FASTonGRASS
New member
my prostock 700 viper needs help. 500 ft grass.
121 track just lengthend to 136.
rathburn performace engine
jaws pipes
hauck clutching with my own cam arms
taper bored stock carbs
problem is always runs 1.4 60' and 5.4 at 89 mph. need to be at 99 to101 with 5.1 to 4.9 to be competitive.
tried over drive clutch sheaves and no help
also tried big carbs
121 track just lengthend to 136.
rathburn performace engine
jaws pipes
hauck clutching with my own cam arms
taper bored stock carbs
problem is always runs 1.4 60' and 5.4 at 89 mph. need to be at 99 to101 with 5.1 to 4.9 to be competitive.
tried over drive clutch sheaves and no help
also tried big carbs
what are you geared at?
FASTonGRASS
New member
geared at a 2.05. would like to gear down more.
FASTonGRASS
New member
19/39 gears
thats why your low on mph your too deep, take some gear out of it, if the motor makes good power it will pull taller gears and give you more mph, taller gears(lower numericly) load the motor more, steeper gears take the load off the engine.
If this is a real prostock 700 it should be ALOT lighter then a stocker so you dont need as much gear, whats the sled weigh?
If this is a real prostock 700 it should be ALOT lighter then a stocker so you dont need as much gear, whats the sled weigh?
FASTonGRASS
New member
wheight is 632 with driver
9801srx
Member
like mr.viper said your geared to low .2.05 at 8500rpm =89 mph on paper .try 21/39 which is good for 98 mph at 8500 rpm or 22/39 for 103 mph.
FASTonGRASS
New member
running 10200 rpms
your still geared way too low, if its a prostock sled its lighter and makes way more power, so it doesnt need that steep of gearing like a stocker does to move itself, actually will go faster with taller gearing, less time spent revving the engine and more distance covered by moving the sled forward.
FASTonGRASS
New member
Are the stock carbs better for 500',or should I use the 48mm?
If so what is a good starting point for jetting with stock carbs?
If so what is a good starting point for jetting with stock carbs?
48mm carbs on a 700?? I doubt it......44mm lectron is about as big as a 700 yamaha will take, 48mm would be for a 1000cc engine.
smaller sized carbs will be better in a short run however larger carbs will make more horsepower up topend, but will suffer low end from alot weaker vacum/fuel pick up signal from the larger venturi
you better get ahold of the engine builder for jetting, nobody here is gonna be able to tell you the jetting for that combo, never heard of the engine builder. If they built the engine with pipe combo and carbs etc. thats who you need to be talking to, not a public forum.
smaller sized carbs will be better in a short run however larger carbs will make more horsepower up topend, but will suffer low end from alot weaker vacum/fuel pick up signal from the larger venturi
you better get ahold of the engine builder for jetting, nobody here is gonna be able to tell you the jetting for that combo, never heard of the engine builder. If they built the engine with pipe combo and carbs etc. thats who you need to be talking to, not a public forum.
FASTonGRASS
New member
ok ill check into it. whole setup came from jaws. shouldnt be to hard to find out.
toydoc
Member
I'm thinking the same as Don. 48mm will hurt your 60' and may not add et. It may not like 44's.
IMO, take some test carbs (38's, 44's, 48's) put your sled on a track dyno and see what it does or likes. Also play with gearing. I'd guess you will need 103ish hp to the track to run 4.9's...and thats not easy.
IMO, take some test carbs (38's, 44's, 48's) put your sled on a track dyno and see what it does or likes. Also play with gearing. I'd guess you will need 103ish hp to the track to run 4.9's...and thats not easy.