Topic: Keihin PC 46A stock needle setting?

[cmyoch]

If it were my bike, I'd leave everything stock, restore to her original glory, and ride! My brother ordered the kit based on (what I assume) is a suggestion by who knows where or who knows who that if he's going to run pod filters and 4 into 2 straight pipes that this is what mods were needed.

Maybe I'll just leave everything stock, finish my clean up for him and install. If he runs into problems we can slowly work on what mods would be necessary. I thought the jets were quite different based on the sizes that I gathered up today. I've never customized my bikes to this extent by removing air boxes and changing up the stock exhaust. So I'm not very knowledgable when it comes to carb mods. I think these bikes run fine in their stock configurations.

Anyway, do you think I should stick with the stock jets and settings? I can gather detailed information on the brands of pod filters and the exhaust if it helps?

[TwoTired]

If the commitment is firm to alter the induction (shortening and adding more filter membrane area), as well an reducing exhaust back pressure), it is almost certain that stock jetting will change from those effects to be too lean for a proper running.

The main should increased in size and the slide needle raised to restore fuel mixtures to pre-mod levels.  You will also likely need to find a new idle mixture screw setting (more turns from stock).

Since "Pods" is a style rather than a specification, and there are many brands a manufacturing examples, no data for their operation exists or is published.  The exact degree of change will therefore be unique for the particular combination of parts that were chosen.  he engine will need to be tested, either by dyno and a fuel map readout, or test track, and spark plug deposit reads, to determine what the resultant mixtures are and then recursively changed and checked until something approaching the correct is found.

[lucky]

Lucky, I plan on posting as much information as I can to help answer my questions. I'm at work right now and I'll post info on the stock jet sizes, jet sizes that were in the kit, and the origin of the kit. I'll look back at my original post to see if I stated the origin of this project.

My brother acquired a 77 CB550, bone stock, barely running. He is doing some sort of custom project with it cosmetically along with pod filters and 4 into 2 exhaust which I believe are straight pipes. Given I resurrected and restored my '78 Yamaha XS650 and most recently a '76 GL1000, he asked that I help him with the carbs. He ordered the jet kit and handed me that kit and the carbs and that was it. I'm not in possession of the entire bike, just the carbs, kit, and instructions on the kit. I understand your frustration that I didn't post every bit of information early on and I apologize for that. Please don't convey to the entire board here that there's something fishy going on or that I'm somehow incompetent. I never paid attention to jet sizes because they were already ordered, it's not my bike, I really didn't have any reason to open the package until I'm ready for assembly.

I'll take photos of what I have to help you guys to help me out. I did take a pic of the carb body number and posted earlier in this post. I just looked and I whole heartedly apologize that I posted the wrong info. It's a "PD", not a "PC". In my haste to type up the post, I misspelled. Based on what has been given to me so far, I believe that the second to last clip position is the factory setting here. Unfortunately since the last slide I worked on stripped out, I'll have to figure out how to extract those screws if you guys think that a needle adjustment is necessary based on the jet sizes that I'll post later on today.

Again, I appreciate all the help I'm getting here. If it wasn't for the XS650 forums and the GL1000 forums, I wouldn't be where I am today with my bikes. There's more value in all of these groups than one can ever imagine!

Thanks for that information. Now I have a clear picture in my mind about what is going on. Thanks. I never thought anything fishy was going on.

[Deltarider]

The needle number is E23501 (Barely legible even with a bright flashlight and a magnifying glass) The E could very well be a B.

Just my curiosity: it couldn't be  E2350F, could it?

[cmyoch]

TwoTired-very good information, I seriously doubt that he is going to go through the trouble of putting the bike on a dyno and go through all the motions to properly tune this bike to optimum performance. My read on this (this is totally a guess based on how well I know him) is that he is going to cruise on it, take a day trip every now and then, and not take it to a track. I assume he's looking to ensure that the bike is going to perform well with the mods and not run and sound like crap on the road (popping on decel, etc.)

Lucky-I apologize, I responded while at work, under stress, etc. I'm also frustrated that I took on what I thought was going to be a quick and dirty clean, set everything to factory spec, and hand it back kind of job. I have a hard time handing over a set of carbs tuned for factory spec knowing good and well it's not going to be right then being called later on because the bike ran like crap. I messaged him yesterday asking more specifics about the intake and exhaust. All I got was the pods were foam no name brand off the shelf at a local bike shop and the pipes were cb drag pipes he bought off the local Craigslist. So basically, there's nothing to really work with.

Deltarider- It could very well be E2350F. I had a very difficult time reading the numbers, even with a bright flashlight and a magnifying glass. Maybe half of the "F" was worn off?  I can pull a needle out of a different slide and see if I can read it easier.

[ANDY W]

Like TT said no two pods or exhaust are the same. I don't know why the kit would haveyou install different size jets on the two center carbs, the intakes are the same length, so there would be no need. I think I would start with the 105 mains, 2nd clip position from the bottom on the needles and maybe 4 turns out on the idle screws. Better to be fat then to lean. Spark plugs are easy to change. Popping on decel may sound cool but its not good

[cmyoch]

Thanks for the suggestion. The clip was originally in the second position from the top and I moved them one position down to the center. I can easily move them one more position. That is, until I free up the fasteners on the #4 slide. Those screws stripped and I have to figure out how the heck I'm going to free them. I'm a little scared to drill them for fear I'll screw things up. Hopefully I can find a replacement slide assembly soon.

[ANDY W]

Your more likely to find an intire carb then just a slide. The PD46 carbs were only used on 77 and 78 model years and I'm pretty sure the slides are the same in the A and C carbs. Once u drill the head off the screw the rest of it should just twist right out. just take your time when drilling. Remember slower is better when drilling metal

[Bankerdanny]

Like TT said no two pods or exhaust are the same. I don't know why the kit would haveyou install different size jets on the two center carbs, the intakes are the same length, so there would be no need. I think I would start with the 105 mains, 2nd clip position from the bottom on the needles and maybe 4 turns out on the idle screws. Better to be fat then to lean. Spark plugs are easy to change. Popping on decel may sound cool but its not good

Glad to see someone else comment on this. I suppose that during the tuning process it may turn out that one carb may need slightly different jetting than another, but I cannot imagine why you would start out that way. The presence of pairs of jets makes it seems more likely to me that your jet kit is for a twin and not a 4 cyl.

[Deltarider]

I know, these little screws are a pain. Years ago I almost stripped one myself. What is the recommended type of screwdriver for those screws?

[Bankerdanny]

Technically I believe they are JIS style, which looks like Philips, but is shallower and has squarer shoulders than a philips.

Just search JIS in eBay and you will find several options. I picked up a 3 screwdriver set earlier this year for about $20. If you have an old Jap bike it's a worthwhile add to your tool chest.

[cmyoch]

I used a JIS driver on them but it was the worst carb out of the set so they must be corroded in there. I'm on the search for a left handed drill bit to try to back them out if I'm so lucky.

In the instructions in this kit, there was a summary of the questions I guess were asked when ordering. It was noted that the bike was a CB550 with 4 carbs. It specifically stated in the instructions that there were different jets for the outer 2 carbs and inner two. Maybe air flow due to pods on the inner two play some sort of role in that??

BTW, I was at a local Rural King and looked through the clearance tool bin and got my set of JIS drivers for $10. Couldn't resist. Before these, I had a driver bit that came in a socket set I had. It had a blunt tip and fit the heads on both my bikes perfectly. A lot of us probably have a JIS bit somewhere and don't even know it.

[lucky]

I know, these little screws are a pain. Years ago I almost stripped one myself. What is the recommended type of screwdriver for those screws?

A #2 phillips will work perfect.

Use a long screw driver.
Make sure you have the screwdriver lined up,not on an angle.


If you use a #1 phillips it WILL strip the screw.

[TwoTired]

TwoTired-very good information, I seriously doubt that he is going to go through the trouble of putting the bike on a dyno and go through all the motions to properly tune this bike to optimum performance. My read on this (this is totally a guess based on how well I know him) is that he is going to cruise on it, take a day trip every now and then, and not take it to a track. I assume he's looking to ensure that the bike is going to perform well with the mods and not run and sound like crap on the road (popping on decel, etc.)

The bike is doomed to be a status statement only, imo.  The test tack (rented or chosen from street availability) is just to dial in the carbs for the mods.  Similar to what Honda did to choose the original carb set up.  Yes, it is a pain to re-jet properly, but it is an artifact of the choice regarding pods and exhaust changes from stock.

Anything you do to the carbs will be based on hope and luck toward getting correct mixtures.  Without testing and adjusting, the best you can hope for is lack of rider complaint.

In the very old days when people were finely tuning the carbs for max power, the inner cylinder often ran hotter than the outer cylinders.  Since some of the cooling of an air cooled engine comes from the fuel entering the cylinders, a richer mixture would help cool the inner cylinders.  So, larger jets were used for inner cylinder carbs.  Honda never expected the engine to be run flat out for long durations.  So, all the jets are the same size the cooling fins are relied upon to keep all the cylinder at even heat levels.