Stihl BR 500 blower with low compression 60 psi

[sinful619]

Hi,

I'm trying to help out a relative with a Stihl BR 500 blower that won't start. Fuel and spark seem okay. Compression is at 60 psi which seems low to me. I also noticed it has two valves as if it was a 4 stroke but it uses premix like a 2 stroke. What's the right approach here?

thanks !

 

[ILENGINE]

Sounds like the Stihl 4-Mix engine. Its 4 stroke but uses 2 stroke oil for lube. 60 is way low, and probably won't start or run at that compression.

 

[Rokon]

4-mix engines have valves. It is also possible that a piece of carbon is holding a valve in the slightly open position. Either way 60#'s of compression won't run these two strokes.

 

[sinful619]

Okay so it's probably time to take it apart and find out what the deal is.

 

[Ric]

Hi,

I'm trying to help out a relative with a Stihl BR 500 blower that won't start. Fuel and spark seem okay. Compression is at 60 psi which seems low to me. I also noticed it has two valves as if it was a 4 stroke but it uses premix like a 2 stroke. What's the right approach here?

thanks !

Okay so it's probably time to take it apart and find out what the deal is.

Like everyone else says it's a 4 mix engine, a single cylinder four stroke engine that runs on a gasoil lubrication. How old a unit is the BR 500. I ask because if you have Fuel and Spark it could be something as simple as the spark arresting screen in the muffler needing to be clean, if that screen is plugged it will not start or if it does it wont have any power.

 

[sinful619]

it's two yrs old and they use it a lot..commercial use. I'm trying to see if the 60 psi compression reading is relevant to this particular blower with four stroke technology/2 valve. I need someone to confirm that before taking apart.

 

[sinful619]

I've read somewhere not to rely on a compression test for this particular 4 stroke blower. Stating the compression increase once the engine warms up. I'm confused.

spark arresting screen is clean btw.

 

[Ric]

I've read somewhere not to rely on a compression test for this particular 4 stroke blower. Stating the compression increase once the engine warms up. I'm confused.

spark arresting screen is clean btw.

Are you getting anything at all when you try to start the blower, is it turning over or acting like it wants to start or is it just flat?

 

[angellonewolf]

Hi,

I'm trying to help out a relative with a Stihl BR 500 blower that won't start. Fuel and spark seem okay. Compression is at 60 psi which seems low to me. I also noticed it has two valves as if it was a 4 stroke but it uses premix like a 2 stroke. What's the right approach here?

thanks !

i think i am right in saying you need more than 70 psi for it to work and that still not run as it should but please some one on here will confirm if i am right i think i seen this some where on the net

i would first try about 3ml of fresh fuel open the choke tip the unit on its side pull the throttle and drop the fuel right in there so it goes in to the chamber (you will have to take the air filter out first) close the choke so it full on and try starting it its should start fairly easily if its starts it prob is worth playing with if it dont and you know the psi is low then sell it for spares they do go fairly well even not starting

if it starts and runs for 2/3 secs then you have to decide if it needs more than a strip down carb cleaner and an air compesser( do not get the carb cleaner on the rubbers as it will rot them) or if your in usa prob better to but new carb as have seen they sell cheap there if your in uk you might want to take a seat before ring for a price its about £90 for a carb a new sthil is only £150 lol

hope this helps but there will be someone hear with more know how than me thanks angel

 

[tybilly]

when I went to a stihl service school back in 99,lol...they could've cared less about compression testing,they wanted a crankcase vacuum/ pressure test,..after I checked the spark arrestor screen,id pull the muffler and carb and check the condition of the cylinder wall, and piston if a ball pont pen cant feel any scratches neither can the ring, hope that helps