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Stihl BR400 engine question.

Posted by dlatheman (My Page) on
Fri, Nov 23, 07 at 17:28

I have a Stihl BR400 backpack blower. Engine has become hard to start. Once started it will run to a high RPM and then quit until the RPM drops, it then starts hitting again and returns to the high RPM and repeats above. I have checked the gas tank cap, fuel filter, gas line, air cleaner and carb, all are in working order. I have replaced the spark plug and the exhaust screen is clean. I am thinking the coil may be breaking down at the higher RPM's. I would love to hear from anyone who has experience with Stihl products.

Follow-Up Postings:

RE: Stihl BR400 engine question.

I had a little problem with 4 year old use very little but way was use may been cause coil over heating I run full throttle until gas ran out fill run again four time on hot day coil went out. before went out it would Idle down some and then rpm's to high because missfiring load crankcase with gas. New coil came with washer that insolate heat transfer from block and I add better cooling practice to operation HS 85 mounted on 2x4 to cut tops out 6 acres blackberries.

RE: Stihl BR400 engine question.

Sounds like the carb is not pumping up enough fuel.
Probable causes: 1. Partially blocked impulse passage.Remove the carb.On the black carb mount there is a small hole.Blow compressed air or use a cleaner to make sure this passage is clean.If it is clean, when a few drops of oil are poured into the hole, and the engine cranked over, the oil should shoot out.
2. Pumping chamber blocked.Remove the bottom cover (held with one screw).There is a tan colored diaphragm.Lift it off the cover.If there is any tarry stuff below, clean it off.
On the carb body, there is a small circular well which has a mesh.
Prise the mesh out gently and clean it.
Apply oil to the carb body and gasket and refit the cover.
3.Metering chamber blockage.Open the top cover with four screws.Refit the carb in on its mount.
Hold the metering lever down and crank the engine over.
If everything else is fine gas should shoot up thru the inlet needle.
Refit the cover.At this stage I need to know the type of carb you have.If the blower is old, it has a 3 screw carb without limiters.If its a fairly new blower there are limiter caps on the adjustment screws and there is not much that you can do other than opening the 'H' and 'L' screws to their stops.
Try starting it now.
Don't go to full throttle at once.Take it to partial throttle first and gradually increase the throttle.
And, do all this without the filter elements.


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