Rough Idle/Backfire

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Re: Rough Idle/Backfire

Postby AgTires4295 » Fri Jun 21, 2013 10:23 pm

Alrighty Cub Fam, I had off tonight and was able to get to the Cub. I worked the timing to get it perfect (perfect in that it purrs like a kitten, idles low and fires up immediately on a cold start). So, success in getting it running!! I was pretty happy until I started to drive it and it went from a healthy high idle to a bog and died... in first gear, up hill. So it hit me that maybe I fouled the plugs in running Seafoam through the intake and gas. I replaced the spark plugs with all new. Fired it up, hoping for improvement and nadda... same symptoms: great idle from the lowest to the highest rev. Placed in gear, bogs while driving up hill and dies.

So yeah I know, I havent gotten around to the compression testing and havent even considered adjusting the valve springs yet. Before I go out and drop anymore money from my severly taxed public service paycheck, does anybody have anymore ideas?

It kills me that its running GREAT but low on power when it is confronted with any sort of load (PTO included).
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Re: Rough Idle/Backfire

Postby RaymondDurban » Fri Jun 21, 2013 10:55 pm

Being that the tractor hasn't run in some time, it may take a bit for the Seafoam to loosen the rings to bring the compression up. I'd definitely try to adjust the valves. If they are out if adjustment, it may help a lot with the low power.
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Re: Rough Idle/Backfire

Postby Rudi » Sat Jun 22, 2013 7:46 am

I agree with Raymond ... sounds like a good plan. Take the valve cover gasket off and roll the engine over by hand. It will soon be apparent which valves may be stuck/sticking. Adjust the valve lash. Should show good improvement. The Sea Foam will help a lot with the carbon buildup.
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Re: Rough Idle/Backfire

Postby Hengy » Sat Jun 22, 2013 10:25 am

When it is running rough under load, does it run any better if you pull the choke slightly? Did you ever check and clean the main jet on the side of the carb?

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Re: Rough Idle/Backfire

Postby AgTires4295 » Sat Jun 22, 2013 5:22 pm

I love all of this great input. Ill have to pull the valve cover off next chance I get and see whats what. I have been through the carb several times. In and out that thing is cleaner than when it rolled off of the assembly line :) I was hoping it was a carb issue but nope. Its not apparent that it is although the symptoms scream "carb!" I will say this, the exhaust is blowing cleaner and Hell-HOT since I Seafoamed it. I hope I didnt screw something up by possibly using too much.
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Re: Rough Idle/Backfire

Postby Rudi » Sat Jun 22, 2013 8:36 pm

After I put Sea Foam in Ellie and ran it for a while I noticed an improvement in the idle and when picking up rpms. After a bit, I put my hand over the exhaust (no muffler just a straight pipe) and she was just a purrin .. you could feel the smoothness and the exhaust got hotter as time went on. I think this is a good thing - as the carbon gets cleaned out the engine is bound to perform better and with better performance comes an increase in heat.

At least that is how I figure it. Mind you I am an amateur wrench banger here and I leave much of the mechanical to the real wrench turners :lol:

If you put in too much Sea Foam in the gas the only thing that will happen is that it will smoke more until you empty the tank or dilute the Sea Foam with more gas. I don't think it will do much more in the crankcase. As it cleans, there is less carbon to burn up hence less smoke.

You may be pleasantly surprised after you adjust the valve lash.

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Re: Rough Idle/Backfire

Postby AgTires4295 » Sat Jun 22, 2013 9:03 pm

Im tracking with ya Rudi :mrgreen: With your chart that you posted, I am 99% sure I understand what it advises to do BUT how do you know how much to adjust or not?

Thanks again!
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Re: Rough Idle/Backfire

Postby RaymondDurban » Sat Jun 22, 2013 9:06 pm

Adjust the valves to .014"
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Re: Rough Idle/Backfire

Postby Rudi » Sat Jun 22, 2013 9:48 pm

As Raymond said, 0.014 or 0.015 is about right .. I think mine I did at 0.014". Manual says 0.013" cold but on an older engine a little bit more is ok.

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Re: Rough Idle/Backfire

Postby AgTires4295 » Tue Jun 25, 2013 7:22 pm

Thanks for the great info! I looked at maybe doing the valves today but figured it looked like something that would definitely take more time than I had. I did run the Cub around for a little bit and made a vid: https://www.youtube.com/watch?v=C3HFwv- ... ata_player

There's no new info here outside of what yall already know. I made it as a last hope before I try to adjust the valves in that maybe somebody can see something that hasnt been described previously. Either way, its a Cub vid so enjoy :D
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Re: Rough Idle/Backfire

Postby Jim Becker » Tue Jun 25, 2013 7:54 pm

OK, check the valve adjustments. It probably needs it and certainly can't hurt. But here are the 2 things I would be checking:
1) Timing. Recheck static timing to fire exactly at TDC. Then use a timing light to make sure it advances to the advance mark (16 degrees) at fast idle. It it isn't advancing, you have some work to do in the distributor.
2) Make sure the governor is responding. When you reach that hill, the governor should pop the throttle fully open. If it doesn't, you may have a binding or mis-adjusted linkage from the governor to the carburetor. If that is good and it still doesn't respond, you have trouble inside the governor. You should be able to search for governor linkage to find details on the adjustment.
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Re: Rough Idle/Backfire

Postby Rick Spivey » Tue Jun 25, 2013 9:26 pm

I couldn't listen to the whole video, but I caught a fair amount of it. I don't think your idle is actually all that smooth, there were times when I wondered if you were running on only two cylinders. As it started up the hill, it sounded more like it was running on all 4, but not with any "oomph". So I have two suggestions:
1) check that your wires are in the right firing order, let's be sure we have all 4 cylinders contributing - 1342, 1 closest to radiator, and at approximately 12:00 on distributor cap
2) I still wonder if your coil isn't breaking down; is it magneto or battery ignition, and if magneto, internal or external coil? I re-read the post, but didn't see the answer to this question.
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Re: Rough Idle/Backfire

Postby Jim Becker » Tue Jun 25, 2013 10:36 pm

Rick makes some good points. It is battery ignition (can be seen in the video).

By the way, your coolant is pushing out because it is over full. Even if it has an overheating problem, it probably wouldn't do it in such little time.
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Re: Rough Idle/Backfire

Postby pickerandsinger » Wed Jun 26, 2013 5:58 am

I once screwed up the firing order on my cub....It ran but had very little power...The skip was barely noticeable....I could drive the tractor but couldn't engage the mower...No power...I swear I don't know how I monkeyed up that firing order....But as a last resort I checked it....And I had....Corrected it and ...end of story....
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Re: Rough Idle/Backfire

Postby Hengy » Wed Jun 26, 2013 9:16 am

I agree with what others have said, and also will add my questions about the governor linkage. If there is a lot of slop in there, it won't allow the carb butterfly to fully open and you won't get full power. I noticed that when you had the mower deck engaged and also when you were climbing the hill that your rain flapper didn't fully open. That says to me that the engine isn't breathing fully. I just redid the governor slop on Lewis, and now there is almost NO delay in governor response. Merlin's governor has been partially redone, but I need to finish that work because there is still a significant amount of movement in the rod and a delay in "kicking in" of the governor.

Did this happen all of a sudden or has it been down on power for a while?

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