Stihl br420c backpack blower wont start

[AmericanBuilt]

Picked up a Stihl BR420c backpack blower for free, brought it home cleaned it up, replaced the carb.
After a couple of pulls, it started right away. I tuned the carb and noticed (after running it for about 10 minutes), had oil dripping on the fuel tank. Took the cover off and found the head gasket was leaking the oil.
Pulled the head off then found the head and piston was heavily scored on the exhaust side and the rings were scored to the piston.
I purchased a head kit, replaced bearings and seals, reset the coil pack to .008. I manually ran the crank shaft for about 45 minutes to seat the rings, then performed a compression test and it topped out to 80 psi. Added fresh fuel and tried to start.the motor will not start but tries to kick a bit. Spark is good (set gap to .020) and bright.
Any suggestions would be appreciated!

 

[Tobystihl]

Key on the flywheel sheared?

 

[AmericanBuilt]

NO, That was one of the 1st things I checked.
It was on the short side but still engages in the flywheel.

 

[lone wolf]

Picked up a Stihl BR420c backpack blower for free, brought it home cleaned it up, replaced the carb.
After a couple of pulls, it started right away. I tuned the carb and noticed (after running it for about 10 minutes), had oil dripping on the fuel tank. Took the cover off and found the head gasket was leaking the oil.
Pulled the head off then found the head and piston was heavily scored on the exhaust side and the rings were scored to the piston.
I purchased a head kit, replaced bearings and seals, reset the coil pack to .008. I manually ran the crank shaft for about 45 minutes to seat the rings, then performed a compression test and it topped out to 80 psi. Added fresh fuel and tried to start.the motor will not start but tries to kick a bit. Spark is good (set gap to .020) and bright.
Any suggestions would be appreciated!

Pressure and vac test it! Is that a 4mix motor, if so check the valve clearances. Was it an OEM kit you used?

 

[AmericanBuilt]

No, I did not use an OEM Kit - was out of my budget.
It is a 2 stroke - 50:1 Mix.
I did a pressure test which came out to 80 PSI which should be good for not being broke in.
Not sure which direction to move in now, Spark plug, coil............

 

[slowcar281]

A BR420c is an old blower, I own one. I believe you are talking about a compression test, what you need to do is a pressure and vacuum test where you block off the intake and exhaust with rubber and manually pump up the crankcase with a Mityvac.

80 psi sounds very low for compression. You may want to check it with another gauge to compare.

How is the carb adjusted? Start with one turn out on both needles. Some of those blowers have the red plastic limiters that need to be removed to get a full range of adjustment.

Also make sure the fuel line isn’t pinched anywhere and that the fuel filter is in good shape

 

[AmericanBuilt]

Yes, I was talking about a compression test - what should it test-out at?
Unfortunately I do not have a pressure/vacuum tester available and from the looks of it, Loest price I've found is $100.
I'll play around with the carb tomorrow, But I just don't understand why it would need to be adjusted since I had tuned it prior to the head and piston replacement. It is a new carb without the limiters.
The fuel line is good, no kinks and the filter is new, however the unit floods quite easy - maybe because the carb is maladjusted for the new head.
I'll use the 1 turn out on both the "L" and "H" needles.
I'll let you know how it goes.
Thank you for your advice!

 

[stihltech]

OK against my better judgement- Stihl states (somewhere) that 100 PSI is minimum. If you have a correct gauge, which is always the big question mark.
Internals and pressure/vacuum est is the only way to know
My magic wand is out of order.

 

[AmericanBuilt]

100 psi minimum? Yeah, that's what's been banging around in the back of my head.
I have a Star Products Professional Compression Tester which I picked up several years ago for a song and it's still like brand new. so I trust the 80 PSI readings I'm getting.
I adjusted the carb as Slowcar281 suggested and the motor actually sputtered a bit more than it had in the past (got me a little excited) but still wont run-up. So I'm guessing at this point that the aftermarket head and piston is the culprit. I did replace the seals and gaskets as well so I'm inclined to believe the unit is tight.
Any other suggestions?

 

[singinwoodwackr]

Hmm, 420…
Have you tried feeding it pot?

 

[slowcar281]

100 psi minimum? Yeah, that's what's been banging around in the back of my head.
I have a Star Products Professional Compression Tester which I picked up several years ago for a song and it's still like brand new. so I trust the 80 PSI readings I'm getting.
I adjusted the carb as Slowcar281 suggested and the motor actually sputtered a bit more than it had in the past (got me a little excited) but still wont run-up. So I'm guessing at this point that the aftermarket head and piston is the culprit. I did replace the seals and gaskets as well so I'm inclined to believe the unit is tight.
Any other suggestions?

Where did you buy the cylinder and piston? You may want to exchange it for another, or return it and watch for a good oem P&C on eBay.

Unless the carb is so out of whack that it won’t run it sounds like it’s just low on compression. 80lbs is too low.

My 420 is all original, I’ll throw a compression tester on it today and see what readings I get.

 

[stihltech]

Where did you buy the cylinder and piston? You may want to exchange it for another, or return it and watch for a good oem P&C on eBay.

Unless the carb is so out of whack that it won’t run it sounds like it’s just low on compression. 80lbs is too low.

My 420 is all original, I’ll throw a compression tester on it today and see what readings I get.

Here we go again.

 

[lone wolf]

80 lbs too low cross-check that gauge on something that runs good if it is 80 forget it! I like to see 150, but it would run with 135, just not great. Maybe the cheap kit is the problem, once you test the gauge you will know.

 

[slowcar281]

Here we go again.

What’s the issue here?

 

[stihltech]

This issue has been rehashed as many times as an oil thread.
12 posters, 12 different answers.

 

[Mad Professor]

What’s the issue here?

80psi and a Chinesium? P/C kit, unless the gauge is way off.....

 

[slowcar281]

Just trying to help the guy out. For reference that’s what mine blew after about 9 pulls

 

[lone wolf]

Just trying to help the guy out. For reference that’s what mine blew after about 9 pulls

You don't stop at a number you keep pulling until it stops rising, I wonder if the OP did this right?

 

[slowcar281]

You don't stop at a number you keep pulling until it stops rising, I wonder if the OP did this right?

Yes I should have been more clear. I pulled until it didn’t rise anymore, just shy of 150 psi which ended up about 9 pulls

 

[lone wolf]

Yes I should have been more clear. I pulled until it didn’t rise anymore, just shy of 150 psi which ended up about 9 pulls

Sounds good.