I think my bike may be running too lean.

It's an 85 fx evo with stock setup.

After about 20 miles, the spark plug insulator is snow white, except for a black carbon spot on one side. Both plugs are like this.

I don't think the plugs should be brown because unleaded gas doesn't color the plugs like leaded gas did, but I think there should be some color (The plugs in my truck are almost white and they have been in there for a several years)

I get some knocking when I'm in a high gear at low speed.

The bike shakes at low speeds (less than 25mph), but is fine at high speed.

I'm thinking of replacing the jets (too rich is better than too lean)
pilot from stock 52 to 55
main from stock 165 to 175
but I don't want to do this to mask the real problem which is most likey to much air coming in. I have been looking for vacuum leaks but so far have not found any.

There is also dry carbon soot around the spark plug ring and the top of the threads.

I'm wondering if the plugs are not tight enough in the head and air is getting in on the intake stroke and exhaust is coming out on the exhaust stroke which is causing lean condition and the black soot around the threads.

I usually tighen them hand tight plus 1/4 turn.

Once I take the plugs out should I replace them with new ones to get a better seal?
I may try to torque them to 15 ft/lbs.

 

the plugs should be a chocolet brown definitly running lean the low speed knock is pinging id try just fatining the enrichment screw first the go a size bigger the best way is on a dyno but its not free

 

On some carbs, you can set your needle height up to richen it. It would have 5 rings ground into the top end with a clip you pull off & move to another setting.
You also have an accelerator adjustment screw on the front (or right) side of your carb. this will allow more or less raw fuel while twisting the throttle.
Confirm that the heat range for your plugs is the right one!

 

http://www.4secondsflat.com/plug_chart.html
http://www.usaimports.co.uk/Mopar_Te...ug_Reading.htm

Here is info on plugs, the timing section on the Mopar tech is helpful but like you mentioned about today's gas is getting tough to read plugs.

 

Your plugs should be a nice tan color - not white, not brown, and definitely not black. White plugs mean you're running too lean, and that's bad... both for performance and for your engine. If it's pinging, you need to check your ignition timing, too... pinging is often caused by too much advance on the ignition advance curve. Too lean of a mixture is also a contributor to pinging.

You said your stock idle jet is a 52... did you mean 42? A 42 idle and a 175 main is stock for Bertha's year and model. A 45 idle jet and a 175 main will richen your mixture. I run a 46 idle and a 185 main in Bertha, and my plugs are always a nice tan color, which is perfect. My configuration is in my sig below. Using an older Sporty needle will richen up the midrange when the slide comes up, too.

You didn't mention what air cleaner or pipes you are running... if you are running a high-flow A/C and non-stock less restrictive pipes, then you really need to rejet - the stock jets will be too lean for anything but stock A/C and pipes.

 

A stock '85 Evo would have the Keihin butterfly carb, not a CV (no slide or needle). Stock Evos do run lean, due to EPA regulations, so it wouldn't hurt to richen it up a bit. I'd reccomend going up one size on the main jet and backing the idle mixture screw out a tad. Keep the stock pilot jet. Or you might want to consider upgrading to a CV carb...

 

Thank guys.

Everything is stock. The carb is a Keihin butterfly. The pilot jet is 52, stock. The pipes are stock and the air cleaner is stock too.

 

I just recently swapped out my butterfly for the cv.

On the butterfly, if you are still stock with the compliance fittings then you may have air intake leaks there since they are notorious for having problems. I had mine changed to an SE manifold and it did pretty good for many years but it would still get leaks at the insulator block between the carb and manifold, so I needed to tighten the bolts sometimes.

My last problem before I changed to the CV was lots of hard starting and I could never get the A/F mixture quite right even after increasing the idle jet size quite a few steps. I still had the A/F screw almost all the way out. I concluded there was maybe a leak in throttle body somewhere.

CV is now installed and my hard starts have been cured.

 

If you convert to a CV, you will notice a lot more snot when you twist the wick! check the vacuum line at the VOES & check to see that it's working.

 

the stock jet on my 85 flhtc is a 50. i've been running it since it was new. 90k on it. motor has never been apart. plugs are white with a small area of tan.