OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Victa 4 Stroke Briggs and Stratton 450 Services

Hi Guys,

I aquired this mower from a bloke who wanted a 2 stroke mower as he thought it was stuffed. I thought why not, another good learning experience on a half reasonable four stroke. I don�t ever seem to find many that are not completely stuffed.

The previous owner said it blew smoke like there was no tomorrow so I said I�d take it off his hands. After blackening the street with smoke I proceeded to have a look at the oil level and the bloody thing was full up to the top so I extracted the oil and put the correct 600ml back into the engine. I let it ran for about 10 mins and the smoke cleared up.

I have also given the carb a once over with some carby cleaner and also installed a new diaphram. Everything else looked pretty good. Today I fired it up and mowed the lawn without to many issues whatsoever. It starts easy.

I did notice the units chuggs slightly when you a re mowing. Its not like its good to stall and it just keeps going no issues. It is hardy noticeable at all but I thought it was a little strange.

Id appreciate any thoughts before I move it on as the [Censored] thing looks like its done hardly any work at all. The frame is a bit flimsy but for someone with a townhouse it should suit them well.
I have put some photo�s of the cleaned up machine.
Thank you

Peter, we need more information. First, please post the complete Model, Type and Code for that Briggs engine. Then clarify what you mean by "chugs a bit". Does it slow down? Does the speed cycle up and down? Be as clear as you can, so we can get some idea what it is doing that it shouldn't.

Model - 9T502 Type - 0149 B1 Code - 09060151.

Its sort of hard to explain. The mower runs very smooth and every so often it sort of slows ever so slightly and the engine then regains normal speed. The change is very minor and to a normal person they probably wouldnt worry about it however I like things to be as close to right as possible.

Its not major I just havent encountered it in a 4 stroke before.

Next time I will be more specific Grumpy. I hope this explanation helps.

I appreciate the advice.

So to clarify Peter, its not a chug or the mower missing a beat, the revs simply slow down and then pick up where they should be.....hmmmm.
Ok, i've thought about it and i suspect one of 2 things. A rapid decline in revs and then picking up again(known as "hunting") would be caused by a dodgy governor spring. They are super sensitive on these models because of the lack of weight of the small 16" bar blade. Tweaking the spring/throttle plate mechanism sometimes helps but when all else fails a new spring should do the trick, but make sure you cross reference the model and trim code on the briggs website and get the right part number for your engine because sometimes they're different.
If its not hunting but rather just dropping off a little and then picking up again gradually i would suggest there may be a fuel/carby problem. Possibly contaminated fuel or a blockage in the mesh in the pickup of the carb.
After re reading your post and seeing that it only does it under load, then i would suggest there is probably very little you can do to fix it if the above 2 processes dont help. This is mainly due to the light bar blade setup and hence why these machines are targeted for users with small lawn areas.

That engine was made on 1 June 2009, in one of Briggs' plants at Wauwatosa, Wisconsin. Wauwatosa is the location of Briggs' head office.
Here is the Operator's Manual:
http://bsintek.basco.com/BriggsDocumentDisplay/iorpzNJU0HCjhJvcv4.pdf

Here is the Illustrated Parts List:
http://bsintek.basco.com/BriggsDocumentDisplay/18kvuIXSnfBhU7y.pdf

The engine is called 450 Classic, meaning it is a mildly updated 1960s design. It is interesting that it was made in the US as late as 2009 - AFAIK, all Briggs side valve engines are now made in the Chongqing plant in China. The last to move were the large engines, which were scheduled to be relocated late last year.

I'll add another possibility to bigted's list. When this mower was running grossly overfilled with oil, the whole crankcase breather system would have been completely full of oil and slugging large amounts of it through the breather pipe into the carburetor's air intake. Draining the excess oil from the crankcase did not drain the breather system, which is part of the reason it continued to smoke for some time. (The other reason is that the muffler was full of liquid oil, and it had to cook this to carbon then burn it out.) There is probably a fair amount of oil still in the valve chest and the crankcase ventilation valve may be only working part of the time. There may also be quite a bit of carbon in the muffler. If that is the problem, it will probably sort itself out over a couple of hours' running.

Thanks Bigted and Grumpy. I appreciate the assistance.

It might be better to describe the change in engine sound as a light cough which is noticeable from the exhaust. The change in engine rev's is very minimal to say the least
I thoroughly cleaned the carby with compressed air and carby cleaner and then replaced the diaphragm. I also added from PULP to the tank. Everything looked as it should upon re-assembly. I also re-inspected the governor springs and to the best of my knowledge everything looks as it should.
I should also clarify the unit makes the same sound under load and not under load. Although when I cut the grass on the weekend the engine wasn�t under any form of excessive load due to the fact the grass was fairly short.
Would cleaning out the muffler help? It seems to be on very tightly. I don�t suppose you have a trick for taking it off. I was thinking maybe an oil filter wrench.
I will run the engine again tonight for another 20 mins or so to see how it goes.
I did read a separate post which James87 identified the problem could in fact be related to a warn blade bar and a lack of evenly distributed weight however that was some time ago and I could be mistaken. The blade bar hardy has a mark on it similar to the actual entire unit so I don�t think that will be the problem.
I�ll await your thoughts.
Thank you
Peter

You did not mention having replaced the spark plug, or even cleaned it. It was probably quite heavily oiled back when it was smoking, and it will not clean itself unless it has a longish run at heavy load.

If you are not used to Briggs and perhaps other side-valve engines, you need to bear in mind that they do not scavenge well. I can rather reliably distinguish between side valve Briggs engines, and OHV Honda engines, from one to two hundred metres distance without seeing them, just by listening for missed shots. OHV Hondas do not miss shots, side valve Briggs engines always do, especially at idle, but it is noticeable any time they run at light load.

A very slight irregularity such as you have described could also be due to poor valve sealing. You should check the tappet clearances, and while you are at it you could clean the crankcase ventilation valve, since it is built into the valve chest cover that you have to remove to get at the tappets.

Removing the muffler and inspecting it for clogging is a relatively low priority check, especially when you have not yet made the other checks listed, or run the engine under sustained heavy load. However if all else fails, you might remove the muffler (use an oil filter strap wrench), check it for carbon fouling, and run the engine without it, so you can watch for a flame from the exhaust when it falters.

My best guess at the moment is dirty spark plug, or just the normal side valve irregular misfires.

Peter, i'll have to agree with Grumpy on this one(and he is extremely knowlegable).Briggs engines like to miss a beat every now and then and they do it fairly consistently, you could just about time the intervals.
Looking at your machine it is obvious it hasn't done much work, so changing anything more than just service related items at this stage would probably be a fruitless excercise.

Ok thanks for the wise words.

1) The spark plug has been replaced with a brand new one.
2) Are we agreeing that is worthwhile to check the tappit clearances? This is a process I have not completed before so I would appreciate your guideance. To date my work has mainly been with 2 stroke engines. I have watched some You Tube video's that explain the process and I have also read the Briggs Manual from the Outdoorking Site which also explains the process.

I believe I have all the necessary tools however some guidance would be appreciated as I believe some wise words will make the process much easier to follow.


Thank you

It is (IMO) a good idea to check the tappet clearances on any 4 stroke engine you acquire, as part of your first definitive tune-up. Checking is easy on the side valve Briggs, but adjusting is difficult. Fortunately, on side valve engines you seldom need to adjust, unless something has gone wrong.

All that is required is to remove the two screws from the valve chest cover and carefully remove it, in the hope of not damaging its gasket. You then rotate the engine to a position just past top dead center on the compression stroke (later Briggs manuals say rotate it until the piston has moved 1/4" back down the bore, on the expansion stroke, which is a good way to do it). You will see where you need to make the measurement, in the tiny gap between the top of the tappet and the bottom of the valve stem, which is just below the bottom of the valve spring. Slide a feeler gauge (a thin strip of hardened steel) of the required thickness into that tiny gap. You can see which valve is which by looking at which port is above that valve. One will be directly under the exhaust port, the other directly under the inlet port.

The required clearance for the inlet valve is 0.005-0.007". For the exhaust valve it is 0.009-0.011". You need a fairly sensitive touch when you push the feeler gauge in, because lawnmower engines have very weak valve springs, and you can easily force a thick feeler gauge in just by pushing on it. Just keep increasing the thickness of the gauge until you can feel a slight drag on it as you slide it back and forth. When you feel that drag, you have gone 0.001" too far.

While you have the valve chest cover off, turn it over to look at the back of it, which is normally inside the chest. You will see the breather valve attached to the cover. Wash it in petrol or kerosene in case it is gummed up due to the sustained overfilling with oil.

Ok thanks Grumpy.
To start with I did some conversions to mm�s as this is the measurement unit of my feeler guage
Inlet .005-.007 inch = .13mm - .18mm
Exhaust .009-.011 inch = .23mm-.28mm
At no point during the measuring process could I get a .10 feeler gauge through the top of the tappet and the bottom of the valve spring for the inlet measurement
.20mm fits through for the exhaust measurement however .25mm does not.
I triple checked the measurements to make sure I got the same results.
Regarding the breather disk. From your example I should only be able to fit a 1.1mm feeler gauge through the gap however the gap is much larger unless I am taking the measurement incorrectly.
I have placed some photo�s below as I hope others can learn from this example as well.

Let's begin with the tappet clearance:




The yellow ovals show the junction between the bottom of the valve stem, and the top of the tappet. (I've turned your picture around so that "up" and "down" mean what they would mean on a horizontal crankshaft engine.) Be sure you have the engine rotated to a little past top dead center on the compression stroke - Briggs used a feature called "Ezyspin" which holds the inlet valve slightly open during the compression stroke, to make the engine easier to pull-start, and it is important to rotate the engine past TDC to ensure it is not still operating when you measure the clearance.

I agree with your metric conversion results, so it appears that your inlet tappet may be at least slightly overly tight, unless you find you can increase it by rotating the engine forward a bit more from top dead center. I would like to see a more precise measurement than just finding that a 0.1 mm gauge (0.0039") will not fit in the gap. The exhaust may or may not be tight - you would need a feeler gauge of 0.009" to find out for sure. To correct the inlet valve clearance it is necessary to remove the cylinder head, remove the valve, and grind the end of the valve stem slightly shorter, keeping the grinding exactly at right angles to the axis of the stem. This is a fairly awkward process, because if you grind away too much you have to replace the valve, it can't be made longer again. So, if you are interested in learning more about small engine maintenance, you should consider rechecking the inlet with the engine rotated a bit further beyond TDC, and if this confirms that the clearance is inadequate, dismantle both valves and lap or grind the stems. If you decide to do this, we can talk in more detail about how to do it.

I cannot guess at this point whether your engine would run better with the clearances corrected. It appears that they are below minimum specification, but in general this clearance is not critical unless it is close to zero for the inlet, and less than say 0.003" for the exhaust. Nevertheless on a side valve engine like yours the clearance tends to decrease with time as the valve works its way deeper into the valve seat (where the valve head seals against the engine's cylinder, inside the combustion chamber) so insufficient clearance in a new engine is quite undesirable.

Thank you Grumpy. I appreciate the detailed explanation.

Tonight I rotated the engine a little more past Top Dead Centre and got some much better results with the feeler gauge.

Here goes:
Inlet - .08mm goes through easily and .09mm has to be forced through the gap
Exhaust - .20mm fits easily and .25mm has to be forced through the gap.

So from your detailed explation I gather this engine would be better left untouched unless I am mistaken. I do have to find some long grass to really test it on.

I will await your thoughts.
thank you

It sounds as if your exhaust tappet clearance is about 0.009", which is minimum specification, and your inlet tappet clearance is about 0.003", which is some way less than minimum specification. I see no need to change the exhaust clearance, and no urgent need to attend to the inlet clearance. I agree that the best thing to do next, is to give that engine some work: run it under at least moderate load - say some fairly thick grass at least 6" high, covering a sizable area so it can work steadily for 20 minutes or more. Then let's talk about what you find while running it.

Well I went and found a decent patch of long grass today in the back of my suburb.
I mowed for about 25 minutes and started on some mid-level grass 5-6 inch and then moved to some fairly thick grass knee high and the machine just kept ploughing through the grass. I was actually surprised how well it performed.
The machine was under considerable load for a fair period. I managed to fill up about 8-9 catchers of grass and neatly stack it around a couple of a large trees to keep in neat.
The mower never stalled, always started first pull after emptying the catcher. I gave it a good clean after the hard work and checked the oil to be safe and it was all good.
I appreciate your assistance in thoroughly checking over this engine to ensure its ready for a new home. I do enjoy being thorough with repairs and moving a machine from the scrap heap to a new home.
Unless you disagree Grumpy I am going to put the slight cough sound down too side valve engine misfiring like you suggested earlier.

Thanks for the full report, Peter. I think you've tested that machine adequately, and familiarised yourself with it as well. You can put it to work now with as much confidence as you can ever have in a machine that is relatively new to you. Sometimes it takes months for some fault to mature and become evident, but that is equally true of a new machine you buy from a dealer.

Hi Grumpy,

The guy returned the mower to me yesterday stating it would not start. He was quite polite about it which was good as he understood I do this as a hobby.
He showed me oil which was pouring out the exhaust. This immediately made me think the mower had been turned over to wash it. He assured me it hadn�t however I wanted to check if there was any other possible way this could happen without turning the mower over.
I quickly proceeded to wash the cylinder out with petrol and pulled the rope a number of times. I cleaned the plug and it went on the third pull. After a minute or so the smoke cleared and it proceeded to run as normal missing the occasional shot.
For good measure I also thoroughly cleaned the carby and replaced the diaphragm as I am not a fan of re-using them.
It now looks to be running spot on again.
I don�t suppose you have any additional thoughts?
Thank you as always.
Peter

I can only think of three things that would cause what you have described, without there being anything wrong with the mower. The first, as you suggested yourself, would be turning it upside down, perhaps to wash it underneath. The second would be over-filling with oil. The third would be tipping the mower to an excessive angle while it was running, so that oil flooded the crankcase breather valve.

If the oil level was correct when you received the mower, my guess would be that the problem had been corrected (oil level returned to correct amount, or mower put back to a normal angle, no longer tilted excessively), and the buyer either did not know what had been done to it, or simply chose to deny everything to avoid embarrassment. However, let's see what other people can suggest.

Thanks grumpy .I am a little more curious about the breather valve assesembly.
When I checked the breather unit I can easily fit the wire guage between the valve and the body.

I have cleaned the unit but the gap is rather excessive in my opinion.

Could this be at fault?

I suppose it could be a factor, Jaffa. If you could reproduce the fault, you could then find out whether it was associated with the valve, by trying a known good one. The buyer of the mower may have a sloping block and you may have only tried the mower on flat ground? Or he may have just slightly over-filled it? With an out of specification valve, it might be more sensitive to those factors.