4 - stroke Schwinn Stingray Chopper occ



dmopedMA

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Apr 14, 2017
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157
I adjusted valves on it, no mayor change, they where not really offset, but I realized I was loosing pressure on the junctions between the flex tube and the other parts of the exhaust, so I ordered two of these heavy duty clamps: https://www.amazon.com/gp/product/B00H7YMSES/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

It now bugs less on high RPM just installing one of these clamp, the other one broke while installing, so I'm waiting for the second one to arrive.

I tough that on 4-stroke the exhaust was not that important, just a way of putting gas out of the cylinder... Anyone can explain to me if this is really a thing or I'm just wrong?
 

Frankenstein

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Jun 24, 2016
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5,078
I adjusted valves on it, no mayor change, they where not really offset, but I realized I was loosing pressure on the junctions between the flex tube and the other parts of the exhaust, so I ordered two of these heavy duty clamps: https://www.amazon.com/gp/product/B00H7YMSES/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

It now bugs less on high RPM just installing one of these clamp, the other one broke while installing, so I'm waiting for the second one to arrive.

I tough that on 4-stroke the exhaust was not that important, just a way of putting gas out of the cylinder... Anyone can explain to me if this is really a thing or I'm just wrong?
Well.. Less leaks means more backpressure, which in a 4 stroke means it should be worse on gas, but that means nothing in terms of performance, maybe without the restriction the engine was spinning too fast for its cdi and just plain acting out, much like a bad 2 stroke cdi behaves beyond a certain rpm. The extra pressure may just be keeping the engine within a sort of governed state, which is likely better for it than letting it get spooky at top speed.. I would use muffler clamps, while they are larger and uglier they really seal up nicely. If not then welding is always a good idea, it's much smoother and relatively air tight.

Tell me if you can weld that flexible exhaust tube, I've had odd difficulty with it, namely it wants to melt away before the arc and pool even approaches, maybe I needed to use a weaker welder..
 

dmopedMA

Active Member
Joined
Apr 14, 2017
Messages
157
Well.. Less leaks means more backpressure, which in a 4 stroke means it should be worse on gas, but that means nothing in terms of performance, maybe without the restriction the engine was spinning too fast for its cdi and just plain acting out, much like a bad 2 stroke cdi behaves beyond a certain rpm. The extra pressure may just be keeping the engine within a sort of governed state, which is likely better for it than letting it get spooky at top speed.. I would use muffler clamps, while they are larger and uglier they really seal up nicely. If not then welding is always a good idea, it's much smoother and relatively air tight.

Tell me if you can weld that flexible exhaust tube, I've had odd difficulty with it, namely it wants to melt away before the arc and pool even approaches, maybe I needed to use a weaker welder..
Thank you for your comments. Welding is not an option so far, I don't have the skills neither the tools... These clamps I'm using now are made for exhausts, so I hope they are enough.

Any other idea why it could be bugging on the top RPMs? something else to check?
 

Frankenstein

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Jun 24, 2016
Messages
5,078
Thank you for your comments. Welding is not an option so far, I don't have the skills neither the tools... These clamps I'm using now are made for exhausts, so I hope they are enough.

Any other idea why it could be bugging on the top RPMs? something else to check?
No I don't, I just haven't played with these 4 strokes enough, though it is very likely they just aren't tuned up for high rpm out of the factory, hell most normal car engines arent really meant to top out, they don't need to either, they have transmissions to get the speed up there.

If you look at go kart sites that specialize in the harbor freight 212 you'll see there are quite a lot of mods and aftermarket parts to drag the top speed out of a motor. Maybe give higher octane fuel a shot, check your plug and exhaust for carbon, sometimes you just need a slight carb adjustment of the engine components are at peak adjustment. Hey at least if you screw up you don't need an engine lift to find out what you did wrong, and if you drop a part down the crankcase you don't have to pull an oil pan hoping youll find it, just turn it upside down, one hand!
 

dmopedMA

Active Member
Joined
Apr 14, 2017
Messages
157
No I don't, I just haven't played with these 4 strokes enough, though it is very likely they just aren't tuned up for high rpm out of the factory, hell most normal car engines arent really meant to top out, they don't need to either, they have transmissions to get the speed up there.

If you look at go kart sites that specialize in the harbor freight 212 you'll see there are quite a lot of mods and aftermarket parts to drag the top speed out of a motor. Maybe give higher octane fuel a shot, check your plug and exhaust for carbon, sometimes you just need a slight carb adjustment of the engine components are at peak adjustment. Hey at least if you screw up you don't need an engine lift to find out what you did wrong, and if you drop a part down the crankcase you don't have to pull an oil pan hoping youll find it, just turn it upside down, one hand!
Well, I was playing yesterday with it. I add the second clamp to the exhaust, so now it is properly set up, after that, I removed the air filter and played with the air/fuel mix screw and looks like there is a configuration where it doesn't bug on the high RPMs, so I ordered a new air filter that is less restrictive, and a tachometer to know exactly how I am on the RPMs, I feel like I get to the max RPM too fast.

Right now I'm getting a max speed or 26-27mph which is not bad, but I would like to cruise at 25mph without having to max out the motor, maybe it's time to change the sprocket (again) for something a little bit smaller, I'm running on a 40t, I tried 36t and the acceleration was too poor, maybe now with all the improvements on the exhaust, valves, gas/air mix and air filter, works just fine, but I'm afraid I'll have to order a 38t soon.

That's all so far!
 

dmopedMA

Active Member
Joined
Apr 14, 2017
Messages
157
Well, I was playing yesterday with it. I add the second clamp to the exhaust, so now it is properly set up, after that, I removed the air filter and played with the air/fuel mix screw and looks like there is a configuration where it doesn't bug on the high RPMs, so I ordered a new air filter that is less restrictive, and a tachometer to know exactly how I am on the RPMs, I feel like I get to the max RPM too fast.

Right now I'm getting a max speed or 26-27mph which is not bad, but I would like to cruise at 25mph without having to max out the motor, maybe it's time to change the sprocket (again) for something a little bit smaller, I'm running on a 40t, I tried 36t and the acceleration was too poor, maybe now with all the improvements on the exhaust, valves, gas/air mix and air filter, works just fine, but I'm afraid I'll have to order a 38t soon.

That's all so far!
I just realized I have a 10t pulley around and I believe I'm using the 9t, so that may give me the little more speed I'm looking for...
 

dmopedMA

Active Member
Joined
Apr 14, 2017
Messages
157
I just realized I have a 10t pulley around and I believe I'm using the 9t, so that may give me the little more speed I'm looking for...
Yeah! 10t does the trick! I was able to get 29mph while I still have a decent low speed torque.

Screenshot_20180623-173332.png
 
M

Moto Mark

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I'm starting my first build on a OCC Srltingray. Is there a special motor mount for the 4 strokes? Anything special needed? Debating on 2 or 4 stroke. Like the dependability of 4 stroke.
 
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