2002 Chaparral 196SSI Mercruiser 302 I/O backfiring, loosing power

Allanonjj

Cadet
Joined
Aug 1, 2018
Messages
9
Hello all,... Although I've been a member of several different enthusiast forums over the years this is my first post on this site. I have browsed through several of the threads and gotten a "feel" for how things go in this forum and it seems to be the right fit for me and my boat. I look forward to becoming a part of this online community.

Now for the first issue (hope there aren't many lol). I just purchased this boat about 3 weeks ago. I drove almost 4 hours to test it out a week before purchase. The seller seemed to be a stand up fellow so I was more comfortable buying a 16 year old watercraft. I still believe him to be 100% honest and reputable so please don't bash the man. As I said, I went and lake tested the boat for over an hour, checking all the functionality of the craft and inspecting the common issues associated with them. The first thing that caught my eye is the condition of the boat. Inside and out, engine bay, drive, no noise, VERY minimal corrosion (never in salt,... ever) and the testing was flawless. The only issues with the boat were that the speedo didn't work (fixed that in 5 minutes in my driveway) and the blower motor didn't come on (haven't fixed that yet because of my current issue). I was needless to say very impressed with it and i feel as though I got a very fair price on it.

We took the boat to the local river the day we purchased it and had a fantastic day pulling knee boarders and wake boarders all day. The boat would crank and perform just as it should every time. It reached a max speed loaded with people and gear of around 50 mph and had no issue whatsoever pulling up two people on wake boards while loaded down (no tower,... yet). The prop was the factory one, a 21P. I plan on trying a 19P the next time we go out as long as I can get my issue resolved.

We then took the boat to the coast for short ride out to Dog Island with 7 people on board(4 miles from the bay where we loaded) and on the way out the boat did okay but not phenomenal. It was a VERY windy day so the seas were probably 5" average. It was a very interesting ride to say the least but we made it okay. On the way back in though as soon as we got to the inlet of the bay/river it started loosing power and backfiring. There was another gentleman there in another boat that is more experienced with boats than I am who suggested that it could be water in the fuel and to swap out the separator. The water temp was fine as was the oil pressure (between 40-60 depending on load). I didn't do an in depth assessment of the engine that day because what he said made sense to me. The boat was tossed around a lot in that short ride out and back so it would stand to credit that if there was some water in the fuel it would have gotten jostled around enough to cause the issue. I cleaned the boat and headed back home with no real concerns that it would be something simple. (yes, i flushed the engine/drive immediately and yes, I washed the boat inside and out to prevent salt residue)

I replaced the separator and took the boat out to another local lake we like to go to and it ran great for the first 30 or so minutes. When it started the backfiring and loosing power again it stayed pretty consistent all day. When i let it sit for 30 mins or so and then run it I'll get about 5-10 minutes of great performance and then its back to the spitting and loosing power. I can sometimes feather the throttle back and forth to get it to plane but not always. I cant "ease" into plane either with the lack of power. I took everyone out to the center of the lake to swim and when everyone was out of the boat I pulled the engine cover and inspected the engine (very vaguely). I saw a couple trickles of liquid coming down from the carb and felt/smelled it,... did NOT smell like fuel. No water in the oil, new seperator, full tank of non ethanol.

Ok, so that is where I'm at now. I work a LOT of hours and have a 1 hour commute so it's hard to get the time to go and diagnose the issue without a heads up on where to start. I'm thinking I will start with timing. If the timing seems to be fine then i will try the fuel tank and make sure its not full of water. If that's not the culprit I will see if the tank is under vacuum and not ventilated well enough (which by the way I have never done, I'm hoping that I can leave the cap loose and see if the backfire persists).

I am by no means a mechanic but have built/rebuilt several turbo cars and dirt bikes, street bikes, 350's, 302's, etc.... I have mechanical ability and am a bit of a tool nut so I should have plenty (as concerned to automotive repairs/performance at least)

I am hoping that these symptoms are a common issue and I will get the advice that I need to be able to repair the boat WITHOUT having to take it to a shop. I have nothing against marine shops, only against having to part with $ that isn't necessary when I can learn more about my boat by diagnosing/repairing it myself. Any experienced help and advice would be greatly appreciated!!

Thanks in advance and again HELLO ALL!! :)
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
My first thought is a blocked tank vent. Loosening the cap would prove that.

Chris. ..
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,481
pour the contents into a clear container and look for a seperation line, that is water on the bottom
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
13,894
The fact that your troubles started after a rough run on the water might suggest that some debris in the tank got shaken loose and maybe leaning out your fuel mix. I would dump out the fuel from the water separating fuel filter and let it sit, see if you see a layer of water or debris on the bottom. Another thing that many people miss is the anti siphon valve, this is a spring loaded safety valve on the gas tank that keeps the fuel line form the tank to the pump from leaking fuel in the bilge if the fuel line leaks. The fuel pump must be able to overcome the spring pressure to draw fuel from the tank. If the spring/check ball are rusted, you will lose fuel volume. Worth checking. Beyond that you may have to remove the fuel tank sending unit and look down inside the tank to see if there is crud or water in the bottom of the tank. If get it professionally cleaned out. Lastly make sure the o-ring seal on you gas cap is good, I replace them every few years and have never had water in the fuel in this boat. 30 years old used in salt 100% over the past 16 years.
 

Attachments

  • photo294669.jpg
    photo294669.jpg
    140.2 KB · Views: 0

Allanonjj

Cadet
Joined
Aug 1, 2018
Messages
9
The fact that your troubles started after a rough run on the water might suggest that some debris in the tank got shaken loose and maybe leaning out your fuel mix. I would dump out the fuel from the water separating fuel filter and let it sit, see if you see a layer of water or debris on the bottom. Another thing that many people miss is the anti siphon valve, this is a spring loaded safety valve on the gas tank that keeps the fuel line form the tank to the pump from leaking fuel in the bilge if the fuel line leaks. The fuel pump must be able to overcome the spring pressure to draw fuel from the tank. If the spring/check ball are rusted, you will lose fuel volume. Worth checking. Beyond that you may have to remove the fuel tank sending unit and look down inside the tank to see if there is crud or water in the bottom of the tank. If get it professionally cleaned out. Lastly make sure the o-ring seal on you gas cap is good, I replace them every few years and have never had water in the fuel in this boat. 30 years old used in salt 100% over the past 16 years.

That's kind of funny, I made an educated guess about the gas cap ring to a colleague at work about 10 minutes prior to reading this.

As for the anti-siphon valve,I get the function of the valve, any direction in where I should look first for it? It stands to reason that it would be located on the top of the tank obviously, but are you saying that this check-valve would be in line with the fuel intake on the carburetor line?
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
13,894
just trace your fuel line back to the tank fitting, the anti-siphon is the barbed fitting that is screwed into the pick up tube. be careful trying to remove it.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,384
I replaced the separator and

Ayuh,..... Welcome Aboard,...... as BD says, the Contents of take-off filters is solid diagnostic info,.....

Never just toss it,.... I use a freezer baggie to see what's inside,......
 

Allanonjj

Cadet
Joined
Aug 1, 2018
Messages
9
So here is what I did yesterday. I went a head and completely bypassed the tank by running a line from the inlet side of the fuel separator into a gas can with known – good gas. It seemed to run a little better but still runs like crap. I had a guy come over who knows Chevrolet engines,… It’s a 305 by the way.… And we pulled the carburetor off and put a complete rebuild kit in it. As soon as we put the carburetor back on, it runs extremely, extremely rich. I also picked up an automotive coil from AUTO ZONE just to check and see if the coil was weak or something, no dice. I forgot to mention I had already replaced the plugs, the plugs that came out or completely black. The new plugs I put in after running it for 10 to 15 minutes we’re also black. My gut says ignition but I’m not sure what part. I am contemplating ordering a new complete distributor assembly today and trying that.

I did not check that anti-– siphon valve you guys were talking about yet because I completely bypassed the tank. What are the symptoms of the anti-siphon valve being bad.?

I will post some pictures I took of the engine as soon as I get settled in at work. If someone could help me find the right distributor to order I would appreciate it. I have no idea how much they would even cost.

I am also considering ordering another carburetor just to illuminate that from the list of possibilities.
 

Allanonjj

Cadet
Joined
Aug 1, 2018
Messages
9
(I apologize about the quality of the pics)

Suggestions on where to order dist parts?
 

Attachments

  • photo298646.jpg
    photo298646.jpg
    110.2 KB · Views: 0
  • photo298647.jpg
    photo298647.jpg
    103.9 KB · Views: 0
  • photo298648.jpg
    photo298648.jpg
    115.1 KB · Views: 0

wahlejim

Master Chief Petty Officer
Joined
Jul 23, 2015
Messages
884
Right here on iBoats of course! They keep the forum up, I patronize them when I need parts. Probably throw in a new rotor and wires while you are at it.
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
13,894
well if your carb work resulted in the plugs turning black that fast, go back and make sure you check that:
1) the choke opens all the way (electric choke on this model needs 12V and a good ground to work)
2) the float is not set too high or sticking.
3) needle valve may be defective, did you change it in the rebuild?
 

Rick Stephens

Admiral
Joined
Aug 13, 2013
Messages
6,118
Carburetor rebuilds are the most often repeated job. It is so easy to go through them but not thorough. Time and care must be taken. Every port and passageway must be checked and made certain of being clear. The check balls to the throttle pump, and their passageway must be perfectly clean, or they won't seat and seal, making your carb run rich as they leak fuel directly into the venturi. The float level must be perfect. And the needle valve and seat must be perfect, or the bowl will under or over fill causing lean or rich conditions.

Your problems, offhand, do not sound like ignition issues. That boat ran perfect for you on a test drive, then, magically, the ignition causes all these issues to crop up. Seems unlikely to me.
 

Allanonjj

Cadet
Joined
Aug 1, 2018
Messages
9
well if your carb work resulted in the plugs turning black that fast, go back and make sure you check that:
1) the choke opens all the way (electric choke on this model needs 12V and a good ground to work)
2) the float is not set too high or sticking.
3) needle valve may be defective, did you change it in the rebuild?

1.Choke opens up all the way
2.Per the guy helping me (who I KNOW KNOWS what he is doing) the float was perfect
3. per him and the 2nd guy helping me, the needle was good, it was also replaced yesterday with the new kit
 

Allanonjj

Cadet
Joined
Aug 1, 2018
Messages
9
Carburetor rebuilds are the most often repeated job. It is so easy to go through them but not thorough. Time and care must be taken. Every port and passageway must be checked and made certain of being clear. The check balls to the throttle pump, and their passageway must be perfectly clean, or they won't seat and seal, making your carb run rich as they leak fuel directly into the venturi. The float level must be perfect. And the needle valve and seat must be perfect, or the bowl will under or over fill causing lean or rich conditions.

Your problems, offhand, do not sound like ignition issues. That boat ran perfect for you on a test drive, then, magically, the ignition causes all these issues to crop up. Seems unlikely to me.

When the issues started was after running the boat at HEAVY load without planing out for several miles and loaded down with people and gear. I know I worked it really hard and really should've had a lower pitch prop.... Imagine staying just under plane in ROUGH water for a good 30+ minutes total. When we got back to the inlet of the bay is when it reared its ugly head and hasnt been right ever since.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Running rich can't be caused by any part of the ignition...

As you're getting deeper and deeper, you may be losing sight of 'basics'... Go back and do the basics again, compression test, check timing, check the advance curve, check the plug leads are on the right plugs (firing order)....

Ok, just re-read a few things... Thread title says 2002 boat with a 302 engine. 302 engine is a Ford, and Merc stopped using Ford in 1977. Later you say you had a CHEV guy come over, it's a 305... That's not a Ford...

IF it's a 2002 engine (needs to be confirmed with an engine serial number), and has a TKS carb, you need to start looking at the diode, temperature switch, fuse and associated circuitry... If the diode has failed, or the fuse blown or the temperature switch is malfunctioning (or someone's pulled the thermostat :facepalm:), then any of those will cause the carb to run rich, very rich....

Chris.........
 

Allanonjj

Cadet
Joined
Aug 1, 2018
Messages
9
I apologize about the 302/Ford comment from earlier. That was my own ignorance just not paying attention....like at all. It is in fact a 305,.. and yes, I am a moron. I’ve rebuilt 3 302’s so you would think that it would be second nature to look at one but yours truly didn’t even notice at first.

so I put a new rotor button and cap on earlier and it seems to run a whole lot better. My problem now is that the guy that pulled the carb off the other day and rebuilt it may have caused more of a problem than a solution. As soon as we put the carb back on it immediately started running extremely rich. So now I think I may have solved my original issue but now I have a carb problem. I am ready to just order a replacement so I can enjoy what’s left of the summer. I have looked at a few of them but each listing says it’s for a 4 cylinder engine. I need one for a CHEVY 305 (5.0).
 

Allanonjj

Cadet
Joined
Aug 1, 2018
Messages
9
So I am on flyingfishcarburetors.com and I’ve found the carb for the 305 V8 Chevy motor but it is asking me for the model number. The site gives a visual reference as to where to find the model number on the carb. It looks as if (on the site) it should be etched into the molding on the side of the bowl but there is NOT a number on my carb. There is a sticker on the front of it with “sae J1223” on it but that doesn’t match either of the numbers on the site.
 

Attachments

  • photo298768.jpg
    photo298768.jpg
    10.4 KB · Views: 0
Top