84 force 85hp ign.problems solved maybe............

[84force]

Hey guys,
Need some addional help. got no 3 cyl firing after swapping trigger and switching wires to coil on module. Now I am firing on all cylinders. Thanks! Now the other problem as has always been the case no more than 3500 rpm regardless which prop 17 or 21. What am I missing to obtain higher rpms. 17 foot fish and ski bayyliner. any ideas? Timing? Or am I getting the best performance that I should expect from this setup? Help!!

 

[Frank Acampora]

Re: 84 force 85hp ign.problems solved maybe............

Read my post on timing and carb adjustment below in 90 HP Force sluggish by Perico.
But first: An 85 on a 17 foot bayliner should turn around 5,000 with a 17 pitch prop unless you are carrying a god-awful amount of weight. Check for water under the floor. There should be a rubber drain plug in a well in the stern to allow this out. Trimming all the way in will also lower the rpms. And get rid of the whale tail if you have one.

 

[Matthew A.]

Re: 84 force 85hp ign.problems solved maybe............

Are you running a cupped prop perhaps. I put a cupped 13 x 17" prop on my 17 foot B-liner after switching from the stock 13 1/4 x 17" semi-clever. The motor would run at 5250 rpm WOT using the stock prop. Yet. with the cupped prop the motor would only reach 3800 rpm WOT.
If I am not mistaken, after posting in one of the other forums, I believe Frank was the one who was kind enough to inform me that when switching to a cupped prop from a non-cupped prop you should decrease the pitch by 2".

 

[84force]

Re: 84 force 85hp ign.problems solved maybe............

Thanks Guys,
No water under the floor as far as I can tell. No rubber drain plug in a well as suggested only the standard threaded drain plug at the stern of the boat. As far as I can tell the props I have been using are not cupped so I am back to the orignal thought, timing. Could timing be off enough to cause lack of wot rpms and the motor still start, idle, and accelerate fairly well. Confused. Having trouble adjusting the timing. There are not any marks on the flywheel other than a couple lines. Timing lights I have used (three different ones) are not bright enough to use at the lake, can not see what I am doing. Is there a formula to use involving how many threads are showing on the adjusting link or anything else I can try to get the timing close. Any suggestions? Thanks again for your input!

 

[Frank Acampora]

Re: 84 force 85hp ign.problems solved maybe............

If its an 84, its probably white. Right? if so, use a blact marker to make the timing lines more visible.

The single line on the flywheel is top dead center or 0 deg.This line should be close to the line on the top of the manifold at idle. This line will be right above and behind the centerline of the top carb.

The next group of three lines on the flywheel are : Center line--30deg advance. This is where the engine should be timed at WOT. The line before it is 28 and the line after it is 32 deg advance.

Scroll down and see my long post for 90 hp force sluggish for full syncronizing instructions.

 

[84force]

Re: 84 force 85hp ign.problems solved maybe............

Thanks Frank,
Your input has been very helpful. Do you think the timing being out of adjustment could cause the lack of performance I'm experiencing. I am sure hoping that is the case because this problem has me at a loss. I am disappointed with the performance of this combination of boat and motor. I know there just has to be more power available and hope I can figure out away to unlock it. I have decarbed, adjusted carbs, replaced coils, replaced modules, replaced stator, replaced the trigger two times, tried a 17 and a 21 pitch prop, replaced fuel lines and bulb, replaced ign. switch, etc. I really appreciate the help all of you have provided. Still I have not found the problem, I hope timing is the answer. Thanks!!!

 

[Frank Acampora]

Re: 84 force 85hp ign.problems solved maybe............

Could be--but could be the carbs too. Proper syncronizing of throttle opening to timing advance is important. If either is out, you will lose power. Usually, you lose less power if the carbs are not opening fully than if the timing is off. Reason: Because of the cam on the carb, the timing advances quite far before the carbs open to more than 1/4.
Indeed, if you look at a properly set up engine, economy cruise is about 3/4 throttle lever position and the carbs are only open about 1/4 of the way. The final throttle travel makes a lot more noise and not much more horsepower while using a lot more gas.
If you try to manually open the throttles while running slow, you will see that without timing advance, the engine will kind of bark and almost stall. Timing advance is more critical to engine speed.

 

[MWBROWN]

Re: 84 force 85hp ign.problems solved maybe............

All the above may be true. But.......... :^
When one uses two props that much different there should be an RPM change, even if the engine is not making power. If not, what would make an engine reach exactly 3500 RPM's. Is it possible the tach is not correct?
I did not see a speed that you were going with the different props. When I put on my 15 pitch, on my 85 HP I get about 34 MPH GPS and 6500 RPM. WIth my 20 pitch, I get 38 MPH at 5500 RPM.
I agree you must have some of the above issues, I just thoght of these other possibilities.

Mike

 

[Frank Acampora]

Re: 84 force 85hp ign.problems solved maybe............

Agreed! with a 4 pitch change you should see about 400-600 rpm difference. And with an 85, 34 to 38 MPH is about right. you can't really expect more.

 

[84force]

Re: 84 force 85hp ign.problems solved maybe............

Thanks guys,
The speed I am able to get from this set up is 28 mph topped out only myself in the boat. As far as I can tell the tach is reading correctly. The motor also just does'nt sound like it is reaching any more rpm's than the tach indicates. As soon as the cold weather here in Indiana decides to pass I will take my problem child to the lake and adjust the timing to see if that helps any. It has been suggested that I need to do a cylinder leak down test. Maybe I have a broken or stuck ring or maybe the cylinders are worn enough to cause the problems I am having. Maybe a high speed miss? I wiil keep you posted. if you guys have any other ideas please let me know. I am still very confused about this lack of performance. Thanks again.