flat / bog in mm700

M

maxco

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coloraDO
first a little history. my machine seems to have a flat spot in it's running. It engages well at 4000. then builds rpm nicely to 5000. from 5000-5500 it seems to be sluggish. at 6000 it takes off. I have been through the carbs. they are clean, and I have done lots of plug tests. all says it is running fine. nice white tip on electrode, cardboard colored around the edge, oil 3 rings down. As far as I know perfect. I went through the clutches. silver spring hartman a3 helix. all working. But maybe need to adjust tension? it's at 70deg now. new belt (washed). no oil on clutch surfaces. So I am a little stumped. I have not been around snowmobiling long. Do all machines have a little flat spot? I mean it may be just the way carbs work when transitioning from mid to full. A friend said that oddly I may try to lower the octane of my fuel. Drop to midgrade 87 octane. I don't understand why, but he has been around longer. He said to the effect that high grade and high altitude means that the gas burns to fast on high octane for the amount of air it gets. mid grade may ignite/burn slower. the altitude thins the air soo much it might be beneficial. :2strokes: I should add that I ride at 10000-12000ft . my machine is set up for riding double. Aka heavy spring, lowered gearing. Any thoughts out there? thanks
 
Higher octane fuel burns cooler. When I had my Audi (4 cyl. turbo) I had to run regular in it in the winter to help with starting since low grade burns hotter. Your machine might just be finicky enough to run bad on premium at high altitude so it wouldnt hurt to burn a tank of mid grade or regular through it just to find out. But keep an eye on your plugs if you have re-jetted the machine!!!!
 
My sx/mm did have a small flat spot as well. For your elevation I would drop to 87 or 85 if the exhaust and the head are stock. Pipes or a thinner headgasket/different head will need a little more octane.
 
more info

the machine is a 2000 mountain max with hauck pipes, and it is ported. So it has of course ben rejetted for these mods :2strokes:
 
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Try raising the carb needles half a position, sounds like it might be a bit lean in the mid-range. If you haven't done it before there should be info in the tech section.
 
jetted

mains 60, pilots piston 1 138.8 pistons 2-3 137.5. eclip 3rd down, one washer above one below. 2 turns out on fuel screw. set up is for 10,000 ft plus. ported machine with slp pipes (replaced the hauks). Drilled shelf in airbox. I am wondering if the needle jet might be the culpret. slp specs say 499 series Q-2. but I am unsure how to check or change needle jet.
 
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needle

I get confused alot about this, but the needle is stock ( I belive) 6dgm5#3. however the needle jet is currently unknown to me. Slp recomends 499 Q-2 for needle jet, not the needle. I have never removed the needle jet which is the channel that the needle goes into. I have had the carbs completely apart and adjusted or looked at both side of it. I have had the mains off of the needle jet, but do not really know how this removes. My clymer book is not much help. '' remove jet needle after removing main." ? I would assume that it is marked on this part, but haven't had it out of the carb ever. The needles come out of the top of the carbs pretty easy. :2strokes:
 
Back Out The Top.

If You Have The Carbs Apart, (already Removed The 2 Allen Screws That Hold The Slide Cap To Slide) Remove The Slide Cap(for Lack Of Better Term) And Needle With Shims (locate All Shims) Pushing Up On The Slide Itself To Get It Out Of The Way, Push On The Emulsion Tube ( U Are Calling This A Needle Jet) Towards The Top Of The Carb And It Will Press Out. Its A Tight Fit And They Can Be A Little Hard To Get Out. They Will Barely Clear The Bottom Of The Slide, And There Is A Notch That Will Line Up With A Teet In The Carb Housing (when Assembling Make Sure The Teet And The Cutaway In The Tube Line Up.)
 
caps

sorry bout the caps folks our operating system is ancient and will only recognize caps. when it goes into ty it changes it to the first letter caps only.
 
the good and bad

well the good news is it is gone. no more bog no more stutter. awesome. the slightly bad news is I changed two things and I don not know which one fixed it. I put on slp pipes instead of the hauks. hauks were piped out the side of the machine and were loud. I mean really loud. then I cranked up the secondary spring to 90 deg. so between these two it fixed my bogging. thanks for all your help. It has been an excellent season here. :2strokes: :letitsnow
 
and the ugly

Its Baaaaaaaaack. So after a spring/summer/fall of working on my machine, this flat spot seems to be back. My machine seems to have this flat/dead spot when I go through the range from idle to full throttle. It is around 5000-5500 rpm range. It runs great after and before, but in that range it seems to be struggling. For a little current info, I put on a peak performance head. had to have the one of the jugs decked to make them line up. I had the transfer case ported to allow for srx reeds. Anyway I re-jetted up for safety. I upsized the pilot,main,needles. I have been doing plug tests. They look good on the WOT run. They Look good on the 3/4 throttle run. however I still have a flat/slow spot at 5000-5500. The machine idles ok. Idle needs to be adjusted depending on how long the machine has been runing. Usually cranked up a little.
Ok for the stats. mains 1-142.5, 2-3 141.3. pilots 65. needle 3rd clip 1 up 1 down. on a ported, SLP piped, mountain max running at 10,000 ft.
I am leaning a few ways. The "mix" is to rich in the midrange. The pilot needs to go down a size, or the needle needs to be dropped a hair. Or the clutch is loading a little too hard after engagement.
My question (finally) is.....how can I determine what this might be?
 
Not apples to apples, but I have a bender piped, mad max ported, single head gasketed, airbox modded mountain max. At 8000'+ I run 140's, needles at 3 with both washers over and I can't remember the pilots, but 57.5 sounds right. Based on you being 2000 ft higher I'd say your rich but ..........."
 
sooooo

Maybe the pilot is too big at 65? SLP has a recomendation for Pilot at 60, but not for a ported machine.
 
I have a very similar set up in my MM700. You are running fatter mains than me. You should be fine running the 65 pilot. If you haven't changed the needle jets per SLP's recommendation, you should. Based on where your flat spot is happening, the needle jet change can clean that up. Not sure what you are running in your primary set up, but seems like you are running a ton of spring in the secondary for that motor.
 
I had thought about that

To be clear you are talking about the needle jet, or nozzle, not the needles. I do not have my Slp cheat sheet in front of me, but I recall a 499 Q-2 something. I will look at that. I have never changed the needle jet, I searched around about it. It is apparently a press fitting? Any words of wisdom on how to do this?

Also where do I go to get a decent price on needle jets? Thoughts?

The clutch is set per SLP piped (no spec on ported). SLP install sheet. they recommend for 7-10,000 ft, 100 deg or 1-9 for a black/silver spring. I need to clean my primary, so I will look at that later this week, and get back about the arms/ weights. I have them written down somewhere, but lost it. ;(

All help is appreciated. Thanks ;)!
 
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