Disparate and out of ideas!!!!!!!!!
 

Ok, here I go again and I don't even know where to start. twin 454's in a 1984 36' Sonic that are either having an electrical or fuel problem of some sort the best I can guess causing intermittent partial engine power loss.

Problem: When I apply power to get up on plane, the tachs go up to about 2300 to say 2800 rpm's. The nose pitches up and then the thing won't get over to plane. If I apply more throttles, doesn't make anymore power. The boat plows along through the water. If I let it set there at that setting, eventually it "sometimes" all the sudden starts developing more rpm (I hear the engines turn up) and the boat goes on over and planes but you can tell it's sometimes still not developing the power it normally did at that throttle setting. So there we are rolling along when all the sudden the rpm's maybe jump up more and the engines are finally producing what you normally expect; she'll run about 68 mph. Your running along say at 3800 rpm, all appears normal and then all the sudden the rpm's drop off on maybe one, maybe both engines (usually one), you hear the engine(s) reduce power output. So you run along a bit longer and then all the sudden the rpm's come up again and the engine (or maybe both of them) come back up to normally expected power again. If the rpm's drop off real good, you do get some popping through the carb of the effected engine.

The problem began occurring once in awhile after I had the engines rebuilt and after spending a couple of weeks sorting out the cracked spark plug, installing new MSD 8.5 mm wires, new fuel pumps and assortment of things chasing an occasional popping I was having then at high rpm's, some of you may remember that. Once that was all resolved and I began putting a few hours on the engines (now have just under 10 hours on them) this "surging" issue began appearing and got progressively worse. It's now to the point that you really can't take the boat out unless you want to plow around in the water all day waiting for the engines to catch.

I've cleaned every electrical connection I can get to from the battery to the selector switch, starters, coils and grounds. As usual, I've been chasing the problem so long that I'm fresh out of ideas, but if I buy one more part for this thing and it doesn't fix it, my old lady is going to be over this boat thing and we all know what that means; there'll be hell to pay and I go back to the honey do's instead of my dream of 20 years or more!!!!!! So please, I sure could use some help. Thanks guys and I'm really sorry for the "novel" but I guess I'm probably approaching the end myself. I really would like to enjoy this thing after fighting it for just over a year now (always one thing or another). Never have got to enjoy it for more than an hour or so. Sure wish I could afford a brand new one. Thanks


Al

It may be that one of the engines has sticking advance weights in the distributor. If one engine is lagging,the other one will not pull the boat over onto plane. Once it breaks over it uses less power so you can run,but this would also explain the "catching up" after a while. Check it with a timing light on both engines.

have you checked your fuel lines/filters/ separators for blockage? try installing a mechanical fuel pressure guage on the carb to see if you are getting adequate fuel pressure to the carbs.

Get fuel pressure gauges on both engines and sit someone back there to watch them while any of this is going on.

I'll check it out and let you know. Thanks for the response.

Al

I pulled the filters/seperators last night and install new ones. I did find some water in them which was a little rusty looking (specially the starbroad side) and seemed to have some rubbery pieces in it to, never saw that before when changing them in the past. After changing the filters, I took it out today and tried them; didn't see any change. Maybe the lines from the tanks have a restriction? Can I blow some air backwards from the filter? My thought here is that if they are restricted, this would maybe clear them at least long enough to see a difference. If I see a change, I open the tanks and see what's going on in there. What do you think? Thanks for the reply.

Al

I've got those "blue" metal feed lines at the Holley 750 dual pumpers and noticed an allen screw on the "knackle" where the fuel line attach and just before the split to the two carb feeds. Is this a port for gauges? They appear to be about 1/4" allens. I'm deffently going to find gauges and install them to see what's going on there and will let you know. Thanks for the reply.


Al

I had simular problems with my boat earlier this summer....fuel filters had some watery crap in them....replaced the filters but still had problems..pulled the carbs apart and found water and more crap in one of them. I rebuilt the carbs, replaced the filters again, but before cranking the engines, I pulled the fuel tank sending unit out and used a hand pump to remove the remaining water and crap from the bottom. I got about a cup of it out of a 140 gal tank. Put it back together and have had no problems since. Maybe you have the same problem.

Definetly sounds like a fuel problem. Four stroke engines do not digest water well at all.

did you notice what your fuel gauge was before experiencing this, and did you investigate your fuel pickup tube for a cracked pipe yet

Alcor-
Intermittent problems can be a pain in the a$$!! But on the bright side, it is usually something simple. The debris in your seperators is possibly related to this problem and it would help to do some investigation into the entire fuel system.


Popping can be caused by:
1) fuel starvation
2) erratic or incorrect timing
3) bad exhaust 'situatuion' such as bad cam lobe or bent pushrod.

1- fuel starvation-
I believe that you should have about 4-6 lbs fuel pressure, and that could be checked with a fuel pressure gauge.

If it varies or is low then-

You may have a crack in a fuel pickup tube that is randomly exposed/covered. The next suspect is the anti-siphon valve. Also, what is the condition and type of fuel pumps you have???


If the pressure to the carb is ok, check the carb itself. check for:

water/crud in the fuel bowls and/or jets
fuel bowl level settings
power valve condition

2- erratic or incorrect timing
Put a timing light on the engine and note any jumping, etc at idle. Raise rpm to about 12-1500 and check again. Finally run up to about 3000 and look for any variation. Variations can be caused by stuck advance weights, slack in timing chain or faulty ignition module.

3- This is probably not your problem, but good to check if all above are OK. check rocker operation.

I may work late thursday 8- 9pm , but feel free to call me at 985-893-3831. If I am not there leave a message, and be sure to mention the boat so my burnt out brain will kick into gear.

PS- I grew up on Bengal Road by Airline Highway

Bulldog aka Ronnie:frog:

alcor, I would also remove all your fuel lines and blow them out with an air hose, and blow out the feed lines (you will hear air bubbling in the fuel tank) if there is no restriction in any of your fuel lines and you have adequate fuel pressure at the carbs (checked with a mechanical guage) then you probably have **** in the carb.

I had a problem like this earlier this year and found a voltage drop at the ignition box along with a bad ground. I replaced the primary wires with new ( positive and neg.) and it started running corectly.. Check the power input wires going to the ignition box (MSD) and make sure there is a full 12v while under load.

Had a simular problem with a sonic, did you put in new fittings on the tanks ?

Alcor-I feel your pain. I have a similar problem on my cruiser. Both engines run fine for a while. Then the starboard engine starts losing rpms/power. It drops to about 1800 rpm. I have changed fuel pump, ignition module, coil,did voltage checks, changed fuel filters, changed fuel lines, took the check valve out and still can not find the problem. I believe that air is somehow getting into the fuel line. I can not take the pickup tube out without pulling the engine as it is a side tank under the gunnel. I am still looking for ideas so I will follow your thread closely. Good luck.

SGrady,

Could you explain further? I just replaced fuel tanks and have some kind of electrical short, tachs jumping all over the place, and motors popping

Fuel Pickups?
 

Maybe clogged/unclogged because of junk in the tank?

Alcor. Friend of mine had something similar to that last year. Ultimately what we noticed each time the symptoms would happen was, the voltage meter would drop to 12v (vs closer to 13.5-14). We'd be crusing along, and the RPMs would drop to 3000. There was also some intermittent popping.

It always sounded though like some sort of fuel problem.

As I recall last he did was to trace back and make sure the output from the alternator was good back to the electrical block area.........and it was perfect after that.



Bob

Thanks guys!! The responses have been great. Thanks for the call today Ronnie (Bulldog), enjoyed the conversation.

Based on the response, I'm betting on "crarp" in the tank, lines and probably crabs by now. Checked time at idle and about 1500 rpm and seems to be normal, no variation, of course they run great in teh driveway, seems to happen under load. So my plan is to:

1. Take the crabs apart, clean'em out and put them back together. Had just had them rebuilt with the engine job.

2. Blow out the lines all the way back to the tanks.

3. Install fuel gauges so I can see what's going on there. Sounds like that's a good thing to have on them anyway.

Since I can't access the fuel pickups easy, I figure I'll run it after that and if the problem is gone or has change significantly then I'll open the tanks (not looking forward to that in this boat) like AGGRAVATION28 suggested and clean them out while checking for cracks in the pick-ups at the same time.

Hey if nothing else, it sure is good to here from other guys who have had similar problems. Thanks again and I'll let you know what I find. Hey Jersey Tom, let me know if you find anything in the meantime, sounds like we definitely have the same problem.

Al

This will sound crazy, but I had a 290 PQ that I had a similar issue with. It just did not seem to have any power and was also sooting the transom. After checking everything I knew to check, someone suggested I look at the battery and battery switch connections. I thought the guy was crazy as the batteries were charged fully and the volt meter showed 13.6 volts.

So I checked the connection and they were tight, but not real tight. So I cranked them down.....on the battery, battery switch. Problem went away.

It may be worth a try.....it costs nothing and only takes a minute or two:D

It always started fine and idled great....just had no power.

Alcor-I installed a see through glass in line filter on the fuel line from the tank pickup to the first filter. The glass showed what I believed was happening, air in the line. I retraced my steps and found that my original problem was a bad check valve. When I was first trying to fix this I took the check valve out and replaced it with just an open fitting, figuring that would fix the problem. It turns out that the lack of a good check valve causes siphoning of gas back into the tank from the filter every time the motors are shut off. The filter is higher then the fuel level in the tank. When I was running at high RPM for extended periods, the filter would run low on fuel as the air prevented a good suction from the tank. With a good check valve, air can work it's way out after running for a while. With an open fitting, the air would return whenever I shut the motor off. I replaced the open fitting with a new check valve and now the glass filter shows full with no air. I still have to run the boat hard to verify that the problem is fixed but I think I got it.

Jersey - Where's the check valve your speaking of locked in your system, I'm not familiar.

I've taken on carbs apart (on the worse engine) and didn't find anything. The filters were clean and I've blow all lines out and installed the fuel pressure gages on the dual pump manifold at the carbs. Blew backwards into the tanks and will run it in the monring to see if that made any difference.

The carbs have a 3752 B number stamped on the top and the throttle body has a 12R 4770 B stamped at the base. Tried to look them up on Holley site but couldn't find any of those numbers. They have "71" jets in one side and "80" in the other. Any idea if these are close to sounding right for 454's? Based on everthing I've found on this boat so far, wouldn't surprise me to find out that these are automotive carbs, not sure if that would make a difference or not. They've run pretty good but they still may not be marine carbs. Will let you know how I make out tomorrow.

Al

Hey, at this point, I'll try anything. Took they off and cleaned them again and tight the hell out of them. Will see if that helps in the monring.

Al

Alcor-the check valve is located on the fuel tank. It is where the fuel hose attaches. Take the hose off and unscrew the fitting. The check valve is part of the fitting. New ones cost $11-$12. I ran the boat today and so far it's ok. Looks like it was the check valve and then air in the line.

Got it. Decided to have an alternator checked and it was found to be erratic. It would only produce 13 volts tops; dropped from there occasionally on the test machine to about 12.5 and also indicated that it had a bad diode, sometimes it worked then it did then it did again, kind of like the problem I'm having. A new alternator on the machine showed 14.5 volts which the guy said was what I should be getting. Replaced it this evening too. Will run it in the morning. Man, glad to hear your's appears to be solved, now good enjoy it! I'll let you know how I make out.

Al

Well after a couple of weeks of trying this and that, looks like I finally got them running like a top; turns out it was a combination of a number of small issues: here's what I found:

1. Plug wires caps were loose and wires were breaking down - replaced them with MSD's best 8.5 mm wires.

2. Installed fuel gages and found one fuel pump fluctuating - changed both fuel pumps as the one's they had on it turned out to be automotive anyway, no rupture tube (hose) to the carb.

3. One alternator had voltage dropping as low as 12.5 volts, the other one was putting out 13.9 - had them rebuilt installing 14.75 volt internal regulators and both are now 65 amp (one was 55amp the other 65 amp)

4. Finally. Even though the carbs had been "rebuilt", turns out they didn't do anything but change a couple of gaskets and screwed up the float settings in the process. Had them rebuilt by a reputable rebuilder where they test them on an engine and then tell you not to mess with anything but the idle screw. THIS WAS THE CAUSE OF THE RPM's (and engines) SURGING FROM SAY 3000 RPM THEN 3,500 OR VISE VERSA.

The occasional pop through the carb on the top end is gone and the plugs are a nice light tan/brown instead of the white white they had been. Bottom-line; after rebuilding the engines and going through the accessories getting them right, THE DAM THING RUNS LIKE IT SHOULD. The guy(s) that had it before me went way out of their way to screw it up over the years!

Many thanks to you guys for all the thoughts and suggestions, I hope I can return the favor when you get desperate. Based on the threads which I now read on a daily basis, it's not a matter of whether you will ever get desperate with these boats, it's a matter of WHEN! But hey, if it was easy, you'd have girls doing it! Thanks again.

Al

Great news, Al. I guess a lesson here is to never, ever underestimate the ability of some people to totally screw things up.

Bulldog aka BulLfrog

:frog:

alcor,
Glad to hear things finally came together for you!! Now relax and enjoy that thing!!

Dick

Glad to hear you got it running well. :)