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As some may know, I've been dealing with the setup and engine issues of a 1977 13'. I've had the boat a little over a month now and I've been trying to sort out the issues of this "ready for the water" boat. It was suggested that due to the number of issues I'm starting to have, I should start a thread specifically on my issues so as to make it more helpful for others who may have to go down this path.

Before I even start to get into the prop and performance issues this boat has, I feel it's important to get the engine running 100%. So here we go:

My current setup:

1977 Whaler 13'. Started life as a tiller boat. Previous owner converted it to a Sport. I have continued this and converted it to a Super Sport. It now has the full Super Sport interior, 1984+ style Super Sport full railing kit. I have a Moeller 14 gallon tank mounted under the front thwart seat, a 40 quart cooler centered right behind the aft seat and a 600 cca battery in the starboard aft corner. The boat has a full Faria Chesapeake gauge set with battery, 7000k Tach and depth,water/air temp gauge.

The engine is a 1997 Yamaha 2 cylinder, 2 stroke C40PLRV 40 HP engine running an aluminum Hustler 10.125 x 15 propeller. I also have an SE Sport 300 hydrofoil attached. Filtration is a Yamaha screw on water/fuel separator and the factory screen filter mounted on the engine. I run marine fuel with Yamalube oil 75:1 and 1 once of Yamaha ring free per 10 gallons.

Within the month, I have changed the plugs, using factory recommended NGK's, rebuilt a set of carburetors with a factory rebuild kit and changed the lower unit oil and water pump. Settings on the carbs are 1 3/4 turns out on the pilot's and idle RPM is 1100.

Current performance numbers were measured with myself, 180 lbs, a half full cooler and full tank of gas. 95 degrees @ 80% humidity.

Average speed up and down the river at slack tide was 29.6 @ 3550 rpm. Trimmed up to a mild porpose.

Current issues with the engine:

Rough idle and it will sometimes mildly surge at 50% throttle on up to WOT. But not always. I bought a set of 1996 C40 carbs, cleaned and rebuilt them with a factory kit. Idle smoothed out but I gained a mid to high RPM miss. Problem got worse the more I adjusted the carbs. Ended up running better when cold, but after warmed up, it started chirping through the air box. Sounded like backfires to me. I put the old dirty carbs back on. Back to rough idle and mild surge. Note: the engine has NEVER quit. Even when backfiring. It has not left me stranded yet. However I have no faith in the engine. I have since purchased a compression gauge and two stroke timing kit (dial gauge) so I can test the compression readings and set the timing. I should have them by next week. These engines are simple and if the compression checks out, 100+ within 15%, and then reset the timing.

I'm going to take the rebuilt carbs apart again and verify the float setting, double check for debris. The sync of these carbs is simple. Loosen the top linkage screw, push both carbs closed and 're tighten the screw.

I feel like I just did all of this to no avail. But I'll do it again. Basically I'm starting at the beginning with this engine. The low WOT rpm is fishy. The Tach is set to 6 pole as recommended. Rpm's are at 1100 at idle and it sounds right. Any other setting on the Tach gives clearly inaccurate numbers. I also bought a hand held Tach that connects to a plug wire so I can verify the Faria Tach. Should get that in by next week as well.

This thing is just weird man. It runs ok. Gets me out and back. But it's just not running right. Like most 2 stroke Yamaha's I've seen, it takes a few tries to start when cold. Once it's started in the morning, it will start within a second for the rest of the day. There are sweet spots within the idle range where it runs like a sewing machine. When I'm coming into the marina, I usually try to find one of them and leave it there. Outside of that sweet spot it rarely has that healthy 2 stroke gurgle and almost sounds like it's missing a little. The plugs look healthy if slightly wet.

I'm going to document this troubleshooting path with the hope that 1 I can get this thing sorted out and 2 maybe help someone else. Though it runs, in the back of my mind I constantly think that something is wrong and it's taking the fun out of operating this boat. Needless to say, I'm not happy with this engine. Suggestions and opinions are openly requested and I will continually update this thread until its sorted out. Once I get the engine running right, at that point I'll tackle getting this thing propped right. 29 seems slow to me with 40 HP.

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Man, what did we do before YouTube.....this video and the comments below it give me faith in my rebuilt carbs. This is exactly what it started doing. I needed to get the boat going so I pulled em. Tomorrow, I'll put them back on and continue adjusting the carbs. They are CLEAN and properly assembled so maybe I can at least cross this off my list. I didn't think of the sound being caused by a backfire past the reeds....

https://youtu.be/Z5y-rSh4AO4

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You said you got 29MPH at 3350 RPM. What's the speed at WOT?

My 2 stroke is funny too. Sometimes you just have to accept it's an older engine, and run it till it dies.

and get a SeaTow membership!

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Hello BT, that IS WOT! :) The boat came with a stainless prop on it. That prop had no markings on it whatsoever. I've seen everything from 26-34 mph with that prop. Because I couldn't tell what size it was, I decided to start with a new aluminium prop. I went to turning point props and used their prop wizard and that prop was recommended for my combination. The props are only $50-$70 so I didn't really care, I just wanted a known starting point.

I agree that 3550 sounds funny. I don't trust what I'm seeing so that's why I bought a hand-held Tach to verify. It should be in next week. I went through all the different settings regarding poles on the tach. It's current setting, 6 pole, is what Faria recommended and it's the only one that's even remotely close. Once I receive the tuning Tach, if it reads the same, I've got a problem. If it's different, I'll try syncing the Faria to the tuning tach.

Though I must point out, I think something's wrong. It runs that speed and RPM regardless if I have 1 gallon of fuel or 14. Not to mention, there is really no difference between the two props in rpm or wot speed. Yet they are clearly very different in size and shape.

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Check for markings on the inside hub of the SS prop, it has to be marked somewhere and it would be good to know the size.

I still think your cavitation plate is low and you are dragging that fin under water. You really need to check this out. You can't lean over and look on a boat this size because you shift the weight too much, so either find someone riding around that can follow you for a few minutes or strap your wife's phone off the back and take a quick video.

Quick quote from the other thread>>>


Shock Treatment = De-carb, Ring Free = Seafoam. You have the poster child of an engine that needs a de-carb or the faster cure of a carb rebuild. The engine has sat with very little use and the gas evaporated leaving deposits. Every time it was used another layer is formed. All of that isn't going to go away with one quick gas treatment. This is why I said to mix one can of Seafoam in a gallon of gas, run the engine & spray half a can of Seafoam in the carbs. Shut it off and let it sit. Run it again and use up the rest of the Seafoam spray, and let it sit again. Now run the rich one gallon mix for a few minutes before you shut it down after every use, until it is gone.

The more times you can get that rich mix in the better, because it works when it sits. If you just ran the rich mix until it was gone you really didn't let the chemicals work the way they are meant to.

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MG, there is seriously nothing on the stainless prop anywhere. I don't know if it is ground off or it was a Chinese knockoff. That's why I bought the Hustler prop, I had to get a known starting point.

I had put the old carbs back on to keep it running while I sorted out the new carbs. My carburetor's are clean enough to eat cereal out of and have been rebuilt with a Yamaha carb kit. Disregard the old carbs as they only get out back on when I pull the clean carbs off. I went through my new carbs again last night and they are spot on. I'm reinstalling them this morning. I will spray seafoam into the reeds this morning and let it sit while I install the Super Sport rail kit. Should be a good 6 hours or so.

I understand the idea of why putting ring free into the tank won't fix anything. It was a maintenance step that I will continually use. I was simply outlining everything that has been done so far. I'm not a fan of miracle cure spray wonders; hence why I bought a second set of carbs and rebuilt them. Originally, I did the recommended decarbon treatment as per Yamaha's instructions, using ring free. $$$$$ version of Seafoam.

I'm not sure about the cavitation plate. With the new prop, 10.125x15, I'm getting some prop slip and slight ventilation under heavy acceleration and anything above a slight chop. This is new and started when I raised the engine. It is one hole from max height. I almost regret raising it the last time. I gained nothing and added slight ventilation. It is rarely calm water here so capability in rough water is important.

I'm going to get my new carbs back on and get them tuned right today. I'll take the 3 gallon tank back down there and run it with that (heavy dose of ring free), spray seafoam into the clean carbs until it stumbles at high idle, shut it down and let it sit overnight. A third decarbonizing if you will.

There are so many small issues I don't even know where to begin....heavy decarbonizing and getting the rebuilt carbs set up right seems like a smart place to begin though. Once I'm satisfied with the carbs, I'll strap my phone to the back and make a Ytube vid of the whole process from idle to WOT. Thanks for following: more to come.

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Additionally, this week all my replacement tuning tools should be in. I'll be able to report my compression, timing and verify my actual rpm. I'm going to start at the beginning of the "periodical checks and adjustments" chapter of my Yamaha service manual and go through the entire thing. Hell, for all I know, the carbs might not be opening all the way and my cables need adjustment. This is why I titled the thread starting at the beginning. I'll go through and document the entire process from start to finish. Eventually, there is no other outcome other than success. Unless the engine blows up. I will get this thing running right. I'm blind without my diagnostic tools though. (How do things get lost in a move???????? Boxes don't walk or open themselves up!!!!!!)

I am VERY curious as to what I will find once I get my new tools this week.

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The tach can't be working properly. I believe that you have 1.85:1 gear ratio (you should double check). Using a prop calculator, with 3550rpm and 30mph, the gear ratio would have to be around 1.30:1 assuming some propeller slip. Even with no slip propeller slip it would be 1.5:1. Those 1.3:1 and 1.5:1 gear ratios are only used on go hi performance fast motors. My Evinrude didn't have a tach when I bought my boat, so I added one and initially it didn't work either. I remember researching and finding that some aftermarket tachs didn't work with my engine and sometime the rectifiers were damaged did not provide a proper signal. [My tach wasn't working at all because the installer didn't wire the factory harness properly]

I don't know what the idle rpm is for your 40hp Yamaha, but my guess is that it is lower than 1100 rpm. The higher rpm idle could be masking another other issue. Marine carbs are pretty simple and the idle adjustments could be affecting the upper range. I would first figure out the tach.

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Hello Dgood, I agree. That's why I bought and am waiting on a hand held tach to verify.

I put the double checked rebuilt carbs back on today. I also sprayed seafoam into the reeds and let it all sit and soak while I installed my super sport poem railing kit. Took about 6 1/2 hours so I think the seafoam soaked long enough. I pre set the pilot screws to 2 turns out.Yamaha specs 1 3/4 +/- 1/4. It was hard to start as expected and blew white smoke once it did. I set the idle to 1100 after letting it warm up for 20 minutes. Yamaha specs call for 1050 +/- 50. The second time around, as with the first, it idled much better than the old carbs. I took her out and just like last time, throttle response was slow and it surged at 1/4 throttle until 7/8. Wot is fine. I am convinced that it's not carbon build up or dirty carbs at this point.

I had bought this set of carbs off eBay. I cleaned them and rebuilt them with a factory kit. Something isn't right with these carbs.

I decided to get in touch with the guy I bought them from and asked if they were pulled from a good engine. He replied that they were pulled from an engine with a burned piston.

This has me thinking. If one of my cylinders is leaning out, it would cause the fluctuations I'm hearing. It would cause a lot of things but all of my symptoms could apply. I wonder if there is something wrong with one of these carburetors that is either not easily found or does not get replaced with a rebuild kit. I cleaned all the jets but......? The shoe fits here. I'm beginning to think I need to buy another $80 rebuild kit and clean/rebuild my original carburetors. Or drop $650 on some brand new ones. I've got an idea regarding troubleshooting this but I have to figure out how to do it. If I can partially block one of the carburetor barrels while it's surging, if one of the carbs is in fact leaning out, it should richen the mixture while doing this and smooth out while I'm blocking it. Correct? I'd hate to have to buy another carb kit but if one of my cylinders is leaning out it won't be long before I'm FORCED to repower.

Still waiting on my tools but that's what's been done so far.

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Just to make sure it's clear: the surging issue only presents itself with the Ebay rebuilt carbs. It is a separate issue from the rest. The original carbs do not do this. They just idle like crap and make the engine sound like it's missing a bit until I clear the idle circuit. 25% to WOT is smooth.

I've got to get this carburetor issue sorted out before working on the other issues.

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Still waiting on my tools. However, I give up on the Ebay carbs. I'm beginning to think that they may have different main jets installed and that they may not have come from my exact engine. Today was the last time I mess with them. The 25% and more throttle surging got really bad and I started to fear for the engine. It reallt sounded like it was leaning out. I had to idle back the 20 miles to the marina. I did a quick clean of the original carbs and slapped them back on. I'm waiting on the rebuild kit for them but this will have to do for now. This is taking forever. I can't troubleshoot the rest of the issues until the carbs are sorted out. I believe Yamaha specs a 170 main jet for this engine but of course they didn't mark it in any way. I have access to, and have cleaned and verified every single little passage in those carbs. It can't be anything else.

While Im working with the carbs, I noticed that the previous owner had the automatic choke solenoid disconnected. I applied 12 volts to it and it did not move. The Ebay carbs came with a set of reeds and that choke solenoid and I verified that it does move under power. I do need to buy a few of the little parts that connect it though. Is this system worth hooking up?