Hi. No serial number needed.
There's a number of things that could still be wrong, so I'll try to get to the point...usually I'm kind of wordy.

The fact that it fires on a prime is promising...usually when there's a bad vacuum leak like a blown cylinder gasket, they often won't fire on a prime as the tranfer system won't work properly, so I feel there's most likely only one of two reasons for the no-start condition now.

One would be the carb still has a restiction in the fuel delivery passageways. While fuel cycles through it when you prime it, that only proves the pump side, screen and inlet needle system allow fuel to pass. That doesn't mean the delivery passageways are clear.

The second reason, while unlikely is still possible, the carb may not be seated fully and allow a vacuum leak there (the "bad" leak I mention in the first paragraph pertains to a CC leak, not immediate intake).

I would focus on the carb. Pull the carb off and tear it down again (I know, I know). Remove the mixture screws. Using a carb spray with a "straw" tip (spray must NOT contain xylene, which can damage check valve diaphragms and neoprene components) spray through the mixture screw bosses and see if the fluid enters the main metering area (the chamber with the inlet needle valve). If not, there's the reason - a clog. If so, well, it should work.

Reed valves aren't really used anymore on OPE units...about the only place I know they're still used on 2-stroke engines commercially is on Rotax snowmobile engines.
IF, and only IF the saw is at least like 20 yrs. old is there a chance it has reed valves. Can't miss 'em, they'd be right behind the carb. And it's really rare to see one melted down...can count on one hand how many reed valve issues I've seen other than plain old worn out, and to wear them out you would have to have enough dirt ingestion in which case the piston and cylinder would also be worn. They really don't wear or distort under normal use.

 

Hmm, think I was wordy anyway LOL. P.S. With 120 compression it should be pulling fuel fine unless the intake side of the piston skirt is damaged (rare).

 

Thanks for the reply Paul...I see what you are saying. I have done exactly what you describe several times already. The screen is new also. I even took the carb to work an ran it through our sonic cleaner for several hours to make sure it is spotless. There are no passages clogged. I did not replace the carb to intake gasket but the old one looks good and I did even try flipping it over just in case. It seems to be seating good...(why dont they include those base gaskets with the rebuild kits anyway)....
Oh yea, Im pretty long winded my self .........when I say it will start on a prime, I mean when I shoot a shot of starter fluid in the cylinder...(just so were on the same page).....Is there a chance that the fuel lines are routed wrong? if I swap the two lines on the carb, the prime bulb will collapse so I think its good, but I have seen them run with the lines wrong but die at a continued full throttle so there is always the possibility. The lines were all rotted an missing when my buddy brought the saw to me so I just ran them the way it made sense to me.
Any other ideas......By the way, I will tear it down and do as you suggested again, you never know, 28th time may be the charm....ha ha ha......
Thanks again my friend.............

 

Thanks for the reply Paul...I see what you are saying. I have done exactly what you describe several times already. The screen is new also.

Oh yea, Im pretty long winded my self .........when I say it will start on a prime, I mean when I shoot a shot of starter fluid in the cylinder...(just so were on the same page).....Is there a chance that the fuel lines are routed wrong?

There's a big difference between priming a 2-stroke directly into the cylinder via the spark plug boss, and priming it through the intake via the carb. throat. If there's a major vacuum leak or bad piston skirt, it may not run on a prime through the intake.

On the other hand, a 2-stroke in poor condition may fire on a prime in the plug boss, but not via the intake. THIS can tell you a great deal about the condition of the crankcase etc. Run on a prime via intake is promising, but if not there's probably a major leak or wear issue.

I know you've been working on these a long time, but please remember the basics are essential and easy to overlook. I was going to say I feel the carb. is NG but without knowing exactly how you're priming it I can't render an opinion.

Paul

 

Is it possible a check valve is damaged? I have learned not to use an air hose directly into the ports. Bad crank seals?

 

Okay, check valves. Small carbs use one of two methods for anti-scavenging in idle conditions. One is a check valve, the other is capilary action. BOTH only prevent the main metering chamber from emptying out at idle. NEITHER prevents starting, neither prevents nor impedes high-speed operation. Go to walbro's website and download the repair manual, read through it and you'll understand what I'm saying.
As I just said on another post, if it'll run on a prime it'll usually at least start on the carb even if there's a CC leak. In my 40 yrs. of working on 2-strokes, a nominal CC leak will usually give you either full-throttle issues, acceleration issues, or idle issue, but will not prevent starting unless it's a major leak. A leak though can cause catatrophic failure though as a lean condition (detonation and more).

The fact that it runs on a prime is indictative. I'd say you're dealing with a clogged carb, and I'd price a new one.
I just said in another post, but being mindful of our labor rate in the northeast, that if a carb is about $70 or less, don't even bother with a rebuild that may or may not work, replace it and have the guarantee of proper fuel delivery.

 

Just realized capillary is spellllled wrong. I'm tired, forgive any SP or GM errrrrors. Thanks.

 

ok thanks again guys....I have been busy with other work for the last couple days, but I am still gonna pull the carb again and go through it...
Thanks again.....

 

The model number would be helpful (at least to me).

If the carburetor is attached to the crankcase there will almost always be a reed valve. Reed valves are still used on a few applications (Echo CS-341) is one that I know of. Most newer chainsaws are ported designs and do not utilize a reed valve. I cannot recall ever seeing a reed valve assembly that was melted. Usually I see debris caught in the reed, this will prevent the engine from running, but it will generally pop or give the impression that it might start when pulling it over.

Most all small 2 cycle carburetors have some type of High Speed check valve that does affect high speed operation, but will usually not prevent the engine from starting. Most of the newer carburetors do not have serviceable check valves and it's cheaper and much easier to just replace the carburetor.

I agree with Paul and most likely there is a still a problem with the carburetor, such as a restriction in the metering circuit of the carburetor. You can have good fuel flow through the carburetor, but if the metering circuit is clogged fuel will not make it to the engine. Does the carburetor have High and Low speed adjustment screws?

 

Hi again guys, and thanks for all the helpful advice so far....OK, so this thing is still putting the beat-down on me.....I took the carb apart and ran it through our sonic cleaner again for several hours, flushed it in the parts washer for a while, soaked in WD-40 and blew it out again....Installed it and pretty much the same thing.....If I pump the holy snot out of the bulb, I was actually able to get it to run for a few seconds on an off but that's it and that's after several pulls and pumps.....
Now this is weird too....I know when you pump the bulb, it pressurizes the tank and if you pull the fuel lines off the carb gas will flow out rite....After it ran a few seconds here an there, i opened the tank an pulled the fuel lines off...an no gas flows from the lines. Well, soon as I put the gas cap back on, fuel starts flowing again. no pumping the bulb or any thing. Remove the cap fuel stops, put cap back on an fuel flows again. Makes no since......where is the pressure coming from. I have never seen one do this. I think this saw is possessed.
I do admit that after more carb cleaning, it actually started although only barely an it took a lot of fiddling to do it, it did better than before, so that leads me to think I may be in for a new carb.
I just hate that I am working on this saw for someone else and have already bought a rebuild kit and hate to tell him to buy a carb now and I don't know 100% that that will fix it.

 

oh.... and yes it does have high and low mixture screw.....

 

Fuel tanks will build pressure with a little shake or movement and gas will spew out of the lines, I see this happen all the time. Since it has adjustment screws, try opening the High speed adjustment 1/2 turn or so and see if you can get it to run some. Do you know if this is a strato charge induction model?

 

I have tried it with the adjustments from almost wide open to closed and all in between with no help. I have been working on these things for a long time and never had one do like this...
I do not know if it is the strato type like you ask but I can look......
thanks...........

 

ok....so the new carb finally got here, I install it and BAM!! SAME THING!!!
holy crap I cant believe this. So here I am asking for more help.....
I wanna make sure I have the fuel lines routed right....starting at the filter, line goes from filter to the nipple on the carb side where the diaphragm is with the two flappers. next, the other line goes from the carb nipple which is next to the high an low mixture screws and the end where the diaphragm activates the main needle, to the IN side nipple of the bulb. Then, the other line goes from the other bulb nipple, back to the tank. Is this rite......It pulls fuel like it is rite. If I reverse the lines, it collapses the bulb....
Also, with the carb off, when I pull the starter cord, I cant feel any vacuum on my finger when I cover the intake hole....Should I feel any???? Dont know how strong it should be.
I have great compression and spark.......
When I say it will start and run a couple seconds on a prime, I mean when I open the carb throat an spray starter directly in the intake.....
What do you think now.....Im a carb and a rebuild kit deep in this piece and still not running....I cant tell my buddy it still aint running and expect him to pay for the parts.....the intake to carb gasket is the old one but seems fine. Could this be a problem......oh an the serial number info sticker is gone so I cant give any solid numbers for that. It was bugger finding the rite carb...
Please help.....

 

There may be crankcase vacuum leak or worn or damaged intake-side piston skirt. The fact that it runs on when primed through the intake is promising, although I've had a saw run with a broken piston (ex. side), was hard starting wouldn't idle but ran ok at top end.
You've got the fuel lines routed correctly, it may be necessary to perform a crankcase pressure/vacuum test. Have you got a mityvac?

 

Can you explain how to perform a crankcase pressure/vacuum test with a mity-vac? I would like to put it in my notes so I can remember.
Thanks

 

Can you please start a new thread for this question or email me?

 

Have you check the plastic insulator where the carb. is mounted on.I have seen it come loose from the engine and cause a air leak.Also check the spark arrester screen to see if it is clogged.Try to see if it will run with the muffler off it could be clogged also.Hope this helps.

Jerry

 

Thanks Paul...I do not have a mity-vac but may need to invest in one....Looks like I'll be pulling the piston to get a good look at it......
Thanks, and I'll post what I find.....

 

Just so we're clear here, a 2-stroke crankcase is part of the intake manifold. Everything between the combustion chamber and the carb. is part of it. The piston skirt, the transfer ports, the crankshaft seals, the cylinder gasket...everything. If there's wear or damage in any of these areas, fuel delivery and engine performance will suffer if it runs at all.

http://www.walbro.com/servicemanuals.aspx

On certain model type backpack blowers we've been seeing advanced inlet needle lever wear after 2 yrs. of commercial use. What the wear does, is effectively make the inlet needle the main jet as the fuel delivery into the carb. becomes insufficient. The symptoms can be slows from high RPM or won't achieve full RPM. In the decades working with diagphragm carbs. I can say I've never seen this as an issue until these strato-engine blowers. However, it's become predictable as clockwork. Exhaust port restriction also affects these same units at the 1-year mark, unlike most blowers.

It goes to show that a return to basics is often a valuable diagnostic avenue...but you have to understand how (as 30yr says) it works to understand how to (diagnose and) fix it. An engine is a pump, and any pump has to have good sealing in all aspects for it to work properly.

 

IT IS FIXED!!!!!!!!!!! Thanks so much for all your help......I had decided to remove the motor and pull the piston to check for damage. This particular saw's engine is mounted to the saw body from the bottom using the lower crank case bolts. When I went to loosen the bolts, I found that the bolts were loose already so on a hunch, I decided to tighten them an put the saw back together and check since I wasn't too far into it, and that was it. massive air leak....Runs like a charm now.....I wanna give a special thanks to Mr. Paulr44.....You are a wealth of knowledge and a very nice gentlemen. Thanks again...... :thumbsup:

 

:thumbsup::thumbsup:

 

You're welcome.