1977 1150 lose power when at load

[tavacska]

It happened yesterday on the lake. I drove 9 miles away to the site. Everything works perfect.

When I returned, in the half way, the RPM slowly down from WOT to 1800 in 5 sec. Speed down from 30 mph to 7 mph.
The fuel tank almost empty. I thought it was because no fuel. So I combine both the almost empty tank together, which will be enough for return. The symptom remains, and I drove back to ramp with 6.5 mph, 1800 RPM. The idle is harsh and stroke to death if I get it engaged forward or backward. All I have to do is to push it forward quickly to make it drive forward and not die.

When I returned back to home, I checked the compression, all 120-130. Checked all the spark, all 1/2-3/4 gap sparked. Checked the fuel filter, no clogged. Checked the spark plugs, all seems fuel soaked and carbon ed, very dirty, but they still sparked with a in-line tester.

What's the reasons for losing power?
1. Residue in fuel tank? I did see small black pieces in the tank when I tried to move left gas fuel to the other tank. One tank has at least 6 months gas in it.
2. Water in fuel tank? I do not know and don't know how to check it.
3. Sparks? It didn't sound to me a lost of cylinders, but it does have more vibration when I drive. I can feel it. At that time, I am afraid if they can be overheat and burned if it is because of short of fuel.

 

[racerone]

Have you installed a new impeller recently , yes or no ?-----One ignition coil or 6 coils with 2 switch boxes ??

 

[tavacska]

Have you installed a new impeller recently , yes or no ?-----One ignition coil or 6 coils with 2 switch boxes ??

No. It's still the old impeller, but I forgot to the check the impeller, it did have a sting here and there in that trip.
The ignition has one coil and one switch box with a distributor.

 

[jimmbo]

When it was running, any fuel dribbling from the carbs, or from the vent orifice on the inlet housing?

 

[merc850]

Aren't you the guy who replaced the coil with some NAPA car part one because the guy at the counter said "they're all the same"! Could be the coil has failed or it's damaged the switchbox. Seems to me you were also having distributor cap troubles.
(Just for my education where is the "vent orifice on the inlet housing"?)

 

[tavacska]

When it was running, any fuel dribbling from the carbs, or from the vent orifice on the inlet housing?

Didn't check it. Not test run at home yet. Will check it tomorrow.

 

[tavacska]

Aren't you the guy who replaced the coil with some NAPA car part one because the guy at the counter said "they're all the same"! Could be the coil has failed or it's damaged the switchbox. Seems to me you were also having distributor cap troubles.
(Just for my education where is the "vent orifice on the inlet housing"?)

Yeah, I am that guy with an auto coil before. That's another story. Tried different coils and finally bought a OEM mercury coil. The truth is only OEM coil can pass the ignition gap 3/4 test. The distributor cap turns out to be not the problem, it just because the arc from auto coil is so weak, that can not pass through the distributor cap.

So in summary, factory OEM brand new coil, cleaned distributor cap, and perfect run for 4-5 times on lake. Switchbox should be good, I have tested the ignition gap of 3/4 last night. Switchbox is also brand new in shelf.

BTW, the "vent orifice on the inlet housing" I believe is the hole on the carburetor cap. The cap also has a pipe link to nearby the throat. It is for the pressure release of bowl. If the bowl is overfilled, fuel will spray out from the hole.

 

[merc850]

OK, the only thing that is not new is the trigger in the distributor? A failing trigger will work sometimes then not; do you have spark now? You can test the trigger by following these steps: The vent orifice is for the back drag carb fuel economy circuit it reduces the atmospheric pressure at around 2500-4500 rpm which cuts fuel consumption. I don't know what happens if the hose(s) are removed from the carbs but I would guess that they would run rich. I left mine attached.

 

[jimmbo]

(Just for my education where is the "vent orifice on the inlet housing"?)

 

[tavacska]

OK, the only thing that is not new is the trigger in the distributor? A failing trigger will work sometimes then not; do you have spark now? You can test the trigger by following these steps: The vent orifice is for the back drag carb fuel economy circuit it reduces the atmospheric pressure at around 2500-4500 rpm which cuts fuel consumption. I don't know what happens if the hose(s) are removed from the carbs but I would guess that they would run rich. I left mine attached.

The trigger is also new. It's from CDI. Only thing that is original is the stator.
All the spark except for 6th pass the gap test. The 6th is built deep and too hard to do a test.

 

[jimmbo]

The vent orifice is for the back drag carb fuel economy circuit it reduces the atmospheric pressure at around 2500-4500 rpm which cuts fuel consumption. I don't know what happens if the hose(s) are removed from the carbs but I would guess that they would run rich. I left mine attached.

For the past 3 decades the recommendation is to plug the hose of the Back Drag circuit. It seems what worked well during the days when Gasoline was Gasoline, does not work with the Ethanol laced garbage that is being marketed as Gasoline. Alcohol chemically leans the mix and combined with the Back Drag results in a too lean mix at part throttle. A small Ball Bearing in the hose works well.

 

[Chris1956]

Check the spark plug wires for arcing to ground. You can usually hear them snap as they arc. Are the spark plugs steam-cleaned? If so, you may be getting water into the cylinders.

 

[tavacska]

I don't quite get it. So the orifice at point 2 keeps the bowl at atmosphere pressure.
There is a link between 1 and 2. Why there is a link? What's the purpose of it?

Where does 1 go to? I saw some 3 small holes inside the choke valve, which I believe belong to the idle holes.
There are 2 small holes outside the choke plate, are they belonging to the nipple 1?

I am also considering installing a OMC enrich valve to the carburetor. Should I connect the wee lines to the nipple at 1? Should I split the wee lines to three carburetors or just the top one?

 

[tavacska]

Updates:

I prepared the clean empty fuel tank for 2 days. And filled it up with fresh 93 gas.
At driveway, the engine starts in 10 sec and run at idle about 1000 rpm. 5 mins later, with throttle only no engaged, the rpm can clime to 3000 rpm. I dare not to do it higher on driveway. But things seem to come to normal for now.

I will test it on lake this weekend. If it's the problem of fuel quality, things get much easier on every aspects.

 

[jimmbo]

The hose that goes from #1 to #2 is the secret. It, at part throttle high rpm provides a vacuum source, then in conjunction with the metered/calibrated vent/bleed orifice, that vacuum reduces the atmospheric pressure in the fuel bowl. Lower atmospheric pressure means less fuel is pushed through the main jet thus leaning the mix. Very simple and the carb maker was able to do it without a major redesign of the carb, just a couple of holes and fittings, a calibration orifice, and a hose.

The vent/bleed #2 is calibrated to provide a specific reduction in atmospheric by bleeding off the vacuum. At WOT the vacuum in the hose drops and then the orifice functions as a regular bowl vent

#1 would not be an effective location for an enrichment system to be discharging fuel. Downstream of the carb, or the transfer port cover is a better location

As I mentioned earlier, plug the hoses with a small steel ball and reattach to the fittings. Your engine will live a lot longer with the hoses plugged running on todays garbage gasolines. I guess if you only ever could burn fuel with absolutely no Ethanol, you could leave that circuit operational, but...

 

[tavacska]

As I mentioned earlier, plug the hoses with a small steel ball and reattach to the fittings. Your engine will live a lot longer with the hoses plugged running on todays garbage gasolines. I guess if you only ever could burn fuel with absolutely no Ethanol, you could leave that circuit operational, but...

Thanks, Jimmbo, very knowledgeable. It seems I come to understand it bit by bit now.
You mentions the small ball. And you mean it's a total blockage, right?

 

[jimmbo]

Thanks, Jimmbo, very knowledgeable. It seems I come to understand it bit by bit now.
You mentions the small ball. And you mean it's a total blockage, right?

Yep