Briggs 18.5 hp Wont Run

kkjfjns2014

Member
Joined
Mar 20, 2023
Threads
2
Messages
34
you have fuel restriction. check your fuel pump, and make sure when cranking your getting a good fuel supply. If you're getting good fuel supply it's the carb. Many aftermarket carbs are made in China, and they do not have qualoty control. They do not check carbs before they are sold, so a brand new carb can have a manufacture flaw.
The pump is providing plenty of gas as it cranks. I agree, it's probably a Chinese knock off that wasn't built properly.
 

RGSERVICES

Member
Joined
Oct 19, 2022
Threads
0
Messages
10
There is a solenoid shut off on the bottom, but I cut it off because the wire wasn't giving a reliable connection. I did notice it blowing some gas back and found out that means the valves may be out of whack. Do you know what the valve clearances on this engine are?
i should power the solenoid back up, you can do it with a live and earth directly off the battery to test it first if you want too.
 

Zue

Member
Joined
Aug 15, 2022
Threads
0
Messages
17
I set the Briggs valve gaps at .004. / .006 for intake / exhaust. Cutting wires to fuel cutoff solenoid on bottom of carb will do nothing if solenoid is stuck in upward position. Solenoid will still block flow. If you replaced the carb, it should’ve come with a new fuel solenoid. Don’t bother cutting up the new one, just use the old one from the original carburetor and cut it up. The solenoids can cost up to $80 each if you buy them direct from Briggs and Stratton. Of course the Chinese carburetor ones would be much cheaper.
 

kkjfjns2014

Member
Joined
Mar 20, 2023
Threads
2
Messages
34
I set the Briggs valve gaps at .004. / .006 for intake / exhaust. Cutting wires to fuel cutoff solenoid on bottom of carb will do nothing if solenoid is stuck in upward position. Solenoid will still block flow. If you replaced the carb, it should’ve come with a new fuel solenoid. Don’t bother cutting up the new one, just use the old one from the original carburetor and cut it up. The solenoids can cost up to $80 each if you buy them direct from Briggs and Stratton. Of course the Chinese carburetor ones would be much cheaper.
I've posted about 4 times I didn't cut the wires, just the plunger on the end of it. I've been swapping the one I cut around on the carbs I've been using so I don't waste multiple of them.
 

Forest#2

Well-Known Member
Joined
Apr 17, 2022
Threads
0
Messages
463
What I've done to get a test run so as to bypass the fuel tank/fuel pump is to take a 12 to 24 inch fuel hose and connect it directly to the carb input and then tie the fuel line elevated and take a small funnel and fill the hose with fuel and then start the engine. A small engine will run long time with a 5/16 hose full of fuel.
I also have a plastic fuel tank with hose/petcock and filter for subbing if I want to do a run/load test or need a more permanent supply when testing.
 

kkjfjns2014

Member
Joined
Mar 20, 2023
Threads
2
Messages
34
What I've done to get a test run so as to bypass the fuel tank/fuel pump is to take a 12 to 24 inch fuel hose and connect it directly to the carb input and then tie the fuel line elevated and take a small funnel and fill the hose with fuel and then start the engine. A small engine will run long time with a 5/16 hose full of fuel.
I also have a plastic fuel tank with hose/petcock and filter for subbing if I want to do a run/load test or need a more permanent supply when testing.
There is no issue getting fuel to the carb. I've verified this several times. It has something to do with how the carb is feeding it into the engine.
 

Forest#2

Well-Known Member
Joined
Apr 17, 2022
Threads
0
Messages
463
Right: I did notice that.
I was just indicating how to quickly test a small engine fuel supply using a fuel hose if no spare tank was readily available as a test.

Good luck on your Nikki overhaul and keep the LMT carb in mind that I mentioned as a replacement. I keep a eye and ear open for the Walbro LMT carbs so as to use as spare replacements for the Nikki's.

I've seen some of them Nikki clones quite often not operate correctly when new. Really erratic and some cold natured. Some rough at high rpms, others rough at idle, some spit back like valve issues.
 

kkjfjns2014

Member
Joined
Mar 20, 2023
Threads
2
Messages
34
Right: I did notice that.
I was just indicating how to quickly test a small engine fuel supply using a fuel hose if no spare tank was readily available as a test.

Good luck on your Nikki overhaul and keep the LMT carb in mind that I mentioned as a replacement. I keep a eye and ear open for the Walbro LMT carbs so as to use as spare replacements for the Nikki's.

I've seen some of them Nikki clones quite often not operate correctly when new. Really erratic and some cold natured. Some rough at high rpms, others rough at idle, some spit back like valve issues.
Good advice 👍🏻, I'll keep the carb in mind thank you. I just got done cleaning the nikki carb out real good. I'm going to try it out within the next couple of days and see if she'll run.
 

TobyU

Well-Known Member
Joined
Jun 1, 2014
Threads
0
Messages
563
Okay, several things. I understood from the beginning that you cut the plunger tip off and not the wire and someone else misunderstood that. That person did talk about doing that as a poor man's fix and the other text who insist on doing things a certain way of replacing Parts need to not worry about it because it isn't in their shop and anyone that would replace that solenoid that had been cut off when someone brings to your shop is really doing a disservice for the customer and costing them needless money and that's what gives repair shops a bad name and one of the three reasons I actually run a repair shop because I won't do it that old school established way.
The fact is that solenoid has been pushed if not required by the EPA or at least it makes them feel all warm and fuzzy inside and it was originally designed or at least named to prevent the popping sound which some people call a backfire after you turn off the engine but it's not really a backfire. It's the unburnt fuel as the engine spins down which pulls up the vapors in the muffler and then when the rich auction at the outlet of the muffler allows enough in to hit those papers they explode and you hit the pop.
The sad part is what is designed to do... It rarely even does!
Anyone who's worked with a good number of riding mowers over the past 25 years can tell you time and time again how they have had mowers and even owners have had these were that solenoid is functioning absolutely the way it's supposed to but they're more still routinely 4 to 6 times out of 10 pops like that when they shut it off.
It's off and recommended to idle them down for 15 to 20 seconds before turn them off is this sometimes helps but still for 20 years it was the most overpriced part on any riding lawn mower and they took advantage of that being 48 to $60 minimum but luckily they popped in on eBay a few years ago at $6.84 so now they're usually under 11 so it's tolerable but still kind of a waste to replace them since they don't work but less than half the time anyways.
Okay enough of that soapbox ranting of facts but it sounds to me like you're not getting enough gas and not too much. Something probably floated around and clogged up the jet inside the carb.
I don't remember from all the previous posts if it's a walbro or Nikki style but regardless I would take the bowl off and make sure the jet is clear. The Nikki is often put in improperly and put in from the bottom when it's supposed to go in from the top so when you slide the bowl on with the plastic piece inside it pushes the jet and holds it into the proper place. It will still work on the bottom but people often lose them and this will cause extremely rich condition but if you can't get the mower to run with the air filter off and the choke off and especially if you can spray a little bit of car cleaner or gas into the intake carb hole and then get it to run a few seconds it's almost certainly got something clogging up the jet inside.
Even new ones do this with a piece of plastic or metal or whatever manufacturing piece left that will float around and clog the hole.
Always go back to the basics. If it won't start and run leave the choke off and spray some card cleaner in the hole for a couple of seconds and then try it. If you do this three times and you still don't get it to hit it all then and only then take out the spark plug and see if it sucked and while it's out see if it will spark when you spend the engine with it out plugged back into the plug wire and then put your finger in the hole or do a compression check for those of you who just must screw a compression tester into them but that's such a moot point of what the number is.
With their ACR setup it's a joke anyways. All I need to do is stick my finger in the hole and feel it go puff puff puff puff and make sure it doesn't suck on my finger and make sure it's a rhythmic consistent puff puff puff with no double puffs etc and I know exactly that the engine has enough compression to run.
Now, getting back to the previous part though I wish people wouldn't throw Parts at things so quickly. You hardly ever need a new carburetor. You just need your old and cleaned out. Typically the old carburetor on your machine is a better quality and will last longer than I knew when you will purchase today regardless of which brand it is so stick with the old and clean them out.
I think yours is a fuel issue now and not getting enough of it so try some car cleaner in the hall and if it hits and runs pull the bow off of the carb and go from there.
 

TobyU

Well-Known Member
Joined
Jun 1, 2014
Threads
0
Messages
563
Hello all, I have a 2006 briggs and stratton 18.5 HP [31N707] engine that came off a craftsman. We put it on a small ariens zero turn. It worked very well for awhile, then got it where it wouldn't run unless the choke was on. Eventually it quit running all together. After this my dad parked it and it sat for 2 years.

I decided to try and fix it for him this year. There was water in the gas, so I took that tank off and drained it and dried it in the sun for a few days. I put it back on put in fresh gas. I also replaced the carb and all fuel lines and vacuum lines and filters. I put the choke on and started it and it ran for about 10 seconds, I took the choke off and now it's back to not running at all again. Tried tinkering with the air/fuel mix a bit, still no luck. If you feed it gas directly into the carb it will run. It has good spark, everything else seems to be functioning, I have no idea what else to do. I'm about to pull my hair put. Any advice on next steps would be greatly appreciated. Thank you.
Also, on these valves. The 31xxxxand 33xxxxx and most of these Briggs engines set with the Piston one quarter inch past top dead center so going down in the bore at least one quarter inch after top dead center when both valves are closed on the compression stroke, and even better if you want to go an inch or two down because it's irrelevant after that point until you get all the way to bottom dead center....and most of them sat at 004 - - .006 intake and .005 to .007 exhaust.
There are not a whole lot that set at .005 for both except your Kohler courage.
Since these numbers are also close it often works for people so then they just decide that that's the proper spec when it's actually not.
Also, since they wear loose when you pull these valve covers off you typically find them in the at least .010 to .012 range if not looser. The intake is more important than the exhaust because that's where your ACR works off of and it will be hard to crank over and act like it's bouncing back against the rubber band wall if your intake valve is too loose.
The black smoke you mentioned though is NOT indicative of the valves being out of whack. Technically, only being hard to start is indicative of the valves being out of whack. If the thing is running the valves are good enough for all intents and purposes but I would hate to see them too tight but that would only happen if someone adjusts them too tight because they don't wear tight.
Valves being tight is what burns them because they only cool when they're closed.
But other than being hard to start, if it's smoking or low on power or anything else.. it's not the valve adjustment.
 
Top