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my motor seems like it is holding back?

petersfield

petersfield

Member
Yesterday I was out boating and I was giving it full throttle and I could only get 5000 rpm's out of it! 150 hp 21p prop 17 ft boat, while I am giving it every once and a while it rpms come up and it seems like it has more power wanting to come out! my top end is nothing to brag about maybe the motor has more and just needs to be adjusted? It runs fine and idle's fine. It should be able to do more tha 5000rpm with that prop? thanks in advance Shawn p.s. when it did kick in it would go to 5300 rpm but only for a second.
 
Mine did that after the break in was completed. Try this, next time you are out and running wide open and it seems to be holding back, have someone squeeze the primer bulb. Did the engine pick up? What I found was a weak fuel pump diaphragm. Converted to a carter electric and no more problem.
 
I had a similar problem the day I left aplug wire off. Ran great, just lost top speed. Check your plug wires...............one might be a little loose.
 
Id go with the cheap and or free items first check the fuel screen on the tank(free) then see what your fuel lne is 5/16 or 3/8 my starflite came with 5/16 now i have 3/8 and a larger primer bulb as well . I never had a fuel prob but its sure cheep insurance to do the little thing first. Aaron
 
Another on the cheap side, after you check your fuel system & plug wires, check the cap & points. If they're clean, check the spring on the points, you may be getting a little point float.
Machone
 
machone said:
Another on the cheap side, after you check your fuel system & plug wires, check the cap & points. If they're clean, check the spring on the points, you may be getting a little point float.
Machone
Click to expand...

This is an outboard motor...Mercury has NEVER used points on a V6 outboard.

Anyway, you need three things for a motor to run, spark, fuel, compression.

1st check compression.

2nd. As other have said you can do some basic fuel things, if you squeeze th primer bulb while underway and it picks up speed you probably have a weak diaphragm. You should be changing these every 5 years as a regular maintenance item. Could be a bunged up anti siphon valve. Could be others but this is where you can start.

3rd. Spark. I have found that it is often difficult to differeniate a v6 running on 5 or 6 cylinders at idle. Short of testing and perhaps replacing ignition components, your best diagnostic tool is a timing light. No spark, no flash, missing will show up too.

My advice on electrical stuff is pay a dealer. It is easy to think you have found a problem and that is not it, It can get very expensive, very quickly if you are wrong because you can't return parts.
 
Sounds like a fuel restriction. Go thru the whole thing from tank to carbs. Anti-siphon valve on tank? (remove it if you have it) Check filters and prime bulb. If that fails, you should order a genuine Merc service manual from the dealer for that model and do a systematic troubleshoot. Don't just throw random parts at it.
 
xsive said:
This is an outboard motor...Mercury has NEVER used points on a V6 outboard.
Click to expand...

Sorry dude, didn't know it was an outboard as it doesn't state what motor it is.
And I do know how a motor works, just tryin' to help.
mach
 
Sorry I should have listed it is a merc 150hp XR4 1993 I did have a fuel problem last year it would shut off at full open! I tightened all the conectors and it has never done it again. thanks
 
I had a 235 Rude that would do the same thing, turned out to be bad coils. Had a 200 Merc that broke a trigger wire and was intermitently loosing a cylender. Electrical problems can be a real pain in the @$$.
F150GT
 
Try a fuel system cleaner

You should be running quicksilver fuel cleaner (I forget the technical name) at least twice a year. I use it every tank. The directions say something like adding 1 ounce per 5 gallons. Thick motor carbonation always hampers a motor. This stuff really works. Make sure your using quicksilver premium 2 strock oil. These 2 items will leave your cilinders in the best condition possable.
 
an easy way to check out the fuel system is to hook the engine up to a 5 gallon tank and line. if your problem disappears you'll no where to start looking
 
I had a similar problem w/ a 200 hp merc. sometimes it ran like a beast other times during the same day it lost about 300 to 500 rpms. it was a stator going bad.
 
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