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Post by humanshield on Jul 23, 2017 21:19:56 GMT -5
geoffh is correct about the flooded crankcase.Iv'e run into that on occasion with my Yammies. If the float sticks open fuel can fill the lower part of the crankcase and if it sat outside, even water can work it's way there (very bad news tho if water gets in there). And if the crankcase is flooded, you will NOT get it started. IIRC....the last time I had that issue I put it in 3rd gear and pushed it a few blocks down the road both ways with the spark plug out and MAN did that junk come shooting out! But beware.....if there's a spark you could have one massive explosion so you have to MAKE SURE there's no source of spark by removing the battery, disconnect the coil and cover the plug hole with a towel. Problem with a scooter is you need to lock the clutch so that you can do that. Geoffh gave you good advice. I'd try that before I replaced the seals. I had forgotten about that.....that's what makes a forum community so great
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Post by gsx600racer on Jul 24, 2017 0:03:16 GMT -5
It,s a big job doing the bearings,never been there,at 3200 they should be fine,if you,ve been trying to start it over and over all that unused oil,fuel will have gathered in the crankcase and make it impossible to get the air fuel ratio correct,you will need to pull the barrel off and syphon off any gunge that's in there.rags and pipe cleaners did the trick for me. geoff Like geoffh mentioned or you can also remove the oil injector pump and lean/lay the scooter to that side and try to suck out any excess fuel or oil thru the pump hole. You could also crank the engine with the e-starter, but it might make a mess when it comes spraying out. If its a older scooter and has a few miles, injector pumps are know to start leaking and filling the crankcase with oil. With the abundance of oil in the case, they wont run.
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Post by pinkscoot on Jul 24, 2017 7:46:58 GMT -5
I would do two things: A compression test so that you know you have enough compression and aren't assuming because the cylinder looks good. You can rent/borrow a tester from a local auto parts store. A leak down test so that you can find any leaks in a motor that needs to be sealed to run. You can make a leak tester for about 15-20 dollars. Here's a thread on different ways to make them: 49ccscoot.proboards.com/thread/506/make-2t-leak-tester-waysThere is an issue with Photobucket, so some of the pictures are missing in the thread I agree with Spaz on the leak down test. My Pinkscoot was a hard starter and I did leak down test and both seals were leaking, I replaced them and all was good, until I found a crack in the exhaust that was causing a leak there. An exhaust leak can also be a problem. 2 Strokes like to be sealed tight between the intake and the exhaust out.
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Post by humanshield on Jul 24, 2017 11:22:47 GMT -5
Lots of good advice going on here....Hopefully the OP will report back the fix for the benefit of others
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Post by dubloman on Jul 24, 2017 14:37:24 GMT -5
Hi
Great advice indeed
Here is the report as we had a few problems
I have made a leakdown kit for under £10 so when I have time I will post a video and add the link here so others can do the same
The engine was taken out but before we did that we cleaned the carb and changed the vaccum pump, this helped slow down the fuel as it was only pumping the fuel it needed now.
We did the leakdown test and found that it had a hole (between the fins) in the block and as such it was pissing out from there. We had another block from another scooter and put that on, but the reason it was changed was that it had a few scores in the walls but we are getting about 85 psi on the compression test. When we changed the block (and gaskets) there was a small amount in the case but not a lot, the seals were fine and did not leak
We have not fitted the exhaust so after that we will fit the exhaust as it has been suggested that the loss in compression will prevent starting.
I will report back when we have got her running as it is only a matter of time.......Thanks for the help
Just for the record, with the exhaust off is 85 psi a good compression on a 50cc 2 stroke or bad, we do have another block we can put on but just wanted the feedback?
Cheers
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Post by gsx600racer on Jul 24, 2017 14:57:49 GMT -5
Minimum is usually 90 psi.
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Post by dubloman on Jul 24, 2017 15:45:06 GMT -5
I felt it was a bit low, I was looking for 115 psi but it looks like I will have to try another block and see what the compression is on that.
I will have try and see what we get with the other, I will have to change the rings as well
Thanks
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Post by pinkscoot on Jul 24, 2017 16:43:57 GMT -5
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Post by dubloman on Jul 24, 2017 17:49:37 GMT -5
Interesting video I will have to check the clearance tomorrow and see what we have.
I do have a kit to put on this engine but need to know it will run before putting it on.
I assume that if the test is higher than the recommended then this could explain the reason for low compression?
Other than the rings not sealing or leaking block or head (I should do another leak test on the replacement block as it might have issues as well
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Post by pinkscoot on Jul 25, 2017 7:33:25 GMT -5
Always do a leak down test when you open the cylinder.
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Post by dubloman on Jul 25, 2017 11:32:36 GMT -5
We have done the squish test and I used 1.2mm solder, it did not even touch it.......so I am changing the head gasket as well as the head for a smaller one and see if she starts. I will alway do a leakdown test and check the case to check for fluid before trying to start it
I will report back to help others......hopefully
Cheers
Dave
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Post by dubloman on Jul 25, 2017 13:15:21 GMT -5
Reporting back
Put a thinner head gasket on and picked a head that has a smaller gap in the combusion chamber, done the squish test with 1.2mm solder but it is still not squishing the solder so the gap is greater than the 1.2mm. If the ideal gap for 2 stroke (as per the video) is between 0.6 & 0.9 mm then this could be the reason for low compression.
We have changed the compression from 75 psi to just below 90 psi with the improvements above, we have done a leakdown test and the block that had the hole has been put back on but we have repaired the hole by welding and then metal putty, we have no leak on the head.
One thing we did do was the crankcase did have a lot of fuel in it, we removed it(we are looking to do this after every change) but we are still having lots of fuel getting into the air box through the carb, the mixture has been turned almost all the way down
How do I increase the psi in the chamber (remove the head gasket) or reduce the thickness of the head
Any help is appeciated
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Post by lostforawhile on Jul 25, 2017 13:45:48 GMT -5
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Post by spaz12 on Jul 25, 2017 14:15:31 GMT -5
You can run it with no base gasket as well, but make sure that the top of the piston is below the exhaust port at BDC. If it is, then use some copper spray as your gasket. You can do the same for the cylinder head. Make sure to check your squish again.
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Post by lostforawhile on Jul 25, 2017 14:23:48 GMT -5
here's a good gif sowing one going through the cycles, you can see how any leak at all can upset the mixture, even a bad reed or intake leak or exhaust leak can upset it enough to not run, the exhaust is also tuned different for a 2 stroke, vs a 4 www.animatedengines.com/twostroke.html
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