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Discussion Starter · #1 ·
I have a 01 MXZ 800 that had flat slides on it. It is fed by a single outlet fuel pump to a central connection that feds both carbs.

I'm putting round slides on it and the round slides each have their own fuel inlet. Usually, these round slides are fed by a fuel pump that has 2 outlets on it and separate fuel lines.

Can I just put a T connection in the single outlet fuel pump line and run it to both carbs? I don't need to replace the fuel pump do I? I assume since the single outlet fuel pump was able to pump out enough fuel for 2 flatslide carbs, it should be able to handle 2 roundslide carbs.

Main jets will be smaller in the round slides. Am I missing something? I don't have my round slides back yet, so I can't try this out. I just don't want to spend money on a new fuel pump.
 

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Use a new fuel pump with duel outlets, they're only $25. You'll get better flow than a T.
 

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Ok i'm gonna ask a stupid question. Why go from a flatside to a roundslide? I thaught a flatside was a better carb.
 

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Gimme rounds any day!! Ski doo has always performed superior with round slide carbs. The ONLY advantage(IMO) is the ease of throttle pull. Everyone pissed and moaned to get flats on doos because all the other brands were using them and they pulled easier. Newer isnt always better. If you cant pull a 40mm round you shouldnt be riding a 800cc sled in the first place. Gunner wait till you see how consistent it gets and how much you fuel consumption is reduced, Im sure itll be worth the hassle. Im not saying rounds are better than all flats, just the rack mounted junk were getting these days.
 

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Gunner I would just T- off the single feed pump, if it can keep the fuel bowls full on the flat slides it should keep the rounds full.
 

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Gunner & TT,

I have three 38 mm roundslide carbs for sale, but first.....Here's info from Olav Aaen's carb tuning book..

The flatslide carb offers some worthwhile advantages over the conventional round slide VM design. Improved volumetric efficiencies related to the new design offer quicker throttle response and more power than the round slide carburetor in the same venturi size.
Why do you get a better throttle response and more power with a flatslide carb? The biggest advantage comes from the shorter distance across the slide itself. The needle jet and needle are centered in the slide on both round and flat designs, but because the distance is less on the flat slide, the vacuum increases more quickly and results in a stronger negative signal pressure for the needle jet to react to, thus improving the delivery of fuel.
The round slide also creates a "turbulence pillow" located right above the orifice of the needle jet passage that creates some low-end, acceleration tuning problems. The much narrower flatslide largly eliminates this area and this is one way the flatslide offers better carburetion.
The fuel charge is also pulled further into the air stream and atomized better as a result of the stronger vacuum signal through the shallow flatslide venturi. The stronger signal pulls the fuel into the air stream faster to give better throttle response. The improved atomization makes the fuel charge better suited for combustion and therefore improves both response and power in comparable applications.
Flatslide carbs also flow air better than round slide VM's because the throttle is shorter and has less obstructions. Special inserts in the sides make it act almost like a smooth bore carb, and this helps power on top end.

No disrespect boys, but it's nice to see that there will always be someone following the pack.
 

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Bogie, could I borrow your dictonary? I have headache....pillows? are we talking bout the latest sale at the Brick?

Air streams, did you call Northwestern on that one?
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Very nice info otherwise, thanks


Gootch
 

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If you install those roundslides, I think you will be disapointed with the results. All things being even (jetting, carb bore size, etc), you will loose throttle response and top end power by going to a roundslide. You will pick up a little fuel economy, but that is it. So I am with the others and ask "Why?"
 

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Before you knock the guy for trying maybe you should get on a roundslide equipped mxz800!! been there done that, Imo its a better overall setup, it isnt less responsive, in fact its much more tuneable. Ive got all of aaen's books, great reading!! And for the most part I agree with what he says, However we dont live in a perfect world and what works great for one machine doesnt always work great on another, or even for 2 different people on the same model machine.Ive been working on rotax engines for a long time and I dont think gunner will be unhappy with rounds.Did the '00 mxz700 suffer? Hell no!!! As a side note, before doo went to these rack mounted 40mm flats, a carb calibration issue on a ski doo was VERY RARE!! In fact before the last major one I can recall was the 93 machz. With these flats is every season and often multiple times per season, tell me whats wrong with the picture here? On the other hand why doesnt any other MFG have these issues, and dont Blame DPM, NON dpm doos have the same issues.
 

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Get Hooder to pick me up as I have no wheels
 

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everyone that changes is happy,I agree with tt670 on this.yes on paper they(flat slides) are better but wait till more guys make the switch,more will follow.and the reason my '00 700 had round slides is because doo could not get the peformance/calibration right on the flat slides.
 

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Okay Boys.....Change away....I have yet to see a year 2000/700 even come close to a 2001 or 02, stock or trail mod. That's on top end or drag racing. I also own a 99 t-cat, and would never go back to those VM's.
 

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Originally posted by gootch@Nov 14 2002, 12:22 PM
Get Hooder to pick me up as I have no wheels
Wheels??!! Who needs wheels when you have a brand new sled? ...oh yeah...


Pil at the caddy shack sounds good. Gootch, double or nothing on the Western Final?
 

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i would not go from flat slide to round slides. i have a set of 46.5mm round slides and i could get me hands on a set of flat slides ,.....man. but the flat slide carb does offer better throtle responce and more consistant running and easier cable pull.
 

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Originally posted by dooman@Nov 14 2002, 02:54 PM
everyone that changes is happy,I agree with tt670 on this.yes on paper they(flat slides) are better but wait till more guys make the switch,more will follow.and the reason my '00 700 had round slides is because doo could not get the peformance/calibration right on the flat slides.
I dont think they can get the calibration right even now, and its 03 model year. my 01 was calibrated like ####, still is until i fix it this winter.
 

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Bogie "Okay Boys.....Change away....I have yet to see a year 2000/700 even come close to a 2001 or 02, stock or trail mod. That's on top end or drag racing. I also own a 99 t-cat, and would never go back to those VM's. "




GLH "I will put the round slide from a doo up against any flat slide twin from doo. I would even spot you some room.

The point is that the flat slide is not designed correctly for MAX POWER in the case of the series 3. We ran a 2000 mxz 700 to 2 title wins. Sure we had the opportunity to use the flat slide but the round made more power.
On a dyno it is worth about 5 HP with the mods that gunner is doing. Even boring the flat will not match the power of a stock VM 40 in this engine. The hrottle response is just shy of instant. The 2000 mxz 700 had great throttle response, the 800 is even better.

Been there done that and I will be one of the few with a 2003 REVX800 with 40 rounds."

GLH
 

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Discussion Starter · #19 ·
Great discussion.

I'm going to rounds because I never had a problem jetting them.
I could get them dialed in and they stayed there.

These flats have been nothing but problems for me. I finally
got them close, but I'm not completely happy. On my 00 700,
the rounds are a better carb IMO.

Plus, once the carbs are broken in, they pull easily anyway.
A few snips of the spring and they pull even easier. I don't
really notice that much difference in pulls.

I didn't buy a new sled this year and I can't stand not doing
anything - so I'm making a few changes. This is one of them.
 

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If TT670 and GLHRacing both agree that rounds are better that should be all you need to hear. Those guys both know their sh!t!
 
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