Power loss

[IanDMacDonald]

I have now. The set of carbs I have on right now are 42.5 pilots, 140 mains and one notch lean on the jet needles.

As of this morning when it stops raining I'll be back to 42.5 pilots, 137.5 mains and one notch lean on the jet needles.

I'll se how that runs.

I have a feeling u'll be back to the 140's, but who knows. Yes, I understand your situation and why you question why ur bike randomly pukes-up a proven good tune. Who knows? But, it'll sort itself out.

[TopCatGr58]

Hey Greg,

Okay, I'll dive back in. The exhaust does sound vaguely familiar with regards to it getting clogged? I can't recall if you have worked on the mufflers and the baffles? My MAC 4-1's baffle is a simple louvered pipe design, so not much chance of it getting clogged. But if your baffles were Steel Wool or such, then years of carbon could build up in the mesh to cause a restriction??

I remember having a Ford T-bird with a 4 cylinder turbo, it was quite peppy. But then it became boggy, wouldn't take much throttle, etc.. Turned out that the innards of the Cat. convertor had broken up, got all turned sideways and such, so not smooth pathway thru the honeycomb structure, and essentially shut down the outflow. Once the Cat. Conv. was replaced, the engine came back to life.

JAT. T.C.

[BA80]

Update!

I think I may have stumbled upon the cause. And yes, it is a STUPID oversight on my part.

While I was putting together another set of carbs with stock jetting. Since I only have 2 sets of slides with good diaphragms I've been swapping them in and out between sets, I was swapping in the ones from my current set and accidentally snapped a needle off.

It's relevant here to say that the ORIGINAL carbs I pulled off had 3 of 4 diaphragms with tiny pinholes in them so I used another couple sets from parts carbs.

I went out to the pile-o-parts to get a needle of the same # however when I looked closely at the broken one I didn't see the Mikuni emblem and it seemed to be an unfamiliar number Y265 so I found a set of needles in my carb parts with the Mikuni emblem and sure enough I've been arguing with a set of aftermarket K&L needles. I haven't taken one from the other good slides I have but I'd be willing to bet they are K&L also. I did pull one from my original slides to see and sure enough, it's a Mikuni 5GZ6.

Here's a pic of the K&L and the Mikuni side by side....



The Mikuni 5GZ6 on the left and the K&L Y265 on the right. A VERY noticeable difference in taper.

I still need to pull the slides out of the third set and check to be sure but I'm pretty certain of what I'll find.

I'll be back.

[dbeardslee]

That'd sure do it. Did you say D'oh when you found it?

[BA80]

Well, crap!

I just checked the other set of slides and it has the CORRECT needles.

Back to square one.

I'm going ahead with my original plan for today but I'll be using the Mikuni parts.

[IanDMacDonald]

I think I may have stumbled upon the cause. And yes, it is a STUPID oversight on my part.

While I was putting together another set of carbs with stock jetting. Since I only have 2 sets of slides with good diaphragms I've been swapping them in and out between sets, I was swapping in the ones from my current set and accidentally snapped a needle off.

It's relevant here to say that the ORIGINAL carbs I pulled off had 3 of 4 diaphragms with tiny pinholes in them so I used another couple sets from parts carbs.

I went out to the pile-o-parts to get a needle of the same # however when I looked closely at the broken one I didn't see the Mikuni emblem and it seemed to be an unfamiliar number Y265 so I found a set of needles in my carb parts with the Mikuni emblem and sure enough I've been arguing with a set of aftermarket K&L needles. I haven't taken one from the other good slides I have but I'd be willing to bet they are K&L also. I did pull one from my original slides to see and sure enough, it's a Mikuni 5GZ6.

Here's a pic of the K&L and the Mikuni side by side....



The Mikuni 5GZ6 on the left and the K&L Y265 on the right. A VERY noticeable difference in taper.

I still need to pull the slides out of the third set and check to be sure but I'm pretty certain of what I'll find.

I'll be back.

Good deal Greg! Too bad ur not gonna be at XSSE.

[dbeardslee]

Well, crap!

I just checked the other set of slides and it has the CORRECT needles.

Back to square one.

I'm going ahead with my original plan for today but I'll be using the Mikuni parts.

When I look at the pic of the 5GZ6 I'm seeing some weird pitting and what looks like some wear about 1/3rd of the way down from the top of the needle. Do they all look like that?

[BA80]

Hey Greg,

Okay, I'll dive back in. The exhaust does sound vaguely familiar with regards to it getting clogged? I can't recall if you have worked on the mufflers and the baffles? My MAC 4-1's baffle is a simple louvered pipe design, so not much chance of it getting clogged. But if your baffles were Steel Wool or such, then years of carbon could build up in the mesh to cause a restriction??

I remember having a Ford T-bird with a 4 cylinder turbo, it was quite peppy. But then it became boggy, wouldn't take much throttle, etc.. Turned out that the innards of the Cat. convertor had broken up, got all turned sideways and such, so not smooth pathway thru the honeycomb structure, and essentially shut down the outflow. Once the Cat. Conv. was replaced, the engine came back to life.

JAT. T.C.

The baffles are not removable on these turnouts. Welded in.

I worked at Midas for 20+ years and I've experienced clogged exhaust A LOT. A clogged exhaust will limit RPMs, My RPMs aren't limited. In lower gears it'll tach up to 8-10K. It's just under load it messes up.

Doesn't mean I won't drop the mufflers and terrorize the neighborhood just as a test though.

[BA80]

When I look at the pic of the 5GZ6 I'm seeing some weird pitting and what looks like some wear about 1/3rd of the way down from the top of the needle. Do they all look like that?

That's me cleaning the crud off for the pic. It has some marks at the top of travel ( slide down) but as I said, I just pulled it out of the parts bucket.

[ernie elmore]

Re Power Loss as you open the throttle and carb slides. You may cure the problem with the correct slide needles, re the needle problem you discovered.

You mentioned that some of the carb slides had pinprick holes. This may have some effect in raising the slides in the CV carbs.

Some of us have replaced the XS1100 diaphragms the easy way. JBM Industries has a replacement diaphragm for the Mikuni 34MM CV carbs that takes the risk out of replacing this vital part. The new diaphragms slip into the old diaphragm grove on the slide, just follow directions on website. Best part, the diaphragms only cost $30 each. Only takes an hour to replace the diaphragms.

Good Luck

[BA80]

Re Power Loss as you open the throttle and carb slides. You may cure the problem with the correct slide needles, re the needle problem you discovered.

You mentioned that some of the carb slides had pinprick holes. This may have some effect in raising the slides in the CV carbs.

Some of us have replaced the XS1100 diaphragms the easy way. JBM Industries has a replacement diaphragm for the Mikuni 34MM CV carbs that takes the risk out of replacing this vital part. The new diaphragms slip into the old diaphragm grove on the slide, just follow directions on website. Best part, the diaphragms only cost $30 each. Only takes an hour to replace the diaphragms.

Good Luck

If you go back and read my post ernie you'll see that I'm not using those diaphragms. I have good ones in there now.

I've looked for diaphragms for these early carbs, seems they only make the replacements for the late carbs.

[BA80]

Just took a test ride. Still got some stumble at WOT in low gear, WOT stumble in high gear is nearly gone. I can still hear a little through the intake when I open it up at highway speeds.

I'm at stock 42.5 pilot, stock 137.5 main and needles 1 notch lean (1notch from the top)

Contemplating dropping the needles to the last notch.

Still not understanding why it likes it this lean now, especially with the Mac exhaust and pods.

I wonder if I should try a larger air jet??????????

[dbeardslee]

If you go back and read my post ernie you'll see that I'm not using those diaphragms. I have good ones in there now.

I've looked for diaphragms for these early carbs, seems they only make the replacements for the late carbs.

I think ernie actually had something with the JBM Industries diaphragms. Not that it's going to fix the current problem, but it does appear that they work on the early model slides. Here's a thread that shows the installation on BS34 carbs using 73mm diaphragms - Carb diaphragm replacement.

[dbeardslee]

Just took a test ride. Still got some stumble at WOT in low gear, WOT stumble in high gear is nearly gone. I can still hear a little through the intake when I open it up at highway speeds.

I'm at stock 42.5 pilot, stock 137.5 main and needles 1 notch lean (1notch from the top)

Contemplating dropping the needles to the last notch.

Still not understanding why it likes it this lean now, especially with the Mac exhaust and pods.

I wonder if I should try a larger air jet??????????

I'd try the needles on the last notch first. Your mains determine how much gas gets through, but the slide needles determine where in the rpm range that happens. On stuff like this I always try to only change one thing at a time so's not to muddy up the water.

[BA80]

On stuff like this I always try to only change one thing at a time so's not to muddy up the water.

Oh definitely, I was just thinking. My only other choice here if dropping the needles again doesn't work is a 135 main jet and raising the needles all the way.