‘83 250r low compression

[joenovosel]

My son bought this bike. We just replaced the rings and all top end gaskets. It still is around 90psi compression. I’m wondering if it would be different gaskets we need to replace. I did notice the reed valve has a tiny pin hole in one. The bike starts and idle through 1/4-1/2 throttle is fine. Any more throttle it sputters and doesn’t have any power. I took the silencer off to see if it was clogged and no changes. Carb is cleaned. Any help would be awesome.


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[El Camexican]

Are you sure that you’re doing the compression test properly?

That would be, open throttle, kick repeatedly until needle stop moving.

If that’s what you’re doing and the reading is still low you might want to check your squish to see if in fact the gasket thickness is an issue.

Can you put a picture up of that reed with a hole in it? That’s not a good thing, but I’ve never seen one with the hole in it before. Sputtering in the top and is usually a sign of overly rich jetting, or an ignition problem.

One last thing, did you do a pressure test on the engine after the rebuild? I know a lot of people don’t, but it’s important of you want to be certain your engine lasts.

[joenovosel]

If we take it apart again, or when we do I can try to get a picture of it. It’s a very tiny hole. Maybe pushpin size. We did a compression test before and after. Haven’t done a leak down check yet. I’ve jetted it down from 140 to 128 and it hasn’t changed anything. I’m pretty new to 2 strokes and didn’t check the squish. Maybe tomorrow.


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[El Camexican]

You don’t do a “leak down” test on a two-stroke, that’s for four strokes. You do a pressure test on a two-stroke to test your seals and gaskets.

When you did your compression test, did you hold the throttle wide open and continue to kick in till the needle stop throwing up?

[red_russian1]

You don’t do a “leak down” test on a two-stroke, that’s for four strokes. You do a pressure test on a two-stroke to test your seals and gaskets.

When you did your compression test, did you hold the throttle wide open and continue to kick in till the needle stop throwing up?Well, there you go! Learn something new everyday! I never knew that a leak down test was specific to four stroke engines only. Or, is it 4 cycle?? [emoji848]

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[El Camexican]

Well, there you go! Learn something new everyday! I never knew that a leak down test was specific to four stroke engines only. Or, is it 4 cycle?? [emoji848]

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Stroke/cycle same thing.

I learned something today as well; You can ask people the same question twice and still not get an answer.

[MrConcdid]

I am not a 2 stroke guy, but I have heard of the reeds getting cracked and can cause leaks/poor compression, that may not be true but I have heard it several times. Someone please verify this before I repeat it again.
Just stirring the pot, I have little to no experience working on a 2 stroke. lol
MrC.

[El Camexican]

I am not a 2 stroke guy, but I have heard of the reeds getting cracked and can cause leaks/poor compression, that may not be true but I have heard it several times. Someone please verify this before I repeat it again.
Just stirring the pot, I have little to no experience working on a 2 stroke. lol
MrC.

Reeds needs to seal, just like valves on a four stroke. Any defect will decrease performance.

The way to test your reeds and block is a suck test. You shove the block into your clean shaven face from the intake side and suck. If your cheeks don’t cave-in you need to replace something.

I highly recommend not having any friends around who might videotape you while performing this test lest you end up being an unpaid star on an alternate lifestyle website.

[Dirtcrasher]

There are leak down/pressure tests for any engine.

Your compression is super low, something is out of spec, upside down, backwards, something isn't right.

We can only re-ring when the piston to cylinder is still in spec as far as the amount of wear goes, but otherwise it's in very good condition. Those measurements change from top to bottom to the middle and 90 degrees to all of those measurements.

Compression has nothing to do with reed valves or anything else with a 2 stroke, piston to cylinder clearance, ring sealing and the head gasket or spark plug gasket is all there is...

[joenovosel]

Going to take it to a shop to get the cylinder and piston checked out and measured out. Making sure we have/get the right rings. It does smoke quite a bit(even for a 2 stroke).


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[yaegerb]

If we take it apart again, or when we do I can try to get a picture of it. It’s a very tiny hole. Maybe pushpin size. We did a compression test before and after. Haven’t done a leak down check yet. I’ve jetted it down from 140 to 128 and it hasn’t changed anything. I’m pretty new to 2 strokes and didn’t check the squish. Maybe tomorrow.


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Pull the cylinder, get it bored to next size with new piston and rings. Unless you have verified that your sleeve is not out of round with a bore gauge I am willing to bet its in need of a bore. Also replace the reeds while you are in there. Any holes in the reeds is not a good thing, they are trash.

[joenovosel]

Got the compression fixed. It runs like a champ on 0-1/2 throttle. Past 1/2 it bogs down. Would the reeds cause this problem?


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[El Camexican]

Got the compression fixed. It runs like a champ on 0-1/2 throttle. Past 1/2 it bogs down. Would the reeds cause this problem?


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Marvel Mystery Oil, or some other compression restoring secret?

[joenovosel]

I actually picked up another 250r last night. Put the cylinder, piston and head on this bike. I’m thinking It has a carb issue at this point. Jetting should be good enough to get some high rev out of it. Tomorrow I’ll try swapping carbs and see if that helps. It fires first kick. I swapped the pipe and cdi no changes.


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[joenovosel]

Got it running now. Used a little magic. Swapped carbs and it runs great now. I think the carb has a problem or two.


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