8hp Briggs Engine

I have a gilson 8RE rear engine rider lawn mower that probably hasn't been used since the 80's. It has a 8hp briggs and straton engine. The engine was not seized up so I cleaned up the carb, put in a new plug,
put in fresh gas and oil. It starts right up and runs. But, every now and then it will miss and blow blue smoke out the exhaust and then go back to running fine for a bit until it misses again and blows blue smoke. I
don't want to just start replacing parts. Does this sound like something that may happen when the ignition module starts going out? Or should I be looking at the valves or a possible compression issue?

Any help is appreciated.

It could be any of the things you mentioned.

But the last one I saw that did those symptoms had problems with getting oil through the crankcase breather hose into the intake. Then the oil was carried into the cylinder with the fuel/air mix and was burned, causing all the smoke. And yes, it would run fine for anywhere from 20 seconds to 2 minutes between puffs and sputters.

What oil are you running? If you are trying to run 5wX or 0wX, change over to 30wt or 10w40. and try again. If your oil level is over the full mark, does it have gas in it? If you are sure its just oil and over full, drain it down to the full mark. Oil over the full mark is picked up by the crank and cam and whipped into a thin airy froth that goes right through the crankcase breather while not lubricating very well at all.

I don't know what crankcase breather system that 8 hp used. I am more familiar with the later over head valve Briggs engines.

You may want to remove the crankcase breather-I think it is in the tappet cover on your 8 Hp.- and either replace it or make sure it is not stopped up, especially the drain hole(s) which should be at the bottom. if the breather was ever taken off, it may be possible to reinstall it with the drain hole at the top which would allow it to trap oil. If the valves were ever worked on and they put the breather back on with RTV they may have blocked the drain back hole(s) in the crankcase breather.

Then there is always the possibility the engine is worn out and just getting too much combustion pressure past the rings into the crankcase.

Thanks for the advice.

About what compression should this engine have? Ill check that tomorrow.

Unfortunatly i do not know the history of what work has been done to the engine in the past.

My first lawn mower on my farm in 1979 was a new, $1200 JD rider with a single 30" blade and the 8 hp engine. I wore it out in 2 years (using oil) and I do keep my equipment serviced. In the tear down I found that the cylinder had no steel liner! Once I found that out I decided against any restoration.

Smoke is oil and you might have an oil ring sticking such that it isn't fully expanded in the cylinder bore, especially with the aluminum bore and as such the problem of uneven wear up and down the cylinder. Otherwise you might have a valve sticking with a bad valve guide leaking oil.....I can see the valve problem possibility but would be more inclined on cylinder problems.

Get a 16 oz can of Sea Foam at your favorite auto parts establishment and do a "decarb". Do a www search on the word. If you don't have any luck go to the Iboats Forum and look in the archives for the word.

Give that a try before you pull your hair out. Might be the problem and will give you some more time before major surgery or scrapping.

I agree with trk. Had this happen last year. The carb leaked down and the crankcase was almost filled to the top. Same symptoms. Check your oil level just for giggles.

If it is the engine I am thinking it is, it was equipped with compression release and I don't think Briggs ever published a compression spec on it.

If it has a hose going from the side of the engine to the carb in take where the hose goes in the block is a PVC valve which maybe be sticking and will let the suction of the intake pull oil out of the engine into the carb so yu then burn some oil. Easy fix it s to replace the PVC valve

Did a leak down test and lots of air coming out the intake. Checked intake valve clearance and there is zero so the intake is not closing completely. Ground the stem down to get the required clearance. Hopefully this will fix the issue when i get a chance to put it all back together.

Breather