Missing, Popping
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Road Warrior
Joined: Nov 2005
Posts: 1,484
Likes: 82
From: Mountain View, California
Missing, Popping
98 carb'd 1340 motor with mild cam, V & H Short Shot and SE filter.
Here's a long description, but maybe it'll give you guys (and gals) all the info you need to noodle through this with me:
Steady-state mid-RPM cruising I get an occasional miss (once ever 5 seconds or so, but not like "clockwork") and occasional popping through the exhaust. There's no x-over between pipes and the inside of the rear cylinger exhaust pipe is noticably (but not dramatically) blacker than the front. On cold idle, rear cylinder doesn't seem to fire fully as evidenced by the sound of a hard "hit" on the rear cylinder every fifth revolution or so (place your hand an inch from the exhaust and you can feel it hit harder). Compression is great and within 3 lbs per cylinder. Wires are Accel: 1 rear wire (shortest one) has 60-ish ohms resistance, front has 250-ish ohms. The timing "seems" about right, but it's so damned hard to really see those marks. It does seem to wander a bit, but I associate that (perhaps wrongly?) with loping at ide. Rear cyl spark pug looks like it's leaner than the front but I hear that's normal (rear cyls run hotter, no?). Front plug has a region of dark black on one edge of the insulator, rear cyl has a region of dark tan. I assume this is just indexing and is normal for these motors?
So... what do you think?
[IMG]local://upfiles/5626/03E9C621316F4F6A8F842D02AD4A92F5.jpg[/IMG]
[IMG]local://upfiles/5626/062ABFB6C9C545B9A1D1E60016894F58.jpg[/IMG]
[IMG]local://upfiles/5626/7FB2B63BECA54D3797B62389461B488F.jpg[/IMG]
[IMG]local://upfiles/5626/C62FBE9DC55048B4B8EF0E9AA8A1C55F.jpg[/IMG]
Here's a long description, but maybe it'll give you guys (and gals) all the info you need to noodle through this with me:
Steady-state mid-RPM cruising I get an occasional miss (once ever 5 seconds or so, but not like "clockwork") and occasional popping through the exhaust. There's no x-over between pipes and the inside of the rear cylinger exhaust pipe is noticably (but not dramatically) blacker than the front. On cold idle, rear cylinder doesn't seem to fire fully as evidenced by the sound of a hard "hit" on the rear cylinder every fifth revolution or so (place your hand an inch from the exhaust and you can feel it hit harder). Compression is great and within 3 lbs per cylinder. Wires are Accel: 1 rear wire (shortest one) has 60-ish ohms resistance, front has 250-ish ohms. The timing "seems" about right, but it's so damned hard to really see those marks. It does seem to wander a bit, but I associate that (perhaps wrongly?) with loping at ide. Rear cyl spark pug looks like it's leaner than the front but I hear that's normal (rear cyls run hotter, no?). Front plug has a region of dark black on one edge of the insulator, rear cyl has a region of dark tan. I assume this is just indexing and is normal for these motors?
So... what do you think?
[IMG]local://upfiles/5626/03E9C621316F4F6A8F842D02AD4A92F5.jpg[/IMG]
[IMG]local://upfiles/5626/062ABFB6C9C545B9A1D1E60016894F58.jpg[/IMG]
[IMG]local://upfiles/5626/7FB2B63BECA54D3797B62389461B488F.jpg[/IMG]
[IMG]local://upfiles/5626/C62FBE9DC55048B4B8EF0E9AA8A1C55F.jpg[/IMG]
Tourer
Joined: May 2006
Posts: 319
Likes: 0
From: Cape Coral, FL
RE: Missing, Popping
The front cylinder will be a little richer, an inherent design thing with intake. Have you replaced just the rear plug? I had one go bad on me 50 miles out of the box. Shorter wire should have less resistance but if you have or can borrow a bud's wire change back one after changing plug and testing. Do the spray wd 40 around the intake seals of the back cyl when idleing to check for any intake leaks.
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