What did you do with your XS today?

Lou: yeah, I was wondering if the p.o. changed the jet to compensate for another issue. Or maybe he stripped the original #117.5 and could only replace it with a #120 - I checked XS650 direct, who carries parts for the BS34 carbs on the DOHC bike, and it looks like they don't carry the #117.5, only the #115 and #120. Maybe I'll check with my local dealer. (Manual says #127.5 LH and #117.5 RH).

bcware: thanks for the tips.
- Diaphragms looked perfect the last two times I pulled the carbs apart to clean them.
- Air box is clean, and I blasted the filter out with compressed air. I'll clean it again, or think of replacing it.
- The rubber o-ring and washer for the mix screws were both replaced during the last carb rebuild.
- I've tried testing the butterfly seals by spraying the outside of the carbs with starter fluid, or fogging oil. Neither seemed to make the RPMs fluctuate, although the seals on the inside of the carbs are harder to get to. Might just order new ones for the next rebuild.
- The exhaust baffles had just a bit of surface rust, but they cleaned up and look good.

Also, the plugs on the carb boots are sealed off on both sides (I converted the petcock to an on/off when the diaphragm got a tear in it. haven't rebuilt it yet).

The choke/enricher does seem to act a bit funny. If the bike is idling and I put the choke on, the bike will die. If I rev up the engine to 2.5k or 3k and then pull the choke out half way, it will generally stay up there for a few minutes. Occasionally it falls back down and needs a bit of throttle to get it back up to 3k, and then it'll stay there while the choke is still on. Once I start riding and the bike warms up it idles fine down at 1.5k (I bumped up the idle so the throttle doesn't take as long to get above 2k when I'm ready to go again).

Did my first compression test finally. Right had 95, left 110...
The bike runs decently as is. Been riding since March and plan to end the season in September.

How do I fix this?

The way you're describing it you definitely sound too rich. Your plugs don't look bad though. Have they been replaced with new?

Is your throttle cable play properly adjusted?

Do your emulsion needles have clips or shims on them for adjustment or are they stock?

How many turns out are your mixture screws?

The larger main jet on one side should not have an effect at idle or in the mid range; it is only going to matter at high rpms or wide open throttle. It is unlikely to be the cause of your problems.

jthiessen said:

Did my first compression test finally. Right had 95, left 110...
The bike runs decently as is. Been riding since March and plan to end the season in September.

How do I fix this?

Click to expand...

Make sure you're doing the compression test right; hold the throttle all the way open. Give the bike several chances to turn over/kick it over several times.

Once you're done with this do a wet test; put a tablespoon of motor oil in each spark plug hole and repeat the test. If your compression goes UP when the oil is in the cylinder your rings are probably the issue. If there is no change your valves are probably at fault.

If it turns out to be the rings before doing anything else you might try putting something like marvel mystery oil in each cylinder to free up the rings/break up any carbon causing issues (if this is the case). I had issues with mine; the rings were stuck due to carbon build up. It is worth a try!

bcware said:

Make sure you're doing the compression test right; hold the throttle all the way open. Give the bike several chances to turn over/kick it over several times.

Once you're done with this do a wet test; put a tablespoon of motor oil in each spark plug hole and repeat the test. If your compression goes UP when the oil is in the cylinder your rings are probably the issue. If there is no change your valves are probably at fault.

If it turns out to be the rings before doing anything else you might try putting something like marvel mystery oil in each cylinder to free up the rings/break up any carbon causing issues (if this is the case). I had issues with mine; the rings were stuck due to carbon build up. It is worth a try!

Click to expand...

Throttle was wide open and I got the same results after adding oil.
Would I possibly see results using Marvel Mystery Oil or the like even though I drive it all the time? I was thinking of trying a seafoam treatment soon.

Is the worst case scenario opening up the top end and replacing rings?

If the compression stays the same with and without oil added to the cylinder it is likely not your rings; I would suspect the valves. The valves may not be sealing tightly.

Usually what we do is take off the top end and lap the valves, but you also need to make sure they are closing all the way. This can happen if there is too little valve clearance.

Finally, don't fix it if it ain't broke. If it seems to be running fine I would not tear it apart. Definitely check the valve clearances though. Tight valves can get burned. Valves tighten over time; they don't loosen. The valve essentially beats its way into the head of the motorcycle over time; this brings it closer to the rocker arm and as a result clearance is reduced and they get tighter. If it is bad they won't fully close.

Hay you two, go get your own thread! He is a mean looking guy.

We have all done this, regardless it is good info.

personally, This week I have checked out a valve, and went the opposite way than when I last rebuilt it. I had went to the loose side of the Exhaust valve spec (.020) and reduced it to the stricter side, of .016, and since close is .015, I left it a hair looser than .015.

That Valve side was producing more noise, Right now I tend to think it is better, there does seem to a noise I can associate with the Tach, or the cam chain.

Its running great right now! Been driving it all week now!

installed my piston rings and new fuse box, can someone tell me if the orientation of the rings are correct? It's been awhile and the manual doesn't have any pictures. I don't think they can fit any other way, but the top and center looked close to being able to swap.

I got my engine running nicely, right before I found a hole in the gas tank.

The old girl took this old girl up the mountain - part way. The bike couldn't handle the climb and altitude very well. It only went about 45 mph at 7000 RPM. I turned around at about 5500 feet above sea level.

It's probably time to clean the carbs, but I wonder how well it will do then? It works great commuting to work on the streets.

http://www.iwt.com.au/mikunicarb.htm all the way on the bottom, next to figure 8.

My first link I checked out, had a section on Altitude. It seems that if you live at that elevation, you might needed to change a jetting to be running well at that elevation. (as well as temp changes) Since I live at sea level, in MN, I haven't worried about that one. except for that one time I tried to go over the Mountains in Oregon (near Bend) Gas pedal all the way down, and still going about 45 or so. (crater lake, Or) Awesome place.

Thanks Tobie, this is great information. I'll definitely use this when I get into my carbs for the first time.

It looks like given the temperature range we have here, I'd need to have a summer setup and a not summer setup. Ditto if I want it to run well from my house at about 3000 feet to the mountain at about 8000 feet.

Don't consider that article to be gospel. It is written about the Mikuni flat slide carbs, not our CV carbs. It is easy to get confused and follow tuning suggestions that are wrong for our carbs.

Thanks for the heads-up Dave.

Today I took the honda shocks off and put the originals back on. At some point I think I wanted to make some kind of bobber thing and wanted to lower the back end. Well back to stock and now the center stand works again. And more clearance to work. Also cleaned and prepared the petcock for rebuild. Ordered the rebuild kit. Read all about rebuilds and lets hope that goes well

yesterday i filled out DMV paperwork for new plates, salvage reversal, salvage title, and registration.

today I got my VIN verification completed.

next step, brake and light inspection!

then i can finally explode it to pieces on the frame jig and workbench, woot.

Today, I tightened the chain, and topped off the oil. Just when I had thought I had the oil leaks fixed.

I wished I was riding. But I'm stuck doing chores at the cottage and drinking imported German beer like it was water (aka Coors Light). Monday can't come soon enough!

Treated it to a new one off seat

That seat looks great! Really like the way you matched the slope to the tank's shoulderline.

This weekend I took another run at laying up a fiberglass seat pan, and this time it seems to be coming out more straight. I installed a new mini-speedo/idiot light gauge. I also tried firing it up for the first time in months but no joy. Both my batteries are flat and possibly done for. Hopefully that's all that's preventing it starting. 'Swhat I get for not putting them on tenders.