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View Full Version : 86 351 Misfire (can't find solution)


erat
07-23-2011, 07:13 PM
First i should say, i've been browsing these forums for a while now. Never made an account, but today i needed to.

It's a pretty hefty story, so bare with me.

Took the boat out Friday for the first time this season. I did a dry fire (with the hose) in the driveway the day before, and it ran fine. So we tow boated Friday (pulling SST 100's in when they break down) didn't have a single problem. We got hit with rain for about 45 minutes. Filled up the bulge, with water, when we found out our bulge pump went out. But that's a problem solved. So i hot lapped the course twice and pulled it off the water. Water did slosh up on the engine but didn't start running bad till the next day.

It sat all winter with a full tank of 91 octane gas. So i got gas in the morning (saturday morning, it ran fine all friday) filled up with 91 octane, and took it out on the water for another day of tow boating. It ran fine for about a half hour before it developed an extremely bad misfire. So bad where it wouldn't idle, and under any type of load it would stall. It would get so bad it would take WOT to even get it to start after it stalled.

At first, I could run it WOT and when the secondaries opened it would smooth out. The second time i went to run it WOT when the secondaries opened it would bog down and run at about 25 - 28mph just chugging.

Got it back home, seen it needed new rotor, cap, and points. So all that was replaced. But it didn't fix the misfire. So i put 93 octane in it. 6 gallons of it because that's all we used today. That didn't fix it (maybe slightly). Pulled the plugs, checked for compression and got 140 across the board. Found one loose spark plug. Didn't fix it. Gap the plugs (.035?), Still didn't fix it. Bought new spark plug wires, but the old wires read less ohm's than the new ones. Checked for spark on all the plugs and i have spark. Poured octane booster in the gas, didn't fix it. Sprayed the carb out with carb cleaner. Can't find a fix.

The only thing we noticed is the left side exhaust water was colder than the right (driver). We're thinking i have about 15 - 20 gallons of bad gas (should have been 91, but i must have gotten watered down 87). 5 gallons of 91 old winter gas (that it ran fine on) and 5 gallons of some trusted 93 octane. With octane booster.

If you have any other ideas other than gas, please help.

TLDR

Still have misfire, good spark, thinking it's bad gas?


I hope i covered everything that needs to be known, i'll answer any other questions.

Cloaked
07-23-2011, 07:41 PM
The only thing we noticed is the left side exhaust water was colder than the right (driver).
Original or old exhaust hoses? I have seen these collapse internally and not allow full flow of exhaust (actually backwash into the riser) to allow proper cooling. If your hoses are old, I'd replace them. As for the misfire? Could be several things. While you're fixing, I'd consider converting to an electronic ignition kit.


.

erat
07-23-2011, 07:47 PM
I have video uploading of the flow, sound, and vibration. You can be the judge. IMO water is coming out at the same rate. But yes, they are the original hoses. Oh, and fuel filter was replaced.

The boat i'm dealing with.

http://i25.photobucket.com/albums/c94/erat/DSC03271.jpg

http://i25.photobucket.com/albums/c94/erat/DSC03274.jpg

My dad bought it new in 86, original owner and has used it every season. I've been using it and maintaining it lately.

Cloaked
07-23-2011, 07:55 PM
I would almost bet money that you have this issue with the hoses. Just a hunch after 32 years of fooling with the old school boats. Regardless, if you do business with Discount Inboard Marine for parts, order new hoses. They will collapse sooner than later. Been there too.

If you repalce the hoses, while ordering, order two new riser-to-manifold gaskets and 8 new bolts for reinstallation. It's much easier to pull the risers while doing this than to wrestle the hoses without an open end to work.

Water flow will fool you. I thought the same thing when I went through this the last time.

Good looking boat....



.

.

erat
07-23-2011, 08:01 PM
Even if the temperature difference is different at the top of the riser?

At first we thought the left bank was misfiring more than the right, but all plugs were firing. And compression test was good, so no burnt valve.

Or are you saying the 5/8th hose that goes from the splitter (don't know the name) to each of the exhaust manifolds?

Cloaked
07-23-2011, 08:07 PM
Even if the temperature difference is different at the top of the riser?

At first we thought the left bank was misfiring more than the right, but all plugs were firing. And compression test was good, so no burnt valve.

Or are you saying the 5/8th hose that goes from the splitter (don't know the name) to each of the exhaust manifolds?Replace the 3" dia. exhaust hose. And yes, even if the temp is hotter up near the riser. The pic above is a hose I replaced last year on an 85 model. It had collapsed internally and the water was going in between the internal layers of the hose, where the bottom end (internally) was not seperated, and water was backflowing right back up into the riser.

I replaced the other side a few weeks ago and it too was ready to do the same thing.

thatsmrmastercraft
07-23-2011, 08:09 PM
Sorry that it is such a problem that brought you out of the shadows, but welcome just the same. Nice looking '86!

I'm thinking water in the gas. I would seriously consider pumping out what is in the tank. If your boat has a water separator, that probably needs to be serviced.

erat
07-23-2011, 08:12 PM
Oh alright good call. Never thought of that.

This is the video. The sound doesn't do much justice. But it may be worth a look.

http://www.youtube.com/watch?v=pSdfRev-5l4

thatsmrmastercraft
07-23-2011, 08:16 PM
Sure doesn't sound right. What temp was it running on the lake?

erat
07-23-2011, 08:17 PM
On the Detroit river which is pretty cool it was just below 150. Even when towing a boat the temp wouldn't rise much. Never past 175. Also, not sure if it has a water separator or not.

thatsmrmastercraft
07-23-2011, 08:20 PM
With that temp I wouldn't think you are dealing with collapsed hoses. You could be having some carb issues. Did you backfire through the carb prior to it running lousy? Blown power valve is a possibility.

Cloaked
07-23-2011, 08:22 PM
Oh alright good call. Never thought of that.

This is the video. The sound doesn't do much justice. But it may be worth a look.

http://www.youtube.com/watch?v=pSdfRev-5l4I'd like to have that red Playmate cooler on the right side of the garage (facing the open doors). Is it for sale? I'll pay shipping.

Replace your hoses. Temps (running the engine in the driveway) are not true indication of aynthing other than something isn't right. At 25 years old, they need it. Preventative maintenance. The misfire is another issue of which I have no dog in that race.

.

erat
07-23-2011, 08:25 PM
With that temp I wouldn't think you are dealing with collapsed hoses. You could be having some carb issues. Did you backfire through the carb prior to it running lousy? Blown power valve is a possibility.

It backfired through the carb multiple times when trying to start it after it stalled.

I'd like to have that red Playmate cooler on the right side of the garage (facing the open doors). Is it for sale? I'll pay shipping.

.

You're kidding? That's my dads. Plus it fits absolutely perfectly behind the driver seat on the boat. He might not like the idea of selling it.

Cloaked
07-23-2011, 08:31 PM
It backfired through the carb multiple times when trying to start it after it stalled.



You're kidding? That's my dads. Plus it fits absolutely perfectly behind the driver seat on the boat. He might not like the idea of selling it.Timing may be an issue with a backfire. Convert that thing over to an electronic ignition, set the timing and be done with it.

And NO I am not kidding about the cooler. I need one just like that. I know how well they fit. That's why I'm asking... :D I have two now but need one more for watermelon.... $35 and shipping is my offer....

thatsmrmastercraft
07-23-2011, 08:42 PM
I would check that power valve. Remove the primary fuel bowl and unscrew the power valve. While holding the large end, try to turn the small end. If it turns it is bad. If you need to replace it, make sure you get the same one. They are numbered for what level of vacuum they engage. Also get a blue gasket for the bowl. They are reusable, and work well.

thatsmrmastercraft
07-23-2011, 08:56 PM
So if your power valve failed, it goes full rich. That would explain being able to run WOT at first. You might take a look at a spark plug or two.........they should be black if the power valve blew.

erat
07-23-2011, 09:31 PM
All of the spark plugs were clean and dry. They were dark colored, but i wouldn't say black. I'll check the power valve tomorrow. I called the dealer about this issue, but they were closed. I'll see about getting new 3" pipes.

thatsmrmastercraft
07-23-2011, 10:22 PM
All of the spark plugs were clean and dry. They were dark colored, but i wouldn't say black. I'll check the power valve tomorrow. I called the dealer about this issue, but they were closed. I'll see about getting new 3" pipes.

Can't go wrong with new exhaust hose.

milehigh970
07-23-2011, 11:39 PM
Is that a indmar? Guessing so cause it looks different then my 86 pcm.lol did these have a ballast resistor for they coil if it is. It sounds alot like how mine started running on the water before it died last week.

oldairboater
07-24-2011, 02:16 AM
Still could have a fuel issue. Old gas is bad gas. It clogs carbs and causes engines to run bad. I harp on old gas because where I live if you leave gas in it.---You will be working on it and it will run bad for a long time.

erat
07-24-2011, 09:47 AM
It is an indmar 351.

TLR67
07-24-2011, 04:19 PM
Sounds like the Ethanol BS Issue I went through.... Check your siphon valve on top of your tank and see if its clogged....Mine was gummed up and I even drained the gas last year and put stabil in the fresh stuff I topped it off with over winter.... Couldnt beleive it was something that small...

erat
07-24-2011, 06:59 PM
Wasn't the power valve.

Next step is to make sure the tank is being vented properly. After that, i have 5 cars that will be sharing 30 gallons of crap gas. Or good gas, if it turns out to be good.

One thing i never did was check timing. Hmmm.

Edit* Tank is vented properly, no problems there.

thatsmrmastercraft
07-24-2011, 08:47 PM
Wasn't the power valve.

Next step is to make sure the tank is being vented properly. After that, i have 5 cars that will be sharing 30 gallons of crap gas. Or good gas, if it turns out to be good.

One thing i never did was check timing. Hmmm.

Edit* Tank is vented properly, no problems there.

Shame on you for skipping the basics.:D

TLR67
07-25-2011, 11:37 AM
Dont forge that siphon valve.... even if the tank is venting good that damned ball bearing and spring can cause you a real headache... Damned Coast Guard BS....

erat
07-30-2011, 06:35 PM
Bottom of the tank.
http://i25.photobucket.com/albums/c94/erat/stuff/DSC03584.jpg

Color after we've taken most of the bottom crap out.
http://i25.photobucket.com/albums/c94/erat/stuff/DSC03587.jpg


What i thought all along. The gas is complete junk. Doesn't even look like high octane, which i thought was blue(ish)? Still, it should be clear. Keep in mind, we burnt off all the old winter gas on that friday, and put ALL new in. So the place we filled it was and is selling garbage gas.


Going to go through the fuel system tomorrow. Pull the fuel filter, and the 2 screens, the one on the pump, and the one before the accelerator pump.

Cloaked
07-30-2011, 06:38 PM
I have seen worse that ran better than your described ailments. Just sayin'. I keep Sta-Bil in my fuel year around.

Glad you found the issue if this is truly the root cause. Let's hope so. The nice thing is that the fuel cells in the old boats are easy enough to remove and reinstall. While you have it out, tighten or replace the hose clamps on the exhaust hoses and grease the rudder zerk.

thatsmrmastercraft
07-30-2011, 08:32 PM
I have seen worse that ran better than your described ailments. Just sayin'. I keep Sta-Bil in my fuel year around.

Glad you found the issue if this is truly the root cause. Let's hope so. The nice thing is that the fuel cells in the old boats are easy enough to remove and reinstall. While you have it out, tighten or replace the hose clamps on the exhaust hoses and grease the rudder zerk.

Good idea.

erat
07-31-2011, 02:40 AM
I siphoned it out through the filler neck. Still have about 15 gallons to go. Not sure if this will 100% fix the problem until i get some new fresh gas to put in it.

Also, lucky me. My miata started knocking today. I'm having such good luck this season.

woodrowskis
07-31-2011, 10:20 AM
I had an '86. Lot sof great times on the Pearl River in Jackson MS.
Anyway, water separator is mounted inside the engine box. It is on the left side and mounted to the angle iron the runs the length of the engine box by a bracket the is appx same height as the floor.
There is a bolt in the bottom. Loosen the bolt and you can drain. Catch the all the gas and it will be easy to tell if there is water in it.

Hawksinkalispell
08-02-2011, 10:00 AM
Erat,

Have you cleaner you Spark Arrester? I had multiple issues and did the majority of what you have or are doing. The gas definetly looks bad but part of my issue was restricted Spark Arrester, not enough air.

I used Purple power but you could use any number of degreaser, critus based or otherwise. I cut an old milk jug and soaked and roatated it the solution for 15 minutes and then rinsed it with water and blew it out with compressed air. The solution turned grimey even though the arrester did not look that bad. The (Air Filter) looked like new and the boat idles great and is not stalling out. Easy, cheap and won't hurt to try. I'm going to make it yearly maintence.

Lakeview
08-03-2011, 01:40 PM
Just finished chasing the gremlins out of my '90 prostar-It was hard starting,stumbling,hard hot starts-
I cleaned rotor cap,replaced both fuel filters( lots of debris,water,rust),fresh fuel,checked power valve,installed new blue gaskets,turned out idle screws 1 1/2 turns after seating,adjusted electric choke after determining it was getting voltage,started right up-checked timing,it was right on-started hot ran smooth.IMO-the fuel today is crap!!!!!!-now I know why Jay Leno keeps Cam 50 race fuel in his collection.

thatsmrmastercraft
08-03-2011, 03:32 PM
Just finished chasing the gremlins out of my '90 prostar-It was hard starting,stumbling,hard hot starts-
I cleaned rotor cap,replaced both fuel filters( lots of debris,water,rust),fresh fuel,checked power valve,installed new blue gaskets,turned out idle screws 1 1/2 turns after seating,adjusted electric choke after determining it was getting voltage,started right up-checked timing,it was right on-started hot ran smooth.IMO-the fuel today is crap!!!!!!-now I know why Jay Leno keeps Cam 50 race fuel in his collection.

Everything gas powered except my truck gets Stabil (or equivalent) at all times.........especially the boat.

oldairboater
08-05-2011, 10:00 AM
With the humidity we have here Stabil is a must. I actually install fuel cut off valves on everything I own that has a carburetor. Run them dry. If it sits and I don't use it in the next month to two months, I drain all the fuel out. Running different types of boats and with my portable generators---wise fuel management keeps them out of the shops or me spending days cleaning gunk out of the fuel system. Good thing that we have almost year around boating.

erat
10-30-2011, 10:51 AM
Well ended up not finding the solution.

I'm not sure i got all the gas out of the bottom of the tank. Siphoned what i could out, then put 6 gallons of 94 back in. Still ran rough. You could give it a good rev and it just shot gas through the engine and nothing was getting burnt. All the gas was just being sent out the exhaust.

Anyway, it was winterized. Shrink wrapped and put away for the winter. Going to have to attack it sometime next spring. Or just send it to the dealer where it was bought and have them figure it out. It's nice being the only owner after 25 years.

Kevin 89MC
10-30-2011, 04:43 PM
just read through the whole post, missed it first time through. I would highly recommend rebuilding your carb. It was not that hard, and the kit is relatively cheap from Skidim. I struggled with some bad gas as well and tried several things to fix it. After rebuilding the carb it ran perfect. I was experiencing similar issues. When pulling off the gaskets, a lot of them had basically disintegrated. Mostly due to age I'd guess, but also I blame a lot of it on ethanol that is mandated in our fuel.
Good luck.

Cloaked
10-30-2011, 07:01 PM
just read through the whole post, missed it first time through. I would highly recommend rebuilding your carb. It was not that hard, and the kit is relatively cheap from Skidim. I struggled with some bad gas as well and tried several things to fix it. After rebuilding the carb it ran perfect. I was experiencing similar issues. When pulling off the gaskets, a lot of them had basically disintegrated. Mostly due to age I'd guess, but also I blame a lot of it on ethanol that is mandated in our fuel.
Good luck.I'll agree and even go so far as to say to put a new carb on it. Just for the sake of knowing it's new and has another 25 years...

erat
11-01-2011, 03:14 PM
Carb was rebuilt once, um. Well i can't remember how many years ago, it was around 10 years ago.

I suppose it's due again. Dang ethanol.

mikeg205
11-01-2011, 07:59 PM
seafoam in every tank and for winter storage...stuff is magic...I also ad stabil ethanol treatment in every tank - probably over kill...but never have problems...

erat
11-07-2011, 06:40 PM
Oh well, i'll be back here in the spring time with hopefully a solution.

Winter time is for my turbo build on my fun car. :D

Reverend Bob
11-30-2011, 10:48 AM
erat,

Pull your intake manifold, replace the gaskets, (carb base gaskets too while you are at it), I think you might be surprised by the results.

Cheers mate,
Rev Bob

mikeg205
11-30-2011, 11:46 AM
erat,

Pull your intake manifold, replace the gaskets, (carb base gaskets too while you are at it), I think you might be surprised by the results.

Cheers mate,
Rev Bob

Erat - if y ou do post pics... before and after... always fun to see...