1982 430CR Performance Mods

when the reeds shut? theres a flow problem? .......do you know the purpose of using reeds in a two cycle engine?

500 pipe has bigger diameter stinger, at least

The boost bottles work on twins and triples because they fire at 180 degree or 120 degrees and the excess pulse of fuel and air can escape from the intake being pressurized to the tract which is under suction. This does not work in a reed valve single because if the reed is designed properly and is functioning properly there is no fuel/air charge forced past it backwards into the intake tract. Since the boost bottle is in between the reed and carburetor there is no possible way it can do anything unless the reed is damaged or not designed correctly. On a piston port engine like the one in the video there is no reed valve so there is massive reversion of the fuel/air charge as the piston is on the down stroke and in that case the boost bottle does work.

The 430 and 500 pipes are not the same.

Would a built 430 use a 500cr pipe?

I notice with the boost bottles they offer nitrous setups too. That would be so cool to pull up to a light and bleed it off then race the guy next to me? Kidding. I did hammer a young kid in his import with my 98 Husqvarna 250wr of a red light. That bike had more get up and go than Rambo with no Botox.

Here are some photos of a 430 cylinder I picked up a number of years ago. Bought it because it had a mossbarger reed assembly on it and was surprised when it arrived and was ported as such. The photos on the sellers site did not show the side with the European pro Porting Stage 4 markings on it !! and it is on standard bore.

Two stroke exhaust pipes are tuned primarily for reflecting the sound pressure wave back towards the combustion chamber to help stop the incoming intake charge at the exhaust port before the piston closes off the port. There are many variables but stroke is a main factor and a pipe designed for the 500 with its much longer stroke than the 430 would probably make significantly less power than the stock 430 pipe.

In the mid to late 90s I raced jet skis and several guys built two strokes with nitrous. It never worked as well as with a four stroke because the nitrous blew the fresh charge right through the combustion chamber and out the exhaust, wasting most of it.

would be interesting to to take measurements and/or degree it to see what alterations were made.

A quick measure seems to follow the Husky porting measurements in the article above.

Think of it this way. There's a one way valve in front of the carb." Reeds". There open and the slide is open on the carb the 2t mix is flowing in the cylinder. Now everything slams shut. The cooler atomized gasses are trapped between the carbs sleeve and reeds. They get hot from the engines heat and expand. Now if a boost bottle is present the hot gasses charge the boost bottle relieving some of the pressure between the carb and reeds. If no boost bottle is present the gasses get a tab of pressurized and the throttle can get a little rich and soggy. This is why the boost bottle smooths out the throttles transistion.

I'm just trying to think this through. If the carb is jetted correctly it should be noticeable on exactly what the boost bottle does.

I must think this out and go slow it could turn into a frankenstien (430) and then frankenstien needs a bride next (390)? Porting I'm sure of I tested different cylinders already. The 81 250cr had all the different porting I tested in one package. She was mellow till you wicked it. Grant you its just a 250 but she ate any other 250 that came near it.

I'd like to see the pic of the exhaust port.

I open up the exhaust port, arch the upper part of the port and raise it a tad. Then widen it a little like 1/16" then polish it. Once you do all the porting the engine is right there on the throttle. There is no lag when you twist it its response is right there. You will see the difference.

How many different stages of porting is there?

On the Yamaha banshee they tap both cylinders into one boost port. This balances the cylinders in a way.

In the

In the cylinder there showing the rear port window with the VEE cut. Why is it a VEE? Remember the cr cylinders with the extra window between the transfer port and the rear intake port? I don't like the VEE cut with the piston ring going by it. I would remove the VEE shape a tad.

With the difference between the 500cr pipe and the 430cr pipe. If we look at the more modern bikes the after market chambers are larger over the stock pipes. I believe this allows the gas flow to happen quicker from the transfer ports.
As the hot gasses leave the engine quicker with the larger chamber it sucks in the fresh mix into the engine smoother.
Can we have too much of a pipe/chamber? At a low rpm maybe. But at a higher rpm it's all about smoothing out the flow.

these bikes do not have problems like you are trying to make them out to have. do you know the reed opens and closes almost exactly along with rpm? so if a bike is revving 6000 rpm, the valve is opening and closing 6000 times?
there is more to pipe design than size and volume..if you havent, you need to read "2 stroke performance tuning" by A Graham Bell.
you like to praise the swede engineers, but think they accidentally put the 430's pipe on the 500?

I'm just putting some ideas out there nothing's in cement. In my teens I was building drag race engines. Porting was a must. But some guys thought adding a four barrel carb was it. They left out the cam and headers. My point Is just one change won't make that much of a difference. It could even run worse.
Building drag race engines was my passion I'm sorry I didn't pursue it. Doing all the changes works together we could end up with a monster on our hands.

No, this totally wrong. The incoming charge does not heat up at all, it is only stopped for a millisecond, (1/100th of a second at 6000 RPM) and in fact if you touch the cases on a two stroke jet ski on the intake side by the reed valves, they are cold to the touch because the incoming charge cools the bottom end. So, the incoming gasses do not expand, on a piston port the secondary compression (crank case pressure) pushes the fresh charge backwards when the piston is on the down stroke, since the carb only acts on vacuum pressure, it does not know or care if air is moving forwards or backwards, it adds more fuel to the charge creating a rich condition. The only function of the reed valve is to stop the reverse pulse on the intake charge backwards through the carb. Boost bottles are on the carb side of the reed, which makes them virtually useless because IF the reed valve is doing its job there will be little to no pressure on that side of the carb. In addition, if there was pressure on that side, the boost bottle does not allow them room to expand, what it does is the same thing as an accumulator tank on an air compressor, it increases the volume of the system to minimize the change in pressure, the greater the volume of the accumulator the less change in pressure there is when air is added or released. That is the idea behind the boost bottle, and that is why it does work on a piston port engine but does not work with a reed valve intake, if your reed is designed correctly and functioning correctly, there is absolutely nothing to be gained by adding a boost bottle.

I'm sure there is a good reason the engineers at Husqvarna changed the shape of those ports. Why second guess them?

The shape of the expansion chamber tunes sound wave travel, not gas flow. The sound pressure wave is what creates the extraction of the spent charge, and more critically, the stopping of the fresh charge from going all the way through the combustion chamber. This is why changes in bore make very little difference to pipe performance, but stroke has a large effect, the timing of when the sound pressure wave has to meet the incoming fresh charge is dependent on stroke.

Why question engineers? I worked for one of the top ten engineering groups in the country as a lead tech running the r&d test lab floor. Trust me I watched them closely sometimes. I seen everything from both sides of the fence. I always kept quiet till I was asked my opinion. I seen many changes before a new design as accepted.

I ordered the two stroke tuning books mentioned. Next month I'll get the $99 one.

I have three 400cc two stroke go kart engines sitting here too. So many projects so little time. The bikes are first.

http://www.klemmvintage.com/mikuni-tuning.htm

Wouldn't a boost bottle SIGNIFICANTLY increase the manifold volume & weaken the inlet signal on ANY engine?
Keep the back and forth going,guys. We can all learn from discussion like this!