Force 125, thought I had a bad reed valve

[redfury]

So, end of the season, brought the family on the boat, had a gunshot like backfire that destroyed the rubber exhaust boot. Couldn't get the engine to run without the hood off, and it didn't run that great. Used the trolling motor. Brought it back out and it ran, but a bit rough, I could hit 38 mph with it, which is pretty normal, but the engine would run up the rpms and then drop them and surge. Actually had the engine quit for a moment like I had forgotten to open the vent on the fuel tank...started right up and kept running. Last time out, had a terrible time keeping it idling, would die when put into gear. Midrange cruising seemed pretty smooth, but it would still surge, just not as much during WOT.

So, I put it in my tank of water, with muffs and water from the hose ( seems to be the closest I can get to lake pressure ) and checked spark. I was getting spark on all cylinders, very strong snapping arc. However, I did a cylinder balance test and found the 3rd cylinder down from the top didn't change the operation, so I am running on 3 cylinders. A compression test showed pretty equal pressure in each cylinder ( my starter is needing replacement, so I couldn't get really good cranking readings. So, I figured that I might have a reed problem, since the lower carb was dirty with fuel/oil residue. Well, I pulled the carbs and reed valves out and they all physically appear perfect. I didn't see any distortion, any cracks. I did see milky oil in the passage just inside the block, but I can't be 100% certain of a bad head gasket as I had the cover off the engine and it had rained 2 nights before. I had the covers off the front of the carbs, though I suspect not much moisture would get in that way, particularly since the motor was trimmed up for trailering.

It had been running great prior to the backfire ( literally like a gun...scared everyone half to death ). I was able to troll for quite some time without any hesitation or loading, changing gears was smooth and never had an issue with the engine quitting. Something happened during that backfire and I can only suspect the head gasket at this point, but before I drop $40 on the gasket, I hoped to gleam some insight here first...perhaps a few nods in that direction , or something else I can check before I commit to replacing that gasket. I have photos on my phone that I can upload if there is anything you want to see.

 

[jerryjerry05]

#3 operates the fuel pump.
​The backfire could be the diaphragm in the pump is damaged?
ANY drops of water on the plugs? NO then the head gasket might be ok.
​ONE drop and it shows you have a problem with the gasket.
I had a small miss and the compression was 145 on all cyl.
​Saw a tiny spot of water on 1 plug.
​Removed the head and found a bad spot about 1/16" on the gasket.
Replaced and it ran great.

​Each cyl has a intake port cover, the boom could have blown the gasket out.
​Not sealing the port(sucking air) causes poor idle, backfiring, poor performance.
The pump is mounted to the #3 port cover.

​Start the motor, on muffs or in the water.
​Spray starting fluid around the intake ports and the carb base.
​If spraying makes a change in the way it runs? then the gasket is probably bad??
​Resealing can be tricky once they've been blown.
​You might need silicone on the gasket to make it seal.

 

[redfury]

I have new gaskets coming, the reeds are out currently and it dawned on me this morning that I may not have released pressure on the tester when I checked the cylinder. Can I do a compression test without the Reed assembly on?

 

[Jiggz]

I wouldn't recommend it although it can be done as long as you spray fuel oil mix in each cylinders for each cranking. As Jerry said, check on the fuel pump diaphragm before going any further. And the other issue is the milky fluid in the crankcase cavity. This cannot be from the rain especially if the engine was tilted for trailering and the reeds fully intact.

That said, there's a good chance the exhaust gasket is damaged leaking water into the cylinder. Personally, this will be the last item I will check as it's really a pain to work on.

 

[redfury]

Looking at the exploded parts diagram, it appears that the exhaust gasket you are talking about should affect all cylinders equally, so I'm going to suspect that last, and it does look like a real PITA. What I'm not understanding is why there is focus on the fuel pump, considering that I have no power only in one cylinder. I'm not sure I understand its relevance to the dead cylinder. My reed and carb gaskets should be here next week, ( as well as the new starter ) so I think I will hold off until I can reinstall the reeds and carbs to seal up the block properly. My lack of fully understanding the working relationships of 2 cycles is hindering my personal diagnostics in regards to figuring out how each component plays a part/affects the engine as whole.

I'm open to suggestions though, I may question motives based on my wanting to understand WHY that direction is pointed to, not that I am whole sale discounting it as an avenue of diagnostics. My access to gaskets is about a week away, so I'd prefer to not disturb anything unnecessarily. If I could have gotten my stupid USB endoscope to work well enough, I would have just probed the reeds through the carbs and probably had not even pulled them out for inspection. However, that being said, at least I can rule that out, and I have the opportunity to look deeper into the crankcase via the reed openings.

 

[jerryjerry05]

The fuel pump is operated by #3 cyl. That' seems to be the problem area????
IF??? the pumps diaphragm is bad, it dumps fuel into the cyl.
That overloads/floods that cyl. and kills it.
From my previous post:
"Spray starting fluid around the intake ports and the carb base.
​If spraying makes a change in the way it runs? then the gasket is probably bad??
​Resealing can be tricky once they've been blown.
​You might need silicone on the gasket to make it seal."
​You can over tighten the screws holding the port covers.

​One backfire, cough or stutter can blow the port cover gaskets.
​#3 if the diaphragm is bad that can make the gasket go bad when it coughs stutters or backfires.

The exhaust chest gasket can affect just 1 cyl.

 

[redfury]

Okay, I think I get a clearer picture of what you are talking about. I just did a quicky compression test without the reed valves and I was seeing 75psi on every cylinder, which I am going to assume is going to give me a clean bill of health in regards to cylinder #3 I think I will just order new fuel pump parts, for as much as I try, I haven't been able to fill up every time with Non OXY fuel. The fuel pump doesn't look like it's been serviced recently, so it's probably not a bad idea to give it a little love anyway...not to mention if it is bad, it's a cheap fix. I may still order the head gasket as well, since the boat is going to be down anyway...Not sure yet though....

Now, when you say the exhaust chest gasket, are you talking about the side cover, or the one on the bottom of the motor that requires removing the power head?

 

[redfury]

So, I pulled the pump off and apart, there's a tear on the larger part of the diaphram....glad to find it too. The whole picture becomes much clearer when I think about how the backfire happened, how the cylinder has compression and spark but no power. I am ordering parts as soon as I am done writing this and once I have the boat back together completely, I will report back the results.

 

[jerryjerry05]

Side cover.
The head gasket can be a BIG job??
The screws get seized and twist off. If you don't need to fix it?? don't.
​So it was the diaphragm like I said.
​If it's a fresh water motor? then the job should be a bit easier but can still be a nightmare.

 

[redfury]

Yes, freshwater motor. At this point, since the problems I had had and was having all directly relate to the fuel pump problem with the cylinder, I am proceeding with replacing the fuel pump diaphram/related parts and reinstalling the reeds/carbs with new gaskets.

On that note, is there a trick to getting the reed valve intermediary plate loose from the gasket without damaging/cracking the thing. It's pretty tight, and I don't want to ruin a part that I cannot replace without a lot of trouble.

Wish I had just come here first and posted before I started tearing into this thing, but sometimes that's how you have to learn...the hard lessons stick a little better than the easy ones.

 

[jerryjerry05]

Not sure what your talking about?

The reed block is held on with 2 screws. The gasket might be covering them.
When you reassemble there is a tiny hole in the plate.
Make sure it's pointing down.

 

[redfury]

Separating the plate between the carb adapter and the reed plate. I managed to get them off with a little patience and a wood chisel and a small hammer in the old gasket. I will look at the assembly again, I wasn't aware of the hole, thanks for that. What is it's purpose? Just an indexing mark?

 

[redfury]

Ah, I found it. Looks like it would be really hard to install it the wrong way, but it's good to know what to look for.

 

[jerryjerry05]

I think it can be installed as a unit upside down????(maybe???)
The hole is a drain for fuel that might get accumulated, it will drain down and not build up.

 

[redfury]

Yeah, it is only able to be installed one way, the bolt holes index it so you can't screw it up. I'm probably going to have to rebuild/clean the carbs now. I got it together, put it on muffs, got it to start, it ran pretty good...I could tell all 4 cylinders were banging again. Took it to the lake and I lost power and had to paddle the boat to the dock the last 10 ft. Since I didn't have an inline filter between the pump and the carbs ( I will now ) I can't guarantee that nothing got into them and screwed them up. It was running like it was misfiring though. I am going to check the basics again, but I'm not really sure where I need to look other than the carbs. When I was on the lake I realized that I had shifted the carb synch linkage and it was keeping the throttle open so the idle was way high. I adjusted that and started having some stalling issues. It would sound rough through the lower range of RPM and then once got out of the idle circuit, it would clean up and run better. Near the end of my fiddling however, WOT wouldn't give me anything, felt like I was dragging an anchor on the bottom. Seems to me that since I messed with the fuel system, that I may have to clean out the carbs. I can't imagine that I did anything wrong installing the reed valves....that went smoothly, unless I missed a detail that wasn't covered in the book.

I'm kind of at a loss at the moment. Frustrated too, especially since it was running nicely at home, I let it cool down and got my permanent fuel tank installed and the restart was good, other than that I did have a pop through the exhaust. I dunno, maybe I've got a timing problem? I need to focus and diagnose this properly, but I'm at a bit of a loss. I am going to start at the basics and work my way through it.

 

[redfury]

So, I had it running smoothly in the driveway again, and it started running poorly...I shut it down and restarted it later, it ran smooth again after I had opened up the fuel tank. It was low on fuel so I refilled the tank. I'm really starting to question what is going on. The plastic fuel tank was brand new a couple of years ago with the clicking lid and the push button relief valve. I have it turned out counter clockwise the whole way. On the lake, from the launch is started up nicely and we shot off like a rocket, but after a bit it died down again. Seems like a classic case of vapor lock? I didn't want to commit to filling the 20 gallon tank at the end of the year and run it that way, since there's no chance of that happening the way it's configured with the port venting...there's nothing to stop air from breathing in and out of the tank to fill up the empty space.

I'm thinking out loud...I was veering into "maybe the ignition system is getting hot and starting to fail due to heat" but the ignition system just about twisted my arm into a pretzel when I tried to do a cylinder balance test without using a rubber glove ( even though I had a test light grounded to the block. I'd say the spark is strong...

 

[jerryjerry05]

Remove any inline connectors.
Never really heard of the ignition getting hot and failing after it's been running.
​The packs usually work or not.
It definitely sounds like a fuel delivery problem.

​A new squeezie can be bad, any inline connectors can suck air.
​The tank vent line can get a twist and shut off the air?
Try another hose/squeezie.

​Check for water, once the boat is running, usually the nose goes up and water can slide to the area where the pickup tube is getting fuel.

​When it slows down, does it feel like there is a miss?
Check the trigger wires and stator wires.
​Check the ground connections on each pack and coil.

 

[redfury]

I'm going to go run it in my tank and muffs today and just let it run for a while. The last time I took it out, it ran like a bat out of hell, and then started to chug and got worse and worse to the point where full throttle wasn't doing much of anything. Really reminded me of another problem I had early in my boating days were I think we forgot to open the vent on the fuel tank and that 50 merc sucked the air out of it shortly after taking off and started running rough. The bulb and hose are over 10 years old, so I think it's high time that they get replaced anyway ( plus, I got the 20 gallon tank installed finally with new copper fuel line to the bulkhead and it's going to need a new line anyway... Hopefully I can report back with the all is well. I can't imagine that the ignition system is giving me fits suddenly since I only messed with the fuel system. I might install a fuel pressure gauge on it as well.

 

[redfury]

Well, it sat and ran for 20 minutes @ idle and just kept running. It's not overheating, I felt the water coming out, it was nice and hot like it should, but the head felt warm, not hot at each cylinder...fairly consistent at each cylinder. I guess I will save up a little extra and get the fuel line and bulb for the permanent tank and see how that goes, if I get a chance this year. I'm wondering if the battery might not be an issue, it struggles to turn the starter motor over and I lost a 45% charge over the last week. I tested the cells specific gravity and I had most of them in the fair territory with only a couple being "good". Might be time for a new battery as well.

 

[jerryjerry05]

No Title

The "NEW" battery's can last 3 years, if your lucky.
​My Suburban, diesel had new batteries in 2014 one went bad last month.
The other tested good so I'll hope it last another year.

​I have a battery in my boat that was made in 2008 and still holds a charge.???

​I bought a load tester at Harbor Freight $20
​That's one of the better tools I bought.

​Another tool is a heat gun. $16 Amazon It REALLY comes in handy when I suspect a blockage in the cooling passages.
​I used to use the touch method when checking for overheat.