1974 Sportster Starts misfiring and popping while pulling a hill or grade.

[50Panhead]

I picked up a ironhead sporty (price was right) It starts easy and idles fine. It rides ok fair amount of power but when i go into a pull it starts missing and popping, Front Cylinder I'm sure. I pull over and its idles fast. I mess around with it a little bit and the idle rpm drops to normal and its firing on both cylinders again like normal.  It does this ever time it goes into a pull.  I might note that I'm riding very conservative testing the bike out.  I pulled the plugs and the front plug is starting to foul. I see oil in the front exhaust pipe, rear pipe is just normal suet.  Compression test shows 90# both cylinders. Leak down test showed about 12psi.

I'm thinking it may be mechanical advance, or maybe a weak valve spring.
Bike has a Mikuni  carburetor. 

Your Thoughts Appreciated
Thanks
50

[nibroc]

exhaust valve guide worn

[kik]

Yeah, sound like a guide valve is bad, but the popping is probably the advance. They get kind of frozen with age. You can try to remove it and put some oil on the springs but it's probably worn out. I had the same problem with my old 77 XLH, I went to electronic and had no more problems.

[50Panhead]

Thanks Kind of what I thought the problem would be.
When the weather turns cold I'm going to turn this bike into a Then Came Bronson bike.
Anybody know where I can find the  stock exhaust that was used in the late 60's early 70's?


Thanks
50

[nibroc]

bike looks to be a 68XLCH to me but could be a highly modified 74-ol ralph done away w/mags in 70

[50Panhead]

bike looks to be a 68XLCH to me but could be a highly modified 74-ol ralph done away w/mags in 70

You are correct the photo is of a 68 with the stock exhaust

Here is a photo of the one I'm working on converting, its a 1974 XLCH

[Mailman]

  Also, 90 is way below the normal rebuild limit of 120 on an ironhead.

[garyajaz]

yep, blowing smoke, low compression.
rebuild time.
also that is not a xlch.
xlch is kick start only and has small batt and different oil tank.

problem with these old irons is more than one problem at once.
so off into it you go.  fix A problem.  then tear it apart for the next problem.
best to go thru it once.  all bearings and wear parts.
then should have a nice reliable bike.

(hell, stroke it   lol)

oh, and get a chain guard.  if not convinced I can send pix of my leg scars.
I like the Bronson eye on tank.
hell if can find a "Bronson rock" can fix anything with that.
even turn that sporty into a sprint for hill climbs.

[50Panhead]

Ok Guys as an FYi sportsters are not my cup of tea. But wrenching in general is.  I just pulled the heads off and I must say I did not know that you have to remove the rear head and rocker assembly all together as there is not enough room to pull the rocker covers off alone.
Anyway I think this motor has been gone through recently  as the valves and guides are TIGHT. I guess Harley never thought of valve seals. Valves look very good. Although the Exhaust valves seat is carbon black, no shinny ring where it seats like on the intake valve.
Pistons have marginal side to side movement (normal with cars) Very little to none front to back movement. No top of cylinder ring lip.

And the bike does not smoke. I never said it smoked.

I think the problem is in the centrifugal advance with the points. Now I think the oil in the exhaust pipe is from the front cylinder missing out.
I have a set of Chevy valve seals and I tried one on and they fit a little tight but I think they will work.  I'm just not sure if that is something I should do with the ironhead.

I'm still open for your thoughts.

[Mailman]

Ok Guys as an FYi sportsters are not my cup of tea. But wrenching in general is.  I just pulled the heads off and I must say I did not know that you have to remove the rear head and rocker assembly all together as there is not enough room to pull the rocker covers off alone.
Anyway I think this motor has been gone through recently  as the valves and guides are TIGHT. I guess Harley never thought of valve seals. Valves look very good. Although the Exhaust valves seat is carbon black, no shinny ring where it seats like on the intake valve.
Pistons have marginal side to side movement (normal with cars) Very little to none front to back movement. No top of cylinder ring lip.

And the bike does not smoke. I never said it smoked.

I think the problem is in the centrifugal advance with the points. Now I think the oil in the exhaust pipe is from the front cylinder missing out.
I have a set of Chevy valve seals and I tried one on and they fit a little tight but I think they will work.  I'm just not sure if that is something I should do with the ironhead.

I'm still open for your thoughts.

  Ironheads don't need valve seals.  Your rods should have slight side to side, no up and down, which should be checked at several spots of the rotation.

  Not smoking is a good sign.

  If you want to work on one, the factory service manual and parts manual are a requirement.  Period.

  If interested, there is a very good ironhead section at http://xlforum.net/vbportal/forums/forumdisplay.php?f=7

[50Panhead]

I pulled the jugs off this evening and what I saw explains the 90 # compression reading I got before I started taking things apart. Looks like some moisture set in the cylinders for a while. Front piston and rings are scared.  The motor has been worked over once before, pistons are marked .010 over. I'm going to take the heads and cylinders to a machine shop and get them reworked. Valves just need a little touch up and they will be like new. Looks like the next size oversize pistons clean things up.  Rods feel OK so I'm not going to tear the bottom end apart.

Conclusion is from talking to others, is that when the bike starts pulling it draws more oil up passed the rings and fouls the plug. When it sets for a minuet or two the plug clears and starts hitting again.

Thanks
50

[saltcaveminer]

since you have the heads and jugs off i might suggest that the shop check the springs, guides and valves & seats.when you get her back together and start break in make sure you prove oil to the oil pump before starting and then to the oil bag once engine is started.break in should be short starts with cool downs (lots of friction= heat).the advance can be checked above 2200rpm with a strobe light or static.now would be a good time to check that mikuni and see what jets and needle are in there.also check the throttle cable, carb slide and spring to see why she doesn't return.when dialing in a mikuni roundslide think in terms of throttle opening (not rpms) sudco has a good picture of this.lastly check the fuel filter in the tank .hope this helps.Salty

[50Panhead]

Thanks Salty
You would like this guy who does my machining, He is an old guy who spent his life working bikes. He has a two car garage with paths around all the years of accumulation almost hard to see the machining equipment. Anyway I ask him to check the springs when he dressed up the valves.  I'm replacing the mikuni with the original Bendix Zenith carb.   I have the tank off and I'm sandblasting the paint off for repainting. So the fuel strainer will get cleaned before it goes back in the tank.  Thanks for the tip on the oil. I read something about priming the oil pump in the shop manual.

Thanks Again
50

[saltcaveminer]

One thing you can count on from this forum is very willing and able folks to help.PS I definitely can appreciate your wrench Salty