4/6 EGT temps?

[gixxer6]

IT'S ALIVE!  I finally got my modded 4/6 running.  New crank seals, crank replacement, cylinder issues, broken gas tank filler neck repair, a full day of removing and greasing stuck suspension shafts, new rear shock, rebuilt fuel pump, 4 cans of carb cleaner, rebuilt recoil, and probably a dozen other things, it runs! 

This 80' 4/6 LTD came with Aaen pipes, ported cylinders, Wiseco pistons, K&N pod filters, non-power jet carbs with adjustable mains, and an EGT gauge. 

I've never ran a sled with the adjustable carbs and EGT gauge.  What temp should it run???  Am I only concerned about WOT temps? 

[Tory944]

...  Probes located 8-10" from the exhaust ports...  if  the probes are too close it will actually read too low.  Correct temps should be in the 1100-1350 range.  Ideal...  1200-1300.  If you see anything near 1400 or higher "you betta pull ova."  Give er h--l.

[jimvw57]

what?? no video???   That's cool it is running!!! 

[gixxer6]

The probes are 6" from the cylinders.  That should put them about 8" from the pistons.  Does that sound right? 

I didn't see anything over 1100, but the engine isn't broke in yet.  So I didn't run it very hard, just a 3 or 4 second WOT burst.  Its still running premix along with the oil injection.  Once its broke in and tuned, I'll try to get a video... 

Am I only concerned about the WOT temps?  Or any temps that that get close to 1400?  Can I use the EGT's to the pilot and needle? 

[jimvw57]

I would guess that with the extra oil, it will run a bit cooler..

[Checkmarks]

Tom,

Never trust some number as the correct heat range for your motor.  Make note of the temp the motor runs at WOT.  Verify the piston wash.  When you have the correct wash then that is your number.

Easy with the two plug holes to look at the piston wash.  Pull both plugs, put a light down one hole and get a good look with the other hole.  Too simple.

Many variable elements.  How accurately your gauge represents, how far the probes are from the piston, the probes themselves...  See the solution?  Check the pistons, they will tell you.   

[gixxer6]

It's 35 degrees out today, I balanced the carbs and rode the sled for about 15 minutes.  It was running around 1100-1200.  I pulled all four plugs and inspected them.  Ground strap is a dark brownish color.  I looked at the piston wash.  The old piston was solid black, and the piston that I just replaced still looks new.  What does this mean? 

[Checkmarks]

The new piston, piston wash is not measurable yet.  The old piston wash says you are clearly not running rich since the carbon would have 'washed' off in larger sheets or chunks relatively quickly.  There is not much to to note with a short run time and piston wash other than an overall view of correct A/F mixture.   

Plugs are my idea of 'getting close' and I have a little extra money.  Here is Marks how to, works.  Warm the motor to operating temp.  Put in one new plug (brand new shiny), the rest old not fouled is fine.  Put the sled on a jack stand.  Fire the motor up and run WOT for four full seconds.  It is not necessary for any more than four but then necessary for at least four.  Kill the motor holding the throttle WOT.  Pull the was new plug and "used up plug" never to be used again for this procedure UNLESS your motor was marking RICH.  Hence the always start rich with your carburetor settings!  Get it?      Inspection of the grounding strap.  There will be a burn line where the metal on the strap goes from shiny new to a faded dull.  Where that line draws or burns the line is what tells you the motor is rich or lean at WOT.  The goal for perfect is the burn line being centered in the corner bend of the grounding strap.  Visualize the grounding strap straighten out making the plug gap around 5mm instead of thirty thousands of an inch with the 'bend' as a reference marker.  As the burn line approaches the bend reference mark the motor is rich.  After the burn line passes the corner reference mark your motor is lean.  The further the burn line is past the reference mark and starts touching the plug thread, panic and put in richer jets before you melt down.  As only a reference, I do not warranty, when you get the burn line down to the plug threads you are four jet sizes too lean.  Graduate that measured mark on both sides of the reference mark.  Start rich and you will watch the line move down the grounding strap.   This procedure apply to middle throttle checks also.  Last the burning plug line trick can only get you from four sizes and checks rich toward perfect before the burn line becomes un-readable.  Two new plugs and you can have the whole job done with a final burn line on the new plug saved in your tool box.  Just because you cannot see the burn line approach perfect carburetion you can still use it to verify your motor is not lean.  After you are into the lean side of the burn reference run the plug it is useless for this procedure. 

Using plug color is in the air a little with fuel additives.  Color does not apply to the grounding strap only to the insulator ceramic the protects the center electrode from sparking any where except the tip of the grounding strap.  This color is another visual check so that you have three A/F mixture checks.  One, burning grounding strap, plug color and piston wash.  The color never better be white unless you are 'burning' the plug in the above procedure.  After you have the plug burnt literally and metaphorically the color will begin to start marking.

Plug chopping ie: cutting the threaded portion of the plug off with a grinder.  New plug gets a 1/4 mile run WOT.  It will create a black soot line on the ceramic insulation.  The relationship of that soot line, much like the grounding strap burn line, identify the motor as rich or lean.

I draw my egt worry line (not really) at 1300 and panic at 1400.  In truth until you watch the egt's and see the piston melt temp that gauge is just another measure that has little value.  In the end that egt gauge tells you, if you need to pull a plug checking for color or verify the piston wash with any concern.   Think of it as a no work, constant communication, to the A/F mixture gauge. I use the gauge all the time in race motors.

Tom, I am going to have to barter information with the price of 4/6 cylinders next time.

[gixxer6]

Wow Mark, that is a lot of good information.  Thanks!  Your next cylinder purchase will be at a discount. 

From what you are telling me, it sounds like it is running lean.  The carbs have 370 mains and have the adjustment screw in the bottom of the bowl (dial-a-jet?).  I have never ran these type of carbs before, and have no idea where to set them to start.  I started with 1.5 turns out from full seat, but it sounds like this is too lean...   I will turn them out some more. 

[kawhead]

the dail a jet equals 90 jet points added at 1 turn out;ie; 370 main jet closed =370...1/2 turn out 370 + approx 45;1 turn out, 370 +90... no effect added after 1 turn....they  used these on the nitro and twister f/a motors stock,easy adjust when it gets warm.....

[gixxer6]

I've got 370's and the screw all the way out, which is equivalent to 460's.  That seems really high to me.  Could this be right??? 

[kawhead]

does sound rich....add up invader jets,120 and 145 =265...thats with an airbox....and stock pipes.....if it has good power it cant be too rich

[gixxer6]

The stock 4/6 jets at 120 and 130 (250 combined) are even smaller than the Invaders (not sure why , seems like they should be a little larger...).  It seems like it makes a lot of noise, but not the power that I'd expect.  It currently turns about 8800-9000 rpm. 

Maybe I should try going leaner?  It's a lot easier than buying and installing bigger jets.  If I'm real careful and keep the EGT's down below 1100 I should be safe? 

[Checkmarks]

Tom,

The plug burn will tell you. 

1100 Egt tells you nothing until you run the plug burn.

After the plug burn, EGT noted temps tell you the next piece of data.

Last the piston wash will identify with absolute precision for that day's air temp, altitude and humidity (high or low pressure weather system).

Safe is burning a plug and watching where the line burns WOT.  The verifying 1/2 throttle plug burn and last 3/4 plug burn.  This way you check all of the vital metering systems of your carburetor.

[gixxer6]

Ok I gave it a try.  Warm engine, WOT 4 seconds, the entire ground strap is dull. 

I am going to try a set of 480's.  I can't believe I just said that...480's are HUGE!