Briggs 16HP V-Twin falters & surges, runs rough: Please help


Old 06-06-07, 06:54 PM
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Briggs 16HP V-Twin falters & surges, runs rough: Please help

Briggs 16 HP OHV Vanguard V-Twin runs rough, surges & falters, loses power; PLEASE HELP
Engine: Briggs & Stratton, Model 303447 Type 0447-01 3441 Code 3441, 189 hours, horizontal shaft
Compression (PSI): Cold; Right 154.5, Left 153.5 / Hot; Right 154, Left 153.

My Dad was having a hard time getting it (Ingersoll 4016 tractor) to run or run correctly before he passed away. Since it hadn’t been started in 2 years when I began working on it this spring, I pulled the spark plugs, squirted oil into the cylinders, let it set for a week, then gently turned it over by hand, (it turned freely). With a spray of some WD-40 & some starting fluid down the carb and a good jump, it fired right up. I started with replacing the carburetor (with new one), since I knew he’d had it apart and was quite notorious for leaving things apart sometimes. It wasn’t getting fuel; I ended up replacing all the fuel line carb to tank (which had ‘hardening of the arteries’ – the insides had swelled up, cutting off the fuel supply), fuel filter, hose barb off tank (was clogged then broke off), cleaning out the (dirt in) tank, replacing the fuel pump (w/ new B&S part). It started and ran, but surged, far more noticeable at an idle than at 2/3, ¾ or full throttle. And it had a tendency of spitting a little oil out the breather tube into the air cleaner when ever the engine would falter. Also, it sprayed small fuel spray out the carb air cleaner throat when it faltered. Adjusting the mixture screw didn’t phase the surging/faltering, but it ran best after removing the limit and unscrewing it almost all the way out. (Go figure making it running overly rich would make it run better?) But it did. I changed the oil and filter, filled to oil proper type & level, mowed 4 or 5 hours; it ran fine, but still surged and faltered just like it had before. One day after about an hour of mowing, it started cutting out, lost power and would barely run. After sitting ½ an hour it would barely creep at near an idle w/o dying. It had plenty of fuel. 4 Mower mechanics said that it sounded like it had a bad coil. I replaced the coils and adjusted them with a business card. It stopped surging and faltering and ran great for 1hr,40 min, then again for an hour a little while later same day, then started stumbling, faltering, losing power then would barely run at all. It would start and die as soon as I tried to put it in gear (hydrostatic trans). I screwed mixture screw in to gently seat it then back out 2 turns. It didn't run any better. The next day, it would start and die as soon as I tried to give it gas, and wouldn’t start w/o choke. I removed the fuel solenoid and replaced it with the plug that had come on the new carburetor. No change. I (momentarily) replaced the electronic ignition module with one off a used B&S 14HP OHV Vanguard engine (which was in unknown condition), result; no change. I took compression test [cold] (see above), changed
spark plugs (they were black, wet and fouled); new Champion RC12YC plugs. It started and remained running, running better with choke, but faltering and stumbling / running good, faltering and stumbling / running good, throughout the throttle range. I tried adjusting the mixture at full throttle w/o choke, starting from out 1 ½ - 2 turns, out till it ran rougher (very difficult to find that, with it constantly running rough, faltering and re-gaining), turned in until it (barely noticeably) ran better, then faltered, then back out ¼ - ½ a turn. Then I ran it at varied throttle with an inductive timing light; the strobe never faltered, got the engine good and hot, checked the compression again (see above). It doesn’t burn oil (make blue/white smoke) but blows out a little black smoke only upon acceleration (running too rich?). After it was warmed up and mixture screw adjusted, it ran pretty smoothly at an idle (no choke), but if I gave it gas, it would falter all over the place, sometimes spit a little (gas) and die. (Oh, and with the plug instead of fuel solenoid still in carb). I pulled one coil wire at a time off each spark plug. Each time it started, would run on one cylinder at an idle and die if I gave it throttle.
So I don’t think it has a blown head gasket, cracked ring, slipped valve seat, ignition problem, but you’re the experts; what do you think? Does it sound like there’s something amiss in or with the carburetor? Got any ideas? Does this sound like a flooding problem – or something else? What can be done to correct it? I am totally stumped, except maybe to check the (new carb’s float needle valve and float level). What is the float level on a (part No. 809011) carburetor for this engine? I looked all over the net and couldn't find it. Can you please help me? Should I clean the carb or rebuild the old carb and put it back on…? Had to make a special wrench just to get to the bolts, but changing a carb on this engine is far easier than replacing coils!
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Old 06-06-07, 07:12 PM
puey61's Avatar
Join Date: Apr 2004
Location: Upstate New York
Posts: 3,224
The only thing that comes to mind is an air leakage between the carburetor and the cylinder which would be either the carburetor mounting gasket(s) (there are two such) or one or both intake manifold gaskets, or both areas, carb and manifold. FYI and not that it has any effect on my diagnosis, but the engine code number you posted is not correct.
Old 06-06-07, 09:29 PM
cheese's Avatar
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Join Date: Jul 2001
Location: USA
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I sounds like either a defective carb, or an air leak after the carb, before the head. The only thing that makes me scratch my head is the fact that it ran good for 1hr and 40 min after replacing the coils. I don't see what that could have changed, other than making sure the ignition is good. The black wet plugs indicate rich running, but you said it doesn't smoke except when throttling up. Maybe the constant choking is causing that. Try unplugging the kill wire from both the coil, not at the junction terminal. If the coils are cancelling each other through the kill wire (bad diode), this will show it. You won't be able to shut it off with the key though, so be prepared to choke it out or pop the plug wires off.

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