Losing power on plane

[Daveamd]

Hello all, kinda new to this forum, but it looks like the right place to get some help. My friend and I recently bought my grandfather's boat from him. It is a 16' starcraft with a 70 HP Chrysler outboard on it. He mentioned to us that if you held it pinned on full throttle, it wouldn't run very well, but if you backed it off just a tad, it would. Well, unfortunately, on full throttle, the boat didn't seem to have a whole lot of jam to begin with (Not nearly what you would expect from a 70), and backing it off would just make her wobble between plane and coming off plane (Boat unstable-not good!) So, my friend is a heavy duty mechanic (not to be confused with a marine mechanic hehe, and he decided he was going to fix it. Well, long story short, but essentially, 2 hours later, we could actually start the motor again. Anyway, what we found now was that, if he held the throttle cable on the motor itself, that boat would go like greased lightning (We are talking fast here-no speedo, but lets just say the hole shot lasted about 2 seconds between 0 and full speed). It would run absolutely wonderful like this all day long (As long as he held the throttle linkage at the motor). If he let go, it would act like it was going to stall (although it never would), and it would also idle absolutely perfect. Now, he said he checked the fuel lines-says they are staying hard, and he tried to adjust a few other things (Yes, he got around to the timing, and no timing light-we found out how to troll back the 14 km's we had travelled on the 4.5 hp kicker). So, upshot of this long story is-has anyone had this happen to them, and if so, what did you do to resolve it? The points are this: Starts perfectly-no sputtering or backfires, Idles like a dream (all day long if you want, no problems), Builds power part way through the hole shot without a hitch, then starts to hiccup and acts like it's being starved (Also, there is a distinct smell of unburned gas when the covers off. My friend believes it might be a timing issue, but isn't a marine mechanic (I think Cat engines and outboards might be a little different). Any help would be greatly appreciated. Thanks in advance.

 

[12Footer]

Re: Losing power on plane

Stay clear of timing adjustments for now.
Timing rarely drifts from original settings on this motor, so if nobody has messed with it, timing should be accurate, or close enough to it.
I would check for a bad fuel pump diaphram (cheap rebuild, even if it turns-out good to begin with). Besides, they are only goood for a couple seasons anyhoo.
But the symptoms (hard bulb,performance issues,and GAS SMELL all point to a holy diaphram, flooding carb).
Looking for spillage from the bowl overflow or throat durring operation should detimine a stuck float tho.
Next, perform a compression test, and look for values under 70psi, or one UNEQUAL compression. Lettuce no what you find... And welcome to iboats.

 

[QuadManiac]

Re: Losing power on plane

If I'm reading this correctly... you say that if you control the throttle at the motor, everything is perfect. If you use the remote throttle, it's a slug. Am I getting this right?

If so, it certainly sounds like a throttle cable issue. Nothing else youve said points to anything else so far.

Why mess with timing, fuel pump or anything else, when it works just fine when throttle is controlled at the carb/s? What am I missing?

OR... does it only work well when the carb/s are fully opened manually, but not anywhere else?

 

[Daveamd]

Re: Losing power on plane

Thanks for responding so quickly. Yes, it's probably a good idea to replace the diaphram, I mean new parts can't hurt much I suppose. The timing matter is a little too late, looks like we'll have to try to get the timing back in order, because my mechanic friend already played with it (That's what ensured we had a nice leisurely troll back home on the 4.5 HP kicker motor ). But I'm sure we can get that done (What you do, you can almost surely un do, right?). To QuadManiac, yes, you understand correctly, when he held the throttle linkage directly on the motor itself, it ran 110% (I don't even think the boats gone that fast in it's life time either). No gas smell or anything. But the funny part is that all he was doing was pulling on the end of the linkage cable-and moving the handle on the boat we did confirm it does move the cable, so the hard part for us to understand here, is, what is the difference between him pulling on the linkage cable, and me pushing down on the "remote" and moving the linkage cable? I "think" there lies the problem, because when he pulls on it, works awesome, when I push on it, it still moves, but doesn't work so great. I'm not ruling out something so simple as adjust the linkage and life is good, but when my friend is steering clear of doing that and saying he thinks it's timing or this and that, I wanted to see what other people would say, and maybe have some other ideas to take back to him. I do appreciate very much your replies and we will give it a go this weekend, and let you know how we made out. Thanks again, Dave.

 

[roscoe]

Re: Losing power on plane

ON an engine that has been around that long, it needs a mechanic that is willing to read a service manual before he tinkers. If he messes with the wrong stuff (like the timing) it could get very expensive to rebuild.

Examine your cables, looking for cracks or splits along its entire length.

 

[QuadManiac]

Re: Losing power on plane

Thanks for responding so quickly. Yes, it's probably a good idea to replace the diaphram, I mean new parts can't hurt much I suppose. The timing matter is a little too late, looks like we'll have to try to get the timing back in order, because my mechanic friend already played with it (That's what ensured we had a nice leisurely troll back home on the 4.5 HP kicker motor ). But I'm sure we can get that done (What you do, you can almost surely un do, right?). To QuadManiac, yes, you understand correctly, when he held the throttle linkage directly on the motor itself, it ran 110% (I don't even think the boats gone that fast in it's life time either). No gas smell or anything. But the funny part is that all he was doing was pulling on the end of the linkage cable-and moving the handle on the boat we did confirm it does move the cable, so the hard part for us to understand here, is, what is the difference between him pulling on the linkage cable, and me pushing down on the "remote" and moving the linkage cable? I "think" there lies the problem, because when he pulls on it, works awesome, when I push on it, it still moves, but doesn't work so great. I'm not ruling out something so simple as adjust the linkage and life is good, but when my friend is steering clear of doing that and saying he thinks it's timing or this and that, I wanted to see what other people would say, and maybe have some other ideas to take back to him. I do appreciate very much your replies and we will give it a go this weekend, and let you know how we made out. Thanks again, Dave.

Was he able to get good performance over the entire throttle travel by manually controlling the linkage, or only WOT? Carefully take a look at the throttle linkages and determine what is being acutated with the lever operated cable verses what is being actuated by manually manipulating the throttle at the engine. I'd bet you can quickly see a difference somewhere, leading to your problem.

Good luck!

 

[Frank Acampora]

Re: Losing power on plane

Check the timing belt on the distributor. If it is too tight, it will bind the distributor. Proper tightness iw when a .010 feeler gauge will depress the belt about 1/8 to 3/16 without bending. Push the feeler gauge like it is a finger. Also check the bushing that the distributor rotates in. If the grease is old and hard--Ditto-- Binding linkage. Yet when you pull it by hand, it seems to work perfectly. Lastly, check the clamp that holds the cable. There is a groove on the thick part of the cable that is located in the clamp.

Timing should be about 0 deg plus-minus 2 at idle and 32 deg at wide open throttle. 32 is the important setting. This can be static set in the driveway, since you either have points or magnapower ignition. Either way you need only to turn over the flywheel by hand with the key on to get a spark.

 

[Daveamd]

Re: Losing power on plane

To quadmechanic:
Yes, the entire throttle range was absolutely great by hand. Only idle would work good from remote. That's a great idea, definitely shall do this weekend.
To Frank Acampora:
This is nothing but gold for me, thank you very much. This will take care of the issue of not running and may help/solve the other issue (As I mentioned before, my friend had already fiddled with the timing out on the lake, which made for a fairly lengthy drive back on a 4.5 HP kicker). I will get my friend to set it back to these numbers and then at least we can start troubleshooting the main issue again. I don't know where you got these numbers, but I really do appreciate you taking the time to pass these along to me.
Dave.