J&P Community

 I have a 78 sporty with the jugs bored to .020, stock heads with valves and guides near outside tolerance, short pipes, keihin carb with .60 pilot jet/1.70 main, running 4R plugs, stock coil/bosch regulator, new odessy battery, new flyweights/points/condenser.  I've had it running for about 5 min tops, I've fussed with the timing (static?) with no consistent results.  I really want to ride this bike!  Any suggestion, bring 'em on.

What is it doing when it quits?  is this something that just started or have you done major work to it lately?  will it start again or do you have to wait a while (i.e. for it to cool)?  do you have gas in the carb (look in the carb throat)?  does it have spark (no spark often means bad coil)?  is the choke hoooked up and working properly (I know mine was a *** until I replace it with an S&S E)?

guess I am saying, we need more info on the problem to offfer suggestions

hope this helps

Arc,

  Could be a bad coil. Look in your manual, and check the coil with an ohm meter after the bike shuts down. Or you could replace it with a known good one to see if that's it. Five ohm coil for points fired ignition.

A few things I neglected to mention...the sporty hasn't been ridden in 16- 18 years, back then it was tuned for a elevation of about 350 ft, since then i did the work mentioned (and then some).  Now we're at 3500 ft, i've done a complete tear down and rebuild short of cracking the cases and messin with the tranny.  shimmed the cams, replaced the clutch pack, all new wiring. 

When it quits, it just pitters out.  A few times there was smoke puffing out of the carb, but only when i gave a squirt of carb cleaner.  Many times the plugs are fuel fouled.  There's gas in the carb, the choke works, it has spark although it is weak.  A couple times it will start right up again, it's mostly been a gamble, and hard on the knees.

I've tested the coil on the bench, but not when it's warm.  It tested to spec. according to the ol' service manual which was just over 3 ohms, if i remember correct.  The higher ohmage FX referred to might do the trick.  I still think i may have some carburetion issues ( fine tuning, vacuum leak?).  My main concern is wether the valves are sticking due to wear, and it ain't updated for unleaded fuel.

I think that covers it!  It's been alot for ME to chew on.

 is it possible to get the wires crossed on the ign coil?

 1975 was the start for unleaded valve seats IIRC..

 arc

primary resistance for the coil is 4.7 to 5.7 ohms (doesn't say hot or cold - I suspece it is cold

secondary resistance is 16,000 to 20,000 ohms

have you checked the timing with a strobe light through the plastic window on the left of the crankcase?

If they are ok, I am suspecting carb

Arc,

 I believe late 78 Harley went to electronic ignition. If your bike is such, someone may have changed it to points without installing a 5 ohm points fired coil (that was a very common mistake). I'm still leaning towards the coil breaking down when hot.........

 If the wiring was wrong, it shouldn't run. One end of the coil (it doesn't matter which one) goes to ignition switch, the other end is your points wire, and tach, if you have one.

If the coil is OK, I am thinking stuck choke.  the klein on my '77 had a mickey-mouse connection for the choke and running for 5 minutes then dying (gradually) sounds, to me, like a choke stuck on (wet plugs, fire, hard to restart) 

just my nickle and a half

Is the fuel supply constant? A clogged screen that allows a little fuel through, but not enough to keep the bike running is a posibility.

 I agree with Xea that it sounds like a constant supply problem. Those keihin carbs in my oppinion were  junk, if you can afford it put a super e on it,  it'll be like a totally different bike. Also 78 still came with points ignition with a solid state regulator, so that bosh isn't stock althought it will work. By the way hows your compression, you didn't by chance over tighten the push rods when you put it back together?

 Hey, thanks to everybody for the helpful input.  The ign coil ohms out to 4.1, 4.2 max, it took about 10 or 15 sec. to get there.  I hadn't ran the bike (or tried to, long day at wk).  The secondary reads 16.5 or so.  I may replace it anyway. 

As for the carb, i think the slow jet bypass may be dirty.  Last time i had the carb apart i wasn't able to get the main jet out, so i didn't clean it as completely as i normally would, i'm wondering if it needs to be re-jetted.  With the combo of short pipes and re-jetting, i'm perplexed.  Is there some rule of thumb for that?  Otherwise i could try to dial it in w/ the idle speed and mixture, bad feeling about that. 

I'm also curious about elevation changes and changing jets.  It probably doesn't say much now that i've done all this work to it but the bike ran OK in the valley but that was 3,000 ft lower than where i'm at now.  What the rule for tuning at higher elev.?

Either way i'm lookin' at a new coil, and hopefully just a carb overhaul.  Again, the advice has been more than i hoped. 

is it possible i have pre-unleaded heads?  'cause when i had the heads apart, the valve seats didn't look like inserts, kinda pitted too. 

on an ironhead, the valve seats aren't inserts - unless someone has remachined the heads to install inserts.  My '77 runs fine on unleaded gas.

pitted seats, were these on the exhaust side? were they pitted enough to allow compression to escape when the engine heated up? 

 The coil didn't really check out so I ordered a new one.  That should isolate the carb if I have further problems.  I would love to get a super E, tell St. Nick to drop one in my sock.  I have hope for the junk kiehin.  I cleaned it best i could w/o a chem-dip.  The gas in the float had some sooty particles, o-ring matter, maybe? 

I don't have the clear timing plug, but i do have a really old timing light, don't even know if it works, so i've been static timing.  Seems to work well enough.  As for the heads, the compression is good.  I would like to replace the valves, springs, and guides at some point.  Could i do that in my garage, w/o major machining?