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I've got a few older weedeaters I'm trying to get running, and I am having some difficulty. Take for example, a couple of featherlite models of different vintages. Both have 120lbs compression, as measured via a compression tester replacing the spark-plug, both have good spark, as indicated by a visual in-line spark tester. One has brand new carb, the other has a rebuilt carb. New fuel lines and in-tank fuel filter. Both will pump up gas into the primer bulb. Neither one will go. Very frustrated at what should be solvable. I have had great success with Lawnboy 2-cycle lawnmowers. What am I missing here?

Crank case Vacuum.
120 lbs is good but not if 50% of it came past the crankcase seals and not the carb.
Check the carbs are functioning by removing them , leaving fuel lines attached, and blowing through the air passage with low pressure air.
I use one of those old reverse vacuum cleaner type spray painting kits for this ( saved it from the tip ) .
Blowing through the carb you should see the air fuel mix coming out the end of the carb, Dont smoke while doing this and be wary where you are bowing the explosive air/fuel mix.

Next step is to check the crankcase seals.
This is a PIA job as you will need to bank off the carb and muffler and then do a leak down test with the piston at BDC to open the inlet port.

Well, on these 2-cycle engines the only place that would have a crankcase seal is where the crankshaft exits to the flywheel. Only one seal. Behind the flywheel. Are these readily available and replaceable, as they are on Lawnboy 2-cycle mowers? The crankshaft is not supported with a bearing front and back, only the flywheel side. The back is sealed off with a piece that also includes the back shroud and gas tank on some models.

I do not do seals on Weedeaters because the owners can buy a new one for the cost of the repair.
And yes same deal as on the lawn boy.
Usually there are two, one under the flywheel and one behind the clutch.
Easy to replace, parts are listed in my suppliers catalogue, not expensive, just 3 billable hours @ $ 60.00 /hr.
Usual sign of seals is difficulty of starting from cold ( seals dry & leaking bad ) revs a bit high but runs OK when hot ( seals wet & sort of working but allowing air in ).
I would check the crank case vacuum first, new seal won't hurt , but still might not be the problem.

Is the exhaust port clean and not blocked, choking the engine ?

I realize that most weedeaters are cheap enough that it is not economically feasable to figure shop labor rates for extensive repair. However I am a hobbiest, and I enjoy working on small engines just for the satisfaction of making them run. Parts are certainly cheap enough, and if I sell them for more dollars than I put into them in parts and acquisition of the broken weedeater, I'm fairly happy. I am finding these very tiny 2-cycle engines and carbs are more difficult to get running than the Lawnboy lawnmower engines I am much more familiar with.

Do the vacuum test and let us know.

Phototone said:

I realize that most weedeaters are cheap enough that it is not economically feasable to figure shop labor rates for extensive repair. However I am a hobbiest, and I enjoy working on small engines just for the satisfaction of making them run. Parts are certainly cheap enough, and if I sell them for more dollars than I put into them in parts and acquisition of the broken weedeater, I'm fairly happy. I am finding these very tiny 2-cycle engines and carbs are more difficult to get running than the Lawnboy lawnmower engines I am much more familiar with.

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You are not alone on that one.
There is a reason why there are no more bottles left in the wine cabinet.
And it is small cubic shaped & made of alloy

motoman said:

Do the vacuum test and let us know.

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I don't think I have a way to do a valid vacuum test.

Have you tried spraying starting fluid in the air intake and attempting to start it? If so, what were the results?

I have worked on a lot of trimmers (20 or so) including two Weed Eater Featherlites, and not one of them had problems with its crankcase vacuum. I don't have a way to do a valid vacuum test either, and I can usually get them running.

And I do have the equipment which is quite cheap.
Well you can get a cheap pump for around $ 20 or so called a vaccum brake bleeding pump.
You then need to make a few bits & pieces.
There are hundreds of U-Tube videos of how to make on one the cheap and cheap ones work just as well as $ 3000 snap on ones.
You can not properly access any two stroke engine without having some means of checking the primary compression and the primary compression is highly dependant upon the condition of the crankcase seals.

You also should test cube carbs both under pressure and vacuum.

Oh and I have replaced crankcase seals, generally on high end chainsaws.
And I do around 6 two stroke engines, each & every week.
About 1 in 10 will have faulty seals.

primerbulb120 said:

Have you tried spraying starting fluid in the air intake and attempting to start it? If so, what were the results?

I have worked on a lot of trimmers (20 or so) including two Weed Eater Featherlites, and not one of them had problems with its crankcase vacuum. I don't have a way to do a valid vacuum test either, and I can usually get them running.

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Now not meaning to be nasty here, but if you do not have a vacuum tester how do you know none of your engines had a crankcase seal problem ?
I can get an engine with poor primary compresson to run by adjusting the carb to compensate for the air leaks but it is only temporary . And it is not a fix.

Remember for a stroker to run the seals need to work both under vacuum, or it won't "suck' a full charge in and pressure or it won't "blow" the full charge into the combustion chamber.
5 Signs.
Hard cold starting, Ok hot starting
Poor initial acceleration
Lack of power at full speed
Over reving ( lean burn )
Over heating ( lean burn )

And a sample of 2 is not particularly represantative considering they make around 1/2 million a year.
I give one of the local rehab groups around 50 trimmers a year for them to pull down & rebuild.
Nearly all of them are either Weedeaters or Ryobis at least 1/2 needed new seals.

bertsmobile1 said:

Oh and I have replaced crankcase seals, generally on high end chainsaws.
And I do around 6 two stroke engines, each & every week.
About 1 in 10 will have faulty seals.

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Most of the machines I work on are low-end.

Top end, bottom end they all work the same.
Some are financially viable to have some one else fix while others are fix it yourself jobbies.
After all, seals & gaskets run out to around $ 10 to $ 30 and rings are 5 to 15 so all very economic to do yourself, just not viable when you have to factor in labour costs.
I have repaired a dozen or so Featherlites , bcause the customers liked them & wanted them fixed. They knew them to be good ones and they did not want to chance being stuck with a pretty new lemon from a big box store where warrantee is a swear word for the sake of $ 20 more than new price.

Could you suggest a good vacuum tester and compression tester for me to buy? I don't want to pay a whole lot, and I am not expecting 100% accuracy, but I am certainly interested in making sure my machines keep running for a long time.

When I open up the crankcase on a 2-cycle engine, I always replace the seal. I make a new seal out of a sheet of rubber fiber gasket material. Is this acceptable, or should I be using something else?

Firstly I am in Australia so no good asking me which one to buy.
Mine is a Mitymax which I bought at a swap meet with a broken gauge.
Prior to that I was using a vacuum brake bleeder I bought from the local car parts store hooked up through the manoneter I use for balancing motorcycle carbs. Hooked up backwards for pressure testing and normally for vacuum testing.
Contry to popular belief you never pump over 10 psi for any test and in most cases you are looking for an inability to hold a constant pressure/vacuum not an absolute figure.

Secondly jambing in a lump of rubber is just not good enough and way more expensive than using the correct seals.
I do hope you were using petrol proof, heat stabilised butyl rubber and not common neoprene, otherwise they will go to jelly over time exposed to modern fuel.

When I started I wasted hundreds of hours pulling down cleaning & reassembling carbs for tools that were beyond repair or carbs that were functioning properly in the first place.
Now the first test is the in line plug tester and the aerostrat down the carb.
Next phase is off with the muffler and check the bore.
Most "repairs" end right there with a scored piston or bore.
If they look OK then it is block off the exhaust, plug the carb and do the primary & secondary compression tests.

If they are good and only if they are good then I look at the carb.
No profit in spendng 4 hours fixing a carb & changine filters / fuel lines only to find the bore is scored ,thus the unit is a non economic repair.
Even if the owner tells you to keep it. You have lost money unless you can salvage enough in salable parts to cover your costs ( and you never do ).

This is the gasket material I use: Fel-Pro 3157 - Gasket Materials | O'Reilly Auto Parts Like I said before, it is rubber fiber.

It costs $6 per sheet and I can use it for intake gaskets, exhaust gaskets, crankcase gaskets, and air filter gaskets. Usually I only open the crankcase if the machine is an older Homelite blower. You have to break the crankcase seal in order to get the gas tank off on those. I have considered cleaning out the crankcase on every 2-cycle machine I get though, because so many 2-cycles end up having lots of old 2-cycle oil collected in the bottom of the crankcase. Is this a good idea?

For years I have used a Harbor Freight vacuum "pump" to bleed brakes. It is currently available as I just bought one with coupon for $17. The old one lasted 20 years. There are no moving parts. It is listed probably under AC pump on the site. Smaller than kleenex box . One side fitting is air pressure from your compressor. The other side is vacuum out. On auto application I reduce the air pressure in to around 30 psi so seals will not be pulled within the brake system. You can fiddle around and get just what you need. Try it, you like it.:laughing::laughing:

PS This is another jewel thread that should be a sticky or in a paperback.

primerbulb120 said:

Have you tried spraying starting fluid in the air intake and attempting to start it? If so, what were the results?

I have worked on a lot of trimmers (20 or so) including two Weed Eater Featherlites, and not one of them had problems with its crankcase vacuum. I don't have a way to do a valid vacuum test either, and I can usually get them running.

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:thumbsup::thumbsup:

What i do when in your shoes, confirm spark and if plug not wet, spray the starter fluid in the carb and try it. just get it to run for a second at least this confirms it is a fuel\carb problem to narrow your troubleshooting. As above all the ones i find only 1 ignition problem, 1 motor frozen, 2 or 3 cyl screws are loose, all others (30+-) carb\fuel problem.

if u see clumps of dirt behind the flywheel, it will run just not idle and u can change it later.
if u see clumps on the engine block then make sure screws are tight.