August 27, 2010

Harley Davidson Panhead: “Tune Up Checklist”

Several weeks ago I had my 1959 Harley Davidson (with sidecar) out for a pretty long ride.  Round trip, I probably logged about 75 miles.  Unfortunately, the last 25 miles or so were not very fun.  The bike started to miss around the 25 mile mark, but just slightly.  My initial thought was that something was just working its way through the carb, but it persisted, and actually started getting worse.  My next thought was vapor lock since it was pretty hot out, so I unscrewed the caps to see if that helped, but it didn’t.  Finally, I tinkered with the carb settings a bit to see if I might loosen something up that was restricting fuel flow, but that didnt help either.  At this point, I decided to just get home since the problem was likely to leave me on the side of the road if it kept getting progressively worse — which seemed to be happening.   To make a long story short, the bike died about a mile from my house and I coasted to the bottom of the hill I live on.   Since this bike has a big old sidecar attached, pushing it up the hill was not an option.   I ended up towing it up the hill with a rope tied to the sidecar frame, and I parked it in frustration.

This past weekend I finally had a chance to dig in and try to find out what the problem was.  I went through a bit of a tune up checklist that I have come to rely on when diagnosing a rough running engine.  I still consider myself a relative novice as I have only been doing my own wrenching for a couple of years, but this list has successfully led me to a solution, on many occasions, that I probably would not have identified otherwise – at least not easily.   I have found that running through this checklist will generally solve most problems related to an engine running rough, so I thought I would share it here.

I always start by confirming that fuel is flowing and that plugs are sparking.  As my friend Charlie Hudson likes to say….”if you’ve got gas, and you’ve got fire, then something is going to happen!!”

So I took the carb completely apart and gave it a thorough cleaning with carb cleaner and some forced air from my compressor.  This is hard the first time, but easy to get the hang off with some practice.  There isnt really any damage you can do.  While the carb was off, I checked the fuel flow from the gas tank which looked good, and I also checked the manifold seals to make sure there was no air leakage there.  I reset the float, reassembled the carb and attached it back to the bike.

The next thing I did was replace the plugs and confirm that they were indeed firing.  I did this by kicking the bike with the plugs out of the engine but hooked up to the wire and grounded on the engine block.  The engine turns over very easily with the plugs out so you can actually do this by hand.  I did see that both were generating a nice blue spark, so I knew that I had fire.   I also knew the battery was well charged and I confirmed this with an amp meter.

With all that done, I decided to give the bike a kick and see what happened.  To my delight, it fired right up and with a few adjustments to the carb, the engine settled into a nice idle.   However, as soon as I got it going down the road, it started to hesitate and miss on me again so I turned around and went back to the garage – problem not yet solved.

The next thing I checked were the points, to make sure they were clean and spaced correctly.  If they aren’t, the timing can be thrown off enough that it can cause the engine to misfire.  They looked fine, but I did widen the gab just a tad.  I have been told that it is always better to set them a little wide.  At this point, I also checked the plugs to see how they looked after firing up the bike and running it a bit.  I noticed one plug was brown from running (as it should be) but the other was still white – as if it hadn’t been fired at all.  With that, I decided to check the coil connection and sure enough, it looked poor on that particular cable.  I cut the wire so I had a clean end, and then re-attached the cable to the post inside the coil box and tightened everything back down.  That coupled with resetting the points definitely did the trick.  When I test drove the bike it ran perfectly.   Had I not run through my checklist, I would probably still be fussing with it.

So this is what I typically do when I have to tinker on a rough running Panhead.  Its probably an incomplete list, but it’s likely to flush out many issues without a lot of trial and error.   As I continue to learn more, I’m sure this will grow to include more items, but this hits a lot of the less serious potential problems

– Clean Carb and Fuel Filter, Set Float, Check Flow From Tank to Carb

– Replace/Check Spark plugs for blue spark.

– Confirm battery has full charge

– Check spark plug cables and attachment to plugs and to coil unit.  Confirm coil unit is good.

– Check points, re-set if necessary.  Confirm condenser is good.

One footnote to all this — It is possible that a coil or the condenser could be bad.  A bad condenser can wreak havoc and cause the bike to run very poorly and its difficult to diagnose if your not looking for it.  They cost about $5 at an autoparts store.  The coils can also be bad and cause problems, although thats a little more expensive fix.   I unfortunately don’t have a good way to check either one other than good old trial and error.   In any case,  hope this checklist is helpful to anyone trying to sort out their Panhead.  With my limited but growing experience, it has worked well for me.


Filed under Classic Motorcycle Maintenance, DMF's Blog by dmf1

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