Story, I just purchased this quad and the gentleman said it was hard to start and wouldn't idle. I did see it run but it took starting fluid to get it to fire. Once it warmed up it still wouldn't idle. I figured it just needed a good carb cleaning.

So,
1. I bypassed the filter and made sure gas was running through the line without issue.
2. I cleaned the carbs, pulled the jets and everything including the floats. They all looked fine and gas poured out of the bowl when I took it out.
3. Cleaned everything, took out the jests and ran a bread tie metal strip through the holes, carb cleaned, and blew it out with air.
4. Reinstalled

Now when I turn it over I am not getting any gas into the cylinder. Its bone dry. I stuck my finger in the plug hole to make sure there was compression and there was. I did not test the PSI.

Next I put my hand over the intake and could feel pressure in AND out when turning it over.

I assume this is a gravity fed device and since its getting fuel into the bowls that is has what it needs, its just not pulling it into the cylinder. Ideas?

 

Starter fluid is a lot lighter than gas and can crank most machines to where gas wont if the compression is low,crank seals leaking,etc. Do a compression check! This is the heart of the machine and if it's below 115 psi,it will need work. Compression can be above this ,but if crank seals are leaking you'll have the same results. You must have good top and bottom end compression on a two stroke engine. OPT

 

Thanks. Do you know if the 300 has reeds?

 

Just checked compression. 60lbs.. Guessing you are spot on.. Thanks for your help.
Time to order parts.

 

Check the bottom end out before you just slap a new top end on!!! You need to check for any up and down play on the rod and also crank bearings that are noisy or feel rough as you turn the rod.You take a chance on a top end only! The cylinder has to be measure to see what over size piston is needed. Don't just order a std piston and rings as some have done as the bore will usually be too enlarged/egg shaped for it to work,plus it may already have an oversize piston in it!And no it doesn't have reeds! It's a simple piston port 2 stroke engine. OPT

 

Its got the stock piston in it. The measurements show that its completely round so that is good. On the wall there is a discolored mark but I cannot feel anything, not even with a metal pick. It looks like it might have gotten hot.

Seeing the dark area on the wall, should I have it bored or see if I can find a remanufactured one?


Second, how do I check the pressure on the bottom end. There is no slop in the crank and everything feels smooth. I already ordered a complete gasket kit knowing that I would need that at very min.

 

The cylinder has to be measured at the top,middle and bottom against the stock specs with bore gauges. I haven't seen one yet that is perfectly straight,not egg shaped and within specs to where a standard piston could be used again. Cylinders just wear over the years and over size pistons are made for this reason. The proper way is to determine what over size is needed,than order the piston kit.Then bore and finish hone to the proper clearance called for. The stock bore on the 300 is 74.5mm/2.935 inches.
Piston to cylinder clearance is .0012-.0026 max.This is critical!! The service limit in the manual is a too generous (IMO) .006 as this is where piston skirt damage can happen. If you have a clutch puller and own a steering wheel or harmonic balancer puller(Plus many places can loan/rent them to you) to pull the flywheel, just replace the crank seals as they are cheap!Plus they take as much wear as the piston over time. OPT

 

So I took the cylinder in and had it "honed and balanced" or something to that measure. It cost me 70 bucks. I have the new rings on and compression is odd. When I first got it ( well oiled ) it tested at 120lbs. I cranked it over trying to get it to start but it didn't. I sprayed starting fluid into the carb and it still wouldn't fire. I took the top back off and everything inside was wet and while I was turning it over a couple drops of fuel came out the exhaust port. ( I have the muffler off right now ). I retested compression and it showed 95. I called the guy and he said that this is fairly normal until the rings seat. That I should wipe some oil on the walls and the compression will come back up and that even at 95lbs it should have plenty of compression to fire.

So, I did as he instructed and the compression did go back up to 110 but I don't think I added enough oil since I barely put on a skim coat.

Its getting fuel, spark, and has compression. The stator plate doesn't have much play and I tried it in almost all the positions but never got it to pop off even once. Ideas?

I did replace the top and bottom gaskets.
ARG this is getting frustrating.

 

Did you ever replace the crank seals or clean the carb(new carb kit)? Plus if its been sitting could need fresh gas. 110 to 120 doesn't sound too much,it should be close to 140 with a new top end. Did you measure the piston to cylinder clearance after the machine shop work was done? Plus marks on the rings always face up. OPT

 

I didn't measure anything. I just dropped of the cylinder and told the guy the compression was low and I needed it up around 120 for it to run. Maybe I should have told him 140.

I changed out the gas with fresh gas and cleaned the carbs. The plug does get wet even when I don't try a little starting fluid.

This part is going to sound s little odd but the noise it makes might be telling. It turns over and you can hear the compression part which sounds ok for 3 times and then on the 4th it sounds like the batter is laboring or that the compression is building up higher on the 4 time around. I did not change the crank seals only because I am not sure exactly what seals you are referencing. I will see if I can look it up. I do know I have them since I ordered the entire seal kit so its just a matter of finding them. Will that cause a drop in compression if they are bad and / or are there any easy ways to tell?