Gentlemen, start your mowers!

[FergusonTO35]

Well, another mowing season is upon us and I'm going to push mow much of my lawn for exercise. Mowed for an hour yesterday and wow, I'm really out of shape! I used my low hours Yardmax push mower with B&S 450E engine. This one has the usual surging when encountering heavy grass problem. I took the carb apart and cleaned it out really good, including running a tip cleaner through the jet. I read somewhere that you need to drill out the jet to .020 on these. Anybody ever try this? Otherwise this mower is great, cuts nice and lightweight.

 

[nbbt]

Well, another mowing season is upon us and I'm going to push mow much of my lawn for exercise. Mowed for an hour yesterday and wow, I'm really out of shape! I used my low hours Yardmax push mower with B&S 450E engine. This one has the usual surging when encountering heavy grass problem. I took the carb apart and cleaned it out really good, including running a tip cleaner through the jet. I read somewhere that you need to drill out the jet to .020 on these. Anybody ever try this? Otherwise this mower is great, cuts nice and lightweight.

Needing a bit more fuel is likely only part of the problem. On many EPA goofed up small engines, we needed to slightly enlarge the hole in the throttle plate along with the jetting change to nearly eliminate those surging issues.
Could verify this by looking at the hole size from something pre-1996. IIRC that is when many of these issues started presenting themselves. And then there's the ever changing available fuels that don't make things any better either.

 

[Squareground3691]

 

[LAWN BOY]

Started my custom 19.5hp Murray 42 inch yesterday. Runs like a top! Next warm day I’ll wake up everything else including the neighbors.

 

[nbbt]

View attachment 411612

Could make for a long season if the moistures stays around.
I need to get back to NE sometime sooner than later.
We really enjoyed the fresh seafoods, especially from Boothbays Lobster Warf.
I actually enjoyed sea scallops as much if not more than hardshell lobster.

 

[Squareground3691]

Could make for a long season if the moistures stays around.
I need to get back to NE sometime sooner than later.
We really enjoyed the fresh seafoods, especially from Boothbays Lobster Warf.
I actually enjoyed sea scallops as much if not more than hardshell lobster.

Good stuff,

 

[FergusonTO35]

Needing a bit more fuel is likely only part of the problem. On many EPA goofed up small engines, we needed to slightly enlarge the hole in the throttle plate along with the jetting change to nearly eliminate those surging issues.
Could verify this by looking at the hole size from something pre-1996. IIRC that is when many of these issues started presenting themselves. And then there's the ever changing available fuels that don't make things any better either.

Thanks. This one is right on the edge of running good, the problem presents only when you hit a clump of high grass. It doesn't stall or anything. What is the purpose of the hole in the throttle plate anyway? I've always wondered about that. My other late model small engines run great, including Honda and other B&S engines. I have two mowers with the very late Quantum engines and you can bush hog with those things!

 

[Lnk]

Thanks. This one is right on the edge of running good, the problem presents only when you hit a clump of high grass. It doesn't stall or anything. What is the purpose of the hole in the throttle plate anyway? I've always wondered about that. My other late model small engines run great, including Honda and other B&S engines. I have two mowers with the very late Quantum engines and you can bush hog with those things!

Allows minimum amount of air at all times. 14.7 to 1, remember.

 

[FergusonTO35]

Hmm, never thunkit!

 

[nbbt]

Thanks. This one is right on the edge of running good, the problem presents only when you hit a clump of high grass. It doesn't stall or anything. What is the purpose of the hole in the throttle plate anyway? I've always wondered about that. My other late model small engines run great, including Honda and other B&S engines. I have two mowers with the very late Quantum engines and you can bush hog with those things!

IIRC, when increasing main jet size for more power at throttle, when returning to no-load or low load the plate closes and pulls more fuel also at ide., which is usually not needed. The larger hole reduces the vacuum slightly, which should lean it out at idle, enlarge only if needed.
On some Lawnboys that I increased the main jet, I bumped the hole size by about 0.010" at a time, LB's have responded well with a 0.020" bump in the throttle plate air bleed hole size.

 

[FergusonTO35]

Aahh, makes sense! I ran the mower some more today. The surging isn't gone completely but has greatly improved. It is more subtle and doesn't last as long. I may open up the jet a bit more and experiment with the hole in the throttle plate. I have a spare used carb for it.

 

[Al Smith]

If the weather stays fit I'll fire up the Toro zero turn. in the late morning. Probably take a jump box to get it started .Last years leaves are every where need ground up .That's what you deal with living in the woods. Damned 100 foot oaks drop them measured in tonnage .

 

[Larry B]

Well, another mowing season is upon us and I'm going to push mow much of my lawn for exercise. Mowed for an hour yesterday and wow, I'm really out of shape! I used my low hours Yardmax push mower with B&S 450E engine. This one has the usual surging when encountering heavy grass problem. I took the carb apart and cleaned it out really good, including running a tip cleaner through the jet. I read somewhere that you need to drill out the jet to .020 on these. Anybody ever try this? Otherwise this mower is great, cuts nice and lightweight.

I really dislike these plastic carbs. All kinds of problems. There is a small brass jet in the white plastic piece inside the carb. You can drill it out just a little bit bigger if you have a set of micro drills. If you mess it up the white piece is cheap to replace.

 

[FergusonTO35]

I'm going to put some more hours on mine and maybe open it up a bit more. Just reaming it with a tip cleaner made a big improvement. Another thing I've been thinking about is these might benefit from a pinhole vent in the gas cap. Far as I can tell the tank is not vented in any way.

 

[nbbt]

I'm going to put some more hours on mine and maybe open it up a bit more. Just reaming it with a tip cleaner made a big improvement. Another thing I've been thinking about is these might benefit from a pinhole vent in the gas cap. Far as I can tell the tank is not vented in any way.

Some gas caps have slots in the threads that act as vents.

 

[FergusonTO35]

Didn't know that about the threads on the cap! I went ahead and ordered a .020 drill bit. This bit is so tiny and the jet is just brass, I figure I could just use the bit by hand like a little rat tail file to enlarge the hole.

 

[Larry B]

These are handy when working on mower carbs

21pc Mini HSS Twist Micro-Drill Bits Set Index 61-80 w/Aluminum Hand Drill hobby | eBay

The set includes 20pc HSS twist drill bits in storage plastic case and an aluminum hand drill. 20pc index bit set includes the following sizes #78 (.0160") #68 (.0310"). WARNING: Many food and beverage cans have linings containing bisphenol A (BPA), a chemical known to the State of California to...

www.ebay.com

 

[FergusonTO35]

Thanks, will put that in the cart!

 

[Al Smith]

We used to drill out the jets on those carbs of a John Deere model A's used in pulling contests .I forgot the size .Problem was they blowed black smoke if they weren't under a heavy load. Under a heavy load they'd blow flames a foot higher than the straight stack exhausts .If they were really souped they'd burn a gallon and a half of gasoline on a 300 foot pull .

 

[FergusonTO35]

Mowed some more last night, and I think I'm on the right track. It only surges if you go over a bump like a molehill now, and corrects itself pretty quickly. I didn't use the drill bit yet, just reamed the orifice in the jet a bit. I have another mower with the same style carb that actually stalls so I'll try drilling it.

As an aside, push mowing is great exercise. Our back yard takes about an hour to mow and is kind of steep, I can feel it afterwards.