I'm a believer... (now) UPDATE!!!

F

Fish Guts

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So I was having this issue with my sbc 5.7. I wasn't reaching WOT or even close to it. The boat would not even get on plane. So another full tune up and still not going anywhere. I was thinking there must be a serious problem with the engine. I always read on here about making sure to have a clean bottom and running gear, but didn't think it could cause that much loss of power/speed. Hauled it out and pressure washed, sanded and antifouled the drive and trim tabs. The hull was pretty clean. Tons of barnacles on the running gear though. So, dropped her in this morning and she jumped right up on plane. What a relief... The moral to the story is... Never assume that it couldn't be something so simple/stupid. There is a reason people here give advice. I am a believer now.

Okay so... That one day I put it back in it seemed to be good. It was a quick ride, but she seemed really good. A week later, I go out fishing and she's running bad again. wont get up on plane. Bottom and running gear still clean. I'm wondering about the exhaust flappers... I had put some new aftermarket rubber flappers in at the beginning of this season. Let's say they are not "flapping", maybe stuck closed... Do you think this would cause the loss of power? I would think if it was holding back the exhaust, the engine would start getting hot, but she doesn't. Took her out today and she's still the same, doesn't run well over 2200 rpm, at one point, if I throttled really slow, I hit 3000 rpm and she planed. But, as I tried to trim or use the trim tabs she popped through the carb,Electrical problem? I am really getting disappointed at this point. Oh, one other thing, A new SEI outdrive...Has anyone had a bad experience with these? It was the right ratio for the engine.

Going to do another compression test after work tomorrow, I will post the results.

Thanks all,

Richard
 
Should be 1.5:1 gear ratio. May be 1.47:1 which is virtually the same. If it's a 1.33 or something, it'll never get on plane with a prop for a 1.5.

Could very well be a blockage from flaps falling into the exhaust.
 
Charlie, it is a 1.47. I'll check on the flappers tonight, but wouldn't the engine heat up if there was blockage?
 
Depending how much blockage. When making my SS exhaust system, I had to adjust the amount of baffels in the muffler section. Too many or too large baffle plates quieted the exhaust noise quit a bit but the restriction reduced power enuff to reduce WOT but didn't overheat...but it can very well create enuff heat that it can burn up both the flappers and rubber connectors on stock exhaust.
 
Is it missing, sputtering, coughing, backfiring? Or just doggy, as if somebody pulled your engine and put a smaller one in?
 
j-d, Just like someone swapped for a smaller engine. Although, when I am trying hard to get on plane, if I try to trim the engine or trim tabs it does for some strange reason give a backfire or "pop".
 
Your power trim motor is sucking needed battery power away from your ignition when hit the Trim Switch. Check, Clean, Repair, Replace Battery Connections. I've had this happen with ours. Also fixed a MerC powered boat that had simply quit in the ICW by cleaning battery connections. They told me that it would miss when they worked the trim, right before it quit.
MerC products are Battery Sensitive. I don't know if a weak battery would limit engine power or not. Do you have a Battery On/Off or Select Switch? Check those connections too. Operating the switch through all its positions a few times before you start the engine may help.
You've been at this awhile. I remember you had several threads about it but I don't remember if you checked Distributor Cap and Rotor. I've had to replace ours three times. The center contact in the CAP is spring-loaded and gets stuck. This causes poor contact with the center terminal of the Rotor.
 
j-d, yeah, already new cap, rotor, coil, plugs, wires and ignition module.
Thanks,
 
Then get your Battery connections up to speed, including Grounds, and report back.
 
Richard, be CERTAIN, too, that your Spark Plug Cables are properly installed, snapped down on both ends, and that you have installed them in the proper Firing Order. I once had one cable not snapped all the way down onto the plug. It ran "OK" and it would plane, just didn't seem "right." Remember the Chevrolet Prayer. For All Eight and best recited in order: "One Eight Four Three Six Five Seven Two." Charlie mentioned that the way Five and Seven are physically adjacent AND in firing sequence, a cross there can be hard to notice.
I'm wondering if conditions on your first test run weren't somehow more favorable than the second. Less people/gear in the boat. Different current, etc. It seemed OK first run but couldn't hack the second...
 
j-d, I just put the new wires on 2 weeks ago. Put them on one at a time so i would get it right. Actually double checked they were all on good Sunday Morning before I went out. I will be pulling the elbows tonight to check the flappers. Do you guys think the T-bolt IV module could cause this problem? It's the only ignition piece I haven't replaced yet.

Thanks,
 
Can't comment on the TBoltIV other than to say if whatever controls spark advance isn't controlling it properly, it'll be a dog.
I installed Sierra Flappers in ours recently. I had to trim some plastic nubbins off of the outsides of the brackets. If I'd crammed them in, they would have bound up.
 
Kinda like jd said, sounds like your trim circuit is somehow connected to the ignition circuit and robbing power and preventing a spark plug from firing. When that happens, the intake of fuel/air mixture is sent out the exhaust as raw fuel. The next cylinder that fires, ignites the fuel/air in the exhaust that can cause a very loud bang. Not good for the engine or the exhaust.

A thing to check on the TBIV. There's an upside-down toothy thingy connected to the rotor. Those teeth have to pass cleanly and evenly thru firing sensors. Instead of buying new sh*t every tune-up, I would re-use the old stuff. That toothy thingy gets bent a little trying to get it off every time. That's all it takes for it to NOT pass cleanly pass the pick-up.

I also filed down the center post that the rotor sits down on so it comes off easy.
 
Charlie, why would that toothy thingy get bent when I take it off? The rotor slides on and off easily, is there supposed to be some type of adhesive?

BTW, didn't make it down last night to pull the elbows and check the flappers, family first, ya know. Will be there tonight.
 
Maybe they finally got smart. You used to need two screwdrivers to lift the rotor...and they recommended blue loctite. Anyway, this was just another thing to check that effects engine performance. Turn the engine over by hand and carefully look at to make sure each tooth passes exactly evenly between the pick-up.
 
Well, flappers are fine, working perfectly. never realized though, that the water goes right up to them. But then, I never had the exhaust apart while the boat was in the water. I guess I'm back to the valves/heads. I am going to do another compression test sometime this week/weekend. Last time I did the compression test they seemed to leak out pretty quick. If worse comes to worse, I sit and enjoy the boat at the slip for the rest of the summer and pull the engine in the fall for a rebuild... UNLESS, one of you fine fellas' have anything else I could check???

Thanks for all the help,
 
When you tried it out and it ran good, were you alone in the boat with a liht fuel load?

When it doesn't perform is it full of fuel and "stuff"?

Are you sure it doesn't have a load of water in the bilge?
 
O.H., when it seemed to run good, I had just filled the tank, with just me and my wife. Same as this past weekend. It was out of the water for a week, so bilge was dry.I always drain as I no wake out. I thought it was the flappers because of the low pitched "buh,buh,buh" when I'm trying to plane out, just no power.

Thanks,
 
Charlie, I think I remember you saying you rebuild your own heads. When I replaced a few of these valves, there was quite a bit of play between the valves and guides, this is bad, no? Would that kind of valve play cause that type of loss of power (rhetorical question I guess)?

Thanks,
 
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