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Discussion Starter #41
Yeah I've heard that.
But I think I will try without a belly first. If it's not works good I will add a belly 馃檪
Upper midrange to highrange is where I want the power 馃檪
If I can't make it as fast as I want with 40 or 44mm cylinder I think I will swap cylinder to a closed port husqvarna cylinder. It's 44mm also
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What's the targeting rpm of the engine and the port timings, then I can help you with the exhaust. Total length from the exhaust port to the second cone is 70 - 74cm a good rang for these engines.
 

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Add two inches to the belly and take out one inch off the j bend
 

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Discussion Starter #45 (Edited)
What's the targeting rpm of the engine and the port timings, then I can help you with the exhaust. Total length from the exhaust port to the second cone is 70 - 74cm a good rang for these engines.
Yeah my target rpm is 14-15 000 rpm. I might not get to those rpms but you know "Aim for the sky and you'll reach the ceiling. Aim for the ceiling and you'll stay on the floor." :)
Durations are about 105掳 open time on transfers.
Exhaust open time are 165掳
I'm not quite sure that's the exactly the numbers. But will take new measurements tomorrow and also measure the width of the exhaust port.

The exhaust i've started modding was already the second from top minus the stinger
Add two inches to the belly and take out one inch off the j bend
Seems a little, are those exhaust almost good then? :)



I picked up a exhaust, or it was a bike with a exhaust without engine. Four stroker frame, but the exhaust is for 2 stroke and the manifold is for 4 stroke. Very strange.
It's a bit thicker than the one i started to modd.
Both the expansion chamber and header.
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Edit.
Here's the stock exhaust.
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Forgot to upload the picture of how i was thinking to weld the exhaust.
But i'm open for changes you guys know this better than me.
Stinger not added just did a quick edit of how i was thinking to build.
156806
 

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the flywheel will blow apart long before you hit 14k those bilt SPX engines can hit those kind of high RPMs

My nitrous cag would hit about 12k

You will know your getting close when you have so much compression you have to wear a leather glove and hold the bike down with your knee to start it
 

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Discussion Starter #49
Okay. I'm hope I get to 12 000 rpm then 馃檪
40mm cylinder revs higher than the 44mm cylinder?
Not by much maybe?
I suppose I am very limited with stock 1 piece cylinder.
But I might just saw the top of and use a real head on it.
Then I could set the squish clearance and squish band.
 

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Start with a engine with a 44mm piston you need the crank with correct balance factor upgrade the crank bearings to SKF you need to upgrade the crank seal's as well JDM is the way to go the China seal's won't take high rpm the rubber will melt!

You need the cylinder with the split transfer ports then case match the jug to the crank case I think it's cylinder 44-5 lightly taper the small port side going up.

Add one small boost port!

Change exhaust Port shape like a football

Take 2mm off the piston skirt boost port window in the center with anti para mod don't forget to knife edge the skirt as well

Turbo crank mod ( just make the crank counter ballance ends pointey to lower wind resistance)

Balance factor needs to be 55%

Mod the stock fly wheel take out every third fin do not use those stupid lightened flywheels you get off eBay that is to light!!!

Mod the Reed cage for better flow the Reed stops so the reeds can open farther use the stock reeds the aftermarket junk will flutter at high rpm

Open up the stock intake manifold

Use the stock carburetor!!!!
Do the petkock delete mod
Wide mouth air intake mod
Drill the fuel channel slightly bigger
Open up the fuel bowl
1/4 in fuel line
Add larger fuel vent to tank

Plan on re jetting the carby

Yes after mods the engine burns fuel really really fast !!!!

Upgrade the spark plug wire to 8mm copper core with a premium spark plug boot

Here is how I mix the fuel for this engine

20% ace #1438571 xylol paint thinner 1oz Lucas oil octain booster #10026 1/2 oz sta-bil fuel fuel stabilizer Lucas raceing 2 stroke oil #10828 mixed at 60:1 ( yes I said 60:1 ) in 91 octane ethanol free pump fuel

Expect engine life to be about two or three hrs running time.

Rember it's a knock off Robin NB 411 weed eater engine!!!
 

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Discussion Starter #51
Start with a engine with a 44mm piston you need the crank with correct balance factor upgrade the crank bearings to SKF you need to upgrade the crank seal's as well JDM is the way to go the China seal's won't take high rpm the rubber will melt!

You need the cylinder with the split transfer ports then case match the jug to the crank case I think it's cylinder 44-5 lightly taper the small port side going up.

Add one small boost port!

Change exhaust Port shape like a football

Take 2mm off the piston skirt boost port window in the center with anti para mod don't forget to knife edge the skirt as well

Turbo crank mod ( just make the crank counter ballance ends pointey to lower wind resistance)

Balance factor needs to be 55%

Mod the stock fly wheel take out every third fin do not use those stupid lightened flywheels you get off eBay that is to light!!!

Mod the Reed cage for better flow the Reed stops so the reeds can open farther use the stock reeds the aftermarket junk will flutter at high rpm

Open up the stock intake manifold

Use the stock carburetor!!!!
Do the petkock delete mod
Wide mouth air intake mod
Drill the fuel channel slightly bigger
Open up the fuel bowl
1/4 in fuel line
Add larger fuel vent to tank

Plan on re jetting the carby

Yes after mods the engine burns fuel really really fast !!!!

Upgrade the spark plug wire to 8mm copper core with a premium spark plug boot

Here is how I mix the fuel for this engine

20% ace #1438571 xylol paint thinner 1oz Lucas oil octain booster #10026 1/2 oz sta-bil fuel fuel stabilizer Lucas raceing 2 stroke oil #10828 mixed at 60:1 ( yes I said 60:1 ) in 91 octane ethanol free pump fuel

Expect engine life to be about two or three hrs running time.

Rember it's a knock off Robin NB 411 weed eater engine!!!
Alright. I've got 2 engine's with 44mm cylinders. So will see which of those cranks that works out best.
Also my 44mm cylinder with split transfers are a nice one. The piston btdc is slightly under the exhaust port without base gasket.
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How much shall the Flywheel weight? I've got one that I removed every third and that's heavier than the other stock Flywheel I've got.

Also how much shall the reed stop open? It differs a lot between the ones I have.

If the balance factor is 55% and if the flywheel is out of balance wouldn't that change the balance factor?

Thank you so much for your help
 

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Discussion Starter #52
Hi! So I am about to start the blueprint of the 44mm cylinder engine.
Cylinder skirt shall I grind that down so it's a smooth transition from cylinder to the case?

Then I need to grind down the case where the transfer channels are

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Discussion Starter #54
Did I screwed it?
When looking on other cylinders people don't cut the edges on the skirt on the exhaust side
 

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It looks good now smooth everything out with some 400 grit sand paper
 

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Discussion Starter #57
Great i will do that.
I have not done the exhaust port yet.
Needs to assemble the cases first so I can measure the durations.

Reed basket or what we call the reed plate thing.
It is turned the wrong way stock.
I will turn the reed plate 180掳 so the flow gets right
 

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Do not turn it around a member spent a lot of time doing that very mod with a very negative outcome
 

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Discussion Starter #59
Do not turn it around a member spent a lot of time doing that very mod with a very negative outcome
What happened?
Didn't he check the clearance between the reed stop and the crankshaft/crank? Cause when flipping it around it will not spinn freely if not grinding away a bit from the the reed stop.
 

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He used a milling machine and shaved it to make everything fit and work. At mid and high throttle it had massive Reed flutter he tried all different kinds of reed materials as well
 
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