88 OMC 5.7 Idle Stall & Backfire at Higher RPMs

[Chris5280]

Finally began working on the boat again after she's sat in the driveway for 3 years (job took over my life for a while). Engine was fogged and winterized before storage.

I replaced the Quadrajet carb with a rebuilt Quadrajet a couple of weeks ago, as I'd had some issues with the old one bogging/stalling under load. Replaced fuel filter/separator and added new gas. Replaced plugs as they had a lot of carbon buildup.

Engine starts and idles smoothly for about 5 seconds, then stalls unless I increase throttle. With more throttle I can keep her running but very rough and with lots of backfiring.

What should be my next move?

 

[Scott Danforth]

did you clean the fuel system (tank, lines, etc) if not, your simply pumping the crud into your carb

sitting for 3 years, any fuel in the tank long ceased to be fuel

backfiring at higher RPM is either timing, or a lean sneeze (your running out of fuel)

your next move should be to go thru your fuel system, verify your timing, and probably run from a separate 1 gallon tank until you get the main tank cleaned.

 

[kenny nunez]

In addition to Scott’s suggestion did you also replace the points and condenser. Do not buy any ignition parts from those “Big Box” auto stores. NAPA is a good source or Sierra Marine. You could have either a Mallory or Prestolite distributor. Hopefully you did install a Marine quadrajet and not an automotive version.

 

[alldodge]

If your sure the timing is set correctly, I would do a compression and leak down test, think you have some valve issues

 

[Chris5280]

Scott, I jacked up the bow and pumped out literally all but maybe an ounce or two of the old fuel. There was no fuel left in the lines. I did replace the aluminum fuel line from the pump to the carb- could the line be under or oversized? Couldn't find any specs on it so I tried to match them as best I could.

I haven't touched timing as that scares me, but it was running fine before 3 years of storage. The timing shouldn't need adjustment, or?

Kenny, I checked my records and I also replaced the points and condenser toward the end of the last season I ran the boat, so there are probably 2-3 starts and minimal hours on the engine since. Should I replace those anyway?

 

[Scott Danforth]

with points, every season, you file the points, adjust the points and set the timing. its what you do with a points ignition.

because as the wiper shoe wears, the timing changes on the ignition.

you dont need to replace the points, however you do need to service the points.

 

[Chris5280]

OK, thanks Scott. I do pretty much all my auto and marine mechanical work but for some reason timing is intimidating to me. Is there a step by step for setting timing on this engine? I have a PDF service manual but the timing page is fuzzy.

 

[Maclin]

Dwell then timing will need to be checked/adjusted after any points regap/replacement event. Points gap affects dwell, and timing. Points, along with the rubbing block, being mechanical items wear anytime the engine is running.

 

[kenny nunez]

Get a Petronics conversion for the points or for the time being replace the points. Any time a boat is laid up for any length of time they should be replaced. Once points absorb moisture fron sitting they are no longer useful. Make sure the fly weights in the distributor are not sticking You want the engine idling as slow as it will run to set the timing.

 

[Lou C]

I've had this boat with points 16 years and only had to replace the points maybe 3 times. You use a screwdriver, feeler
gauge and a tach dwell meter (ideally a remote starter switch). You remove the old points and condenser. Then install your new parts. Use the remote starter switch to bump the engine over so the rubbing block is on one of the high points of the dist. cam. Then set the gap with the feeler gauge. Next hook up your dwell meter and crank the engine over to see how close you are to the spec. Keep in mind point gap and dwell are inversely proportional. Big gap = small dwell angle and vice versa. So to keep it in spec longer I like to set it at the lower end of the dwell range (larger gap). Then replace the dist. rotor and cap. Then start the engine and set the curb idle down to about 600 rpm on your tach dwell meter. Then set the timing at this idle rpm. If the timing adjustment changes your idle speed go back and re-adjust it to 600. You do dwell, timing and idle in that order, because dwell affects timing and timing affects idle. Keep in mind these are very simple mechanical advance distributors with the advance weights and springs under the point plate. They need so lubrication now and then. If you go with the Pertronix electronic conversion keep in mind you have to wire up a diode fix so the OMC ESA will still function. The ESA system must be functional or you will have trouble shifting out of in-gear to neutral.

Points & timing are auto shop 101 for those of us, of a certain age lol....

 

[Chris5280]

OK, checked points, set dwell. Now, I can't get my timing light to flash on #1 wire. It's just a cheap harbor freight light, but it gets decent reviews. Any thoughts?

 

[alldodge]

If you can get it to work on any other plug wire then look at the plug, wire and cap for the number 1 wire.

If it doesn't work on other wires then its the light