Topic: PD Carb Questions

[I Zombie]

Well it's come to the point where I'm rebuilding the carbs on my 78 750k. I've decided I'm not gonna half ass it, so full kits will be ordered. The big question I have is do I stick with the kit for a 78 or can I use the 77 kit with adjustable needles & bigger jets. The bikes got pods & 4 into 4 open exh, 140 mains. My plan is to get the 4 into 2 mufflers back on it & play with some smaller jets once I've got the carbs back together.

[mrrch]

Go with the adjustable needles (make sure that they are actually adjustable)

[I Zombie]

Pretty much what I was thinking, just wanted to make sure they'd fit before I started ordering parts.

[lucky]

Go with the adjustable needles (make sure that they are actually adjustable)

The 76's had adjustable needles. The 77's and 78's were non adjustable.

I do not know if the 76 an 77,78 needles are the same.
I would love to see the two needles side by side.

Need to measure too.
But having adjustable needles in the 77-78 PD carbs sure would be useful.

Let us know and give us a photo if you get those 76 needles.

Thanks- LUCKY

Make sure the accelerator pump system is actually working after you get them put back together. You can do it on the bench.

Fill the float bowls with fuel and when level on the bench actuate the throttle a couple times and make sure you can see gas squirt out of all 4 nozzles.

[bollingball]

IZ I will be watching this. So you have the 42B carbs now? I will not go with pods but I have thought about the adj. needles. Have you read anything that says they will just bolt on the 42b rack or what model carbs are you going to try 77 what? I don't see any issues with the jets. I also have a rack of 42A carbs but have not popped the top to see if they have adj. needles.

Ken

[I Zombie]

The 77  PD carbs (A?) have adjustable needles, the 78 PD42b don't. This is the kit
http://www.outwestmotorcycles.com/catalog/index.php?main_page=popup_image&pID=332  I just ordered. Gotta get a new Accel pump Diaphram & a few more Jet sizes & the fun will begin. I'd love it if the search was working agian, then I could double check a few things.

[brewsky]

I'm going thru the same process right now (although slowly)

Started with uni pods, 127.5 mains and 3 needle shims, MAC 4/1 with baffle, but wanted to go back to stock airbox.

Here's where I am now (attachment)

Will be adding a shim and see from there.

I think sometimes people buy into the need for re-build kits when they really don't need them. I have 42,000 miles on mine with all orig internals except mix screw o-rings and bigger slow jets....and they have been opened up several times.

[bollingball]

Reply #9 on: August 18, 2010, 01:17:44 pm »QuoteThe rubber tubes between the carbs are part of the accel pump distribution system.
The aluminum tubes between the carbs are part of the fuel distribution.

I suspect that the only nipple you've shown us is the fuel inlet.  But, the picture is too close in to see the rest of the carbs and locate a place where a vent nipple might be.

If there is no other nipples on the carb bank, then the stand pipes in the bowls provide the needed venting.

I understand that the 77 CB750K carbs have adjustable needles in the slides.

Cheers,

« Last Edit: August 18, 2010, 07:57:18 pm by TwoTired »

Here is one thing I dug up I have one from HondaMan I will try to find it I think I read that they have to be from a (F) model

Ken

[bollingball]

Normally you will not need any hard parts just rubber. But who is to say some PO ran around the beach with just stacks. I have not heard any good things about after market needles. Time for the old microwmeter.

Ken

[I Zombie]

I agree with the not needing the kits, I've been in & out of these carbs a few times. The some of the gaskets are junk & the float needles are shot. Plus with all the fun things the PO did, I kinda figured that all new stuff would be a good starting point.

[bollingball]

The 77  PD carbs (A?) have adjustable needles, the 78 PD42b don't. This is the kit
http://www.outwestmotorcycles.com/catalog/index.php?main_page=popup_image&pID=332  I just ordered. Gotta get a new Accel pump Diaphram & a few more Jet sizes & the fun will begin. I'd love it if the search was working agian, then I could double check a few things.

 

What is the # on the 77 (42A)?? I just have not heard good things about Keyster hard parts.

Ken

[I Zombie]

yes 42a

[bollingball]

yes 42a

Good I have a spare rack of those. Now just so I clear. Do you think they would all ready have adj. needles or do I need to get some. I can not see in there and did not want to take off the choke butterfly until later this year in the fall.

Ken

[I Zombie]

As far as I know, yes the 42a have adjustable needles. Had me really confused the first time i did the carbs & ppl kept talkin about clip positions in their posts

[bollingball]

Well this is good to know I allready had them and did not know it. I might did into them a little early. Now if someone would just make 2&4 insulator boots. I have doubled up on 1&3 and did the 180 turn and it does work but not perfect.

Ken

[I Zombie]

yeah i did that too, still have my old ones but haven't tried to soften em yet

[SOHC Digger]

42A are the 78F carbs.  41A are the 77K carbs.

[I Zombie]

hence the reason I wish the search worked

[lucky]

The 77  PD carbs (A?) have adjustable needles, the 78 PD42b don't. This is the kit
http://www.outwestmotorcycles.com/catalog/index.php?main_page=popup_image&pID=332  I just ordered. Gotta get a new Accel pump Diaphram & a few more Jet sizes & the fun will begin. I'd love it if the search was working agian, then I could double check a few things.

I do not see 5 grooves on that needle in that very poor photo.

[lucky]

I'm going thru the same process right now (although slowly)

Started with uni pods, 127.5 mains and 3 needle shims, MAC 4/1 with baffle, but wanted to go back to stock airbox.

Here's where I am now (attachment)

Will be adding a shim and see from there.

I think sometimes people buy into the need for re-build kits when they really don't need them. I have 42,000 miles on mine with all orig internals except mix screw o-rings and bigger slow jets....and they have been opened up several times.

Which year motorcycle?
What is the thickness of the three shims on each needle?
What idle jets?
Mixture screws set at
Is it a baffle or a muffler?

[brewsky]

All that info is included on the attachment except the shim thickness, which I didn't measure. They are not true shims, just small washers from local hardware store,.....probably 2x thickness of true shims, but I will measure.

The A/F readings are from onboard Dynojet meter, and shown at various marked throttle positions (except first reading, which is from actual dyno test)

[brewsky]

I'm going thru the same process right now (although slowly)

Started with uni pods, 127.5 mains and 3 needle shims, MAC 4/1 with baffle, but wanted to go back to stock airbox.

Here's where I am now (attachment)

Will be adding a shim and see from there.

I think sometimes people buy into the need for re-build kits when they really don't need them. I have 42,000 miles on mine with all orig internals except mix screw o-rings and bigger slow jets....and they have been opened up several times.

Which year motorcycle?
What is the thickness of the three shims on each needle?
What idle jets?
Mixture screws set at
Is it a baffle or a muffler?

Lucky,
I finally found my extra shims and they measure as follows:

0.50mm thickness (after sanding the burrs)
6.75mm OD
3.10mm ID

I think they are simple 3mm washers, but need to be de-burred

I also think the 42 pilot was over doing it from a stock 35.

If you look at the spreadsheet, you will notice that changing any one item, can affect other circuit totals.

The reason I went with the live Dynojet A/F meter was too be able to tune for less than WOT on the road, and get smoother transitions from circuit to circuit. And I was suprised to find how much of the actual riding time the throttle position was very low (1/8 to less than 1/2).

78 CB750K8
PD42B's
Stock airbox drilled (4 1" holes in back of box)
K&N
MAC 4/1 with baffel in muffler
112.5 mains
42 pilots
1 shim (0.5mm) under needles
Mix screws 1 out
2500' elev
65-80F

Still a little rich on top and bottom, and lean in middle, but definitely better than with pods.

[lucky]

I'm going thru the same process right now (although slowly)

Started with uni pods, 127.5 mains and 3 needle shims, MAC 4/1 with baffle, but wanted to go back to stock airbox.

Here's where I am now (attachment)

Will be adding a shim and see from there.

I think sometimes people buy into the need for re-build kits when they really don't need them. I have 42,000 miles on mine with all orig internals except mix screw o-rings and bigger slow jets....and they have been opened up several times.

Which year motorcycle?
What is the thickness of the three shims on each needle?
What idle jets?
Mixture screws set at
Is it a baffle or a muffler?

Lucky,
I finally found my extra shims and they measure as follows:

0.50mm thickness (after sanding the burrs)
6.75mm OD
3.10mm ID

I think they are simple 3mm washers, but need to be de-burred

I also think the 42 pilot was over doing it from a stock 35.

If you look at the spreadsheet, you will notice that changing any one item, can affect other circuit totals.

The reason I went with the live Dynojet A/F meter was too be able to tune for less than WOT on the road, and get smoother transitions from circuit to circuit. And I was suprised to find how much of the actual riding time the throttle position was very low (1/8 to less than 1/2).

78 CB750K8
PD42B's
Stock airbox drilled (4 1" holes in back of box)
K&N
MAC 4/1 with baffel in muffler
112.5 mains
42 pilots
1 shim (0.5mm) under needles
Mix screws 1 out
2500' elev
65-80F

Still a little rich on top and bottom, and lean in middle, but definitely better than with pods.

Thanks for that excellent run down and all the right info.

You are right on over doing it with the #45mm idle jets.
I am back to #42mm's now also.

The .50mm shim is .019 thousandths.
Did that washer sit down in the pocket? Or did it go over the top of the pocket in the bottom of the slide?
My first try with stacks I use .044 worth of shims but the were over the pocket so that would be +.012 = 56 thousandths.

You have 112 mains.
I have 120's.

I am at sea level though so that is a consideration you know.

Does that A/F meter have a  sensor in the exhaust?
I will try to look it up.

I bought one of those for another project (different brand)
but it was crude and not very helpful.

It is great that you are sharing this valuable information with the forum members.
I appreciate the time you have taken to share it .

[lucky]

Question.

On the last row of your data sheet it has numbers and i assume those are fuel air ratios?
So 14.5 is 14.5 :1 air to fuel correct?
If so then at WOT it shows 11 or 12 .(11:1 air fuel ratio)?
Why not increase that main jet size a little?

Also if the main jet is larger it would cross over into the needle position a little and help fatten up the mid range.

Oh, Just wondering why you drilled 4 one inch holes in the air box?
How did you decide on that? just asking.

What do you say?

[brewsky]

Question.

On the last row of your data sheet it has numbers and i assume those are fuel air ratios?
So 14.5 is 14.5 :1 air to fuel correct?
If so then at WOT it shows 11 or 12 .(11:1 air fuel ratio)?
Why not increase that main jet size a little?

Also if the main jet is larger it would cross over into the needle position a little and help fatten up the mid range.

Oh, Just wondering why you drilled 4 one inch holes in the air box?
How did you decide on that? just asking.

What do you say?

All the numbers inside the chart are A/F ratios read from the meter. The higher the number, the leaner the mixture.
The meter reads from an onboard wideband O2 sensor in the exhaust and black box.
14.7:1 is the supposed "ideal" ratio, but I'm looking for something in the neighborhood of 13 - 13.5.
Even at WOT, 12 is still a little rich, so I may even have to go with a smaller main if I raise the needle to richen the mid range.
The reason I drilled the box was to allow more flow. I'm not sure it will be of any benefit unless I open up the exhaust or replace the muffler with a less restrictive model.
I have done it before on other bikes with good results.