38 tmx flatslides?

vipertripplexxx

vipertripplexxx

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Anybody graft in 38 tmx flatslides in there yami's? These are polaris carbs out of 99 xcr 800. Baseline info needed. 780 big bore, cpr pipes, simons head mod, stock reeds, stock air box. Estimated power gains? Thanks Steveo
 

i have some goin in my srx but haven't gotten it put together to see how they do. a lot of people say they like them from what i've heard because they keep really good bottom end, and with the being 5mm bigger than stock it has great top end. i hope this is all true!!!
 
SRXtreme, your correct, spacing is 1/8" wider on the polaris. I'm thinking the boots will flex that much? If not I was thinking some offset carb rings on the two outside carbs, with slightly oversized boots. The tps sensor is reversed direction but that shouldn't matter as long as they ohm out the same. If they don't might have to reverse two of the wires, and use original sensor. Gonna check those out tomorrow. Happy New Year!! ;):D ;):D ;):D :ORC
 
SRXtreme, Whats your jetting, pilots, nozzles, and needles? I need A baseline to start. Vented to airbox? Airbox modified? Pipes?

Thanks, for the input! :rocks:
 
Sensors are the same, just have to switch the two end pins in connector because of reverse rotation. Ohm Readings on viper- 5.5Kohms, end wire to end wire (total ohms) low side .85K ohms, high side 4.7K ohms(center to end wires). Readings taken in idle position. Does anyone know the proper way to setup position sensor? I would like to check it, even though it ran fine. Polaris is close to the same, except for the fact at wide open throttle it seems to have a little more rotation. Changing the readings slightly at full open position.
 
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SRXtreme, Whats your jetting, pilots, nozzles, and needles? I need A baseline to start. Vented to airbox? Airbox modified? Pipes?
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I just installed the carbs and haven't done any testing. I am running pods. I am using the 2000 Mach Z specs for a starting point..........SRXtreme
 
Let me know how they work out, and jetting specs, etc. I've been looking to do the same thing as well. I hear they work especially well with case porting.
 
I used 01 XCR800 on mine. I used a set of phazer manifolds and had to open them up a little bit with a cartridge wheel. I used brass hex head pipe plugs to fill the boost bottle hole. I also had to slot the end manifolds about the 1/8 " mentioned. The throttle response was amazing with those 38s. I burnt the mag and pto pistons down last year with 390 mains and 50 pilots. ( I believe I also had air in the cooling system). I have the needle in the third position and the airbox in place modified to fit on the carbs (no shelf). The motor has lake race ported cylinders, Vforce2 reeds, Mountain Perf Viper head with 21cc inserts, and CPR pipes ceramic coated.
I found the 50 pilots to be way to rich. You will need to drop down to 45s. I currently have 410 mains in it right now and the needle in the 4th position and the plugs are colored real nice. I am going to jump up to 420s for a little while to see if they are to rich. I burnt down again on my last ride due to air in the cooling system. The Mountain Perf viper head is real hard to get all the air out of. I just didn't have time to check it real well. Oh well new piston and relating again.
The TPS was a bit tricky, don't have to change the wires, but you do have to rotate the TPS to the other end of the adjustment. The resistances on the two outer wires oppose each other. One goes up and one goes down, just crank it the other way and it should be good. The throttle pull on the Polaris carbs is a little different; therefore you cannot get the same range as the Yamaha TPI. The best way to do it is to set your idle at the speed you want it then set the TPI adjustment at the point just after the check engine light goes out. The light will flash like 3 times to tell you there is a problem with the TPI. If you want to tolerate the light flashing at idle, set the ohm range to the WOT settings. If you don't want to see the light flashing, just adjust to the point the light goes out at idle. It’s not off that far at WOT.
You will have to change the cable length. Hope you have a bike shop that can put a new lead end on it.
The fuel bowls are deeper in the Polaris carbs. You will have to cut the bowl drains off and epoxy them closed. The Polaris carbs have two fuel inlets to feed the three carbs. They are T'd between them so you will have to plug one supply line or t two together (that's what I did).
I now have UNI filters on mine. At idle with the airbox in place my EGTs were off a little bit. With the airbox off they were all close to the same. The mag carb appeared to be getting less air since the shelf is no longer directing air right to it. I figured there was no point using the stock shelf since it was designed to supply air to the smaller 33s.
My next purchase is going to be a 01 SRX CDI. Oh yeah and make sure I have all the air out of the cooling system. Even with the rear heat exchanger, 165 hp needs all the cooling it can get. The motor sure sounds nice spinning at 9100rpm too. That’s everything I could I think of that was a pain in the butt.
 
Yamablue,
Thanks for all of the great info! Iv'e been finding out that stuff, and have been slowly getting everthing in order. Got the carb boots, throttle cable, choke cable, position sensor, fuel line issues staightened out. Just tring to decide whether to vent to airbox or not? What temps are you jetted for? air screw? Having too much fun riding right now! ;):D Will probably do some testing this week. ;)!

Thanks once more, Steveo
 
The temps with the 410 jet were around 8-10 degrees F. I figure I'll run into colder temps so I am probably better off jumping up to the 420s. My air screws don't do a whole heck of alot. I think they aid in starting a bit but I've had them all over between 1 and 4 turns and it is about the same. Maybe I should throw a vacuum gage on the carbs and set them that way. As far as the venting, I did mine to the belly pan just as they were in the XCR 800.

BETHEVIPER: I caught a little of your temp sensor deal. Will the temp light still be functional or should we just go ahead and put a digital gauge in. ( I plan on doing this anyway). What is going to the lead on the CDI right now that we have to tap into?
 
I'd stick with the stock air box (maybe with more holes on top) if your running stock rpms. the air box is a resonator that is tuned to the engine, like the exhaust pipes. you should make more power with it.
 
It's tuned to the engine with the 33mm carbs. who knows what's going on in there with the bigger carbs. If the barrels of the carbs are anything like a pipe organ for resonance, then the box resonance will have to be lowered due to the larger diamerter pipe. It would probably need longer tubes on the plate.
 
Yamablue said:
It's tuned to the engine with the 33mm carbs. who knows what's going on in there with the bigger carbs. If the barrels of the carbs are anything like a pipe organ for resonance, then the box resonance will have to be lowered due to the larger diamerter pipe. It would probably need longer tubes on the plate.
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that logic makes sense, but I don't think it's ever been tried, not to my knowledge anyways.

I was talking to some QUB guys awhile back and they where experimenting with running 2 airboxes, a group airbox for all cylinders, then a smaller one, with volume equal to the volume of the group airbox/number of cylinders, and they where saying that it made more power on there dyno, and showed better scavnging ability.

don't think it's particularly practical given how tight those engine bays are already, but who knows, could be worth a couple horses. those guys are the guru on 2-stroke engines
 
wow, thats interesting, kind sounds like a viper box eh? big tuned box down below with a smaller box up top, about 1/3 the size! with tuning horns in the middle.
 
The internal horns tune the box to a specific frequency. The carbs are considered the drivers, increasing the driver size, should have very little effect on box frequency. In speaker box design they don't even care what size speakers are being used, just want to know what frequency your going to drive the box at. In speaker design the pressure waves are designed to be negative in the box at tuned frequency, opposite of what you would want for your sled. On the viper airbox I don't think the horns are the restriction, seems like the top cover is the problem? Man those slots are small! :o|
 
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.
 
Oh yeah, I agree with the fact that the slots are the big restiction of the airbox.
I also asked Jeff at CPR what he thought I should do about opening up the airbox lid and he said to just get rid of the shelf since it is tuned to the smaller yami carbs.
 
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
 
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