Topic: PD41A vs PD41B carbs .. 77 CB750F

[hashvm]

Here we are again .. I hope you all are enjoying your summer rides

A while back I started a thread about the 1977 CB750F I bought over summer (I also have to update the thread  )

I managed to get the bike running (First time in about 10-ish years?)
and last week I managed to get it moving and stopping on its own! (It was last registered in 96 so you do the math  )

However, when I finally got it running, two of the four cylinders were firing (2&4)

They all have new plugs .. new timing plate and statically timed ..

Things I haven't done yet: valve adjustments and Timing chain adjustments ..

So today I took the carbs off again .. and opened them up

As you can see on of the carbs (#4) has one of the float rod's posts broken .. any way to fix that?





While I had the carbs open I noticed something about the non-running cylinders (I suspected carbs to be the cause of the problem)

Carb #1 had the floats pin sticking outwards that it hits the bowl when they come on, causing the floats to stick in the up position (closing the valve needle circuit and not causing fuel to flow to the carb body?)

and carb #3 had the needle valve's spring loaded stuck (I took it out and manged to get it working)

So tomorrow I'm gonna put them back on and hope that all four would fire!

Another question: anybody knows why carb #4 keeps getting this white powder?



Here is as she sets now



Along its other sister (my 1980 CB750F)



I hope to get this running in time soon so I can enjoy it a little bit before the cold, and my engineering classes get serious!

Hashem

[hashvm]

Just put the carbs back on with no luck 

Cylinders 1,4 still don't fire

Is there anything I'm missing here?

[madmtnmotors]

First you say "two of the four cylinders were firing (2&4)"

then you say "Cylinders 1,4 still don't fire"

So which is it? What are you using to determine whether these cylinders are "firing" or not? Are you getting spark to these cylinders? If you're not getting spark (not firing) then why are you taking the carbs apart?

"Firing" to me means "spark".

Finish the rest of the 3K tune up (valve adj, timing chain tension, etc.), then determine whether spark is present for all cylinders, and report back.

[flybox1]

No way a float will operate properly with a broken post.
That carb will always cause running issues. 
If the post piece was in the bowl, it can be micro welded back on.  A forum member here offers that service.
or....
Contact forum member harisuluv....he buys/sells carbs/parts....and probably has a dozen of these carb bodies ready for use.

[ekpent]

 The white carb looks to have had a bunch of water in it at one time probably and like a cancer the corrosion keeps returning. Don't waste your time putting them back on till the post is fixed proper or the carb body is replaced with a better one(my choice).

[hashvm]

First you say "two of the four cylinders were firing (2&4)"

then you say "Cylinders 1,4 still don't fire"

So which is it? What are you using to determine whether these cylinders are "firing" or not? Are you getting spark to these cylinders? If you're not getting spark (not firing) then why are you taking the carbs apart?

"Firing" to me means "spark".

Finish the rest of the 3K tune up (valve adj, timing chain tension, etc.), then determine whether spark is present for all cylinders, and report back.

My bad .. I meant Cyl 1,3
what i mean by saying they aren't firing is the two exhuast stay cold and don't heat up as the other two
all have new spark plugs and they all have sparks (i checked them)

I'll try to finish the 3000mi tuning soon

thanks

[hashvm]

No way a float will operate properly with a broken post.
That carb will always cause running issues. 
If the post piece was in the bowl, it can be micro welded back on.  A forum member here offers that service.
or....
Contact forum member harisuluv....he buys/sells carbs/parts....and probably has a dozen of these carb bodies ready for use.

When I first opened the carbs this particular one had some sort of material that looked like clay to hold the pin
the weird thing is this carb is attached to one of the firing cylinders

I'll pm harisuluv .. Thanks!

[hashvm]

The white carb looks to have had a bunch of water in it at one time probably and like a cancer the corrosion keeps returning. Don't waste your time putting them back on till the post is fixed proper or the carb body is replaced with a better one(my choice).

Thanks .. I'll try to find a replacement as I was planning on getting her running soon 

[hashvm]

So unfortunatly I couldn't find a parts PD41B carb (that's the one for the "77 CB750F) .. however, I was able to get a body of a PD41A (from a "77 K model) .. anybody knows if these two are different?

I looked around and I can't see to find any differences except for jets and needle positions which are I can easily change

[Ericcb750]

You're absolutely right on that, The PD41A and PD41B are literally identical except the jetting (Main jet size). The A's were for the F model and the B's were for the K's . I know on my PD42B's the jets were 35pilot and 110 main with non-adjustable needles. The PD42A had 35's , 115's and non-adj needles.

I think the PD41's are pretty much the same except they have the adjustable needles and I think the Slides were not hard chromed or something..... Someone else may be able to chime in and clarify.... The float setting may be a couple mm's different too, but as far as swapping parts , I think you're good to go with that , No problems that I can see.

[hashvm]

You're absolutely right on that, The PD41A and PD41B are literally identical except the jetting (Main jet size). The A's were for the F model and the B's were for the K's . I know on my PD42B's the jets were 35pilot and 110 main with non-adjustable needles. The PD42A had 35's , 115's and non-adj needles.

I think the PD41's are pretty much the same except they have the adjustable needles and I think the Slides were not hard chromed or something..... Someone else may be able to chime in and clarify.... The float setting may be a couple mm's different too, but as far as swapping parts , I think you're good to go with that , No problems that I can see.

Thanks Eric, It's been a while and I've been working on wiring my other 76 CB550 project from the ground up .. I'll differently let you know if this works!

[Don R]

 I fixed a post by JB welding a brass bullet cartridge over it after drilling the post hole first. I made it slide on until the pin was in the notch left on the post. It was a wildcat round something about a bee. Sorry, I found it in my brothers tool box.