Carbs, I think?

[jeffmock]

I have a 1987 VIP 17 ft Fish and Ski pushed by a 1987 125 hp Force. The motor has always seemed to run pretty well for what we needed although never above about 4300 rpm wot with a 19 p prop and just me in the boat. It pulls a skier but could not get a wakeboarder up a few weekends ago. I found a reconditioned 15 p prop and bought it thinking this is the fix for the low rpm and thus quicker hole shot and less time to plane, etc. Well, things didn't turn out as planned. Almost no change in rpm or in planing speed or hole shot. I read where the jet size may be changed, but we are only at 365 ft. I do think it runs too rich because there is raw fuel dripping from the <br />bowl(s) and it would not start Saturday am until I removed the cowl. I had both carbs rebuilt last year about this time when I bought the boat. I plan to do a decarb on it tomorrow as I do not know when this was last done. Could this help the problem if it is a stuck float and what improvements could I expect from this process? What other things should I do (compression check, spark check etc.)? Thank you for wading through my rambling and for all the good advice. <br /><br />Thanks again,

 

[The Marine Doctor]

Re: Carbs, I think?

When the 15pitch prop was put on...how much of an RPM change was there?<br /><br />TMD

 

[jeffmock]

Re: Carbs, I think?

maybe 100 max. The boat was loaded (2 adults and 4 kids) and we maxed out at about 4200-4300 with the 15 p and I was running 4300 by myself w/ 19 p, so I would say gained 100 and lost 200 from the load. Does this sound logical?<br /> <br />Thanks,

 

[eurolarva]

Re: Carbs, I think?

If you cant get the motor to start or run for any length of time I dont think you should do a decarb. If you cant get the motor to run the following day to burn out the decarb spray you might hurt your motor if it sits in there for a long period of time. <br />I would guess your gas has water in it. It has been really humid lately and if you maybe didnt close your vent on your gas tank that might be your problem

 

[jeffmock]

Re: Carbs, I think?

Thanks to all who replied but the problem is not that the motor is not running. The motor starts and runs fine, always has, but it is just not running high enough rpms and almost no change with a 4" change in prop pitch. I think the problem may have something to do with the carbs (fuel/air mix) as TMD suggested with the jetting for different altitudes, or something along those lines.<br /> <br />I did the decarb today and ran the boat with only one other person and experimented with trim. With the motor trimmed out I could turn nearly 5000 rpm but could not turn the boat due to ventilation, had to trim in to turn. Hole shot not improved but top end about 4 mph faster with trim out. So trimmed out to the point of ventilation the motor will turn 5000 rpm, which is useless for the hole shot. Trimmed in still only about 4200. Any suggestions would be much appreciated.<br /><br />Thanks

 

[The Marine Doctor]

Re: Carbs, I think?

Remove the head..if you have not already and inspect the cyl's.<br /><br />We are not looking for scoring but "smoothness"<br /><br />If the walls are smooth like a baby's bottom..you have found what is wrong with your engine. Its worn out<br /><br />^Just another thing to look for^<br /><br />TMD

 

[clanton]

Re: Carbs, I think?

Is the engine smooth at 43OO, or coughing a little. Some model carbs have solid steel float needle with plastic seal inside brass needle housing. The seals do not like carb cleaner, and thay start to crumble with age. When the seal is in this condition the carb runs rich/lean. Dealer can should have new style needle and seat, needle will have plastic/rubber tip.

 

[jeffmock]

Re: Carbs, I think?

Ouch Doc. "Warn out" brings images of replacement or rebuilding or scrapping or such as that, but I will check that this weekend.<br /><br />The engine does run smooth at 4300 and really smoother now that all that carbon is gone. And ran smooth as I trimmed out the motor and got into the 5000 range, and the speed increased.<br /><br />Thanks for all the replies and any other ideas would be greatly appreciated.

 

[The Marine Doctor]

Re: Carbs, I think?

We have had engines that have had the same symptoms as yours. This is the only reason I suggested worn out.<br /><br />As this was the case with them.<br /><br />TMD

 

[clanton]

Re: Carbs, I think?

What were the compression numbers?

 

[jeffmock]

Re: Carbs, I think?

Thanks Doc. I understand what you are saying. I appreciate your advice on Forces and the time you spend helping the rest of us.<br /><br />I am going to check the compression tonight after work and I will post the numbers.<br /><br />Doc, I assume that worn out means that the cylinders have been used to the point that the rings do not make a good seal. I also assume that this would be evident in lower compression numbers. If all this is true, can the motor be bored over with new pistons and put back together like a car engine? <br /><br />Thanks Guys,

 

[The Marine Doctor]

Re: Carbs, I think?

You can in some circumstances oversize the cyl's to larger pistons. If they are still available.<br /><br />Compression of around 125 could mean a worn out engine as these engines ran @ 150-160 new.<br /><br />I have seen Force engines with broken rings still blow 125 or better.<br /><br />I will get some flack for that I know. <br /><br />Once the compression drops to the 125psi range the engine is not creating the original HP it was designed for.<br /><br />TMD

 

[jeffmock]

Re: Carbs, I think?

I didn't get the compression checked last night, but I would be willing to bet its not much above 125. I think I remember the local mech that checked it out when I bought it last year say 125-130. So...<br /><br />I hate to keep on with this before getting the compression numbers but the fuel spilling fron the front of the carbs and the strong smell of fuel even when the cowl is on the motor, is this normal for a Force (just inefficient) or should (could) this be adjusted out to run a little leaner. Doc, that post you posted about that motor getting too much fuel and only running low 4000's even with a smaller prop just got me thinking especially when a smaller prop didn't work for me. Any ideas?<br /><br />Thanks for your time,

 

[The Marine Doctor]

Re: Carbs, I think?

When you dropped in pitch the increase in RPM should have been 250-300Rpm. Now you stated earlier that the rpm did not change. This would lead me to believe that the engine is choking itself out...or getting too much fuel..or is worn out.<br /><br />I reread your original post. Have you tried running the engine on the water without the hood?<br /><br />It's possible that the exhaust snout has a tear in it. Look down behind the engine within the cowling. There is a rubber snout halfway down the leg. See if it is torn.<br /><br />TMD