I've been having some of these same issues and decided to post in this thread.
My 2002 1600 has a distinct pop/flaring coming from the rear exhaust pipe. The front cylinder exhaust sounds regular and subtle as I would expect both to sound. I have placed my hand softly over the exhaust pipes one at a time and feel/hear a distinct difference. The pop/flaring sound seems to hit at every other combustion cycle on the rear cylinder only. When I ride, I can hear the distinct sound in the exhaust, hear a plunking sound coming from the engine that hits in unison with the exhaust sound, and a very heavy vibration that gets worse as the engine gets warmer. I checked the compression and it is within specs. I installed new intake O rings on the intake which seemed to improve greatly. The vibration almost disappeared, but the popping/flaring remained. My brother-in-law rode it 10 minutes and said it ran better than when he had it --- until the next day when I drove it 25 minutes to work. As it heated up, the vibration returned and got worse with heating. (I'm not sure, but the rear cylinder seems to get hot, although I did not compare with front.)I removed the intake again and applied high-heat silicone around the flanges, re-installed it and let it sit for 24 hours. I took it out and the noises and vibrations were evident from the start. I was going to swap the coils and plug wires to see if there is any change, but found that the wires were attached to the coils and did not want to pull them apart. I'm thinking of getting Nemesis coils and wires in hope that they would resolve this, but don't want to be disappointed if this is not cleared up after spending more $ .
I have been considering valve timing, valve damage or lash and do not know how one cylinder can be hitting harder every other combustion cycle. The popping sound is like one would expect from and exhaust with no baffles installed(which I have). I have been a backyard mechanic all my life and have spent countless hours on gas and diesel engines and am confused over this one. It is a really nice scoot, but I can't ride even 50 miles on it. I want to clear up this problem and am ready to pop off the valve cover on the rear.

Sorry for being long-winded , but any direction or help would be GREATLY appreciated.

Rayjay

I printed out some My Star parts schematics and pages from the service manual I found online and will be checking things. Does anyone know where the ignition pickup coil is? I looked on the Yamaha My Star parts list and it's nowhere to be found.
Rayjay

When I take off the carburetor or the intake manifold there is some raw gas in the intake manifold. Should this be? Is this common or am I looking at a high fuel level or some other issue here....and can that be causing the previously described conditions on my scoot ???
Rayjay

I went to my downloaded Service Manual and printed out pages from section 7-14 thru 7-16 describing troubleshooting sequence for ignition electrical problems. My Dad and I went through all the steps (except one where I didn't have the dynamic spark tester described) and found that the ignition PICKUP COIL was defective (according to my ohm meter).
I went to local dealer and ordered the parts -- pickup coil, gasket, damaged screw, oil drain plug w/ gasket -- and will get back next weekend on this.

After I discovered the above, I remembered a Park Avenue I had that would run badly and then die out when I reached a certain point in my commute until it got worse. It turned out to be the crank sensor warming up to the point of failure! Same type of device as on my R* Hope this it!

BTW -- All the interior wire retainer screws and the oil plug had loctite on them!! I eventually heated them to get them out except the oil plug. I'll work on that this week. The Y parts manager said to not heat the engine case to loosen the locktite on the oil plug because the case is cast and it will ruin the threads making matters worse. However, I think some heating is advisable, or it's not coming off!
Also, the pickup coil is listed on the stator page from the blowup/parts list on the Yamaha's listing. Total cost so far not including new synthetic oil and filter = $80.00
Rayjay

Refer to CARBURATOR COMPONETS AND JETTING You Notice Raw gas in the intake.... yer running to rich... possibly your accelerator pump! Turn only the accelerator pump screw in.... crack open the throttle till it pops out of the carb which means it is too lean back screw out 1/4 to 1/2 of a turn they always set them a little to rich! generally 2 1/2 turns from seated against the upper jam nut.

Black Snake

Here's where I found the Owner's Manual and the Service Manual online. I downloaded them and access them on my PC. When I need pages I print out only those I need to reference.
http://www.ras123.com/roadstar/docs.htm

Thanks for the info on carb settings Blacksnake. I'll check it out .
Rayjay

Blacksnake, I checked the screw and it was out 5 turns. I set it at 2 1/2 as you recommended. I don't know yet if the raw gas has disappeared. I think it might also be related to the rear cylinder possible coughing back (see below), causing gas to coat the manifold from the disturbance.

In addition to my vibration situation stated above in this thread, I replaced the pickup coil and changed the oil. Put in Mobil One 10w30 and a new filter from Walmart. I checked the manual and put in the lower weight for cooler temps.

The vibration seemed to improve and I installed the stock seat which is cushier and eliminates alot of felt vibes. I don't like it because it pushes me forward about 3 inches and I need to stretch out (6'3).
I still have a vibration as the engine heats up it gets worse. I can only describe it as a bumping or heavy hit on the rear cylinder every other or so combustion cycle. I drove it at 8 mph in 1st gear with just enough throttle to keep the slack out from gearing. The bike would *surge* slightly every third or so combustion cycle. The rear cylinder exhaust seems to not cycle smoothly every cycle. It has a spurt or disturbance every second or third combustion cycle or so evidenced by a flaring of the exhaust sound rather than a mild bom bom.

What would be the symptoms of a bent valve stem, burned valve or sticking valve in a cylinder?? What would be the symptoms of a bad coil that hits bad every several firings??

The front cylinder is running perfectly. I would appreciate any suggestions as I don't want to go to the dealer and/or spend my way replacing parts to gain success.

Rayjay

Right now my options seem to be:

1) Swap coils to see if the front cylinder becomes the bad one.
2) Pull the rear cylinder head and check for valve damage.
3) Check timing and gearing to see if something is *off*
4) Check plugs to see if they are firing correctly (how?)
5) Get a new bike

Rayjay

Glad to hear that the "sewing machine" sound is normal. It concerned me for a while, but I couldn't think of any way to describe it. It could be coming from anywhere, but I seem to hear it towards the front of the bike. (because of the windshield, perhaps...)

Anyway, thanks!!

See my two previous posts on this thread.
Well got home and switched out the Dyna 3000 with the stock unit and no change in engine. Put Dyna back in. Switched coils to fire other cylinder -- no change in engine.

My next alternative is to either check valve timing or remove the head to check for bad valve(s) or cam.

For the life of me I can't figure out why the rear cylinder would hit harder every other firing cycle. When I ride I can feel it and as I go faster it becomes a vibration since the cylinders are not firing equally. The rear cylinder hits harder every other cycle causing an imbalance in the engine. I don't know how to explain it any better.

I haven't had a single response from this thread addressing this issue.

If I don't get any help here giving me another lead, I will just tear into the motor and find out what's going on.....eventually.

Again:
What would be the symptoms of a bent valve stem, burned valve or sticking valve in a cylinder??
Could the cam be damaged or the valve timing be off?
Could it be sucking in air from somewhere???

Rayjay