1997 Force 120 bogging at WOT, but not every time....

AZJamie

Cadet
Joined
Oct 30, 2016
Messages
6
Attempting DIY repairs on my motor..after reading what must be every post about the topic, I'm breaking down to see if anyone has any new ideas to save the trip to the shop...thanks in advance, and thanks for all the great info I have already gotten from these boards!
I have a 97 force 120 on a 97 Astro 17ft bass boat..ran pretty well last few years but started bogging at WOT a few months ago. Here's the catch, she doesn't bog down every time, it's more like 2 out of 3 times. Sometimes she will get up and go like normal and run great pushing 40mph as usual. She might take off great at launch, or not, or after fishing for an hour, or not. I can give her throttle 2-3 times in a row and she bogs, then after idling another few minutes, I give her throttle and she responds.
Out of water, in the driveway on muffs, she runs and sounds great, starts, idles, never dies, in and out of gear smooth...so it seems like an under-load situation. In water, she starts fine and will idle all day, but when I try to get on plane, she doesn't have the power. Seems like a fuel starvation issues, but with the work already done, and the fact that sometimes, she does get up on plane, it makes me wonder if I am missing something.
What's been done since it first happened...
Replaced Stator, Trigger, CDI units and voltage regulator ( this work done as side job by mercury tech who thought it might be electrical / spark issue. I had used him to do my lower unit previously. Didn't fix the problem this time and I'm not comfortable going back to him to pay for more non-fix repairs)
replaced in-line fuel filter
re-built fuel pump
replaced squeeze ball
inspected all fuel lines, no issues or blockage, re-installed fuel lines with new clamps, zip ties to ensure no leaks
Carbs- took apart, replaced gaskets, cleaned, they were both super clean with no varnish at all..floats are good, no seating issues.
With motor running. sprayed gas/oil mix into carbs, and motor would begin to die, as it should
No gas tank venting issues, pick-up in tank is clear, gas is good/fresh (its a 50:1 oil gas mix)
Visual reed inspection when carbs were off..looks good, clean
Compression is 130-140 all 4 cylinders....got new plugs, they are all dirty after use, but not wet or oily.
carbs are synched, butterflies open equal at full throttle
removed prop, no obstructions..(.impeller was replaced 2 seasons ago)
I have not done any adjustments while on the water, just on muffs.

I guess I am hoping someone might be familiar with the intermittent bogging and might have any more ideas what to check.

Thanks again...

AZJamie
 

pnwboat

Rear Admiral
Joined
Oct 8, 2007
Messages
4,251
Is the in-line fuel filter the clear see through type so you can clearly see the fuel flowing (or not flowing) to the carbs?
 

AZJamie

Cadet
Joined
Oct 30, 2016
Messages
6
Thanks for the response....
The filter is clear..it is between the fuel pump and the carbs...squeezing the bulb, you can see fuel flow, but I have not looked at it while the motor was in the water running.
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,923
IF?? the motors running at wide open.
Then it sounds like it's getting fuel and you replaced the filter so it shouldn't be the problem.
​The tank, can you see the bottom? Run it till it's close to empty.
Then check the bottom of the tank and see if there is anything in there??
Sometimes you can have a floater and it only clogs the pick up sometimes??
If you find anything in there?? the tank needs to be emptied and cleaned.
​SAFETY first. Latest thing on the news was a person trying to vacuum up spilled gas, BOOOOM
​Years ago I had a motorcycle tank that had a leak.
​I flushed that tank 5 times. The guy welding it waved a torch over the tank and it burned the fumes that don't go away.


​The next time you go out, unhook the tach and see if that helps.?

​The fuel we run has Ethanol in it.
The E melts the inside of the hoses and you can't see the damage.
​Check it for soft or mushy spots, better yet replace it all.

The carbs can be very touchy too.
​I rebuilt and cleaned a carb 3 times and it wouldn't run right.
​Did the same thing all 3 times.
The 4th time I cleaned it again and it worked????
​The complete system was spotless BEFORE I started.
Never did see what was in there??


Oh yea Welcome.
 

AZJamie

Cadet
Joined
Oct 30, 2016
Messages
6
Thanks JerryJerry05....
I will double check the tank...I previously pulled out the pickup hose from the gas tank...it was clean and the filter/screen in the end of the hose was clean as well, but I will check for any floating solids..
The hoses are all in good shaper from the tank to the carbs..no interior damage from ethanol...
I can certainly double check the carbs with a good overnight soaking instead of just cleaning.


On another note...do you guys thinks its worth it to buy a tank/tub to test the motor vs. just the muffs. Will a tank simulate running under load more than the muffs, or are they pretty much the same effect?

Thanks....I really appreciate the feedback.

AZ Jamie
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
When you sprayed gas/oil mix into the carbs was the control lever in full WOT position? If it was in WOT position, it means it is not fuel related at all. However, if it was only idling or not in full WOT position, you might want to do a test again with control lever in full WOT position. Obviously you would have to do this while in the water with the top cowling removed. You also might want to have another guy do the driving.

You want to do the test when the symptoms are occurring meaning when it will not go to full speed. If after spraying and she jumps out of sleep, then it is fuel related. If not, then you can rule fuel out. This will allow you to focus on other causes. FYI 2 stroke engines do not perform well for long idling. It tends to pool unburned fuel in the crankcase cavity causing too rich of a fuel mixture.
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,923
Running in a bucket or hose?? No real difference.
​You'd need a special test wheel to test in a bucket, and a HUGE bucket.

​When the carbs are off, check the reeds to see if they are ok.
Also check the vent hose for sharp bends.
It should have a loop but no sharp bends.
 

AZJamie

Cadet
Joined
Oct 30, 2016
Messages
6
Jiggz....I was on the muffs when I sprayed the gas/oil into the carbs..just 1/4 throttle. I will try at WOT on the lake this week. Great tip! Also thanks for the long idle info, that would explain why she likes to stall when I take her out of gear after a while of idling.
JJ05....I figured as much on the bucket vs hose theory..and the reeds looked great when the carbs were off. Also no venting issue, even opened the gas cap to confirm last time out and there was no change in performance.
Looking to get her on the water this week..I will test the things you all mentioned when I do..maybe even post pics or videos.

Thanks very much!!!

AZJamie
 

AZJamie

Cadet
Joined
Oct 30, 2016
Messages
6
So, it's been a few weeks and I was finally able to get back on the water to test a few things in search of my Bogging at WOT issue. I went out the other day to try more troubleshooting, and when I tried to start the motor, she wouldn't turn over. (Previously she would start and idle, just usually bog at WOT) Tried her with neutral throttle, and would start for a second and die. I took off the cowling and noticed gas coming from the top carb, so I trimmed up the motor and proceeded to fish for a few hours with just the trolling motor. Got home and dove into the carbs again. Took off the top carb to find the entire reed assembly was cracked!! Removed the upper reed plate and found 1 assembly cracked and the other assembly had a reed petal broken off. Checked the lower reed assembly and found one reed petal broken. So I am taking the good petals off the cracked reed assembly to replace the other cracked ones, and there is a local shop that happens to work on older motors so they have a new reed assembly in stock that already has the petals. So I am hoping that replacing the reed assembly and broken petals gets the old Force running as good as new..and if not, I at least resolved one more issue through the process of elimination.. I had previously looked at the reeds and hadn't noticed the broken petals and didn't see the cracked assembly after carb removal, so for anyone else checking, take off the reed plate to really confirm the condition of the reeds.
First pic is view of upper cracked assembly, 2nd and 3rd are looks at the cracked assembly after removal. 4th is the lower reed plate showing one cracked petal and last one is motor with both reed plates removed.

Thanks for all the help and I will post results asap..

AZJamie
 

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jerryjerry05

Supreme Mariner
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May 7, 2008
Messages
17,923
You need to figure out why?
​The breaking of the reed bracket is puzzling ??
Any damage past the front area?

Maybe check the timing after it's all back together??
Make sure the recirc system hoses aren't blocked?
 

Grub54891

Vice Admiral
Joined
Jun 17, 2012
Messages
5,908
Everything was fine on the one I repaired, except the reeds. The owner said he looked in to it a bit, and them reeds are prone to breaking. I did not research it myself, just replaced the reeds and checked synk and link/timing.
 

AZJamie

Cadet
Joined
Oct 30, 2016
Messages
6
Reeds! Reeds! Reeds!..So I got the new reed assembly to replace the cracked assembly..I took a few reed petals off the old assembly and used them to replace a few other cracked ones I had found...I tested the motor on muffs in the driveway and she ran and idled great, and I am happy to report that I put the old Astro in the lake today, and that 1997 Force 120 ran like she never has before. Started right up, idled beautifully and when I gave her a little throttle, she responded with more power than she has since I got her a few years ago. I was up on plane in a few seconds and she hit 43 mph at 5200 rpm, WOT.
Another story with a happy ending, and I owe a ton of thanks to all of the info I got from the Force Forum on iBoats. Thanks for all the tips and help!!!
 
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