Stumbling at Cruising Speed - OMC 5.8L

[dubs283]

Ground the coil secondary wire and turn the engine over with the ignition switch on. Observe dwell reading and adjust accordingly. Once it's all back together and running check dwell again. If it's in spec, great. If not adjust accordingly until correct then set the idle timing to spec

 

[Scott Danforth]

OK. Got the dwell meter. What is the best method to set dwell? Can't really adjust the points with it running like other models, due to the distributor cap, unless I'm missing something

With dizzy cap off and rotor off. Use dwell meter and remote start switch. Crank motor while adjusting points with the screwdriver slot.

Takes about 20 seconds

 

[Lou C]

With dizzy cap off and rotor off. Use dwell meter and remote start switch. Crank motor while adjusting points with the screwdriver slot.

Takes about 20 seconds

That’s how I do it; as long as you can easily get to the S terminal on your starter it’s the easiest and fastest way. I look at the faces of the points first to decide if I want to replace em or not. I think the set that’s in there is going on 8 years old! I have a couple sets of spark plugs that I clean and just rotate use. They really don’t wear out…it just doesn’t get enough hrs like on our old cars when we changed them once a year or every 12,000 miles. Funny thing doing points on an old Chevy makes you feel like a time traveler lol. One of GM’s best ideas was that Delco window distributor and the points & condenser mounted on one mount together. Very easy compared to the Fords at least though Ford had the distributor up front. As well as the oil filter and the starter bolts were easier to get at than GMs

 

[LakeMichiganBoater]

OK... dwell set to about 28 degrees, timing is 10 BTDC, coil replaced, belts replaced, and took it for a test drive.

Not getting the stumbling at cruising speed, but still having the issue where is starts great on muffs, idle set at 800 rpm. I get it on the water, starts great right away, run it for a while at cruising speed, and it dies at idle. I have to crank the idle screw up every time i start it to keep it at 800 rpm... any thoughts?

 

[Scott Danforth]

Marine carbs do not have a cold idle cam. Adjust your choke a bit. Idle should be set when warm, in gear in the water

 

[LakeMichiganBoater]

Marine carbs do not have a cold idle cam. Adjust your choke a bit. Idle should be set when warm, in gear in the water

Ah... ok. It was set on muffs, warm, in neutral. I'll give that a try

 

[LakeMichiganBoater]

Ok... new thought. Engine temp.

My gauge has always shown 160 and never noticed any signs of overheating but...

The largest hose from the front is always very hot and the other three are cool (on cold hose water).

I removed the big one and ran the engine for a few seconds and cold water is coming out of the thermostat. Why would this big hose be so hot. The water inside it is almost scalding when i removed it. Could there be a blockage somewhere?

Exhaust manifolds are always cool. Water is exiting the rear of the out drive when running.

 

[dubs283]

If you ran the engine as it's pictured and noted cold water exiting the large barb hole for the circulating pump hose that's normal

You're seeing the raw water supply from the pump in the drive. Thermostat controls water flow exiting the engine block and would only release hot water to exit via the exhaust cooling hoses/system

The circ pump hose is hot because it's connected to the pump that is circulating hot water through the block. The raw water cannot overcome the flow created by the hot water so it exits through the exhaust. Only when the thermostat opens does the raw water enter the block through the hose due to the difference in block pressure

 

[LakeMichiganBoater]

If you ran the engine as it's pictured and noted cold water exiting the large barb hole for the circulating pump hose that's normal

You're seeing the raw water supply from the pump in the drive. Thermostat controls water flow exiting the engine block and would only release hot water to exit via the exhaust cooling hoses/system

The circ pump hose is hot because it's connected to the pump that is circulating hot water through the block. The raw water cannot overcome the flow created by the hot water so it exits through the exhaust. Only when the thermostat opens does the raw water enter the block through the hose due to the difference in block pressure

Thank you, i pulled and tested the thermostat and it checked out. Kinda an odd system compared to a car, had to pull out the manual to figure out the flow.

 

[Scott Danforth]

Thank you, i pulled and tested the thermostat and it checked out. Kinda an odd system compared to a car, had to pull out the manual to figure out the flow.

It's used as a mixing valve to mix block circuit with the constant flow to exhaust

 

[LakeMichiganBoater]

Thermostat checked out, but I replaced it anyways... needed the new gasket.

So idle is good now, points are set with dwell meter, timing is checked, coil replaced, plugs replaced, carb was rebuild, idle air jet adjusted using a vacuum gauge, fresh oil, fresh fuel filter and I am still getting a slight stumble. Feels almost like a misfire...

Is it worth going to an electronic ignition? If so, what is the proper Pertronix conversion kit to use? There seems to be a lot out there.

 

[froggy1150]

Stumble on throttle up? Try adjusting accelerator pump. Could be a lean stumble. Just cuz carb was rebuilt doesn't mean all adjustments are dialed

 

[Scott Danforth]

Is it worth going to an electronic ignition? If so, what is the proper Pertronix conversion kit to use? There seems to be a lot out there.

No, especially not Pertronix

 

[LakeMichiganBoater]

Stumble on throttle up? Try adjusting accelerator pump. Could be a lean stumble. Just cuz carb was rebuilt doesn't mean all adjustments are dialed

Seems to be the same misfire feeling across the throttle range.

 

[LakeMichiganBoater]

No, especially not Pertronix

Is there any that are suggested?

Points and capacitor were replaced also.

 

[Scott Danforth]

Is there any that are suggested?

Points and capacitor were replaced also.

the old Mallory YLM distributor for your ford. however its now Sierra as the mallory line for marine was sloughed off to Sierra. I do not know the quality since the change.

 

[Lou C]

OK I don't have your engine in my shop manual (1988) so I don't know for sure what distributor you have, but if it's like mine (Prestolite points dist) it has mechanical (centrifugal) spark advance. This unit is under the points plate and it advances the timing with RPM using fly weights, and then retards the timing using springs. There is a lubricating wick in the dist. shaft you will see when you remove the rotor, this should get a few drops of oil each season to keep the fly weights and springs from rusting. You can also check your total timing advance at the specified RPM, using an advance timing light to make sure you are getting the correct total advance.
This is very old tech, it works just fine but most young'uns, ain't never seen it before lol. I stuck with the points because I really have not had much trouble with them at all over the years.
the fly weights and springs are under the points plate, you can see the wick in the dist. shaft. a coupe of drops of oil is all it takes, yearly.