# Carbeurator Jet adjustment



## Chaser (Sep 28, 2007)

Our family has an old Starcraft fishing boat, I believe its a '68. Anyway, we inherited it from my grandpa after he passed away back in 2004. It had sat for a while following some hydraulic problems with the rams on the inboard. Well we got that problem fixed, and a few other issues taken care of, and took it down to Fishlake back in July 2005. The engine sounded like it was running OK, but it had a very VERY hard time getting up on plane. Following that trip we changed out all the plugs and wires, and I believe my uncle had a new distributor cap installed as well. We figured it had sat for so long that maybe we just needed a tune up and some fresh gas. Didn't get it out much the following two summers, but last year we did manage to take it out a few times. The engine seems to run OK when we ran it at the Berry last year, but for some reason it tends to struggle up at Fishlake. 

After all that, here's my question: could higher altitudes have enough effect on the gas/air mixture to keep the engine from running at its best, subsequently keeping the boat off plane, or would the problem more likely have to do with the angle of prop we have installed currently? This was suggested by someone my dad spoke with, but I am skeptical. The boat will plane after a bit when we run it at Strawberry, but it never really planes at Fishlake. 

Any thoughts or suggestions?


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## Huge29 (Sep 17, 2007)

I can't claim to be a pro, but...here is my $0.02. Using the same prop on the same boat at Powell at an elevation of about 3,700 or so and at Scofield elevation of about 8,200 or so??? Never had any troubles, altough our boat mechanic has said that we should use a different prop. Point being, I would look at the carb first. Personally, I find it hard to understand how the pitch makes that big of a difference, I guess it is similar to just using a thin pitch at the same lake where the prop is spinning too fast, but not grabbing enough water to get going...?


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## gunplay (Apr 28, 2008)

Sounds to me like it is definately a prop pitch issue. Go to a steaper pitch prop and you will be slower at the high end but you will get it up on plane much better.


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## Chaser (Sep 28, 2007)

gunplay said:


> Sounds to me like it is definately a prop pitch issue. Go to a steaper pitch prop and you will be slower at the high end but you will get it up on plane much better.


I think we will give this a try. After speaking in person with the guys at the boat shop, it makes much more sense. Props ain't cheap, that's for sure!


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## Huge29 (Sep 17, 2007)

They can get pricey; may want to try Ebay and KSL. I got a 15x19 stainless on Ebay once for $150 instead of retail at about $300 a few years ago. Let us know how it goes! I still don't fully understand how that works as far as the elevation factor goes.


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## Troll (Oct 21, 2008)

gunplay said:


> Sounds to me like it is definately a prop pitch issue. Go to a steaper pitch prop and you will be slower at the high end but you will get it up on plane much better.


Wrong advise. Steeper pitch props go faster on the high end but take more power to get the boat on plane.

To get up on plane faster go to a smaller pitch of the same diameter.

About the boat, I'm assuming a straight 6 GM power plant? Which Outdrive unit? OMC, Volvo or Merc? each has different drive gear ratios. The reason I ask is that our altitude and especilly the altitude of some of our lakes makes a big difference in performance of lower HP boats. A V-8 in the typical 19' boat will plane it on about any water, if you have a 6 or 4 banger it will work harder. (Typical V-8 is 240 hp, Staight 6 is 175 hp, 4 banger is 135hp)
I have 3 props for my 19' 4 banger. A 19" for Powell, a 17" for UT Lake and Willard, East, Jordonelle, ect. and a 15" for Schofield and high elevation lakes. I can swap out a prop in less than 15 min and always carry a brand new thrust bearing and installation kit in case I need it.

As for testing and getting the right prop, Check out places like Jacks Prop and welding. They will let you take 3 props with a credit card slip and not charge you for the ones you don't keep unless you damage them. Jack also has used props and remanufactured props. (ones he has welded back to spec and reground).

Good luck, I doubt it has anything to do with the carburator unless there is varnish and sludge in it, or old non stabilized gas.


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## Grandpa D (Sep 7, 2007)

Try some sea foam in the gas tank.
Even if the carb isn't gummed up the sea foam will help keep everything clean.


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## Chaser (Sep 28, 2007)

The sea foam sounds like a good idea. We had the boat out last Saturday at Strawberry, and it ran just fine. It did take 30 seconds or so to get up on plane, but the engine has been running pretty good. It will fire right up at first turn of the key even on a cold engine, so I think we have clear fuel lines and a clean carb. 

If I hadn't mentioned it before, the boat is an old '68 Starcraft Mercruiser. It has a 120 horse 4 cyl. engine. My grandpa only had two props for it (both aluminum). One had a 19* pitch, and the other a 17*. Both actually had a pretty big diameter (15 inches is what the guy at the shop said). He recommended going down to a 13 or 14 inch diameter, with a 15* pitch. He said it would allow the engine to turn it faster, thus creating more thrust, and allowing it to plane more quickly. He said that the stainless props are too heavy for that small engine, and that aluminum would be the best (only) way to go. 

This boat is far past its years of towing skiers, so we don't need it to be capable of a quick hole-shot, but it would be nice for it to get up and boogie without making everyone but the driver climb up into the bow and jump up and down. (Yes, we found this to work)


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## Troll (Oct 21, 2008)

All of my props are 14".
It sounds like good advise has been given to you by the guy at the shop and he has seen the boat. If he thinks it needs that dramatic of a change then do it. 
If you could test a 14" 15 pitch and a 13" 15 pitch one right after another you could know for sure.


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## whiteknuckler (Apr 1, 2009)

I have a 40hp Merc outboard on 16ft Tracker boat, that I run almost exclusively at Fishlake. Fishlake is above 9000 ft., so their is less oxygen of course. In addition to a smaller prop (I run either a 10.5 pitch or a 9.5 pitch), you need to have high altitude jets in your carb. The leaner jets made a world of difference for me. What motor is on your boat?


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## Chaser (Sep 28, 2007)

whiteknuckler said:


> What motor is on your boat?


See my earlier posts.

So we tried out the smaller prop with the different pitch. We had a 15" prop with 19 pitch on it originally. We bought a 13.75" prop with a 15 pitch and the damned thing wouldn't go anywhere! The engine would rev super high but we couldn't go more than 10mph! It was unreal!

So we took off the new prop, put the old one back on, and bingo, up and running like a champ, planing and all! We can't figure that damned boat out. My grandpa always called it his "stupid ass boat". Now I know why!


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