Baffle vs. spark plugs

[jonr]

Ok, I have sifted through MANY back-posts concerning backpressure and
lean/rich fuel mixtures. My predicament is this:

Charging system is good as well as the coils. I am running B7ES plugs because the 8's ALWAYS foul out. My 7's stay clean enough for the bike to run well (in my eyes at least). The electrodes are a nice gray color, but the rim and the ceramics always have carbon on them. I have a Mac 4-1 megaphone exhaust on my bike with no baffle. However, I do have a steel plate with a 1" hole in it to reduce to noise. I've got tons of power past 5000 RPM, but could use some more in the low end in my opinion.

After reading all the posts about fuel mixture vs backpressure, I am beginning to think that I need to address this problem further. I am pretty sure the jets are stock - which might be a problem. Is this something that is going to require re-jetting or fiddling with backpressure and the baffle?

All the wisemen here in the forum say that running 7s for plugs is treating the symptoms, not the disease. I want my baby to be cured!

 

[scotty]

back pressure should improve low end torque but cause the motor to run richer. i would take out the baffel and see what the results are as a start

 

[AOD]

if you're running K&N pods and a 4-1 header, you are running leaning with stock jetting.

what is odd is the plug fouling problem, which is usually a rich situation, or oil fouling. the backpressure could be causing richness which might foul plugs faster, but i would think with the stock jetting you're more lean than rich.

i used B8RES plugs a few times when B8ES weren't around, they actually work quite well. A side note about them, they seemed to foul less on a bike that would foul plugs if it sat for a week or so. You may want to try the R type plugs and see if it helps.

~Adam

 

[jonr]

Adam,

Actually I have the K&N stock replacement filter, not the pods. I've only been running that for a few weeks now and my plugs still read the same as they have for the last two or three years with the stock filter.

What specifically is the difference with the R on the plugs (besides less fouling)?
-j

 

[AOD]

i think it's just got a resistor in it...which is what R stand for. i had no side affects or problems with mine...and i've used them on both bikes.

~Adam

 

[bwringer]

The R just indicates a resistor plug. I'm fuzzy on the reasons for these, but I think it has to do mainly with reducing the amount of RF interference generated.

With a modified engine, you have to roughly balance air in with exhaust out. It sounds like you've done that with the pods plus the exhaust. I remember it was a little loud, but not at all obnoxious. If you just modify the intake OR the exhaust, it's a lot harder to get things working right.

You could take out the baffle to see if it then starts to run a little leaner, but you probably don't want to deal with the increased noise.

In any case, if you had the stock jets, you would be running very lean. It sounds like you're actually running very rich, assuming the deposits aren't oil.

Two things: find out what the stock jet size is supposed to be on your bike. I have no idea what it would be on your bike, but you can often find this tidbit on the microfiche.

If they appear to be the stock jets yet you're running rich with intake and exhaust mods, you might be dealing with the aftermath of someone else's ham-handed attempts at tuning.

If someone else rejetted your bike long ago and far away, it's possible that they just drilled out the stock jets. It's bad and it's wrong, but I've seen it happen. Look for scratches and other evidence of this travesty, or just get your hands on a new set of jets with the same size stamped on them and see if you can see a difference. It's also common (and bad and wrong) for people to sand down the carb needles in a misguided attempt at retuning.

It's not pretty, but I've seen carbs where this has happened and I've even heard a few pinheads advise their friends to do this, as if new jets are going to bankrupt anyone.

It's worth verifying your current tuning just to make sure you're working from a good baseline.

 

[jonr]

Scotty, Adam and Brian,

Ok, I will start experimenting. I've got the fiche and the factory manual for my ride, so i will start there with jets. I'll take it out for a spin (with ear plugs) w/o the plate I stuck in the exhaust and see what a few miles do to the plugs as well. My exhaust is starting to get a bit too rusty near the engine, so I have been contemplating putting a new one on when the tax return comes in the spring. If I am going to have to re-jet, I'll probably wait until then.

Thanks for the suggestions.
-Jon