ported engine theory. do I suck or does it suck?

[mthomps]

Man, maybe I'm just bored, I donno. Or maybe I'm right (probably not)

I have 3 skis. a bone stock 94 sn, a 91 sn 701 transplant ported with every gadget possible besides big bore and zeel., and a kawi 300sx. The 91 is my main ski. It's a ported x motor at 718cc, a set back Skat mag pump, jetworks A propped bored nozzle dozzle. Msd enhanced cdi, b piped lightened flywheel girdled with the fancy ada head at 180 compression, and I have to be honest I dont like the response of the motor.

On the built up 91 ski, no matter how I tune it, there is that "light switch" spot. Where it just takes off. At first it was cool but I'm not an upside down guy, I'm just a chump who surfs waves from big boats and what lake erie gives when I sense it doesn't want to kill me. I'm not a mechanic, I just read manuals. The 650 and the fancy pump felt better. It was linear.

Maybe I'm doing something wrong, but I ride hard when I go at it. I like site seeing near the shore as much as shredding. But when 1mm difference in throttle shoots me to the moon where as my stocker allows me to predict my tradectery, honestly i'll take a piped stocker.

I bought a jetworks ported cylinder from a member here and there was nothing wrong with the sale, absolutely stand up dude, but when I tuned it to jetworks specs its just super rich, even after multiple carb rebuilds. Art said run a 2.3 ns, and I cant remember the jet sizes. It always feels rich till the sweet spot. But, damn man, I want all the spots sweet.

I guess I'm just bitching, but if i could do it again I'd just pipe it, prop and nozzle job and say f u to the porting.

 

[TheBuzzard]

I've never noticed light switch power with quality porting but the crazy Russian got in there and ported his cylinder and I did experience the light switch effect. It was in a pos eme micro thats already basically unrideable. Maybe try water screw adjustment to change where it comes on. Best bottom end is water injected closest to the exhaust ports.

 

[MADMAT]

I need to shred your 94 just to remember that I completely agree.

Super mild porting only here...same718....same comp.....just light switchy enough but not too much.

I have ridden what you are describing and hate it.

The only diff I see is I am stock pump and you know my prop.

 

[joeschuit]

What carbs are you using? I had a jetmaniac 718 with jetted 38's that had a similar effect. Feels like a 125 2 stroke dirtbike powerband. Moving to zeel and dual 44's improved the horsepower under the curve to eliminate the burst of power. Sounds like you need more timing down low and more fuel.

 

[mthomps]

I've never noticed light switch power with quality porting but the crazy Russian got in there and ported his cylinder and I did experience the light switch effect. It was in a pos eme micro thats already basically unrideable. Maybe try water screw adjustment to change where it comes on. Best bottom end is water injected closest to the exhaust ports.

I've rode an eme one time and it sucked. Tippy mess. Now the same bro let me ride his vision and it was like a superjet on steroids. Thank you, velociraptor.
Yeah, I'm going to seriously screw with the.....screws next year. The motor just runs so hot I'm afraid to lean this crap out. But i really dont know what I'm doing. I'm just a dude that likes using his ass as a tubby.

 

[mthomps]

I need to shred your 94 just to remember that I completely agree.

Super mild porting only here...same718....same comp.....just light switchy enough but not too much.

I have ridden what you are describing and hate it.

The only diff I see is I am stock pump and you know my prop.

You're in luck matty! I'm back home close to the edge. Ride both and tell me what you think. I donno man. Maybe I'm missing something simple but right now I'm thinking what was the point.

 

[mthomps]

What carbs are you using? I had a jetmaniac 718 with jetted 38's that had a similar effect. Feels like a 125 2 stroke dirtbike powerband. Moving to zeel and dual 44's improved the horsepower under the curve to eliminate the burst of power. Sounds like you need more timing down low and more fuel.

It's just a simple wetjet single carb 46. For what its worth the timing is advanced on top of the msd curve. This ski is an absolute beast in the mid and i truly enjoy riding it. I just hate the fact that I wanted more linear power and what i have is a rubber band thing. We all have are opinions on reading plugs, but mine are always dark and usually wet with fuel mixture.

I really dont want to lean this thing out much more. Even with dual cooling this thing is hot as all at the end of the ride. I guess I have to just mess around with the b pipe screws and see what I get. All I know is I don't like how this motor responds.

 

[Half flip95]

sounds like its a combination of things. It is probably not ported enough... as in ports haven't been raised enough to broaden out the power. 61x with all those parts thrown at it will get on the pipe really fast and go 0 to 45 in like 2 seconds. Water screws are a good place to start, but i would try to run it as dry as possible with only the bottom screw open about an 8th. I think that will help smooth out the hit.

also that big single carb is adding to the light switch feel. I have the same set-up on my wifes square. Going to a single 44 would tame that thing down for sure. I havent tried dual 38s on the x cases, but that is also an option.

 

[kevbo]

The rush of power is your pipe working. You can alter the effect but it will never go away any time a good tuned pipe is used. If its a B-pipe try killing it with more water. If you want very linear power install the stock pipe.

 

[mthomps]

sounds like its a combination of things. It is probably not ported enough... as in ports haven't been raised enough to broaden out the power. 61x with all those parts thrown at it will get on the pipe really fast and go 0 to 45 in like 2 seconds.

Yeah, thats pretty much exactly what it does. After 1/4 throttle it just takes off like a rocket. I bought the 94 for my ex gf and she wouldn't ride my ski because she was afraid of it. As far as the porting goes I couldn't tell anyone how mild or aggressive it is. All I know that its from jetworks and its their freeride porting. I bought it from a reputable poster here who went bigger.

I'm tempted to try my extra 44mm carb on it but its attached to my back up set up and tuned perfectly for it. Just a 650 with protec pipe, but its so crisp and snappy I'd hate to mess with it.
Besides messing with the water settings on the pipe do you guys think its worth getting a set of 62t cases and going dual 38's? I don't really have plans to go any bigger than what I have but if its worth it I'd definitely consider it.

 

[fastgtfairlane]

I bet you would love a 62t/62t ported setup with dual 44s. Very linear power from idle to max rpm my setup is very linear. Which chamber are you running? Limited or mod? Limited is gonna make more power on the bottom than the mod. Definitely try playing with the water screws they do make a difference.

 

[mthomps]

I'm...70% sure its a mod chamber. When I bought the cylinder I emailed art, sent all my stuff to him and had him do his thing. First thing I did was install the new prop and the ported nozzle. I was so happy with the snap on a 650 with a protec pipe I sat on the cylinder for a year. Then I built the 61x with the jetworks cylinder, I couldnt find a way to prevent the protec pipe from rattling off the 701 motor so I said screw it, I'll get a b pipe. And then I went nuts and got every possible bolt on you can do to an sn sj.

And just to emphasize, the driveline is healthy, if anything it's detuned because I'm scared of blowing up all these expensive parts that cost more than the ski did. After years of building this thing up, while its a fun and powerful ski, its exactly what I didn't want. I want the linear response of a stocker but way more power. So I'll start with some serious b pipe tuning and go from there I guess.

 

[MADMAT]

I would like to try a properly setup 62t 62t someday. I had a non ported non decked and I hated it. Linear of course but no snap.

 

[Big Kahuna]

If you open the middle screw this will soften it up some, also agree on the bottom screw. Single SBN 44 (Aftermarket version, but not modified) will work really well also. I ran the 44 for a while then switched to a TLR Modded 48/44 (Bottom was bored to 48), It worked great for freestyle, but not so good cruising.

 

[Half flip95]

Going to the t cases and dual 38s would be a big expense.
tuning your current components might be cheaper and more effective.
pump load is a place you can really change the attitude of the power delivery. A stock nozzle might smooth out the hit.
putting the stator back at 0 advance could help , but that is more labor intensive

its hard to say for sure because we all have our go to set-ups. When you deviate from what you know works for you it can be a process to get everything working together. Of any of the suggested mods, I would only do one at a time. I know the 44 will choke that thing down and slow the power output. I would try the stock nozzle first, but you might end up going back to the bored nozzle if you go 44

 

[Sparkplug]

Ride different. Or get a stock ski

Bursts of throttle are how you make the ski handle in a short small area. Or incredibly fast. You let of the throttle. Turn the bars where you want them. Then blip full throttle. Constantly. Over. And over. And over. The throttle is never held in a constant position unless it's wide open in a linr. It is ALWAYS being varied. And always being opened at least 3/4. It's a much different way to ride than the old guys used to do in the 90s. And how most rec riders ride nowadays. It is why alot of old skool guys can't ride short hulls with power. They are riding it wrong.

If you want to cruise the lake. Lower compression. Smaller carbs. Wet the pipe. And get a heavier throttle spring. 2 strokes want to be on the pipe.

 

[Jhucke]

I feel like most people have their engines built to purposefully obtain light switch, crazier throttle response. If you don't appreciate this type of power delivery & are riding to site see, maybe a built engine + mag pump really isn't necessary for you. Nothing wrong with that. You can mellow out your pipe though by messing with the injection screws, but you will lose performance. The pipe is what is really giving you that hit.

 

[MADMAT]

Constantly. Over. And over. And over. And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.And over. And over.

Until the tank is empty! Yea baby! BRAP!

 

[mthomps]

Maybe im being misunderstood. I ride really hard and really fast. If i could find one Id race. Not sure how saying i like to site see meant all i do is plop around. Not sure why a maxed out superjet cant do both, as if ported motors and pipes mean you cant take a moment to look at some rocks, lol.

Nascars can chill behind a pace car, why cant a 30 yr old sj.

Im gonna take the advice given and play with my b pipe.

 

[bored&stroked]

I have a 61x cylinder I had bored to 84mm and ported it myself using the port templates sold on here. I had a head shaved and cut for the 84mm bore and big race gas compression. In my old square nose, I put this on the stock 61x cases and carb, with a protec black pipe. This combo was very linear and great to ride.

Then I got a deal on a RN I couldn't pass us. I kept my cylinder and head from the square [just swapped them between skis and sold the SN] and put it on the RN. The differences are the RN has oem 760 dual 44's, and a limited chamber B pipe. It now rides exactly like your 91. Anything below half throttle, it is linear and adjustable. Right around half throttle, it explodes like a cannon and more throttle doesn't feel like it does much extra. Pretty sure 5/8ths throttle is about as fast as 8/8ths lol. Yes, its much faster now. But I really hate this light switch response. I want to be able to cruise at half throttle and get half throttle power.