Squish help.

[Ud_luz]

OK, my 07 300 has been an utter jetting nightmare at idle. Even the slightest touch of the bleed screw makes a big difference in RPM and the bike wildly varies in idle speed.

I borrowed another carb and it does the exact same thing on my bike. I talked to RB and they said the squish was probably off. I took some solder and tried to measure it. The solder is 3.16mm thick and it doesn't even touch the edges of the head. I don't have a depth micrometer but the eyeball says it's at least 3mm+. Looking at the base gaskets it appears I only have one very thin base gasket.

I'm not all that much up on this so what's the next step here?

Thanks.

PS: Other than this the bike runs very well. CCK, 175, 40.

 

[webmaster]

Hi,
With a CCK needle - suggest you up the pilot to a 42 or 45 and back out the idle screw. You are a tad too small on your pilot and the idle screw might be "in" to compensate. This makes it pretty finicky right off the bottom.

You might want to take your squish measurement with one base gasket. In the past, they were sometimes delivered with 2 - There are 3 different base gaskets available with varying thicknesses.

jeff
webmaster
GasGas Riders Club

 

[Ud_luz]

Hi,
With a CCK needle - suggest you up the pilot to a 42 or 45 and back out the idle screw. You are a tad too small on your pilot and the idle screw might be "in" to compensate. This makes it pretty finicky right off the bottom.

You might want to take your squish measurement with one base gasket. In the past, they were sometimes delivered with 2 - There are 3 different base gaskets available with varying thicknesses.

jeff
webmaster
GasGas Riders Club

I've tried a 38, 42 and a 45. I pulled a carb, CDI and tried my spare ignition that was working perfectly on another 07 EC300 and still the idle is erratic. No air leaks and I checked the reeds. Once I'm off idle the bike runs OK. The bike only has one base gasket.

My bike only has one base gasket and I don't know how thick it is. The eyeball test tells me I could pull it completely out and still have too much squish. I've never had this problem with my KTMs. I'm kind of wondering if Gas Gas has a minor QC issue with either the cases, cylinder or head. It kind of reminds me of my old shovelhead Harley, no two were alike.

Here's a picture of the piston if it means anything:

 

[GMP]

The head is recessed into the bore so the piston will appear a few mm below the head surface. Just get some thicker solder and do the measurement again. My '03 250 was well over 2mm measured squish with a single .3mm gasket. They are set high to deal with questionable fuel in different countries, there is only one motor for the whole world.

 

[Ud_luz]

We just finished measuring the squish at 4.2mm using depth gauges. This is the distance between the outer rim of the cylinder head and the piston.

If thicker solder than this exists I would sure like to know about it. My neighbor is going to cast some slugs out of lead (he makes all kinds of bullets) so we can get an accurate measurement of the squish. I'll have to ask Ron if that will suffice.

I'm aware there's only one motor. Sometimes quality control on machining isn't what it could be. This is far enough off that it seems a little odd.

 

[GMP]

I twisted a few pieces of core solder together to increase diameter, and the flats from the head/piston could be measured fine. Solid lead is too hard. What else should work if your careful is some epoxy putty, after you spray the head and piston with silicone so it will not stick. So, I assume what you did so far was measure the head from the edge of the dome to the deck surface, and subtract that from the cylinder deck surface to the edge of the piston measurement? The edge will always be the tightest part of the squish, getting larger toward the center of the dome. Much of the cutting is to keep this relatively equal. What is your compression? If the squish is as bad as you think I would expect it to be low.

 

[Skidad]

To make matters more interesting are the transfers and exhaust port completely uncovered when the piston is at BDC? If not then you need to actually add more base gaskets to get that corrected and then do the squish measurment. I know one guy on this forum did this and had to have quite a bit removed from the cylinder to get the proper squish again. I don't know maybe it's not such a big deal but that's what I would do.

 

[Ud_luz]

I twisted a few pieces of core solder together to increase diameter, and the flats from the head/piston could be measured fine. Solid lead is too hard. What else should work if your careful is some epoxy putty, after you spray the head and piston with silicone so it will not stick. So, I assume what you did so far was measure the head from the edge of the dome to the deck surface, and subtract that from the cylinder deck surface to the edge of the piston measurement? The edge will always be the tightest part of the squish, getting larger toward the center of the dome. Much of the cutting is to keep this relatively equal. What is your compression? If the squish is as bad as you think I would expect it to be low.

I measured the depth on the head and subtracted it from the depth of the piston, beginner stuff there. I'll run down and do a quick compression test and see where I'm at.

 

[Ud_luz]

To make matters more interesting are the transfers and exhaust port completely uncovered when the piston is at BDC? If not then you need to actually add more base gaskets to get that corrected and then do the squish measurment. I know one guy on this forum did this and had to have quite a bit removed from the cylinder to get the proper squish again. I don't know maybe it's not such a big deal but that's what I would do.

I'll check that too.

 

[Ud_luz]

The transfer and exhaust ports line up perfectly. The compression with a little oil on the rings is 140lbs. Does this compression roughly correspond with what the approximate squish I measured is?

Further, might this be part of the whacked out idle?

 

[GG27]

When I first bought my 250 EC 2008, I had a terrible time getting the off idle response right with all sorts of jetting combinations but never had decent results.
When I changed my first piston, I measured the squish and it was 2.1 mm, way off from the ideal 1 to 1.5mm, so I just used a single 3mm base gasket(factory had set it with a .5 and a .3mm)and had a great off idle response with no loss in top end.
Now you have measured a 4.0mm squish and 130psi compression, now that needs your head to be done by Ron and you will get what you are missing.

 

[GMP]

140 PSI sounds low to me. A fresh 250 (OEM) runs around 185 + and the 300s in the 170 range from what I've seen here. Those who have measured 300s recently please correct me if I'm wrong.

 

[goose202]

My '04 EC300 with about 30 hours on it only did about 145psi. That was done when cold though. I suspect my squish could do with some adjustment too.

 

[GMP]

Do the newer ones have a bleed hole in the cylinder? If so, this would make your compression reading more kick speed dependent. I know for sure my old KTM 300 (same bore and stroke, perhaps diffferent exhaust height) ran 172 PSI with a new top end. This was a motor without a compression bleed hole.

 

[Eric K]

To better understand the symptoms of your idle issue...

At a single given carb setting and constant temperature/altitude, does the idle speed vary?

What effect does ambient temprature change have, if any, on the idle speed.

 

[Ud_luz]

To better understand the symptoms of your idle issue...

At a single given carb setting and constant temperature/altitude, does the idle speed vary?

What effect does ambient temprature change have, if any, on the idle speed.

The idle varies quite a bit from minute to minute. It does it at any temperature or altitude, on flat ground, pointed uphill or downhill. I borrowed another 07 300 and swapped the carb, reed valves, CDI and ignition. The bike will not idle consistently. I checked the compression on the other 300 this morning and it was 165 cold with a squirt of oil versus my 140.

I've never had a 2 stroke do this before. I'm putting a .3 base gasket in, measuring the squish and going to have the head done then see what happens. This makes no sense whatsoever.

 

[Eric K]

Does the engine have an idle speed where it will consistently idle for a few seconds? If so, when the idle fluctuates does it rev up or down from that idle speed?

Does the engine have good off idle power & response when you open the throttle?

Is the mid range and top end power strong and consistent?

Have you checked for intake air leaks?

Have you changed the spark plug?

Have you verified there are not any loose parts or electrical connections?

When you swapped the carb did you also swap the slide and needle?

 

[Ud_luz]

Does the engine have an idle speed where it will consistently idle for a few seconds? If so, when the idle fluctuates does it rev up or down from that idle speed?

it will sit there and idle perfectly forever if you don't touch it. after riding it for a second it will idle higher or lower.

Does the engine have good off idle power & response when you open the throttle?

Perfect.

Is the mid range and top end power strong and consistent?

Yes.

Have you checked for intake air leaks?

Replaced the entire thing with a known to be good unit.

Have you changed the spark plug?

Yep and the coil.

Have you verified there are not any loose parts or electrical connections?

When you swapped the carb did you also swap the slide and needle?

Not much of a point in swapping the carb and reed assembly and putting all my internals in it is there?

The crazy thing is if the idle is low, it stays low until you ride the bike. If it's high then it stays high until you ride. When you stop it can be high or low. It's not the throttle or cable assembly either. Usually you can't get it to change by just whacking the throttle. I've had a number of people very experienced with 2 strokes check this thing out and it's been a mystery. The bike runs flawlessly the second you get off idle with no stumble or anything.

The only thing I can think of is the low compression which actually is around 137. I checked this with two gauges, one read 135 and the other 138. The engine passes a leakdown test so I can rule out faulty rings.

The only difference in the two 300s I have sitting here that I can find is compression. I've swapped everything external to the engine between the two bikes. The surprising thing is the one with the low compression actually seems to be smoother throughout the power band and just as strong.

 

[blitz11]

I've been kind of following this, and a last piece of information has me puzzled.

it will sit there and idle perfectly forever if you don't touch it. after riding it for a second it will idle higher or lower.

However, this seems to contradict this statement (I mean no disrespect, just trying to understand):

The idle varies quite a bit from minute to minute. It does it at any temperature or altitude, on flat ground, pointed uphill or downhill. I borrowed another 07 300 and swapped the carb, reed valves, CDI and ignition. The bike will not idle consistently. I checked the compression on the other 300 this morning and it was 165 cold with a squirt of oil versus my 140.

Given my confusion, I'll assume that if the carb isn't touched, it idles fine.

The dynamic of moving the slide changes things.

1. Slide possibly hanging up? When you changed carbs, did you change slides, too? Or did you take one slide from another?

2. Could the slide / idle speed screw have some sort of "deformity" (for lack of a better word) so when the slide is raised and then lowered, it doesn't lower to the same spot? it doesn't take much change in slide elevation to change the idle speed. (My old BMW had worn the idle speed adjuster flat from 100,000,000 impacts such that you could not adjust the idle with the adjuster as the "slope" was impacted by the wear by the slide. I had to buy new idle adjusters in order to properly adjust the idle.)

3. Could the throttle mechanism (Domino) have an issue? Frayed cable, weak return spring, boogir on the throttle tube, etc., which would keep the slide from consistently returning all the way to the bottom? How much free play on the throttle?

4. Is there any way that the needle is NOT fully captured by the plastic retainer? If the needle can move up and down just a bit, it will affect the mixture.

My guess is that it is something mechanical not allowing the slide to come to a rest in precisely the same spot everytime the throttle is moved. if it idles well w/o touching the throttle, and you move the throttle, and it doesn't return, it might be something to do with the throttle/slide/needle/spring.

5. OH, one more thought, although this you would hear, so it is a long shot. Is the powervalve operating correctly? Can it bind up? If you blip the throttle (enough), you might open the valve. if it doesn't close consistently, you do change (theoretically) the compression ratio, which would affect the bike's ability to idle consistently ('cause they run open loop). higher compression, more torque, higher throttle speed, and vice versa

anyway, those are questions.

good luck.

blitz

 

[Ud_luz]

I will repeat, I took the carb and reed valve assembly off another bike and put it on mine. Now, why would I take the other carb apart and put my slide and needle in it if I'm trying to figure out if it's a carb issue? Didn't I happen to mention it isn't the throttle or cable assembly? Kind of basic stuff there.

The powervalve appears to be free and operating correctly. I have no real way of checking if it's properly working when running.

I might not have made this clear as far as the idle. If the bike is sitting there idling you can rev it up or do anything you want, it generally goes back to whatever the idle was. If you ride it down the trail for a second and stop it may idle OK, it may idle high, it may idle low. Same deal on starting, it may be OK, high or low.

I've been messing around with this for over a year. Real motorcycle mechanics haven't been able to figure it out. I finally got a hold of another 07 EC300 and swapped out almost everything. My bike still has flaky idle, the other one doesn't.

I guess I could swap the cylinder and head next, nothing else has made even the slightest difference. I don't think the trans seal is leaking because I have no oil loss. Maybe it has a faulty ignition side seal, I really don't know at this point. All I get from everybody that's checked it is..huh???

This shouldn't be rocket science, there's very little involved with this engine. If I had to bet I would say it has an air leak someplace. The question is where? It's not in the intake tract and I see no oil around the case half seams. I haven't tried sealing around the cases with a little silicone, maybe that's worth trying. I really don't know. I've only ridden and wrenched everything on my dirt and street bikes for over 40 years. This one has me stumped.

I had never checked the compression before and it's well on the low side. Might this be the problem? Low compression hasn't bothered the idle on any of the other 2 strokes I've owned. I'll find the problem since I'm getting rather annoyed with it.