Probably dumb WOT rpm question

[wormboy]

My 1989 150XP has low WOT rpm-- should be 5-6K, but reads 4K on the tach. I borrowed a timing light/tach to check the tach, which could be off-- but need to get to the water to look at this. However, the prop on this motor is 14 X 24-- which seems highly overpitched and is probably contributing to the low rpm-- i am planning to change. My dumb question: if the tach is ok, and I am looking for additional reasons for the RPM to be low (other than the prop), can i just put the boat in the lake, take it out of gear and rev to WOT briefly to see what the rpm gets up to? Should it get close to 5600 or so w/o a load if the prop is the main or only problem? Will a quick pulsed WOT rev cause damage?:}
Thanks!

 

[Solittle]

Re: Probably dumb WOT rpm question

No - No - No Do not rev to WOT in neutral on the lake or any where else.

You may have both a prop or set-up issue. Where is the cavitation plate relative to the bottom of the hull?

 

[Silvertip]

Re: Probably dumb WOT rpm question

Absolutely not. The engine can run away with no way of shutting it off. If the tach is accurate at 1000 to 1500 (in neutral) and 3000 to 4000 in gear you can assume it is reasonably accurate at anything over that. Check the dial on the back of the tach. It should be set to 6P.

 

[Bruce San]

Re: Probably dumb WOT rpm question

Worm, Do Not rev your motor that high without a load on it. Will cause serious damage.

You MAY have a set-up problem like wrong prop or mounting position but start with the basics first.

An accurate tach is a good idea. beyond that do a compression test and check the easy stuff like clean fresh fuel, spark on all cylinders. Pull the plugs and check their condition. Do they all look the same?

Post your model # and type and size of boat and one of the experts will be along shortly to correct me and help you on your way.8)

 

[wormboy]

Re: Probably dumb WOT rpm question

Ok-- thought it might be dumb. I assume by "absolutely not", you mean "absolutely do no do this"-- not "a quick pulse absolutely won't cause damage"?
sorry- your answer is a little confusing relative to the question.

the tach is set to 12 pole-- I switched it to 6 pole and the rpms basically doubled to beyond what seemed reasonable-- i.e., pegged at WOT. Someone else told me this should be set to 12 p--- are you sure 6 p setting is correct?

thanks for replying, and i appreciate the advice!

 

[wormboy]

Re: Probably dumb WOT rpm question

I will have to get back to the question about the level of the cavitation plate when I get home tonight.
the compression is ~100 for all 6, with no variation detectable from the accuracy of the gauge. Plugs all look great-- were just replaced and are correct type from other threads I've read. the power pack, trigger, and stator are all less than 6 months old-- replaced trying to track down a strarting problem with intemittent loss of spark from various cylinders (i've seen old posts identical to this for this exact same engine E150STLCEM)-- both the trigger and the power pack had to be replaced to solve this.
I just bought a carb rebuild kit to see if this helps with excessive exhaust smoke-- which may also help the rpm issue.
Fuel is fresh-- engine actually runs pretty well except for the smoke and a bit of a rough idle-- which the carbs may solve.
I had a fuel leak from one of the hoses at the fuel manifold, replaced clamps and it went away-- but i have noticed fuel puddles in the engine compartment after I put the engine up for storing on the trailer. Does this indicate an obvious problem to anyone?
All advice appreciated!!!

 

[wormboy]

Re: Probably dumb WOT rpm question

By the way-- in terms of the tach-- can i safely bring the engine to 1000 rpm or so on the muffs? I can test this tonight if so-- otherwise i have to wait until I can drive out to the lake and fight my way in line at the ramps....

 

[wormboy]

Re: Probably dumb WOT rpm question

Note to Solittle: the cavitation plate is right at the level of the bottom of the boat-- is this the correct positioning?

 

[LFK]

Re: Probably dumb WOT rpm question

Note to Solittle: the cavitation plate is right at the level of the bottom of the boat-- is this the correct positioning?

yes, it the bottom is the lowest point (unless it's a sail boat).d

 

[jtexas]

Re: Probably dumb WOT rpm question

Ok-- thought it might be dumb. I assume by "absolutely not", you mean "absolutely do no do this"-- not "a quick pulse absolutely won't cause damage"?
sorry- your answer is a little confusing relative to the question.

Absolutely not. The engine can run away with no way of shutting it off....

No - No - No Do not rev to WOT in neutral on the lake or any where else....

Worm, Do Not rev your motor that high without a load on it. Will cause serious damage.

It's possible you could get away with it...and if you did, it might not have a noticeable effect on the useful life of your motor...but what you are risking is total self-destruction of your engine, on the spot.

 

[rickdb1boat]

Re: Probably dumb WOT rpm question

What kind of a Tach. is it? Normally you would set the dial on the back to 6 pulse(Not pole). If you only have settings for poles, then 12 would be correct. You can run the engine on the muffs up to around 1500 Rpms safely. Do you have VRO on this engine? If so, check all fuel lines for air leaks. If it's not getting the proper amount of fuel, it will smoke excessively, especially at idle. Sounds like you still have a leak from your explanation of excess fuel in the engine pan. Pump up the bulb and look real good at all the lines going to the primer and carb. Have someone hit the primer(Key switch) while you watch for leaks near the carbs.

 

[wormboy]

Re: Probably dumb WOT rpm question

Ok, ok--- no rev'ing w/o load; I warned you it was dumb!

Rick,
the VRO system has been disconnected on this motor and I pre-mix 50:1. I will check for leaks with my son priming-- I have heard or read that a common cause of excess smoke is air leaks in the fuel line but hadn't thought to check the primer lines.
I am also waiting on my OMC manual to arrive-- the SeLoc I have is completely confusing to try to understand how to link /synch-- is there a good thread for this? The manual seems to name parts differently than the BRP parts exploded diagrams, making it uninterpretable (coupled with drawings that have nothing that look like them on the engine!).
Also-- I read a thread in which someone mentioned a Joe Reeves post on setting timing with plugs removed and grounded (followed by final adjusting at WOT on a lake)-- can anyone direct me to this?

 

[wormboy]

Re: Probably dumb WOT rpm question

I should probably move this to another thread, but here goes--- I checked for fuel leaks and there is suddenly a big one-- when I pump the priming bulb, fuel comes spitting out of the lowest of the 3 carbs from a hole in the top of the carb; from the brp diagram it looks like maybe the idle orifice ( the hole between the mounting holes for the air silencer)? It got too dark for me to keep at this, but my guess is that a plug or maybe the idle air bleed has come all of the way out.
Any ideas-- and thanks!!

 

[Silvertip]

Re: Probably dumb WOT rpm question

Sounds like the float and or inlet needle is not functioning in that carb.

 

[wormboy]

Re: Probably dumb WOT rpm question

Hi silvertip-- thanks for your continuing help!

I just bought rebuild kits today, so i am hoping that this should take care of the problem. The fuel is pumping out of the hole in the top of the carb that, in the brp diagram, looks like it leads to the chamber that appears to be called the "idle passage". I am thinking that the idle orifice/or jet? was loose and popped out when i replaced the priming bulb (which now holds pressure)-- leading to presure build-up and failure at a weak spot in the carb??
thanks!!

 

[91cajun]

Re: Probably dumb WOT rpm question

I had a problem with the inlet needle on my OMC kit. Turns out the original one on the new motor had a rubber tip and the replacement kit did not. Apparently the lack of rubber tip caused one of my carbs to leak out the front. I pulled it and put the old inlet needle in and the problem went away. I have since bought Seloc after market kits and there inlet needles aren't rubber tipped either. I haven't put them in yet to see if the problem returns.

 

[wormboy]

Re: Probably dumb WOT rpm question

thanks, cajun-- i'll see what happens in my rebuild and let you know if a have a similar problem