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The wandering idle and reading spark plugs

Joined Apr 2007
190 Posts | 1+
Gormley, Ontario, Canada
Been making some changes to the setup with Dale's jet kit. Clip now in 3rd groove down instead of 4th down as recommended. (needle drops to lean out mixture)
Adjustable idle air scew at the recommended half turn out. Fuel screw at half turn out instead of the recommended 1.5 turns out. #48 pilot jet. Engine is running well, but feels like it could be a little crisper off idle. No bog or sag when snapping the throttle, but not easy to levitate the front wheel until about half throttle (big fuel tank with about 12L on board).

I *think* it could stand to be leaned out on the pilot as per Taffy's thoughts. My question is: How much fuel screw change is equal to the next lower jet size? i.e. #48 pilot at half turn = #45 pilot at 1 turn = #42 pilot at 2 turns?

The idle speed is not really stable and tends to vary, but always increases and more so when the engine is really hot on the tight trails. Does this variance indicate rich or lean?

After a run down forest roads at about 1/3-1/2 throttle (going back to the truck), the plug shows good colour. Light tan on the outer electrode. Light tan on the insulator. Dark grey on the center electrode.

I put a photo in my gallery to show the plug colour.

I stumbled across an interesting colour chart at this site:
http://www.dansmc.com/Spark_Plugs/Spark ... talog.html
 
Hi Neil,

Have/had the wandering idle on all my bikes, think it´s normal as engine-temp varies and as a result requests a
slightly different air/fuel mix.

Taffy made a good pj/paj-relation chart in the owner´s doc, don´t know if this helps you?

Just my thoughts about the reading of the plug-colour: I believe that with our modern unleaded fuels it´s almost
impossible to read the correct jetting from taking only a look at the plug-colour.
Yes, the colour can give you an Idea about where you´re with your jetting, but to be accurate you need other tools.

Wasn´t a big help for sorry.

regards
 
Re: RE: The wandering idle and reading spark plugs

Hi Neil,

I put one of Dale's carb kits in and it bearly ran with the #48 pilot jet and had to be compensated with the mixture screw like you have done 1/2 a turn.
You need to go to a #40 pilot Taffy say's even down to a #35, back the mixture screw back out to 1 1/2 turns and my PAS is out about 3/4 of a tun idles perfect the idle stays constant no wavering up or down.
I think my next step is to try a #35 PJ just to see the reaction. Hope this my help.

Regards

Sparks.
 
Neil_E. said:
I *think* it could stand to be leaned out on the pilot as per Taffy's thoughts. My question is: How much fuel screw change is equal to the next lower jet size? i.e. #48 pilot at half turn = #45 pilot at 1 turn = #42 pilot at 2 turns?

the fs is irrelevant as a tuning screw. it must be set to stop a hesitancy off idle so that you can snap a wheelie in first while rolling along at 3mph. ok?

i call it the snap wheelie test.

we need to set the fs for this first and if you have then we need to know how many turns out from closed it is. my guess is that it's about 1 turn and may even be anywhere as you are so rich.

essentially you might even be outside the zone of work.

suggest far smaller PJ.

oddly enough though, the raising of the idle as the engine warms up would indicate that it is lean (the mixture is lean at idle and the needle is 80% of this) on the needle straight. what is your needle code?

regards

Taffy
 
RE: Re: The wandering idle and reading spark plugs

I have Dale's custom needle (no code). Let's compare this to the OBDVR needle used by the WEC riders.
Shank diameter: Lineaweaver .1085", OBDVR .1082"
Shank diameter at 2.6" down (approx 1/4 throttle) Lineaweaver .1075", OBVDR .1061"
In both cases Dale's needle is slightly larger and would allow less fuel through the needle jet/emulsion tube.
This could require a slightly larger pilot jet to obtain the best air/fuel ratio.
I am hesitant to put a 38 or 40PJ in right away, so I will install a 42 for my next ride and see how it does.
 

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