Take a Look at These Plugs Please

[Broz]

I would like to have some opinions from the experts on plug reading here.

These are out of our 1996 670 Summit with Jaws pipes.

The plugs were almost new and I cleaned them with Carb cleaner and a wire brush before the test. This is what they looked like after 3 runs. Each run was longer after we felt is was safe to do so. All three of these pics are of the same plugs after the last run at WOT and at 8300 rpm for a good long blast. Kill switch was cut before throttle was closed.

P 380 / M 370 mains. @ 4200 feet @ 31 degrees F.

I feel they are a little lean for a 31* day. What you say??

Thanks
Jeff

 

[fatguy1]

Do you have an old set of plugs to test with?

New plugs/clean plugs make it more difficult to tell if it's too lean.

the way I was told to read them was to look at the eletrode strap, and just as it starts to bend and head down to the threads you should see a "burn" line. looking at your pics I would say your line is a touch too far in the lean direction. That's just my two cents

I would look more at piston wash than the plugs.

hope this helps.

 

[drewski]

shouldn't you be doing a proper plug chop with new plugs? at least thats how I've always jetted.

 

[markoo]

I would say a little lean

 

[Broz]

Thanks! I am learning. I have a ton of experience reading plugs from Blow Alcohol and Blown Nitro in Drag racing. But my experience on two strokes in limited. I am learning..

I wiped the oil off the rim of the barrel with a towel to look at the burn there. I wanted to see if the cadium plating was burning off. This is how I read them in the race cars. I can see that my old way does not apply here.

I thought a newer set of plugs would be good since we just milled the head and re jetted. My bad.

I think I will jet up 10 on each side and run it some more with these same plugs. Then do as Drewski says and cut the barrels off.

I too feel they are lean just a bit. Especially since it was a warm day so may as well feed it a bit more. If it will burn more fuel it should make more power anyway.

Anyone else??

Thanks
Jeff

 

[drewski]

You will not get a good reading on your "mains" if you use the same plugs. You need to warm up the machine on old plugs, shut it off, replace with brand new plugs,start up and do a wide open pull and hold it open for 6-10 seconds, then shut down right away after. Take out plugs, replace with old ones and go back to your truck or shop and chop the new plugs.

 

[Broz]

Thanks Drewski, got it. That sounds good to me. We use to put new ones in every pass on the race car to read abd ballance each cylinder.

I had not seen the info you posted before. Looking forward to seeing how new plugs look after a blast. I will use the existing plugs to warm up and change them right before we head down the test area.

Are the plugs in your pic from a 2 stroke? sure are clean.

Jeff

 

[drewski]

Thanks Drewski, got it. That sounds good to me. We use to put new ones in every pass on the race car to read abd ballance each cylinder.

I had not seen the info you posted before. Looking forward to seeing how new plugs look after a blast. I will use the existing plugs to warm up and change them right before we head down the test area.

Are the plugs in your pic from a 2 stroke? sure are clean.

Jeff

Yes they are from a 2 stroke. That's what they should look like. that is only about 25-30 seconds on the plugs. they read a chocolate brown smoke ring that are 2mm thick(Perfect main jet).

 

[drewski]

here is a vid on how to do it YouTube - Spark Plug Chopping

 

[POWDERCHOWDER]

I think they are fine i ran crankshop twins on my 800 my plugs were lighter then that after big pulls in the mountains had it on the edge all the time, thing hauled.

 

[Broz]

Thanks Guys, I will do the test and chop a set of plugs then post a pic and results.

Thanks to all.

Jeff

 

[Taylzee]

I would be more interested in what the piston wash looked like...To me those plugs are fine.

 

[Broz]

I would be more interested in what the piston wash looked like...To me those plugs are fine.

I have thought of pulling the head too. I just milled .020" of it and was right at .050" on the clearences. Might be nice to make sure all is clearing ok.

I dont think I could see enough of the piston domes any othe way.

Jeff

 

[Taylzee]

I have a little $5.00 snake light from PA that works great. It fits down the plug hole and I can see everything at BDC. If no you can pull the exhaust and shine a flashlight throught and look throught the plug hole. There are bore scopes now that are getting cheap too! They are available at almost any parts store now.

 

[Broz]

I took a look and need a smaller diameter flex light. I will pick one up. But I want to do the chop too. Seems to me the wash would be a slower reacting observation where the plug chop is a direct indication of what was just going on a WFO... oops I mean WOT.

Thanks to all.

Jeff

 

[Broz]

Update! We pulled the cabs off of the 96 Summit 670 and found that the float level was a bit low. So we raised it to specs. .772". Then we installed the larger mains of PTO 390 Mag. 380 It was colder today so we felt we were going to get a better test as far as normal conditions and temp.

We took her out and warmed her up good riding back and forth packing some new snow down for the WFO test beat. Then we lined her up on the track and installed a new set of plugs. My son started her and immediatly pinned the throttle. He held it WOT for a loooong blast and hit the kill before letting off. We pulled those plugs and came to the garage for the chop off of the barrels.

The burn line is a nice medium brown but was a bit on the low side with an average measuement of 1.8 mm. So we richened her another 10 and will test again soon, but I feel we are close to perfect now.

I will also look at the wash again as soon as we get a little more run time on her. The wash prior to today was showing it to be close.

Here are the specs again along with the pic of the chop test. Also, I was pleased to see that the plug with the slightly hotter chop test was also definatly showing more cad plating burnt from the rim of the barrel. Being a old drag racer it gives me comfort knowing that you can relate cad burn to this too. You will see this in the pic. The hotter plug (M ag)has about 1/3rd of the cad burt as the slightly colder plug (P to) has very little burnt.


Specs as of the added 10 to the mains after this chop test:

1996 Skidoo 670 Summit with HAC and Jaws twin pipes
milled the head .020" for a compression of 125 psi @ 4200 feet.
Temp was 5 degres F.
4200 feet of altitude
Floats are at .772" using Vinton tipped 1.5 needle and seats
Pilot jets are #75
Needles are 7DPI1 in notch 2
Mains are PTO 400 Mag 390
Idle mixture screws are at 2 1/4 out
Clutch clicker is at #2 and engine turns to 8000 quick and then slowly gains rpm to 8200 or 8300

Jeff

 

[drewski]

1 size up and you're perfect for those temps and elevation. Glad to see people using the plug chop method! Another rule for temp changes. For every 10 degrees C of difference, change your main 1 size. 1 up for colder or 1 down for warmer. This is approximate, You should always do a chop in severe temp changes.

 

[Broz]

Thanks Drewski, The plug chop test worked well. It is nice to be able to see and read the results of a test. So many methods of plug reading leave you wondering and not positively sure.

It is hard to tell from your photo of your plugs, but they looked almost identical to mine as fa as color and ring width. Was yours 10 lean too at that point or do the rings just look a bit narrower in the pic than they really are?

Jeff

 

[drewski]

Thanks Drewski, The plug chop test worked well. It is nice to be able to see and read the results of a test. So many methods of plug reading leave you wondering and not positively sure.

It is hard to tell from your photo of your plugs, but they looked almost identical to mine as fa as color and ring width. Was yours 10 lean too at that point or do the rings just look a bit narrower in the pic than they really are?

Jeff

those pics I posted were a perfect 2mm ring. Prior to that test I was 1 jet size smaller(lean) and the plugs revealed a 1.8mm smoke ring like yours. I'm guessing you are running minkuni carbs judging by increments of 10 for jet sizes. I was running Keihin carbs on that motor. I would guess 1 size up would be perfect for you at those temps and elevation.

What are you going to do for elevation and temp changes? Re-jet every time? Or are you going to do a vari-flow altitude compensator, dial-a-jets or something along those lines?

 

[drewski]

sorry, I see what you were asking. the plugs in the pic are longer than yours.