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mzimme
06-10-2012, 11:40 PM
I have an 83 S&S with 351 and slot trans. As I was pulling up to the ramp to pull the boat out, the engine started surging both in neutral and while in gear. If I give it any more gas than just the first idle "click" on the throttle, the surging stops and it runs fine.

Haven't had any issues with this before now. The water was really rough coming in, not sure if that would play a part in this.

What things can I start looking for a surging idle? Also, while in gear just idling forward, the RPM's have been abnormally low. Like around 6-700. Any ideas where to start troublshooting for this?

Tom190driver
06-11-2012, 12:04 AM
i bet you have a holley 600cmf carb. i run LUCAS IN MY 1990 prostar 190/351w an that was a easy fix.

mzimme
06-11-2012, 09:01 AM
Yeah, it is a holley carb. Not sure if its the 600cmf, however. Are you talking about a fuel additive?

JimN
06-11-2012, 09:44 AM
I have an 83 S&S with 351 and slot trans. As I was pulling up to the ramp to pull the boat out, the engine started surging both in neutral and while in gear. If I give it any more gas than just the first idle "click" on the throttle, the surging stops and it runs fine.

Haven't had any issues with this before now. The water was really rough coming in, not sure if that would play a part in this.

What things can I start looking for a surging idle? Also, while in gear just idling forward, the RPM's have been abnormally low. Like around 6-700. Any ideas where to start troublshooting for this?

Make sure the throttle linkage isn't worn and sloppy, causing the RPM to drop. Look at the helm for loose mechanical connections, too. Remove the throttle cable from the carb and see if it runs better, too.

If it runs fine with the throttle cable off, it's not the carb. If it still runs bad, I would also look at the distributor- the advance weights and springs may be sticking, the points may be worn (if you still have points) or the distributor shaft bushing may be worn. Check the timing- if the advance is wrong, re-set it but make sure the advance is working correctly. If the advance is OK, make sure the indicated timing is stable, not jumping around (this would indicate bad bushing).

thatsmrmastercraft
06-11-2012, 10:34 AM
Could also be as simple as time to replace the spark plugs or dist cap & rotor.

mzimme
06-11-2012, 03:30 PM
Thanks for the suggestions. I'll probably start with a tune up of the plugs, wires, cap, and rotor. I don't know when they were last changed, so it's probably time for that anyway, then I'll troubleshoot from there.

thatsmrmastercraft
06-11-2012, 05:21 PM
Before doing that, you might check for a vacuum leak around the base of the carb. Spray some carb cleaner (with caution) around the base of the carb and the base plate to intake gaskets with the engine idling. If the idle speed increases, you found your vacuum leak and the source of your problem.

Does your boat still have points or have you upgraded to electronic ignition? If the points are old, they may be the culprit.

zekedog
06-11-2012, 05:42 PM
The rough water may have shaken up some sh*t in the bottom of your gas tank and you were sucking some bad gas? Just a guess. How much fuel was in your tank after you got it on the trailer? How old was the fuel? I have some friends still running on last seasons fill up with no additives.

mzimme
06-13-2012, 10:13 AM
Before doing that, you might check for a vacuum leak around the base of the carb. Spray some carb cleaner (with caution) around the base of the carb and the base plate to intake gaskets with the engine idling. If the idle speed increases, you found your vacuum leak and the source of your problem.

Does your boat still have points or have you upgraded to electronic ignition? If the points are old, they may be the culprit.

It still has points. I still want to do all the regular maintenance just so I know when everything has been tuned up for my own piece of mind. She runs fine as long as it wasn't idling. Had no issues whatsoever under power (past forward idle).

The rough water may have shaken up some sh*t in the bottom of your gas tank and you were sucking some bad gas? Just a guess. How much fuel was in your tank after you got it on the trailer? How old was the fuel? I have some friends still running on last seasons fill up with no additives.

I've been through probably 6-7 tanks already in the last few weeks. Definitely wasn't old fuel. I took it out last night just to see if it was still acting up. The surging was gone, but it still had a low idle. I just adjusted the idle screw on the carb and it got back up to normal and ran fine. Everything seemed good after that. :banana:

thatsmrmastercraft
06-13-2012, 10:23 AM
It still has points. I still want to do all the regular maintenance just so I know when everything has been tuned up for my own piece of mind. She runs fine as long as it wasn't idling. Had no issues whatsoever under power (past forward idle).



I've been through probably 6-7 tanks already in the last few weeks. Definitely wasn't old fuel. I took it out last night just to see if it was still acting up. The surging was gone, but it still had a low idle. I just adjusted the idle screw on the carb and it got back up to normal and ran fine. Everything seemed good after that. :banana:

Could just be a slight miss. Full tune-up will take care of it if this is in the ignition system. Could be dealing with a fuel issue as well. If you have a float starting to weigh a bit too much, you can get some surging from overflow of fuel in the fuel bowl.

Good plan to work through the basics first.

JimN
06-13-2012, 10:28 AM
It still has points. I still want to do all the regular maintenance just so I know when everything has been tuned up for my own piece of mind. She runs fine as long as it wasn't idling. Had no issues whatsoever under power (past forward idle).



I've been through probably 6-7 tanks already in the last few weeks. Definitely wasn't old fuel. I took it out last night just to see if it was still acting up. The surging was gone, but it still had a low idle. I just adjusted the idle screw on the carb and it got back up to normal and ran fine. Everything seemed good after that. :banana:

Re: the idle screw- if you find that the RPM alternates between normal and high (over 1000RPM) now that it's idling OK, you may have a worn pivot on the throttle plate. I have seen this a couple of times.

mzimme
06-13-2012, 11:14 AM
Re: the idle screw- if you find that the RPM alternates between normal and high (over 1000RPM) now that it's idling OK, you may have a worn pivot on the throttle plate. I have seen this a couple of times.

Funny you say that, after I adjusted it initially, I did have to tone it down a bit on a start later that night because the idle was too high. What's the part you're talking about? Any pictures?

JimN
06-13-2012, 01:35 PM
Funny you say that, after I adjusted it initially, I did have to tone it down a bit on a start later that night because the idle was too high. What's the part you're talking about? Any pictures?

Look at the rod that the throttle plate is screwed to- the ends are where it pivots.

Make sure your throttle cable/linkage isn't hanging up, too.