jetting question

[overkill131313]

engine is a 779 triple Rotax.....was just wondering what is ball park for jetting if you add Pipes (jaws)? reeds? pods with no air box? and im sure this will screw it up but mixed fuel at 32-1???? stock jets are 390 (PTO) 380 (Cen) 400 (Mag) pilots are 40 (PTO) 45 (Cen) 45 (Mag)......I have already upped the pilots 40 to 45 (PTO) and the 45 to 50 (Cen, Mag) and going to mess with air screw tomorrow.....then I will start to play with needle and mains.....I plugged the Power jet (recommended) and info on how much richer to go above stock with the mods would be great! been watching the EGTs at 3000-3500 and the PTO with the 40 was running real cold (200 vs 650ish) so I closed the air screw a full turn which brought it up.....I gave it some choke (enrichment circuit) and it brought it up perfect......so Im thinking I should be in the ball park tomorrow with the 45-50-50 pilot jet......just wondering about the Mains! oh and I removed the varri flow till I get this jetted then I will add it back on......any one know how many sizes of main jets this will adjust? and do I just add it with the set up I will end up with and then it will lean out? never had the Variflow.....I have installed 3 holtz auto altitude temp....and I love them over the years but this sled had the Varflow with race pace so I can see the EGT's so going to go with it.....so any info would be great! sorry for the book! lol

 

[Clode]

depending on the bushings used in the vari-flow tubes they can reduce fuel flow by up to 20% if I remember correctly, vari-flows work great, the last sled I had one on I jetted for -25 at local elevation, and was able to keep sled running crisp at 0 at 6000ft

 

[overkill131313]

so if my gas mixture 32-1 that means oil and gas have to go through the main jet....which mean less fuel is going through by I think 3% so on a 400 jet does that mean 12% more fuel needs to be added or go from a 400 main to a 410? I don't know......today I hate a modded engine.....but when it runs nice it will be nice.....Im a perfectionist and the EGTs are driving me nuts how the 3 cylinders are perfect (well with in XXXX + or - xxx5) then it changes to where they are a few hundred apart then it changes again.......going to play again tomorrow but she rips pretty good today! wish the snow was not like slush so I could hook up and feel the g's.....I look back and I look like a jet boat......lol

 

[Clode]

as for jet numbers I can't help you out, make sure you check piston wash and plug color, the egt's are a reference tool, probe placement affects temp's a lot...once happy with plug color/piston wash then keep the egt's in that area and it will run well for you

 

[slededjr]

410 main PTO. 420 mains mag and center cylinder. 45 pilot in pto, 50 pilots in center and mag. Air screw at 1.5 turns out, jet needle in middle position. This is what the last one I put together ran. Might be a starting point for you. Every engine is different, so check piston wash at low, mid, and WOT.

 

[overkill131313]

EGT are low (1000-1050) so went down from the 410-420 set up to 400-410....made it worse so I pulled the plug out of the power jet and put in the only set I had besides the plugs.....performance came back but still low EGT.....going to add more fuel to mains tomorrow.....oh and the bottom end is running much better now with needles 1 clip down from middle (fattened up the mid) and it made the air screw go from 3/4-1 ish to 1.5-1.3/4 was going to replace the idle jet with some 55 but Im going to play around a bit more on all this......sled is get quicker but there is a fine line when it goes boom......lol I want to get it perfect then install the vari-flow.....going to start looking at plugs and piston wash cause EGT just seem out to lunch....now that I think about it when I had 430-440 the EGT where higher.....guess maybe it to lean that it is actually cold.....Im going to go out to a clients farm and test it out in his field cause I can not hold it pinned for 30 seconds on the trail and look at the gauges......dam near bit it when the frickin bar grip came off in my hand at 70 mph lol I need to find some grip glue that doesn't release when the grip heaters are on.....grips are great till I turn heat on.....lol

 

[DRD]

What elevation are you at? I'm surprised you need mains that big. My 809 is almost perfect at 5-6K with 310's.
Stock mains for say a 98 Mach Z are 290/300/290 at 2000" and -10 for example.

 

[slededjr]

he's running a 780 with Jaws pipes. Fatter stock jets those years as well as carbs were different.

 

[DRD]

he's running a 780 with Jaws pipes. Fatter stock jets those years as well as carbs were different.

My 809 is running 94 carbs with Jaws Hi-Altitude pipes, full deal Split Second motor, made 197 hp on Ralphs dyno. My 96 Mach z runs fine with 340's at 3k and its fat and happy. Plus 400 mains seem big to me


Sent from my iPhone using Tapatalk

 

[overkill131313]

we are sitting at 1000 feet...just weird how much fuel this thing might need!

 

[overkill131313]

the bone stock 779 that we parted out had 340-350-360 plus the power jet (cant read the numbers but they are not plugs) with bone stock pipes. the crank shop engine had way bigger (just blank right now cause I just worked 28 hours and taking a break right now) lol

 

[overkill131313]

the technical data sheet I have that was the revised one about plugging the power jets and using a PTO-390, CTR-380, MAG-400......Im sure that is sea level but we are only 1000 ish feet.....plus the jaws pipes....with the jet set up right now it pulls the ski's through out the RPM....just cold EGT and Jets that seem big from what I'm hearing.....

 

[DRD]

If plugs and wash are good and It seems nice and clean and crisp don't worry about EGT, it is what it is


Sent from my iPhone using Tapatalk

 

[overkill131313]

with the 340's what is in the power jet? stock 96 Mach Z at 0 deg C (we are sitting about 0 deg C right now)is showing 360-350-360 and 40-45-45 on the pilot jet (im running 50 but would like a 55)but can not find the power jet spec for that set up......

My 809 is running 94 carbs with Jaws Hi-Altitude pipes, full deal Split Second motor, made 197 hp on Ralphs dyno. My 96 Mach z runs fine with 340's at 3k and its fat and happy. Plus 400 mains seem big to me


Sent from my iPhone using Tapatalk

 

[DRD]

I have clippard type power jets installed instead of the factory PJ, usually leave them closed unless it's extra cold out though,


Sent from my iPhone using Tapatalk

 

[overkill131313]

going to head to a field in the next day or so....to check plugs and wash.....thanks for the help....