38 tmx flatslides?

Thanks for that tip SRX. I think I will jump up to 440 mains. I should probably go with the next richest needle, but not to sure how to go about that. All I know is it the stock 2001 XCR800 needle. I also have a couple other avenues to explore before I can figure out the real culprit behind my second meltdown.
 
SRXtreme said:
I am led to believe that the airbox is tuned to boost low end response. I run pods on 3 of 4 of my sleds and I had to jet up and incredible amount. I still haven't got to the largest main jet I require for high pressure as my last ride of last year i burned down again. I am going to have to go to a low elevation and cold temp so I can get my sleds jetted properly. The pressure changes in Revelsoke are extreme. The 2 times I have burned down was on hot sunny days, go figure..........SRXtreme
Click to expand...

ya I think you're definatly on to something there, I also notice having to jet up a crazy amount when using pods (like 10 sizes on stock carbs) :shock:

yamablue said:
I’m going to have to disagree on the relation of the carbs to the driver of a speaker. I would say the piston going up and down and the reeds closing set up the oscillation and would be the driver. On that note we should consider is that the airbox is probably designed to be most efficient when the motor is oscillating the air at the designed peak RPM. Since it is possible for a forcing frequency to excite a resonance within 5 or 10 percent of the actual resonant frequency, it’s likely the box is still resonant around 7800-8000. That and the flatsides should not pose a restriction of the standing wave since the engineers likely tuned the depth of the box to locate the node or the location of least amplitude of the wave, to be directly at the point of the slide so there wouldn’t be reversion of the wave. (Wow now my head hurts, college physics lab seems to have either screwed up my head or I am onto something here.) I could probably go on but I don’t want to think anymore.
Click to expand...

this is FAR from my forte, but wouldn't the reeds be the drivers? I think that we can safely assume (from what we know about using pods) that whtever yamaha did to engineer the stock airboxes, they did it wrong, or we're not seeing something.
 
Sorry Junior I forgot to add the connection to the piston action and reed opening and closing as the driver reference. I was piecing that post together going from one thing to another and it might seem a little fragmented.

Wow 10 jet sizes, so maybe I should throw some smaller needles and jet up to 480.
 
Wow,
great discussion, I'm very happy with all of the input. This is definetly making me think alot! I was just going to make a couple of points real quick.
Extreme...If you had to jet up so much with pods, the first thing that I think is wow huge gains in horsepower, right? If you actually had that much more air going into the engine that you needed to jet up 10 jet sizes, you would be getting more horsepower than pipes, or any other mod that I can think of. Whats happening? well I talked to a friend who runs pods on his race sled and he said, There was no way your getting that much more air into your motor, more than likely you starting to foam the fuel. when you remove your airbox and install pods, your carbs vibrate alot. No support, and extra weight hanging out. This can cause rich & lean conditions depending on whats going on. Float levels changing, fuel foaming, ECT. He said to fabricate a bracket to stiffen up the carbs to the motor. Couldn't find much on the internet, Hope this helps you out.



Blue & junior,
I think you are correct on all of your box tunning ideas. I was just wondering what people thought, and I believe you have changed my way of thinking on this. Thats doesn't mean I won't try something stupid! LOL! I might mess with it when i get some dyno time, duno when that will be though, probably not till next year.

Thanks STEVEO​
 
ya it's possible that the carbs are shaking and foaming the fuel, easiest way to brace them would be from engine side tho I think, I will make something up and try that, shouldn't be to hard or heavy.

as far as your jetting yamablue I was meaning on stock carbs 10 sizes, and that's just a rule of thumb, go up 10 then slowly work back down. and that was on the stock 33's. I think this foaming the fuel stuff might be on to something.

agreed guys, this is a damned good thread
 
Spec,
Does this mean that you are getting 32% more air into the motor? If this is the case pods would give you 32% more horsepower, assuming volumetric efficency stayed the same. All I'm saying is if you gut an airbox, and open up the top, it's still only a couple of jet sizes, not 6-8. Also I'm just letting you know what a seasoned veteran has to say, take it for what it's worth. I do know that yamaha has had alot of problems with vibrations leaning out the motors in the past. Two I can think of are the old SRX's, and the not so old exciters.

http://www.totallyamaha.com/forums/showthread.php?t=2182&highlight=lean+exciter
 
Last edited:
The pods I run rest against the oil resevoir and are held pretty firmly in place. I built another SRX MOD with 38TMX carbs and it is running 350's at 6000'. The bottom line is more fuel = more HP. The foaming is a pipe dream, the fuel is sloshing in the carbs irregardless(unless the carbs are flapping in the breeze). I know from my experience is that on my 600MM twin, 700MM tripple and SRX I have had too jet up a fair amount over stock. As a matter of fact another customer of mine with his motor built by myself done exactly the same as mine minus megapowr heads, his jetting is 143.8 with the attac. Mine were jetted at 152.5 with vari-flow at full rich on my last burndown at 6000'. On my 700MM, I run if memory serves me is a 65 pilot with a .7 bleed because of such a lean bog off the line. My SRX is running a 55 pilot in the stock 33's. So believe what u will and maybe take what I say with a grain of salt but my experience says otherwise. On the mountains I know what is working for the Yamaha's I have built and alot of people have taken notice. The day before my last burndown a guy had a 1010 cat and came over too me to ask what BB I was running. Needless to say his big cat wasn't going anywhere my 700 SRX went. Bragging rights is where it is at and I look for every last bit out of the Yamaha's I build. Junior has seen some of my work and I think he was quite surprised............SRXtreme
 
Like I said if your getting 32% more air into a motor, you have 32% more horsepower, assuming volumetric efficency is the same. This would also increase your dynamic compression so much that you would certainly have detonation, regardless of mixture. I'm just putting some thoughts out there for you to contemplate. As for the fuel vibration issue, (we are talking about sonic speed vibrations, not high amplitude vibration you can see) it's real, and proven, talk to Barry Holtzman and tell him it has never happened. As for experience with two stroke mills, I have built more 125cc-250cc race motors than you can shake a stick at. Ten years ago, A 125 that put out over 40 horse.(toot your horn, and I'll toot mine) Lets see...........700 divided by 125 = 5.6 ........ 5.6 x 40 = 224 horsepower. Iv'e learned that, just when you think youv'e got it all figured out, bamm you burn it down again. (Kinda sounds like you burn down alot) It's usually best to at least consider what other people have to say. I do believe you are probably right though, it's more than likely something to do with no vacuum whatsoever to help pull fuel up. Maybe try raising you float level slightly? Please don't be upset with me, knowledgable people have a tendency to disagree sometimes, don't you think? By the way, polaris has found that by changing the tps position, this can help with midrange timming problems. hmmmmmm?????????

http://pages.cthome.net/barts/Tech Tips.htm#TPS

http://www.totallyamaha.com/forums/showthread.php?t=6206&page=2&pp=10&highlight=lean+vibration
 
I think XXX has some valid points. Foaming of the float bowl will happen , but not really that effective in the real sledding world, unless the sled has solid motor mounts and is tied down to the dyno table, ask me how....I know first hand, wasted all day and lots of $$$ at the dyno and found this out, and the bigger the mains I put in, the leaner the sled went......., why??? because it sucked even more of the foam out of the bowl faster. The sled only does this being tied down to the dyno table, the field testing(solid mounts still) doesnt show this condition, because the suspension sucks up some of the vibration. On a trail sled with stock rubber mounts your never going to see this condition, and it doesnt matter if you have a airbox on it or not, wont ever foam the bowls with rubber mounts on the trail,lake, whatever. The harmonic vibration from the crank will not effect a srx based engine until way over 11,000rpm, (who runs them there anyways) I have run them at 10,200 rpm and never once had a problem, with solid mounts and on asphalt for a 1/4 mile WFO!!! So, the foaming of the float bowls is not really going to be a factor on these engines on trail,lake,ice........I ran the sled without a airbox also, you have to jet up because even with a case reed engine, there is still a degree of spitback from the carbs, ever see the film of oily residue inside the airbox on a stocker?? that contributes to fuel mixture, its a very slight vapor inside the box while the engine is running.
 
Last edited:
Vipertripplexxx.....yes the K&N's flow roughly 32% more air than a stock air box (I'd have to dig through my flow charts to verify this completely). They made exactly 4 hp over the stock air box. We only ran the K&N's in the grass mostly because of the improved filtration to keep the dirt out. We normally had to jet up about 4 sizes. This was all on stock 33mm carbs. It doesn't matter how much air flow you pick up, the stock reeds will only flow so much as well.

Mrviper700, you're correct the fuel won't foam even on a solid mount engine even when spun up to 11,000 rpm out in the field. We played on the track dyno for a long time trying different timing & clutching from 9900 rpm up to 11,000 rpm and never had a fuel foaming issue with solid mounts. I've never heard or seen anyone with a fuel foaming issue when using rubber mounts with the stock air box or pods.
 
well I talked to a friend who runs pods on his race sled and he said, There was no way your getting that much more air into your motor, more than likely you starting to foam the fuel. when you remove your airbox and install pods
Click to expand...
Is that a fact? Foaming the fuel is definetly not the issue, and NO I DO NOT BURN DOWN ALOT, once when I first built the sled and once at the end of last season. If fuel foaming was an issue I would be burning down everyday with all 4 sleds wouldn't you think? You also must remember I am running my sleds at typically around 7000'. Air density is going to play a large part of the equation. The way I call it is the airbox is designed to flow a specific volume of air at a given resonant value. I can gaurantee you Yamaha didn't design thier airbox for my conditions. Let alone the porting & port matching ,reeds, silencer etc.
It doesn't matter how much air flow you pick up, the stock reeds will only flow so much as well.
Click to expand...
Let alone the engine............SRXtreme
 
38 mm carbs

i have a 98 700 with a bender moter. boseen reeds and air kit with egt,s. i just want to know what carb boots to use for the 38mm carbs. i have a set off of a mach Z. and i think this will boost my sled a little on top. ;)!
 
I used Phaser manifolds. They should go right on, but I had to relieve the ID of the carb mounts to get my wider spaced polaris carbs to go on.
 
Bottom line we have still not resolved the issue of having to jet-up 7-10 jet sizes, for 4-6 horsepower gain. Spec says 4 jet sizes, Thats not to bad, sounds more realistic. I'm just saying 7- 10 sounds like alot, why? I like the fuel in the airbox holding mixture, because of spitback, but wouldn't the pods hold some of that in the filter and release it? I can see it with open carbs. If you have any ideas on this please feel free to post, don't worry I won't call you a pipe dreamer, or lier
Is that a fact?
Click to expand...
even if your incorrect on you theorys.
 
ya I think you're definatly on to something there, I also notice having to jet up a crazy amount when using pods (like 10 sizes on stock carbs)
Click to expand...
Bottom line we have still not resolved the issue of having to jet-up 7-10 jet sizes, for 4-6 horsepower gain. Spec says 4 jet sizes, Thats not to bad, sounds more realistic. I'm just saying 7- 10 sounds like alot, why? I like the fuel in the airbox holding mixture, because of spitback, but wouldn't the pods hold some of that in the filter and release it? I can see it with open carbs.
Click to expand...
I never said I was jetted up 10 sizes personaly but now that you are on the topic. Typically with a moded aibox I install 135 mains for the temp and altitude we ride at. On my last burndown I was jetted 138.8's and 140. Looking at my pistons mag needs 3 jets larger center needs 2 and pto could use 1. This would just make the motor safe at 7000' with the vari-flow at full rich. So with that being said I am 4 or 5 sizes larger than a similar sled with the airbox. Also take into account I have never burned a sled down with the airbox and jetted as above so I would easily say I could be jetted maybe even 7 or 8 jets larger than with a similar sled running the airbox. Another point worth mentioning is spitback, if you notice under the airbox thier is nothing but a mess of oil residue, with pods this mess is either soaked into the filter medium or drawn back into the engine I haven't looked into this any further but might be worth while............SRXtreme
 
Just wanted to tell you guys that XCR's had their carbs vented to the airbox not to the belly pan.
 
Matty, I'll argue that one with you since my 01's had the venting straight down from the carbs. Unless those lines plugged into some more elaborate system, they vented to the bellypan.
 
No elborate system. Just 3 plastic fittings on the airbox. I worked at a Polaris dealer for 3 threes and all '99 - '03 800 XCR's had their venting to the box.
 
SRXtreme

Junior has seen some of my work and I think he was quite surprised.........
Click to expand...

ya, no doubt there, SRXtreme takes this stuff pretty seriosly, and to him the devil is in the details so to speak, there's not a whole lot of intricacy's he hasn't thought of.

MrViper700
I ran the sled without a airbox also, you have to jet up because even with a case reed engine, there is still a degree of spitback from the carbs, ever see the film of oily residue inside the airbox on a stocker?? that contributes to fuel mixture, its a very slight vapor inside the box while the engine is running.
Click to expand...

I know the residue you mean, I'm sure we all do, but I don't think that's enough to make a real contribution to jetting. if that was the case, it'd be immediatly present in sleds as soon as they have been run, but they are all run in japan before they are shipped here, and I haven't noticed it on new ones while doing PDI's even 500mile checkup, it's not common. there's no doubt that there's spitback, I just don't think it's enough to effect jetting

sucks about the spending a day on the dyno just to find out that your bowls where foaming man!

vipertripplexxx
Bottom line we have still not resolved the issue of having to jet-up 7-10 jet sizes, for 4-6 horsepower gain. Spec says 4 jet sizes, Thats not to bad, sounds more realistic. I'm just saying 7- 10 sounds like alot, why? I like the fuel in the airbox holding mixture, because of spitback, but wouldn't the pods hold some of that in the filter and release it? I can see it with open carbs. If you have any ideas on this please feel free to post, don't worry I won't call you a pipe dreamer, or liar
Click to expand...

it was me that said 10, and I use that as a starting point and work down, better to have it burbly for a day then to blow it up.

just wanna point out that the K&N's are an oil based filtration system, the oil being in them is what catches the dirt, the way they are woven I BELIEVE the oil will only flow one way thru them (out)

I already brought up the spitback, I don't think that's really enough to be in the equation here

SRXtreme
Also take into account I have never burned a sled down with the airbox and jetted as above so I would easily say I could be jetted maybe even 7 or 8 jets larger than with a similar sled running the airbox.
Click to expand...

I've seen those type of results, in particular with the 698cc engine, but I think that airbox is more restrictive than the SRX/Viper engine.

I was told for a long time that the SRX/Viper engine flowed the same with pods or airbox, but that was the competition telling me that, and I burned a sled down when I attempted same jetting as stock on an SRX with pods.

from then on I follow same rules as I did with the SX's, go up 10 and work back down
 
You must log in or register to reply here.


Back
Top