Troubleshooting 1993 Force 150

[HotTommy]

Disregard

 

[pnwboat]

You probably do need a new flywheel. The stator on you motor is only used to charge the battery. You should only have two yellow leads coming off of the stator that go to the Rectifier/Regulator. Seeing how this ignition system is battery powered, there is a chance that this may be the cause of your problems. Looks like you were probably just running off the battery as your charging system was not working. The two stator leads should read about .5 OHMs. Almost a dead short but not quite. If thats what it reads, it should be OK.
http://www.ebay.com/itm/NOS-OEM-Genu...90fce8&vxp=mtr

 

[HotTommy]

I'll check the stator when I get home. ... Meanwhile, here's my half baked theory. I assume the six magnets I saw were supposed to be adhered to the flywheel. I also understand the trigger assembly gets its signal from magnets on the spinning flywheel. Is it possible the missing/misplaced magnets are sending mis-timed signals to the trigger assembly? If so, I envision it affecting the spark timing and engine performance. How's that theory hold up under scrutiny?

 

[Jiggz]

Yup, ditto with PNW on a new flywheel or even a used one with all magnets still intact.They have some on *bay you might want to grab one. There's one in there stating it is for a 150HP Prestolite for less than $70! The truth either prestolite or t-bolt flywheels are the same. Double check though but I'm sure they are identical.

Edit: After examining this flywheel it does look different starting with the magnets which seems to be missing.

 

[pnwboat]

Almost right except the magnets that are broken/loose are just for the charging coils on the stator. The trigger magnet is the circular collar around the hole in the middle of the flywheel.

 

[Jiggz]

Ditto again. The main caused as indicated by the broken/missing magnets is the low charging in the stator. With only two magnets in place vice 6 the charging capacity was reduced to a third thus draining the battery at higher rpm. Here's a used flywheel at *bay for a bargain.

 

[HotTommy]

I'll check the circular collar when I get home. There was lots of debris from the one magnet that had come apart. It's possible some of it is interfering with the signal from the collar.

 

[Jiggz]

Double check the trigger and stator for any insulation or wiring damage also.

 

[HotTommy]

An update and an apology. It's tough enough for you guys to diagnose something from a written description. It's even tougher when some of the information I provided was wrong. I started getting suspicious of some of the readings from my old multimeter so I bought a new one. Turns out some if not all of the voltage and resistance readings mentioned earlier were wrong. So here is where we are as of today.

I examined and am using the original stator and trigger assemblies. I installed a brand new flywheel. The FSM says the resistance for each of the five trigger leads should be 1100-1400 ohms. Mine range from 1075 to 1300 ohms. ... With a freshly charged battery the non-running voltage was 12.9 volts. The engine cranked and started normally. Volts were about 14.2 with the engine running. It took one or two extra squirts from the primer until it warmed a little. It settled into a good sounding idle. After is was warmed up, I took it briefly to full throttle and adjusted the timing to the factory spec 30 degrees. The engine sounded strong and normal at full throttle and at idle. But there was an obvious miss (like a cylinder was not firing) at mid-throttle. For example, I was running smoothly at full throttle and began to gradually reduce the throttle. As it slowed by what sounded to me like 500-1000 RPM, it abruptly changed sound and thrust as one or more cylinders sounded like they dropped out. As the throttle continued to come down, the miss became less noticeable until I could not discern it at idle. I briefly tried idle mixture screw settings between 1 and 2 turns out at mid-throttle but did not notice any change in the misfire.

I am unable to do any more of the factory tests of the ignition system without a DVA meter. So, who are the usual suspects for an engine that sounds good at full throttle but misses as mid-throttle? Should I go ahead and buy a DVA meter to confirm the condition of the rest of the ignition components. What would you guys do next?

 

[pnwboat]

I don't think I would go out and buy a DVA, at least not just yet.

When you had the carburetors apart, did you happen to notice what size main jets were in each of the carburetors? The top and bottom carbs should have a .094 main jet, and the middle carb should have a .078 main jet.

I got the impression before when you adjust the idle mixture on the upper and middle carb, it made a difference in the engine idle, but the idle mixture on the bottom carb didn't have an affect. Is this still the case?

Make sure the butterflies in the carbs are sync'ed up through out the whole range of the throttle.

Have you checked to see if any trigger wires are not nicked with exposed wires that may be shorting out to the block when you move the throttle?

 

[Jiggz]

When you moved down the throttle from WOT position, basically only two ignition components move with it, i.e. the trigger advancing plate and the throttle linkages. Throttle linkage is easy to diagnose just make sure all the carbs throttles move in synch. As for the trigger, if there is any loose wire or broken insulation that can touch to ground, it can easily cause a misfire. You can do a cold insulation check by touching one wire of each of the set of trigger wires with a probe of an ohmmeter (set to auto) and the other probe to ground. Slowly move the control lever to WOT and back and watch the ohmmeter if it will read any low resistance to ground. Obviously, you will need to do this 5 separate times for each set of wires. Any low resistance to ground should be corrected.

 

[HotTommy]

Thanks for the ideas to both of you. Jiggz, I did much of what you said while testing between each trigger wire and the common, but I didn't think to test to ground. I'll do that next. ....pnwboat, help me understand how the wrong jet size would cause the engine to run better at full throttle than at mid-throttle. It might help me figure out where to look first.

 

[HotTommy]

I tested all six trigger wires over the full range of throttle movement and none revealed a contact to ground.

 

[HotTommy]

I suspect pnwboat's question about the jet size may have been a polite way of asking if I inadvertently swapped two of the carburetors during their rebuild. The short answer is, I don't think so. The longer answer is that I rebuilt each carburetor one-at-a-time and was careful to note which was which. I did not change out the jets, so they each have the jets they came with. Because of the way the hoses connect to the carbs, the only two that could be reasonably switched are the bottom two. I pulled the float bowl off the middle carb and could read the .078 jet size. So I assume the carbs are properly jetted and in the right places.

 

[HotTommy]

I just checked and slightly adjusted the carb sync. It's a difficult job because the bottom carb sits below the lower cowl, making it impossible to clearly see the butterfly. While doing that I noticed that the carb butterflies get most of their movement during last bit of throttle movement. It occurred to me that a carb that was synced to have the butterfly not properly positioned during the first portions of throttle movement might start working a lot better at full throttle when the butterfly finally got fully open. Could the symptoms I described earlier today be entirely a result of an incorrectly synced carb?

 

[HotTommy]

More information. I followed some advice given earlier and ran the following test.
1. With the engine running at a fast idle, I turned each idle mixture screw all the way in, one at a time. The engine coughed and wanted to die when I adjusted the screws on the top two carburetors. I could not discern any change when I turned the screw in on the bottom carburetor.
2. I swapped the trigger wires and the spark plug wires between 1-5 and 2-4. My intent was to have the switch box and coil packs for 1 & 2 firing 5 & 4, but at the right time. I then repeated the idle mixture screw test. The results were the same.

This tells me that either the trigger switches for 4/5 are not sending reliable signals or the carburetor for cylinders 4/5 is not operating properly. My plan is to remove, soak and recheck the bottom carburetor before trying again. If anyone has a better idea, I'd love to hear it.

 

[pnwboat]

If you swapped the trigger and coil wires between 1,2 and 4,5 and it had no affect on the symptoms, then it's not likely an ignition system problem. Like you plan, I'd take another look at the bottom carburetor. Maybe even swap the top and bottom carbs if possible.

 

[Jiggz]

The fact that the bottom carb with the idle mixture screw closed or screwed in all the way and not making any difference with the engine rpm, as you mentioned indicates both cylinders not firing due to bad ignition or carb. You got the same result after switching the trigger wires. One final test will determine if it is electrical or fuel related (carbs) by spraying fuel oil mix directly into the bottom carb. This is better done in fast idle so as to discern changes in rpm. If the problem is fuel related, by spraying fuel oil mix directly into the affected carb, the engine rpm should increase. If the rpm does not increase after spraying fuel oil mix, then the problem is electrical. But if the rpm decreases, it is an indication either one or both cylinders must be working properly and are getting too rich of fuel mixture when you sprayed fuel mix into the carb.

However, after yourswitching the trigger wires and coil wires with no change in rpm is noted, I'll put my money, it is fuel related.

 

[HotTommy]

Jiggz,
I concur with your reasoning. So I ran your test. With the engine warm at fast idle I squirted fuel-oil mixture into the bottom carb. It had no effect. It didn't run better or worse. I did the same squirt on the top two carbs, one at a time. Each time the engine stumbled and lost RPM for a second or two. That tells me the problem is not fuel related. So, it is most likely a problem with the part of the trigger assembly that fires 4 & 5. So I'll be shopping for a trigger assembly today.

 

[Jiggz]

This test that you did, "I swapped the trigger wires and the spark plug wires between 1-5 and 2-4. My intent was to have the switch box and coil packs for 1 & 2 firing 5 & 4, but at the right time. I then repeated the idle mixture screw test. The results were the same."

When you said results were the same, I infer adjusting the bottom carb idle mix screw had no effect on the engine rpm after the wire swap. And yet when you sprayed fuel mix into the same carb, there was no effect either. UNLESS, WHAT YOU ARE SAYING IS THAT ADJUSTING THE IDLE MIX SCREW ON #1 OR TOP CARB (AFTER THE WIRE SWAP) DID NOT HAVE ANY EFFECT ON THE ENGINE RPM, THEN YOU CAN HYPOTHESIZED THE PROBLEM TO BE IGNITION COMPONENTS ON #5.

Your swap test above tested the trigger wires and coils and CDI's on #5 to be working on #1, assuming my inference is correct that the bottom carb stayed the same. The fuel mix spray tested the carb to be working as it did not have any affect on engine rpm, indicating it is a firing and not fuel problem and yet, the previous test indicates all ignition components to be working.

The only components between these two tests are the reed valves assuming there is good compression on both cylinders, i.e. #4 and #5. I wonder if you have verified both.