1990 Force 50hp will not get to high RPM

[roadkingkid]

I inherited this little 4 seated Bayliner, redid interior and the lower unit was gone. Found a used one on Ebay, Engine runs great till you put it in gear. Will not get to high rpm, but runs smooth carb. butterfly full open, main jet clean. Had a 12-1/2 pitch prop on it, changed to a 10 which is the lowest. Still not to full rpm or plane. Installed Hydrofoil, a little better bow came down but still will not get to a cruising speed. Engine seems to be only running 1/2 throttle, confirmed it carb. is wide open while in gear in the water. Is there different ratio's of gears in the lower unit causing it to load the motor to much? The boat is rated for the 50hp engine according to the coast guard sticker.
1990 Force by US Marine model 507X90D s/n 023612

 

[legalfee]

Try disconnecting the two wires from the stator to the rectifier / regulator and see if it runs full RPM. If it does replace the rectifier / regulator. And don't get a cheap one. Get a CDI.

 

[jerryjerry05]

They only made one gear housing for the 50 all were using the same gear ratio.

First thing is get tachometer.
Or get a tiny tach.
They sell on e-bay.

Do a spark and compression test.

Hood it up and go for a ride.
Record the readings as you go.

Take the cover off.
The linkage, as someone drives go to full throttle, you reach and push the throttle on the carb and see if it can go farther.

Post the results of the tests.

How big a load is on the boat??
3/4 people, 2 dogs, cooler and 2-3 cans of gas??

Do the test with 2 people and the coast guard equipment a 1 can of fuel.

Was at the ramp one day and saw a guy in a 15ft. Bayliner.
He was complaining about the performance.

On board was 4 people, 3 humongus girls, a big cooler a day and 12 gal. gas.

It's only a 50hp and this guy was expecting a drag boat.

 

[Jiggz]

Personally, I'll do the following in the listed order:
1. Do a cylinder drop test. If anytime the engine dies during the test, you're most likely not firing on all cylinders.
2. Compression test
3. Make sure the choke butterfly valve is in neutral (full horizontal)
4. Verify the throttle butterfly (way back at the throat of the carb and probably need a flashlight to see it clearly) goes to full horizontal with the throttle control lever at WOT position. Do not rely on the external lever of the throttle butterfly instead check visually inside.

 

[roadkingkid]

Thanks Guys will do a spark test, but engine seems to run smooth.
Jerry
Compression was 95psi both cylinders, prior to starting it after sitting for 5 years, did not recheck after starting it.
Manually checked that Butterfly was horizontal at full throttle position both static and running
Load was only me 180lbs
6 gallon fuel tank 1/2 full, fresh gas
When I redid the floor I did not take the soaked foam out from under the seats, would not have been much, but did the rest.
put a little more bracing under new floor but not excessive, same thickness of plywood.

 

[roadkingkid]

The little boat just seems heavy in the water and short of power.

 

[kbh121956]

95 lbs is low, try a different gauge. Decarb the engine, easy to do. Mercury has a powertune spray. After decarb recheck your compression. As Jerryjerry05 said the 50 will run great on only one piston firing.

 

[jerryjerry05]

What size prop?
What rpm's at wide open?

 

[legalfee]

HIGH SPED MISS FIRE OR WEAK HOLE SHOT: 1. Connect DVA meter to the blue and blue/white wires and do a running test. The voltage should show a smooth climb and stabilize, gradually falling off at higher RPM's (above 3000). If you see a sudden drop in voltage right before the miss becomes apparent, the stator is likely at fault. Repeat the test for the red and red/white wires. There should be a smooth climb in voltage with no drop at all up to wide open throttle. 2. Connect DVA meter to the red and red/white wires. The voltage should show a smooth climb throughout the RPM range, a sudden drop or decline in voltage indicates a problem usually found in the stator, although a rectifier can cause the same symptom. 3. Disconnect rectifier/regulator and retest. If the problem disappears, replace the rectifier/regulator and retest. 4. For a high speed electrical miss, rotate the stator one mounting hole and retest. If the miss is still present the stator may be bad

 

[jerryjerry05]

95# is low but both at 95 is probably the way the test was done or the gauge.

 

[Jiggz]

Do the cylinder drop test, i.e. pulling off plug wires one a time while the engine is idling and listen to change in engine tone. If no change in engine tone with one plug wire pulled, then it tells you that cylinder is not firing at all. If it continues to ran with either cylinder with slight change in engine tone, then the next step is to check for timing. It' not unusual for people new to 2 cycle engine to claim a smooth running engine despite one cylinder not firing.

 

[roadkingkid]

Well finally got to look at the engine, and did the spark checkk. Sure enough the Top cylinder is not firing. I would have lost money if someone would have bet me. Been around all kinds of engines my whole life and wrenched on them all, but never seen a two cylinder engine run smooth on one cylinder. Will check the coil 1st, then the trigger.
Thanks for all the great advise, will let you know how it comes out.

 

[roadkingkid]

Swapped the coil primary input and output, problem stayed with the top cylinder, so will move on to the trigger. Looked at youtube to se how to check and everyone they showed only had two wires, mine has four. Anyone know how to test it off the engine?

 

[Jiggz]

The quickest way to check for the trigger is to do a resistance check. By comparing one reading with the other it'll give you a very good indication which sets of trigger wire is not working. And most of the time, NOT EVERYTIME, the cause is either broken wire (caused by corrosion or rubbed off the flywheel) or poor terminal connections and seldom it is a burnt trigger coil. For the 89-92 50 HP, trigger resistance should be around 48-52 ohms. Make sure when conducting readings that at least one of the wires you are testing is totally disconnected.

If resistance is good, the next best check is to do a voltage output check but this requires you to use a DVA as the voltage is low and quick. I believe the 89-92 50HP came either with the T-bolt or Prestolite ignition system.

If you have the Prestolite, try switching the two CDM circuits between #1 and #2. Note when you do this, you switch both the input trigger wires and also the output wires going to the ignition coils. If the problem stays at #1, the problem is not the trigger nor is it the CDM but likely the ignition coil. If the problem follows to #2, then most likely the #1 (original circuit) on the CDM is bad, assuming the resistance of the trigger wires are good.

 

[legalfee]

NO SPARK ON ANY CYLINDER: 1. Disconnect the stop wire AT THE POWER PACK. 2. Disconnect the rectifier. If the engine sparks, replace the rectifier. 3. Check for broken or bare wires on the unit, stator and trigger. 4. Check the stator and trigger resistance and DVA voltage as follows: WIRE READ TO OEM RESISTANCE CDI RESISTANCE DVA Brown/Blue (or Blue) Brown/Yellow (or Yellow) 680-900 250-350 180-400 V Connected Brown/Blue (or Blue) Engine GND Open Open < 2 V Disconnected Brown/Yellow (or Yellow) Engine GND Open Open < 2 V Disconnected White/Orange (or Orange) White/Yellow (or Green) 45-55 45-55 0.5 V + Connected White/Red (or Red) White/Green 45-55 45-55 0.5 V + Connected

NO SPARK OR INTERMITTENT SPARK ON ONE CYLINDER: 1. Check the stator and trigger resistance and DVA voltage (see NO SPARK ON ANY CYLINDER above). 2. If readings are good, disconnect stop wire from the pack. If the dead cylinder starts sparking, the problem is likely the blocking diode in the pack.

 

[jerryjerry05]

The trigger wires are very thin and can break under the shrinkwrap.
Try pulling on them and see if one comes out?
outboardignitiondotcom has test procedures.

 

[roadkingkid]

legalfee, will try that. Was running on one cylinder, swapped coils problem stayed. Purchased new trigger, installed last night, now have lost all spark to both cylinder. Going backwards,,,ha

 

[roadkingkid]

Finally got it going after changing several parts. last to change was the CDM, that was it.
Thanks for all the help.