Mikes commando mufflers, carburetor tuning question

[tkurt]

Hi everyone, This is my first time posting but I have been appreciating the collective wisdom for awhile now.

My situation is this: i have a 1977 xs650 that was running great. It has new OEM air filters. I decided to change to MikesXS commando style mufflers. After swapping out, the bike started to stumble in 1st gear or neutral, but really lunged forward when shifting into 2nd and ran fine from there.

I decided to go to a size 27.5 pilot jet and 127.5 main, one up from stock because all I changed was the mufflers, no pod filters. Is this correct? It doesn't seem to have changed the problem. I tried to adjust the fuel/air mix by the dead cylinder method, and the bike runs OK on the left cylinder and plug, but I can't get the right cylinder to fire at all. When I hook up the left plug & wire to the right cylinder I get some backfires through the carb, but nothing else. Did I screw up the jets? Is something else off?

Thanks for your help!!!

 

[rusty rocket]

I cant help you. But damn you have a nice looking bike.

 

[tkurt]

thanks Rusty!

 

[acebars]

Yea I like it too almost exactly the look I'm going for.. Less is more... Looks sweet and rugged... (and much nicer than the bobber/chopper crap people do to these bikes)

 

[5twins]

You may have had an electrical problem manifest itself at the same time you changed the mufflers. You can't just swap the plug wires. The cylinders fire 180° apart so the timing would be way off. That's why it just popped and backfired. If you want to test the plug/plug wire/plug cap/coil on the opposite cylinder to see if the problem changes sides, you need to switch the wires running to the coils from the points along with swapping the wires and plugs side to side.

 

[retiredgentleman]

Why don't you go back to the former jets you were using, as a test. As 5twins said, you can't just change the plugs leads over. That method only works with a single dual fire coil.

You should do a visual look at the spark, on the side that's not running, to determine if you have lost spark or not.

 

[tkurt]

Hi 5twins, thanks for the advice - i didn't realize that. I was looking things over again and discovered the right plug wire/cap connection is bad! Made a better connection and it seems to running fine now (hopefully that continues). I think I was led astray by all the carb work, and figured I had clogged something up or something. Thanks for the help.

 

[tkurt]

Good advice RG, thats what let me know there was a bad connection.

Acebars - believe it not this bike was hit by a car a couple months ago (I wasn't on it at the time, and both drivers are OK). I wanted something cafe-ish but relatively simple and not too much $$. Still working on it, but I like the way its going.

 

[5twins]

I see you changed the plug caps to NGKs (which is a good thing). You should also change out those 30 year old plug wires. That all black bike is just crying out for a splash of color. Yellow or red plug wires would do that. At the very least, you should trim the originals back 1/4" to 1/2" to get to some fresh wire then install the caps and connect to the coils. I like to strip the insulation back an additional 1/8" and fan the wire strands out like so. This insures you get a good connection .....

If you go for new wires, you can install the protection sleeve from one of the old wires on them. Cut it in half and use half on each wire to protect just the upper portion of wire where it exits from under the tank .....

 

[scabber]

Welcome to the site. That is a nice bike glad you got it sorted. The commando is the right choice nice sounding. 5twins you nailed it again.

 

[Rsteen]

Not trying to hijack, but what front fender is that?

 

[jd750ace]

Not trying to hijack, but what front fender is that?

Looks like stock 77 to me.

 

[tkurt]

i think the fender is off a '78 but any of the later years would probably fit.

Sweet tips 5twins, thanks!

 

[crashcourse]

I'm looking at switching to the commandos. People seem to like the sound, and if you're rejetting to get a good mixture then air flow is up. But how has the feel of the bike changed?

 

[nj1639]

Not trying to hijack, but what front fender is that?

Looks like a Special........stock'77 has a bit more angle or squareness to it.

 

[nj1639]

I'm looking at switching to the commandos. People seem to like the sound, and if you're rejetting to get a good mixture then air flow is up. But how has the feel of the bike changed?

Commandos with Unis here, TCI and bs34's on my '77...no change in jets and she runs great, sounds great too.

 

[tkurt]

I have the commandos and airboxes, and the bike runs great. This might be due to getting my carbs tuned better. I can't say it changes the ride, but it "feels" like a new bike in that it sounds so much better than the mufflers that the PO had on!

I have BS38s and went up on the pilot jet and main (see below)