78 Sportster Carb

[mnjoe]

I've been having problems lately with sputtering and backfiring out the pipes & carb.  It idles fine until I crack the throttle more than 1/4.  I've cleaned the carb, changed plugs, points are good, good spark from both wires, compression's at 125 & 124, sprayed starting fluid all around the intake, and changed oil.  A mechanic in town said he's seen many Keihin's that get little cracks inside them and the only thing to do is get a new carb, he suggested S&S E.  I don't have a lot of extra cash to go towards the bike with the family so I need some advice.  Does a cracked carb seem realistic?  I guess I can see it as a possibility with sub zero weather in northern MN & storage.  Besides S&S, I was looking at other Harley CV carbs using an adaptor, but I'm not sure which carb(s) to look for.  Anyone have reasonably priced alternatives?

[Lew]

Don't buy a carb until the problem has been verified.  Backfire through the exhaust is nearly always caused by delayed ignition.  Spitting or coughing out the carb can be either but is usually fuel/air related.  Before messing with the fuel I'd double check the ignition system for any problems.  Check voltage at the coil positive terminal and have a look at the points for proper gap and condition issues.  May want to replace the condenser as they can break down and cause problems like you describe.  While in there check the advance unit for problems by moving the points cam with your fingers and making sure it returns then verify it works by checking with a timing light.
Pull the fuel line from the carb and check for good fuel flow.  Float level ok?  You can check for cracks around the metering ports in the carb by looking with a strong light.  Hope this helps some.

Lew

[olpigiron]

                               What Lewy Said,
I've Heard Somewhere That 80% of All Carb. Problems Are Electrical.
                                  Good Luck!!!!

Cheers
OPI

[mnjoe]

Well, after the response I got on here along with similar advice from a different Harley mechanic, I decided that I'd buy a couple cheap parts: condenser & accelerator pump diaphram for a total of $20.  I put the condenser in first, fired up the bike, and she cranked right up.  Took it for a little ride and it's back to life!!  Ran a little bit rough, but I'm thinking it could be the high concentration of Sea Foam that's in it, or my rough measurement putting the points back on.  Either way, for a problem that sounded like it was starving for fuel, and a $450 fix diagnosis from one of the local Harley mechanics, a $5 condenser did the trick.  Thanks to lewy, olpigiron, my father in law (suggested condenser 2 weeks ago), and the Hawg Pen (local shop with knowledgable mechanics), my ol iron head is back on the road!!
Joe

[Lew]

 

Lew