1990 force 150 running issues

[Shifflett115]

I have a 1990 force 150 , compression is great , runs great on all cylinders , wot is about 5000 rpms , once in a while it won’t reach 5000 at wot , why is that ?????

 

[pnwboat]

Which ignition system do you have. That motor came with two types of igniton systems. Prestolite with the 5 sky blue coils and 3 sky blue CD modules, or the Thunderbolt with the 5 really dark blue coils and a Switchbox ignition module?

When it's acting up, what RPM does it get to? Is it just below 5000 RPM, or is it significantly lower?

My first instinct is to suspect either fuel delivery or ignition system problem.

I would suggest to try the simple, inexpensive solutions first.

1. You said you checked the compression but what exactly are the compression numbers?
2. Make sure the fuel pump primer bulb gets firm after 4 or 5 squeezes. This would indicate that it is probably working OK, and that the needle valves in the carburetors are seating properly. If it doesn't get firm and gas starts leaking out of one or more of the carb's, then you may have a bad needle valve or a float adjustment is not set correctly.
3. Check the fuel pump diaphragms in both fuel pumps. You might try squeezing the primer bulb while underway while it's acting up. This pumps more fuel to the carbs. If this fixes the problem, then you may have a bad fuel pump diaphragm(s).
4. Make sure the gas tank vent tube is open and not plugged.
5. Check the spark on all the plugs with a spark plug checker. You should have a strong snappy blue spark.
6. If you have the Thunderbolt ignition system, make sure your battery is fully charged. Unlike all of the other Force ignition systems, the 5 cylinder Thunderbolt ignition system uses the battery voltage instead of the stator under the flywheel to generate spark.

 

[foodfisher]

Failing tach? Corrosion at connections?

 

[jerryjerry05]

The 90 150 should have the Prestolite Ignition System.
The trigger, the connectors, the wire and shrinkwrap can be a problem.
The wire breaks under the wrap and when it gets hot or during acceleration the
connection can break down causing a miss.
Try pulling the wire GENTLY and see if you can wiggle one or more free??

The screw down connections, make sure they're all tight and not burned.
Check the back of the packs for burned spots.
Check the connections/ grounds on the coils and packs.

When it doesn't get to top rpm's does it miss or run different?

The early 150's didn't have a filter in the fuel system.
This allowed tiny pieces of crud to get in the bowls of the carbs.
Fram G-2 G-3 G-12 will work in your system.
Install it between the second pump and the first carb.

You have a primer system instead of a choke.
The primer can cause excessive fuel to be sent to the carbs.
This can cause it to break down and not work right?