PDA

View Full Version : Runs rough at idle speed in no wake zone


ski n fly
08-08-2005, 12:18 PM
I have a 87 Prostar. I tends to run rough after an extended period of time while motoring through a no wake zone. I live on a lake in Colorado that is at 5500' msl. This problem just began. I have an electronic ignition with a holey 4 barrel 600cfm carb on the boat. What should I do?

east tx skier
08-08-2005, 03:24 PM
Hi, welcome. Don't know the answer, but here's a BUMP.

6ballsisall
08-08-2005, 03:31 PM
Do you smell fuel in your oil? You probably overloading it with fuel. A rejet on the primaries may be necessary to correct the issue.

Hoff1
08-08-2005, 03:45 PM
Sounds somewhat similar to when a power valve goes out. The longer I would idle, the more the plugs got fouled. When I revved the engine to a certain throttle position and held it constant at that position, the rpm's would jump to say 2500. After a few seconds, the excess fuel would eventually burn off and the rpm's would rise to 3000. Seen anything similar?

ski n fly
08-08-2005, 03:53 PM
I do not smell any fuel in the oil. The carb was replaced 2 years ago. Prior to that I had a power valve problem and it doesn't seem to be the same issue. After about 5 minutes in gear at about 750 rpm, the engine begins to knock, run rough and then cut out. I can provide temporay relief by revving the engine out of gear. I just checked the pvc valve, all spark plugs, the water-fuel seperator and the fuel filter. Al check out OK and then I sprayed some carb cleaner in the carb. It runs great in the driveway with no load on the engine. The boat also runs great in gear with rpm above 1000. Gonna test it in the lake gain this afternoon. Any suggestions.............

Hoff1
08-08-2005, 04:02 PM
My knowledge is basically limited, but if you smell gas in the exhaust at idle it's probably the power valve. Have you had any recent backfires, they'll blow out the valve.

You could also check the air/fuel mixture. This thread will tell you how to do that.
http://www.tmcowners.com/teamtalk/showthread.php?t=4273

ski n fly
08-08-2005, 04:48 PM
No recent backfires and no gas in the exhaust water.

prostar190jap
07-26-2007, 01:26 AM
if there is fuel in the water that comes out of the exhaust that means there is a power valve problem? cuz when my boat is in idle is its real loopy and it runs at like 100-200 rpm. and sometimes i can see gas in the water that comes out of back.
if it a power valve problem how much does it cost to fix?

thanks
Jeff

randyb
07-26-2007, 10:13 AM
It could be just that you are running rich due to the altitude - this will definately foul plugs during idling along. Does the carb have stock jetting or has it been changed for your altitude?

Good luck!

JimN
07-26-2007, 10:34 AM
ski n fly- how old are your plug wires? Check your spark plugs after it runs this way and see if any are fouled. If they are and your plug wires are more than a couple of years old, replace them. The cap and rotor or plugs could be at fault, too.

Checker/Schuck's/Kragen sell Borg-Warner cap and rotor and they have a brand of plug wires that come with a limited lifetime warranty. I just replaced mine yesterday and I had bought my cap/rotor less than 5 years ago (The had a 5 yr warranty then) and asked what limits the warranty- basically parts breakage or other physical damage.

prostar190jap
07-26-2007, 09:38 PM
the plugs are black and some are wet. there is a fine gray dust under the distributor cap.

JimN
07-26-2007, 11:05 PM
ski n fly- You said in a previous post that the motor knocks, run rough and cuts out after about 5 minutes at 750 RPM. Is this a hard knock or pinging? If it's a hard knock, is it possible that it overheated or froze recently? An overheat can damage the head gaskets and it will act the same as you described. Running it with no load doesn't matter and it doesn't tell much.

You didn't say how old the plugs/cap/rotor/wires are. Some performance issues will creep in over time and you won't really notice them until they reach critical mass. My truck did that recently and while I thought it was OK as far as get up and go, it was using a lot more fuel. I replaced my cap/rotor, wires and PCV this week and my plugs a couple of months ago. The performance difference is huge. Unfortunately, putting it off for as long as I did killed my catalytic converter. Again, if your cap/rotor/plugs/wires are more than a couple of years old, replace them. Once you get all of these items to the point of knowing that they are new, fresh and set correctly, you can see where the next step is.

JimN
07-26-2007, 11:10 PM
prostar- If your plugs are wet, you probably have a black, oily residue around your exhaust flaps, right? Are you using any oil?

The first thing I would do is clean out the dust under the cap, gap the points and lube the wedge that rides on the distributor cam, verify the correct timing advance, check/reset the plug gap and check/verify the idle speed. If these don't improve it much, do a compression test or if you can, do a cylinder leakdown test and a vacuum test. These will indicate the general health of the motor.

rektek
07-27-2007, 11:30 PM
I have a 87 Prostar. I tends to run rough after an extended period of time while motoring through a no wake zone. I live on a lake in Colorado that is at 5500' msl. This problem just began. I have an electronic ignition with a holey 4 barrel 600cfm carb on the boat. What should I do?


sounds like a carb fault, leaky power valve etc.. if you had secondary ignition faults they would be worse under load.

has the boat ran at this elevation before ? any backfires ?

post more details

Cheers

JimN
07-27-2007, 11:40 PM
Good question about whether it has run at this elevation before.

ski n fly- did the boat come from somewhere else, at a lower elevation? I would thing it need re-jetting if it was originally from a location close to sea level. At least a good adjustment, anyway.