570A is running horribly - HELP Please

S

sbbamafan

Member
Joined
Jul 28, 2001
RO Number
5516
Messages
54
I have not been on here in a long time. My boat is (still) a 1991 Chaparral with a 570A Duoprop with almost 1200 hours. I have an issue that has been getting worse over the last couple of seasons. I really want my boat to run right again and have grown incredibly frustrated. I'll tell you what I have done over the last couple of years trying to make it better. This has all been the result of intermittent skipping and some backfiring,etc. I replaced the fuel pump and filter and got nowhere. I then replaced the coil as the problem seemed worse after the boat warmed up. It seemed a little better. Fast forward to this year. I took the boat out and it was as bad as ever. Last weekend I changed the cap, rotor, plugs and wires. The boat started right up and I was optimistic. I backed out of my dock and idled to where I could gently apply throttle. It instantly bogged down and started backfiring worse than ever. Back to the dock I went...

It runs in idle and I have taken it to 3,000 rpms and it sounds ok - as long as there is no load. I then ran it and blipped the throttle some from the back with the hatch up. From there it feels as if there is a skip. After a minute or so, it backfired doing that too. I have a video of it if it will help diagnose - if I can figure out how to post it.

I am down to what seems only a couple of other possible issues as I see it now: distributor, ignition sensor, ignition module, or carburetor (Holley 4150). What are you smart people thinking the problem is? I am really desperate to get this fixed? Thanks in advance for your help!!
 
Any of those things could be the problem, but I would not throw any more parts at it until you check the engine compression. You could have something else going like head gasket issues, valve issues, etc...
Compression testing should tell you the basic health of the engine.
 
No load it revs up fine and with a load it wont go to top speed/revs is a classic fuel obstruction/restriction problem.

Not to sound like a broken record but there is a brass screen that is usually brazed to the end of the pick up tube that is in the gas tank. The smallest bit of dirt and electrolysis will clog this screen. I cut the thing off altogether. Between your filter , separator and a possible carb filter I think the thing causes more problems than it solves. While you have your pick-up assembly out, get a flash light and look in the tank there for any garbage you can manually remove. One sign of this problem is the hose between the pick-up and pump will collapse- its sucking against the obstruction so hard. Depends on the quality of hose.
Hope this helps
Steve
 
quote:
Originally posted by Steve the plumber

No load it revs up fine and with a load it wont go to top speed/revs is a classic fuel obstruction/restriction problem.

Not to sound like a broken record but there is a brass screen that is usually brazed to the end of the pick up tube that is in the gas tank. The smallest bit of dirt and electrolysis will clog this screen. I cut the thing off altogether. Between your filter , separator and a possible carb filter I think the thing causes more problems than it solves. While you have your pick-up assembly out, get a flash light and look in the tank there for any garbage you can manually remove. One sign of this problem is the hose between the pick-up and pump will collapse- its sucking against the obstruction so hard. Depends on the quality of hose.
Hope this helps
Steve

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