OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Mower only starts with manual prime

I get runs when repairs to mowers are easy and I think I'm really good and then a period (like now) when I can't fix anything and it brings me back to reality! I now have this 5 HP Rover with a Briggs engine. It came without a cowl so I can't give the engine number. The problem is, it won't start unless I squirt some fuel into the carburettor, then it will run happily. I have done the dance of "remove carburettor, disassemble, clean (compressed air, carb cleaner and carb files), re-assemble many times. It's still the same (cry). There is a bulb fitted to the air cleaner assembly but I don't think it does much. Is there something specific in the carburettor that I can address that will fix this? Obviously there's something wrong with the choke section but my knowledge of carburettors is pretty woeful.



The last photo shows a shot of my "squirter" which I got from Supercheap for a few dollars. I find it really good for this job especially for the OHV mowers where you need something to reach into the spark plug hole for testing.

The Primer bulb does the same as you are "manually putting fuel in carby" It's supposed to put fuel in to carby when pressed a couple of times.
May need a new primer bulb?

if that is the gasket , or whats left of it theres your problem , they push air not fuel into the float bowl so need to be sealed / gasket in good nick , i have made them before and worked well , depends on how far away your parts shop is . new gasket and it should work , or as super d said , could be primer bulb but while its off new gasket and see how you go .

hope it works out for you . simple fix sometimes hard to find

It doesn't squirt fuel like other primer bulbs do on other models. There's no connection to the fuel line or carb. I think I read where it works on air pressure some how but can't remember exactly. You may be right but the bulb seems to be in good condition.

its what i meant , they put pressure in the float bowl push up fuel but need to seal first soo , a new carb to air cleaner gasket should fix your problem or a good place to start

If you've cleaned the carby out and sometimes it takes multiple attempts to get it to work properly, (I'm looking at an ultrasonic cleaner to do this)then that perished gasket will be the problem. You can make those gaskets out of cereal cardboard but a replacement gasket should not be too expensive. If you can't get the spare part easily a homemade cardboard one will at least be better than what you've got now.

You guys may be on to something because that gasket is in a bad state with part of it missing. I attempted a repair with some aviation gasket goo but not a good one. I have some gasket paper here somewhere and I'll give it a go. I didn't realise it could make the difference. I have also been thinking about an ultrasonic cleaner. I have been thinking about this one as it has a 6L container and I can do other stuff with it Ultrasonic Cleaner

Sorry vcomm I posted at the same time as you did and so missed your answer.

Yep, these Briggs with the Walbro LMS carby use a 'dry primer'.

This primer pumps air into the float bowl vent, via a gallery in the air cleaner base, a hole in the gasket, and another gallery in the carby flange. The air pressure forces fuel through the main jet, and thence into the venturi.

So for it to work properly, there has to be a very good seal between the carby flange and air cleaner base, and around the hole in the gasket between the two. This is the small hole just below the left hand bolt hole in the carby flange.

That gasket shown in the pic won't be up to the job any more. While gasket paper is easy enough to get from auto parts shops, as a one-off it would be cheaper to just buy a genuine gasket, as it's a very fiddly one to cut.

These primers can also leak air if the sealing surface of the air cleaner base isn't flat any more, so be careful the bolts are not over-tightened.

Thanks Gadge. Now I know where the air is forced in.

I tried making a gasket ( I am the son of Sir Titus Canbee) but it didn't work. Went down to the shop and bought one ($7.50-a bit steep I thought). Put it on and it started first pull! Great. However, now it isn't getting enough air as it revs and chugs very slowly but if I unscrew the air filter a little bit it roars to life. Air filter looks newish. Oh well, one problem solved another one to overcome.

Edit: solved. I'd left a rag in the snorkel. Better close this thread or I'll go on and on with every little nut and bolt.

Sorry to Hi-jack this thread but I do have the same issue but on a auto prime(?? no manual primer)3.5hp 12 series briggs.Could I have the same issue of leaking gaskets around the air intake?I have cleaned the carby, head and valves but reused a head gasket from another 12 series that looked ok ,just a bit flater than a newy.

There is a bit of an art to making these gaskets, Vcomm is an expert at making them.

wotwozthat, if you have the same issue it may well be the same cure. Is that the carb with the hard black (non-pressable button)? I've had issues with them where the choke won't come on. I had to take off the airfilter and move the throttle lever and observe if the choke butterfly closes. When it didn't I had to move the cable along until it did.

adjust the cable so it just shuts down , might not be getting choke . look in the air intake and see its working when really full throttle . older ones didnt have a primer just a choke .
if its the case , adjust the cable , trim the outer if you need to . its a quatum i take it ?

You beat me to it. My edit was again at the same time

This one has nothing there sparker,I just did one that had the plastic pretend primer and it went great.I am in the same boat as you "Is there nothing I cant fix!" then SLAP,back to reality.I'll have a go at the things that are mentioned most likley tomorrow and see how it goes. Like I said sorry for Hi-jacking but I didnt see the point in starting a new thread when I had a similar problem. Oh and yep it is a Quantum

Now that mine is fixed I am back to being awesome again. Good luck with yours.

they either have a primer or a choke , some have a temperature thingy from the muffler but still have a primer , i think only the newer OHC has an auto choke but dont quote me on that bit .
and good cond' or new gaskets are always the way to go gents , no point messing about if it looks bad ? it IS so make a new one or go get one

Yep well now dont I feel like a dill.It wasnt getting any choke(oops),ajusted cable and started staight away.Thanks fellas. Back to the corner I go

pointy cap time ? dont ya hate it when you did all that and then ooooooooooooh .
good it worked out though