2011 250ec/300 cylinder swap

[smccoll]

Hey guy, i have a 2011 ec 250, i would like a little ore bottom end out of it,i was thinking of putting a 300 jug on it.
Here are my questions
1 will the 250 head work with the 300 cyl.
2 is there a better(cheaper) way of getting bottom end torque out of this bike , i just pit a piston and rings in it last year.
i guess what iam looking for is a little more bottom end , my dad rides this bike now and he rides a little slower but still wants some bottom end grunt !!! thanks in advance guys

 

[gasgasman]

Welcome to the forums.

1)The 250 head won't work on the 300.
2) There are several options.

a) Install a flywheel weight.
b) Install a high volume power valve cover-on left side of cylinder. Non e-start only.
c) Adjust the power valve actuator to open the valves later. You will have to pull the clutch side cover off to do this.

 

[smccoll]

Welcome to the forums.

1)The 250 head won't work on the 300.
2) There are several options.

a) Install a flywheel weight.
b) Install a high volume power valve cover-on left side of cylinder. Non e-start only.
c) Adjust the power valve actuator to open the valves later. You will have to pull the clutch side cover off to do this.

This is great thanks gasgasman, i will try the power valve adjustment , i have a estart so for the rest iam up shit creek without a paddle . i was really hoping that head would work lol. thanks again.

 

[gasgasman]

You're welcome.

For massive low end power, you'll have to get a 1998 Gas Gas.
The motor has a counter balancer and a heavy magnetic type lighting coil.

 

[smccoll]

You're welcome.

For massive low end power, you'll have to get a 1998 Gas Gas.
The motor has a counter balancer and a heavy magnetic type lighting coil.

is the lowend alot different on the 300 compared to the 250 or should just gear it for the old guy lol

 

[noobi]

You could get the head set up properly, they are notoriously poor from factory.
Jet it a bit fat.
Bigger rear sprocket, 52T.
An FMF gnarly pipe.

 

[Jakobi]

You could get the head set up properly, they are notoriously poor from factory.
Jet it a bit fat.
Bigger rear sprocket, 52T.
An FMF gnarly pipe.

This would be my suggestion.

Included in the head setup, check the port timing (number of base gaskets/position the cylinder sits in relation to the ports), and then have the head milled to reduce the squish and correct the compression.

I feel that my well setup 250s will tractor down about as well as one did when it was a stock setup 300. The 300 just seems to start pulling your arms around a 1000rpm sooner than the 250.

 

[Zman]

IMHO while a flywheel weight will reduce the hit in an engine and make it less likely to stall, it will not add low rpm torque.

I am not sure that the powervalve mod will help the bottom end. If it is already functioning properly it should be fully closed already at low RPMs and the modification will only change when it opens. That should occur at some point in the upper mid range and the adjustment will change the rpm when it opens.

A very easy 5 minute option is to add a few degrees of ignition timing via the slotted screws on the ignition plate. You need to rotate the ignition plate opposite the rotation of the engine to advance the timing. I would try about 3mm / 0.1 inches. If you hear pinging or detonation you will need to reduce /retard the timing advance or use a higher octane fuel. This should not be a problem for a stock engine.

Another option is to shorten the base gasket stack which will advance the port timing and also move the power band toward lower rpm efficiency. You can probably drop down to one of the 0.014 inch base gasket. You should check the head clearance but that should be fine got a stock engine. This change will also increase compression and add power across the board.

After those options I would go to the previously mentioned head mod.

I would double check your reeds and make sure they are in good shape too.

 

[Fred1956]

Hey guy, i have a 2011 ec 250, i would like a little ore bottom end out of it,i was thinking of putting a 300 jug on it.
Here are my questions
1 will the 250 head work with the 300 cyl.
2 is there a better(cheaper) way of getting bottom end torque out of this bike , i just pit a piston and rings in it last year.
i guess what iam looking for is a little more bottom end , my dad rides this bike now and he rides a little slower but still wants some bottom end grunt !!! thanks in advance guys

If you decide on the 300 swap, I have an extra cylinder & head that I might be interested in swapping for a 250 setup....300 wears me out for racing so I'm happier with the 250