1st post: just acquired XS400

[Lemonysword]

I've got gaiters on my bike too, and Emgo KZ bars. The ergonomics are perfect for me (but I'm 5'6 and have the short-arm long-leg power combo going) and it looks pretty sharp.

I changed the mirrors and some of the luggage since this photo, but you get the idea.

I also noticed your engine looks shiny and brand new. How did you clean it up so nicely? A friend recommended a 600 grit buffer wheel for my angle grinder followed up by some polish on a foam polishing cone, but I am a bit hesitant to remove material

 

[avemachina]

It looked pretty gunky before, and I tried hand-polishing with Mother's Mag/Aluminum Polish (usually my fave) but it was such a slow process, I just slapped a brass wire wheel (or steel? it's been a minute, I feel like it was probably brass) on my angle grinder and let 'er rip. I tried the easy way--hand polish (nope), then green scotchbrite (nope), then one of those paint stripper attachments that look like muddy tumbleweeds (nope), then metal brush (yup!).

There's something so ridiculously stubborn about the yellowish/blackish oxide on the engine case and brake drums/hubs. Once you get it off and the case is more or less smooth-looking, polish it up with Brasso or Mother's or whatever you thought was going to work at first

edit: full disclosure, I do have brush marks on the casing that isn't visible at a distance. I kinda like the look though.

 

[Lemonysword]

Tuesday I rode to the lake and back. Put about 26 miles on the bike and it rode great the whole time. I sat in this parking lot and let it idle for about 5 minutes and it did so perfectly maintaining 1200 RPM.

Today I started it, let it warm up while I put my gear on, then rode a couple miles to the auto parts store to buy some detailing products. At a stoplight, I noticed my idle had dropped to maybe 800RPM and I had to blip the throttle to keep the bike from stalling. The issue persisted on my ride home, even after parking in the shade while in the store.

I'm not sure what the issue is. The weather is almost identical to Tuesday. I can only suspect that perhaps a carb has gotten gummed up. I added a fuel system cleaner to the tank when I filled it up last week. So maybe it has worked some hard stuck gunk loose and created a clog.

 

[GuyS]

Tuesday I rode to the lake and back. Put about 26 miles on the bike and it rode great the whole time. I sat in this parking lot and let it idle for about 5 minutes and it did so perfectly maintaining 1200 RPM.

View attachment 39076

Today I started it, let it warm up while I put my gear on, then rode a couple miles to the auto parts store to buy some detailing products. At a stoplight, I noticed my idle had dropped to maybe 800RPM and I had to blip the throttle to keep the bike from stalling. The issue persisted on my ride home, even after parking in the shade while in the store.

I'm not sure what the issue is. The weather is almost identical to Tuesday. I can only suspect that perhaps a carb has gotten gummed up. I added a fuel system cleaner to the tank when I filled it up last week. So maybe it has worked some hard stuck gunk loose and created a clog.

Not sure what it could be either. The pilot jets have such a small opening…….?

 

[Lemonysword]

Took it for a short ride to let it warm up, then tried adjusting the adjusting the idle set screw and still had the issue. The right muffler was popping the whole time I was riding. I went down to inspect it and found that the cap over the right side intake boot port had somehow fallen off. Replaced it, readjusted the idle, and it ran great while I rode around for a half hour or so

I also washed, buffed, polished and waxed it yesterday. It didn't fix all the errors in the paint, granted I did it by hand and I'm sure a machine would have made better work of it, but it looks pretty good now. I also took the tank emblems and painted them since they were really delaminated. It looks good up to about 5 feet away, so as much as I like the yellow pop of color, i ordered some new emblems from mikes XS.

 

[GuyS]

Good to know. Ya that vacuum leak (from the cap missing) would do it for sure. You must of went to a manual shut off for the petcock? Your bike is looking really nice! These old 400cc Yamaha’s are really the quintessential classic bike. I’m waiting for parts but spending some time on detailing mine. I’m using rubbing compound on the engine case covers. While not all of the black spots are coming out, they’re starting to clean up real nice.

 

[Lemonysword]

Good to know. Ya that vacuum leak (from the cap missing) would do it for sure. You must of went to a manual shut off for the petcock? Your bike is looking really nice! These old 400cc Yamaha’s are really the quintessential classic bike. I’m waiting for parts but spending some time on detailing mine. I’m using rubbing compound on the engine case covers. While not all of the black spots are coming out, they’re starting to clean up real nice.

Nope, I kept the vacuum petcock. The left side is connected to the petcock, the right side was capped. I have no idea how a cap wriggled itself off of that, but if it happens again I might just epoxy the spigot closed.

Did you use an electric buffer on the engine covers? I used some mother's metal polish on all the chrome as well as the engine covers. It didn't remove the spots but it lightened them up a bit. Eventually I'm going to buy an electric buffer and really make this shine.

Here are some before/after shots of the main defects in my tank paint.

 

[GuyS]

Good to know. Ya that vacuum leak (from the cap missing) would do it for sure. You must of went to a manual shut off for the petcock? Your bike is looking really nice! These old 400cc Yamaha’s are really the quintessential classic bike. I’m waiting for parts but spending some time on detailing mine. I’m using rubbing compound on the engine case covers.

Nope, I kept the vacuum petcock. The left side is connected to the petcock, the right side was capped. I have no idea how a cap wriggled itself off of that, but if it happens again I might just epoxy the spigot closed.

Did you use an electric buffer on the engine covers? I used some mother's metal polish on all the chrome as well as the engine covers. It didn't remove the spots but it lightened them up a bit. Eventually I'm going to buy an electric buffer and really make this shine.

Here are some before/after shots of the main defects in my tank paint.

The vacuum is T’d from both carb boots on mine. I wonder why they did that instead of just one vacuum line to the tank? I haven’t got to the stage of testing my petcock yet. Apparently it doesn’t take very much vacuum on the petcock to allow fuel to flow through to the fuel line/carbs. I just bought some drill buffer attachments from Amazon and used the drill to apply/polish using ordinary automotive rubbing compound. Seems to work OK but like you didn’t get rid of everything. And is takes some time and work on the buffing process too.

 

[Lemonysword]

Good to know. Ya that vacuum leak (from the cap missing) would do it for sure. You must of went to a manual shut off for the petcock? Your bike is looking really nice! These old 400cc Yamaha’s are really the quintessential classic bike. I’m waiting for parts but spending some time on detailing mine. I’m using rubbing compound on the engine case covers.

The vacuum is T’d from both carb boots on mine. I wonder why they did that instead of just one vacuum line to the tank? I haven’t got to the stage of testing my petcock yet. Apparently it doesn’t take very much vacuum on the petcock to allow fuel to flow through to the fuel line/carbs. I just bought some drill buffer attachments from Amazon and used the drill to apply/polish using ordinary automotive rubbing compound. Seems to work OK but like you didn’t get rid of everything. And is takes some time and work on the buffing process too.

I might have to get some line and a T; I rode a few miles today and experiences the same symptoms. Pulled over and the cap I put on the line was gone again. I put another one on and zip tied it, rode around some more and it seems to be holding on.

A side note, when I first reached down to feel if the cap was on while the bike was running, I received some shocks from the spark plug cables, so I guess it's time to replace those too.

 

[JohnP]

I had polished a lot of side covers. I found it best to use paint stripper on them first as they usually are clear coated from the factory. If they have any deep scratches I would start with a fine flat file then #320, #600, #1000 grit wet/dry paper with water followed by buffing compound. If I had the covers off I used my bench grinder with a buffing wheel and on the bike I would use a drill and Dremel for the tight spots. once done Mothers was the best I found to maintain the finish.

 

[Lemonysword]

I had polished a lot of side covers. I found it best to use paint stripper on them first as they usually are clear coated from the factory. If they have any deep scratches I would start with a fine flat file then #320, #600, #1000 grit wet/dry paper with water followed by buffing compound. If I had the covers off I used my bench grinder with a buffing wheel and on the bike I would use a drill and Dremel for the tight spots. once done Mothers was the best I found to maintain the finish.

Thanks for the writeup. I found a pic you posted of your bike and the side covers look great.

 

[avemachina]

JohnP's got great advice. My Spinning Wheel of Death is more of a brute-force, still-on-the bike way to do it. Do as he does, not as I do!

Mother's really is incredible stuff, I've gotten near-mirror shine on some of the parts I've used it on.

 

[Lemonysword]

JohnP's got great advice. My Spinning Wheel of Death is more of a brute-force, still-on-the bike way to do it. Do as he does, not as I do!

Mother's really is incredible stuff, I've gotten near-mirror shine on some of the parts I've used it on.

I'll probably leave the right side on the bike to do it, the left side panels I'm more willing to take off.

I bought some mothers last week when I detailed my bike. It really made all the aluminum and chrome shine. It didn't remove the oxidation on the fork covers or the engine case but it did mute it.

 

[GuyS]

These are such gorgeous old bikes!

 

[Lemonysword]

Well I've put 120 miles on the bike. It's been running great; warms up by the time I reach the end of my street and idles perfectly at 1200.

the last couple times I rode it, however, I had difficulty starting (required me to hold some throttle), rpm would stay below 1000 during idle and eventually stall out. Starting with a choke, I'd get idle over 2000 rpm, then it would stall out and die. The idle does not improve even after it is fully warmed up, and while riding I can tell the engine is inconsistent; the sound of the exhaust favors one side over the other and sounds jumpy, if I had to pick a word to describe it. The left side also does not warm up as fast or as much as the right based off the temp of the header.

I have two theories and I will attempt to rectify them tomorrow. The first is the spark plug cable: they are original and the shield around the cable is completely degraded. I remember feeling sparks jumping onto on my hand when I was messing with the little plug over the intake port on the carb boot a while back. A leak in the cover I put over the intake port on the right side is my second guess, as a leaner condition on the right side would definitely make that side hotter. However, a bad spark plug cable on the left would also lead to that difference.

Tomorrow I am going to Napa to get more spark plug cable and cable insulator if they sell it. I'm also going to buy some more vacuum line and a T connector to have both intake ports connected to the petcock instead of relying on a little rubber condom to keep air out of the right side.

 

[GuyS]

It would be interesting to find out what is the cause and what works Lemonysword. All of these “curve balls” these bikes throw at us eventually get answered!

 

[JohnP]

I'll probably leave the right side on the bike to do it, the left side panels I'm more willing to take off.

I bought some mothers last week when I detailed my bike. It really made all the aluminum and chrome shine. It didn't remove the oxidation on the fork covers or the engine case but it did mute it.View attachment 39089

They clear coat the aluminum from the factory and to get down to the actual metal that has to be removed. Minute scratches and chips let the aluminum oxidize under the surrounding clear. Using paint stripper first removes that barrier.

 

[Lemonysword]

Well, new spark plug cables and I connected both input ports to the vacuum line on the carb. I also swapped the throttle cable and greased the handlebar under the twist grip. It runs better but still doesn't want to idle at 1200 and I don't have much room left in the idle adjustment screw on the carb. I am assuming it is the air screws that need adjusted but I don't have a manometer nor do I know exactly where they should be set.

 

[GuyS]

Did you check the pilot jets? Are they the 42.5’s (I’m pretty sure that’s the spec’s)? How about the main jet sizes? Are they stock sized? How about the valve clearances? I once had a 320i BMW that was not happy idling, in fact it wouldn’t pass emissions. Then I discovered one valve had no clearance at all, and was in essence staying open. Set the valve clearance and bingo,…. it ran like a new car.

 

[Lemonysword]

Did you check the pilot jets? Are they the 42.5’s (I’m pretty sure that’s the spec’s)? How about the main jet sizes? Are they stock sized? How about the valve clearances? I once had a 320i BMW that was not happy idling, in fact it wouldn’t pass emissions. Then I discovered one valve had no clearance at all, and was in essence staying open. Set the valve clearance and bingo,…. it ran like a new car.

I had adjusted the valves per the manual last time I worked on the bike 5 years ago. I'd hope they wouldn't be out after just 120 miles.

I'd be more inclined to believe that I may have a clog in the carb. Maybe something shaken loose that hadn't come out in my deep cleaning. I'm not sure offhand what size the jets are but they are the ones that were in the carb already; they were in good shape and I reused them.

I suppose it could also be a float depth setting, but it's a little odd that the bike was running perfectly and all of a sudden is not.
It's not atrocious, but it's not running as well as it was last week.