High idle with resistor-type plugs?

Matt Rain

Matt Rain

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I've been experimenting with spark plugs on my FJ600. The OEM-spec D8EA's seem to be the best overall choice, although the iridium DR8EIX seem to make the engine more eager and easier to cold start vs. the D8EA and DR8EA. One issue with the "R" plugs, both standard and iridium, is that the bike idles erratically when it's up to temperature. Stopping at a red light, it'll idle anywhere between 2k and 3k. With the D8EA, it goes back down to ~1.2k every time.

Anyone notice something similar? I really like the extra "pep" from the iridiums but the high idle seems like a waste of gas (I spend a lot of time in stop n' go traffic.)
 
So... the erratic idle was due to a nasty air filter. Now that that was replaced, I just get a high idle with the "R" plugs. If I set the idle at 1200 RPM on the D8EA's then swap those for DR8EA's/DR8EIX's, the idle jumps to 2k.

So ok, I just have to lower the idle when using those plugs... I'd still like to understand the physics behind the phenomenon.

Anyone?
 
iridiums will burn a improper / not optimal fuel mixture better.
 
Iirc, for cb550s, different grade of plugs works best at different temperature. D7ea would be standard where d6ea would be used in hotter areas and d8ea in colder area for the cb 550. Each type plugs i belive have their own operating temp for maximum operation and minimal to no
damage (wiki, 2013)
 
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Matt Rain said:
I do like them. They sound totally different and they produce more engine braking.
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Iridiums are much better for carb'd bikes, they will burn the improper idle / first start up mixture better.

I don't think I can tell the difference between brand new iridium plugs vs. copper plugs, they feel about the same to me when they'r new. But as plugs age - the iridium do seem to make my stuff run just as well, vs. the coppers go down hill. Especially when its cold outside, the iridiums make a difference.

NGK also makes an EiX plug, its a slim tip iridium ; Which I find does a great job even after 20-40k they still work fine.


My personal opinion, go with cheap copper plugs and replace them more often. Plugs will get carbon fouled anyways, so you might as well have fresh plugs in there. Iridiums are generally 2-3x the price of copper plugs.
 
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I understand what you're asking OP, and I should know the answer as I had a YX600 which has the same motor more or less ... I just can't remember at the moment.
 
Matt Rain said:
I do like them. They sound totally different and they produce more engine braking.
Click to expand...

How does spark plugs affect engine braking? I thought it was just the compression ratio?
 
I may well be imagining the engine braking and/or misdescribing the difference in performance & feel from the iridiums.

I just tried adjusting the idle down, gave it a full turn counterclockwise. Now it's idling too low and I get some popping. Will go back a half-turn tomorrow.
 
I can't help but wonder if something else is going on here. Are the D8EA plugs in good shape? Gapped correctly, have electrode left?
 
All the plugs are new or nearly new. I clean them with brake cleaner and a wire brush (delicately) and I check the gaps when swapping them.

The D8EA's perform exactly the same as the equivalent Champion RA6HC - much lower idle an generally tamer performance/feel than the DR8EIX and DR8EA.

I've settled on the Iridiums for now, just gotta get the idle right.
 
Matt Rain said:
All the plugs are new or nearly new. I clean them with brake cleaner and a wire brush (delicately) and I check the gaps when swapping them.

The D8EA's perform exactly the same as the equivalent Champion RA6HC - much lower idle an generally tamer performance/feel than the DR8EIX and DR8EA.

I've settled on the Iridiums for now, just gotta get the idle right.
Click to expand...

Alright ... for the time being, I wouldn't use the wire brush on the iridium plugs. The fine electrode is not nearly as sturdy as it would be on copper plugs.
 
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