Author Topic: PD42A carbs on my 78K (Read 5202 times)

eurban · « **on:** February 20, 2006, 07:07:11 PM »

So I just noticed that the carbs that I currently have on my 78K project are the PD42As which are apparently stock for the 78 F rather than the K model. These carbs were an Ebay buy from a while back and are in wonderful shape. These mounted up perfectly to my K motor with the stock 78 K intake rubbers (NOS parts) without any discernable issues, mounted just fine to the KN pods that I had used on my original K carbs and seemed to work fine for the 200 miles that i put on the bike before I took it off line for the winter. I recall recently someone on this site mentioning that the 77/78F carbs had larger connectors on the intake side of the carbs that mounted to the heads with F specific rubbers . I can find no evidence of this from their ease of install but I have not yet pulled them to measure. Anyone know for sure the differences between the 78K and F carbs other than the easily replaceable parts? . .FYI I have 77K adjustable needles in them with the matching needle jets (bushings not be confused with main jets), #35 idle jets drilled to aprox size 40 and currently 115 mains. Float levels are set to the correct 14.5mm. I also removed a shim underneath the acelerator pump spring which I assumed was added by the hot rodder previous owner of the carbs (they had 145 mains in them when I got them!) but upon reflection might be an f model thing. Thoughts?

eldar · « **Reply #1 on:** February 21, 2006, 08:04:46 AM »

I would have to remember to look, but I might have the pd42s also. Cant remember for sure though. I will try to remember to look tonight as I have the carbs in my home.

Lumbee · « **Reply #2 on:** February 21, 2006, 08:27:25 AM »

...I'm always surprised to find all the differences in the the 77/78 model carbs, so I'm hesitant to say I know all the ins and outs. For sure the F/K models had different jetting (stock). As you said, the F had 35 idles to the K's 40, in addition, the main jets was 105 and 110 respectively...

scondon · « **Reply #3 on:** February 21, 2006, 10:46:49 AM »

Most likely it was me who mentioned difference in size. I have two 78 750F's and have tried different parts on both. The only '78 K part I have used is the motor. I have '76 F carbs and a K3 head on one bike and a stock F3 set-up on the other and I can not interchange carbs/rubbers/airbox between the two bikes due to size differences. The F3 carb boots are a loose fit on the K3 head due to the fact that the intake ports are larger on the F3 and so are the rubbers at that end.The pods on the '76 carbs will not fit the PD42A carbs. I'll measure the parts tonight (carb diameters/intake diameters) and post them here.

I am currently using a K8 head on my 836 F3 motor and have been using '76 carbs/boots for a proper fit, my K8 intakes are the same size as the K3. In reading your post I am beginning to wonder if the F3 carb rubbers are bigger on the engine side only. It would be nice to get this nailed down.

Lumbee · « **Reply #4 on:** February 21, 2006, 10:58:02 AM »

...I'm pretty sure the boots are just a differnt size (2mm I think) at the head, and not at the carb. I've ran all combinations of 78K and F carbs interchangably on my chop (78k) and stocker (78f) by just switching boots.

scondon · « **Reply #5 on:** February 21, 2006, 12:04:24 PM »

Quote from: The great "Lumbee" on February 21, 2006, 10:58:02 AM

...I'm pretty sure the boots are just a differnt size (2mm I think) at the head, and not at the carb. I've ran all combinations of 78K and F carbs interchangably on my chop (78k) and stocker (78f) by just switching boots.

Thanks Lumbee, When I get home I'll post the OD of air intake/engine side of both the '76 750F and '78 750F carbs as well as the OD of the F3 and K3 head ports. In the meantime, anyone with a set of carbs laying around willing to measure and post size/year/model? It would be nice to figure exactly what the size differences are and where they occur(carbs,boots,head intakes) and add to the spec sheet in the FAQ.

Clyde · « **Reply #6 on:** February 21, 2006, 04:20:31 PM »

I have sold all my F2 enine parts including the head and carbs, Also sold the 2 sets of K7/8 carbs (to Terry I think)
i did use one set of K7 carbs on my K2 special for a while but eventually went back to the early carbs
There was no virtually difference externally to the F2 and K7/8 carbs, but the rubber manifolds were different on the head side. Jetting was different though
The K7/8 use an F1/F head which has 2mm smaller dia than the F2 head intake stubs

eldar · « **Reply #7 on:** February 21, 2006, 04:42:30 PM »

Ok I looked at my carbs and they have stamped on them: PD42BAPL nd some weird character which looks like a combo of L and an upside-down 4.

eurban · « **Reply #8 on:** February 21, 2006, 06:06:33 PM »

Hey all thanks for the thoughts . . . .I got off my butt and measured a PD42A set and the original PD 42B set from my 78 K. I did not write down these numbers but the air filter sides were identical as were the engine sides . . . . .So from the standpoint of actually fitting and working with the stock(for either the78 Fs or the 78 Ks and presumably the 77s as well) intake rubbers, airfliter, throttle and choke cables the carbs are completely interchangeable. As Clyde mentions the F2/F3 heads had larger intake stubs so the rubbers themselves must be the correct ones for the head type but the carb side of the rubbers would seem to have to be identical. As to differences other than the stock main jet size I am still unsure. Lumbee you mentioned that the Ks had #40 idle jets but this is not the case. They both have the #35s stock. I drilled a set of the #35s to an aproximate #40 for my project bike. It is possible that the slides have a different cut away pattern or that the needle profiles are different or that the emulsifier tubes have different characteristics, but I have not gotten this far yet. Did anyone find a shim underneath the acellerator pump spring? Basically I have not yet found a difference other than main jets that can be easily switched. The bodies seem to be identical but I will have to take a closer look. . . .Eldar the number on your carbs would seem to indicate that they are the correct carbs for the 78K model which I presume is what you have . . . .

scondon · « **Reply #9 on:** February 21, 2006, 06:26:59 PM »

OK, back from the garage and here's what I got with my POS caliper. These are Outside Diameter measurements

Carbs:

7A ('75 750F) Air: 41mm Engine: 37mm(ID 31mm)

PD42A('78 750F) Air: 46mm Engine: 41mm(ID 32mm)

Head Intakes:

K8- 37mm

K3- 37mm(ID 29-30mm)

F3- 39mm

Both my F3 and K8 head have carbs attached so I'm going from memory(backed up by Clyde/eurban/Lumbee's posts and an email from Mrieck), please correct if I am wrong.

DISCLAIMER**** I'm going to go out on a limb and make some broad assumptions based on limited data...

Carb dimensions were the same on all 69-76 750K and 75-76 750F. Carb ports were identically enlarged for both K and F models for 77-78. For some reason, Only the F model got larger OD head ports (maybe due to different head design i.e. larger valves).

A 750K bike of any year can fit any carb of any year(69-78 K, 75-78 F) provided they use the corresponding carb boots(77-78 K boots are needed when using 77-78 F carbs). A 77-78 750F with stock motor can only fit 77-78 K or F carbs, and only 77-78 F carb boots.

What about the airbox? Well I'm glad you asked

The only experience I've had is fitting a '76 F box and '75 F carbs to a K8 motor in a F3 bike. Fit just fine. I'll just guess that airboxes can be split in two general categories for carb fitting only (whether they fit in your bike is anyones guess) and those are 1) 69-76 2)77-78. In any case be prepared to use pods.

DISCLAIMER*****

This is a mix of fact and assumption. If you are reading this and have something to add or discount as utter BS, please do not hesitate.

Terry in Australia · « **Reply #10 on:** February 21, 2006, 06:34:25 PM »

I think all your assumptions are correct mate, and after comparing a set of F2 carbs with those from a K7 that Clyde sent me a year or two back, the castings at least are identical. I'd suggest that the different part numbers were to make it easier to order a complete set of carbs set up for either the K7/K8 (ugly ducklings) or F2/F3. (fragile swans) Cheers, Terry. (owner of a dead duck!)

scondon · « **Reply #11 on:** February 21, 2006, 10:57:02 PM »

Quote from: Terry in Australia on February 21, 2006, 06:34:25 PM

K7/K8 (ugly ducklings) or F2/F3. (fragile swans) Cheers, Terry. (owner of a dead duck!)

Terry, you crack me up

What's with the "dead duck"? Did your K9 Junkyard Dog eat it for lunch? And, if the F3 is a fragile swan then that would make my F3 836 Japanese Monster a what? Fragile Pterodactyl? OK, OK...I'll stick to wrenching and leave the humor to the pros

eldar · « **Reply #12 on:** February 22, 2006, 08:29:55 AM »

I think terry is showing his distress. I think he might have found out that my K8 is lighter than his F2!!

Bob Wessner · « **Reply #13 on:** February 22, 2006, 09:48:23 AM »

Quote

either the K7/K8 (ugly ducklings) or F2/F3. (fragile swans) Cheers, Terry. (owner of a dead duck!)

Sounds like you're going to the birds and opening an aviary.

Terry in Australia · « **Reply #14 on:** February 22, 2006, 06:56:02 PM »

Quote from: eldar, Master of the K8 Thunder! on February 22, 2006, 08:29:55 AM

I think terry is showing his distress. I think he might have found out that my K8 is lighter than his F2!!

The only way you could use "light" in the same sentence as K8 (I think Mike Rieck referred to them as resembling a fat lady bending over?) is when you are discussing the things that require occasional bulb replacement, ha ha! I believe the heads are good though, with a little porting...............

eldar · « **Reply #15 on:** February 23, 2006, 08:30:29 AM »

Ahh terry just check the specs on each model right here on our own beloved site. You will see the glorious truth! My "fatl lady" still weighs less than your "cow"!!

dusterdude · « **Reply #16 on:** February 23, 2006, 09:43:21 AM »

damn,hammer time!!!

scondon · « **Reply #17 on:** February 23, 2006, 09:55:41 AM »

Quote from: eldar, Master of the K8 Thunder! on February 23, 2006, 08:30:29 AM

You will see the glorious truth! My "fatl lady" still weighs less than your "cow"!!

That's "bull". The extra weight comes from the "balls" that the "fat lady" is lacking

"Go!........."

eldar · « **Reply #18 on:** February 23, 2006, 11:25:59 AM »

Ha! It dont lack anything other than bad looks! Nasty-assed comstars!

scondon · « **Reply #19 on:** February 23, 2006, 11:44:07 AM »

Not true, it lacks a girdle and a paper bag

"Go!......."

dusterdude · « **Reply #20 on:** February 23, 2006, 11:46:50 AM »

lord,its gettin deep in here.

eldar · « **Reply #21 on:** February 23, 2006, 12:07:15 PM »

since it does not have ugly looks, it dont need a bag. Now it DOES get a bad name but when you are related to vanity child f 2 a& 3s that never want to work, that is bound to happen.

scondon · « **Reply #22 on:** February 23, 2006, 12:12:45 PM »

"UNCLE!.......UNCLE!........hahahahaha"

Now I know why Mama told me not to talk back to my Eldars. OUCH!!!

eldar · « **Reply #23 on:** February 23, 2006, 12:50:03 PM »

Once in a while mothers DO know what they are talking about!
Now I shall continue my quest to be come grand dictator of the universe!!!!!! AHHHH HAHAHAHAHAHHAHAHAHHAHAHHAAAA!!!!!!

Terry in Australia · « **Reply #24 on:** February 24, 2006, 01:21:10 AM »

Quote from: eldar, Master of the K8 Thunder! on February 23, 2006, 12:50:03 PM

Once in a while mothers DO know what they are talking about!
Now I shall continue my quest to be come grand dictator of the universe!!!!!! AHHHH HAHAHAHAHAHHAHAHAHHAHAHHAAAA!!!!!!

Well you never know Eldy, that guy with the big ears isn't doing much of a job of it. But regarding Comstars, if you go back to your earlier posts, I'm sure you said that you actually liked the Comstars on the F2/F3 and asked if they could be fitted to that plug-ugly ol' K8?

Man, you should be a politician Eldy, you change positions quicker than I change my underpants, ha ha! Grand Dictator, or just Grand Dick? Har de har har, Cheers, Terry.

eldar · « **Reply #25 on:** February 24, 2006, 07:41:22 AM »

They are still ugly. They are still better than spokes though. I dont change my position! am still sitting on my ass!
I prefer to be grand dictator! However grand dick is fine, I could star in thousands or adult movies then!

Terry in Australia · « **Reply #26 on:** February 24, 2006, 01:14:22 PM »

Quote from: eldar, Master of the K8 Thunder! on February 24, 2006, 07:41:22 AM

They are still ugly. They are still better than spokes though. I dont change my position! am still sitting on my ass!
I prefer to be grand dictator! However grand dick is fine, I could star in thousands or adult movies then!

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Author Topic: PD42A carbs on my 78K (Read 5202 times)

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