I have been given a masport with a 4 stroke briggs and stratton - model number 98902. Mower had been stored incorrectly and had oil coming out through muffler. Went to local mower shop and purchased new oil, air filter and spark plug. Drained mower of all oil, had muffler off as well to drain exhaust. Cleaned muffler with some petrol, installed new air filter, installed new oil, new petrol and after a number of pulls and primes got mower running. Mower now starts easy but when throttle is pushed on the mower is revving up and down (Other terms may be surging or hunting.) I took the air filter off and the flywheel cover to observe what was happing - there is a plastic vane that regulates the governor (? I guess). This appears to be going in and out which is affecting the revs. It appears the carby could be running rich as the exhaust smells like petrol (Not just the fact that I cleaned it with petrol) and the governor may be trying to counter the rich mix? I'm only guessing as 4 strokes are a new kettle of fish to me. There was a period before the fuel tank ran dry that the mower ran really smooth, but upon refilling back to surging problem. Any ideas? Also does the air filter foam need to be soaked in oil before using? I thought I read this somewhere but not sure if it applies to this model? I have uploaded a video so you can here and see the problem.
Cheers Mark
Last edited by Bruce; 12/08/1704:02 PM. Reason: Corrected Youtube
Your engine is 9 cubic inches (148 cc), ninth design generation, with vertical crankshaft, Pulsa-Jet carburetor, plain main bearings, and rewind starter. It was made on 8 October, 2003. I believe it would be US built - I don't think suction carburetor side valve engines have been made in China, but I stand ready to be corrected if someone has contrary information. Edit: Joe Carroll has posted later in this thread that these engines were in fact made in China, and it emerges that the one this thread is about, is a Chinese engine. Thanks, Joe.
The parts list shows your engine as having a foam air filter. That type of filter is wetted with engine oil, then wrung out, as shown in the operators' manual. I do not know why you would have needed a new element for it, after someone had apparently stored the mower with the crankshaft horizontal. The foam is very likely to have become saturated with oil, but all you need to do is wring it out then reassemble the air cleaner.
If the mower is stored with the crankshaft horizontal or nearly so, and the cylinder downward, the engine oil will pass through the breather tube into the air cleaner and oil will also run into the intake port. If the intake valve is open it will run into the cylinder, and if the exhaust valve is open as well, it will then run out through the exhaust port into the muffler and possibly onto the floor.
To cure that problem it is necessary to put the four wheels of the mower on a level surface, wring out the foam from the air cleaner, turn the engine over a number of times with the spark plug removed to allow oil in the cylinder to be ejected through the plug hole and exhaust port, and unless you want an unholy mess when you start it, drain the muffler. Refill the sump with clean oil. Because your engine has a Pulsa-Jet carburetor, it has a small lift tank inside its petrol tank. Very likely, if your mower had fuel in its main fuel tank and was stored cylinder-downward, fuel will have run into the small lift tank inside the main petrol tank, and through the second pickup tube that draws from that tank, into the main jet, and thus into the intake pipe and possibly into the cylinder. At the same time some oil may have run backward into the small lift tank from the intake pipe then through the main jet. So, the engine may not run very well when started. There is likely to be blue smoke for a while due to oil in the cylinder, and the mixture may be lean temporarily if there is oil in the main jet or the small lift tank.
Hunting of a governed engine consists of an endless series of speed cycles, with a cyclic period typically of a couple of seconds. It is typically caused by lean mixture, not rich mixture, but it can also be caused by a damaged or partly jammed governor. Your engine has an air vane governor - you should check that it moves smoothly with very little force on the vane, and moves the linkage and the throttle. If your engine is hunting continuously you should look for possible causes of lean mixture. Since your carburetor appears to be an emissions model without a mixture adjustment screw, lean mixture is likely to be due to either not having an effective air cleaner installed at the time, or some obstruction in the fuel system, probably due to dirt. Is the inside of the fuel tank completely clean, or is there some sediment or grass residue? The primary fuel pickup tube in the tank has a fine filter at its bottom (open end), and this is quite prone to becoming blocked and causing fuel starvation under load (usually it is all right at idle, but gets lean at higher speeds and loads).
If your engine is continuously blowing blue smoke, it is possible that it has oil contamination of the fuel, and this could cause symptoms of lean running. Strangely enough lean running can cause the exhaust to smell of hydrocarbons, due to poor combustion efficiency, but the smell is of singed hydrocarbons, and it is quite different to the smell of rich mixture.
After working through these points, if your engine is still hunting and you found debris in the fuel tank, you will need to partly dismantle, and clean, the carburetor. We can talk about how to do this if you find that debris in the tank.
Last edited by grumpy; 03/01/1204:06 AM. Reason: Correction: Chinese manufacture
Thanks Grumpy. Knew this would be right up your alley. The guy who gave me the mower paid a considerable amount of money for it some years ago so I thought it would be a decent model. Thanks also for the links to parts and user manuals. I have got the mower starting no problem and there is no blue smoke from exhaust. I had the cowling off and the air vane moves freely. I only purchased new air filter element on advise of my old man who said engine would not run with the old one all clogged up with oil!!! I'll instal the old one back on and keep the new as a spare.
Mark, it appears you will have to go through the process of removing the fuel tank and carburetor from the engine, then removing the fuel tank from the carburetor. In between the two is the fuel pump diaphragm. Inspect it, looking especially for flap valves that are stiff or will not lie flat. If the diaphragm has deteriorated, it has to be replaced with a new one, which will cost you about $10. If the diaphragm looks good you'll need to clean out the fuel pickup strainer, and the fuel passages in the carburetor, with clean fuel, or with carburetor cleaner. Do not let carburetor cleaner spend any time in contact with the diaphragm, and it might be wise not to use fuel with ethanol in it in future.
Thanks guys. Joe - yes there are vertical stripes on back of block - so china built? Also it has a bar for cutting instead of a disk. Guy at mower shop said they did make a cheaper line that came through bunnings / Kmart etc but he wasn't sure if they had the sprint motors on them.
I soaked the old air filter in oil and then squeezed excess out and installed but no joy. So its remove tank and carby. I found a good clip on you tube where a fellow does the exact process outlined by grumpy above.
Thanks again. I'm having a rough run with mowers at the moment. The misses is starting to question my abilities...... This all started when I wanted a simple Victa utility.... I'll get there. I prefer to restore an older model than buy something new. Call it blind ignorance but I prefer the old stuff. Does anybody know if the Briggs will bolt onto an older Victa utility frame? This will be my goal once I get the 4 stroke going. I believe there may be issues with the length of the shaft and fitting the victa disk? If it's too much hassle I'll just keep the masport but it has rust holes quite close where the left hand side handle is attached
Mark, the early Chinese-built Briggs engines have an unfavourable reputation for build quality. I doubt that is the cause of your lean mixture problem, but it does suggest you should not regard that engine as something marvellously valuable. In other words, this is a great opportunity to work on that carburetor and practise to increase your skills and experience. If the engine has lived this long, it may be a rare instance of an early one that by sheer luck, they built properly (or it could have even been an example built by experts as a training exercise, who knows?) That in itself may make it a future classic, but not for 20 years or so. Meanwhile I suggest you learn from it without feeling too badly if you make mistakes.
I might have missed it, but did you check the valve clearances?
Id try that, on most the inlet is closed up a bit. It will probably have a graphite head gasket, if it cant be reused you could get a metal gasket off an older briggs and use it.
Remove the nut that holds the starter cup on and check the flywheel keyway is not sheared or defomed. Thats a common fault with mowers with bar blades. Incorrect timing can give you mixture like symptoms.
Loose inlet manifold, or if its cracked or another common thing is the shroud or cover or air deflector wearing through the plastic inlet manifolds. If its been loose at the two little 1/4" headed bolts the gasket may also be damaged.
(sorry, didnt read all of each post above)
You could put the motor on any other Victa, but in the case of the utility it will need to be a power torque base and it would want to be drilled so that the motor faces forwards so the starter points the right way. The pan of the full crank utility is the wrong shape. Old catcher steel bases had the stamping to be punched out to suit full crank or 4 stroke, then came the dimple for the power torque. Power torque is the same pattern as a 4 stroke. Later steel bases are dual drilled for the side ways power torque or forward 4 stroke. Its easy enough to redrill, just use the power torques tin flywheel cover as a template. And measure carefully using to make the center circles concentric. You could also use card board or ply or tin.
I do kind of like the engine facing back on a Utility, less things poking out the front to break. You can push it further under cars and the like.
Depending on what starter, if its riveted then you could easily move it to the right spot to suit where the engine faces.
Ok - thanks for the responses. Problem resolved with new carby gasket and diaphragm kit. Gave everything a good clean and let dry for a day. Installed new bits and she's purring like a kitten. At the risk of offending some on here I quite like the quieter operation of a 4 stroke compared to the screaming 2 stroke. Total cost of getting myself a working (Chinese built) mower $30. Also previous owner contacted me and he found the original catcher so that's good.
Bob - Not sure if you remember my other post on the 2 stroke utility? (Still a work in progress) that has pictures of the utility mower, but I'm thinking it's not a power torque base. I'll focus on getting 2 stroke sorted and make my mind up after that. I like the utility as my front yard has some sharp slopes and the utility handles them quite well. My back lawn and the council strip out the front are quite flat so perhaps it's 4 stroke with catcher for them and utility 2 stroke for front yard. This will justify me having 2 mowers!!!!
Thanks for updating us on the outcome, Mark. These threads are much more useful in our archives if people can not only read the development of the case history, but also have the confirmation of seeing what the problem actually was. Otherwise it's like a detective story with no solution.
I'll close this thread. If any member needs it to be re-opened, just PM a moderator.
with new carby gasket and diaphragm kit. Gave everything a good clean and let dry for a day. Installed new bits and she's purring like a kitten. At the risk of offending some on here I quite like the quieter operation of a 4 stroke compared to the screaming 2 stroke. Total cost of getting myself a working (Chinese built) mower $30. Also previous owner contacted me and he found the original catcher so that's good.
