Jonsered Rebuild Gone Wrong? HELP!

[eggsalads]

Hi folks, been lurking on this forum for a while and I need your help.
I did a top end rebuild on a JONSERED CS2150 Turbo after it was run on straight gas and The cylinder walls and piston were scuffed bad!

Now, it doesn't start. I tried putting some mix in the carb and holding the throttle wide open as I pulled. After a couple pulls, I see a little smoke and I'll hear a loud POP noise. I also tried putting some oil in thru the spark plug hole in the hopes of temporarily solving a compression issue-- no luck there it seems.

Obviously, I'm new at all this and I need some help on what my next steps are.
I took the spark plug out and it didn't look bone dry or soaking wet. Put my thumb over the spark plug hole and I felt some "suck". The cylinder appears to be moving smoothly in the head and its travel doesn't make it hit the top.

please help. thank you.

 

[bulletpruf]

When you say "top end rebuild" did you replace piston, cylinder/jug, and piston rings? If not, what did you do?

Do you have access to a compression tester? If not, when you hold the saw by the recoil rope handle, does it drop or stand fast?

Did you check to see if it has spark?

 

[Ck0461]

I would check for spark, and check compression. If both are good, it should be a fuel delivery issue. Take the carb apart and clean, replace the diaphragms if needed. Double check fuel lines and filter.
Not to insult you but did you make sure the ring and piston were not installed backwards? The pop could be the ring hanging in a port if not installed correctly.

 

[eggsalads]

bulletpruf,
Yes, I replaced the piston, cylinder and ring.
It drops when I hold the saw by the rope handle.
I checked the spark plug, no spark. Put in a new one, spark, but same results -- POP! And some smoke, I noticed, when I took the spark plug out to check it after the POP.
Ck0461, I am afraid that I probably did put something in backwards. Could be quite a few things wrong at once..?

 

[Ck0461]

The small arrow on top of the piston points to the exhaust, piston ring can be installed upside down, but I doubt that would cause the popping. Pull the cylinder and check. Replace the ring/piston if it's damaged. Hopefully it hasn't scored things to bad. Welcome to saw repair. Lessons cost money so remember them. Throwing them to make yourself feel better doesn't work, and costs more money.

 

[bulletpruf]

bulletpruf,
Yes, I replaced the piston, cylinder and ring.
It drops when I hold the saw by the rope handle.
I checked the spark plug, no spark. Put in a new one, spark, but same results -- POP! And some smoke, I noticed, when I took the spark plug out to check it after the POP.
Ck0461, I am afraid that I probably did put something in backwards. Could be quite a few things wrong at once..?

If it drops, then you don't have sufficient compression. Which means you have an internal problem of some sort. Pop noise could be a ring hanging or busted.

 

[SEAM]

Pop noise and smoke can also be a timing problem (key on the crankshaft sheared off and shifted flywheel)... but in this case there seems to be a compression problem. Rings can break if the cylinder is forced onto the piston without compressing and aligning the ring(s) properly.
The safest way would be disassembly and checking all the components.

 

[Griffdog1]

Do the simple things first before you pull the saw down again - but you also need to consider what had caused it to need to be rebuilt in the first place and was that rectified. A scorched top end is a trailing indicator of another problem (often a non sealing intake boot on a 2150, or non sealing bottom end.
Can you feel compression when you are pulling it over and is it pulling over smoothly (if you don't have compression then it is likely that you have has some issue with your ring on installation. Another option is that you have not put the decompression valve in the new top end and it effectively has a big hole in the cylinder!!! That will do it.
Either way you are going nowhere until you have compression, but check the simple things first.
Also, how much fuel did you throw down the carb - most people put too much, you only need a coke bottle caps worth - saws are easy to flood and one the plug is wet they wont start.

 

[eggsalads]

Thanks to everyone for all the responses! I did the compression test again and it does stop dropping -- It drops at first but then catches and holds itself.
I didn't own the saw when it ran, but the previous owner's story was that it ran fine, he accidentally ran it with straight gas, and it stopped -- the piston I took out of it also told that story.
It seems to pull over smoothly. I did install the decompression valve, though I certainly may have installed it incorrectly. I used a cap to measure out fuel when I put in down the carb, the cap was about a teaspoon and half's worth.

 

[eggsalads]

Should I mainly be focusing on a possible timing problem, then, assuming the compression is actually good?

 

[stevetheboatguy]

Thanks to everyone for all the responses! I did the compression test again and it does stop dropping -- It drops at first but then catches and holds itself.
I didn't own the saw when it ran, but the previous owner's story was that it ran fine, he accidentally ran it with straight gas, and it stopped -- the piston I took out of it also told that story.
It seems to pull over smoothly. I did install the decompression valve, though I certainly may have installed it incorrectly. I used a cap to measure out fuel when I put in down the carb, the cap was about a teaspoon and half's worth.

Just a simple thought. But that may have been to much fuel down the carb. You may have just flooded it out. If you did flip the kill switch off and rope it over a few times. Then put a little two cycle oil down the plug hole . Install the plug, flip the kill switch to run, hold the throttle wide open and pull it over with all you have. If you have spark and even mild compression it will start.

Just be careful if you still have the bar and chain on it.


Steven

 

[Ck0461]

You can't accurately check compression without a gauge. Tractor supply or auto stores sell em $20-30. It'll save you from beating your head against a wall chasing unicorns. If you haven't taken the fly wheel off timing is probably ok. I would double check what you've done prior to looking other places.