521: Intermittent loss of power

[MicroMachinery]

So the other day I was on a drive(about a 4 hour drive; 2 to my destination, 2 to return), and a 2 hours into it, I felt my truck hiccup(felt like a misfire). I thought nothing of it, until it continued happening at a rapidly increasing rate. What would happen is I would lose power; felt like I was starving for gas, with backfiring. My foot would go to the floor, and I would get nothing but popping, or nothing at all. Sometimes I would get a surge, but overall, I would lose power until my engine just flat-out wouldn't run. When it would happen, I took off the air cleaner to look into the inspection glass on the carb - fuel level right where it should be. Not low, not overly full.

I didn't make it home for about 8 hours worth of dicking around on the side of the highway. I suspected at once that something had found it's way into my carburetor, but 2 tear-downs and clean-outs have somewhat put my suspicions to rest(I've even looked down the throat of it when it's running badly, and it looks like the spray pattern in the primary barrel is good and even). I have cleaned and gapped my points. After trying that, I replaced them altogether. I've re-set the timing, also cleaned and lubricated my vacuum advance(thought that was it until yesterday the gremlin re-appeared). I switched out the wires, the cap, the rotor, the coil with known good ones. I replaced the fuel and air filters. The choke is operating as it should. The only things I haven't replaced are the spark plugs.. I did, however, pull them out and examine them. I got new plugs 2 years ago when I rebuilt the engine, and they look fine. I'm running out of obvious solutions here, and what makes it even more puzzling is that it is an intermittent problem. It will run fine for a while, then, it will go to hell on me. Sometimes it will fire up and run great, others, it won't give me the time of day.. is there anything I'm missing here? Any mystery relays or ignition boxes along the side of the engine compartment that I need to examine? I was thinking a poor connection somewhere, but I cleaned and checked all those as well.

Anybody? :huh:

[patd]

Did you see my posting? Sounds like what was happening to my truck, I did exactly what you did to try and fix it, Turned out to be the fuel filter. I removed it and hit it with a hammer to open it and it was full of dirt and brown/red fluid, and the little filter was almost completely clogged. The truck was not getting enough gas at full throttle while going up grades along the highway, it would lose power, backfire, hesitate, even when I got home and started it the next day it would do the same thing driving in the neighborhood. I replaced the filter and presto it drove like a new truck.! Good luck :)

 

http://community.ratsun.net/topic/19223-truck-backfiring-at-full-throttle/

[MicroMachinery]

Thanks, and yes, I did read your post; in fact, I responded to your post with what I THOUGHT to have fixed mine.

Like I said in the original post, I replaced the fuel filter already. My carb isn't starving for fuel, because I have the stock Hitachi, and it has the inspection/sight glass on the front, and you can see how much fuel is in there. It is staying steadily full, even when it starts running like butt.

Glad to hear yours is all better, though. Nice job ;)

[patd]

Darn I should have read your posting more carefully, How about your fuel pump? I used to have a 73 240Z that would if I remember right would hesitate and loose power, It died on me going down the road at a stop sign, and would not start for around 30 minutes, then it would run again, I described what it was doing in a auto parts store and one of the customers said that it sounded like the fuel pump was going bad as they work intermittently when they are going bad. I bought a new one and that fixed the problem, Funny I have not thought about that problem for 30 years. give it a shot, might fix it. :unsure:

[MicroMachinery]

Like I said before, I'm not starving for fuel. The sight glass indicates that I have fuel. If the fuel pump were bad, the carb wouldn't fill up, seeing as how the pump is upstream from the carburetor.

[patd]

I looked this up on the internet about fuel pumps that are beginning to fail. It might not be pumping enough fuel at highway speeds, but enough in your garage.

 

http://www.associatedcontent.com/article/1510963/diagnosing_a_failing_fuel_pump_on_your.html?cat=27

[datzenmike]

What's the temperature you're driving in. Is it also damp/rainy/foggy or higher altitude. This is a prescription for carb icing. Was there any frost on the primary venturi? Is the pipe from the air filter snorkel down to the exhaust manifold there or hooked up?

[DISLEXICDIME]

i say coil or wiring to the coil

how's your ignition switch?

[greybeard]

you didn't mention changing the condensor.... is it new?

[MicroMachinery]

What's the temperature you're driving in. Is it also damp/rainy/foggy or higher altitude. This is a prescription for carb icing. Was there any frost on the primary venturi? Is the pipe from the air filter snorkel down to the exhaust manifold there or hooked up?

Today was mid-60's and sunny. No icing. No pipe hooked up.

 

i say coil or wiring to the coil

how's your ignition switch?

I switched out the coil with a known good one. As far as I know, the ignition switch is fine.

 

you didn't mention changing the condensor.... is it new?

I have not changed the condenser. It looks pretty old.. the outside is very rusty. What affect would this have?

 

Thanks everyone!

[DanielC]

The fuel pump must pass two tests, pressure, and capacity.

Pressure test, put a tee fitting in the line by the carb, and the pressure must remain between 2.6 and 3.4 PSI at any engine rpm.

If that test is good, then disconnect the fuel line, and put it into a container that will hold about two quarts. The pump should pump more than 1000 CC of fuel a minute, at 1000 RPM.

[MicroMachinery]

... When it would happen, I took off the air cleaner to look into the inspection glass on the carb - fuel level right where it should be. Not low, not overly full. ...

 

 

 

... Like I said in the original post, I replaced the fuel filter already. My carb isn't starving for fuel, because I have the stock Hitachi, and it has the inspection/sight glass on the front, and you can see how much fuel is in there. It is staying steadily full, even when it starts running like butt. ...

 

 

Like I said before, I'm not starving for fuel. The sight glass indicates that I have fuel. If the fuel pump were bad, the carb wouldn't fill up, seeing as how the pump is upstream from the carburetor.

 

 

Thank you very much for your input(s), but it isn't the fuel pump. Trust me.

[greybeard]

replace the condenser.

 

if it's bad it can give the symptoms you're describing,

 

condenser absorbs the flow of power when the points open. sounds to me like its failing

and the causing a misfire when it gets hot

[datzenmike]

The engine will run fine without the condenser so just unplug it and see if the problem goes away. The condenser is there to prevent/reduce points arc.

 

Carry a spare plug with you and the next time it quits pull a wire and put the plug in the end and lay on a grounded surface and crank it.

 

If no spark then you have an electrical problem. Something is loose or fails intermittently.

 

If spark, then logically there isn't fuel. A full bowl does not indicate that you do have fuel only that there is fuel that far. I had a 521 that would baff out intermittently and it was a piece of crap low in the fuel bowl that would get sucked up into the primary jet and partially block it. After sitting for a time it would fall off and settle to the bottom again and it would start and run fine till next time.

[MicroMachinery]

 

... I suspected at once that something had found it's way into my carburetor, but 2 tear-downs and clean-outs have somewhat put my suspicions to rest(I've even looked down the throat of it when it's running badly, and it looks like the spray pattern in the primary barrel is good and even). ...

 

This is what I had immediately thought; that something had slipped by the filter or come off the inside of the fuel line, and plugged my primary jet. I took the carb apart a few times, and cleaned out the jets. Nothing came out. Also, I've had this happen before, and at an idle, the truck would run fine, but as soon as I'd crack the throttle, it'd do what it's doing now and starve out. If something gets stuck in the primary jet, the Primary circuit is what suffers. It SHOULD still idle, seeing as how the Idle circuit is a different circuit altogether. However, it fails to even run at idle when it starts acting up.

 

I've replaced the condenser, so we'll see how that goes. I've had a few people tell me that they've had the identical problem, and that it was their condenser. I figured the same, that it was just somewhat of a cushion, much like an electrical capacitor, but apparently, if that goes bad, it can give the same symptoms I'm having.

Thanks guys, I'll let you know how it turns out.

[datzenmike]

It is a capacitor that when working right is connected across the points to ground but is open inside and there is no electrical connection. If the inside insulation should fail and connect intermittently then this would defeat the points and there would be no spark. If you have replaced then this is now a non issue.

 

I would still carry a spare plug and if the problem re-appears check for spark and go from there.

 

Next time remove the cap and wiggle the rotor. If the mechanical advance or vacuum advance is sticking the rotor may suddenly release and return to it's proper position. (grasping here)

[MicroMachinery]

Well, today I went out and gave my 521 a good bit of running around, without so much as a peep or a hiccup. I'm still skeptical, but if everything stays as is, then I'd say that it's safe to say that the condenser was my issue all along. I never would have thought that THAT could be the issue.. Thanks everybody :)