Ski-Doo Snowmobiles Forum banner
1 - 14 of 14 Posts

·
Registered
Joined
·
1,325 Posts
Discussion Starter · #1 ·
quick explanation...I have a very worn set of 03 mxz800 (rev) carbs on a basically stock 05 800ho,was planning to pull jets and needles and put in a spare low mile set of 07 summit 800r carbs I have..started to question why as the rev chassis 800s got newer they seemed to keep jetting bigger and bigger..ie 03 stock is 380 mains (Im 370s),my 04-05 I think were 400-420...07, 470..is this size of main jet due to the matching needle diameter and tapers ? a difference in the amount of fuel required as the engine electronics advanced? I guess where Im going here,is my intention is to put the 07 800r carbs into my 03 sled with the newer 800ho engine in it...is there possibly a better/smarter needle/jet combination than the stock 03 stuff Im pulling from my original carbs ?..oh and all have dpm...thanks Hardy
 

·
Registered
Joined
·
1,325 Posts
Discussion Starter · #3 ·
Interesting...not that I guess I really "need" to know,but curious as to why/how the ecm would change the engines jetting requirements ...maybe more timing,more fuel?
 

·
Registered
Joined
·
709 Posts
The first 800's I believe were about 133-135HP. The 800HO went to about 138HP. The P-Tek I think is 140-142HP. Then you have the 800R at 151HP.

So I think the main jet could be attributed to the increase in HP.

The needles I believe are different to the hooded jet needle and non hooded. May also explain the main jet too some. Unfortunately I can't remember which were hooded and which weren't.
 

·
Registered
Joined
·
1,325 Posts
Discussion Starter · #6 ·
I did think about timing...hadnt really considered the hp differences as they get newer....well...remember this is a rev chassis 03,with a newer 05 800ho (in there more than 5 years already)...I put original 03 needles and 370 mains 20 pilots into 07 800r carb bodies...synced carbs...ignored tps sensor (taped over it) hooked up to stock 03 dpm (and has had an 07 airbox for awhile) flashed up no problem,Idles smoother and lower than it has in a long time (aprox 1600rpm) only have enough snow here to get a few hundred feet,but seems to have good throttle response,after a quick WOT it idles down to about 3000rpm for maybe 10 seconds,then drops to about 2000rpm for a few seconds,then smooths down to 1600...I would like it to drop a little quicker,but is soo much better than having to continually blip the choke to idle it down like last year...maybe we will get enough snow to actually run it and do a couple plug chops just in case...thanks...Hardy
 

·
Registered
Joined
·
1,325 Posts
Discussion Starter · #8 ·
my 03s I dont believe were hooded...that ended maybe 2002?? I dont think rev chassis ever used hooded ?
 

·
Registered
Joined
·
483 Posts
All rev 600s and 800s besides for maybe the 03 800 non ho use a hooded needle jet but I believe they did aswell. The actual needle itself changed from year to year changing the requirement of the main jet selection. I know timing was messed with also but main jet size has more to do with matching the needle taper through the fuel circuit
Chris
 

·
Registered
Joined
·
1,325 Posts
Discussion Starter · #10 ·
so my memory maybe is backwards...again...so the rev chassis use hooded I know the carbs on my 03 are the same as my 04 and 05 all 800s.and 07 800r other than jetting and needles,and tps etc
 

·
Registered
Joined
·
483 Posts
Yes hfrick if you look in the carb where the needle comes down into the main jet the is a half moon c shaped hood at the bottom of the venturi, the non hooded had to run a much larger main jet to achieve proper fuel mixture because that design did not displace and atomizer the fuel aswell as the hooded design
 

·
Registered
Joined
·
9 Posts
Has obtained better used carburetors TM-40. according to brp catalog i have TM40-B322 .. While the others that I have which btw looks exactly identical is called TM40-B247 then just below the text is W291 written. Is there any more differensens except main/pilot/needle? (i will be moving it over from my current carb) like needle valve or more etc?

Skickat från min iPhone med Tapatalk
 

·
Registered
Joined
·
4,452 Posts
Hfrick, jet your carbs with the Doo parts fiche for the engine and exhaust of the year. I'm building an 800r engine and another 770 in the off season, and when I jetted my '04 800ho and 770, I used '04 800 settings as a base. The '04 needle is substantially leaner than the 800r needle. I have one that is 7steps richer than the '04 800 needle from a 600 HO, and I did some comparisons. The richer needle had basically the same taper, but a shorter starting point, in other words the clip location was about .050" down on the needle compared to the '04 800 needle. I put together an 800ho engine for my son this season, and anything richer than the stock needle with no shim wouldn't work, to rich. Stock main and 17.5 pilot. RKtek ignition curve. All engines and exhaust are a bit different, so do plug chops, but it sounds like you're close. My 770 with 800ho porting, and a dmax head and pipe was lean with the '04 800 needles, and bigger mains. It's all about the Venturi signal.
 

·
Registered
Joined
·
1,325 Posts
Discussion Starter · #14 ·
thanks zxmodv I put the 03 jets and needle into the 07 carbs back in february...rode maybe 2km...have no snow for testing...seemed to respond better,after ripping on it for a short blip,would Idle down to about 2200 rpm right away,then maybe 4-5 seconds down to 1400 or so...much better than before,but havent really had a chance to ride...Hardy
 
1 - 14 of 14 Posts
Top