# Solved: Craftsman leaf blower only runs at full throttle and half choke



## lexmarks567

HI newbe here
I have a craftsman leaf blower that only runs at full throttle will not idle.Move the choke to run it dies.Someone said to replace the diaframe.What do you think.It works 175MPH.Its a blower/vac combo.I do not know the model number.All I can say is thats its a older model


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## kiwiguy

I would start by cleaning out the carburettor, if the diaphragm needs replacing then do it.

Certainly sounds like a fuel issue, but be careful you don't end up spending more on it than a replacement!


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## lexmarks567

kiwiguy said:


> I would start by cleaning out the carburettor, if the diaphragm needs replacing then do it.
> 
> Certainly sounds like a fuel issue, but be careful you don't end up spending more on it than a replacement!


OK I'll try it. I hate messing with 2-cycle carbs.Too many parts.4-cycle carbs are better.


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## wacor

these kind of engines drive me crazy. that is why i now drag wires around and go electric.

you could try running some carb cleaner thru it. not likely to help but simple to try

on my snow blower which is 2 cycle there is a little orifice that plugs up. you can take it apart and not find anything and then put it back together and it is ok. 
Edit: what i meant was that it is a very tiny orifice and not always do you see something in it. in my case i took it out and found nothing but it obviously dislodged something in the process.

not sure how one goes about figuring out which screw is the one that is the valve though as there are some adjusting screws for fuel and air that look similar


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## thecoalman

There's two little screws on the carb side by side (should be), They will probably have springs on them. They are for the fuel/air mixture. One is for the high speed and the other is for the low speed. Try turning them about 1/8 a turn in either direction, can't tell you which is which but you should figure it out pretty quick. Be careful with the high speed adjustment, you can increase the power with this but if you lean it out too much you'll blow it up.


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## lexmarks567

thecoalman said:


> There's two little screws on the carb side by side (should be), They will probably have springs on them. They are for the fuel/air mixture. One is for the high speed and the other is for the low speed. Try turning them about 1/8 a turn in either direction, can't tell you which is which but you should figure it out pretty quick. Be careful with the high speed adjustment, you can increase the power with this but if you lean it out too much you'll blow it up.


The only screw I can adjust is the Idle.the High and low screws have stops on them.They can't be turned


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## wacor

try to see if there is not a model number somewhere on the unit if you have not already. that might help some.


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## lexmarks567

OK Model 517.797941 it says see owners manual for adjustments and mantanece but I don't have one.



wacorsaut said:


> try to see if there is not a model number somewhere on the unit if you have not already. that might help some.


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## wacor

no luck trying to google that 
you sure that is the model?
you could contact sears about it online


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## lexmarks567

wacorsaut said:


> no luck trying to google that
> you sure that is the model?
> you could contact sears about it online


www3.sears.com


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## thecoalman

lexmarks567 said:


> The only screw I can adjust is the Idle.the High and low screws have stops on them.They can't be turned


I can say with 90% certainy that the adjustment is what is causing the problem, if you can't turn them....well you're pretty much stuck. What do you mean they have stops on them?


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## lexmarks567

thecoalman said:


> I can say with 90% certainy that the adjustment is what is causing the problem, if you can't turn them....well you're pretty much stuck. What do you mean they have stops on them?


They have plastic caps over the screws that lock them so they can't be adjusted


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## thecoalman

There has to be a way to remove them otherwise a mechanic would have no choice but to replace the entire carb for something that is very simple to fix.


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## lexmarks567

My guess Is they put the caps on so it can't be adjusted.Only the idle can be adjusted.Cause like said.It will run at half choke and full throttle but dies when you let go.


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## wacor

take a couple of pictures if you can with a close up of the carb.

I know somebody in the area that works on everything and will see if he has any ideas.

like Coalman said i would guess those plastic caps can be removed. it probably destroys them but guessing that the only purpose of them is to detect tampering. but dont rely on me as i am not an expert.


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## lexmarks567

OK I will get some and post back.Just so you know now the carbs a walbro


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## lexmarks567

OK Some enigne INFO. 25cc EM 08652-08 engine family SH20254B24RA 
Blower model 517.797941 Ser RS25520969 Unit was made 09-97

Heres picks of the carbs
Primer








Choke and the stops on the screws


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## thecoalman

wacorsaut said:


> it probably destroys them but guessing that the only purpose of them is to detect tampering.


I was going to suggest he cut them off but it's possible they are there for a purpose such as a locking mechaniim to prevent them movig during operation. Mine has springs...

Anyhow it's hard to see from your picture.... but hey look very aceesible so they should be adjustable. have you tried pulling them straight out or prying them off? Gently try to pry them off... without actually seeing it's really hard to give any advice and I certainly don't want to give you advice that's going to ruin it.


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## lexmarks567

Those 2 stops don't just sit on the screws.The screws and the springs are covered with the stops


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## wacor

Pictures are too blurry on my computer

are the stops the red and then kind of white plastic caps that are on the left?


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## lexmarks567

Yes the stops Are red and white.Click on the pic it makes it smaller


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## wacor

did you try gently prying on them. as thecoalman said you never know for sure and would not want to damage anything but they look like they are just stops that should come off.

if you can wait a day or two i can check with my sons buddy


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## lexmarks567

Yeah go ahead. I just sent a email to my parts guy we will see what he says about it.


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## wacor

I forgot to mention. Never work on a sears product  

Learned that a long time ago with water pumps


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## lexmarks567

Its not really A sears product.Its made by ryobi for sears and sears just slaps there name on it.Sears does not make anything.They have the lowest bidder do it.Then sears puts there name on it.


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## wacor

i am aware of that on many of their products but was not certain about garden tool stuff.

same applies though. they spec out garbage on some of their products and dont stick with one manufacturer very long


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## thecoalman

Cheap lawn equipment is only for people with very small yards that use it infrequently. The blocks and the piston may be the same but that's about it, everthing else is different. I used to work at bike shop that also sold lawn mowers, Ariens a very good brand. Full axles with bearings even on the walk behinds.  People woul ask "why is this so much?" Then the 200lb. salesman would jump on the floor model.  Buy something like that and you can have it forever.


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## lexmarks567

Ok Talked to my guy heres what he said

"They put those there so you will either take it to a dealer or they can sell more parts. Its just a scam to make more money"


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## ffparts

Those limiter caps are there so that the carb cannot be adjusted too richly, and go out of emissions compliance. Your problem is 99% probably caused by leaving the machine sit for an extended period of time with fuel in the carb. it plugs the little passages inside the carb, and won't let enough fuel through the carb. it needs rebuilt or replaced. Any dealer or repair shop who removes those caps and does not replace them can be hit with a very large fine from the EPA.


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## thecoalman

ffparts said:


> it plugs the little passages inside the carb, and won't let enough fuel through the carb. it needs rebuilt or replaced.


<rant>if the purpose of those are to prevent someone from adjusting the carb it's just another example of EPA regulations actualy causing harm to the enviroment. My brother was in the tree business for a while with top notch husky saws that always had fresh gas... he still had to adjust them. So the owner of the equipment is stuck with something that instead of being adjusted has to be replaced? How many homeowners do you think are going to foot the bill for a new carb when they can buy a brand new piece of equipment for a little bit more? Laws like that will actually increase damage to the enviroment as opposed to help it because now you have the increased pollution to manufacture the equipment not to mention all the pieces of equipment that are going to be uncessarily disposed of for the lack of being able to turn a screw.... Doesn't make any sense at all. </rant>


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## ffparts

Yep, tell me about it, I go through this almost every day. I don't mean you can't adjust them at all, there is a small adjustment you can stilll do. Theoretically the dealer removes the caps, adjusts the carb so that the engine runs within specs, and reinstalls new ones, in the position that the carb cannot be adjusted any richer.


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## lexmarks567

well I think its time for a update as Im about ready to toss the thing in front of a moving car. I had the carb rebuilt so now it idles but will not go to full throttle. Try to give it gas it dies. tryed reversing the fuel lines no go. The carb can't be adjusted as it as those stops that prevent you from adjusting the carb yourself instead its there to force you to take it in so they can make money off of you. any ideas what to try next


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## Stoner

I just saw it's Robi product.
I have a Robi weed wacker that acted like you first described.
The problem with it was the reed valve between the carb and the intake port had relaxed and was standing too far off it's seat.It was acting like a lot of fuel standoff at the carb as a lot of the fuel air charge came back out of the crankcase at idle and low speeds .
On mine, I think the reed gap was at about .020" 
Replacing the reed fixed it.

Hope that helped.....good luck.


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## JohnWill

FWIW, I had a similar issue with my snow blower, and I just bought the whole carb, it was around $30. A total replacement made it like new. I got 12-13 years out of the first carb, if I do that well with the second...


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## lexmarks567

hmm maby a new carb would work but I just had it rebult why is it not working


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## ffparts

Sometimes the small passages get gummed up inside the carb where you can't get to them, even if you could adjust it, it may not help. BTW that is a homelite product, any homelite dealer should be able to get that carb for around $50, IMO the unit might not be worth putting that kind of money into. Also check for a plugged exhaust screen, it will do exactly what you have described, idle but not run wide open.


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## JohnWill

It's hard to say why it's not working. I went a couple of rounds with a carb on a lawnmower years back, and never could resolve what the issue was. A new carb fixed that one too. Everything looked OK, but it just didn't run right.


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## lexmarks567

maby I should toss it then. The carb been rebult has good spark good compression. Before it would go full thottle but not idle. Now it idles but no thottle. No leaks anywhere (take a can of WD-40 and spay around gaskets on the engine block see if it speeds up or slows down) nothing no change. the carb has stops like I said to prevent it from being adjusted. I could break those platic tabs off but might break the carb


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## Stoner

That is a 2 cycle engine, correct?
Does it have a reed block between the carb and intake port?
If so, again, I recommend you check out the tension of that reed.


Another thought, have you checked the seals on both ends of the crankshaft ?


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## JohnWill

Well, if tinkering with the carb changed the symptoms that much, I think he's working in the right area.


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## Stoner

Or made it worse


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## lexmarks567

no reed the carb sites on this plastic 1 inch seat that leads to the intake. There air fliter sites on top of that carb and is bolted down.go to www3.sears.com enter model number 517.797941 click diagram


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## ffparts

Also, I just thought of something, if the carb was not rebuilt professionally, a lot of times people will just put everything in like it came out, and not adjust the metering lever for the inlet needle. That could also cause your problem. Just a thought


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## SurferJoe46

Quite frankly, these are not a "carb" but really a simple diaphragm-driven form of fuel injection.

They rely on case pressure pulsations or changes in the engine to actually pump the fuel by squirts into the throttle body where it is ingested by the inward flow into the engine.

Most problems with these units are from gum or varnish build-up to the point of not allowing fuel to flow during one or more of the circuits or adjustments to supply sufficient gas to keep the mixture correct and the engine running.

There is a Walbro and a Tillotson, and these are the most typical types that occur in US 2-cycle devices. These also show up on Trail engines which are a Canadian manufacturer, so you can see they are quite universal.

Anyway, usually the act of disassembling the unit and reassembly takes care of the problem "mysteriously" as the diaphragm was usually stuck from the gum and is now freed up by the act of "looking" for a problem...which isn't really apparent to the tinkerer.

The plastic limiter caps should be pried off the stems of the high and low speed mixture control needle valves, as you don't have to worry about any guarantees or warranties at this late date anyway.

The reason for taking them off is so you can GENTLY! bottom the needles into their seats to remove any debris that might be caught there. Try to count the number of turns you made to get them to the bottom, and return them to their original positions as well as you can.

Both needles will affect the others' territory for mixture control unfortunately.

Turning the high speed will also cause a small loss of adjustment at low speed and vice versa. It is a "seek & destroy (and learn)" experience and once you do it correctly, you'll know the procedure for a while.

Start with the low speed jet, this is assuming you have taken the unit apart and don't see anything amiss...like I said, it may not have been anything but a stuck diaphragm anyway.

Try to get a good idle mixture at low speed...if you need to use the choke to keep it running, the mixture is too lean so back out the screw a little more.

After you get a decent (but not perfect) idle, then go for the high speed adjustment. Here you need to be a little carefull...too lean can overheat the engine and it will run badly. ​There are a few things to consider here.

Lean creates a lot of speed for a few moments..but it will usually "sag" and lose speed and stall.

Rich creates a "fat" running condition that will break into a four-cycle-type of sound...firing on every other beat or skipping a few and then firing randomly. This can be adjusted by turning the screw IN a little until you get a clean "on the pipe" type sound. We aren't done yet.

Repeat the idle adjustment..trying to get it better than the first time.

Now go to the high speed again, and when you get it running very well, just back out the high speed screw a tiny but until you hear a slight change of exhaust note. It should lose a little speed, but not too much.

We want the engine to be slightly fat at high speed to keep it cool and keep the power up when it is really working harder.

Another thing that most people get wrong is this:

Adding more oil than necessary or specified in the premix will make the engine run hotter, as the gasoline content is what counts here. More oil = less gasoline in the mix and that means overheating and engine damage. Do the little guy a favor and keep the mix in the proper ratios.

Don't buy outboard engine mix/oil, as this is designed for water cooled engines, and yours is NOT water cooled! They are very different oils for very different purposes.

DO NOT USE engine oil in the premix either! It is not designed to go thru combustion...​


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## lexmarks567

well I was messing with it a few days ago. it will run in choke but when it dies your supposed to go to 1/2 choke does not start or not for very long. before I sent the carb out for repair it would only run full power no idle. then after awhile it would not start at all. He replaced the diaphragm as the old one was stiff there was a long blade of grass in one of the ports. and alot of dirt and a spring was streached out.theres 2 screws missing on the aircleaner cover there should be 4 could that cause anything.


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## lexmarks567

im going to mark this solved as I just broke down and got a homelite gas leaf blower.


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## lexmarks567

OK I thought of something after talking to my guy. Im going to adjust the carb as much as the stops will let me if still nothing Im going to break them off. This thing is old anyway I got it used with 9 lawnmowers all but 3 I got working


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## SurferJoe46

That diaphragm being hard is a tip off to the alcohol in the new fuels. It destroys the elastomer qualities of the rubber and they fail to flex as they should, rendering them inefficient or inoperable. 

The piece of grass is revelatory too. Wonder how it got past your air filter? It might have been introduced by a field attempt of a repair. You can't guarantee cleanliness in those conditions. 

Good to hear you got it all figured out...

Maybe it's time to run an expose on alcohol in fuel and the dire consequences of it. If left in contact with rubber or flexible plastic parts, things can get brittle and fracture or fail to flex as needed. 

Use good gasoline...stay away from brands with the first letter of "A", "B" "M" or "T" as a rule try to get some Chevron...but use the lowest octane you can get. 87 Octane R+M/2 is correct for your engine. 

R+M/2 = Research octane plus Method octane divided by 2.


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## lexmarks567

update I got it to stay running in half-choke and a little with no choke but it won't idle for long. but its a start. I just adjusted the carb a little bit


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## joecbryant

hey lexmarks567, i have a leaf blower that will sit and idle in lower setting, but when I move the lever up to the rabbit position, it just dies. Do I have something clogged up ?


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