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Message started by Yellow96 on 06/08/07 at 13:05:02

Title: Spark Plug help
Post by Yellow96 on 06/08/07 at 13:05:02

I have a modified bike that seems to always run lean at idle even though my edelbrock carb is tuned all the way rich.

A guy I know asked me if I had considered a different spark plug to solve the problem. Anyone ever try that?

Not sure what the thought is behind it, looking for ideas.

Title: Re: Spark Plug help
Post by Savage_Rob on 06/08/07 at 13:17:52

If your talking idle only, have you changed your pilot jet size? Can you increase it?

Title: Re: Spark Plug help
Post by Yellow96 on 06/08/07 at 14:19:33

The edelbrock doesnt have a pilot jet. it's a flat slide with an adjustment knob to run it leaner or richer by drawing out the needle or running it deeper in the slide. kinda cool set up unless it doesn't go far enough.

Title: Re: Spark Plug help
Post by BornOnFire on 06/08/07 at 17:17:52

I think what he was implying is what controls the pilot circuit on that carb? Is it a needle with an adjustable clip under the diaphram or something? Maybe it needs to be moved up a notch. Sounds like a pilot issue to me as well, but I don't know if a hotter plug will solve that. Nonetheless, it's a cheap remedy to at least try out. I'd be curious to know if it helps you out at all.

Title: Re: Spark Plug help
Post by thumperclone on 06/08/07 at 17:21:25

is the plug wet???

Title: Re: Spark Plug help
Post by Yellow96 on 06/08/07 at 21:02:54

Right, On the edelbrock the pilot part is controlled with a knob that can be adjusted by shutting the bike off, rolling on the throttle and twisting the knob right for rich and left for lean (controls idle to 1/3 throttle). The rest of the mixture is set by the needle size. I have the idle mixture set at full rich and it still backfires after I shut it off.

I am running a new stock NGK. What plug do you recommend? I don't have much background here.

Not sure what you mean thumperclone, is the plug wet? Do you mean gas soaked?

The strange thing about this is that the full open part of the needle is too rich. I have tried other needles but havent had any luck, I have one more size to try. Good that they aren't too expensive.

Title: Re: Spark Plug help
Post by Savage_Rob on 06/10/07 at 09:34:11

Ahh, I completely missed that you said it was an Edelbrock. I've never used one though I've considered it as I'm generally a fan of simplicity. I believe Lancer has some experience with them. If he doesn't see this thread anytime soon, you might try sending him an email or a PM.

Title: Re: Spark Plug help
Post by Yellow96 on 06/10/07 at 17:59:59

So can someone help with how to pick a hotter/cooler plug? Which one makes it richer. How does that work? What number plug should I try?

Title: Re: Spark Plug help
Post by justin_o_guy on 06/10/07 at 19:37:25

I step gingerly onto the limb. I would guess I would go with a cooler plug if I was lean & a hotter plug if I was rich.

Title: Re: Spark Plug help
Post by Reelthing on 06/10/07 at 20:59:11

Yellow96 wrote:

So can someone help with how to pick a hotter/cooler plug? Which one makes it richer. How does that work? What number plug should I try?

??? which sparkplug will change the mixture ???

Title: Re: Spark Plug help
Post by justin_o_guy on 06/11/07 at 05:04:21

I know a plug wont actually change the mix, but IF I am lean, then I wouldnt want a hot plug, too. Right? Or would it matter to the piston at all? Once a lean mix fires, its hot in there. If it's gonna hole the piston, no cooler plug will stop it, I'll be betting.
But, if I am rich, then shouldnt I be running a hotter plug?

I know the real answer is to get the jetting right, but that wassnt the question.

Title: Re: Spark Plug help
Post by Yellow96 on 06/11/07 at 06:13:21

Exactly what I hope to learn Justin. If I run a cooler plug for a lean condition, then what I'm doing is trying to have an incomplete burn in the cylinder, right? I know its not the right way to solve the problem, but the guy who put this edelbrock on (long ago and a few owners back) probably used the wrong one and I really don't want to drop carb money in this bike.

If I run a cooler plug though, won't it effect the burn at all rpms? That would be a problem since the carb runs a little rich from 1/3 to open throttle. I could fix that with a new needle, which is pretty cheap.

Title: Re: Spark Plug help
Post by barry68v10 on 06/11/07 at 07:39:21

Ok, I'll wade in here now...

A cooler plug or a smaller spark gap will cause a lean engine to act "richer." The reason is the burn will happen slower, especially a smaller spark gap which will act like retarded timing, and basically has the same effect. If you're running too rich at WOT, then either of these "fixes" will make your WOT problem worse and much more pronounced.

Hope this helps. BTW, what exhaust are you running? Stock backpressure will greatly simplify tuning, and cover a multitude of "tuning sins" ;D

Title: Re: Spark Plug help
Post by Yellow96 on 06/11/07 at 14:55:22

I have the Dyna muff and the drop-in K&N, Lots of flow on the bike and that carb is pretty free flowing.

Title: Re: Spark Plug help
Post by barry68v10 on 06/11/07 at 16:56:26

Ok, that's not that radical. You may not like the unintended consequences of completely eliminating "backfires after I shut it off." You may experience poor "hot weather" performance and greatly reduced MPG. Backfire, or more accurately "post ignition" is part and parcel with an efficiently tuned single. My bike gives a modest "poof" on shutdown and is turning in just under 70 MPG on the highway.

You might try 1 heat range cooler plug, or decreased spark plug gap of .005-.007 inches, and see how you like it.

Title: Re: Spark Plug help
Post by Yellow96 on 06/11/07 at 18:28:34

Thanks, that makes sense. I think I will try the leaner needle for the top end and then mess with the plug after that. I wish I was getting 70 MPG, I think i'm about half that.

Title: Re: Spark Plug help
Post by Rockin_John on 06/11/07 at 21:10:41

barry68v10 wrote:

I concur. I live with the after killing "blurb" on both Dyna equipped bikes. As long as I don't get shotgun blasts at any speed or shutdown, I'm not to worried about a bit of popping and spitting. Though I have minimized it a lot through fine tuning on one bike. I got lucky on the other one, and it sounds/feels like someone jetted it correctly. From the more even pull, they perhaps even got it more spot on than I did the first Savage!

As for plug heat range changes, I wouldn't wade into a hotter plug unless it was an extreme case of last resort.