No start - flathead briggs and stratton

[jeepman3071]

So I've just acquired this 8 hp briggs and stratton flathead engine on a riding lawn mower. I've never heard it run. It does have a nice blue spark, and I cleaned the carb really well. After pulling it over a few times the plug will be wet with fuel. It will pop every so often but will not run. Any suggestions? It seems to have ok compression, and I popped the head and both valves are opening and closing.

 

[Trav]

Are you using the choke?

 

[Quest]

Please find specific model/type plate number and post it here online to share, otherwise: it's really hard to make guesses (there's a whole lot of different B&S in the family, you know what I mean).

(1) you mean you cleaned the carb very well, did you perform a complete teardown, dunking in carb cleaner dunking liquid, scrub clean/poke-clear all the orifices, jets, passage ways, etc compressed-air blow clear/dry of all the passageways/components, etc. and then rebuild it with a B&S carb kit? including the float? (if you are the sidedraft walbro clone types of deal, not the pulsa/vacu-jet style.)

(2) what kind of choke configuration you have on this 8hp? is it manual (level or), or auto-choke type?

(3) what kind of compression reading you getting from your engine? is the compression within range?

(4) is this a single cylinder 8hp?


(*strongly suspect that it's the carb*)

Q.

 

[FowVay]

Make sure the flywheel key hasn't sheared and gotten the timing off too. With a unknown history anything is possible.

 

[jeepman3071]

Yes, the carb has been cleaned really well and a briggs and stratton rebuild kit was used. This is a vertical shaft single cylinder flat head 8hp briggs with the "choke-a-matic" carb. Model# is 190702-5831-01. The plug is wet so it seems to be getting fuel. There seems to be compression, and I pulled the head and the valves are opening and closing correctly. I do not have a compression gauge. The previous owner said it ran but not well. I have tried starting it with choke, no choke, WOT, idle, and everywhere in between.

It will occasionally pop a few times but that is it.

 

[jeepman3071]

Originally Posted By: jeepman3071
Yes, the carb has been cleaned really well and a briggs and stratton rebuild kit was used. This is a vertical shaft single cylinder flat head 8hp briggs with the "choke-a-matic" carb. Model# is 190702-5831-01. The plug is wet so it seems to be getting fuel. There seems to be compression, and I pulled the head and the valves are opening and closing correctly. I do not have a compression gauge. The previous owner said it ran but not well. I have tried starting it with choke, no choke, WOT, idle, and everywhere in between.

It will occasionally pop a few times but that is it.


Also, the flywheel key is not sheared, I checked that as well. I am trying to start it without the air cleaner on. Could that cause it to not start? The air cleaner was in multiple pieces so a new one is in the mail.

 

[Quest]

popping on B&S flatheads typically means "too rich", or valves not closing completely(backfires) or timing issues.

wet-plug is a sign of rich fuel-air mixture, or the inability to ignite the fuel-air mixture.

Q.

 

[jeepman3071]

Originally Posted By: Quest
popping on B&S flatheads typically means "too rich", or valves not closing completely(backfires) or timing issues.

wet-plug is a sign of rich fuel-air mixture, or the inability to ignite the fuel-air mixture.

Q.


The valves seemed to be closing all the way, of course that is just by eye I haven't done a compression test yet. The engine will occasionally pop a few times and run for maybe 3 seconds or so. Spraying carb cleaner into the carb and trying to start it doesn't help much. Think its running too rich?

 

[2oldtommy]

When you rebuilt the carb, did you follow the instruction in the kit to reset the idle jet and the power jet? these need to be set near to optimal setings for the engine to start. Then, adjust accordingly for running on your available gas, (either E0 or E10).FWIW---Oldtommy

 

[Tones]

It shure sounds like a timing issue. How did you check the flywheel key? You can't really tell by just removing the top nut. The only way to really check it is to remove the flywheel. It would be unusual for a belt drive to shear the key though. Are you using a new spark plug? Old gas? Water in the gas?

 

[wag123]

If is has good spark and the flywheel key is good, here are your other possibilities;
A. old gas (won't burn),
B. water in the gas (and water won't burn),
C. low compression... either the intake valve is sticking (due to the use of old gas, the valve stem will be coated with varnish), one (or both) of the valve seats have come loose due to overheating, or you have a burnt valve. It is a waste of time to try and use a compression tester on a small L-head engine.

 

[jeepman3071]

Originally Posted By: Tones
It shure sounds like a timing issue. How did you check the flywheel key? You can't really tell by just removing the top nut. The only way to really check it is to remove the flywheel. It would be unusual for a belt drive to shear the key though. Are you using a new spark plug? Old gas? Water in the gas?


The gas is new. Spark plug is ok. I even swapped one out of my other running mower just to check. I get blue spark when grounding to the block. I checked the flywheel key and it appears to be in its original groove on the crank shaft. One thing that puzzles me is if I play with the mixture screws it will run for a couple seconds more. There weren't any instructions in my carb kit on how to set the mixture screws. The only instructions said to make sure the float was level when the needle valve is closed.

 

[Quest]

http://www.partstree.com/parts/?lc=briggs_and_stratton&mn=190702-0664-99&dn=58520003

It's the choke-a-matic carb still at fault if you ask me.

what was the condition of the fuel bowl section? any greenish corrosion? jets/orifices/passages cleared with a thin wire? blow clear with compressed air?

(*for minor issues, my trick is not to dunk the carb into carb cleaner pail but to scrub it in warm soapy water and dawn and then blow-dry with compressed air. Works every time*)

did you get the full rebuild kit (with all the jets, etc.) or just gasket? did you replace the mixture needle with a new one? I may have to go home to look around to see if I have the adjustment spec. for that type of carb.

While I do not rule out the possibility of other issues at this moment (valve(s) not closing fully, etc.) but granted that the fuel is fresh and you have strong spark (it's a magnetron solid state type ignition), then ruling out timing issue and a seriously plugged up exhaust port (muffler, don't rule that out esp, on severely neglected flathead B&S engines), the engine may still require a bit more attention (check compression for valve sealing, upper cylinder wall scouring and ring issues, etc.)

Q.

 

[TFB1]

Originally Posted By: jeepman3071
The plug is wet so it seems to be getting fuel.


Have you tried another plug(if so I missed that)... Had one that fooled me last year, plug was wet but looked good otherwise, just would not fire under compression... started first pull on another plug...


Originally Posted By: wag123
It is a waste of time to try and use a compression tester on a small L-head engine.

Maybe, but even small engines with compression release should register 35-50psi, without approx 65-90 is the norm... Still cranking "resistance" is a fairly good indicator, last 4Hp Briggs I dragged in required zero effort due to the intake valve seat being loose...

I used to run a old chainsaw that that had 25psi due to a badly scored cylinder, was a booger to get started but ran great at WOT...

 

[jeepman3071]

Well, tried a new plug and that didn't change a thing. Looks like I will be looking closer at the valves tomorrow.

 

[TFB1]

If it has enough compression to push your thumb off the spark plug hole when cranked, it should have enough to start...