Plugs fouling, top end rebuild?

[Tecrekka]

Hello everyone. I am so thankful to have this resource for this beautiful bike that I have. For a cycle that is touted by some as one of the most reliable made at the time, I have yet to see this reliability. I bought this 1970 XS1 as a rebuilt wall decoration about 4 years ago. When I purchased it, it had been tore down and rebuilt, only needing the wiring harness installed and the carbs tuned/synchronized. Due to being a full time student and employed full time, it was easier for me to take the bike to have someone do this work than to do it myself. It has never been "right". After about 3-4 trips to the mechanic and about $1500-2000 of work, it's is still not "right". Last year was the last time I rode it because the plugs kept fouling out bad. As a bandage to the situation I carried a plug wrench, wire brush and spare set of plugs It finally got so bad that I parked the bike and really haven't touched it in over a year. I had recently had another old bike act the same way and it burnt a valve and rings, and I didn't want that to happen here, too.
So here I am, the mechanic who has had me come back and back again suggests that I need a top end rebuild, but that just doesn't seem right to me, or others that I have described the situation to.
Basically, if I was flat out the bike was just fine. Highway and side roads were all good until I had to idle down to say, stop for a light. Then it woulds stall and the plugs would come out black, but dry.
I've read that it could be jetted wrong, so I tore them down today just to see what I had going on in there.
Attached are several photos, as you can see the jets are "25" and I'm not sure how to ID the others. I have downloaded and read the carb guide and all other carb tech guides, but I still seem to be a bit unclear on what is going on.
As you can see the photos of the plugs now aren't bad, I think I cleaned them off right before I put the bike up last time.
In addition, I would think that these are B38's but there is not mixture screw, as outlined in the carb guide. I have also attached a photo of the only stamp on the carb, if anyone can help me positively identify these carbs.
I am at about 2000' above sea level, and I am running K&N pods.
Thanks in advance for any input, I can't tell you how much I appreciate it. I am so READY to get on this BIKE AGAIN!

 

[Tecrekka]

That's right, I'm not married......lol

 

[vr3506]

Maybe this helps you,

Text at pictures is in dutch, other
text is in german.

http://www.xs650.de/literatur/vergaser38/index.htm

 

[5twins]

I think you have the wrong style and size pilot jets installed. You appear to have the "no hole" version of what's probably a VM22/210 style pilot. Those were used in the later sets. Your carb set uses BS30/96 type pilots with bleed holes. The big difference is in which end the metering orifice is on. Your float bowl is designed to use that BS30/96 type and the ones you have won't flow right. That's probably why you're fouling plugs. Here's how to tell the 2 types apart. Like I said, I'll bet you have VM22/210 pilots installed .....

Here's a chart showing the stock jet sizes for the various years. As you can see, you should have #45 pilots of the BS30/96 type. Also check your main jet size, it will be stamped right on the head of the jet next to the screw slot .....

Oh, and here's a shot of the normal pilots with bleed holes and the "no hole" version. You want the bleed holes in yours .....

 

[5twins]

And yes, you do have mix screws. I can plainly see the one in your last pic. Once you get the proper pilots, set the mix screws to the spec in the chart above to start, then fine tune from there .....

 

[Tecrekka]

I think you have the wrong style and size pilot jets installed. You appear to have the "no hole" version of what's probably a VM22/210 style pilot. Those were used in the later sets. Your carb set uses BS30/96 type pilots with bleed holes. The big difference is in which end the metering orifice is on. Your float bowl is designed to use that BS30/96 type and the ones you have won't flow right. That's probably why you're fouling plugs. Here's how to tell the 2 types apart. Like I said, I'll bet you have VM22/210 pilots installed .....

Here's a chart showing the stock jet sizes for the various years. As you can see, you should have #45 pilots of the BS30/96 type. Also check your main jet size, it will be stamped right on the head of the jet next to the screw slot .....

Oh, and here's a shot of the normal pilots with bleed holes and the "no hole" version. You want the bleed holes in yours .....

You know I was looking at that information and I thought that the jets should be the bleed hole versions, thank you for verifying that.
Also, I see now that the mixture screw arrows are pointing to a screw that does correspond to my carburetors, when I was looking at the photo on my phone with no glasses it was hard to see the white arrows....

As for the needed/clip slot, that designates the needle,and the clip position from the top position down?

Mix screw setting, that is one or 3/4 turns out from bottom down?

Is there any reason to believe that I may have the wrong needle, too? I just didn't want to mess with the diaphragm unless necessary.

Thanks so much, I will get the right jets in there and we'll see what happens.
As an aside, this is the first time I've messed with carbs on a motorcycle, and it's been 20 years since I've mess with a carb at all. These seem to look pretty good/clean, am I correct in that assumption?

Thanks you so much for your help guys, I will let you know what happens!

 

[5twins]

That "-4" at the end of your needle number designates the clip slot to use. In the case of your 4JN19 needle, the clip should be in the 4th slot from the top. Needles rarely get changed but it wouldn't hurt to verify that yours are still the right ones. Yes, the mix screw setting is from the fully closed position. Turn the screws in until they GENTLY seat, then back them out 1 turn.

Examine the ends of your current pilot jets to see where the metering orifice is and let us know if they are indeed the wrong type. Your float bowl is designed to feed a metered amount of fuel through the bottom of the pilot jet and add air to that fuel through the bleed holes in the sides of the jet. This air/fuel mix then flows out the top of the jet. With no bleed holes on your pilots, you're flowing just fuel, not a weaker fuel/air mix. That's probably why you foul plugs at low speeds. The pilot circuit is the low speed circuit and yours is set up too rich.

You may want to find a different mechanic. I think that guy is just after your money (which he's already gotten quite a bit of). Now he wants to rebuild your motor for what is probably going to amount to a $6 fix (2 new pilot jets). He might be an OK mechanic but he's obviously not very knowledgeable about XS650s.

 

[Tecrekka]

That "-4" at the end of your needle number designates the clip slot to use. In the case of your 4JN19 needle, the clip should be in the 4th slot from the top. Needles rarely get changed but it wouldn't hurt to verify that yours are still the right ones. Yes, the mix screw setting is from the fully closed position. Turn the screws in until they GENTLY seat, then back them out 1 turn.

Examine the ends of your current pilot jets to see where the metering orifice is and let us know if they are indeed the wrong type. Your float bowl is designed to feed a metered amount of fuel through the bottom of the pilot jet and add air to that fuel through the bleed holes in the sides of the jet. This air/fuel mix then flows out the top of the jet. With no bleed holes on your pilots, you're flowing just fuel, not a weaker fuel/air mix. That's probably why you foul plugs at low speeds. The pilot circuit is the low speed circuit and yours is set up too rich.

You may want to find a different mechanic. I think that guy is just after your money (which he's already gotten quite a bit of). Now he wants to rebuild your motor for what is probably going to amount to a $6 fix (2 new pilot jets). He might be an OK mechanic but he's obviously not very knowledgeable about XS650s.

Argeed. It's unfortunate but after the first two trips to him and things still weren't like they were supposed to be, I should have known better. I can take solace in knowing that I've still got less into it than it's worth, when it runs! I've got more time now so hopefully I can just do most of the work myself. I've sourced the proper jets locally, although they only had the 42.5 and lower, not the 45's. I am about to double check the main, and they have those also, should I need them. Thanks again for the information.

ps- now that I think about it, don't I want to run a bit leaner with the pods as opposed to the standard air box set up?

 

[5twins]

Make sure you're getting the BS30/96 type pilots, with the metering orifice on the bottom end (opposite the screw slot end). The 42.5 pilots should work OK, just use the 3/4 turn mix screw setting speced for them instead of one turn. These settings are just for initially setting the screws. You should adjust them in/out from there to find where the bike runs best. That will usually be within a quarter turn or so from the initial setting in either direction.

 

[Tecrekka]

Make sure you're getting the BS30/96 type pilots, with the metering orifice on the bottom end (opposite the screw slot end). The 42.5 pilots should work OK, just use the 3/4 turn mix screw setting speced for them instead of one turn. These settings are just for initially setting the screws. You should adjust them in/out from there to find where the bike runs best. That will usually be within a quarter turn or so from the initial setting in either direction.

Will do, thanks again!

 

[Tecrekka]

Huge difference. They only had 140 Pilots & 132.5 mains, but I figured it would be a good start.

 

[5twins]

130 is the stock main jet size for your bike. As long as it's not modified (which it doesn't appear to be from your pic), that should be fine. Yes, it looks like you got the proper style pilot now (BS30/96 with the metering orifice on the bottom) and with the needed bleed holes. And yes, I can see your old one was definitely wrong, an VM22/210 style (metering orifice at the top) and no bleed holes. The size 40 pilots may be OK. Try your mix screws open a bit more with them, like at 1 1/4 or 1 1/2 turns out. If you experience lots of popping out the exhausts during decel or if the RPMs hang and are slow to return to idle, then you'll need the bigger pilots.

Your mains are located under the drain plug on the bottom of the float bowl. Like pilots, Mikuni makes different styles of mains. Your carbs use the small round type. The large round type is more common but won't fit up into you float bowl. You must use the small round style .....

 

[angus67]

niche cyclce source has all the jet sizes you need.
If 5twins says you should start with a certain size, you would be wise to adhere. He knows his stuff, He's just too modest to tell you what Ive said.
But yeah, we'll get you hooked up. Looks like you got a handle on those pilots....carry on.

 

[5twins]

I see you added a "PS" and are running pods. That might require some larger than stock jets but maybe not and probably not by much if that's your only mod. The early bikes like yours were set up richer from the factory. They came before the E.P.A. stuck their nose in things. Actual riding and road testing will be the only way for you to tell.

I should also mention that the kind of pods you use makes a big difference. The cheap K&N clones don't work well at all. In fact any K&N pleated style pod isn't the best choice for these CV carbs, even a genuine K&N. They disrupt the air flow which messes with the slide action. This can make tuning very difficult and you may never get it perfect. If you want pods, get the UNI foam ones, they work the best with these carbs.

 

[Tecrekka]

Thanks Angus, I've read many 5twins posts and am very confident and grateful for his input. Thanks for the heads up on the source, so far I've been lucky and the local guys have had what I need to get started.
We got the bike up and running today and so far it's running better than ever! Not perfect, but changing to the proper jets was a tremendous starting point. I was just able to go a little ways down the road but I feel full out it's smooth, low end could probably use adjustment but I think we sort of expected that, with only the 140 pilots in stock. Still, it runs, and it didn't before! I'm about 1.25 turns on the fuel mixture, and the pods I've got are genuine K&N.
Thanks so much for the invaluable input, I'll keep posting as I progress, as well as when I can really get it on the road!

 

[XSLeo]

140 pilots, I think you mean 40. A 140 is big even for a main jet.
Most any idependent shop that works on dirt bikes, atv's and such will most likely have a selection of lightly used jets at reasonable prices. They might even let you try a few at the shop to see what works best. Then you only pay for the ones you need.
Won't hurt to ask.
Leo

 

[Tecrekka]

140 pilots, I think you mean 40.

You are absolutely correct, my mistake. I was only able to take it up and down the road last night, barely getting in to third gear. It seemed that is was nearly perfect above 2.5k or so, and not bad below, but room for improvement for sure.
The new jets were only a couple dollars, but yeah it would be really nice to be able to test ride them! Thanks for the idea.

 

[Tecrekka]

The good news is the jets were working great. The bad news is I've developed a short. It's been around 5 months since I sold the last of 5 Jaguars and therefore I've no idea where my multimeter has gone. On the bright side, while hunting for it I found a brand new, non-cloudy headlight for the XS!

 

[gggGary]

Having owned Jaguars you should be a wiring problem whiz! Shorts can be anywhere but a favorite spot is missing or cut grommets at the back of the headlight shell.

 

[Tecrekka]

Having owned Jaguars you should be a wiring problem whiz! Shorts can be anywhere but a favorite spot is missing or cut grommets at the back of the headlight shell.

Indeed I am! Luckily it was easy to find. The leads that were supposed to make my tail turn signals into running lights had come loose and melted to the top of the exhaust during my short ride yesterday. I had gone to the bucket first, thinking the same as you. When I didn't find anything wrong there I called a few friends to borrow a multimeter and start the process of elimination when I found the small brown wire on the pipes.
Having completed what I had anticipated to be a couple hours of work, it was a bit of play time. I took the back pegs off, which were serving no purpose since I have a solo seat anyway. While doing so it dawned on me that this is what secures the pipes.....[gears turning].."Man, I bet this sounds bad a** with the pipes off..."...yes, it did, lol. Being that everything else it's completely dialed in and I was concerned about the lack of back pressure, I still only went up and down the road but man, did it sound sweet. Also the issues at low end seemed to be a bit exacerbated but I would assume this should be alleviated to some extent by the proper size pilots? As 5twins had mentioned it did pop a bit while getting up to speed, and it seemed like I really needed to pay attention to the gas or it would stall. Once I was rolling though, it was great.
I guess my next step would be to jump to the 45's, or do you all think I would be safe just going all the way to 50's? (To recap, I currently have 40's, and 132.5 mains)
Also a) can anyone comment as the sensitivity of back-pressure on these motors and the ramifications of the lack of it and b) if there are any short, off the shelf solutions to adding a baffle that would keep the pipes very short and loud but produce the necessary back-pressure? I've seen a ton of custom pipes that look like drag pipes and I can only assume that either back-pressure isn't an issue or they have some type of restrictor built in.
Finally, I really love the bobbers but I just don't want to cut this bike, it's too clean and together. I still may take a few more things off but I would like to keep from making any irreversible changes if possible. Am I just being too sensitive? This bike obviously isn't bone stock but it hasn't be cut, either.
Thanks again for everyone's input, I truly appreciate it!