RideRed264
Active Member
Hi,
What are some of the best modifications to make on a js440 to make more hp?
Thanks, Ed
What are some of the best modifications to make on a js440 to make more hp?
Thanks, Ed
Js440 Upgrades
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Dr Honda
Well-Known Member
There's a ton you can do to that little engine. IT was super reliable, as long as you don't let it go lean.
1) Exhaust. The best thing you can do is pitch the factory waterbox, and get an aftermarket pipe. The OE pipe was OK... but you can easily find 15 hp with the right pipe. I personally liked the Westcoast pipe... but there are a lot out there. Oh... I also turned mine into a rear exhaust to get rid of that stupid pipe on the side that will put smoke in your face.
2) Carbs. The stock carbs are ok, but the stock airbox is restrictive. I almost never say to remove the factory airbox but in this case, any aftermarket filters are better. The Ocean Pro units are good. The carbs themselves are small. Simply going to the set that came on the 550 engine will help. If you are serious... find a set of old Buckshots.
3) Reeds. The factory reeds are going to be tired. Replace with fiberglass Boyson. (not the carbon reeds)
4) Compression. You can really bump the compression, but don't just shave the head. All kinds of bad will happen. A properly shapped new combustion chamber is a must. Either send your head out to Group K... or find an old Westcoast head. As I recall... I was running a 165psi static compression, and running premium to keep pre-ignition at bay.
5) Porting. This is a little bit of black magic... but raising the exhaust ports about 0.010" will boost top speed, at the expense of a low idle. Also, widening the bypass ports will help mid.
6) Pump. If you find a bunch more power... the stock little pump isn't going to like it. Back in the day, Skat-Trak made oversized impellers, and it was common to bore pumps... but I doubt you can get them anymore. SO... just make sure you have a good impeller, and tight tolerences. Oh... boring the nozzle will be needed just to get the water out with your new, higher RPM's.
7) If you really want to get crazy... there are stroke kits, and big bore... but since we are talking about +30 year old engines... it's getting hard to find some of this stuff.
Good luck
1) Exhaust. The best thing you can do is pitch the factory waterbox, and get an aftermarket pipe. The OE pipe was OK... but you can easily find 15 hp with the right pipe. I personally liked the Westcoast pipe... but there are a lot out there. Oh... I also turned mine into a rear exhaust to get rid of that stupid pipe on the side that will put smoke in your face.
2) Carbs. The stock carbs are ok, but the stock airbox is restrictive. I almost never say to remove the factory airbox but in this case, any aftermarket filters are better. The Ocean Pro units are good. The carbs themselves are small. Simply going to the set that came on the 550 engine will help. If you are serious... find a set of old Buckshots.
3) Reeds. The factory reeds are going to be tired. Replace with fiberglass Boyson. (not the carbon reeds)
4) Compression. You can really bump the compression, but don't just shave the head. All kinds of bad will happen. A properly shapped new combustion chamber is a must. Either send your head out to Group K... or find an old Westcoast head. As I recall... I was running a 165psi static compression, and running premium to keep pre-ignition at bay.
5) Porting. This is a little bit of black magic... but raising the exhaust ports about 0.010" will boost top speed, at the expense of a low idle. Also, widening the bypass ports will help mid.
6) Pump. If you find a bunch more power... the stock little pump isn't going to like it. Back in the day, Skat-Trak made oversized impellers, and it was common to bore pumps... but I doubt you can get them anymore. SO... just make sure you have a good impeller, and tight tolerences. Oh... boring the nozzle will be needed just to get the water out with your new, higher RPM's.
7) If you really want to get crazy... there are stroke kits, and big bore... but since we are talking about +30 year old engines... it's getting hard to find some of this stuff.
Good luck
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