any lawnmower tinkers - briggs issue

[steveo3002]

i bought a spares n repair lawn mower a few weeks ago it has the briggs 375 engine, been cleaning it up etc

its always started first pull regardless of how long its stood , starts with no smoke but once going theres a small mis /putt every 10 secs or so

any ideas what it might be ? its usuable but not mint , or am just being fussy

thinking rich or a valve problem

 

[mechman]

Diaphragm. About £2 each done a few. cheapest easiest option.

 

[angellonewolf]

try above but got the same with mine i changed every thing carb clean, spark plug,diaphragm even keyway part shearded cheaked but mine was fine (and these fixes normaly fixes it)mine still does the same i just got mine down to the vales need ajustment and i dont know how to do this so left it as i got a honda engine sat as a spare when it goes unuseable and will do the swap over i realy want the honda engine on the mower but cant do the change over untill it needs it as its working now

ps all the changes did make a differance it pops just every so often now the spark plug made the big differance

 

[mechman]

The ones I repaired, you have to file the top of the valve stem to achieve the required clearance as there is no adjustment on them.

 

[angellonewolf]

^^^^^^^ where do you file and how much ?

 

[mechman]

You'll have to file the top of the valve stems I think they need 6 thou clearance, if there isn't any clearance it probably means the valve seats or valves have worn a bit. best to recut seats etc, It's a bit time consuming but it does the job. I think one or two guys on here have done same job, same probs etc,

 

[Scruffywelder]

Yep, they tend to do that when the valves are getting a bit worn.

Head off, valves out, recut seats, lap valves back in, file the end of the stem down to get clearance (go a wee bit loose as they'll close up a bit after it's run), reassemble...

Only worth doing if it's your own machine and you've nowt better to do.

Reminds me I have to service the mower at some point

 

[angellonewolf]

^^^^when you say recut seats just using a lapping compound and the sucker on a stick like doing the old engines of years ago ?

or does it need removing and mechining ?

 

[Scruffywelder]

Total overkill but I used dads old Black and Decker vibrocentric seat grinder to get a nice clean chamfer on the valve seat.

Like this:

Have to be a bit careful with the little engines as you can whip too much off if you're heavy handed.

He had (has?) a Black and Decker valve refacing machine too but it was more economical to just stick a pair of new valves in if necessary. It had the facility to grind the ends of the valve stems down but it was usually less bother just to file them.

Pogo stick and lapping paste to get a good seal after that...

 

[steveo3002]

if you look on youtube ...lawnmower valve job /briggs valve job theres several videos showing the repairs

 

[angellonewolf]

sounds like if i not got the tools to do it better of buying a good working one with a duff deak

 

[mechman]

Yep, they tend to do that when the valves are getting a bit worn.

Head off, valves out, recut seats, lap valves back in, file the end of the stem down to get clearance (go a wee bit loose as they'll close up a bit after it's run), reassemble...

Only worth doing if it's your own machine and you've nowt better to do.

Reminds me I have to service the mower at some point

Correct

 

[steveo3002]

right got the carb off and yes the diaphram is all floppy and theres bits in the carb so hopefully that will improve matters

next problem..seller mentioned recoil problems , seems the ratchet pawl? is worn both on the steel and plastic , any ideas on bodging that up ? its worn enough that the ball bearings jam and stop it it returning ...cant see any on ebay , i thought maybe try and build it up with weld and some new bearings...the actual cord and spring work good off the motor

 

[mechman]

New diaphragm has to go in the right way up as it can go in upside down, if its the same as previous ones it's made of two different thickness materials, not sure myself now. These Briggs engines are renowned for their healthy appetite of diaphragms.

 

[Robotstar5]

I've found Briggsbits good for spares.

 

[steveo3002]

cheers...seems its called a starter clutch , finding a few bits now