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]

Originally Posted by 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

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]

Originally Posted by 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.

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]

Originally Posted by 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.

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?