Export thread

Kawsaki Fd 750 D-AS04 Eng. Backfires during left turns & on grades w left side uphill

Hello,

I've got a backfiring problem I need advice with figuring it out.

The engine is a Kawasaki model FD 750D-AS04 Twin cylinder gas engine. It's on a Scag Turf Tiger model STT61A-27KA mower.

When mowing on level ground and moving at a steady mowing speed it runs fine. If mowing in this manner and you decelerate it may backfire or it may not.

If you run it at full throttle and turn to the right it is fine with no abnormalities; however, if you turn to the left it will backfire every time.

When mowing on a grade....it will backfire rapidly if the no. 1 cylinder is elevated. (uphill) ....But if the no. 2 cylinder is elevated (uphill) it doesn't backfire. Same thing happens when turning on a grade depending which cylinder is uphill.

I drove it at full speed and full throttle down the lane with no problems in the operation. I turned to the right and drove in fairly tight circles with no problems. Then I started turning to the left and it immediately began backfiring and stopped backfiring upon decelerating. It also stops backfiring upon decelerating and continuing in a straight direction.

Item checked are Air Filter (replaced), fuel filter (replaced), cleaned carburetor inside and out, Cleaned air filter housing, checked fuel pump for proper volume...seems good. cleaned choke cables and throttle cable and lubricated. checked spark with coil tester seemed good...both cylinders appeared to be the same. Replaced both spark plugs and set gaps to .030 thousands. (Found original cyl. #1 spark plug to have cracked porcelain near the tip. (didn't cure anything). Checked Valve cover gaskets found them good, with no damages, looked like new,

Have not checked compression yet.
Was wondering if I could possibly have a bad coil for that cylinder that isn't testing to be bad when testing in a stationary position.

I would appreciate any and all ideas. As My wife says "Somebody please HEEEEELLLLLLLLLLLPPPPPPP! this guy out!!!!

Re: Kawsaki Fd 750 D-AS04 Eng. Backfires during left turns & on grades w left side up

Couple of ideas:

1. check your safety switches at the sticks. Jack up the rear wheels, pull the left stick rearward, if that makes it misfire, adjust the safety switch. If it doesn't, then push the right stick forward to check for misfire. If that makes it misfire (which it shouldn't since it doesn't misfire going straight or turning right), then you may have either a safety switch problem or a strain relief may be loose internally.

2. With the rear wheels off the ground, engine running and sticks both pulled and pushed for forward and reverse. Lean hard on the right side of the seat. If it then misfires, you'll need to adjust the seat switch so that your seat movement doesn't allow the seat switch disengage.

Hope that helps,

Max

Re: Kawsaki Fd 750 D-AS04 Eng. Backfires during left turns & on grades w left side up

Hi Max.

Thanks for the good advise.
I will be testing that soon.
I had thought about the seat switch, but hadn't done any testing, as I kept thinking about the engine components.
When I get the testing completed I'll post the results. It won't be until Monday 7/1 when I get back to working on it.
Thank you again for the input, it's very sound advice.
Enjoy the 4th of July Holiday!
Deamer1

Re: Kawsaki Fd 750 D-AS04 Eng. Backfires during left turns & on grades w left side up

Loosen gas cap turn fuel valve off underneath disconnect fuel line Check the flow. With fuel on slightly blow air back in your tank with cap off. Grass and other stuff gets trapped in the small flow brass tube connector take a bright flash light look in tank. Might have to drain if a lot is in there. ?

Re: Kawsaki Fd 750 D-AS04 Eng. Backfires during left turns & on grades w left side up

Hi LuffyDog,
Thanks for the input and for taking the time to consider my engine/mower problems.

I'll take the time to check your idea. I've been there, done that on previous owned mowers.
Found one with huge amount of grass in the tank. Found it using a flashlight like you suggested.
Surprisingly it isn't too hard to clean out the fuel tank once it is drained.
I empty the fuel tank, let it sit to dry , then use my air compressor with a long wand to blow everything in the tank round and round with the gas cap off. Keep your face out of the way as the debris will come out of the tank like a hurricane. Over a short time it will be cleaned out.

I'll be working on the mower again Monday 7/2 will post my results when I finish on Monday.

Re: Kawsaki Fd 750 D-AS04 Eng. Backfires during left turns & on grades w left side up

THE MOWER REPAIRS ARE COMPLETE!

Special thanks go out to Mhavanti (Max) of Arkansas and Luffydog who both had ideas to help me solve the problem.

The cause of the backfiring problem turned out to be the Switch, Interlock-Seat (SCAG Part no. 481638)

I tested the mower as suggested by Mhavanti of Arkansas by jacking the mower up getting the rear wheels off the ground. Then testing as he suggested.
It was somewhat difficult to determine just what actually was happening with the left side of the stick control, but everything seemed to be correct with the right side of the control operation.

I actually could not detect much about the Seat Interlock Switch while sitting in the seat and moving about or operating hand controls.
What I actually did was to slow my movements and make very purposeful moves with one hand control at a time numerous times while sitting as still as I could.

Finally I tilted the Seat forward and placed a gallon milk jug full of water on top of the seat switch.
Testing again I had lots of backfiring at times or very seldom or none.
Upon removing the milk jug and holding the seat switch down by hand the backfiring stopped.

Holding the switch down 100% of the plunger travel, the backfiring ceased, but a slight movement of the switch plunger would cause the backfiring to begin again.
Removed the switch and tested it with a Ohmmeter, and at first I thought it was good.
I then moved the plunger very slowly through it's travel and found it to operate properly through approximately 10% of the plunger travel.

I didn't have a replacement switch so I improvised. I pulled the switch out of the Harness, removed the wiring harness from under the seat. (Plastic keeper holder comes right out)
Cleaned the switch holder very well, it appeared to be in good condition. I made a "U" bent pin out of number 14 gauge copper wire. Slipped a insulation piece over the center of it leaving the ends exposed approximately 3/8 inch. Went to the Anvil with the wire and a hammer and beat the ends of the wire flat like a Seat Switch terminal. Then inserted the hairpin into the Seat Switch socket. Fired up the Mower and the backfiring ceased! It was cured! Hadn't heard it run smooth like that for some time! Whew! What a relief!

We mowed three acres with it this evening.

Getting a new replacement switch in the morning.

Thank you again to Mhavanti (Max) of Arkansas and Luffydog for taking the time to offer some good advice. It worked!
Luffydog, I checked the tank, etc. It was clean.

Re: Kawsaki Fd 750 D-AS04 Eng. Backfires during left turns & on grades w left side up

Deamer,

Glad to have been able to give you some ideas. The description didn't sound like a stick safety switch considering it goes straight with zero misfire or ignition interruptions, however, it did sound as though there wasn't a continuous seat switch depression during left turns. Makes me happy to know I have another conservative friend out there. lol Ok, no political jokes here. Meaning you fixed the problem without purchasing any new pieces.

Keep us all informed and stay in touch,

Max