2010 300 Cylinder Base Gasket Question

[coopernicus]

In looking at my riding partner's 2010 300 I noticed there are 2 cylinder base gaskets poking out from the bottom of the cylinder...Is this normal? There is a slight "deadness" off of idle riding here in the mountains that has mostly resisted jetting changes (he's now running an N1EI with a 45 pilot and 168 main with stock gearing). Everywhere else in the RPM range the engine is pretty much magical and I'm fine with the way it runs for my riding style. I was just wondering about the extra base gasket? Any thoughts?

Eric

[twowheels]

Twinned base gaskets are common place, and OE gaskets are available in three thicknesses. Changing stacked gasket height changes port timing as well as compression, so use that to your advantage. Most guys time their ports with the gaskets then measure squish and have the head machined to the optimum value.

[rod]

As twowheels stated, there are 3 gaskets available(.15/.3/.5mm) giving you heaps of options to get port timing to your liking.
I believe the preferred setup is to have the exhaust port match exactly the top of the piston at BDC, then start looking at your head squish measurements aiming for something between 1.2 to 1.8mm.

I've yet to carry out either checks on my '10 ec 300, i'm only going on what i've read and been told, going <1.2mm on squish could cause pinging issues.

I'd like to know more about this '07 ec275 ex nambotin wec machine you have, can you divulge the jetting specs, particularly what needle he was running?

PS: I just re-read my post, he probably had different jetting everytime he raced depending on where in the world he was.
What was the jetting you got?

[Jakobi]

Continuing to beat the dead horse!!

The 2010 Models came with 2 x green base gaskets which is a 0.6mm stack. Grey are 0.5mm. I know the 2011 come with one gasket, unsure which size though.

As stated, most people raise to get the top of the piston at the bottom of the port at BDC, and then work on squish and compression from there.

This is what I was told by a rep gg mechanic.
"A high comp engine (thin base gasket ) will give more low end power and build revs quicker through the middle, but it will flatten the top end (thin gasket drop the ports as well low ports = more bottom but less top). A fatter base gasket set up will give the bike a more lazy bottom end, not as quick to pull through the middle but will rev out better."

So general approach is to set ports for a nice top. Then modify head to get the right compression to give you a nice usable bottom end, strong mid, and decent top. As stated, squish between 1.2 - 1.8mm. I have been told using the S3 head I should be able to achieve 1.4mm which puts me right where I want to me. Not mild, not wild.

[Jakobi]

Note: I'm also doing this because a) first top end is due, and b) to clean up said off idle jetting issues.

[husley]

Great info as I was unaware that there were options with the base gasket.

I have been wanting to increase my low-end pull by a bit and I am willing to give up top-end........sounds like this might be a easy relatively low-cost option.

thank you

J

[coopernicus]

Thanks for the responses! So it looks like this is normal which is good to know and I suspect it may be causing the "almost imperceptible" deadness off of idle (it has to not be above 1000 rpm to get this condition to happen) he wishes was gone as he wants to keep the stock gearing if possible. He is just worried about the deadness of the throttle response while in second/third gear at a slower than walking pace speed when he "whacks" the throttle open. Until the top end needs replacement I'm going to tell him to add a couple teeth to the rear sprocket or get a flywheel weight that will keep the RPMs from dropping so much when he releases the clutch lever. Excellent, this site is awesome with the worldwide resources! BTW, I misstated his jetting: 38mm AS-1, 165 main, 45 pilot, and N1EI needle, air screw at 1.5 out. Thanks to everyone!

Eric

ps: I will answer the 275 Nambotin bike jetting question in a PM later when I get more time!

[GMP]

The gasket selection from the factory varies quite a bit. I suspect to keep the compression and squish safe for some of the crap fuel used in various countries. All three of my 250s were different, my '03 having three gaskets.

Eric that bike should already have the 2K-3. I'd do the head with one .3 or .5mm gasket, jet to suit, and be done with it. I'm becoming a beleiver in the fact that a head mod on a 300 two stroke(any of the three brands) is like adding handguards, basically neccessary to jet the bike right. Your thin air makes it even worse.

[wasp4banger]

Originally Posted by coopernicus

In looking at my riding partner's 2010 300 I noticed there are 2 cylinder base gaskets poking out from the bottom of the cylinder...Is this normal? There is a slight "deadness" off of idle riding here in the mountains that has mostly resisted jetting changes (he's now running an N1EI with a 45 pilot and 168 main with stock gearing). Everywhere else in the RPM range the engine is pretty much magical and I'm fine with the way it runs for my riding style. I was just wondering about the extra base gasket? Any thoughts?

Eric

Do you think the pilot at 45 is possibly too rich?

I reduced the base gaskets to a single 0.15 thick, and the bottom is now superb. My mate who rides an orange bike is most envious of my grunt.

[Jakobi]

I agree a 45 pilot is quite fat. I'm no where near that elevation, way bigger on the main, and run a 38 pilot.

By dropping base gaskets you are sacrificing top end, but beefing up the bottom considerably.

Overlapping the port timing adds to bottom end, and by removing gaskets you are increasing compression, as well as reducing squish. All of which will give the bike more bottom to mid. Just be careful not to reduce squish below 1.2mm or you might run into problems.

I have also wondered about all of this as I spend most of my time low to mid range single track, but still like having a wild top when it opens up.

I figure by lifting the port timing and then reducing squish and increasing compression I should be able to maintain the best of both worlds. If anything a slightly soft or smooth bottom end is going to be less tiring in the tight than a super punchy off idle.