after 1 and 4 stopped firing.  Problem now is some popping from exhaust #1 and believing my garage sale tach/dwell that it is indeed idling at 500rpm, ls that possible?  Same tach needle won't settle down enough to tell if mixture screw adjustments are having much effect unless closed all the way.  My points are arcing a bit, will that or a bad condenser cause the tach problems?
Appreciate the help.

[flybox1]

If you dont have your airbox on while testing, youre running lean.
Any mixture diagnosing/screw adjustments are futile unless everything is installed...

Get your airbox and filter on, your idle up to 1000-1400, and do a proper plug chop on fresh plugs.
Adjust mixture screws as needed.

[Paintedseat]

Set them to 12.5. You should invest in bigger pilots. 38s. Your idle is going to suck with those stock 35s. Too lean. Did you adjust the needles? If you are going to stay stock on intake and exhaust you should be ok with the stock mains and the needles set at the 2nd notch. But they are set up from the factory very lean to pass the changing emissions standards of the time. The engines benefit greatly from a little more fuel even when in factory configuration

[kerryb]

Thank you both Flybox and Paintedseat,  stock airbox is on, and it made a big difference.  The stock 4-4 exhaust is in somewhat degraded condition, but most of the bafflees are still in there.  I need to go back and reset the float heights.  I've got to order some larger jets and hope it will help with the cold-blooded behavior at startup.
Appreciate the advice, will let you know my progress.

p.s,  number 6 in the cool 2 club

[Paintedseat]

The pilots will help alot. Also i said the needles had notches but that is not the case. The 77 had the adjustable needles. The 78 did not. You have to shim

[flybox1]

shims not needed unless you are changing your intake or exhaust.
your idle will not suck if you have the correct fuel level in the carbs and your IMS are properly set after an idle plug chop.
if the correct PD42bs are on this bike, 14.5mm (or the same height as the flat surface of the pilot jet) is the proper float height to achieve the correct fuel level.
you can confirm this with the clear tube test.

[Paintedseat]

I disagree. The carbs are set up lean in stock form and with today's fuels its worse. You need at a minimum level of bigger pilots and I would also raise the needles if it were me. One shim. The mains are good.

[Paintedseat]

Oh yeah set the floats at 12.5

[colvinry]

Oh yeah set the floats at 12.5

What's is your reasoning for the lower loat height?

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[Paintedseat]

It's higher.

Oh yeah set the floats at 12.5

What's is your reasoning for the lower loat height?

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[colvinry]

Your right, it is higher. Why??

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[Paintedseat]

It's probably not totally necessary if you leave the jets and the needles in stock configuration but when you start going up in fuel needs and you go up in jet sizes and needle height the carbs can actually run dry. You want that extra fuel in the bowls so the fuel never gets too low. Basically if gives you 2mm of extra fuel to compensate for the higher use. Thus bikes do not run at top performance with the stock carbs in stock settings. It's a fact.

Your right, it is higher. Why??

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[colvinry]

Makes sense to me. I have been battling some fuel starving issues on the highway with my CB400t. I am gonna give this a try!

Thanks for the details behind the recommendation.

Ryan

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[Paintedseat]

Makes sense to me. I have been battling some fuel starving issues on the highway with my CB400t. I am gonna give this a try!

Thanks for the details behind the recommendation.

Ryan

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That is where it will cause problems. Cruise at highway speeds. Especially if you roll the throttle quickly. It will starve.

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[kerryb]

Floats set at 12.5, pilot jets clean "vigorously" , boots not leaking, airbox leak repaired....starts right up, responds well to choke, idles smooth after warmup, revs up real nice and settles down.  Woot, Woot!,   thanks guys.  May or may not put the bigger jets in when they get here, may save 'em for the next set of 42b's.  Sure wish I hadn't put the 41's on the bike I just sold...new info too late.
Gotta get new plugs for "chopping".

[flybox1]

It's probably not totally necessary if you leave the jets and the needles in stock configuration but when you start going up in fuel needs and you go up in jet sizes and needle height the carbs can actually run dry. By what scientific testing?     Absolutely not possible.  Fuel supplied will always be greater than demand until fuel is completely exhausted.  Do you think HONDA engineers would have made it any other way?  I'm not disagreeing with you that these carbs were designed lean for EPA reasons, but that claim is total BS.  Do recognize how deep in the bowl the main jet sits?  The bike doesnt care if the main jet is under 5mm of fuel or 20mm of fuel.  You want that extra fuel in the bowls so the fuel never gets too low. Basically if gives you 2mm of extra fuel to compensate for the higher use. Thus bikes do not run at top performance with the stock carbs in stock settings. It's a fact.

Your right, it is higher. Why??

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If your bowls start weeping gas after the bowl gaskets sit in gas for a while... revisit your float height, or at least clear tube test bow 1 and 4 to verify its too high.  fuel level should be 3mm below the top edge of the bowl, which is achieved at 14.5mm float height.

[Paintedseat]

Your kidding right?

[Paintedseat]

It's true of all carbs. At 12.5mm the fuel level is still below the bowl junction. You do understand that a float needle is not an on/off switch right?

[flybox1]

Your kidding right?

14.5mm is not low for PD42b carbs.  It is exact.

[Paintedseat]

For stock set up lean as hell.

Your kidding right?

14.5mm is not low for PD42b carbs.  It is exact.

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[flybox1]

If float level is correct, IMS and pilot jet changes are needed to correct lean/rich mixture....not raising the fuel level.