question for you IC tinker-erers

crueby · May 17, 2014

Okay, this is not a question about a model engine (unless you consider this a 1:1 scale!), but given that there are so many experts here in getting cantankerous gas engines to start, thought you might be able to help with a problem that is keeping me out of the shop recently....

I got a 2-year-old John Deere push mower (Briggs engine) that needs an expertly placed whack with a hammer... (old joke about sign in repair shop: Hammer, $5. Knowing where to whack with it, $100)

This spring its been a pain in the swarf to start - lots and lots and lots of pulls, not a sputter. Checked all the usual stuff, fresh gas, plug is clean and gapped right, all linkages moving properly, carb seems clean, gap on coil pickup is right). Still no luck. Then, turned it on its left side (carb/gas tank up in air) to check to see if something was blocking the blade, all clear.

Then turned it back upright and Bingo - started on next pull. Ran fine.

Okay, odd....

Turned it off, tried to restart, same thing - no luck till tipped on its side.

Head scratch, shrug, went and mowed lawn - worked fine till done, tried to restart - same thing - no luck till tipping it.
:wall:

Asked neighbor about it, he didnt really believe me till I showed him the sequence, got wide-eyed blank look, blink, blink, we both shrugged and walked away.

Talked to guy at local dealership, he was stumped, but not enough to not want big bucks to stand there and scratch his head over it. No reason to do that for something this minor.

Now, must be some engine builders here that ran into same kind of thing on a model at some point. Any of them care to share the secret? Not a big problem since I know how to work around it now, but it really bugs the engineer in me not to have an explanation of the reason!.....:hDe::rant:

End of rant - back to the shop!

hitandmissman · May 17, 2014

Sounds to me like the float in carburater is gummed up and stuck.

Steve J · May 17, 2014

hole in the gas line so it sucks air. once tipped it gets gas, starts and has enough suction to continue running

bobsymack · May 17, 2014

Did you check that the choke is closed when the engine is cold ,if the choke is closed and it will not start ,I would take the bowl of the carb and check that it is getting enough fuel or else you might have a blocked jet.
Regards Vince

crueby · May 17, 2014

Thanks for the ideas. The choke is working right, and carb float and needle are clean and moving fine, though possible a jet is clogged. The air leak idea is plausible have to check for that too. These motors dont have a priming bulb, so if it cant get gas at the low revs of pull starting those two things could be it. Will report back... Thanks!

Spent more time today working on latest project, an 8 planet orrery (not nine since Pluto got laid off by the astronomers a couple years ago). Mostly done making parts, final gear count is 59! Lotsa practise cutting and planting gears....

RonGinger · May 17, 2014

A common hard start problem is a broken or split key between the crankshaft and flywheel. These often have aluminum keys so that they will shear if the blade hits a stump or rock and not twist the crank. The flywheel shifts enough to put the magnets out of timing with the magneto coil. Pop off the flywheel replace the key and all is well again.

Cogsy · Jul 6, 2014

Bit of an old thread but I just found it and had to chime in as I had a similar issue last weekend. On my mower the 'cut off' is just a small button that gets depressed by the throttle plate on the carb when the throttle is shut off. This presumably earths the ignotion or something and it won't spark. My little cut-off button decided to stick down and the mower wouldn't spark, but tipping the mower up dislodged it and it started. Could easily be your issue as well as mine has a Briggs engine too.