Dr Chipper 18hp Briggs Stratton engine laboring...

idrobnjakOctober 29, 2011

obviously i'm a newbie here. i have followed these forums over the last couple of months as I have searched for a chipper to clean up around the new house we bought. the house is on half acre - half acre of nothing but woods and trees grown in with about 50+ giant honeysuckle bushes/trees all around the house. the place has been neglected and i plan on cleaning it all up - all the brush, trim trees, plant some grass, etc. there are about 10 fallen trees to be cut up etc. so when i started cleaning up i realized i really need a chipper to do this on my own time when it comes to all the branches. i am in the city and breaking them up and putting in trash bins to be picked up once a week wasnt gonna cut it. wasnt really planning on spending more than $500 or so for a used chipper, but after looking through all reviews on this site i really wanted a mackissic 12pt. since i was in a hurry and couldnt even find a used one under 1200-1300 or so and even those were far away and to be freighted to me, i gave up on that thought. finally i found a dr chipper 18hp towable model which new is ~$3600 for $800 - about 10 years old but hardly used according to the widow selling her late husband's barn possessions. and from what i understand mackissic builds chippers for the dr chipper brand. she did say the guy working for her did something with carburetor to fix it - either replaced it or something since the thing hasn't been used. but now it works fine. so i bring it up here, check oil, fill gas, check blades - very sharp still, check air filter (original and very clean - supporting what she said about lack of use). i then start it up and have a nice afternoon of chipping. the only issue is it would backfire every time I would stop the engine. 2 days later i have another pile to be chipped - so i bring it out, check oil, start up and after a bit the engine is laboring. it is revving itself up rhythmically every 2 seconds or so. but it is working and chipping fine so I just go on with the work. it is sitll backfiring every time i shut engine off. it was in back of my mind and i thought - maybe it was having trouble getting fuel, so i get a new in-line fuel filter, drain old fuel and fill up fresh with stabilizer, check oil and add a little and start up today just for troubleshooting purposes. the thing is laboring again, revving itself rhythmically except it is getting a little worse and now it is revving every half second to a second or so. i look around and see the carburetor is pulling on a rod as it revs. now i think it is definitely something with carb or fuel / gas mixture and hopefully a minor adjustment? i like this thing, seems like a rugged machine and hoping to get years of service with good maintenance but first i want to get it running good. i still have piles of branches waiting for me but i am afraid to keep chipping with engine sounding like this - i am worried that i will ruin it. any help or ideas would be appreciated. the engine is a briggs and stratton 18hp twin cylinder vanguard, model 422437 type 1899 E1.

as you can tell i am not handy with small engines but take on an attitude of - i can learn just about anything. thanks in advance for your advice. below is a gallery of pics of the piece that gets pulled by carb with every rev.

my upcoming purchase is a riding lawnmower to tow this thing around the house since pulling and pushing couple of hundred pounds with only my wife to help occasionally is no fun - our property is all on a slope to boot.

Here is a link that might be useful: pics of piece moving when engine revs

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The rhythmic rpm shift can be caused by varnished fuel components in the carburetor, which leads to lean mixture. As the engine begins to stall, the governor spring pulls the throttle back open, increasing the rpm's, and the cycle repeats. You might be able to cure this by adding some carb cleaner to the gas tank. Or, you might need to get the carburetor overhauled.

    Bookmark   October 30, 2011 at 12:42AM
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thanks for the tip. i was sort of afraid it was going to be the carb. i added stabil to the fresh fuel just now and according to it - it has some sort of cleaner in it. is this what you are talking about to try first, or is there a different carb solution to be added to the fuel? beacuse the stabil thing didnt really work - it almost got worse. i saw at home depot a spray can of something called "carburator cleaner" but i dont think that is to be added to the fuel - more like to spray somewhere, or possibly use during carb rebuild?

second question, if I were to rebuild the carburetor - what would you suggest? I've never done it, how hard is it to figure out by following online instructions? i just looked up parts - rebuild kit is $15-20 and time it takes to learn and do it. the new carb is $150-$160 but could just plug and play. if i were to take on rebuilding it myself - would i need any specialized tools? if i were to take off the carb and take it to someone to rebuild it - how much would that typically cost? thanks again - trying to weigh options as the branches are piling up...

    Bookmark   October 30, 2011 at 10:17AM
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Common problem when engine sets alot and occassionally used. Carb gummed up probably as suggested as above. I would first try to use fuel additives to clean the passages. If that don't work I would then remove the bowl on the carb. and spary (carb. cleaner using the red nozzle provided and safety goggles) the needle and seat any small passages you see and up throught the middle. Last resort IMO would be to dissassemble the carb. clean all the find passages.

Removing the fuel bowl on the carb. not that big deal providing you can get it back on without pinching the gasket or o-ring creating fuel leak or over tighten the bowl mount bolt smashing the gasket or the bowl creating leak. Again I would run additive through it first (gum-out if you cheap, more costly are seafoam or lucas which work better IMO. Would be good idea to change the fuel filter and use additive regularly especially if you are running corn gas!

    Bookmark   October 30, 2011 at 9:18PM
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As for the backfiring, are you bringing it down to idle and letting it idle for awhile before shutting it off?
This might help, it only needs to idle down for around 30 seconds.
As everyone else said, for the surging while running, most likely some varnish in the carb. Try cleaning it first before attempting rebuild.

    Bookmark   November 1, 2011 at 11:20AM
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i realize it has been almost a year since I posted this and I never did say thank you for the great advice given. So thank you. I bought a can of "Mechanic in a Bottle" from Home Depot ($5 i think) and used that as additive. after about 10 minutes of running on that stuff, it cleared up and was running steady RPM. been using stabil since then in the fuel. after sitting for 8-9 months and starting up - it was doing it again. but this time after about 10 min of running with just stabil in the fresh fuel, the revving went away. Thus thanks to everyone. though it still backfires every time I shut off the engine. There is no option to rev-down the engine, just a switch start-stop, electric engine starter button and that is it. no throttle control.

    Bookmark   October 17, 2012 at 1:43PM
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"briggs and stratton 18hp twin cylinder vanguard, model 422437 type 1899 E1."
A 422437 is an opposed twin. Vanguards are OHV engines, not flat heads!

Does the carburetor have a fuel shut off solenoid?
They are designed to stop the fuel flow through the Main Jet to prevent afterfire (backfire).
If it does, is it intact?

    Bookmark   October 18, 2012 at 12:24AM
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