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Diagnosing a hiccup


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7 replies to this topic

#1 Sickly

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Posted 03 August 2013 - 02:08 PM

A few months back I bought this car... paid way more than I should for this 78 Subaru DL wagon... 2wd. It's in sweet shape cosmetically, but I think I got hosed. I have had nothing but problems with it.  So far I have had to replace the carb, fuel pump, alternator, in addition to plugs, wires, cap, rotor, new points and air filter.  Now it seems to run and drive fine except that it randomly will hesitate on takeoff.  I put a multimeter on the coil today to see what kind of voltage I was getting.  First I put the negative probe on the negative battery terminal and poked a few spots.  Hot side of the coil said it was getting ~10v.  Then I touched the resistor posts. One side was getting ~13, the other ~10, so that seemed good.  Then I put the positive probe on the positive battery terminal and poked the negative post on the coil and I got confused... it was showing me ~7.  Then I put both probes on the posts of the coil itself and got ~3.  I referred to my shop manual and saw that the ignition coil does in fact ground through the breaker points, but I am not sure how that would affect the numbers.  Can someone tell me whether these numbers are normal?  

 

There is also a small silvery cylinder mounted to the coil bracket that has one wire going to the other side of the same bracket (grounding I assume) and it looks like a wire is broken off the other side.  Could that be affecting my voltage readings?  



#2 talldude

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Posted 04 August 2013 - 12:44 AM

Your coil resistor sounds right; test your coil by testing resistance with all wires disconnected.  Your manual should give you acceptable values for primary and secondary circuits.  The silver cylinder is likely a condenser used to help minimize arcing at the points.  A hesitation off idle might be an accelerator pump or some other fuel delivery issue.  Look down the primary throat of the carb while you move the throttle briskly.  You should see a healthy shot of fuel spray into the venturi.  Make sure your float level is correct and that the fuel pump is keeping up (fuel level in sight glass should be mostly consistent as you run throttle up and down).  Even a new fuel pump can struggle if there is a restriction in the lines somewhere.  Also make sure your choke isn't stuck or needing adjustment.  While you're hip deep, check timing and valve adjustment if they haven't been done for awhile.  Enjoy this wonderful car, but don't forget she is also middle-aged!



#3 Sickly

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Posted 04 August 2013 - 03:58 PM

Thanks talldude!  Yesterday I noticed that my little plastic fuel filter right before the fuel pump is sort of sucked in on the sides and the fuel just sort of trickles in.  It seems like that should be flowing a little more freely. It would seem that there is restriction in the lines.  I crawled under the car yesterday to see if I could find anywhere that the line looked damaged but found nothing.  Is there some kind of diagnosis process to find where it is clogged? 



#4 talldude

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Posted 05 August 2013 - 11:22 PM

If you have an air compressor take your gas cap off remove your filter and back blow air  through to the tank.  There may just be a bunch of gunk at the sump in the tank.  I have also seen steel fuel lines clogged with buildup.  You should be able to send air back through without too much restriction.  Do a little at a time so as not to blow lines off and such. If you do clear a restriction, it may come back unless you flush the fuel tank clean.  Have fun!



#5 Sickly

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Posted 07 August 2013 - 12:07 PM

That's a good idea. I will try that next time I am around an air compressor.  Do you know if there is an easy way to flush the tank without removing it?



#6 Sickly

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Posted 05 September 2013 - 09:12 PM

I switched it to electronic ignition, leaned the crap out of it and it stopped doing it.  The fuel thing still seems to be happening, but so long as it runs fine (which it does) I don't mind.  Now to pass DEQ.



#7 Leeroy

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Posted 06 September 2013 - 02:07 AM

Early Subarus were notorious for flat spots on initial acceleration. Stomp on the gas and there is often a moment of hesitation as the fuel moves from the centrally mounted carburetor, through the intake manifold and into the widely spaced cylinder heads. Any period road test/magazine article usually makes reference to this flat spot.

 

This was a trait of most flat fours and was only eliminated with the introduction and widespread use of fuel injection.



#8 talldude

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Posted 22 September 2013 - 10:43 PM

Did it pass?






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