briggs v twin runs rough

88-1175 · Jan 4, 2017

have a 18 hp v twin,started running rough,took muffler off and blows fire out rt hand cyl.it has a 1 barrel carb on it with a common plenem.the rt side gets very hot very quick,pulled head to check ex valve seat,seats are good,lapped valves at this time,reassembled,same problem.put left coil on rt side same problem.the left side seems nice and smooth at all times,put degree wheel on it timing is 19-20 on left.rt seems very eratic..looking for sugestions

sotxbill · Jan 4, 2017

Compression test both sides... check valve clearance as they then to drift, or even push rods come off... Timing irratic due to broken coil mount and coil is vibrating or wiggling??? single points or sensor for both sides?

blue water massey · Jan 4, 2017

check compression on the bad side
could be plugged intake passage but most times its a valve not opening or closing that messes them up
also swap plugs like you did with coils may have a bad plug seen them bad right out of the box

M w J · Jan 4, 2017

Could the shroud be full of trash or mouse nest? The 1 side would overheat.

88-1175 · Jan 4, 2017

shroud is off motor,it overheats in like 20 seconds.with the muffler off the rt side blows a orange flame and ex is extremely hot to your hand say a foot away,left side is much much cooler

Geo-TH,In · Jan 4, 2017

No clue what would cause fire to come out the exhaust on just one side. I leaning towards a valve problem, crack in head. Then I wondering if you may not have a cam issue. Sometimes the intake valve is used for decompression and sometimes I seen where the exhaust valve is used. If your engine is using the exhaust valve, that may explain the valve being open during compression pushing some fuel/air out, shooting a flame.

I think you have an unusual problem. But if it running ruff, there is definitely something wrong with a cylinder.

Recently I replaced the cam on a single cylinder briggs, decomperssion release part of the cam was damaged.

Let us know what you find.

John B. · Jan 5, 2017

IF it's running hotter than the other cylinder that means it's running lean. I suspect you have a vacum leak on the right cylinder. Spray some WD40 around the intake manifold whith it running and see or listen if the engine rpm changes. If it does you found your vacum leak.

John B. · Jan 5, 2017

When you had the head off did you check for loose valve seats?

Rodney51Cub · Jan 5, 2017

First the motor will heat up in a hurry with the fan shroud off. The cooling air is not being forced across the cylinders. As suggested, check valves on other cylinder also and then plugs. You did not say what the model number is. If valves and plugs do not fix it, here is a SWAG. Some briggs twins have diodes in the kill wires of the coils. Disconnect the kill wire ( usually black ) at both coils and where it plugs into the mower. Ohm the wires. If the diodes are good you will have continuity in one direction only. If diodes are bad you can buy a new harness. If diodes check good and there is a solenoid on the carb you can leave wires disconnected at coil and run engine to see if the problem is still there. The only draw back to this test is the engine will run for a few seconds after you turn it off. Also what did you set the air gap to on the coils when you swapped them. It is normally .010 to .012 thousands.

jeffcat · Jan 5, 2017

I reread this several times and all of the replys. Did have something close two years ago on a 22hp twin V Briggs. Check the flywheel key. Mine was a parcial sheer and it overheated like crazy. One side of the muffler was actually glowing. When you take the big nut on the flywheel off you will see a waffle washer. Mine lost it's tension and the wheel would try to sheer the key. Put a good hi quality lock nut on and problem fixed. They need to be pretty dang tight. Do not use your air gun. It will sheer the key. I went through 4 keys till I figured that one out. Hope this helped.

jeffcat · Jan 5, 2017

Oppps!, a hi-quality lock washer and then put the nut back on to propper tourqed speck. Pull a spark plug and shove a long hunk of rope in the cylinder. Then you can tourqe it safely. They do have a pretty hi tourqe on these twin v tech engines. Mine has been wonderful since.

briggs v twin runs rough

88-1175

Member

sotxbill

Well-known Member

blue water massey

Well-known Member

M w J

Member

88-1175

Member

Geo-TH,In

Well-known Member

John B.

Well-known Member

John B.

Well-known Member

Rodney51Cub

Member

jeffcat

Well-known Member

jeffcat

Well-known Member

Similar threads