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Bogging - Electrical or Fuel?

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So I'll try to keep this brief, my '74 620 with a stock l18 setup is bogging after several minutes of normal driving. When it starts to bog, there's no power and it feels like it's just not getting enough fuel or running on one or two cylinders. It doesn't die entirely, and out of gear it will rev pretty much normally, but it just can't generate any power in gear at all. I was suspecting a fuel supply issue but the fuel level looks fine in the carb when this is happening. Also thought the electronic choke might be coming back on, but that doesn't look like the case either.


What's very odd (at least to me) is that restarting the truck seems to reset the issue, at least for a few minutes of normal driving. But the issue pops up again, seemingly after I accelerate up to speed normally at least once or twice (but my tests here are less than scientific so far). But again, just pulling over and shutting the truck off and restarting lets me drive away normally again, but only for a limited time.


I wouldn't normally think electrical except for noticing a while back that the alternator was seemingly putting out 18+ volts. This was messing with some of my accessories like the stereo (wouldn't work when running, only on battery). So I replaced the voltage regulator and the alternator and we're back to normal output with accessories working properly. But I wonder if it possibly fried other things on the ignition system in the meantime.


Hoping for some insights before I just start replacing things willy nilly. 



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Drive hard till the engine acts up. Quickly as you can get the ignition OFF and the transmission out of gear. Pull over safely. The intent is to stall the engine as quickly as possible and preserve the fuel level in the carburetor during the problem. If left idling or in gear the engine will have time to fill the carburetor so stall it while moving as fast as possible, then pull over.


Now get out and look at the sight glass on the front of the carburetor. Is the fuel level at the line or dot on the glass???


If full it's not a fuel delivery problem from the tank or fuel pump

If empty or very low....


Replace the fuel filter. They are only $5 so if this doesn't help it's no big deal. Probably getting plugged. Change every 3 years.

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I would make sure all intake bolts and carb bolts are SNUG.

I would do a valve lash check  if you are loosing a cylinder this would fix it.

You have points ignition?  I would make sure this is good also/point gap OK?. maybe the condensor is going out (not grounded)or your bushing is really worn. cause a mist timming.


yes a closed choke would make it run worst when  warmed up cutting off airflow at higher speeds.



water under the dist cap(condensation has giving my issues of this also) gives same symtems.


as for the fuel system you said it stalls out but once you pull over to idle it dont take much gas to run at idle is it still bad?

a long time ago my 510(with weber DGV) would cut out at high speed. idle would be fine. took carb apart find a tiny rock in main jet. Only way to get home was to pull the manual choke so the 2nd barrel would pull more is in and drove it like that home.

Edited by banzai510(hainz)
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Thanks for the ideas. I tried the quick stop to check the fuel chamber levels. They looked okay the few times I tried that.

Just popped the distributor cap to check the points (should have probably looked there before posting as well).


They're pretty badly pitted as you should probably see from the photo, so I'll replace them and the condenser to see if that sorts the issue. But any ideas on what might be going on upstream to cause such bad pitting? As per my first post, the alternator seemed to be kicking up way too many volts so I've since replaced it. Could that have caused it? Could this also mean the coil might need replacing? I guess I can just replace the points and condenser and see if the problem is solved and pitting doesn't appear to be coming back.


And any ideas why, if the points and/or condenser are the problem here, it only affects driving after a few minutes of a restart? The condenser is just a capacitor right, so I suppose interrupting the circuit with a re-ignition might clear it up temporarily, but I'm way out of my depth here. 



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Points wear out, period.  That one looks fine. That would be normal wear depending on the mileage.  No, don't go changing the coil or anything else till you find the problem or the part causing the problem. Stock parts are the best quality, replacing them will always be poorer quality and you might actually put another problem in with the 'new' part. Also points wouldn't run normally, then act up, then run normally. The capacitor appears to be a path to ground when the points open so current flows into it rather than arcing the gap at the points. Running without a capacitor (condenser) would wear the points out from arcing is as little as 150 miles. 


I had a 521 that did the same thing every time I hit a good sized bump. There would be lack of power and it was hard to maintain highway speed. If I stopped and turned it off, count to 5 and restart it, would go away. Turned out to be a piece of dirt in the carburetor that would clog the primary jet. Turn off the engine and it would settle back down out of the way. A quick cleaning of the carburetor found a small flake of aluminum casting. Blocking the jet caused a bad lean condition, lack of fuel.


Before you pull the carburetor off, drive for 10 min with this lack of power then pull over and remove a spark plug. If it shows extremely clean and white porcelain insulator on the tip this would indicate a lean condition.



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I guess if the vehicle was producing 18 volts it could burn out the points faster.

a stock coil should be there with the ballast resisitor. when engine running measure at the before the ballst reisitor it should be about 14volts and at the plus side coil like 6-7 volts.  This will be normal operation.  Now if you put a Wrong ohm coil in there this can be a issue. You have a spare dist?  swap it in.

pitted points will still work ,What happen if one puts a Low ohm coil in there or remove the ballast resisitor there is too much current and arches out the points cause the condensor cant handle it.


Your right why it dont do it all the time when first start its of then later bad.  Really I dont know could be a combination of a few things and me guess from the keyboard as Im not right there.


Maybe pull the choke wire so the choke goes back on and block the carb and see if it actually runs a little better under 40mph. then its a fuel issue as your riching up the circut. mean elelctrical your OK.


Once I went and got a single point dist with a Pertronix most of my elelctrical isses went away and never had to fuck with points again. I still had issue of actually wearing out the distributor or vaccum advance locked up /spring weights brock /bushing worn out wear the shaft would shake side to side.

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