Favorite spark plug

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Favorite spark plug


Post by Sidecar » Tue Jan 20, 2009 9:15 pm

Author: sidecar

I always had good luck with NGK. I had some bad luck with Autolite in a non-motorcycle application.
So tell us......... What's your favorite motorcycle spark plug!?

Post by bigmike

2 wheels: Bosch. 4 wheels: Autolite. The only plugs I've ever had trouble with are Champions (I still run them in my '36 Lincoln, they were OE and it's gonna stay as original as possible)
As long as your ignition and carb are ok, I don't think it matters much with non-resistor plugs. The technology involved is of the same vintage as our Panheads anyway!

Post by sidecar

I finally remembered this name: Splitfire
I ran these in a dresser about 10 years ago. When I first put them in, there was a dramatic increase in throttle response. 300 miles later the bike starting missing. 2nd & 3rd set did the same thing.
I have never used them since then. It's too bad because they seemed to work great when I first installed them.
25 years ago I was a big fan of Nippon Denso ( I think they are now called Denso ) Hot U plugs. I don't know if they make them any more. They worked well in my off road adventures.

Post by billy

I've had the best performance/luck with NGK's in my Pans when I had them. & The same good running in my Flatty ;D Tried Accel's plugs once in Pan, but the motor seemed to me to run hotter! I'll stick to the NGK's A6
18mm for my Flat...Equal a HD #3 ;)

Post by zup

Accels were my first choice in Ca. Haven't seen them in Iowa since moving here, but then really haven't looked that hard either. Autolites are what I'm getting here. I gave up on Champion plugs a long time ago. Seems they have a nasty habit of not being able to recover from being wet fouled. Because of that, I pass on 'em. Put some of the Bosch Platinum Plus' in a few 4 wheelers, and liked the way they ran (held up well) Just never cared for them being as spendy as they are.

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Re: Favorite spark plug


Post by 58flh » Tue Oct 23, 2012 1:04 pm

I have had good performance with Bosch-Plat. plugs!-in my pan!, Just recently I got the Bosch +4-plugs to work!,-I have a Biz. account in autozone from a shop I owned back in the late 80s & early 90s!. So they let me go box after box untill I found the correct short-reach for a pan & correct thread size!--Heres the issue!--They are 5/8s plugs with the taper on them for modern cars that dont use compresion rings for gaskets!--Heres how to make them work!-(chuck them up in a lathe & take .015 off the tapered part that seals to modern heads.-Now put a compresion gasket on it ,& it has plenty of meat to make a good seal & not RUIN the TOP-THREDS in the PAN!. Here are my results!--You no longer have to index plugs as these have 4 gappers!--So you always end-up with a great fireing front across the piston!-(more fuel will get burned!).Throtle response was instantly noticable!-Idle was even Better!,Going thru the RPMs was very smooth & responsive!,I did a fuel mileage check & on the highway I picked-up 3.7 miles per gallon!-(solets round it off to 4-MPG). And that was 2-up!--I have not done a solo milage test!---I pulled the plugs after a 100 miles & they were right where I set the carb. to!--Just on the rich-side!/with a cocobrown on the top of the insulator!---Tune your carb. at full operating temps. with these plugs! Dont cut corners!-Go for a 15 mile ride & ADJ> it then!-As all carbs. should be ADJ. at full op.-temps anyway!--I use copper core 7mm wires, Do not use suppresion wires with a points IG. Electronic IG. need suppresion wires to make good SNAPPIN SPARKS!---OK heres what I also tried!--I put them in without taking the .015 off the taper ,I used old compresion seals & they sealed!--(but I had to use a wire to center the seal while tightening the plug!--IT WORKED!)-BUT I STRONGLY RECOMEND YOU FACE OFF THE .015 off the TAPER!--This provides a FLAT surface for the Seal to rest against!---NOW THE NUMBER for THIS BOSCH-PLUG IS----(4449-HGR-9-BQP)!.Very NICE PLUG & better Flamefront as the +4 sparks ALOT--You can see for yourself when you ground it to the head & give a kick!--Multi-sparks & a GOOD SNAP!---RICHIE----Also my next venture is the new BOSCH-PLUGS!-(They have a matierial in the center electrode called IRIDIUM!--Bosh claims that as soon as voltage is applied they reach operating temps in an instant!-(so when that plugs time to fire comes up its already at a operating temp!-Pretty interesting when you go over thier results & watch the plugs with a gage on them & as soon as voltage was applied to a cold fresh plug out of the box ,that digital meter went to 300 I believe, you can see for yourself on thier (research & development site Bosch/Sparkplugs!)--They are pretty EXpensive compared to the +4-Platinum ones!--I think $14 a plug!---Good-luck if you decide on the +4s, I like them as Indexing is a thing of the past with these! & the DEPTH is PERFECT!--I have a head you can see them installed on !-Its on the post About EXhaust VACUUM-LEAK!--About 9 weeks ago!-& I run OEM heads!-(i belive the post said knuckle valve guide in a pan!).---RICHIE 8)

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