Briggs and Stratton 16hp opposed twin questions

I got an 16 hp oppy for my murray project mower. I got a couple of questions about it. I say that it needs SEA 30 butt would it be bad if i just did some 15W 40 in there. And what is the best en most simple way to get some more power out of my oppy.

Oil - Thinner is probably better in this case so it can get all the way up to the top cylinder. 15w is probably fine.

Power - Which carb do you have? There was a three screw and a four screw carb, one was significantly better than the other. If you're up to it, remove the eyebrows (area between the valves and actual cylinder) and port out the intake and exhaust. Both of which probably have horrible casting left over that hurts flow. Intake should stay just a little rough for good fuel atomization, but the exhaust should be much smoother. Ignition coils are a weak point on oppys, some people switch over to an automotive coil that will last longer.

Thx for helping me . I got the 3 bolt carb. And how do you remove the eyebrows and how does it adds power(maybe it is a totaly stupid question butt i am a total newbie). And is it posible to remove the shielding around the engine (not the shroud) screw the cooling up? I wanna remove it because it is made to fit a way to big mufler underneed and because i want to run a straight pipe i got i gigantic hole in my shielding.

No don't remove the tins. Those are extremely important for an air cooled engine. Here is a link to my hh11 build: hh11

This was a flathead I built up a while ago and most of what I did should apply.

Removing the eyebrows increases flow since that is a flatheads main weak spot. these mods should get you to about 18 hp, which is really a lot. I can do everything I need to with a stock 11 horse.

The 3 screw carb is the better of the two i believe, but can't remember for certain

Here was the best response about porting:

prancstaman wrote:

A short radius side of the intake pathway- the pathway goes into the engine and turns up 90 degrees into the combustion chamber. The side of the pathway with the shortest distance on the 90 degree turn is the short radius side.

Drew a quick pic. Pic is of engine block and is the black lines. The pathway or intake runner is blue. The short radius side is orange which is where you want to grind off metal. The purple line represents the original path of fuel/air going into the engine before porting the short radius side. The red line represents the new path taken after you grind away on the short radius side.


How you need to think of it when you are porting is that the fuel/air charge is being sucked in and the suction starts at the piston when moving down. For the flat head engine, has a couple nasty sharp turns. These turns slow down the fuel/air charge moving into the engine. Your goal is to make these turns as less sharp as possible so the fuel/air charge keeps its speed moving through the pathway. When comparing the purple line to the red line, the red line has less of a bend in it compared to the purple line, so the red line will be faster moving going through the pathway. This can be done to the exhaust pathway also.

Flathead engines, OHV engines, OHC engines, have different pathway designs but the principle is the same, you just need to identify and evaluate the sections to do the porting. So the short radius side of the intake pathway will be in different spots on these 3 engines mentioned. My videos cover this and is done on a 5 hp Briggs and Stratton flattie engine. With other mods too, I made a couple vids on different parts of this engine.

Hope it helps

Thx for al the help. Do you know if there are any mods to make the engine running better without the govenor?

Im not sure I understand the question. Are you asking how to remove the governor or are you asking how to mod it while leaving it intact? Because you can do these mods and leave it perfectly intact and it'll still only run 3600 rpm, it'll just have more torque

No i asked how i got get my engine better for higher RPMs.

If you're comfortable with it, take it apart and pull the governor out. the gear inside has a tendency to self destruct. Also, enlarge the oil passage on the end caps of the connecting rods and clean up where the two half of the mold came together (clean up the casting along the rod). Those are the main points to be concerned with

Does somebody know how the breakerpoint works and how to wire it up. Because on my oppy the owner before me stuffed the wire in the casing for it and just did some chunks of liqued gasket on the hole where the wire goes to seal it.

Thxx!!!

EDIT: to know how to wire up the breaker points?

I haven't messed with points on a lawn mower engine for awhile. One wire goes to the coil and the other one just a ground for shut off wire? If the wires have already been cut off, does it have an electronic ignition coil on it now? Why not just stay with electronic if that's the case?

As far as oil grades, I use all different weights ect. without much issue.

Boring out the ports as big as you can go may be good for high rpm engines with a race cam, but for lower rpm engines closer to stock, hogged out ports can actually hurt flow a bit. In some cases they actually fill the floor of the port to make it smaller. Depends on the rest of the engine ect.

If your into doing a lot of reading on this kind of thing, I would suggest Four Stroke Performance Tuning by A. Graham Bell, It explains not only how modifications work and what they do, but also how stock engines work. Pretty much covers everything, carburation, exhaust, ignition. Even gets into different oils and explains about viscosity and additives. If you search around a bit you may find a better price, when I bought it I think it was around $30. The guy who wrote it is pretty honest about things too, if something is just his personal theory, he tells you that instead of just stating it as fact.

https://www.amazon.com/Four-Stroke-Performance-Tuning-Fourth-Hardcover/dp/B00HTCCULO/ref=sr_1_7?ie=UTF8&qid=1487467589&sr=8-7&keywords=four+stroke+performance+tuning+graham+bell

Thx for helping me out!