Hi guy's need some help. I have a 1975 gpx 433, motor has been rebuilt. Fuel will be c-12 race fuel. motor dynoed at 95 hp@ 9500 rpm with Aaen race open pipes. Putting 102c comet clutch on the sled. Will be using the sled for ice drags 660'. Would like some advice on clutch set up for a good starting point; spring colour and weights. Any advice would be great.
gpx 433 clutching
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get a hold of yamigod3:16 he's guro with the old srx's and gpx stuff.
YAMMIEGOD3:16
Active member
GPX RACER (thanks pro116 ) GOOD MOVE GOING TOO A COMET, ALOT MORE TUNEING OPTIONS. FIRST YOUR GONNA NEED ATLEAST A 6000/6500 ENGAGEMENT. THE SPRING I LIKE YA TOO TRY IS EITHER ONE OF THESE.
PURPLE OR YELLOW/GREEN. you may need afew shims also.
NOW WEIGHTS. AFEWOPTIONS BUT ALL WILL NEED NOTCH FOR ENGAGEMENT
N1- # 209642A
P1- #209782A
C - #202892A
NOW MOST COMET WEIGHTS START OUT AS A ''C'' AND ARE CUT, AND BUSHING INSTALLED. YOUR GONNA HAVE TOO TEST HERE. EITHER SPRINGS WILL WORK , MY GUT IS YELLOW/ GREEN WILL WORK BETTER WITH THOSE PIPES AND AT THAT RPM. 3:16 (tony)
PURPLE OR YELLOW/GREEN. you may need afew shims also.
NOW WEIGHTS. AFEWOPTIONS BUT ALL WILL NEED NOTCH FOR ENGAGEMENT
N1- # 209642A
P1- #209782A
C - #202892A
NOW MOST COMET WEIGHTS START OUT AS A ''C'' AND ARE CUT, AND BUSHING INSTALLED. YOUR GONNA HAVE TOO TEST HERE. EITHER SPRINGS WILL WORK , MY GUT IS YELLOW/ GREEN WILL WORK BETTER WITH THOSE PIPES AND AT THAT RPM. 3:16 (tony)
RJH
New member
We ran the GYT clutch parts in the 433 - but the secondary had to be wound up pretty tight. GYT pipes and cylinders and heads – pump gas. Won a lot of races when the competition was stiff. 8750 rpm with a 5000 engagement no mods.
The best working Yamaha will not beat the best working Thunder Jet in a drag race unless you get rid of about 200 pounds.
On the other hand…that same Yamaha will catch and pass the best TJ on a ½ mile oval – in about 4 laps.
Put the front skid H arm from a GP433 in it, better leverage on the start and GP433 NEW springs.
The best working Yamaha will not beat the best working Thunder Jet in a drag race unless you get rid of about 200 pounds.
On the other hand…that same Yamaha will catch and pass the best TJ on a ½ mile oval – in about 4 laps. Put the front skid H arm from a GP433 in it, better leverage on the start and GP433 NEW springs.
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YAMMIEGOD3:16
Active member
THE GYT SPRING TO USE IS THE SILVER (red mark ) , THIS WILL BRING ENGAGEMENT WAY UP. YOUR USEING A COMET SO THIS WON,T HELP. 3:16 (tony)
RJH
New member
Right ... we used the GYT spring and GYT cam in the OEM Yamaha clutch for 5000 engagement.
The sliding half has to move PERFECT on the splines in order to work.
The sliding half has to move PERFECT on the splines in order to work.
thunderjet440
New member
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- Oct 30, 2005
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doesn't this setup kick in about 5500 to 5700?RJH said:
i have the spring and the cam ring and will be trying it out when we get more snow
RJH
New member
TJ440
That was along time ago - anything above 5K was bad for starts. I'm almost sure the stock GYT spring AND cam gave us 5K.
We used the GYT clutch in our stocker and the the following year in mod stock - but wound the secondary up like a bow string then.
Maybe I fooled with the cam - I seem to recal (maybe) having the outside cut to change the angle of the arms no I forget.
That was along time ago - anything above 5K was bad for starts. I'm almost sure the stock GYT spring AND cam gave us 5K.
We used the GYT clutch in our stocker and the the following year in mod stock - but wound the secondary up like a bow string then.
Maybe I fooled with the cam - I seem to recal (maybe) having the outside cut to change the angle of the arms
no I forget.YAMMIEGOD3:16
Active member
5000 ALL DAY LONG WITH GYT SPRING. 3:16 (tony)
thunderjet440
New member
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Last year i ran the 74 thunderjet 340 spring and gyt cam ring and it kicked in about 4500 or so,i have both the gyt springs(74's] and will try them out.
how much extra do you gain with gyt ring over the stock ring? and what would be a good shift rpm for my setup
75 cylinders and heads.heads have the combustion chamber mod,polished chambers,casting slag ground off the intake side,exhaust polished,stock carbs
and exhuast set up to the factory bulletin. .40 over wiesco's and if i remember right it tested at 180 psi. 8200 to 8500 rpm?
merry christmas and happy new year eveyone
{sorry to highjack the post gpx racer}
how much extra do you gain with gyt ring over the stock ring? and what would be a good shift rpm for my setup
75 cylinders and heads.heads have the combustion chamber mod,polished chambers,casting slag ground off the intake side,exhaust polished,stock carbs
and exhuast set up to the factory bulletin. .40 over wiesco's and if i remember right it tested at 180 psi. 8200 to 8500 rpm?
merry christmas and happy new year eveyone
{sorry to highjack the post gpx racer}
RJH
New member
We ran the 440 GYT clutch parts in both the 340 and 440.
Modding the GYT heads would proably result in less HP after about 5 minutes of running. Ours ran at 8750.
We ran them all GYT stock - on pump gas - won many races.
Modding the GYT heads would proably result in less HP after about 5 minutes of running. Ours ran at 8750.
We ran them all GYT stock - on pump gas - won many races.
thunderjet440
New member
- Joined
- Oct 30, 2005
- Messages
- 114
RJ,my head and cylinders are stock xb units.i had the combustion chamber recessed .20,supposed to get it to fire all around the piston instead of just the center of the piston.i've been told it's worth 3 to 5 horse.