- Joined
- Nov 11, 2012
- Messages
- 427

My '72 has been running very nicely over the last 5-6 months and started 1st kick. Other than a Pazon ignition module failure that was fixed with a replacement box, the bike has ran really strong. I started using non-ethanol 94 octane gas about 5 months ago which improved the bike's performance as well. The last few time I rode I noticed the bike would cough and stumble in the first quarter mile then clear up and run really well. Yesterday I was riding and at a stop I noticed the idle started to get a little rough and the RPMs started to drop a little. I looked in the tank, my gas was low so I put on the reserve and all was fine. I made my turn and approx. 1/2 mile from my house the bike started to studder, stumble, and felt like the right cylinder stopped firing or was only firing intermittently. I limped it home. Once home I found the bike would idle without issue but at low throttle opening there was a really bad studder and the bike would bog. Once above 3000 RPM the bike would run better and above 3500 RPM it was like nothing happened. I pulled the plugs (BP7ES) and found them to be heavily sooted but dry. I changed plugs with the same results as before, shortly thereafter these plugs appeared much the same as the set before. I started checking the carbs, doing a quick cleaning of the right hand side and went for a ride. Same result. The bike will respond to air screw adjustments but not enough to make any difference in off throttle performance. From there the bike has only gotten worse and now will not idle below 1500 RPM and will develop a stumble at speeds over 3000 RPM. The symptoms are worse the warmer the engine is and will have occasional hiccups through the carbs. There is no exhaust smoke noted (no white, blue, or black). In neutral with a blip of the throttle the bike will want to die. A moderate roll of the throttle makes the engine very hesitant and bog with a slow rise in RPM, under a load at launch it will stumble and try to die. Above 3000 or so RPM in neutral it revs appropriately and briskly. The bike still starts but it takes a few kicks to get it there. Here is a list of what I have done:
Cleaned both carbs - pilot jets are free and open, carbs synced, float levels checked (~3mm below), all joints in manifolds sealed, flange o-rings replaced, no gas leaks, tickles fine. The needles and needle jets have about 2500 miles on them. The slides appear to be some kind of chrome sleeved type. All jetting and needle positions are stock. The bike itself has 3300 miles since a total rebuild
Changed plugs x3 - all sooted but fire good
Checked ignition timing - Sits at ~30* at 4000 RPM, checked the Pazon magnetic rotor and is still in the correct compression stroke location. Bypassed ignition switch and directly wired the battery to the ignition module with no change. Did the Pazon trigger test with no issues.
Battery - charge 12.3v at rest, 11.9v at idle and increases over 13v with RPM climb above 2000 RPM
Coils - Resistance measured at 2 to both coils
Valves - Clearances in spec for a Combat, new gaskets placed on rocker covers
Timing - Strobbed at 28* 4000 RPM initially, advanced to ~30* 4000 RPM with no change noted. Currently at ~30*
Gas - Different can of non-ethanol 94 octane with seafoam added
I tried going through previous threads and have noticed others with some of the same issues. However, most people do not return to tell what they found to be the issue and what was done to fix the bike. I have ran out of ideas and here I am.
What am I missing?
Scott
Cleaned both carbs - pilot jets are free and open, carbs synced, float levels checked (~3mm below), all joints in manifolds sealed, flange o-rings replaced, no gas leaks, tickles fine. The needles and needle jets have about 2500 miles on them. The slides appear to be some kind of chrome sleeved type. All jetting and needle positions are stock. The bike itself has 3300 miles since a total rebuild
Changed plugs x3 - all sooted but fire good
Checked ignition timing - Sits at ~30* at 4000 RPM, checked the Pazon magnetic rotor and is still in the correct compression stroke location. Bypassed ignition switch and directly wired the battery to the ignition module with no change. Did the Pazon trigger test with no issues.
Battery - charge 12.3v at rest, 11.9v at idle and increases over 13v with RPM climb above 2000 RPM
Coils - Resistance measured at 2 to both coils
Valves - Clearances in spec for a Combat, new gaskets placed on rocker covers
Timing - Strobbed at 28* 4000 RPM initially, advanced to ~30* 4000 RPM with no change noted. Currently at ~30*
Gas - Different can of non-ethanol 94 octane with seafoam added
I tried going through previous threads and have noticed others with some of the same issues. However, most people do not return to tell what they found to be the issue and what was done to fix the bike. I have ran out of ideas and here I am.
What am I missing?
Scott