My r90 restoration.

[Airhead Wrangler]

Have you checked compression when hot?

[blaine.hale]

Originally Posted by Airhead Wrangler

Have you checked compression when hot?

When hot, no.
Wasn't aware there would be too much variance there.
I pulled the carbs and checked when luke warm and they both were above 145psi within 2-3 psi of each other.

[Airhead Wrangler]

Originally Posted by blaine.hale

When hot, no.
Wasn't aware there would be too much variance there.
I pulled the carbs and checked when luke warm and they both were above 145psi within 2-3 psi of each other.

I'm still betting this is mixture or ignition related, it's something worth eliminating. You said you tried several sets of plug wires, but did you try different caps as well?

[blaine.hale]

Originally Posted by Airhead Wrangler

I'm still betting this is mixture or ignition related, it's something worth eliminating. You said you tried several sets of plug wires, but did you try different caps as well?

Yup. Each cable has different caps. 1 set was brand new out of the box, stock. Another set was from the r75 with 19k miles and another set was the euromoto high resistance set.

[Airhead Wrangler]

Weird. Does the exhaust coming out of that side smell really rich like unburnt gas when it's sputtering like that? It's got all the indications of running too rich. Is the choke assembled correctly? The rotor isn't upside down?

[blaine.hale]

Originally Posted by Airhead Wrangler

Weird. Does the exhaust coming out of that side smell really rich like unburnt gas when it's sputtering like that? It's got all the indications of running too rich. Is the choke assembled correctly? The rotor isn't upside down?

No gas smell, I'm afraid.
A weird thing is how hard it hits at idle. You can feel and hear the right exhaust being louder and hitting harder. The left side is just as you'd expect and not too harsh.
I'll double check my choke but it hasn't changed ever and has replicated all the other carbs I've done. I think there's even a little dot that indicates which way things point.
I'll switch to normal mixture and lean it a fair amount tonight and report back.

1 last thing. When playing with mixture screw, as it is now, leaning or richening has zero effect over the idle on the right side. Leaning it all the way in doesn't bog or kill things, same with all the way out.
The left side is pretty sensitive and bogs and even kills the bike if too rich or too lean (normal behavior.)

[onestop]

u dont't need to hook up cables to test if problem moves to the otherside .
have u checked to see if both header pipes get hot .

[Wirespokes]

Seems like we've got enough data already to figure this out.

It's not ignition since the problem didn't migrate swapping plug leads.

The mixture screw doesn't change idle speed.

Popping in the exhaust.

That tells me the right side is running rich. For whatever reason.

Maybe the butterfly is loose and way off center.

I was thinking you might have some compromised o-rings, but seems that would make for a lean mixture, not rich. Still, I'd check on that. Those o-rings can get split on the sharp edge of the o-ring groove and it'll be hidden from view. Gotta look close and prod a little to see it.

The choke is the other possibility. Not too many places where EXTRA gas will come from.

As difficult as it's been to track this one down, I'd say it will require some close scrutiny to figure out.

[blaine.hale]

I'll take a video of carb disassembly this week. It might drive ya'll as nuts as it has driven me.
That popping is actually the cylinder dropping. I bumped back to the original pilot/idle jet last night and leaned the mixture screw in as far as possible and still got the same issue. The butterfly valve hasn't changed since day 1 but I went ahead and disassembled it before the carb body went in the carb dip.

What are the symptoms of piston rings not seating properly or even being broken/blown? Does any of this sound like a valve issue, maybe one is sticking every other cycle or something?

[Tin Woodman]

I'm in the process of completing (29 year process - I don't like to rush into anything) the restoration of a 73 R60/5. Couldn't for the life of me figure out the routing of the wiring harness from mid-frame to the tail lights. Then I saw one of your photos that showed the cable mysteriously emerging from the frame near the tail light - that was the Ah Ha moment. I rushed to the garage and found the two subtle holes in the frame. Don't know why I didn't figure it out myself - too stupid I guess. Photos are excellent! And your restoration is a great read.

[Wirespokes]

Hey, I was fixing dinner and had an idea what the problem might be, so dropped everything to post this.

One of my bikes had a problem with a float bowl overflowing and it drove me nuts. The float was set properly and turned off at the correct place, but then one time while taking a closer look, it seemed like the float needle was getting stuck.

Upon closer inspection, the sharp edge of the float needle had dug a groove in the brass of the float tang, and was hanging up in that. The float would drop, get stuck down and then not stop the flow. Anymore, I chamfer the edges of those needles to prevent that.

[blaine.hale]

Originally Posted by Wirespokes

Hey, I was fixing dinner and had an idea what the problem might be, so dropped everything to post this.

One of my bikes had a problem with a float bowl overflowing and it drove me nuts. The float was set properly and turned off at the correct place, but then one time while taking a closer look, it seemed like the float needle was getting stuck.

Upon closer inspection, the sharp edge of the float needle had dug a groove in the brass of the float tang, and was hanging up in that. The float would drop, get stuck down and then not stop the flow. Anymore, I chamfer the edges of those needles to prevent that.

I have succeeded in creating a good mystery when I can stop someone in their tracks with an epiphany!
Funny, I was thinking about that when i pulled the bowl the other night. I cut the fuel the unlatched the bowl and the second I lowered it, fuel dumps all over me and the level of fuel in the bowl was about 3/4 to full. That carb has never leaked but I've almost always noticed the bottom of the bowl having a bit of fuel on the bottom.
I'm going to check that one tomorrow...even if not the cause, that's not a good thing to keep around.

[Wirespokes]

...the second I lowered it, fuel dumps all over me and the level of fuel in the bowl was about 3/4 to full.

For whatever reason, it sure sounds like the fuel level is too high on that side. I'll bet THAT'S the problem! Especially from what you just said!

Next step is to figure out why.

[blaine.hale]

Been a while...
I pulled the r90 out yesterday. Cranked right up after not having touched it for 2-3 months, so I figured...why not ride it.
This time, I left the right side choke up (on). Remember, this is the cylinder that has been dropping within 10 minutes of riding the bike.
Wouldn't you know it, dang thing ran fine the entire day. Granted, smelled a bit like gas from running rich with the choke open...but that gives me an idea of what's going on.