Stihl Backpack Blower, Maybe a BR 400? and Coil?

Kirk_Wallace

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Hello. I am working on a backpack blower that I uncovered in my local community compost pile. After much cleaning, it looks to be in decent shape but has no spark. Early research seems to indicate that this is a BR 320 or 400 or similar. I plan to post pictures soon. All of the replacement coils I have seen available have the secondary wire coming out were the frame is so they won't fit. Finding the proper method to check what I have, finding the proper coil replacement, and verifying the correct model number is what I'm working on now. I'll post questions when I get the pictures posted, but I would also like advise on how to get up to speed on Stihl repair information and resources. Thank you for any help.
 

Kirk_Wallace

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Here are some pictures.

I have a pull starter assembly on order and I have enough of the blower to try to run the engine, then go from there. Using a meter on the coil assembly, I get about 1 Ohm between the kill switch lug and the ground lug, which I assume could be the primary resistance. I get 7.5k Ohms between the ground lug and the secondary wire. The readings are the same in both polarities so this acts like a coil and not a CDI/coil module.
 

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Kirk_Wallace

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Well, I got that one wrong. I got the recoil starter assembly in today. It looks like I wasn't able to turn the engine over fast enough by hand. With the starter I got a spark, so I put the engine back together enough to run it. It started and runs well after getting it adjusted. When I filled it with gas, I may have found out why the previous owner chucked it. There is a crack in the tank which may have been leaking for a long time since the bottom of the backpack is really greasy, It leaks a lot now. The tank is molded in with the main fan housing, so it's not easy to replace. I'm not sure if it can be plastic welded or not. I have a separate tank connected for now. The spark arrester seemed dirty enough to be considered clogged. I cleaned it while waiting for parts, so I'm not sure it was a problem. The previous owner may not have known that it needs attention occasionally.

I still have a new coil on order, which should be here in a couple of days. I wanted to see if the different location of the spark plug wire will hit the frame, but since the old coil works, it's not a big deal. The old spark plug wire is too short and has no boot, so I need to work out what I need for a replacement wire and boot.

I suppose I should get the tank sorted out first, before I invest in the balance of parts to make it a proper working blower (screws, orange engine cover, lower half of the harness, end section of the blower tube). I'll post pictures when anything significant gets done.
 

Kirk_Wallace

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I received the new coil and tried to install it. I attached pictures showing where the spark plug wire interfers with the engine frame. It may be that trimming the frame will allow the coil to work, but my old one works, so that is not on my to-do list. The Ohm meter readings (above) on the new and old coil match.
 

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nhyrum

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I'm glad you got it sorted in, for the most part. Honestly, if it were me, I'd just replace the tank. If not, I'd use a plastic epoxy. drain it, clean it really REALLY well with something like 90% isopropyl alcohol. You don't want ANY oils left or you won't get a good seal. You could give that flex seal garbage a try, but I doubt it. Should at least slow the leak down.
 

Kirk_Wallace

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I found a service manual on eBay. It has turned out to be very useful. I finally found out what the difference between the BR320 and BR400. The BR320 has a 41mm bore -- the BR400 has a 46mm bore. The stroke is the same on both, giving a displacement of 44.9cc and 56.5cc. So, the only difference parts-wise is the cylinder and piston. I don't want to take the cylinder off to measure the bore, so I still don't know which I have, but now I know it won't make a difference.

From the manual I found that the spark plug wire screws into the coil pack. The original wire was too short, so I ordered some 5mm wire and easily replaced it. I found a good quality plug cap that I like. It screws onto the wire, but was for a 7mm wire, so I wrapped the end of the wire with tape to make a better fit. The plug socket is a proper brass and spring connector which makes a snug connection but is also easy to pull off. The standard coil spring with a spike into the side of the wire is too flimsy for my taste.

I ordered new Torqs screws to make up for the missing ones. I attached a picture of the new wire and cap. It's not much to show for, but basically I only need to repair the fuel tank and maybe find an orange engine cover. The tank on this particular model is bonded to the fan housing so replacing it would mean replacing both. Later blowers have these as two pieces. I'll probably just glue a patch over the crack and see how it goes. Otherwise, I'll look into plastic welding.
 

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nhyrum

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I found a service manual on eBay. It has turned out to be very useful. I finally found out what the difference between the BR320 and BR400. The BR320 has a 41mm bore -- the BR400 has a 46mm bore. The stroke is the same on both, giving a displacement of 44.9cc and 56.5cc. So, the only difference parts-wise is the cylinder and piston. I don't want to take the cylinder off to measure the bore, so I still don't know which I have, but now I know it won't make a difference.

From the manual I found that the spark plug wire screws into the coil pack. The original wire was too short, so I ordered some 5mm wire and easily replaced it. I found a good quality plug cap that I like. It screws onto the wire, but was for a 7mm wire, so I wrapped the end of the wire with tape to make a better fit. The plug socket is a proper brass and spring connector which makes a snug connection but is also easy to pull off. The standard coil spring with a spike into the side of the wire is too flimsy for my taste.

I ordered new Torqs screws to make up for the missing ones. I attached a picture of the new wire and cap. It's not much to show for, but basically I only need to repair the fuel tank and maybe find an orange engine cover. The tank on this particular model is bonded to the fan housing so replacing it would mean replacing both. Later blowers have these as two pieces. I'll probably just glue a patch over the crack and see how it goes. Otherwise, I'll look into plastic welding.

Looking good! Plastic epoxy will work much better than plastic welding and gluing a patch on, depending on how large the crack is. If it's too wide, you could fill it with some jb weld steel stik. Keep in mind, gasoline is a solvent.
 

Kirk_Wallace

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Well, what I thought was going to be an easy task has turned out to be more difficult. Now that the blower is getting close to being done, I need to get the tubes that fit on after the flex tube with the control handle. The parts lists don't show how these fit together, but I think I need a tube that mounts to the flex tube which has a twist lock on the far end. Then a tube with the twist lock that ends with a nozzle of some sort. I attached a diagram and I think I need item 25 and 28 and/or 27. My guess is 25 slips into 6 and gets clamped by the handle assembly. I expected these to be fairly generic, but do I need to find tubes for this model of blower, or anything that follows the 67mm size, or what? Any advise would be appreciated. Otherwise, I'm thinking some sort of thin wall PVC or sewer or drainage pipe might be modified to work.
 

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