high rpm missing

650rider · WebMaster Joined: Feb 09, 2005 Posts: 431

I have a question? What would be the most common reason for high rpm (around 5000) missing? Here is the setup, I'm pulling on to the highway, not really hard but running perity good and sometimes I get a missing, kinda of a spitting thing around the 4700 to 5000 rpm's. it's not much but it gives me a little uneasy feeling.

BALLZ · New Member Joined: Jun 02, 2005 Posts: 1 Location: canada

mine to i`m thinkin prolly the springs on the advancer are worn out

flavaz33 · Posted: June 15, 2005, 9:24 pm Post subject: Re: high rpm missing

my power drops off when im above 5 grand also, or gettin on it too hard. If i leave off and slowly ease the throttle it seems to hold the power longer. Im running open pipes, thinking it may be too little back pressure, but it sort of did this too me a couple times last year when i still had everything stock.

650rider · WebMaster Joined: Feb 09, 2005 Posts: 431

I'm gone look at the spring and "see" how it looks in there. It seems like a resonable answer, let you know what I find.

But first where is the spring, remember I'm a web master not a mechanic. Smile

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

The advance springs are on the top right side of the head where the chrome cap is,just remove it and check for the return movement. If it sticks,either the springs have lost their tension or the cam bushing ends need to be regreased for this you'll need to remove the complete advance assembly. Check the sparks plugs for wear or maybe the plug wires need to be updated. Check the valve lash. Just do a complete tune up as most misfires are related to ignition and the caburators.............jack

650rider · WebMaster Joined: Feb 09, 2005 Posts: 431

Thanks jack,
I'll be looking into this on sunday.

flavaz33 · Posted: June 16, 2005, 9:19 pm Post subject: Re: high rpm missing

I have an 83 Heritage Special, and i dont have the advance springs, (unless im just not seeing whats right in front of me) so what could my problem be?

mo650chopper · Posted: June 17, 2005, 12:30 pm Post subject: Re: high rpm missing

I raised where my mines starts cutting out up to around 6,000 RPM from about 4,500 RPM by putting the hotter coil from Mikes XS on my electronic ignitioned 80. I'm also running the straight Mac Drag pipes that flow better than the previously cut off stock. I think if I step down a jet or 2 on my main, as I'm still running a little too rich, I'll have it right on!

flavaz33 · Posted: June 18, 2005, 2:33 pm Post subject: Re: high rpm missing

My next project was goin to be upgrading the coil, wires, ect. so hopefuly that will help. I didnt think about playin around with the jets, so i may look into that too. And how do those Mac pipes sound? Are they baffled at all? Thanks again Mo.

Flavaz

mo650chopper · Posted: June 18, 2005, 4:55 pm Post subject: Re: high rpm missing

I'm running mine straight. I'm kinda "Old School" in the "Loud Pipes Save Lives" thing. The new coil and wires helped alot on mine.

grizld1 · Posted: June 20, 2005, 11:07 pm Post subject: Re: high rpm missing

Uh, guys, the advance springs have nothin' to do with a high-rpm miss. When the engine picks up any significant rpm's the little weights on the springs are thrown out against the tabs on the advance rotor. The springs are only there to pull the weights (and ignition cam rod with 'em) back to the start/idle position. Nevertheless, the advance unit causes grief, because sooner or later (usually sooner!) things wear, and the retard/advance interval stretches, so that a bike properly timed on the idle mark will be too far advanced in the running mode. This burns holes in piston crowns.

If this has happened, don't even think about trying to cheat the idle timing back to put the high-speed timing where it should be. At best you'll give yourself a helluva lo-rpm dead spot; and I've seen backfires from retarded ignitions pop XS carbs right out of the boots. And don't try tapping/bending the tabs in. They'll break within 2000 miles. I had to go there and do that and end up DOR twice before I realized that Mama Yama wasn't lyin' when she said not to do it. There are two fixes. One is a Boyer ignition which gets rid of the mechanical advancer. The other is to lay a thin layer of braze on each weight where it's stopped by the rotor tab and file the brazing down till the right interval is achieved. Good luck!

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

Great tip there..............but rather than brazing in extra weight on the mechanical weights thus affecting the mechanical advance timing,it would be best to apply this to the tabs themselfs.........as I TOO have been down that road....................Jack

grizld1 · Posted: June 21, 2005, 10:00 am Post subject: Re: high rpm missing

Not a good idea to get the tabs that hot, Jack. They're tempered, which is why they're so brittle. You shouldn't wind up with enough new material to affect operation if the return springs, ignition shaft and bushings are in good order (or at least I didn't). But you're right, enough stuff could wind up on the weights to cause a problem, so it might be a good precaution to weigh the weights before and after, and equalize by removing material in a noncritical area after filing them in. I went with a Boyer ignition back about 1997, when I found one on sale. A Ford van ate that bike (but I got even--landed on its hood and cracked hell out of its windshield with my helmet) and I moved the Boyer to the next XS650 I built. Tried the new microstep Boyer with the low-impedance coil awhile back, for yucks. The brainbox failed shortly after the 30-day warrantee expired. Put the 8 year old unit back on and bought another 4-stage Boyer and stashed it for future use!

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

It appears Boyer's having a few manufacturing issues which is leading to alot of failures ,which is why I went with a Newtronics sytem and since I"m rephasing my XS,it'll fit right in and I'm still able to tinker with the advance system rather than a box Mr. Green

After recurving distributors for myself and alot of friends for drag racing,it's hard to pull away from what you know works cuz it's a proven system, if kept in working order. Just to old fashioned I guess Laughing

.............Jack

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