Trigger Loose? can only get 3200 RPM WOT- Video included, need your advice.

[GrindKore]

Hi guys, I have been trying to figure out why this motor (1990 Force 90) will not rev up more than 3200RPM at WOT for some time now. Checked everything I can think of;
Spark Tester ? Good spark on all 3 cylinders
Spark plugs ? Good condition, not too dirty and not too clean
Compression ? 120s for all 3 cylinders

This motor starts up right away, idles great, perfect by all means except will not go faster than 3200RPM. I have tried 17P, and 15P props, did not make much RPM change at WOT. I was setting up to do link-n-sync to make sure timing is correct when I have discovered this free play on the trigger when throttle is in the WOT position. Is this normal?

Here is the link to a video clip http://www.youtube.com/watch?v=26PVC9uenVY

 

[jerryjerry05]

Re: Trigger Loose? Video included, need your advice.

Re: Trigger Loose? Video included, need your advice.

The trigger moves.That much is nothing.Is the throttle opening all the way?How fast are you going? Are the carbs all opening to the max.Move the throttle all the way forword and see where the linkage and throttle cam are.Post another u-tube with pics .J

 

[GrindKore]

Re: Trigger Loose? Video included, need your advice.

Re: Trigger Loose? Video included, need your advice.

The trigger moves.That much is nothing.Is the throttle opening all the way?How fast are you going? Are the carbs all opening to the max.Move the throttle all the way forword and see where the linkage and throttle cam are.Post another u-tube with pics .J

The throttle does open all the way. With 19P prop and two people on board I top out around 30 MPH (GPS). This is a small 16' boat, I don't think 19P is lugging it. Furthermore, I have borrowed 17P, and 15P props and had similar top RPM results.

Its as if there is some kind of RPM governor restricting this thing from accelerating past 3200 RPM (I know no such thing exists on my Force). I have even purchased an optical tachometer to eliminate tach as an error source, I'm 100% confident the tach is correct.

 

[john from md]

Re: Trigger Loose? can only get 3200 RPM WOT- Video included, need your advice.

Jerry,

You may have posted this before. Where is your timing set and did you set it using the starter motor procedure?

John

 

[Matthew A.]

Re: Trigger Loose? can only get 3200 RPM WOT- Video included, need your advice.

Although you mention there maybe excessive trigger freeplay, have you checked the timing? Spark set too retarded will kill engine power on Force engines. 5 degrees out and the motor will perform extremely poorly at more then 1/3 full throttle settings Although, you mention that you are getting spark on all three cylinders a bad CDI module will make the boat run as if it has a rpm limiter. Around 2700 to 3200 rpm or about 2/3 of full power/rpms. Even though may continue to start beautifully and idle even better.
Also an air/fuel mix set to rich may be the culprit. Especially when combined with a spark advance that is set low. If the motor has been recently rebuilt, both air/fuel and spark advance may have been set in such a manner. Setting the air/fuel mix on the rich side and retarding the spark advance to 25BTDC or so on these engines during the break in procedure on a newly rebuilt powerhead is recommended by Force to keep the motors hp to a minimum until the parts have broken in and no longer creating to much heat from friction.

 

[GrindKore]

Re: Trigger Loose? can only get 3200 RPM WOT- Video included, need your advice.

Although you mention there maybe excessive trigger freeplay, have you checked the timing? Spark set too retarded will kill engine power on Force engines. 5 degrees out and the motor will perform extremely poorly at more then 1/3 full throttle settings Although, you mention that you are getting spark on all three cylinders a bad CDI module will make the boat run as if it has a rpm limiter. Around 2700 to 3200 rpm or about 2/3 of full power/rpms. Even though may continue to start beautifully and idle even better.
Also an air/fuel mix set to rich may be the culprit. Especially when combined with a spark advance that is set low. If the motor has been recently rebuilt, both air/fuel and spark advance may have been set in such a manner. Setting the air/fuel mix on the rich side and retarding the spark advance to 25BTDC or so on these engines during the break in procedure on a newly rebuilt powerhead is recommended by Force to keep the motors hp to a minimum until the parts have broken in and no longer creating to much heat from friction.

How is it possible for CDI to continue to function while limiting RPM? I thought these were basically a solid state capacitors. Do they "fade", my DVA meter is showing good peak voltage, although I can only test it on the muffs in the driveway. I did buy spare 1990 FORCE 90 ignition system with all the CD modules, stator, and trigger on eBay last year. However I'm not sure what is wrong, I don't like replacing parts if not 100% sure they have failed.

BTW, I have rebuild carbs last season and have followed Frank's and CLYMERS advice on mixture settings. I'm confident my mixture setting is correct. All three carbs are roughly 1 and 1/3 turns out from fully seated, just a tiny bit more on a rich side.

 

[john from md]

Re: Trigger Loose? can only get 3200 RPM WOT- Video included, need your advice.

Grindkore,

I'm sorry, I directed this to Jerry earlier. What is your timing set at and was it set using the starter motor or set when the engine was running?

John

 

[MikDee]

Re: Trigger Loose? can only get 3200 RPM WOT- Video included, need your advice.

Is the spark advance rod moving with the throttle? The plate you're jiggling, does the spark advance rod move it clockwise to full advance when you open the throttle? Is it connected? It don't look like it in the video?

 

[Matthew A.]

Re: Trigger Loose? can only get 3200 RPM WOT- Video included, need your advice.

Within the CDI module there is set of diodes that is used to prevent the module from signaling two coils to fire at the same time when either channel receives a signal to fire from the trigger assem. These diodes tend to be sensitive to high voltage spikes and reversed polarity which can cause them to fail. The OEM modules tend to be especially sensitive to such and are known to fail because of it.
When either of these diodes fail the module will continue to operate but only one channel will do so.
It's not that the CDI module then puts a limit on your motors rpms Your rpms become limited because of the loss of power from not running on all cylinders. If a blown module is the culprit.

 

[GrindKore]

Re: Trigger Loose? can only get 3200 RPM WOT- Video included, need your advice.

Is the spark advance rod moving with the throttle? The plate you're jiggling, does the spark advance rod move it clockwise to full advance when you open the throttle? Is it connected? It don't look like it in the video?

Yes, it is connected and is advancing with throttle. The throttle cam and roller are aligned and from what I can tell are moving trigger assembly as they should.

 

[MikDee]

Re: Trigger Loose? can only get 3200 RPM WOT- Video included, need your advice.

I doubt the play you see is an issue. The arm I see with the bend in it that appears to be the spark advance rod, and it does not look like it is connected, & moving the advance plate to the left all the way?
For some reason, where the advance plate is located in the video, it looks like it's at the idle position, not fully advanced?

 

[GrindKore]

Re: Trigger Loose? can only get 3200 RPM WOT- Video included, need your advice.

Within the CDI module there is set of diodes that is used to prevent the module from signaling two coils to fire at the same time when either channel receives a signal to fire from the trigger assem. These diodes tend to be sensitive to high voltage spikes and reversed polarity which can cause them to fail. The OEM modules tend to be especially sensitive to such and are known to fail because of it.
When either of these diodes fail the module will continue to operate but only one channel will do so.
It's not that the CDI module then puts a limit on your motors rpms Your rpms become limited because of the loss of power from not running on all cylinders. If a blown module is the culprit.

I took your advice today and swapped out the entire ignition assembly with a spare I had. It runs well on the muffs in the driveway, later today I'm going to test it out on the lake.

 

[mmclemore]

Re: Trigger Loose? can only get 3200 RPM WOT- Video included, need your advice.

Is the spark advance rod moving with the throttle? The plate you're jiggling, does the spark advance rod move it clockwise to full advance when you open the throttle? Is it connected? It don't look like it in the video?

I have the same issue (low RPM at WOT) but it is because of a broken plastic piece that connects the 'towershaft' to the spark advance rod. Do you know where I could find a replacement. I have the 125 hp Force on an '89-19' Bayliner Capri Ski.

Thanks

 

[MikDee]

Re: Trigger Loose? can only get 3200 RPM WOT- Video included, need your advice.

I had to replace mine as well, got a replacement at a Mercury- Mercriuser dealer.

 

[Frank Acampora]

Re: Trigger Loose? can only get 3200 RPM WOT- Video included, need your advice.

If all else tests ok, then you need to check crankcase base compression. This is how much the pistons compress the air/fuel mixture within the crankcase to blow it up into the combustion chamber. This ratio will also affect how much charge the piston inducts through the reeds. It is difficult to check but since the fuel pump should deliver between 2 and 6 psi you would expect that crankcase compression would be similar. With all the spark plugs removed, you should be able to feel it as resistance when you turn the flywheel by hand.

Low crankcase compression can be caused by broken reeds, more than .010 opening (clearance) when the reeds are closed, too much piston skirt clearance in the cylinder, and leaking between crankcases through the center bearing seals.

If that 1990 has the rubber covered reed blocks with 4 petal squared end reeds, the rubber tends to distort and crack, causing significant leaking. Those reeds were prone to damage anyway so if you do have them, replace the reed blocks and reeds with the older style 5 petal round end reeds. The slight loss in power will be more than offset by longevity.

Since with low crankcase compression the maximum charge is limited, it will manifest itself as low horsepower yet the engine may start and idle fine.