Engine trouble

[5quarter]

 Guys...I got and older Briggs and Stratton (craftsman) 18HP V twin Thats giving me some real trouble. Saw has been intermittently hard to start lately. in the morning it would start right up on full choke, but then after stutting it off to turn the log or something,it might or might not restart,depending on the amount of time elapsed. this has been going on about a week. I pulled the plugs and they were pretty dirty (carbon build), so I cleaned them up, put them back in and all was good for about 1/2 a day. well today the saw saw started bogging down in a 12 inch cut, backfiring and wanting to quit, which it did a couple times. put in new plugs this afternoon and all was good for about 2 cuts. same thing. any Idea what could cause this?

Thanks in advance.

Chet 

[Bill Gaiche]

5quarter, Had kinda the same thing with my 14hp. Removed carb and cleaned very good and it ran well for a few days then same thing. It was flooding some. Well the real problem was the carb was getting dirty inside the bowl but the dirt/sawdust was getting in through a little vent tube at the top of the carb. I attched a short piece of tubing with a small fuel filter. That was in the spring and I havent had a hicup from the engine since. bg

[Coon]

Those Briggs engines are notorious for hard starting when the valves need adjusting.  Find out the specs and adjust them.  Also as stated it sounds like the carb may need a cleaning too.  Good luck and let us know what works to get it running smooth. 

[Al_Smith]

It's not just valves .Those things or some of them use a pulse jet carb which can give you fits .

It's got a diaphragm fuel pump which works like a chainsaw carb in conjuction with a float carb .The diaphragm and check valves in the fuel pump section can get stiff and starve the carb for gas which will cause that back fire condition from running lean .

[5quarter]

Thanks guys...keep it coming. Here's some more info: I ran the engine at about 30% and the rpms cycle up and down at roughly 5 sec intervals. it is slow to throttle up. I think you're on the right track Al with the fuel being starved somewhere between the tank and the plugs. it idles smooth for the first couple minutes until it comes up to temp. Should I try shooting in some carb cleaner? is the fuel pump the the small, metal rectangular uniton the side of the block? This engine has both a bowl filter and an in line paper filter.

Thanks,

Chet 

[Peder McElroy]

I had the same trouble with my briggs 18 hp on my Lucas and it turned out to be a clogged gas cap vent. It would only run on choke after I ran it for a while, someone told me to check the gas cap and it has worked fine sence.
Peder

[Al_Smith]

The rebuilt kits for those carbs are not that costly and most likely all it needs is the fuel pump diaphragm portion .

If you get the model number from the engine Briggs has a very good web site with parts lists and trouble shooting proceedures .Fact if I'm not mistaken you can even order parts on line if you choose which may or may not be priced according to the local dealer which can vary quite a bit .In addtion there are many online suppliers that carry the parts needed ,Google it .

[Al_Smith]

Yeah  .On the one I have it's on the front of the carb which is an 18 HP opposed L head engine .Two lines ,one fuel from the tank the other impulse from the engine .Don't get them crossed up else it never will work .

I've had two of these things give me fits ,one on that mower and one on a leaf vac .Cleaned them out ,all was fine for a short .Vac is fine I'm going to rebuild the mower , tired of fooling with it .

If you take it  apart be careful as it has a spring behind the diapragm which could end up any where and I think a couple more assundry little  pieces that like to go in orbit .

[sawguy21]

Definitely sounds like a fuel related problem. First of all check the condition of the fuel and vacuum lines. If they are old and hardened replace them, you may have an air leak on the suction side of the pump. How many hours since the fuel filter was replaced? You are using one aren't you? ;) Any scale, crud, or water in your fuel supply?
Next is the fuel pump. With the engine running, pull the line off the carb and aim it into a can, are you getting a steady stream? NO SMOKING during this exercise. Now the carb. First of all spraying carb cleaner down the throat won't help anything. Disassemble the carb and lay everything in order on a clean white cloth. Clean the jets and make sure you do not reverse them upon reassembly, they are not identical. The fuel transfer tubes need to be spotlessly clean. Reassemble preferably with a new kit and you should be good to go. New plugs wouldn't hurt.

[5quarter]

Guys...thanks for your help with this. This morning before leaving for inlaws I went to the mill and examined the fuel lines and come in and out of the pump. The area was clogged with sawdust. I pinched some of it off and sure enough, smells like gas. the lines are old and do need replaced. do you think its sucking air and starving the carb? The higher the load on the engine, the worse it runs. could this be the cause of the trouble?

   I've never rebuilt a carb before, but surely it can't be too hard. :P  Sawguy...cleaned the tank and bowl filter a couple months ago. The in line filter has been awhile. Just installed brand new plugs.  great tips. Al...you real seem to know your way around these engines. if it comes to rebuilding the carb, I may have to lean on you for some guidance. If you haven't noticed, engine repair is where my ignorance really shines :D

   Peder...never thought check that. will do that tomorrow.

   I've got a monster tree to pick up tomorrow so I won't get to the saw til afternoon or later. I'll get to work on it and let you guys know what happens.

Thanks.

Chet

[5quarter]

Ok...Replaced all the fuel lines and installed new fuel filter. ensured gas cap was venting. No go. It idles smooth and I ran it at 1/2 throttle for about 10 min. seemed fine tried to make a cut and 3' in it bogged down, sputtered, backfired and shut down like it was out of gas. wouldn't restart until it was cooled down. The fuel pump either works or it doesn't, right? not one of those things that slowly goes bad. Should I go straight for the Carb now? Have never had a problem that shut me down for this long...and at the worst possible time too! >:(

[gandrimp]

Make sure you have a good supply of fuel getting to the fuel pump. Pull the fuel line from the tank to the pump and let it run into a clean bucket, if the flow slows to a trickle you have a blockage in the tank, filter, hose.

[TimGA]

5Quarter, I used to work on small engines years ago, so basics are the same.You said you ran it at 1/2 throttle for 10 min no load with no problem, but after a few minutes under load you get backfire and quits, I am not saying it is not fuel related on the high side. But you may have a sticking exhaust valve, engine heats up under load carbon on valve and guide stick together making exhaust valve stick open, backfire and quits. I am puzzled though being a 2 cyl why it would not run on the other cyl.  If you can take a compression test cold, run it again and take a compression test as soon as it quits on each cyl should have around 90 plus lbs depending on comp release there should not be much difference between the two. If no compression or very little I would investigate this farther. Like I said been out of it for a while but you still need  (intake) fuel and air (compression) of fuel and air (power)ignition of compressed fuel and air (exhaust) of ignited compressed fuel air mixture. Not sure this is your problem hope it is somthing simpler just being overlooked. Tim

[Chuck White]

Chet; I was having a problem similar to yours just before I got done sawing for the year!

Question: What kind of connector do you have, to hook the fuel line to the fuel tank?
Mine is a quick-disconnect like used on outboard motors.
When mine started acting up, it drove me nuts then the last thing I checked was that quick-disconnect and it was suspected as the culprit.
I took the fitting off of the hose and just stuck the hose down into the gasoline and shoved a rag in the fuel tank opening to keep dirt out and the hose in.
Ran like a top!
The rubber seal inside the quick-disconnect wasn't sealing tight enough and it let air in!

This might not be your problem, but then it might!

[5quarter]

Some new info...I was buttoning things down at the mill today as we were having some pretty high winds and noticed that all three lines had fuel in them. fuel intake from tank to pump and from pump to carb but the return line was 1/2 full of fuel too. I can now see this with new lines installed. I didn't think that should have any fuel in it. my neighbor saw this and said the pump is mot working right something to do with the diaphram...Does this sound right? I have been searching for a replacement pump online without success. NAPA doesn't carry it and the small engine places around here double the cost of all their parts, so I'm hoping to source it somewhere myself.Here is the info on the pump:

Walbro. Corp
Mod. 3028
0107

It looks similar to this pump:
Mikuni Type Single Fuel Pump
Part #: 07-425
http://www.mfgsupply.com/catalogsearch/result/?q=fuel+pump

Thank you for all the gretat help so far!

Chuck...from the tank I have a shut off valve, followed by a glass bowl sediment filter and then a line to the pump, I have steady flow from the tank to the pump, and no leaking fuel at the bowl or tank.
Tim...boy, I hope you're wrong. If that's the case, I might as well lock it all up for the winter. I could not reliably do the work myself, but my neighbor would love to do it for the cost of parts. trouble is, it would be a winter project for him and I'll probabl;y need the saw sometime sooner. ;)

[houtwurm]

 8)   go electric     8)

[ladylake]

 
Dont forget to check for spark after it's hot. a bad coil will run for a while and quit.   Steve

[Al_Smith]

That's a fact .Briggs engines use a sold state self advancing coil and on occasion they will go bad .They either will not work  or they get stuck on full advance  which makes them nearly impossible to roll over .A new coil for a twin is in the 50 dollar range .

[KnotBB]

If it has a float bowl check it for water.  Same for the gas tank

[sawguy21]

You are right the line from the pump to the crank case should not have fuel in it. That means the pump diaphragm is leaking. Briggs 808656 pump won't break the bank.

[millwright]

I tend to agree with sawguy, and that might explain the fouled plugs, this is normally a sign of too rich of a mixture.

[Gary_C]

You need new plugs, not cleaned ones.

I have gone thru this problem every fall with an older gas tractor loader. As soon at the gas stations change to their fall grade of gas, that tractor fouls the plugs. The first year it happened I went thru all the stuff you are doing and more. Put in a new set of plugs and it ran perfect.

Now every fall I make sure I have a new set of plugs on hand and as soon as it starts running rough and lacks power, I change the plugs. Then it runs like a new engine. And I have tried cleaning the old plugs too, and it does not help.

Just put in new plugs and see what happens.  :

[Left Coast Chris]

Sounds like the fuel pump diaphragm.  Just in case though, you also mentioned that there was a sediment bowl in the line.   Be very sure to remove and dump the bowl.  Even a speck can cause fuel starvation.

[5quarter]

Guys...you don't know how much I appreciate your help. How critical is it that I get the OEM fuel pump for this motor? It doesn't regulate fuel flow, just pressurizes the fuel intake line, right? I've found several pumps that are supposed to replace the walbro 3028, ranging in price from $20- $51. Is the #520159 stens pump made in America? I'd prefer to buy USA over any import. I'm going to get something tomorrow one way or the other. Keep you fingers crossed.

   Hout worm...Not practical where I'm at....but at least I wouldn't have to worry about the fuel system! :D

  Gary...I just installed new plugs last wednesday. I try to change the plugs in all my stuff every winter. I was hoping that the trouble was that simple, but since this is me, the solution cannot be simple >:( ;)

   KnotBB..I just recently drained and cleaned my tank and float (about 3 weeks ago or so). I was thinking of replacing the float with a second in line paper filter. Good idea or would it just clog up too fast?

   Al...at the risk of sounding stupid in front of god and country, where on this motor is the coil and what exactly does it do??

Thanks again all!

Chet

[ladylake]

Also if you leaking gas into the oil change your oil.    Steve

[5quarter]

Happy days! I'm up and running! 8) 8) Here is the story for any interested parties.

   I called Briggs this morning to get some guidance and a parts breakdown of this engine. it turns out that this motor originally had an integrated fuel pump, or what the parts manual calls a carburater pump. Years before I got this engine, the pump had failed and rather than rebuild it, the owner had bypassed the original pump entirely and installed an external vacuum pump. The briggs tech  said that pump failure was common on this particular motor, but that officially he could only recommend rebuilding the original. So I went out looking for a vacuum pump comparable to to the old one.  Turns out that lots of places can order one, but nobody, and I mean nobody, had one in stock. So I went to the boneyard.

   A friend of mines dad own a small engine place. His dad wouldn't let me go through the bulk of the yard, but said I could go through a pile of blown engines by the side of the building. in 5 minutes I had my pump. 5 dollars later, I was on my way back to the mill. got connected and ran it to see if that fixed the trouble. bingo!  It ran smooth under load and at idle, and so I finished cutting the walnut on the bunks and shut it down. restarted easy.  I still have to make a mount for the new pump and recut the new fuel lines, but after worrying for several days that it was something worse, the rest seems like nothing. With some luck, I might be able to finish all the sawing work before the snow flies.

   Many thanks to everyone for your excellent advice.

Back to work.

[TimGA]

Super ! Glad to hear you are up and running. Thanks for sharing your fix. Sorry to scare you with valve issue, most times turns out to be simpler like you found.  Tim

[Chuck White]

Glad to hear you have your problem taken care of Tim.

Sometimes it doesn't take much to cause a string of headaches.

[Magicman]

   And we all learned a bit from your experience.   ;)