17.5 HP briggs on a Poulan Riding mower won't start

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  #1  
Old 05-12-12, 08:40 PM
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17.5 HP briggs on a Poulan Riding mower won't start

Having some trouble with my rider mower. I bought it used from a guy and it started up great and ran well. I cut about 3 times with it, then it would cut for about 20 minutes and then just stop, not even run rough but just shut down. I changed out the fuel lines, sprayed the carb, topped off the oil and it cut a few more times with no problems. It is now doing it again, if it sits for 20-30 minutes I can cut again for another 5-10 minutes then it shuts down.
I adjusted the valves and it fired right up, I thought that was the problem, it ran great for about another 10 minutes then shut down and now will not start at all.
I cleaned the carb thoroughly, wire through all the holes, new float gaskets, made sure the needle valve was in good condition. I operated the needle valve with the bowl off and the float was working correctly. The fuel solenoid operates correctly. I put everything back together and it cranks but will not start.
I have a brand new spark plug with great spark.
I checked to make sure I had good flow from the tank, and again checked the needle valve operation.
If I place my hand over the intake with the choke on it will start to fire and I can get it to fire over for about 15 seconds while holding my hand there.
This seems to me like it is running way too lean, so again I checked the needle valve to make sure it wasn't sticking, ran some wire through the jets again and everyting is clean and clear. I am at a loss now, I don't know where to go from here. Can anyone give any suggestions?
It is a Nikki Carburetor, and there doesn't seem to be any adjustments that can be made on it. It seems like I have a carb problem though.
The last time I ran my hand over the intake to get it to fire, I had a real loud backfire after it shut down.
 
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  #2  
Old 05-12-12, 09:01 PM
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have you checked that the fuel cap is vented?
 
  #3  
Old 05-12-12, 09:41 PM
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Agreed, try loosening the gas cap next time it dies.
 
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Old 05-12-12, 09:45 PM
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I will give it a shot. Thanks for the quick response!
 
  #5  
Old 05-12-12, 10:25 PM
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I tried loosing the fuel cap, and I also tried starting it with it off completely. Still no luck. When I first bought the mower the cap wasn't on there and I had to buy a new one.
 
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Old 05-12-12, 10:40 PM
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I checked the breather tub and it is clean and clear, also non of the gaskets or intake are leaking. There are no other obstructions anywhere from the tank down to the cylinder.
 
  #7  
Old 05-13-12, 12:35 PM
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Take the bowl off the carb and let the fuel flow. Note how fast does the fuel run into the carb. I have seen some that the fuel would flow, but not very fast at all, and it was enough that the engine would run for a while, but the fuel supply was a tad less than the fuel used, so after a while, the scales would tip and the engine wouldn't have enough to run. This is usually caused by a collapsed lining inside the fuel line.
 
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Old 05-14-12, 08:40 AM
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Ok, how do I know if it is enough flow?
 
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Old 05-14-12, 09:15 AM
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It should be a constant stream, not a dribble. It should be enough to fill the carb bowl in a few seconds.
 
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Old 05-15-12, 09:50 AM
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Ok it was a constant flow coming out of the carburetor. I took the exhaust off and made sure there wasn't anything clogging it or loose inside.
When I initially took the carb. apart there was a small jet that came out and I wasn't sure where it went back in. The Nikki parts diagrams I found online didn't really show it. I put it on the lower pick up just above where the solenoid closes. Just for grins I removed it and tried to start the engine. It will start and idle now, but dies at anything above idle. I would think this would be a main jet or something. I just can't figure out where it needs to go. I tried attachign a picture of it, but I can't seem to get my camera working. I will keep trying. I also got a very big back fire when I shut down after idling for a few minutes. It seems to have a slightly high idle like it is running a little lean now. Any suggestions?
Thanks again for your help!
 
  #11  
Old 05-15-12, 10:02 AM
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It has a small "110" etched in it, i'm pretty sure it is the main jet. But the diagram is unclear where it goes.
 
  #12  
Old 05-15-12, 10:12 AM
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The jet goes down the long center hole in the white plastic piece that's on the bottom of the carb. Put it in small side first.
 
  #13  
Old 05-15-12, 11:30 AM
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Ok I will probably need a new o-ring because it does not stay in the tube very well. Wonder if this could have been the initial problem?
 
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Old 05-15-12, 06:07 PM
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I don't think I ever saw one that stayed in the tube well, but never had one give me trouble because of it.
 
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Old 05-16-12, 11:46 AM
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Ok I put the jet back in and it stayed in there well enough not to fall out this time. I put it all back together and now it will crank but not start. With the jet out it started but only idled. I'm looking at the valve sequence with the cover off and it looks like the exhaust valve is opening right after the intake valve closes before the compression stroke. I'm going to get into the tech data I have and make sure i'm looking at it right though.
 
  #16  
Old 05-16-12, 01:07 PM
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Not real sure where to go with it from here. How can I tell if the valves are correct?
 
  #17  
Old 05-16-12, 04:05 PM
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If you haven't taken the camshaft out, the valve timing is right.

It ran with no main jet, but not with it. That would tell me something is badly clogged in the carb.
 
  #18  
Old 05-16-12, 09:05 PM
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Yea after I looked at the valves again and spun the engine over by hand it seems like they are correct and they are both about .004". I was starting to think the same thing about the carburetor, but I have had it apart a dozen times and keep cleaning it and rechecking it with wire through the holes. I guess I will get a carb rebuild kit, but im not sure that will really have anything in it that will help. I already installed new float bowl gaskets. And the needle valve seems to be allowing a good steady flow through. I double checked the fuel solenoid today too and it is working fine.
 
  #19  
Old 05-16-12, 10:53 PM
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What about the gaskets between the carb and intake, and between the intake and the engine? Are they intact and sealing?
 
  #20  
Old 05-17-12, 11:07 AM
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Yes they seem to be in good condition and providing a good seal. I went ahead and ordered a carb kit anyways. I will get that in this weekend and see if it makes a difference. That should atleast rule out the carburetor if it doesn't fix the problem.
I will post when I get it installed.
 
  #21  
Old 05-25-12, 11:12 AM
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Ok I got the carb kit in today. There is one gasket in there that has aluminum on once side and gasket material on the other. It has only a portion of the gasket open in the middle. I didn't have anything like this come off of the engine, but it came in the kit so i'm wondering if I need it or not. It seems like the metal side would go against the cylinder because of the heat....?
 
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Old 05-25-12, 06:54 PM
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Leave it out. It's a restrictor plate used on other engines. If yours didn't have it, it doesn't need it and will lower the power if used.
 
  #23  
Old 05-26-12, 08:21 AM
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Ok I left it out and put everything back together and it still won't start. If I spray some carb cleaner down the intake when I try and start it, it will fire over for a few seconds. That STILL seems like it's not getting enough fuel. I don't get it, there is plenty of flow coming from the fuel line into the carburetor, when i take the float bowl off there is plenty of flow coming out, I cleaned every hole in the carburetor numerous times..... I've had the carburetor off and apart probably 10 times now.
 
  #24  
Old 05-26-12, 07:50 PM
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If I wanted to take the flywheel off to check and see if the pin was sheared how do I hold the flywheel when I am loosening the nut off the top?
 
  #25  
Old 05-26-12, 09:11 PM
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You use an impact gun; or a strap wrench to hold the flywheel. I don't think the flywheel key is sheared though, but you can look.
 
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Old 05-26-12, 09:16 PM
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I figure it is one more thing to rule out, I can't afford to pay someone to look at it, and I don't know what else to check. I have to keep trying. It seems like there is quite a big of compression when I hold my hand over the intake while it is cranking, but I will check the breather while I have the flywheel off.
 
  #27  
Old 05-26-12, 09:18 PM
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You feel compression through the intake? There shouldn't be any... just vacuum. Have you re-checked your valve clearances and valve operation?
 
  #28  
Old 05-27-12, 06:09 AM
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Yea, that is what I meant was a vaccum. I didn't mean to say "compression". I double checked the valve clearances, they are both at about .004".
 
  #29  
Old 05-27-12, 10:25 AM
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I pulled the flywheel off and checked the key, it is good and was mating properly. I cleaned all the surfaces and contacts while I was in there, and pulled the breather valve cover to check for obstructions.
I checked the valve adjustment again. I put the engine at 1/4" past TDC on the compression stroke viewed clockwise looking down at the engine and adjusted the intake to .004" and the exhaust to .005".
Put it all back together again and still doing the same as before, cranks strong but will not start, fires over if I spray carb cleaner in the intake.
 
  #30  
Old 05-27-12, 10:28 AM
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Sounds like you still need to do something with that carburetor or the fuel shutoff solenoid isn't working.
 
  #31  
Old 05-27-12, 05:20 PM
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When I pull the solenoid off the carburetor and turn the key I can watch it open and close. Is there any reason it wouldn't work being grounded on the carburetor?
 
  #32  
Old 05-27-12, 07:35 PM
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No, it's working. If it runs when you put fuel into the throat, but not otherwise, then it's the carb. Check the main jet again. How big is the hole in it? I don't know what else to say without being able to look at it myself. You may have to replace the carb. How is the gasket at the top of the float assembly?
 
  #33  
Old 05-28-12, 08:06 AM
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New gasket for the float bowl and the holes in the main jet are clear. Is it common to have to replace a carburetor?
 
  #34  
Old 05-28-12, 09:49 AM
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The main jet is a *110*. I got a new gasket for it when I ordered the carb kit, and it stays in there a lot better now. It is not falling out anymore.
 
  #35  
Old 05-28-12, 10:59 AM
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I don't mean the size stamped on it, but the actual hole in it. I'm wondering if it isn't open as far as it should be. Can you put a paperclip wire through it? It's not common to have to replace a carb, but if you can't find the problem with it, it might be the only option. In some shops, carb replacement is common, but not in mine. When I do replace one, it is usually on a 2-stroke engine.

You mentioned new gasket for the float bowl... you are talking about the large gasket with multiple sealing areas that fits into the grooves in the top of the white plastic piece, right?
 
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Old 05-28-12, 01:07 PM
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I agree on carb replacement, however, it is becoming more sensible on some newer equipment.
IE: Kohler has their name on surely what is a Chinese made engine, (3.5 HP and 4HP) that when you order a "carb kit" you get a replacement carb. Another one is Honda. A needle valve is 22 bux, new carb 18
 
  #37  
Old 05-28-12, 03:01 PM
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Yea the gasket is the one with all the holes on top of the white plastic piece. The hole doesn't seem obstructed, I had a pieced of .041" wire I put through it when I was cleaning the carb.
 
  #38  
Old 06-01-12, 01:10 AM
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I brought the carburetor into a guy I know that works on small engines. He found that I had the float in upside down which changed the way the needle valve went into the seat. We thought for sure this would solve the problem and let more flow through. Still doing the same thing after it was installed, did not fix the probelm. Will only fire over if carb cleaner is sprayed into the intake.
 
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Old 06-01-12, 09:25 AM
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If you had the float in upside down, then what about the needle? Is it clipped into the float?
 
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Old 06-04-12, 12:22 PM
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I didn't have it clipped to the float, but he got that taken care of for me. It is the correct orientation and clipped on the float now and it is still doing the same thing. I think I can get a carburetor for about $55 new. I'm just hesitant to spend the $ because I figured the rebuild kit would have fixed any carburetor problems.
I am going to try and get my friend to come look at it this week and if he can't find anything else wrong I will probably buy a new carburetor and hope for the best.
Thanks again for the advice!
 
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