Iridium failure? (top end carnage) top end time...

[m in sc]

so, check this out.

on my hybrid, which now needs at min a set of pistons, i was working on it saturday. it has had a weird hesitation for years right off idle i havent been able to quite cure, but ran fantastic otherwise.

so, for at least 4 years, ive runt he same igntion curve, not changing it much from 2010 on the zeel.  way back when i swapped over to the VM34s i also started using iridium plugs because i had some (br9eix).  this seemed to allow me to run it a bit rich but keep it together without fouling plugs.  (THIS IS RELEVANT.. KEEP READING)

So, I swapped over to the TM32's a year or more ago. Got it jetted and it ran even better. fyi setup was/is:

40 pilot, 1.75 out
5df? whatever it is needle. (notes at home on that)was on clip 2 (one lean)
P6 Jet tube
250 main.
mzb(vape)/zeeltronic box

always started 1st-2nd kick. running 40:1  and when fully warm between 175-195 water temp. (195 usually sitting at a light)

so, Saturday, I figured id address the off idle stumble or mis.  so, as with tuning, i alwasy err richer and then move from there.

set carbs to:

260 main
middle clip
air screw at 1.5

and moved timing point at 3k to 22 degrees (up 2 degrees from where it was leaving all other points exactly the same, hence not affecting any other part of the curve past the next point, which is at 4200)

the other thing i changed was the plugs. went fromt he BR9EIX to a BR9ES.

warmed up bike, took for a ride and got water temp up to 170-ish. theres a long straight i test on about 2 miles from house, so when i got there i opened it up and it was running awesome. until it wasn't. somewhere in top of 5th gear at 110 mph it lost power.  pulled clutch in and it stalled.    water temp had spiked to 220. 

coasted a few hundred feet and gently let clutch out and it spun and fired but was.. tappy. and on one cylinder.

limped it down the road a lightly and was ok but def dragging a cyl. pulled into the parking lot and immediately pulled the plugs. yup.
aluminum. 

mind you, this plug was on the side that wasn't firing after it lost power so its of course rich looking



heres the shots of all the plugs. from the br9eix (that it ran great on) to the b9es it blew up on.


neither were plug chops. and the iridium plugs last run was a warm-up on choke in the garage then off choke to warm bike up. so they look way rich.

so.. every carb circuit was richer. what happened from one day to the next? there were no air leaks. no timing changes over 3k. (was well over 9k when it went).


this is where it gets weird.
Friday,  I went into the local MC shop with a very competent owner that sponsors quite a few MX racers.  i was going to order a box of BR9EIX'S again, he didn't have any, also said that they had been having problems for a few years with them failing in races and went back to standard plugs with all failures eliminated, and that other teams had reported the same thing. TBH, didn't think much of it. till my motor went.

my theory is: i tuned it with a plug that was probably misfiring somewhat a few years ago.

I put in plugs that were working as they should and.... the bike was then jetted too lean. (even though i jetted it richer)

SO.. lesson learned.  as I've said many times: most jetting issues are electrical.

rebuild time! hopefully just a set of pistons and a hone. it def didn't stick hard so maybe i got lucky.

[Czakky]

So you were tuned with the iridiums, then switched to a good normal plug she destroyed herself?
What's the theory on what is happening with the iridiums?

[m in sc]

exaclty.

what the racers had noticed was misfires and fouling at high rpms. they were tuned with regular plugs then switched to iridiums and thats where they saw the problems. reverse that and you 'create' a lean condition by having full spark events with non missing plugs. thats the theory i'm going with on mine.

[msr]

Well, damn. Another wad of cash that turns into a good story (and a running bike).

[m in sc]

true

TBH its been a LONG time since ive been in this motor because i needed to be.  I dont mind TBH. It'll get other improvements as well on the rebuild. it always does. 

[Kawtriplefreak]

I.am glad it didn't seize. I know it wilI be even stronger in the next iteration.

[teazer]

Let's try a theory here that the smaller electrode Iridium plugs don't retain as much heat so they run slightly cooler that stock fat wire plugs which get hotter at the tip and cause overheating.

If a fine wire burns more of the available fuel/air mixture, and fat wire standard plugs don't burn as effectively, why does that create an issue when it's not on the pipe. Unburned fuel should theoretically cool the combustion chamber and raise exhaust temperatures. At lower speeds that shouldn't hurt, it should help. Mabye at high revs that hotter exhaust is pushed back into the barrel by pipe resonance, causing a temperature rise in the exhaust port and combustion chamber at high revs.

[Czakky]

Honest question. How does unburnt fuel crest higher exhaust temps?

I always appreciate a Teazer post!

[Alain2]

Honest question. How does unburnt fuel crest higher exhaust temps?

I always appreciate a Teazer post!

It's because un burnt fuel in the combustion chamber is fuel burning in the exhaust. Just like when you retard timing, it lowers the head temp but increase egt, it burns slower.

[teazer]

Exactly.

[m in sc]

it was def missing down low. for a few years.  years (10?) ago i went from regular plugs to iridium ones on the rz and saw no tune difference.  It was what i did after i had one dialed in

[Striker1423]

I bought a set of 4 BR9HIX and blew my bike up on the first set. Was gonna try jetting on the second set and just running my old set after. Damn things aren't cheap ya know.  But... maybe I should just order 5 sets of standard B8HS plugs if I can find them and let it eat...

[Jspooner]

I run them, haven't had a problem. However, with my RD before I sold it I was getting a miss at high RPMs and couldn't figure out why as I hadn't changed anything, for the hell of it I put new plugs in (iridium again) and it cleaned it up. They work great in my TZ. 

[m in sc]

yeah Chuck (my local guy) had 'matter of fact' told me some were an issue. Considering i was buying from him, he had no motivation to sell me a cheaper plug except for my benefit . I kind a blew it off at the time for the same reason. never had an issue. considering he goes racing every. single . weekend. (his kids and he also sponsors as well) hes 99% of the time right.

Its no different than a weak ignition causing low jetting.   as far as 'plug heat' they were both '9' series.

[Milan]

So how old were the Iridium plugs that you put in?

Has the problem been fixed with the 2021 batch?

Not much online about it.

M