2001 Mercury 9.9 4-stroke

I have a Merc. 4 stroke that will only get up to about 8-9 mph. This is on a 14' Mod. V jon boat.<br />It sounds like the motor is really stuggling for rpm's It doesnt "wind out" at all. Seems like Im only getting about 1/2 of what should be there in horsepower....Any help or ideas will be appreciated...

Re: 2001 Mercury 9.9 4-stroke

Welcome to iboats. <br /><br />Is that a Bigfoot model? You ain't gonna plane with a bigfoot. Even a standard model will have trouble planing a boat with just 1 person. It probably won't plane if you add another person and gear.

Re: 2001 Mercury 9.9 4-stroke

no it is not a bigfoot. Im not worried about getting up on plane. The motor just sounds like im only getting about 1/2 hp. out of it. It idles great runs good until you throttle up and then it just flat ou struggles...

Re: 2001 Mercury 9.9 4-stroke

Is this a new problem? I'm wondering if you may have a restriction in the carb from varnishing. That frequently happens over the off-season, and small motors don't use much gas. It's easy for it to get old on you. I advise using a stabilizer all year with those. Or maybe a sparkplug fouled from fogging oil? It happens sometimes.

Re: 2001 Mercury 9.9 4-stroke

I have a 2002 and it was the same way (9x9 prop and on a 12' garvey ~ 150 pound boat). After cleaning the carb several times, I was able to get it up to 5000 rpms without any load (17 mph). Add fishing gear, it would only semi-plane and reach about 4500 rpms (12 mph). I eventually replaced the carb with a 15 hp model and my power problems went away. If it's not making 15 hp now, it's very close. I can reach 5500 rpms with two adults and fishing gear.<br /><br />From what I could tell, the carb is the only difference between the 9.9 and 15 for my model year (it's the 323cc Yamaha block). The float bowl assembly is different on the 15 than the 9.9, so you can't just replace the jets. I've had the 15 carb for about a year now, and haven't had any negative effects. <br /><br />BTW, I don't have any horsepower restricted lakes near me, so increasing the power wasn't to get around restrictions. I just didn't expect the 9.9 to be so anemic when I bought it.

Re: 2001 Mercury 9.9 4-stroke

I didnt think you could put a 15hp carb on a 4- stroke??? If you can how much would I be looking at $.. And what carb kit should I buy...Thanks for your help guys.. I think Im going to try a new prop also any suggestions on size and pitch...

Re: 2001 Mercury 9.9 4-stroke

You can order a new carb from Mercury at their parts express. I think I paid around $125 or $150.<br /><br />A lower pitched prop may or may not help. You may find that you're over WOT rpms before you get on plane. With the 9x9 prop and 15% slip (most likely higher at slow planing speed), top speed would be 20 mph at 5500 rpms (2.0:1 gearcase). With a 8" pitch and the same conditions, you'd get a top speed of about 17.5 mph - getting pretty close to minimum planing speed. In the transition speeds prop slip is much higher, meaning that while an 8" pitch could drive the boat at planing speed, it might not be able to get you to planing speed. <br /><br />My boat is fully on plane at 4700 rpms (15 mph), if I put an 8" pitch prop on it, I wouldn't be fully planing until 5500 rpms (assuming the same prop slip). That would mean that going over boat wakes or into the wind/waves would likely slow me below planing speed.<br /><br />If you do buy a new prop, don't go below 8" pitch. You definitely won't plane with a 7". The 200 rpms/inch that everyone likes to use is grossly inappropriate for props this small.<br /><br />You also might want to invest in a TinyTach before switching props. It will help you see what's going on, and then you can use a prop calculator to better predict how changes will affect your boat.

Re: 2001 Mercury 9.9 4-stroke

Thanks,<br /><br /> I dont know alot about what you were saying but then again you made it sound simple..I talked to a guy at a local marina and he suggested going to a 7 pitch. He also said these 4- strokes are just down right dogs...Im not very happy with what Im getting for the money I paid, thats for sure. with the 9x9 im only getting about 8mph w/ 2 people, this is on a 14' ModV jon boat. ??? I also looked up a couple of props on various websites and found anywhere between 10 1/8 X?? and 10 1/4 X??? Will this fit its an 8 tooth spline I think, but they listed all the 8 tooth under a 2- stoke, is it the same prop I would need or do I need to find 1 thats listed for a 4-stroke??? This is a real headache.Sorry

Re: 2001 Mercury 9.9 4-stroke

The 10"+ diameters are probably for the Big Foot version. The 7" pitch is only going to raise your rpms while you're going 8 mph. Your boat is at the point where it's trying to get over the bow wave (transition to planing), but it doesn't have the hp to do it.<br /><br />You may want to try a hydrofoil or smart tabs. They'll give you more lift in the stern, which makes planing easier. I was also really disappointed in the new 9.9 until I switched the carburetor (I had previously used a '71 9.8 Mercury and it would fully plane with two people).

Re: 2001 Mercury 9.9 4-stroke

1 more question for ya....I just got off the phone with Mercury and they would not tell me what I needed or even if it would work regarding the 15hp carb kit. I just want to double check and make sure it will definitely work on a 4-stroke, and if so how do I know which kit to order? To refresh its a 2001 9.9 Merc....Just want to be sure before I throw away a couple hunderd bucks.......Your help has been great Thanks Alot

Re: 2001 Mercury 9.9 4-stroke

Mine is a 2002 9.9 4-stroke Mercury with the 323cc Yamaha block. I don't know if the same powerhead was used in 2001, but you should be able to see from your i.d. plate. If you log on to Mercury Parts Express with your serial number, they have parts diagrams for all the components. Scroll through all the powerhead parts and carburetor parts and look for any differences. On my engine, all the replacement parts (powerhead, camshaft, etc.) were I.D.'d as "9.9 and 15". The only difference was the carb float bowl assembly and jets. I think the float bowl assembly was the same price or just less than the entire carburetor.<br /><br />I don't know if this truly is the only difference between the stock 9.9 and 15, but it gives enough power for me. On my boat, I've run a '71 9.8 Merc., a '57 18 Johnson, and now the '02 9.9 Merc. The Johnson had a slightly higher top speed (22 vs. 19), but only because I'm hitting 5500 rpms with the new Mercury.