thanks for the reply, with a warm engine yesterday with coolant flowing( thermostat opened) it was reading mid 300's, on the stand. With no load( no driving) and just hitting the gas( getting revs to 7000-8400 in short bursts. is was reading 600- 700 F.Mine at idle are between 500 and 600 F on a warm motor. Egts at mid throttle should be (my is any way) around 1050 F and 1100 at wot[/b]
did a CPI conversion, sheilded hoods and converted to a polaris needle( forget the number and taper, but it does have five clips for adjustments, I have washers for shimming.If you are using the stock neddle's, you need to go to the '942' needles from Doo. They are adjustible and are richer in the mid. I run my temps lower due to my timing being advanced. Advancing the timimg creats more cylincer temp and a little less exhaust temp. My plugs are cardboard brown at my temps
The 942 is the last 3 numbers in doo part number. do a search in this forum on them to find out more.
At mid range, pulled the plugs and the bare a very light brown to whitish color, do a pull again wot and i get a nice mid brown color??What do your plugs look like with those EGT temps? Try doing a plug chop (shut the engine off while it's running mid-range and coast to a stop, dont' take your thumb off the throttle) and check the color. Could be you are still safe at the 1300-1350 range because of probe placement?[/b]
According to Olav Aaen's Carb Tuning Handbook (chapter 1 - engine mixture requirements) midrange is designed by to run lean, ie.
RUNNING CONDITION MIXING RATIO (by weight)
Fuel : Air
Low Speed 1:10-13
Light Load-Midrange 1:14-16
Heavy Load-Top End 1:12-14
Hope this helps, his book is reasonably priced, worthwhile investment.[/b]
Try blocking your RAVEs open and do another test. Depending on your probe placement, you may be witnessing the exhaust venturi effect caused by high speed exhaust flow to the probes before the RAVEs open. Common on twin pipe set ups with probes mounted a little too far from the pistons.[/b]
Pull the red caps off and the return springs then pull the RAVEs open and hold them with small vise grips.Please explain more!
How does you block the Raves open?
Are you saying that possibly the raves are not opening soon enough, causing higher egts in the mids?[/b]
Do the TMX 38 carbs accept the same jets that I use in my 40's?Pull the red caps off and the return springs then pull the RAVEs open and hold them with small vise grips.
What I'm saying is that the probes need to be located correctly (see attachment) in the exhaust stream, sometimes people locate them for convenience and see un-realistic readings because the deflected flame front caused by the RAVE guillotine is aimed right at the tip of the probe while the surrounding exhaust temperature is lower. Kind of like the flame kernel on an oxy acetylene torch the blue point is the hottest while the surrounding orange / yellow flame is a lot cooler. The opening point for the RAVE valves is depedant on exhaust back pressure which is more constant with single pipes. Now that you are operating duals, you need to taylor your opening point to less back pressure. A good bench mark to start with would be the RAVE return springs from a Mod 800 P/N 420 239 941 Blue stripe .08 X 52 MM. The other issue here is whether your using the stock air box (tuned) or gutted or Pods. BRP racing uses TMX 38 taper bore carbs on their 800 Mods because of better mid adjustability using Kick A$$ pods. The TMX 38 carbs flow as good or better than the stock TM 40s.
Do the TMX 38 carbs accept the same jets that I use in my 40's?
Yes, long hex jets
Why/how are the 38s more ajustable in the mid? Is it just adjustable needles?
There are more needle variations available and yes they are adjustable
At this point I am still using the tuned air box, but may be pull these as I am trying to set this sled to drag race this year.
Then you will need to tune the part to mid throttle because that's what the air box did.
I will try the diff. RAVE return spring. Would this spring be softer?
Thinking of tightening the squish and compression with race fuel!
Use the CCing method outlined in the Race manual instead of the low tech sqeazed solder approach
Any suggestions of where or if I should adjust the timing? From the stock settings? Esp. if I raise the compression?
Timing should be backed off about 2 degrees for every compression point you increase. Can be retarded through BUDS and the MPEM. Cann also be done by slotting the pick up coils.
Thanks for all the advise[/b]