Talk me in off the ledge

Of course right now is gearing up to be the busy season on the farm. And now I am having trouble with the mower. I have never been proud of the way the engine ran on the big mower - an 18 horse Briggs twin flathead. The carb is ok and so is the fuel pump. Spark is fine. It just doesn't run "right" and have good power. It doesn't use oil but the engine changes running characteristics as it gets hot. I've decided that valve adjustment is the next item on the list. Has anyone done one? I can't believe you have to grind the stem to adjust lash! I should probably just replace the valves at that time but my thinking is that they likely won't have worn out if it doesn't have blowby or use oil. It just sounds like a day long undertaking considering I will have to pull the engine to do it (it's in a Deines ZTR). Is it as big a project as I am dreading? I will need to be in the fields shortly!

This engine has a habit of loosing carb to manifold and manifold head bolts traper

Your carburetor may be running lean. Hal

Checked all of that and sprayed carb cleaner to check for intake leaks. I have been through the carb - it isn't running lean. I can adjust the main it until it drowns out but symptoms still persist. It is acting like tight valves. I just wonder what a rats nest that will be. I've done lots of cars and tractors, just not something without adjustable valves.

I had an 8 HP B&S flathead that just kept going down hill - less and less power. It would run ok but I could tell it was not right and finally it didn't have enough power to cut dry grass. I found one valve would barely lift off the seat, lash was okay just no cam lift.

Sounds like the major part of this repair is removing the engine! You sound a little anxious about this, and if you have never done this before, that is understandable. Years ago, I bought my first Volkswagen bug, everyone said you couldn't work on them. First, I went to the VW dealer and bought a "how to" book, (similar to the Haynes manuals, only better), then I took a good look at the engine compartment and got familiar with it. It turned out to be the nearest thing to a lawn mower that I had ever worked on. Moral of the story; Don't attempt unfamiliar repairs without a decent instruction manual, and DO NOT LET IT SCARE YOU! If you do, you have two strikes against you already. Treat it with respect and caution, but do not be afraid to tackle it! Oh yes, just to be on the safe side, Good Luck!

Is the Briggs 18 HP flate head two cylinder a two cylinder opposed engine? If it is an opposed engine they are not a smooth running engine until you get them above half throttle. If the engine is clean so its getting air to cool it down and still over heating and no power check the timing to see if its in timing. I have one of 18 HP opposed flat heads on a garden tractor with 1,600 hours and uses no oil and still has great power. They do have a gallop and run rough until they hit half throttle or put it under some load.

It is not that hard to do. Just don't grind off too much at once.

Hi notjustair, you should not have to remove the engine from the tractor to check the valve clearances, but you will have to remove the intake manifold and carb (as a unit) then remove the 2 covers and you'll see the valve check the clearance with a feeler gauge if within the specs it ok and you have another problem. I have a couple of those engines and I really like them, another thing to check is the fuel pump it may not be working to full capacity and causing the engine to run lean at high R's.
GB in MN

Check compression first thing. They can be rough on valves and seats. Good engines though.
David

Ironic - I rebuilt my first VW engine at 14. I've 30-some of those things now. That's an addiction. I still have four but those I will probably die with. They are getting harder to do as all of the heads are on their second rebuild and won't hold a valve guide in. I used to be able to do a top notch rebuild for $600. Those were the days!

I don't know if opposed twins ever had a loose seat but if any valves were way
out of spec on clearance I would check for loose seat.
http://www.briggsandstratton.com/us/en/support/faqs/valve-repair-maintenance

I have done valve adjustments on several of those flathead engines. (Back in the day-most of those engines are over 15 years old. Nobody wants to pay the labor to do that any more.)

The best I remember, You can check the adjustment without pulling the manifold. I am thinking there was enough room to get the tappet covers off. If you need to adjust clearance, you will have to pull the heads. I am thinking the last time I did it, I could compress the valve springs without removing the intake manifold too. On most, (if not all), of those, each head uses a different gasket.

Also, check for carbon in the heads. Those engines were known for carboning up, especially if they weren't well loaded.

It did take me something like 2-1/2 to 3 hours to do the valve job.

THIS IS GOING TO BE LONG. I have two Husqvarna garden tractors with twin V Briggs engines and I bet I can tell you some of your trouble. Take the plastic flywheel cover off the engine top. Now on the right valve cover you will see a bunch of numbers.. write them down. If you end up rebuilding your carb you will need ALL of these numbers! Now on the carb there are more numbers, Same deal. Now the first check is to pull the manifold off of the engine with the carb mounted. Get this in your lap and look at where the carb and manifold meet up. You will see a gap where the carb is sucking air! The manifold warps. This happened on both of my machines. Fixed a lot of power problems. Take the carb off of the manifold and reseal. A little bath tub seal will fix it. Next, if you have a kind of hunting problem like the engine is kinda constipated and sound like it wants to take a dump? You have carb trouble. These little NIKI carbs work great but when they need service that is it. You can do a little check while it is in your lap. The screws that hold on the bowl are a BEAR to get out. NEW screw driver-Give them a good sharp rap with the screw driver in the head and a little hammer. Give it a sharp snap like twist while you are really leaning into it. Now clean the bowl out. DO NOT TURN THE CARb right side up!!!!!!!! If the little MAIN jets are going bad they will fall out! Now you will be toast. These little jets have VERY tiny "O" rings you CANNOT get anywhere. Thank ethanol in the gas as it eats up the gaskets and O rings.
If you got this far and your tractor now runs great YAAAA!!! If the carb needs a rebuild you need a carb kit that costs around $30.oo You will also need the two little main jets. They are about $6.oo each. They are #117 in the exploded carb diagram. They MUST be replaced cause you are getting bypass with the old ones and the whole carb is out of balance. Follow good cleaning protocalls and rebuild the carb with care. These NIKI carbs are great when all fixed. I called Briggs and got them direct and were here two days latter. GOOD luck! Jeffcat

I haven't posted using the new look - I hope this attaches. She dropped a seat. It was all still in good shape. I peened it in, lapped the valves, and adjusted all of them. That thing runs like a scalded dog now! I mowed some with it today enough to get it good and hot to make sure the seat was going to stay put.

Way to go!

Been there before with other engines but not a twin Briggs. Good fix! You now should have a very smooth running engine. Yea!