NEWBIE ! 1990 90hp Force no high speed?

dz4r1b

Recruit
Joined
Aug 26, 2014
Messages
5
So I just bought my first used boat, with a 90hp Force (1990 model). Yeah, my first boat ride....wait a minute. Idles fine, good engagement into gear. Now that its warmed up for 10minutes, I should be out here ready for a slow and steady climb to WOT? Well, i move it on up to WOT and ...well there lies the problem. I am only getting about 20-25mph tach at around 3000 rpm. Motor sounds just flat, ro high revs but doesnt spit or sputter either. Not knowing much of the previous owners, and buying from an idividual that ran it in his driveway with the hose hooked to it, I'm at a loss for where to begin? Boat is solid and well cared for, so that's not bothering me. But, if I have a $3000 problem out back then I'm going to be looking at a long winter. Absolutely any planning based suggestions that is warranted, is welcomed as I dont know boo about and outboard. Again, idles fine, sounds good when engaged, but absoultley no top end. I was expecting what other 2cycle boats I've been on in the past to do....wind out like it has a small power band in it. Not in my engine. Appreciate the help, and look forward to the journey!
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
Your mention that it sounds good is very subjective. I have two theories that is probably causing your problem which are very common in this forum. You either have a misfiring cylinder (or maybe not even firing at all) or you have some kind of fuel starvation problem. Usually, common recommendation is to take compression readings on all cylinders first to make sure you do not have a low compression which is a very major issue and show stopper. You can just rent the tool from one of the auto shops. But before doing so you need to view a video on how to do it.

If compression readings are good (usually 100~150 PSI with no more than 10% difference between cylinders), then you need to buy an inline spark tester which costs around $10. Check make sure you have constant sparks on all cylinders. And the next thing is to install a clear fuel filter between the fuel pump outlet and the carb's inlet. Even a G2 model will do and costs less than $5 at walmart.

If sparks are good then do a test run in the water with the cowl off. When the engine starts to bog down or would not come up to speed, check the clear fuel filter. if it stays full or at least 3/4 full, then you probably have carb's problem, i.e. improperly set floats or idle mixture screw, or it could also be a reed problem. However, if it does not stay at least 3/4 full, then you have fuel delivery problem, i.e. leaky fuel hose, faulty fuel pump, leaky primer bulb check valves, restricted pick up tube, or clogged vent tank.

Since this is your very first outboard, I suggest you go to boats dot net find your model and year and HP and familiarize yourself with the components and parts. They do have exploded diagrams of all the engine parts and accessories.
 

SkiDad

Lieutenant Commander
Joined
Jul 18, 2010
Messages
1,518
another thought, if you can get to 20+ mph fairly easily then check the carbs. if you pull the carb cover off and then put the throttle all the way forward are the butterflies flat ? if they are not then your carbs need adjusted so they can open up all the way. You do this test with the engine off. Frank has a video at the top of this forum on it.
 

dz4r1b

Recruit
Joined
Aug 26, 2014
Messages
5
Updates to the rpms: In neutral all I can get the throttle to do is high idle, but engage the prop in the driveway I can rev it to 5000 which I read is normal WOT. So, in the water I can't go above 3000 and pulls crazy to the right in WOT. Wrong prop? It looks new, a Solas RUBEX 1613? other number located on prop are 9411-135-15. Need help understanding prop size on a 18ft Maxum w/ this 90hp Force.
 

NYBo

Admiral
Joined
Oct 23, 2008
Messages
7,107
Welcome to iboats!:welcome:

Running with no load means little. After determining you have good compression and spark, start with the stickies at the top of this forum area to set timing and carbs properly.
 
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dz4r1b

Recruit
Joined
Aug 26, 2014
Messages
5
I found good compression, good spark, butterflies open with WOT, pulling to the right, and won't rev above 3000 rpm.
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
The pulling to the right is nothing but an adjustment of the snout or trim tab to make it neutral. The problem is that under load the motor doesn't go above 3K rpm. From the prop numbers, it seems you have 13.5" prop with 15P which is norm for the size of your motor. The question is you are experiencing fuel starvation at WOT. And the only way to find this out is with the clear fuel filter or if the clear fuel filter stays at least 3/4 full at WOT it could be a carb float is not set properly, i.e set too low that it closes too early and thus at WOT runs out of fuel.
 

dz4r1b

Recruit
Joined
Aug 26, 2014
Messages
5
Update: I had local boat dealer check it out after I ran out of know how. Fuel starvation was the culprit, running strong! Well, better than I expected in repairs so we have a solution. Thanks for everyone's feedback, finally enjoying the boat.
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
Great. You with the help of the forum could have fix the fuel starvation problem had you decided to pursue it. And the best part, learned along the way and saved $$$. Enjoy.
 
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