OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines B&S 550ex won't rev up

A pretty new mower. I said it won't be much........
New plug , got it started with the drill. but it didn't rev and dribbled a bit of fuel out of the carb hole.
Checked coil and flywheel,, sanded a bit and set it. Good spark.
New type of carb haven't taken them apart.
It was missing o ring on carb/ intake.. put one in . cleaned carb, took float out, reset it. all looks good..
Started it with drill, and it started ok, a bit of revs, enough........ mowed a bit of my front lawn.....
And it was revving about 75% I guess for a 140cc engine. did the job.,

Then I was fiddling with the throttle butterfly and , something went wrong and now it doesn't rev.......
I think it is something to do with throttle butterfly
Someone on the net had same problem, but no answers........ given
Doesn't rev and spits fuel out of carb, so it's running way too rich.......
Had the carb off four times so it's a user friendly engine.....
09 P702 0122 H1
DOM 10 06 2017

I'd like one of my own.......... maybe later on when they appear on footpaths.......

Got another job on , have to put a harmonic ballancer in my EL falcon................tomorrow if I want to go anywhere other than on my bike....
cheers
speedy

Hi Speedy
I am not going to be much help, but I would say your problem is something to do with the ready start auto choke system.

As far as I know, the 550ex has this feature; which is a bimetallic spring that opens the choke as the exhaust heats it up
I can't say I have done any of these carbs (except on a masport that had been tipped over and filled the bowl with oil).

Others like AVB are probably significantly more adept with this carby and the issues it has.

This bloke on youtube tends to be really good with precise info. This is how he says to clean them.

I have been saying the same thing about these mowers - picking these up at tips and off the curb in 5-10 years will be great haha.

Best of luck with the EL.

Format your model number as 09P702-0122-H1 for IPL look-up

First here the governed max speeds depending on the color of governor spring. Check with tach, guessing will not cut it. These governor depends on max blade tip speeds. Here small diameter bar blades runs at slower speed to meet safety requirements,

• Blue 2600-2700
• Purple 2800-3200
• Orange 3200-3600
• Yellow 3600-4000

This covers the nozzle assembly in the plastic carburetor.
Nozzle assy service bulletin

Of all things don''t over tighten the fuel bowl retaining screws as they can strip easily. Other than that these are very simple carburetors and are very simply to clean.

But as Tyler said I also don't a whole lot experience on these either as the mowers with these are so cheap most users will not even bring them to the shop. Afraid of a large repair bill.

Thanks AVB.
This has blue spring so revs are OK.
Also older carb part with visable ball, but I will take it apart and clean it.
The autochoke works really well.
speedy

Hi Speedy, can't help much, have only seen one and just ended up doing a dodgey job to get it running for $20, didn't come back so I guess it must have worked. Had a funny one a few days ago with one of these on ebay with the seller claiming it was an Aussie made Victa. I told him I didn't want to burst his bubble because it wasn't made in Aus but made in China. He sent me 2 abusive emails, I replied I was just giving him some advice but I then found the add had been removed and at the $400 price he had on it there was no way it would have sold

Entire thing made by bowl of rice labour or only engine? Looks like an interesting B&S engine. I'm sure it's satisfactory to use when running right. It can be Powertorqued (ie: corrected) in future.

MF, those bases have been made in China for umpteen years, it is the standard as we know and call it a PT base

Steel bases I can live with being made in sweet and sour country, but a part of me would die inside if any thumb latch bases or catchers were made there UNLESS they perfected catchers that rarely crack. That part of me would revive real fast.
Actually, I wish China would churn out reproduction 70s thumb latch catchers. Disregard my earlier statement!!

Nostalgia is dead and buried, nobody cares and if you have the slightest of looks at a thumb latch catcher you can see by the design, the volume of plastic and the thumb latch mechanism it all makes it cost prohibitive. They were all, including the base from a period where people expected a mower to last them 25+ years

Look at a VC 160 flap and catcher set up. NASA would be boggled at such a system for a grass cutting implement!

Such a complicated design to only achieve exactly what the later designed catcher does, just catch the clippings

Its an American made engine, but they put out a modification of carb, at $25 ....
I even see Chinese carbs for $38................... might be the answer, but as it ran good..... why can't it do it again.
I cleaned out module , blew air all over and it just started ,won't rev and spits fuel out out carb.......

As for catchers... I mowed lawns for 7 yeas using them, now I don't use them, just blow the clipping out the back, healthy for the lawn.... and my back...........
cheers
speedy

Speedy, anything you can do with the float level, the fact it is spitting fuel out could be too much fuel getting in. I guess there is no fuel tap on it so you could run it down on fuel to see if the revs improve as the fuel level in the bowl lowers?. Run it off a fuel bottle and try the same method
A pretty new mower. I said it won't be much........, so speedy is this the same problem it had to start with, obviously somebody has been in here before because the "O" ring was missing, I can't understand how it ran when you first tried it because it shouldn't have, would have been sucking so much air

Hi Speedy, replace the plug, with a known working one R12YC, it think, and check the valve clearances

Ok as the machine is 9 mths old , but no warrenty as it was sold....so 2nd hand.
I knew the valves were good as it ran well.
I cleaned the carb as I thought a few times , sick of it......

I mounted a mystery carb I had in the box.... it fitted in well, started good , mowed a bit of front lawn. Roughly set up throttle, but got slow revs and heaps of revs........even connected a breather to carb.
Then I tooks kids to library on school hols, sat if front of computer and googled 550ex carb problem.......
Bingo..... it was on Hanks Garage, the correct way to clean and disassemble the new BS carb and jets and reinstall....


Too late today, but i feel beer........
no I mean better, that was a funny typo......
cheers
speedy

I surprised the Briggs didn't have an heart attack when it seen that Tecumseh Vector carburetor coming, which the way appears to be on backwards.

Speedy, I give you credit for trying that, I don't think I would have looked that far sideways. Hot did you mount it? I thought they were still the same old "O" ring mount to the manifold, at least the one I saw with the new plastic carby was.

AVB you are right, it is on backwards, how could it operate like that, the crank vent running in on the neg pressure side of the butterfly means it is sucking in air/crank gases instead of balanced air/fuel mix, no way should it run

Norm, There is a pipe sticking out and the carb fitted nicely, backwards. It wouldn't fit the other way . Throttle linkage is a bit bodgie.
It would rev till it exploded I think...........
I'd have to put it on the right way round if I was going to settle on that cheap solution, but it shouldn't be that way.

But I took the black plastic B&S carb apart and took the white jets area apart and cleaned them with a reemer , carb cleaner and air...... put all together .
It started easily with my drill of course, but would not rev.........
The owner has spent $200 so far from a mower shop in town, but they said the mower was worn out and rubbish. It's 9 months old.

A mate wants the same mower fixed , as he saw me working on it. He likewise has spent $200 from same shop getting his mower fixed, but it only a mow or two, then doesn't rev.

This is B&S new plastic carb, probably out 2016..... there is going to be a lot more......problems
I'll do some more youtubing and reading.
speedy

Speedy, the pipe sticking out of the carb is for the crank vent but that has to be on the filter side of the throttle butterfly. $200 at the shop on a mower 9 months old, they should have chased a 2 stroke. I just pulled out a probably 60 year old Mayfair from under the house and it probably has another 60 years of service left in it. People still keep buying Briggs so I guess they get what they deserve