Briggs 18hp twin runs backwards!

[Backman]

I've got 18hp twin briggs that runs backwards. It ran backwards when I first started it up. I adjusted the ignition gap and it ran normal for a little while. Then it switched to backwards again and has been backwards ever since.

Things I did before starting it up: (1) new stator, (2) full carb clean (3) new flywheel key, (4) new spark plugs, (5) new oil.

I am having trouble torquing down the flywheel nut. I've heard it needs 145 ft-lbs. (is this right?) I can't lock the engine to get the torque on it. I already bent a belt pulley when I was using a belt and vice-grips to stop the engine so I could tighten it up. Any advice about how to lock this engine so I can tighten that flywheel nut?

I've been playing with the ignition gap but I can't get it to run normal again. Does anyone know why this motor runs backwards and how I can fix this?

Thanks,
Backman

 

[Ken]

Does this engine run backward when shuting off. cannot see it running at any other time.
If so look closely at the valve botton of carb. it is supposed to stop gas from entering the cyl. when ignition is shut off. be careful when removing dealiers like about $75.00 to sell new one.
Electronic ignition shouldn't change good chance wouldn't give spark if it did.
if all is good looking maybe a air leak in gaskets.of carb.
ken

 

[Backman]

Hi Ken, thanks for quick response. Can you please explain exactly where this valve is? Is it in the carb? Intake manifold? That carb is clean as a whistle I promise, with all new gaskets. It has one adjuster screw and I expect it is for idle. I've got it at 1.5 turn open now.

Here is a more detailed description of what is going on: The engine starts right up great but unless I keep it choked it takes off accelerating and accelerating without leveling off. I get nervous and kill it before it flies into outer space. I could probably ride this mower down the highway (but it would be going backwards!).

I know this is hard to believe but the thing just runs backwards from starting it up to shutting it down. Sometimes the flywheel kicks back a quarter turn when shutting down. When I put it in reverse gear I go forward and when I put it in 1st I go backward.

Just one time I was able to get it running right and it didn't accelerate out of control and I went forward in 1st gear. Haven't been able to get it back there though. All I did was flip the flywhere 1/2 turn and reset ignition gap.

I'll look into possible air leaks. Thanks.

-Backman

 

[KubotainNH]

I don't understand how this thing could run backwards unless the starter is spinning the wrong way. Being a 4 stroke you wouldn't think it would be possible to run backwards.

 

[Backman]

Hi K7LN, thanks for the explanation of the governor. That makes perfect sense!

I'm sorry but I misspoke about turning the flywheel. I turned the whole engine around 1/2 turn before resetting ignition gap because I was worried that magnet pulling on ignition coil was causing problems during gap setting. Flywheel key holds flywheel to crank and I did not turn flywheel separately from crank.

KubotainNH, the starter may very well be turning the wrong way (and I have no idea why) but like I said I got the thing to run normal once and the only thing I did was reset ignition gap after turning engine (not just flywheel) 1/2 turn.

Thanks,
Backman

 

[Backman]

Being a 4 stroke you wouldn't think it would be possible to run backwards.

I have seen much skepticism about 4-stroke running backwards in this forum. In fact, the first person I called about this said "4-strokes can't run backwards" and then hung up. But I promise you this engine is running backwards. It is running quite nicely actually, just backwards (and too fast). I may have to post video of it if this is in fact "impossible." I can't explain it anyway, so please don't ask me to explain it. It just is. I just want it to run normal so I can mow tomorrow!

-Backman

 

[Scooby074]

To torque the flywheel you can wedge a prybar carefully in the fins and go at it. Or you can just run the nut on with a airgun

You need to check the gap at the coil. Use some brass feeler gauges. .008-.012 is the spec for most twins, what model engine is it?

I bet you sheered the key . new key and " torque" the flywheel and you should be ok

 

[crazyal]

Just curious but do you have the plug wires on correctly? Also you may have a air leak somewhere in the intake system. It sounds like the timing is very screwed up (hense the plug wire question) and you're igniting the gas too soon or you're running very lean and you're getting pre ignition (air leak).

 

[Scooby074]

Just curious but do you have the plug wires on correctly? Also you may have a air leak somewhere in the intake system. It sounds like the timing is very screwed up (hense the plug wire question) and you're igniting the gas too soon or you're running very lean and you're getting pre ignition (air leak).

Not sure what engine he has, but the plug wires likely wont fit to the wrong cyl (one will be too short). Plus its a wasted spark engine anyways.

 

[The Haymaker]

Is this thing belt drive, ad if yes, are the belts on correctly? If the engine is running backwards, how exactly would it be getting fuel?

Check the belts.

 

[jinman]

Backwards is a very broad term and open to interpretation. Is the engine running clockwise or counter-clockwise looking down from the top? Also, I think the simple mechanism of a B&S starter will not engage the gear into the flywheel if the starter is running the wrong direction to spin the engine counter-clockwise. So, even if you put the battery in reversed with positive ground, I don't think it's even possible for the starter to work in reverse.

 

[Scooby074]

It wouldn't necessarily be wasted if the internal timing was messed up.

timing IS messed up. FW is out of place.

 

[Backman]

Hi all,

Thanks very much for all this good advice. To answer some questions:

(1) It is a 422707-0145-01 Briggs 18hp twin on a Lawn Chief.

(2) It is belt driven, but there is only one way for the belt to go on. Also I know it is backwards because the governor is not working (thanks to K7LN).

(3) The starter is hooked up right. It is probably flipping just after it starts but it must be happening very fast because it is not noticeable.

(4) Spark plug wires will only reach their respective plugs so I can't have them on wrong.

(5) Engine is turning clockwise from the top.

Some developments:

(1) I noticed that the spark plug wires were pinched and fixed that. Also, noticed that one of the wires from the alternator (stator) was pinched and I fixed that too.

(2) Could not find any intake or carb air leaks.

(3) Someone told me that this happened to him once because the armeture (ignition unit) was firing constantly. I'm going to try replacing that ($50!) and see what happens.

Further inquiries:

(1) Does it matter which way the alternator (stator) is mounted? It would fit in two positions: (A) With wires to the left side or (B) with wires to the right side, which is the armeture side. Wires seem to fit better having them facing left.

Thanks again!

-Backman

 

[Backman]

Also, it is a wasted spark ignition system.

 

[Scooby074]

IIRC the coil should be marked this side up or similar.

Before you spend another 50, check your keyway, and torque the FW down

 

[some zilch]

i am going to guess that somehow the belt is on wrong; ie crossed on itself somewhere making an "8" shape. even of the starter was able to electrically spin backwards, it still has to throw the gear out on its shaft, and the threads would now be backwards.

your timing would have to be so far off to even let the engine run backwards......

i have never seen anything other than 2 strokes run backwards for any length of time

 

[hawkeye08]

It will be interesting to see how this is running backwards. I think I have had this discussion before and it is not possible without some changes.

If it was actually running backwards, that would mean that exhaust valve would be the intake and the intake the exhaust. Where is it getting the fuel from the exhaust pipe? How is the exhaust getting back out through the carb?

You can run a 2 stroke backwards, but not a 4 stroke without significant modifications.

Just my opinion.

Also note, 4 stroke engines can run different directions, but they are designed and built to run that way, not just started the other direction.

 

[Backman]

Problem has been resolved. New armeture. Also new starter pinion gear. Thanks!
-Backman

 

[The Haymaker]

I'm still waiting for someone to explain how a 4-stroke engine can run backwards. It'd have to be getting fuel from the exhaust system.

 

[Ken]

Hi Ken, thanks for quick response. Can you please explain exactly where this valve is? Is it in the carb? Intake manifold? That carb is clean as a whistle I promise, with all new gaskets. It has one adjuster screw and I expect it is for idle. I've got it at 1.5 turn open now.

Here is a more detailed description of what is going on: The engine starts right up great but unless I keep it choked it takes off accelerating and accelerating without leveling off. I get nervous and kill it before it flies into outer space. I could probably ride this mower down the highway (but it would be going backwards!).

I know this is hard to believe but the thing just runs backwards from starting it up to shutting it down. Sometimes the flywheel kicks back a quarter turn when shutting down. When I put it in reverse gear I go forward and when I put it in 1st I go backward.

Just one time I was able to get it running right and it didn't accelerate out of control and I went forward in 1st gear. Haven't been able to get it back there though. All I did was flip the flywhere 1/2 turn and reset ignition gap.

I'll look into possible air leaks. Thanks.

-Backman

At some carbs. the float bowl is held in place with a Anti-Dieseling Solenoid and wire attached to connector on solenoid going to the ignition this places 12 volts to coil opening the fuel. key off blocks fuel flow engine quits. B/S and Kohler use simular type of carbs. The adjustment on carb. maybe the high speed adj. and about 2 1/4 turns to keep the engine running top speed. Did you remove the choke plates when cleaning. maybe installed incorrectly. The flywheel can only be installed aligned by alum. key way any other way or even slight miss alignment engine will not run. Govenor inside cover and controlled by air flow. check the springs and rods to carb. maybe installed incorrect. 12 volts to starter +/_ still runs the same direction. run backwards destroys the starter gears. Rethink what happened the first time fail. correct the other work to original configuration. ignition module usually run or fails. carb. all the rest of problems. dirt in needle valve. water corrosion. gas filter plugged fuel starvation. miss alignment or needle valve adj. over rich or lean. in 55+years never seen a engine run backwards more than putt putt and dies. exhaust blows out carb. no fuel sucked in it quits. talking 4 cyc. engines ken