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I have been working on a 90cc kymco engine and it wont fire and there isnt very good compression, the rings are good and the timing is set. What could be wrong with it?

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First do a compression test , it must be around 100 psi + depending on compression ratio and carbon build up , if lower than this add 1/2 teaspoon of oil to the cylinder and redo test , if higher rings or cylinder worn , if still low valves not seating or burnt.

Posted on Apr 03, 2019


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Posted on Jan 02, 2017

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SOURCE: wont start because it isnt firing

filters- oil, fuel, and air?

Posted on Jul 16, 2008

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SOURCE: my 017 stihl chainsaw stopped working this morning

I would double check the muffler side of the piston and make sure it is not scored up like this:barterjoe_7.jpg
Remove the carburetor and make sure the intake side of the piston is not worn (missing more than 10% of the machining marks )like this:

If you do not see these failures and you have good spark the carburetor is the problem. see a local dealer like for parts and support.


Posted on Feb 21, 2011

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SOURCE: 1995 bmw 740i ran perfect,

Total loss of compression would mean a bent valve. car would be running very rough if that was the case. Or a blown head gasket .The lack of compression is probably from being flooded.Check the intake if it is FULL of oil then really bad. It could be the intake valves have gummed-up due to all that oil in the intake. If so, the thing to do is remove the heads, clean, and check for damage. The engine flooded with gas can bring compression all the way down,Gas washes all of the oil off of the cylinders and that's what seals the rings to the cylinders. You spark plugs are most likely gas fouled too.Also other possibility for no compression or low compression is the cylinder walls gets bad thats why no compression car needs a block. ------------ An engine will not start if it has very low compression. It could be possible that the vehicle is getting flooded with too much fuel causing the cylinder walls to get washed down.

What you should try doing is removing each spark plug and then squirt a small amount of oil (3-4 shots from oil can) into each cylinder and crank it over to re-lubricate the cylinder walls. Then re-check compression. It should jump up and be about double your first reading.

If so then re-install the plugs and try to start it. If it does fire up it is going to smoke very heavily for a few minutes due to all the oil in each cylinders.


Try this , but if that is not helping then ignition coils needs to be replaced.Also get the spark plugs checked.If dirty fouled up and very old, then replace the spark plugs too.----------

This should help.thanks.Helpmech.

Posted on Jun 15, 2011

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SOURCE: 94 ranger timing belt broke.

engine size? 4 cylinder? 3.0L V6? 4.0L V6?

Posted on Aug 15, 2011

  • 67 Answers

SOURCE: installed a rebuilt cylinder head set timming to all data and mitchells timming book wont start blowing back threw intake

Sounds like your timing is out 180 degrees. Recheck by making sure #1 piston is on the compression stroke, then retime.

Posted on Feb 29, 2012

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Timing may be off. Have you checked it? Back firing could be valve timing problem; could also be too much gas-check injector spray pattern-should see a cone shaped pattern of fine mist on the throttle plates when cranking engine-this is if you have throttle body injection.
For $20-$30, you can buy a compression gauge tester and check engine compression. On a warmed up engine, pull all spark plugs, disable ignition and fuel delivery (pull injector fuse or unplug injectors), hold throttle wide open, and check compression on each cylinder by cranking engine over about 7-10 revolutions-the same amount for each cylinder, about 4-5 seconds each. All cylinders should be nearly even and balanced. Lowest cylinder should be at least 75% of highest reading cylinder. For any low reading cylinder, put a squirt of oil (about a tablespoon) in that cylinder and retest compression: if compression rises, rings are worn. If compression does not improve, valves are the reason for low compression-valves may be burnt or not sealing good.
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First off, ether is not the way to go at all! You'll end up messing up the piston rings with continuous use. Also with using ether engines tend to get "addicted" to it (its the only way they will start after some time as the rings get burnt and compression under normal cranking isnt enough)

The fact you can start the engine on ether means fuel prob isnt the problem. I would have said the problem was probably your pre-heating system and to check your plugs, wiring and fuses for the pre-heating system but the fact hot start doesnt work either doesnt make sense.

How long have you been using ether? If it has been for an extended period then I have a feeling the piston rings might be shot and full compression cant be reached during cranking and the ether just kickstarts your engine into starting. Any smoke out the tailpipe?

I would still check the glow plugs.

Hope this helps in some way

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