OK Force Guru's Still no top rpm's,85 hp,,Need advice please

[mrtool2u]

A few days ago I posted,and everyone said to get a tach,so I did.1989 Spectrum boat,19 ft aluminum with 1989 Force 85(Without power trim).Motor purrs like a kitten on top end,just no top end rpm's,,,3900 with me in the boat(30mph),,,3750 with 3 other extra large guys in the boat,26mph. Motor is in next to top notch,top notch made no diff. Linkages are all opening full and in sync.Decarbed with powertune today,and no effect what so ever.Cleaned bottom of boat.New plugs.New gas.All the plugs look great,so I cannot believe that I am dropping a cylinder.Compression is around 120 in all 3 cylinders,but could be a tad higher.The starter will not stay engaged,it just spins for a second then kicks back out.I also did not have the throttle open,did not have time to bypass neutral switch.Like I said,it starts and runs like a top,just no top rpms.Could the timing advance under the flywheel be backed off enough to do this.Had 1 carb off and it looked good,,had a 074 main jet.Surely this motor is capeable of a bit more,this boat does'nt feel that heavy.Also,the prop is a michigan 13 1/2 by 17 pitch,so that seems in the ballpark.Any and all info appreciated.Just ask if you have any questions you need me to answer.

 

[The Marine Doctor]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

What size fuel line are you using?<br /><br />TMD

 

[mrtool2u]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

5/8 from the tank to the motor,then 1/4 i.d. about the last 3 feet.Cant believe it would be the line size,,hell my 90 Johnson only has 1/4 i.d. line,but all input is welcome.

 

[The Marine Doctor]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

We use nothing but 3/8id on larger engines.<br /><br />TMD

 

[Navigator]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

mrTool,<br /><br />You have the classic symptoms of a boat that is overpropped. 19 ft with an 85 is really pushing it. Since you said that the rpms drop with additinal weight, this also indicates a prop problem. Go to your dealer and see if they have a 15 or better yet a 13 inch prop you can try out. If the lower pitch prop raises your RPM, then thats your problem. If a lower prop makes no RPM difference, then you know its a mechanical/fuel issue that is to blame. If you keep running with your WOT (Wide Open Throttle) well below the recommended range, you will get bad carbon buildup and eventually damage the engine.<br /><br />Nav

 

[mrtool2u]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

Update today,,,adjusted the timing advance yesterday(5 turns in) and no difference.I tracked down a guy locally who has the exact same boat,only 1 year older,and he can run 37 or 38 mph.And it also has a 13 1/2 by 17 pitch prop,the same that I am running so I cannot believe that it is overpropped.I have plum run out of ideas,,so any and all constructive ideas are much appreciated.

 

[turtle1173]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

Hi,<br /><br /> I would certainly take all 3 carbs apart and double check the function of all the components. It doesn't take much for a carb not to function correctly.<br /><br /> I would also check the correct size of the jet. My 85HP takes a .072 but it is an early '70's Chrysler. If yours is supposed to be at .072 it could at least partially be the culprit. TheMarineDoctor had a good post on this a couple weeks back.<br /><br /> As much gas as these engines use, it might be wise to go with 3/8" all around. You may very well get by with it on a Johnson but perhaps not with your Force.<br /><br /> Just some other things to consider...<br /><br />Shane

 

[mrtool2u]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

In looking at the twin to my boat I noticed that it only has 1/4 id fuel line.Would it be possible for a motor to lose that many R's if there was a problem in the carb's.Like I said,it really runs like a top,,just will not climb on rpm's.But tearing the carbs down is on my agenda.

 

[JB]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

You sure sound like you are complaining that the advice you got here is no good.<br /><br />If that is the case we can get you a full refund.<br /><br />If not, you need to reprop about 2" shorter, like Navigator suggests and you ignored.

 

[mrtool2u]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

Hey JB,dont get in a huff,,,I am in no way complaining,,I just want to have all my bases covered.It just seems strange that the exact same boat can do ok with the 17 pitch prop. Props are'nt cheap,and I will not mind putting one on if that is what it boils down to.You know the old saying,2 minds are better than 1.I just want as much input as possible to try to narrow it down.

 

[DJ]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

A 1/4 " fuel line is too small for any engine over 20 hp.<br /><br />Either it's hitting on all three or it isn't. <br /><br />Have you tried unplugging one spark plu wire at a time and see what happens?

 

[mrtool2u]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

Do you have to have a plug in the boot and have it grounded when you do this,or will it do harm to the cdi.

 

[OBJ]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

mrtool....<br /><br />All boats are not alike....even though the hulls may look identicle, subtle imperfections make them different.<br /><br />The "identical" boat you talked about, does he have the same size engine? Does he have TNT? How does his engine setting on his boat compare to yours? Higher? Lower?<br /><br />I agree with you that 3900rpms is not the top operating range for your engine. It really sounds like the engine is "lugging". Have you tried different tilt pin settings. You did say in your original post that you do not have TNT.<br /><br />Just an after thought....are you sure your tach is giving you the correct rpm's?

 

[mrtool2u]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

Jim, Yes we have the same engine,his is 1 year older.As best as I can tell,the motors are mounted the same. I have my motor in the next to the top setting,the top makes no difference,just blows out a bit on takeoff. As far as the tach,I have no way to calibrate it.At idle,it is 8to 900 rpms which sounds realistic.Before I got the tach,it just sounded like it was not making the rpms,,way to quiet,and the tach confirmed it.We even scrubbed and polished the bottom of the boat and it made no difference whatsoever.When I get to the carbs,it would be great to find something drastic.

 

[The Marine Doctor]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

Hmmm...<br /><br />The only thing drastic that you might find is that you were running lean on the top end.<br /><br />This would kill your motor.<br /><br />How much smoke is being produced at WOT?<br /><br />How about dropping to a 17Pitch and putting a Hydrofoil on?<br /><br />If you put the proper Hydrofoil on...the top speed will increase. "Doelfin"<br /><br />But with the likes of the "StingRay GT" you will lose top end.<br /><br />You cannot argue physics <br /><br />Here is another thing to consider...is your boat waterlogged? Dented? Been on a trailer alot?<br /><br />Also keep in mind...I think I remember telling you before you bought the boat...as you had posted you were looking at buying it. The Spectrum is rated at 150hp.<br /><br />Can you not borrow the other guys prop?<br /><br />TMD

 

[mrtool2u]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

Marine Doctor,, I do not have a excess of smoke at WOT,and I currently have a 17 pitch prop.And as of tonight,I did borrow the other guys prop,which I assume is the stock force prop,,mine is a michigan prop,with the same specs.Do you think that there could be that much difference in the two.The boat seems relatively dry inside,it has been tipped at a fairly good angle and there is no water seeping out.The hull is in pretty good shape,one small dent near the front.As far as the rating,the plate specifies 85 hp,but I believe that it could take quite a larger engine.I was told that this was sold as a package,hence the lower rating.As soon as I get a chance I will be trying the other guys prop,but with my luck,all bets are off.

 

[The Marine Doctor]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

Sorry I was under the understanding that you were using a 19 pitch. I do not think there will be a difference with the other 17 Pitch.<br /><br />I might though consider that your engine is wearing out.<br /><br />Pop off the head...see if the cyl's are smooth. Or have grooves in them...or dark patches.<br /><br />As for the 85hp rating..this might have been the case...years ago. The new ones though are 150hp.<br /><br />TMD

 

[the hangman]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

Mrtool - have you ever had the prop repaired ? I have heard that they may have a different pitch or amout of cup after a repair. Maybe your prop is no longer a 17 pitch - another reason to try the other guy's prop<br /><br />- just a thought<br /><br />Jeff

 

[mrtool2u]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

Marine Doctor,,I will pull the head and check.Hangman,,I just picked up the boat,so I cannot say about the prop,,however I will be trying the other prop on Sunday nite,,mine is a little beat up compared to this other guys prop,and his is the orig. prop,which was a force prop,mine is a michigan.Here is the development for today,,took the boat to a buddys house,who is pretty good with boats.He hooked up a regular timing light,which I assume is a car timing light,(left boat on trailer in pond)and low speed timing looked good,however when he put it in forward and revved it pretty high,the light became very erratic.He had the pickup on the top cyl,which he said was the number 1 cylinder.Can you use a regular timing light on 2 strokes,and is this the proper way to do it.I also remember someone saying that one pack fires 2 cyls. and the other only fires 1 cyl,is this also true.As usual,any and all info much appreciated.

 

[The Marine Doctor]

Re: OK Force Guru's Still no top rpm's,85 hp,,Need advice please

Regualar timing light will work fine.<br /><br />If the light becomes erratic...its misfiring.<br /><br />1 Pack does fire 2 cyl's but they work independantly.<br /><br />TMD