Repairing Stihl Backpack Blower

[GarageDan]

Is this an appropriate place to post about repairing my Stihl backpack blower. I've got an older blower and I'm trying to get it running again, my son's no longer around to rake. It will turn over and tries to run, but it doesn't quite get there.

Today I removed the carb and soaked it for two hours in Berryman's Dip, you know the 1 gallon can. The air filter looked new and the spark plug looked pretty close to new.

The fuel lines are still flexible and don't appear to be damaged. If there is a little fuel filter in the tank, I didn't check it...

I did put fresh gas/oil mixture in it.

If I set the throttle to wide open and fiddle around with the choke it will crank and run for a second and then die.

Ideas?

 

[Mr_fixit]

Try cleaning the spark arrestor. I have the same problem , I didn't fix mine yet but I'm sure that's my problem. you tube can help

 

[Ole Slewfoot]

Most likely it isn't feeding fuel.
Backflush the filter with carb cleaner, if it gets better, replace it anyway.
Failing that you'll be taking the carb apart with particular attention to the fuel pumping section.

Was it apart for the soak?

 

[GarageDan]

Try cleaning the spark arrestor. I have the same problem , I didn't fix mine yet but I'm sure that's my problem. you tube can help

I've been reading about this some...

Most likely it isn't feeding fuel.
Backflush the filter with carb cleaner, if it gets better, replace it anyway.
Failing that you'll be taking the carb apart with particular attention to the fuel pumping section.

Was it apart for the soak?

I didn't take it apart. So far I've had plenty of success just soaking them whole. I think that's the beauty of the dip.

It's a Stihl BR420 magnum by the way.

 

[chaosracing]

There should be a filter in the fuel tank. I would also replace the fuel lines as well. With the ethanol in gas, it destroys rubber. Just because they are flexible doesnt mean they are not bad.

As for the spark arrestor, we just remove them. If your still having issues, remove the exhaust and look at the exhaust port. You might have carbon build up in there. Its easy to clean, you just have to be really careful not to score the piston or anything else in there, and also need to prevent the carbon from getting into the cylinder.

 

[James-W]

There should be a filter in the fuel tank. I would also replace the fuel lines as well. With the ethanol in gas, it destroys rubber. Just because they are flexible doesn't mean they are not bad.

As for the spark arrestor, we just remove them. If your still having issues, remove the exhaust and look at the exhaust port. You might have carbon build up in there. Its easy to clean, you just have to be really careful not to score the piston or anything else in there, and also need to prevent the carbon from getting into the cylinder.

I think this is best advice. Replace the fuel filter and the fuel lines. The alcohol in the fuel can cause issues with the entire fuel system. It is best to use gasoline without alcohol in it. You may need to thoroughly clean or replace the carburator. Some of the carburators are pretty cheap and it may be more practical to just replace it rather than screw around trying to clean it. I would check the cost and if it is not too expensive, I would just replace it.

 

[GarageDan]

I think this is best advice. Replace the fuel filter and the fuel lines. The alcohol in the fuel can cause issues with the entire fuel system. It is best to use gasoline without alcohol in it. You may need to thoroughly clean or replace the carburator. Some of the carburators are pretty cheap and it may be more practical to just replace it rather than screw around trying to clean it. I would check the cost and if it is not too expensive, I would just replace it.

I've switched to ethanol free fuel for my little engines, but for years it wasn't the case.

 

[Ole Slewfoot]

I've been reading about this some...



I didn't take it apart. So far I've had plenty of success just soaking them whole. I think that's the beauty of the dip.

It's a Stihl BR420 magnum by the way.

I'd verify flow through each orifice, and look at all the parts in the pulse pump.

 

[rockettgpw]

+1 on cleaning the spark arrestor /muffler.
Had a plate compactor that had all the usual fixes performed and still no go. Removed the arrestor, soaked it in gasoline to break up the carbon, let it air dry and then burnt it's insides with a primus torch and shook out the last of the carbon crumbs. Of course use appropriate caution re gas and flame.

 

[SimS]

I have resurrected several small engines that have suffered from stale ethanol gas. If they have spark they will generally come back to life after replacing the entire fuel system. If it doesn't have spark you can get a replacement coil for $10 on Everyone's Favorite Auction Site. As stated in the previous posts the fuel system will be ****. The complete fuel system replacement for your beast is $13.68 on EFAS. For less than $25 (the Berryman's probably costs as much or more) you can be back in action. That beats yanking on the starting cord for a zillion times in my book. Good luck.

SimS

 

[GarageDan]

I'd verify flow through each orifice, and look at all the parts in the pulse pump.

I try not to disassemble carbs if I can get away with it. They tend not to run well after "I" do that. I think I'd just buy a new one on Amazon for $20 first.

+1 on cleaning the spark arrestor /muffler.
Had a plate compactor that had all the usual fixes performed and still no go. Removed the arrestor, soaked it in gasoline to break up the carbon, let it air dry and then burnt it's insides with a primus torch and shook out the last of the carbon crumbs. Of course use appropriate caution re gas and flame.

I've been reading that some people just remove the screen in there all together.

I have resurrected several small engines that have suffered from stale ethanol gas. If they have spark they will generally come back to life after replacing the entire fuel system. If it doesn't have spark you can get a replacement coil for $10 on Everyone's Favorite Auction Site. As stated in the previous posts the fuel system will be ****. The complete fuel system replacement for your beast is $13.68 on EFAS. For less than $25 (the Berryman's probably costs as much or more) you can be back in action. That beats yanking on the starting cord for a zillion times in my book. Good luck.

SimS

I was looking at parts last night. I can a new fuel system and coil for about $30. I bought the Berryman's on sale a year or so ago and have only used it three times, but it's worth it in my book so far.

 

[Jeepster04]

I tried the taking it apart and cleaning it... Buying a new one and adjusting it worked great.

 

[GarageDan]

Thanks for the reply guys, I appreciate everyone's replies and education.

I plan to fish the filter out of the tank today and clean the muffler screen. I don't have a filter, but I could go with out a filter for testing couldn't it?

It's been sitting for a 3-4 years - with an empty tank. I seem to recall that it I took it to the mechanic and they tuned it up (lazy) because it wasn't running well. I couldn't get it to run then and just bought an electric one at a yard sale. That is now dead so I'm back to this old Stihl. Back then I did run regular ethanol gas, but I've since switched to 100% gas for my small engines. That tune up is the reason I didn't replace the spark plug. I figure if the filter still looks brand new and was replaced at the same time as the spark plug then it should be good too.

I'll try the screen (which I knew nothing about,) the in-tank filter, and pulling the plug to check and see if I flooded it today. Thanks for the advice guys.

 

[bwringer]

If you soaked the carb without taking it apart, it probably melted the little flapdoodle in there that pumps fuel.

Seriously, a new carb is probably stupid cheap, often about the same as a rebuild kit.

 

[chaosracing]

Since it sat for so long empty, i would buy a new carb as yours is likely corroded inside due to moisture. Ethanol is hygroscopic meaning it absorbs water. At this point, its cheap insurance just to replace entire fuel system now. As for running ethanol free fuel, its a good suggestion. Around me, more stations are offering 93 ethanol free fuel.

 

[DGersic]

it’s probably the fuel pump in the carb is bad (weak). In most cases a whole new carb is cheaper than a carb rebuild kit. Buy one, get some new fuel lines, and give it a yank.

I recently did this on a $100 yard vac I picked up from Craigslist that barely ran. New carb, new spark plug, changed the oil, fresh gas, and it started on one pull and ran great, for about three hours, then the camshaft shredded its gear teeth.

Non ethanol gas is not an option here in corn country. Use Stabil in every can of gas that goes through the small engines.


Sent from my iPad using The Garage Journal mobile app

 

[rlitman]

I'd verify flow through each orifice, and look at all the parts in the pulse pump.

The screen is what clogs in these carbs.

+1 on cleaning the spark arrestor /muffler.
Had a plate compactor that had all the usual fixes performed and still no go. Removed the arrestor, soaked it in gasoline to break up the carbon, let it air dry and then burnt it's insides with a primus torch and shook out the last of the carbon crumbs. Of course use appropriate caution re gas and flame.

Don't bother with the gas. Just heat the spark arrestor screen (not the filter screen in the carb!) until it glows, and by then, all of the carbon will have been burned off. Then let it cool and stick it back in.

 

[GarageDan]

Where exactly is this screen?!?!?!?

 

[Firebrick43]

I don't know which blower you have but I have found that on stihl mid grade products such as hand blowers, home owner weed eaters, and mid grade and home owner saws that to try to clean and rebuild the carbs is a lost cause. I have fought them and spotless cleaned parts, even in an ultrasonic cleaner. Many time the engine would run but rarely right.

A knowledgable gentalman in the local stihl dealership told me just junk them and buy a new one. And it works perfectly every time. Most of the small stuff the carbs are $30~ from stihl and many have good luck with 15$ eBay specials.

The pro saws, large weedeaters, and larger back pack blowers have good carbs worth rebuilding.

What model is it. Some of the bigger blowers are 4 mix engines and have completely different maintence procedures (and should only use synthetic oil) due to the valves.

 

[Davefr]

It's likely not the spark arrestor if it starts and then dies. Sounds more like fuel starvation.

It sounds you might have ethanol breakdown related sludge in the carb's fuel inlet. Soaking is only marginally effective.

Take apart the carb and see if it looks like this. There's a screen under this ****:

 

[GarageDan]

I don't know which blower you have but I have found that on stihl mid grade products such as hand blowers, home owner weed eaters, and mid grade and home owner saws that to try to clean and rebuild the carbs is a lost cause. I have fought them and spotless cleaned parts, even in an ultrasonic cleaner. Many time the engine would run but rarely right.

A knowledgable gentalman in the local stihl dealership told me just junk them and buy a new one. And it works perfectly every time. Most of the small stuff the carbs are $30~ from stihl and many have good luck with 15$ eBay specials.

The pro saws, large weedeaters, and larger back pack blowers have good carbs worth rebuilding.

What model is it. Some of the bigger blowers are 4 mix engines and have completely different maintence procedures (and should only use synthetic oil) due to the valves.

It's a Stihl BR420 Magnum. I think it was a pretty good one originally.

 

[GarageDan]

It's likely not the spark arrestor if it starts and then dies. Sounds more like fuel starvation.

It sounds you might have ethanol breakdown related sludge in the carb's fuel inlet. Soaking is only marginally effective.

Take apart the carb and see if it looks like this. There's a screen under this ****:

I can do that. As long as I'm not taking out all the jets and such I should be okay.

 

[Firebrick43]

Well a quick search shows the br420 having a walbro which is better than the zama that many of the cheaper models have.

 

[spudley]

Couple years back I disassembled a weed wacker carb and found the needle valve disintegrating from ethanol.
I'd order a new carb, and stay away from ethanol in small engines.

 

[manwithtools]

There should be a filter in the fuel tank. I would also replace the fuel lines as well. With the ethanol in gas, it destroys rubber. Just because they are flexible doesnt mean they are not bad.

As for the spark arrestor, we just remove them. If your still having issues, remove the exhaust and look at the exhaust port. You might have carbon build up in there. Its easy to clean, you just have to be really careful not to score the piston or anything else in there, and also need to prevent the carbon from getting into the cylinder.

This ^. Replace the fuel lines and filter first. Every problem I've ever encountered with a Stihl has been related to the fuel lines.

 

[GarageDan]

So, I disassembled the blower again. I found little puddles of liquid around on top of the gas tank and cover. This is a little disturbing for me

These muffler bolts were ridiculously tight... way beyond what seems appropriate to me.

It was very odd. The muffler had some liquid in it? There was about an ounce of liquid inside the muffler. AND the muffler weighs about 5 lbs. Is that normal?

I took a little of the carb apart and it looks pretty good to me. This is exactly how it looked. I didn't do any additional cleaning.

 

[Davefr]

Is that liquid you see fuel mix?

If it's mix then I can't image how it got inside the muffler other then you flooded the cylinder.

If it's mix on the fuel tank then maybe the fuel line is deteriorated where it entered the gas tank. (pretty common area for a leak).

If it's not mix, did you leave the blower outside in the rain.

When you removed the muffler, what did the cylinder wall and piston skirt look like?

 

[GarageDan]

Is that liquid you see fuel mix?

If it's mix then I can't image how it got inside the muffler other then you flooded the cylinder.

If it's mix on the fuel tank then maybe the fuel line is deteriorated where it entered the gas tank. (pretty common area for a leak).

If it's not mix, did you leave the blower outside in the rain.

I'm thinking the liquid was fuel. Is it possible I flooded it so bad that stuff went through the cylinder into the muffler and even out around and such. It doesn't look like it's straight out of the tank, it looks like it's been through something. No rain.

 

[GarageDan]

Is that liquid you see fuel mix?

If it's mix then I can't image how it got inside the muffler other then you flooded the cylinder.

If it's mix on the fuel tank then maybe the fuel line is deteriorated where it entered the gas tank. (pretty common area for a leak).

If it's not mix, did you leave the blower outside in the rain.

I'm thinking the liquid was fuel. Is it possible I flooded it so bad that stuff went through the cylinder into the muffler and even out around and such. It doesn't look like it's straight out of the tank, it looks like it's been through something. No rain.

 

[Davefr]

I'm thinking the liquid was fuel. Is it possible I flooded it so bad that stuff went through the cylinder into the muffler and even out around and such. It doesn't look like it's straight out of the tank, it looks like it's been through something. No rain.

I can't think of any other scenario for 1 oz of mix to accumulate inside the muffler except for severe flooding. (Too much choke while trying to start it.) Is the spark plug wet?

Are your sure the carb. is adjusted to the initial factory settings. Those settings are usually good enough to start the blower?

It doesn't sound like fuel delivery is an issue if you flooded the unit that bad.

Are you able to measure the compression.

 

[GarageDan]

I'm not sure if the carb is adjusted to the initial factory settings or not. I bought it used about 10 years ago and it's been to a mechanic a couple of times over the years. The plug was a little wet when I first pulled it.

I've been reading that this model shouldn't really be choked at all, maybe just once. I'm pretty sure the less it wanted to run the more I choked it.

I can check the compression. That's a good idea. What should it be?

 

[Firebrick43]

Every stihl I have owned, has the same starting procedure. Ignition on, choke on, and throttle trigger locked or held full. If it has a primer bulb fill it by pushing several times.

Pull the cord until the engine coughs. Then shut the choke off and pull again. As it starts Release the throttle.

If you pull it ONE additional time after it coughs with the choke still on you have flooded the plug.

 

[chaosracing]

Your diaphram is shot from ethanol. It should not be bubbled like that.

 

[GarageDan]

Thanks.

 

[Bent Handle]

I agree that diaphragm looks stiff, and is probably not operating correctly. I could be holding the needle open flossing the engine or not allowing fuel through. Obviously either is bad.

 

[Bretny]

3-4years sitting no matter how you stored it..you will be buying a new carb.

Fuel, compression, spark are the basics of getting these little engines running.

Only running on choke is usual a condition of a leak between the carb and cylinder.

 

[redmondjp]

I used to rebuild, or attempt to rebuild these small carburetors as well. I only use ethanol-free fuel, and that helps them to last longer. But the issue that happens eventually to me on every piece of equipment, is that a tiny, microscopic air leak develops somewhere, rendering the fuel pump useless (it ***** air though this tiny leak instead of fuel) and the unit will start and die, or start and idle only.

I have wasted far too many hours of my life trying in vain to rebuild these carbs using all-new OEM gaskets, and still having the same problem once done. This is incredibly frustrating when I am trying to get the yardwork done, especially at this time of year with the short daylight hours, with the unit apart on top of my recycling bin, while I should be blowing leaves or trimming the hedge.

As noted above, I have found that you can get brand-new carburetors for anywhere from $10-50 online. I have just started buying new carbs and stockpiling them. I have two Stihl units which use the same carb, and I found new carbs online for $11 each so I ordered several. It doesn't take long to throw a new carb on, and tweak the mixture and I'm back in the running again.

I think the long-term solution in many cases will be battery-powered units, which are becoming more commonplace and powerful.

 

[nh_yota]

I've found that with Stihl equipment it's better just to take it to a dealer for service than to try fiddling with it yourself.

 

[spudley]

I've found that with Stihl equipment it's better just to take it to a dealer for service than to try fiddling with it yourself.

Then you're a blasphemous heretic that should spend time in a dungeon. Take something to a "dealer" and forfeit pleasurable hours in a garage? Before we go to dealers they'll have to pry old cold dead hands off the toolbox!
Dealer Schmealer.

 

[nh_yota]

Then you're a blasphemous heretic that should spend time in a dungeon. Take something to a "dealer" and forfeit pleasurable hours in a garage? Before we go to dealers they'll have to pry old cold dead hands off the toolbox!
Dealer Schmealer.

I'd agree with you when it comes to the older power equipment but I'd rather spend time with my feet up drinking beer than in a cold garage trying to get a leafblower working on my one day off.