Breaking up @ 4500rpm

OK, well, here's the types of Mikuni jets you're going to need. The air jet uses a main jet actually, just flowing air instead of fuel in this case. It is what's commonly called the "small round main", Mikuni type N102/122. This is also the type of main used in all the BS38s. The actual BS34 main is what's commonly called the "large round" type, Mikuni #N100/604 .....

M98LIeO.png


For the pilot jet, you need a BS30/96 type. It is physically the same size and shape as the VM22/210 type pilot that some of the BS38s use, but the location of the metering orifice differs. Your BS34s need and are designed for the BS30/96 pilot with it's metering orifice on the bottom. It's easy to tell the 2 types apart by just looking at the bottoms .....

Uoaj1xt.jpg
 
5twins said:
OK, well, here's the types of Mikuni jets you're going to need. The air jet uses a main jet actually, just flowing air instead of fuel in this case. It is what's commonly called the "small round main", Mikuni type N102/122. This is also the type of main used in all the BS38s. The actual BS34 main is what's commonly called the "large round" type, Mikuni #N100/604 .....

M98LIeO.png


For the pilot jet, you need a BS30/96 type. It is physically the same size and shape as the VM22/210 type pilot that some of the BS38s use, but the location of the metering orifice differs. Your BS34s need and are designed for the BS30/96 pilot with it's metering orifice on the bottom. It's easy to tell the 2 types apart by just looking at the bottoms .....

Uoaj1xt.jpg
Click to expand...
Thank you so much for this info. I was quite confused about what to order. I plan on ordering several and using this time to experiment and to apply the knowledge shared in the guide. Actually, I am quite excited about the fact that this my next journey with this bike. I'm at the point now where pulling the carbs and taking them apart is a short order. I know I have to be careful with the diaphragms.
Again, thanks and I will continue to update.
Rob
 
Hey FiveTwins and Brassneck and all who chimed in on this issue, I am happy to say that the bike is now running through the entire power band with no hiccups, coughs, burps or farts. I did the gggGary mod and almost really messed things up. I tightened the screws on the plate at the bottom of the slide a little too tightly and it caused the slides to stick open. It took me quite a while to figure out how to fix that and then I just loosened the screws until the slides slid smoothly. I guess that spring at the bottom is to put tension on the plate, but not distort the slide.
Anyway, the PO left me with two 135 mains...there were 132.5s in there. I switched them out. It may run a little rich and if so, I'll try to adjust for that. The pilots are 42.5 andI will probably get the 45s to try at some time. The air jets are 135s and I will probably get a set of 130s to try at some time, but right now I am going to put some miles on it and see how the plugs look. Right now I am pleased.
So thanks again for this forum. I really feel like I have a handle on the carb situation. Five disassemblies and reassembly and reading and rereading the carb guide gives one a little more confidence.
Grace and Peace and safe riding, All!
 
Congrats, sounds like you've got things well in hand. Carb re-jetting for mods is all about experimenting. We can give you suggestions, "ball park" jet sizes that have worked for others, but every one of these machines is a little different. By that I mean the engine's condition. That's what mostly determines the exact jetting you need. For what it's worth, many have reported that 135 mains (one step up from stock) work well even on a totally stock machine having no mods at all, so they should work well for you.
 
Hey 5twins, my problem continues. I am now a carb cleaning and adjusting fool...I mean expert. Thanks for all the jetting advice. I can't wait till the bike runs again so I can learn to fine tune this machine. In the meantime...
The problem continues. It starts one or two kicks, the fuel line is clear and runs perfectly. The floats are set at 27mm. All is well there.
My friend, Michael Coffey suggested that it might be a bad coil. All seems good until the engine warms up 3-5 miles and then break up.
I have scoured the posts on coils and found that if they get too hot they can fail. I noticed yesterday while testing my coils that when I installed Mikes 17-6903, that I used rubber tubing for the stand offs instead of metal ones as Pete suggested in his instructions.
Now, I am going to get metal standoffs and see if they dissipate the heat better, but have I screwed this coil? I supposed that after several seasons of riding and allowing it to heat up that I may have worn it out. Should I just screw it and order another coil and mount it properly?
Does heat+coil = misfiring. It sounds and acts like lack of gas, but it could just be a worn out coil. Whatcha think?
Thanks for all your input.
Rob
 
Yes, I suppose it could be the coil. It's not that they get too hot, it's just that when problems with them occur, it is usually when they are hot or warmed up to operating temperature. Obviously, it's difficult to test for. Testing the coil cold will usually indicate it's fine. As with most electrical stuff, substitution is the best test.

I'm not crazy about the Mike's Chinese coils. A fair amount of problems have been reported on them. Basically, it seems they're just not all that reliable because they're a cheap Chinese product. I suppose you could get a good one but the chances are probably just as good that you won't. Or one like yours that works for a while but doesn't last. I'd rather spend my money on a known brand name or some proven O.E.M. coil from some other bike. And speaking of that, some guys here have had great success using a Honda MP08 coil. It was used on many Hondas throughout the '90s including the Goldwing and is supposedly pretty near bulletproof. Here's a thread with some more info on it .....

http://www.xs650.com/threads/honda-coil.48730/
 
Well, it's not the coil. I put a new 6903 in from Mikes. I also have the Honda coil, which I will try out some day.
I am very frustrated at this point.
The bike starts cold and then starts breaking up when it warms up. I can get about two to three miles and then it's shake rattle and roll all the way home. The part that mystifies me is that is surges like it really wants to take off and then stumbles. I'll get three r fur seconds of surge and then it stumbles and then surges and stumbles.
I believe I am goin to test the Pamco next.
 
I had a somewhat similar problem a little while ago.

Bike would start fine, idle fine, but when I would start riding it would stumble and breakdown at 3000-3500 just like it was running out of gas.

I see you have an 81, so I guess you would have a TCI.
This was on my 77D which has points ignition.
Points were burned, condenser was bad but after replacing those, not as bad but still stumbled.
Turned out to be really loose female bullet connectors on the coil/points wires.

I crimped them all tighter with a small pair of needle nose pliers, problem solved.

Maybe a long shot but check the tightness of all your ignition wire connections.
 
I just replaced the coil. Adjusted the pamco (no tci) Tested pamco. Re timed the engine. Ran crazy great for ten minutes and then Bog.
Will recheck the wires on coil. Still at a loss.
What causes it to do this when it warms up?
 
Not familiar with the Pamco set up.

I would have thought your coil was breaking down when hot as well.

In my case it wasn't a case of warming up causing the problem, it was the vibrations at 3000-3500 causing the connectors to lose continuity.

You're certainly wrestling with a persistent gremlin.
You'll figure it out. Good luck!
 
Hey Noraz check your HT leads and make sure they are not cheap ones with poor insulation. I had an issues when the bike was warm and it seemed like a carb issue as I would grab a handful of throttle and just got no response. When cleaning and syncing the carbs for the third time i got a small zap touching the motor. Hunted down better HT leads and pulls like a train now.
In the photo one on the left is the old cheap one with poor insulation. Right is the new better insulated one.

IMG_20180927_141952.jpg
IMG_20180927_141952.jpg
 
Dude, thanks for that advice. One of the things I didn't change is the plug wires. I have some cool looking braided wires from TC Bros, but I will go back to my silicone ones from the past or find new ones. I don't think that's it, but hey, it's gotta be something. Today I will recheck every element in the combustion system.
Thanks,
Rob
 
ND, here's what happens with electrics that cause trouble when thngs get warm. Resistance causes heat. Heat causes more resistance. When that vicious cycle creates enough resistance, things stop working. Every connection in your ignition needs to be inspected and cleaned. If you've already been there and done that, try new plugs and plug caps, even if the ones you've been using are new. It doesn't happen often, but even NGK puts out a few that are bad out of the box, and many an old hand has been blindsided by assuming that new has to be good.
 
Exactly my plan today. I put in a new coil. I did the pamco test by removing the locator pin and checking for spark on both sides...cold. So I am going to swap out plug wires, caps and re check all electrical connections dealing with charging, Reg/Rec, battery and ignition including switches. It has to be there somewhere.
Thanks.
 
Ordered new wires and caps today. Checked plugs and they look fine. Both sides match. Re soldered all wire connections to and from my fuses. Re connected the connections to the kill/run switch. Retimed right on the money. Just died after ten minutes and won't start. Tomorrow is another day. Will continue replacing parts, but I think I'm on a fools errand. Pamco is working just fine. Did a full inspection, Tightened the advance rod and rotor...less play after the pamco test where you spin the advance rod with the engine off. Got plenty of spark both sides. Couldn't get to the regulator, but my volt meter shows charge under rpm. Battery is solid. Sits at 14.5 under power and drop back down to 13+ at idle.
 
Good, you got charge! Now open the headlight shell and find the wire bundle from the right handgrip. With the main switch on, check battery voltage, then check voltage on the brown wire in the handgrip bundle--it's the wire that carries power from the main switch to the kill switch. If there's more than .02V drop, the main switch needs either cleaning or replacement. The R/W wire in the bundle carries power from the kill switch to the ignition, safety relay, and starter solenoid. Check voltage there. If there's more than .01V difference from the voltage on the brown wire, the kill switch needs cleaning or replacement. Next check power to the coils and to the igniter box and clean or replace contacts if you find drops. That gremlin can hide, but he can't run--you'll catch the nasty rascal. Put him in a jar and shake it awhile, then let your cat have him.
 

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