Looking for some information on moding out a 78 ex440. I have added a set of twin mod pipes off a srx, a set of twin butterfly mikuni 38mm carbs. It to runs good but need to get the engagement up, and look at porting the exhaust, transferports etc. Any tips on porting? Or clutching? Currently using stock clutches for ex440.
Yamaha440
Member
Look into a comet 102c. I'd set the engaugement about 3800-4200 rpm for a good holeshot. You will have to tune the shift rpm to the rpm the engine makes the most power. This will probably be the rpm the srx makes its max rpm.
Also you can shave the heads and go for higher compression, and advance the timing, provided you use race fuel, or a race fuel mix.
Also you can shave the heads and go for higher compression, and advance the timing, provided you use race fuel, or a race fuel mix.
Comet 102C clutch use HE-1 weights (51.7 grams) and a purple comet spring part#207888A as for the secondary use the stock exciter secondary with a polaris red secondary spring put in the #1 hole
This recipe comes from a guy that used to pass me quite frequently.
This recipe comes from a guy that used to pass me quite frequently.
I have the same set up in my '79 that gman posted, but with a silver/black Comet spring and the red Polaris spring in the secondary, and it engages at 4200, works great for trail and ovals...really makes a difference in performance over the stock clutching.
With the set up gman posted, the clutch will engage around 4700 rpm, which was a bit high for my liking.
There is one problem with the HE-1 weights, they are almost impossible to find (it took me over a year to find a set and I paid dearly for them $$) because they haven't been made since the 1980's. Another set up I really liked was AC-1 weights and a HPE (High Performance Engineering) orange high engagement spring, comes in around 4400 rpm and the sled pulls like a freight train until it runs out of steam
...both items are readily available.
With the set up gman posted, the clutch will engage around 4700 rpm, which was a bit high for my liking.
There is one problem with the HE-1 weights, they are almost impossible to find (it took me over a year to find a set and I paid dearly for them $$) because they haven't been made since the 1980's. Another set up I really liked was AC-1 weights and a HPE (High Performance Engineering) orange high engagement spring, comes in around 4400 rpm and the sled pulls like a freight train until it runs out of steam
...both items are readily available.
Last edited:
3g racing
New member
Ac1 weights what r those I have been messing around w a 79' 440exciter for grass was looking for a clutch set up what about gearing and jetting for a stocker
3g racing said:
AC-1 are Comet weights. I have the stock gears in my '79, but it was raced on a 1/2 mile oval, stock Keihin carb with a 145 or 150 jet depending on temps and an AAEN pipe.
I run a 140 or 145 jet in the summer depending on air temperature.