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.