98 Force 40hp Hard to Start and Intermitten Hesitation at WOT

robert0209

Cadet
Joined
Aug 3, 2007
Messages
15
Hi everyone, I'm hoping the mechanical experts here can help me out.

BackStory: I recently had a problem on the water when the screw at the bottom of the carb bowl came loose. I was able to hand tighten it that day to get back. Once home, I removed the screw, inspected the gasket on the end of it, and then put the screw back on and tightened it up. I also replaced the small hose going from the carb bowl to the choke solonoid at the same time. Primed everything up and had no leaks.

Problem: The first outing after this repair, I noticed that the motor was harder to start, but after a couple of tries, it would fire up and we were on our way to the next spot. This happened every-time I stopped and fished for a while. I also noticed that the motor would have a slight but noticeable hesitation after reaching WOT. You can feel boat hesitate for a split second, then return to normal. The GPS speed doesn't show a change in speed when the motor hesitates, and the tach will either show no change, or a very slight drop on the rpm needle.
On this trip, I notice the carb bowl gasket was leaking. I ordered a new gasket. But I went ahead a removed and check the carb bowl to make sure it wasn't something that caused it when I did the previous look. Primed and checked, everything seemed solid.

The second outing went a little worse. It took several tries and several minutes to get it fired up at the ramp. It did get going though. After fishing our first spot for a couple of hours, we went to move and the motor would not start at all. I took a look and noticed a some fuel equal to a couple of drops in the carb throat. Fished for another hour and tried it again. Would not start. Let it sit for a while longer and tried one more time out of desperation. After several tries, it started, but would only idle for a few seconds and then die. I ended up having to jam it into gear the moment it fired to keep it going. Hit WOT and everything seemed fine except for that intermittent hesitation.

Additional information: I ran a compression test, and it showed 95PSI in the top cylinder and 110psi in the bottom. Those compression numbers aren't too bad for a 98 is it? I also noticed while doing this that the brand new plug in the top cylinder that I had replaced prior to the last outing already had carbon build up. Also, while replacing the leaky carb bowl gasket, I measured the float. I read on this forum that it should measure 1/2 inch from carb (upside down) and 5/16 inch from carb right side up. The float measured exactly 1/2 inch upside down, but measured 9/16 inch from carb right side up. Is this a problem?

Does anyone have any idea what the problem might be? I will be running stator tests today or tomorrow to rule those out, but I'm thinking the problem is fuel related.

Any help or advice at all is greatly appreciated.
 

robert0209

Cadet
Joined
Aug 3, 2007
Messages
15
Re: 98 Force 40hp Hard to Start and Intermitten Hesitation at WOT

Sorry, a couple more things. The primer bulb does get hard and stays hard. Also, I replaced the fuel filter, but the old one was not junked up at all.
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
18,183
Re: 98 Force 40hp Hard to Start and Intermitten Hesitation at WOT

98/40 Has a primer/enricher system.
It has a diaphragm that can go bad.(pinch off the line as you run)
Also the fuel pump diaphragm can go bad.(Pull and check)
95# 110#done with both plugs out?(retest with different gauge)
The comp should be 145# with a good gauge.
Possible the carb is dirty?
Spark good on both cylinders?
 

robert0209

Cadet
Joined
Aug 3, 2007
Messages
15
Re: 98 Force 40hp Hard to Start and Intermitten Hesitation at WOT

Thanks for your reply Jerry. I'm concerned about the compression numbers. The compression gauge I used was brand new right out of the package. I'll retest, but I fear that my original numbers will stand. I'll restest compression today as well as do the spark test and post results.

So, I'm guessing that if my compression PSI doesn't come up, it means this motor is a goner?
 

robert0209

Cadet
Joined
Aug 3, 2007
Messages
15
Re: 98 Force 40hp Hard to Start and Intermitten Hesitation at WOT

I inspected the carburetor and everything looks good albeit I'm certainly not an expert with such things. The inlet needle is not worn, is free from debris or trash, and everything else seems fine. I adjusted the carb bowl float a little downward to see if that would help. Put everything back together and tested. The engine fired up almost immediately, but only ran for a few seconds and then died. It tried to start a couple more times, but would only run a few seconds. I inspected the carb throat, and there was fuel standing in it. Way too much fuel. So much so that it actually poured out of the carb throat for a good couple seconds.

Also, I went to inspect the primer/enricher diaphram but could not determine exactly where its at. Can you describe the location of this diaphram? Again, thanks for any help.
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
18,183
Re: 98 Force 40hp Hard to Start and Intermitten Hesitation at WOT

pump.jpg

Follow the gas line in.It should go to the pump.
Take the pump apart and check the diaphragm.
If the ball is getting hard, the pump is probably ok.
Won't hurt to look.
#13 is the primer.
The diaphragm is inside the primer and isin't serviceable.
It has an IN and OUT line.
Pinch off the out line.

The air/fuel mix screw needs to be set at 1 and 1/8th turns out.
It controls the air/fuel for idle.
 

robert0209

Cadet
Joined
Aug 3, 2007
Messages
15
Re: 98 Force 40hp Hard to Start and Intermitten Hesitation at WOT

Thanks Jerry. I will inspect that and pinch off the out line and report back. Also, I wasn't able to successfully test the stator by myself (even though I tried). I will get a helper and conduct a proper test this weekend. I was able to hook up an in-line spark tester with the light in it. The engine started on both tests. The top plug showed a solid light, however the bottom plug, I noticed the light flickered more instead of stay solid. Maybe I have a fuel and an electrical problem?
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
18,183
Re: 98 Force 40hp Hard to Start and Intermitten Hesitation at WOT

Location? Profile?
You might be close to someone who can help?
 

robert0209

Cadet
Joined
Aug 3, 2007
Messages
15
Re: 98 Force 40hp Hard to Start and Intermitten Hesitation at WOT

This weekend's Update: This weekend I was able to get the engine starting and idling perfectly on muffs. I'll test it next weekend on the water. I did a couple of things. First, I noticed I had a bad connector on one of the yellow wires coming from the stator. I don't believe this contributed to the starting problem, but I fixed it when I found it. Second, I re-adjusted my carb float. After the re-adjustment the engine would only sputter and not start, BUT the carb was no longer being flooded with fuel. At this point, I checked the mixture screw. I didn't think to check it before, because I haven't touched it from when it was running fine. Evidently, I must have somehow managed to mess up the mixture screw settings while monkeying with the carb, although I don't know how. The screw was only 1/2 turn out. I adjusted it to about 1 1/4. Engine fired up immediately and idled perfectly. No sputter, no bog, no acting like it's going to die, just solid idle. I revved the throttle a couple of brief moments to make sure no problems would arise with rpms going up, and it sounded perfect.

I'm feeling optimistic that next weekend's run to the lake will be a good one. I'll give a final update if that's the case.
 
Top