87 xp 150 just backfires,won't start

[Daron Dyer]

I have a 1988 17.5' Arrow Glass with a 1987 Rude xp150. I bought this boat new and it has been great to me. I haven't had any problems with it until last year. The VRO pump was leaking. I replaced it withot a hitch. we were on a trip to Cave run last summer. I got into some grass and overheated the engine. I trolled back and put it on the trailer. I have checked the spark and I have it on all six cylinders. The plugs look good, I didn't blow a head gasket. I put in a new impeller.
Now when i Crank it, It just backfires very loud through the exhaust. I think it might be something under the flywheel. I don't know where to start. I don't even have a socket big enough to take the flywheel off. Everything else on the engone looks good. Plese Help!

 

[daselbee]

Re: 87 xp 150 just backfires,won't start

Backfire out the exhaust indicates the ignition timing is off for some reason. Double check the orange primary wires to each coil.
The orange with blue stripe wire goes to the top coil on each side.
Orange goes to middle, and orange/green goes to bottom.
If you have been messing around checking spark...maybe you swapped either the primary wires or even the plug wires.

After you are sure wires are OK, you need to consider the possibility of a sheared flywheel key.

Mark TDC on the flywheel for each cylinder with white nail polish. There will be six marks, spaced evenly all around the flywheel.
Pull all plugs except #1, and rig up a timing light with the pickup on #1 plug wire. Crank engine (don't give it any gas at all...no primer pumping...nothing.) and observe if the TDC paint mark for #1 is hitting on or near the pointer.
Remove plug, put it in #2, do the same thing looking for the paint mark for #2 to be at or near the pointer.
I suggest removing all plugs except the one you are working on because you don't want it trying to start and backfiring....

With this procedure, you have indexed the flywheel and are checking for spark at TDC for all cylinders.

Do them all. If they are way way out....like spark is firing on #1 and you see the paint mark for #3....then possible sheared flywheel key.
You have to get the proper key from BRP. Part number 307480. Of course if the key is sheared, then you will have to remove the flywheel. If you find the timing right on all six, then you won't have to worry about taking the flywheel off.

But beware....a miss-plugged wire can also cause this, so be sure they are wired right first.

Also, when cranking it, tuck the spark plug leads away from the open plug holes, as gas fumes will be shooting out, and sparking is occurring....gotta be careful of a fire.
That's why I said don't give it any gas. It keeps the fuel misting to a minimum.

 

[Daron Dyer]

Re: 87 xp 150 just backfires,won't start

Thanks so much for the advice, I was wondering if I was going to get any response. I will try this and get back to you. I am pretty sure the flywheel key is sheared. Do you know what size socket is on the flywheel?

 

[Will Bark]

Re: 87 xp 150 just backfires,won't start

Agree with everything Daselbee is telling you; however read what he is telling you and do things in order instead of being sure that the key is sheared; that's way down his list. I'm betting on your having switched plug wires somwhere along the way if not the pack wires. Just do things in order the way he has them. Good luck.

 

[boobie]

Re: 87 xp 150 just backfires,won't start

Flywheel nut socket. 1-5/16 ". Re-torque to 100-105 ft lbs.

 

[boobie]

Re: 87 xp 150 just backfires,won't start

An easy way to see if the flywheel key is sheared is to take out # 1 spark plug, stick a screw driver in it and rotate the mtr over till # 1 is at top dead center. Then check your timing marks to see if they line up with the pointer. If not,sheared flywheel key.

 

[daselbee]

Re: 87 xp 150 just backfires,won't start

An easy way to see if the flywheel key is sheared is to take out # 1 spark plug, stick a screw driver in it and rotate the mtr over till # 1 is at top dead center. Then check your timing marks to see if they line up with the pointer. If not,sheared flywheel key.

^^^^^^
Absolutely. Voice of experience there. Much easier than the indexing task that I suggested.
I am gonna remember that one.

 

[emdsapmgr]

Re: 87 xp 150 just backfires,won't start

The above torque spec for the flywheel nut is for a V4 engine. V6 engine flywheel nuts need to be torqued to 140-145 ft lbs.

 

[boobie]

Re: 87 xp 150 just backfires,won't start

Sorry about that, had a little case of HUA.

 

[Daron Dyer]

Re: 87 xp 150 just backfires,won't start

Ok, I checked tdc and it looked off, I pulled the flywheel, but the key did't look sheared. I put a new one in anyway and it started! However, I think the head gasket is blown on no. 1 cylinder. I have water coming out of this hole on the starboard side.

 

[daselbee]

Re: 87 xp 150 just backfires,won't start

Picture is not exact, but you are pointing to the thermostat. Water should be there.

 

[Daron Dyer]

Re: 87 xp 150 just backfires,won't start

Water is actually coming out of this hole. Do you think I have a blown head gasket? Or something to do with the thermostat?

 

[emdsapmgr]

Re: 87 xp 150 just backfires,won't start

There is a sort of diaphram inside that cover. It moves when the engine is running. Likely it has sprung a leak. Minor repair.

 

[Daron Dyer]

Re: 87 xp 150 just backfires,won't start

A word to the wise, Just because it doesn't look like the flywhell key sheared, doesn't mean that the flywhell didn't move. There were no shavings or any scoring on the flywheel or crankshaft, but it did indeed move.
As far as the thermostat housing leaking. The pressure releif valve had melted from the overheating. (It is nylon) I purchased two thermostat rebuild kits and all is good. I want to thank everyone for their help. I am wiser.