Bad Hesitation

Ding said:
Secondary wire should be measured to the male connector and 5.4K - 7.4K ohms - if you leave your plug caps on they should read between 10.K - 12.4K ohms.
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That's weird. I have 5 original yamaha coils infront of me and all have 3300 to 3400 ohms. All in spec with the Clymer book. Time will tell I guess.
Already ordered three new plug caps from Royal D.
 
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Ding said:
The pic nst115 posted matches what I have.
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Those specs look like redhead 700 dual bulb headlight/300W stator specs.

The OEM specs I have for redhead 700 single bulb headlight/175W stator are the same as shown in the Clymer manual pic.
 
Ding said:
Somehow I have a feeling that you issue might be deeper, but start eliminating things one at a time.
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Well sir, you were correct. New plug boots didn't fix it. I verified good spark across all three. Bummer. More troubleshooting to come.
 
Just to recap on what's going on. My engine has a missfire / runs rough between 4000 and 7000 rpms. Starts and idles fine, seem to clear up passed 7k.

So at this point I'll clean my flywheel. Do I need to clean it inside and out?
I'll check the stator with multimeter. I've been told usually a weak stator will cause a dim headlight witch I don't have.

I'm also thinking of trying to fined a used CDI, as in the pass I've seen these cause simular problems on other two stroke applications.

I'm starting to get desperate enough to remove the carbs and check them for the third time!

Any other ideas?
 
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Victory!

Went out for a ride this morning. It was snowing alot. Trails were nice, good -12c weather. Sled ran 90% perfect with only a slight miss at 6500 rpms once in a while. I was so happy to be enjoying my sled again.


shaggyzr2 said:
what were the temps when you were riding? maybe jetted rich for conditions.
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This was probably 1/2 of the problem.

Turned out my problem was combination of things working against me.

-Two spark plug caps were on the verge of failure.

- Flywheel was very rusty. Don't know how much that effected things.

- My air filter screen on my air box had completly deteriated and wasn't sealing right. Causing at time snow ingestion. When i replaced with new foam and sealing strips it seemed to have richen the engine more

-Resetting my carb needles to factory specs. Worked great in the cold -20c weather but made the sled barely drivable when the weather warmed up.

T'ill two days ago started dropping down the needle on #1 carb a bit as it had the darkest plug. That helped. Even though the other two plugs were light in color I tried leaning them a 1/2 notch too. Things improved dramatically! I've been driving , checking plugs, and making small changes. Little by little throttle response improved. What a learning experience. Hoping the mystery is solved

Thanks for all the help guys.
 
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Well victory was short lived. Did bunch of riding without the mysterious 6000 rpm hesitation but my last two rides it started happening again. Most times all is well but once in a while the mis / hesitation returns. Seems more prone to it when the weather warms up. It's not as bad as it was in the past but it still a pain in the ***! I'm out of ideas. Still drive the sled alot and it runs well 95% of the time. Just wish I could find a solution to this problem.
 
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Very interesting as my 700SX has a miss (stutter) around 6000rpm noticed mostly around 25-30*F didn't notice last year and Just rebuilt the motor (top/bottom)
 
Mine gets very noticeable. Like it's running only on two cylinders or the choke lightly on. Weird thing is its not consistent.
 
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I am going to try and run it with the belt off tomorrow and see if it still happens after i pulled carbs and re-adjusted throttle and oil.

If it does I will try and get a video to see if they are similar.
 
Another important detail to add is when the hesitation does happen. If I maintain 6000 to 6800ish rpms the hesitation can keep going for many kms. It can only be avoided by driving in a higher or lower rpm range. Sometimes I'll stop my sled. Check the plug in an attempt to troubleshoot. Plugs are always dry and look the same as when the engine runs good. Once driving again 1/2 the time it will just disappear......? Other times I've gone for rides and you "mite" feel a slight miss in that rpm range attributed to the normal 700 quirks that I read about. It never had this problem for 1000km of riding. Why now? It's soooo weird.

And yes, The plug caps are new and are properly pressed onto the new plugs.
 
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Not saying this is what it is but the fact that it is inconsistent makes me think either a chafed wire/loose connection or clutches. The clutches can easily make it feel/sound like the motor is missing. Usually it is more when at full throttle but maybe yours is "sticking" in that certain spot. If I remember right you had to add a bunch of weight to the tips to get the rpm down 500 rpm. That makes me think something is wrong unless you lowered the gearing a lot or the engine is making a lot more power to be 500 rpm too high. And if I remember you have stock gearing and stock motor. Did you put new springs in the clutches? I remember you did put a new belt on already. Like I said I am not saying this is what it is but another thing to look at.
 
It's not a clutching problem. Since I cleaned and added weights the clutching works perfect. Very consistent and predictable.

But the issue still happening. I've removed the foam from the hood, backed off the choke cable, and shut off the carb heaters (it's +6c anyways). My first 30km ride yesterday the sled ran perfect. Made me think maybe I had fixed it with the choke adjustment. But my second ride it again started hesitating from 5800 rpms on up t'ill 7k. Not all the times but enough to be annoying. This morning it did it alot more. Weird thing is the plugs always look dry and look good. My sled burns a bit over 50:1 so the plugs are always a bit oily and dark. The only thing left would be a wire somewhere has rubbed threw and somehow at times grounds out at that rpm from vibration ( frequency) range. I really don't know want else to think. May have to pull the wiring harness and do a much more indepth inspection.
 
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Went for another 30km ride this afternoon . Consistently the hesitation persistent the entire ride. Good thing is she always gets me home. But I'm fed up and stumped. Mite park it for the season. We'll see.

Decided to change my mind set by giving attention to my other hobby. First start of the year! I build this thing from very rusted steel. Every steel pannel hand made, every wire, every nut and bolt. Did over many hrs and years. You'd think I could fix a much simpler snowmobile?
 

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Have you ever pulled the choke a little when it was getting choppy? se if the added fuel helps it at all?

For the rub through look at the radiator hose near the water pump on the front of the motor the harness runs through there, my tape was worn through and the wire was untouched when i pulled the motor, i re-taped and covered in wire loom.
 
Yes have pulled the choke slightly in an attempt to trouble shoot many times. It only worsens the problem.

I'll check the wires near the water pump hose. Thanks

Keep thinking it's an inconsistent electrical problem.
Mite swamp my cdi with my brother's 600 Venture for fun. I checked the Yamaha's cdi parts numbers and use the same ones for the 600 and 700
 
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