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Garden Tractors and Mowers Vintage lawn and garden tractors, mowers, snow blowers, snowmobiles and other old machinery that is driven by small air cooled engines.

Garden Tractors and Mowers

"Modern" motor, possibly old problem someone might recognize


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  #1  
Old 10-23-2016, 03:53:13 PM
Archaeometrist Archaeometrist is offline
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Default "Modern" motor, possibly old problem someone might recognize

I've posted before about my Struck Magnatrac (2008 model)... it's developed a problem that someone might recognize - and that would help me to fix it. Yeah, it's not an old motor - but new motors can have problems familiar from old ones!

The motor is a Honda GX270U. It originally had carb problems when I bought it - a drip leak. A new float valve and float fixed it (plus I cleaned the carb and lines quite thoroughly). I suspect that the leak problem had been around for some time, because a cut-off valve was added in the fuel line. (I added a new inline fuel filter as well because I DID clean some trash out of the needle orifice and bowl.) After that the Struck ran fine.

A couple of weeks later, and a new problem. It first started with the engine being hard to start - before, a single yank would start it. After the new problem started, it took several pulls before it would suddenly 'catch'. It also seemed to not run nearly as smoothly as it did before (especially would run slightly rough at mid-range to higher RPMs). It wasn't missing - just running uneven. Maybe you could say it was almost like it was stumbling or only partially firing every now and then (it didn't sound the same).

Then it seemed to get worse after it had been running for a while - maybe half an hour or so. I'd let it cool and it was back to what it was before.

Yesterday, after I'd been using the Magnatrac for about 30 minutes, it started "Popping" from the exhaust manifold when under load - and little pops of flame were noticeable. If I stopped pushing, it would stop popping. No blue smoke or anything like that, that I could see. If I let it cool down for a little while, it would run OK again (for 30 minutes or so, then the popping under load would start again). The popping is connected to the previous rough running. (It also would stop popping if I slowed down to an idle.)

For some reason, I don't think it's the carb. Could it be ignition? Compression is about the same.

Some advice and ideas that might lead to a solution would be appreciated!
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  #2  
Old 10-23-2016, 04:17:41 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: "Modern" motor, possibly old problem someone might recognize

Check valve lash, maybe its too tight or valve is sticking.
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Old 10-23-2016, 08:49:19 PM
Bill Sherlock Bill Sherlock is offline
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Default Re: "Modern" motor, possibly old problem someone might recognize

Are you using ethanol gas? If so, that could be your problem. The harder starting and popping sounds are symptoms of stale ethanol gas. Try draining the gas tank and carb and replace with new gas from a different source, preferably non ethanol if available. If that doesn't cure the problem, then you can look for other possibilities.

Bill
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Old 10-23-2016, 09:24:55 PM
Archaeometrist Archaeometrist is offline
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Default Re: "Modern" motor, possibly old problem someone might recognize

Fresh, non-ethanol gas less than two weeks old - I won't have the ethanol crap in any of my motors any more (exception the cars), I learned my lesson! Cleaned out tank and carb and lines when I replaced the float valve and added an in-line filter, and put some non-alcohol carb cleaner in the tank when I did that (make sure there was no crud left anywhere). It ran great for a couple of weeks, then this new problem started (slowly getting worse). I've put the fresh gas in the tank three or four times in that time - the Struck got a lot of use in the last month! (Should be no carb cleaner left in the system now.)
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Old 10-23-2016, 10:30:57 PM
Bill Sherlock Bill Sherlock is offline
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Default Re: "Modern" motor, possibly old problem someone might recognize

OK, another possibility? Premium gas that's stale at the pump? Had an experience with that some years ago. Service station didn't sell enough Premium and it went stale in their storage tank. My 8 HP Kohler on a rototiller which normally started on the first pull took many pulls of the rope to start and would only run with the choke almost full on. (same day that I bought the gas) When the tines were engaged the engine powered out and had to disengage the tines to prevent the engine from dyeing.

Drained the tank and carb bowl and refuelled with gas from another source and all was well.

Bill
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Old 10-23-2016, 11:26:42 PM
Archaeometrist Archaeometrist is offline
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Default Re: "Modern" motor, possibly old problem someone might recognize

Could be... although when I pull the choke, the motor dies - it doesn't even run too well on partial choke (like 1/4). I have to keep the choke full off for it to run. It also starts best with no choke.

I can check that, however. (The station in question is the only one with no-ethanol pumps on this side of the city, and they get a lot of business.) I've almost used up the 5 gallons in the can, so some fresh gas is an easy test and not too expensive.

What about ignition? Could a bad spark plug make it start popping (with little flames) out the exhaust after it had warmed up? Maybe the electronic ignition acting up? I know that hard starting can be a weak plug... but the popping with little flames... that I can't figure. It's a little like bad gas, but...
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Dalmatiangirl61 - when I have some time, I'm going to check that (unless something more likely pops up). I found where the factory does recommend checking the lash once a year. I don't know how long it's been since it was last checked. After things free up here (I'm working on my doctoral qualifying exams through December), I'll check that for sure - sooner if I have to.
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Old 10-24-2016, 12:01:11 AM
pegasuspinto pegasuspinto is offline
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Default Re: "Modern" motor, possibly old problem someone might recognize

Ignition. Bad coil or bad module perhaps. But I'd bet on ignition.
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Old 10-24-2016, 02:47:16 AM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: "Modern" motor, possibly old problem someone might recognize

Quote:
Originally Posted by Archaeometrist View Post
... but the popping with little flames... that I can't figure.
We were having that problem on the water pump for our track watering trailer a few months ago, its a little HF Honda clone. One day it refused to start and kept blowing flames out the exhaust, I let the younger mechanics try to fix it, after 2 hours I stepped in. Fresh gas? check, spark? check, bowl was clean? check, did you check valves? nope,,,, pulled valve cover, exhaust stuck open, sprayed some PB on it, worked by hand a few dozen times and it started back up. But your problem may be different
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Old 10-24-2016, 03:32:20 AM
BobRR BobRR is offline
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Default Re: "Modern" motor, possibly old problem someone might recognize

Sounds like sticky valve. Most likely caused by too much carb cleaner. Bob
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Old 10-24-2016, 11:51:13 AM
Archaeometrist Archaeometrist is offline
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Default Re: "Modern" motor, possibly old problem someone might recognize

LOL! I've used carb cleaner to free up stuck valves before, but never had it cause a valve to stick! That's a new one to me. I wouldn't think I put too much carb cleaner in it (only a little bit - like maybe a quarter to half of a teaspoon to 5 quarts of gas) and only the one time, but...

Funny thing is that it seems to stick (if it's a sticking valve) like that only when it's warmed up and under load - I haven't checked the compression, but it does seem the same when starting it - except that it requires multiple tries rather than a single yank on the cord (it's not easier like you'd expect with a leaking exhaust valve). When it starts popping, it does loose power but keeps running - kind of like the valve timing changes (but I don't know how that could happen).
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Old 10-24-2016, 01:14:47 PM
Andrew Mackey Andrew Mackey is offline
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Default Re: "Modern" motor, possibly old problem someone might recognize

Sounds like a valve lash issue. Pull the head and inspect the valve and seat to make sure they are in good shape. A worn guide or sloppy seat can cause issues. What does the plug look like? Black carbon residue (dry)? Wet balck residue? if wet, oily or does it smell of gas? Put on an inline spark tester. NAPA has them for around 10 bucks. Steady spark, then you have valve issues. Intermittant - then coil or module. One other thing - does your engine have a low oil cut off switch? Low oil or a defective switch can provide the effects you describe.
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Old 10-24-2016, 02:49:50 PM
sprkplug sprkplug is offline
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Default Re: "Modern" motor, possibly old problem someone might recognize

How does it run without the air filter installed?
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Old 10-24-2016, 03:16:15 PM
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Default Re: "Modern" motor, possibly old problem someone might recognize

You know, I haven't checked that - I put a new filter on it when I changed the float valve (about a month ago), and it ran great for a couple of weeks, then I started seeing the problems. It's been really dusty here (rainy season ended with the hurricane) and it might have gotten clogged. Even during the end of the rainy season, there has been a lot of dust.

I think I may spend some time on it today... I'm in the midst of my qualifying exams so I don't have much spare time, but I also know I HAVE to take a break from reading and writing each day (at least an hour or two). First, filter, then spark plug, then check valve lash if the other two don't make a difference.
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Old 10-24-2016, 03:43:55 PM
BobRR BobRR is offline
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Default Re: "Modern" motor, possibly old problem someone might recognize

I figured you added a whole bottle of gumout. Could very well be a lash problem. Try some mystery oil till you decide to actully start checking the things that have been suggested. Bob

Last edited by BobRR; 10-24-2016 at 04:02:00 PM.
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Old 10-24-2016, 05:18:46 PM
Archaeometrist Archaeometrist is offline
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Default Re: "Modern" motor, possibly old problem someone might recognize

Possibly solved - and thanks to all the suggestions!

I found two problems... first, the spark plug was absolutely packed with soot (dry). I scraped it and cleaned it out with carb cleaner, then let it dry thoroughly and checked the gap (couldn't find a spare and don't have the time to run to the store) and that seems to have fixed part of the problem. I then realized I'd not checked and cleaned the plug after I'd fixed the carb - and that was a mistake on my part because the carb had been running very rich due to the bowl having too much gas in it - almost a guarantee of plug problems.

Second issue - it was about a quarter of a quart down on oil. I don't know how much impact that has or if it added to the other issue, but it's possible. I think I'm going to have to check it regularly for a few weeks - to see if it's loosing oil somewhere. There is no evidence of a drip, and no blue smoke - so I don't know what happened. (An oil change in the near future is also in my plans.)

I also checked the air filter and it was almost new looking.

Now it starts on the first pull again - and runs smoothly (and didn't pop under load, but I may not have let it run long enough). I did note that when I rev'ed the engine up a bit, I noticed a bit of black (not blue as in oil) smoke for a couple of seconds - it's still running a bit rich, or it might be shaking soot loose. I think it's time to do some more carb work, when I can find some more spare time. I think I need to pull the cap off the mixture adjust and tweak that.

Thanks again!
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