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Poulan Pro rough running/ back firing at load/high rpm

Posted by central50 none (My Page) on
Sun, Apr 13, 14 at 13:15

Hello,

I have a Poulan Pro HD1842 with an 18 OHV B&S motor.

Motor information:

Family 5BSXS.5012VP 276016

I have been running into the issue where when I would start the tractor at low idle it would normally be fine - once I increase the throttle about half way the engine would die down and start to backfire and want to die out.

If I try to engage the deck the same thing would happen - also if I use speed 5 and up on the tranny same issue.

I changed the plug already today - 45 minutes of running checked the plug and have black build up on it already.

Thanks!

This post was edited by central50 on Sun, Apr 13, 14 at 13:24


Follow-Up Postings:

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RE: Poulan Pro rough running/ back firing at load/high rpm

Has the tractor been sitting for an extended time allowing the fuel to go bad?
Fuel filter changed?

The engine # you gave is an emissions#.
Likely it's a 31xxxx- xxxx-xx
Model & Type, such as 31H777-0202-E1


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RE: Poulan Pro rough running/ back firing at load/high rpm

Hello,

Found this:

3d707 0458e1

Fuel filter has not been changed - ran through new fuel as was not sure how long this tractor was sitting after picking it up.

Thanks!


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RE: Poulan Pro rough running/ back firing at load/high rpm

Carb is probably "gunked up".
I'd try a strong dose of fuel injector/carb cleaner in the gas.
You might get lucky that it'll clean out the passages in the carb.
The fact it runs at all at higher speed indicates they aren't totally blocked.
Simpler than disassembling the carb to give a thorough cleaning, unless you enjoy doing that.


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RE: Poulan Pro rough running/ back firing at load/high rpm

Well,

Got the motor back together. While at it I changed the oil and fuel filter as well.

With the carb cleaned, still ran into the same issue. We are noticing when we push the motor with higher RPM and she starts to die out she is back firing as well. We pulled the plug to do a compression test and we do have compression, but we noticed on a new plug it was black and looks like it had unburnt fuel on it.

We are starting to think this is not a fuel problem and possibly something to do with the ignition - I ran a ohm meter on the coil and was registering between 4-5, and does produce volts when moving the magnet on the flywheel to the coil.

Any other tests that you recommend we should do on the coil, if this is the case?

Thanks!


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RE: Poulan Pro rough running/ back firing at load/high rpm

before you start chasing ignition issues, first try these items:
1) with engine OFF and air cleaner removed, cycle throttle control thru from idle to full throttle. Observe butterfly plate movement in carb throat to make sure that choke plate is NOT being partially engaged. (Such will cause engine to get an over-rich fuel mixture and run rough).

Leave carb air filter off and operate engine thru full RPM range. IF engine performs OK, change out air filter.


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RE: Poulan Pro rough running/ back firing at load/high rpm

I have watched the plate and only see it starting to block the carb throat about 80 to 85 percent of throttle. Not to sure on normal operation on this carb so please let me know if that is not correct.

I have ran the motor without the air cleaner - same issues.

Thanks


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RE: Poulan Pro rough running/ back firing at load/high rpm

There are 2 "butterflies" in the carb throat.
The topmost plate is the choke and that is the one rcbe refers to about possibly partially applying and smothering intake air.
If this plate is in any position except straight up and down when you are running the engine wide open, there is a problem in the choke linkage. The choke plate should just barely close completely when the choke is applied for a cold start, and should move to straight up and down (fully off) when the choke is deactivated.

The lower butterfly plate deeper down is the throttle plate.
Its position is determined by the governor action depending on how much it needs to be opened in order to maintain engine RPM under various load conditions and the RPM setting selected.

So now, is the choke plate partly closed or not, when the engine is running?

This post was edited by mownie on Sat, Apr 19, 14 at 20:39


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RE: Poulan Pro rough running/ back firing at load/high rpm

you may have one of those godforsaken combination choke-throttle control setups on that machine that is either mis-adjusted or being mis-used....
Bottom line, that top butterfly plate that Mownie describes should NOT be in any position but straight up/down while the engine is is operating at normal temperatures at any RPM. It should only be rotated from vertical when the engine needs to be choked in order to initially start when cold.


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RE: Poulan Pro rough running/ back firing at load/high rpm

Gotcha,

When the engine is running, the choke plate is straight up and down when running - unless I activate choke.


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RE: Poulan Pro rough running/ back firing at load/high rpm

With all the other tests, just confirm - under normal (low/high) throttle, the choke plate is not engaged.

The motor will start running rough towards 80-85% percent throttle - backing firing and getting ready to die out unless I drop throttle.

I am beginning to think that I am dumping more gas then plug can burn - or at least the coil/wire can provide.


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RE: Poulan Pro rough running/ back firing at load/high rpm

Look closely at the exhaust stream when it is cutting out.
Can you see any BLACK smoke or black vapor in the exhaust stream?
If that is yes, then there is a serious overfuel condition present.
Overfueling (rich mix) generally will be due to a faulty carburetor in this series engine (31D700) as the main jets are fixed, non adjustable components.
Overfuel or rich condition typically results from a clogged air cleaner (too little air) but you say it does the same with or without the air cleaner in place.
I would not start replacing ignition parts (magneto) without using a spark tester to determine if it is weak.
The magnetos in these engines are pretty reliable.
Some of the carbs are not so reliable.
If this carb has some plastic internal parts, it is probably time for a new carb.
Your engine could have a Walbro or a Nikki brand carb on it.


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RE: Poulan Pro rough running/ back firing at load/high rpm

I do notice black smoke when it is running rough. When we pulled the plug it looked like we had un burnt fuel in it as well.

Going to grab a spark tester tomorrow and test it. From that, then I will have a better idea of which direction I should be going in to solve this.

Thanks


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RE: Poulan Pro rough running/ back firing at load/high rpm

I was referring to a Briggs and Stratton spark tester, which allows you to check spark vitality while the spark plug is in place and the engine is running.
I don't know what kind of spark tester you might be sold.
The Briggs part number for their tester is 19368.


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RE: Poulan Pro rough running/ back firing at load/high rpm

If you can't quite determine that there is a carb issue, my next step would be to inspect the valves for even lift and proper lash . Maybe even a quick check of the flywheel key is in order.


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RE: Poulan Pro rough running/ back firing at load/high rpm

Yes,

I have a spark plug tester that does the same thing so I will test today.

If the flywheel key was damaged, should I expect to see more issues with starting/running in general?

As far as the valves - we were thinking that but also came to the conclusion - if the lash was off - should I expect to see these rough issues across the board no matter in which speed I am in?

Now, to touch on the possibility of a bad carb - what other tests would you recommend to determine this? I do see the rebuild kits for these carbs out there as well.

Thanks!


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RE: Poulan Pro rough running/ back firing at load/high rpm

As of this morning now the motor wont turn over. The starter will spin the flywheel but the motor is not kicking over. It might be due to the battery not having a charge with the frequent start/stops - have the charge hooked up now.

I had my spark inline tester hooked up and when starting the bulb did not even light up - which as per the tool indicates faulty ignition system. I also hooked up spark test tool up which basically grounds one end and the other hooks to the spark wire. I do have a tiny spark on turn over but not bright blue as others on the forum have indicated.

Thanks!


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RE: Poulan Pro rough running/ back firing at load/high rpm

Update -

Starting issue was due to weak battery. She started up and ran. I was monitoring my inline spark tester and noticed during low rpm that the bulb flashing was consistent of the rpm but was weak - which as per the tool indicates faulty ignition.

Once I cranked up the RPM to full speed where it started to backfire and blow black smoke - the flashing on the bulb would throw some stronger flashes with a bunch of weaker flashes and not be as consistent.

As per this tool, at least - its completely powered off the current from the coil - the stronger the power the stronger the tiny little bulb lights up. At least, from what I am seeing - the coil is having an issue - especially since I am seeing a stronger flash rate a few times at higher rpm but not constant.

Thoughts?


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RE: Poulan Pro rough running/ back firing at load/high rpm

You might want to remove the coil and clean the mounting surfaces to insure a good ground.


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RE: Poulan Pro rough running/ back firing at load/high rpm

I replaced the coil last night. I forgot to charge the battery so it would barely crank without a charge. What I did notice that I did not see with the last coil was a backfire through the carb because it got flooded with all the failed start attempts.

I charged her and cranked the motor up. At low speed the engine actually sounded a lot better - as my wife stated it sounded more like a tractor. When I increased speed to top it started to backfire. I did not have time to mess with it as it was 9pm and did not want to upset the neighborhood.

Could this be from residue of the un burnt fuel or am I looking at a bad carb? I just want to fix this thing so I can get ready to use it!


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RE: Poulan Pro rough running/ back firing at load/high rpm

Ran her today, still same issue. I did some research on the and found some people having issues with the solenoid on the fuel bowl.

I heard clicking from it when I would start it hearing it work. I started the engine and pushed the speed up to the point where the engine would start to run rough and backfire - while doing that I unplugged the solenoid. After which, the engine went from running rough to running great and then died out as the solenoid stopped the fuel flow.

I do have a carb on its way as this issue is very persistent.


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RE: Poulan Pro rough running/ back firing at load/high rpm

I have a Poulan Pro same model as yours and mine was doing the same thing and after doing several test I adjusted the valves on it and it cured the problem of starting and running but discovered that it would smoke out the exhaust when I would make a sharp right turn with the mower engaged in deep grass.. Hope this information may be of some help to your problem.


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RE: Poulan Pro rough running/ back firing at load/high rpm

".........to the point where the engine would start to run rough and backfire - while doing that I unplugged the solenoid. After which, the engine went from running rough to running great and then died out as the solenoid stopped the fuel flow.

That indicates the engine was running too rich, as in a the bowl level being too high because of a leaky carb needle/seat.


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RE: Poulan Pro rough running/ back firing at load/high rpm

Agreed - this adds to the theory of the engine running very rich by the gunked plug with unburnt fuel on it.

I was going to try and delete the solenoid but I do not believe that is directly the problem - this is looking at a carb issue as many of you have pointed at.

I have not checked the variance yet - I have done research on that though and usually you have two problems - either a starting problem or overheating/engine running rough after a set number of minutes. The engine starts up perfectly fine, and it running rough is right off the bat - any thoughts though?

Thanks


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RE: Poulan Pro rough running/ back firing at load/high rpm

"Agreed - this adds to the theory of the engine running very rich by the gunked plug with unburnt fuel on it."

I think you have the tail wagging the dog here.

The plug is gunked because you are running rich.

You need to fix the carb needle & seat so that it maintains PROPER fuel level in the carb bowl.
It's just like your toilet tank leaking. The extra "fluid" has to go somewhere.

Carb solenoid just blocks the Main Jet when no voltage is applied to it. It doesn't do a thing about fuel TO the carb bowl or fuel level IN the bowl.


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RE: Poulan Pro rough running/ back firing at load/high rpm

I agree - what I meant is the plug is the end result of the carb having an issue.


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RE: Poulan Pro rough running/ back firing at load/high rpm

Apparently the carb did the trick. When she started she ran great after the new carb. Only problem now is she does not want to start. Charged the battery a few times. Tried to jump The tractor... nothing.

Took the plug out and the flywheel spun freely. I checked the valves and adjusted.. still nothing.

Tried two different coils... The old and new... still nothing. Sprayed some carb cleaner and cranked but still did not turn over.

Ideas?


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RE: Poulan Pro rough running/ back firing at load/high rpm

***" cranked but still did not turn over."***
That is a contradictory statement. If it was cranking, it was TURNING OVER.
Turning over just means the starter is rotating the engine in an attempt to start it.
Now, is that what you mean? It turns over but it will not start up and run?
Or do you mean that now the engine will not spin when you turn the key to the start position?


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RE: Poulan Pro rough running/ back firing at load/high rpm

Correct, it turns over but does not start.


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RE: Poulan Pro rough running/ back firing at load/high rpm

OK, have you checked to see if a spark is being delivered to the spark plug while cranking? At this point I should presume you have but I had to ask.


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RE: Poulan Pro rough running/ back firing at load/high rpm

Yup checked that a few times. I do remember the other day when I swapped the coils I noticed at one point that one spin I had spark and another I didnt, which is why I decided to swap the coil. I misplaced my spark tester yesterday so could not confirm that again.

I will confirm tonight - should I be looking at the flywheel key to see if it got destroyed throughout this possibly if I find again I am not getting spark?

Thanks!


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RE: Poulan Pro rough running/ back firing at load/high rpm

Yes, by all means check the flywheel key.
A sheared (or partially sheared) key WILL NOT result in a LOSS of spark, but the spark will be so far out of "time" that it will be ineffective. Worst case scenario regarding "out of time" is that the spark might occur at a point where a loud backfire may happen.
In those circumstances it usually requires a change of underwear before proceeding.
If you do find that there is currently no spark, unplug the kill wire from the magneto and try starting it with the wire disconnected.
If disconnecting the kill wire allows spark to be generated, you will have to trace the kill wire circuit to find which switch (or a defective wire) is grounding the kill wire.
NOTE: With the kill wire disconnected from the mag, the engine might not stop by turning off the key, it could drop to idle speed and simply run slow when the fuel solenoid closes.
If that happens you will have to connect the kill wire back to the mag to stop it, or you can smother the carb with a rag or apply the choke fully.

This post was edited by mownie on Wed, Apr 30, 14 at 0:17


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RE: Poulan Pro rough running/ back firing at load/high rpm

Readjusted the coil and I now do have a good spark buy motor still will not power on. Every turn is one full turn then there is resistance which I assume is the compression build up?


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RE: Poulan Pro rough running/ back firing at load/high rpm

Are you saying that the cranking slows down at the compression stroke. What did you set your intake valve too?


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RE: Poulan Pro rough running/ back firing at load/high rpm

Yes I believe so. The intake valve is set to .005.


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RE: Poulan Pro rough running/ back firing at load/high rpm

Intake is supposed to be .003-.005", so you are within spec.
Exhaust .004-.006".
Personally, I'd set the intake closer to 3-4 to give a bit of "wear room"

Did you set it with the PISTON 1/4" ATDC?

Compression release is dependent on proper valve lash. (intake)


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RE: Poulan Pro rough running/ back firing at load/high rpm

I would take another look at that intake's valve lash and set it as Bill says, closer to the 3 and see if it works better. If you can check your feeler guage as well. I had a set of feelers from a dollar store once where the 0.005" was actually 0.008". That sent me running in circles for quite a while.


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