Plug chop opinion

[irk_miller]

Can I get an opinion on a plug chop? Running an RD350 converted to LC. Basically TZ porting with RZ pistons. TM34 carbs. I'm comfortable throughout the throttle range to WOT, but then it was completely falling apart at the end of the cable. I was way off on the main jet, so I started going up. This is my last chop with a 280 main, which felt really good by my butt dyno. It looks good to me with a neat 2mm ring, so I'm wondering if I'm still on the lean side, if I'm good here, or if I should maybe go to 290 or above. Seems to be a lot of internet posts where the people are more at 300 or above with TM34s.

[m in sc]

my opinion, looks good. by happenstance,  that's exactly what my main is on my hybrid. 

[irk_miller]

my opinion, looks good. by happenstance,  that's exactly what my main is on my hybrid.

Many thanks, Mark.  I was at 250 before, so way off.  I never melted pistons, but I destroyed a crank seal.  Not sure if a lean condition would cause that, but I can only assume it contributes.  I want to get it right, while I'm still feeling lucky.

[m in sc]

just make sure the needle seats are big enough, i had starving issues on one bike and had to go up to 3.0mm seats. on a tm35 should be ok they way they come, but its worth mentioning.

[1976RD400C]

I have 280 mains in my VM34 carbs. My plug has a slightly smaller black ring with a B8ES plug. I use B9 now.

[m in sc]

yup. after i got mine dialed in went with 9 iridium's.

[teazer]

That mixture ring looks a little wide - assuming it was a real chop. Harder (cooler) plugs will by design, run cooler and that causes them to look rich. So you could jet with 8's in and the switch to 9s to create a margin of safety.

FYI on TD/TR and TZ's we were usually in the 280 (hot low density) to 320 (colder more dense air).

I found the most critical on a street bike is mid range ridden "softly" to not draw attention,  where most of the running typically is at 1/4 to 1/2 throttle cruising and that's needle and needle jet territory.

[irk_miller]

That mixture ring looks a little wide - assuming it was a real chop. Harder (cooler) plugs will by design, run cooler and that causes them to look rich. So you could jet with 8's in and the switch to 9s to create a margin of safety.

FYI on TD/TR and TZ's we were usually in the 280 (hot low density) to 320 (colder more dense air).

I found the most critical on a street bike is mid range ridden "softly" to not draw attention,  where most of the running typically is at 1/4 to 1/2 throttle cruising and that's needle and needle jet territory.

I have the pilot, needle and needle jet on the richer side, and I think that was masking my WOT lean all this time.  Plus, as you say, I spend most of my time going 40 - 60 down city roads and highways, so never really in the upper power band except when I take it out to the country on some of the funner roads.  Mostly cruising at 5k, which is the bottom end of the power band.  This plug chop is with fresh plugs, ignition off and clutch at the moment it bogged.  It only ever bogged or ran poorly that last 25% of the throttle.