Confused on Timing with Force 125

[SkiDad]

I have a 1985 Force 125 - i made a post a few weeks ago but it got lost with all the site issues - i found it via google cache and is attached below.

anyhow - my timing was set dead on at 32 degrees static and I adjusted to down to 28 degrees static. Hoping it might give me some more performance. Took the boat for a ride and it seemed to run great - but when i put the whole family along this past weekend and went skiing it seems to have slightly less pulling power to get me up on slalom and my top RPM seems to be down approx 200 rpm. Seems to run smooth overall and mid range seemed to be slightly better when pulling the kids of tubes.

is this my new normal at 28 degrees static or should I put it back to the way she was. I'm thinking that 32 static (34 dynamic) was probably too high but i didn't have any issues running it that way.

One other thing I found is that I had to increase my idle speed - didn't think that was going to be affected.

hole shot with just me and 1 kid: http://youtu.be/3ufBl6IcZPI

View attachment Force 125 - Timing was off 4 degrees.pdf

 

[Jiggz]

I followed your original thread about fine tuning your 125 by lowering the static timing to 28 corresponding to 30 dynamic. I also posted on the same thread with my manual stating 34 is the max timing advance on the 125. Others posted their manual timing settings also supporting the 28-S and 30-D. But now with real world performance, it seems you lost some rpm and torque by decreasing the timing 4 degrees. Technically, this is expected, the less advance the timing goes at wider throttle openings, the less rpm you will get as a result. However, there is a point of diminishing return on how much timing advance you can do before you start losing rpm again.

I'll say, experiment again by re-setting the timing this time to 30-S and 32-D. Take note how many turns on the timing rod it takes to advance two degrees or even one degree. This way, while in the water and you need to adjust the timing again to experiment, you can approximate it without having to use the timing gun. Take note of WOT rpm so you can tabulate which setting is the best. Make sure you keep the load and trim of the boat constant to get fair rpm's at WOT.

Let us know of your results.

 

[pnwboat]

If you didn't have any issues with it set to 32 degrees static, it might be OK. Be sure to use a good quality gas. It seems that the maximum power band on these Force 4 and 3 cylinder 2-stoke motors is a bit narrower and at higher RPMs than a 4-stroke engine. Tuning them for maximum power is a bit more tricky.

 

[Frank Acampora]

Old Chrysler engines were timed to 32 degrees advance. Along about 1980, Chrysler issued a bulletin advising to reduce timing to 30 degrees advance due to poor quality marine gasoline.

Now, for maximum power, the burn time of the gas/air mixture should be equal before and after top dead center. Since it takes a finite time for the mixture to burn, we must advance timing to 32 degrees advance so that it starts before top dead center. Thus, in our Force engines the total burn time is 64 degrees of crankshaft revolution--32 before and 32 after. MAYBE! If we change this, power will be reduced to some degree
(note: because of the increased turbulence and quicker burn time of loop charged engines, timing only needs to be advanced about 18 degrees. That is one reason they make more horsepower.)

Back to your 125: When timing is retarded, the idle speed will drop and thus, you would need to screw in the idle stop screw to increase the idle speed. Because timing and throttle are mechanically linked, increasing the idle speed by screwing in the stop screw will always increase the IDLE timing advance.

Now: I have seen some Mercury engines that require a 34 degree advance at WOT -- SO---If you always use good quality gasoline or even step-up to 89 octane, you SHOULD (not will) be safe at that advance and you may be making more power. I always run my Chrysler engines at 32 degrees advance. Once, because of a brain fart I did run one at 42 degrees advance and --ta-da---I melted all four pistons.

The 125 is actually a bit weaker than the 120 (because of the bore size) and under load will not perform as well. So, reducing timing advance and then loading down the engine will result in disappointing performance--unless you compensate with a lower pitches prop--and even then you probably will still be disappointed.

 

[Frank Acampora]

Old Chrysler engines were timed to 32 degrees advance. Along about 1980, Chrysler issued a bulletin advising to reduce timing to 30 degrees advance due to poor quality marine gasoline.

Now, for maximum power, the burn time of the gas/air mixture should be equal before and after top dead center. Since it takes a finite time for the mixture to burn, we must advance timing to 32 degrees advance so that it starts before top dead center. Thus, in our Force engines the total burn time is 64 degrees of crankshaft revolution--32 before and 32 after TDC. MAYBE! If we change this, power will be reduced to some degree
(note: because of the increased turbulence and quicker burn time of loop charged engines, timing only needs to be advanced about 18 degrees. That is one reason they make more horsepower.)

Back to your 125: When timing is retarded, the idle speed will drop and thus, you would need to screw in the idle stop screw to increase the idle speed. Because timing and throttle are mechanically linked, increasing the idle speed by screwing in the stop screw will always increase the IDLE timing advance.

Now: I have seen some Mercury engines that require a 34 degree advance at WOT -- SO---If you always use good quality gasoline or even step-up to 89 octane, you SHOULD (not will) be safe at that advance and you may be making more power. I always run my Chrysler engines at 32 degrees advance. Once, because of a brain fart I did run one at 42 degrees advance and --ta-da---I melted all four pistons.

The 125 is actually a bit weaker than the 120 (because of the bore size) and under load will not perform as well. So, reducing timing advance and then loading down the engine will result in disappointing performance--unless you compensate with a lower pitches prop--and even then you probably will still be disappointed.

 

[SkiDad]

I always run my Chrysler engines at 32 degrees advance.

do you think my 1985 Force (looks just like old Chryslers) should be considered a Chrysler for timing ?

when you say 32 degree do you mean on the water (so 30 static) ?

 

[SkiDad]

thanks guys as always - i'll take your points Good point Jiggz on the number of turns - I'll probably try 30 static / 32 dynamic and see how she runs.

just some technical info - my flywheel only had 2 marks - wasn't sure what the left one was - but it turns out it is 32 degrees. I had to do the math to be sure - flywheel is 28 3/4 circumference - divided into 360 it comes out to 12.5 degrees per inch and the mark is 2 9/16 from 0. I made a mark at 2 1/4 for 28 degrees.

 

[Frank Acampora]

Your Force is plain and simple a Chrysler. Chrysler went bankrupt and was Forced by the US Govt. to sell its marine business in 1984 in return for a Govt. bailout. Brunswick bought the engines and changed the name to Force. They produced them for two years with no changes other than the decals.

 

[SkiDad]

I bumped it up to 30 static and i took out the boat this morning and i picked up all or most of my lost rpm (at least it seems) had same load minus some gas... i figured I would go in the middle - Originally (32), 2nd try (28) - now (30)

It was was running at 5300 rpm today instead of 5150 last test. Ran about 10 minutes while getting my idle right - ran into some issues - initially idle a little high and I was setting it - then it wouldn't idle well - i kept on setting it and then it would want to stall 30 seconds later - brought it home and checked it over and cleaned the carbs a little.

UPDATE: I realized what happened was that I didn't tighten the lock nut each time - normally i do after ever adjustment but i wasn't this trip thinking it would stay - but I believe it was spinning out b/c of vibration and lowering the idle after ever take off. I thought I ran out of gas and other things... but I set my idle back to 1100 ish and tightend down the locknut good and went to the lake and all is well.

here is a question i have - is the plastic piece at the top of the timing tower supposed to have a split in it? - seems like it might be there on purpose ? I was careful not to over tighten that last night.

 

[Frank Acampora]

No, that plastic piece should NOT have a split. As long as it works, leave it alone BUT---either buy a new one or salvage one off a junk engine to have in case it breaks completely. Some fellows here make them from square aluminum stock and those will never fail. You might consider that.

 

[pnwboat]

No, that plastic piece should NOT have a split. As long as it works, leave it alone BUT---either buy a new one or salvage one off a junk engine to have in case it breaks completely. Some fellows here make them from square aluminum stock and those will never fail. You might consider that.

Same thing happened to mine. Like Frank mentioned, I made a replacement out of a piece of square brass.

 

[SkiDad]

i ordered the replacement plastic piece it was only 10 bucks shipped - anyhow - do i need to mark anything before putting the new one on the tower?

also - I believe I caused my self trouble - when I was out that day when my boat wouldn't idle (idle screw was backing out and I wasn't catching on) i reved the engine in neutral and goosed it into gear several times to get it moving. After this it wasn't going into gear as smoothly as before. Anyhow I been out a few times but last trip it poped out of gear several times when accelerating - i thought it was maybe my prop slipping but I swapped props and same issue. i've either toasted my dogs or i got this thing out of adjustment. I guess I'll know on saturday when I check my adjustment - hoping for the best, but might be looking at a lower end swap - dang I wish i would have left my engine alone this year.

 

[Jiggz]

It's probably more of an adjustment. I have had the same problems before but with a few adjustment it worked out perfectly.