Small Engines (Lawn Mowers, etc.): Stihl BR 400 Blower, air leaks, piston rings

Question
Hi Paul,
I have an old Stihl BR 400 that's giving some trouble.
I replaced the tank because it was leaking, and the carb along with gaskets and a fuel line.

It's very hard to start, and when it does, it barely runs and dies.

I also put in a new spark plug and tried running with and without the air filter.

Any tips would be helpful.

Thanks,
Chris

Answer
Hi Chris

Have you checked  ex port  and muffler for clogging / restriction?

what is compression pressure like  ? visuall on piston / rings / bore  
should be no signs of of scoring, blueing,  blowby etc  

is the spark  under compression pressure good  , should jump a 6 mil gap minimum

you have a new carb and tank  along with fuel line  - they should be ok

check timming key in flywheel

then try this  -  spray some 2 stroke into the plug hole and try run , if runs on that assume
compression / spark ok ,  next spray 2 stroke into throat of carb - if runs on this thens stops then you have a fuel  or at least a carby problem.

but if it does not fire when sprayed into carb throat , more likly you are dealing with a  crankcase  air leak.

you will need to remove carby, muffler , flyheel and starter assy  , block off  ex port and carb manifold  with rubber and steel plate(s) - make  spark plug adapter to fit in place of spark plug to pressurise  c/case through plug hole , with piston @ bdc   pressurize to 7-8 psi
check for air leaks at   barrell / case gasket, manifold boot , impulse hose , c/case seals
spray around those areas with soapy water  you will see bubbles  if a leak is present

if so  air leak comnfirmed -

air leaks tend to show  up as  , hard to start, no start  inconsistant idle , stalling, low power,  frequent adjustment of mixture screws , excessive revs

sounds more like a air leak to me  - check manifold boot and impulse hose carfully for splits / holes

take look  , let me know what you find

hope this helps  

cheers paul