Force 125 Big backfire, then won't idle, low RPM.

[gpet]

Well, I'm off to a good start this morning. Went to take the family out and tried a couple of starts without the safety interlock engaged, did let it rest for a minute then did a soft start and had a huge explosion/backfire. OK. Let it rest, take a deep breath.

Motor restarted easily a couple of minutes later, but went from a nice idle down to a choking idle then a stall. Tried again, same deal. In neutral, giving it more juice, I max out the RPMs at 1500, then it goes back to a choking idle, and then stalls.

Remove cowling. No obvious problems. Boat starts and idles fine with cowling off.

OK, so I turn to this forum. First most likely thing wrong seems to be the exhaust gasket blown - confirm that there is water coming out of the exhaust gasket. I have no idea if that was true before, but it is definitely true now.

Order new gasket with exact part number provided by you guys - thanks! So now I've got to wait a couple of weeks for that to arrive.

So my questions:
1. Does it seem like I'm on the right track (is it reasonable to assume that the big backfire could have blown a hole in the exhaust gasket & do you think the cowling off=fine, cowling on=stall symptoms are consistent with the exhaust gasket problem?

2. Is there anything else I should check right now while I've got time and patience that I might have damaged in this process?

Many thanks for the help and all the information here.

Boat: 1986 Bayliner Capri 18' with 1985 Force 125.

 

[gpet]

Pic of hole in exhaust. https://drive.google.com/file/d/0B0AQh3eNWfWvT21QMWRkVU1wc0E/view?usp=sharing

 

[kbh121956]

While waiting for your part, I would pull the plugs and by hand turn the engine over turning clockwise. Line up your timing mark to TDC on the flywheel. See if your top number one piston is on top. If the timing marks are off and the piston is up TDC, you may have a shared flywheel key. This may have caused your backfire. At the top of this groups forum thread is a "sticky" called "carb and timing." In the video it will show you how this is done. Don't forget to disconnect the battery before working on it. There are many excellent mechanics on this forum. Two of my favorites are JerryJerry and Norbin. These guy will comment in the early morning hours almost everyday. I hope that this helps you.

 

[jerryjerry05]

Your right about the cover off and on.
​The hole in that rubber piece will cause it to choke out.

Since it starts without the cover??
A can of starting fluid, and get it running(without SF)
Then as it runs spray the SF around the base and around the base of the carbs and along the fuel pump/ intake side of the motor.

​The backfire could be from too much fuel or sucking air.
​The test I gave you will tell if it's sucking air anywhere.

Do a compression and spark test. Post the results.

Does the ball pump up hard or just kinda hard?
That shows the pump might need repair?
Or the connectors need replacing??

​KBH he said it ran so the flywheel key shouldn't be a problem.
And thanks for the recommendation!!

 

[gpet]

Thanks to you both. It will take me a couple of days to get back to do the compression and spark test. I really appreciate the information and validation on the initial diagnosis. I will report back on compression and spark when I get back to her later this week.

 

[Nordin]

gpet ..... That hole in the exhaust rubber seal will definitely make it to stall with cowel on.
I do not beleave that the backfire would have cause the hole BUT who knows if the rubber was old and striff ..yes .
Check out the reads, fuel pump diaphragm.


kbh... thanks for your good words. Just want to correct you. My alias is "Nordin" not "Norbin" d not b.
I am no pro in OB, just love OB since I was a little boy and love Chrysler/Force OB and even old Merc.
Works with OB.s in freetimes.

Have alot of Chrysler/Force engines and also two old Merc (one four cyl. 50Hp 1970 and one four cyl. 80Hp 1972) love the sound from those four cyl. engines.

 

[kbh121956]

Sorry Nordin, I'm bad with the names. There are zero people to work on these where I live. You guys all put me back on the water!

 

[gpet]

No Title

Quick question - I've got the new rubber gasket and ready to reinstall this weekend and do my tests. The plastic piece (4) that fits inside the rubber gasket is shorter on one side than the other. This picture makes it look like the shorter side is the side connected to the spring, and the longer side to the outlet. That feels wrong, but ok. Can anyone confirm that this is the right way (I mean, I assume the parts diagram is right, but wanted to make sure).

 

[jerryjerry05]

The end of the spring if it fits inside? then put it there?

And YES a backfire can blow holes in the hose.
That hose is 31 years old and probably pretty weak.
​A backfire can blow the gaskets out from the intake ports too.

​Once it starts get a can of starting fluid.
Spray around the entire engine and see if it makes any difference in the way it runs??
Check the nuts holding the carb.
Loose? it can suck air and cause a BF