cold weather tommarow worried about engine

C

carter170

New member
tommarow we are going to a race and the temp is going to be from 36-50 degreees any advice about a purple plate jet number for these freezing temps I was going to go high on the jet to richen the engine up but I want some advice for these temps in purple plate.
 
Flashpoint of alcohol is around 51* -- keep some heat in the engine if you don't have an electric starter.
Also helps to have a small squirt bottle of gas that you can prime through the airhorn just to get it started.

Jet-wise you might be alright. You won't know unless you have it tuned on a dyno and watch your DA.
If the engine shuts off at peak rpm (end of the straightaway), then you're too rich -- go down until the engine runs cleanly all the way through the rpm needed for the track.


-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cuts
www.CarlsonMotorsports.com
Celebrating 25 years of service to the karting industry
765-339-4407
bcarlson@CarlsonMotorsports.com
 
Cold air, in almost all cases, means higher air density, (AD) this means more air going into the engine with a corresponding need for an increase in fuel.

Cold air means a cooler engine, meaning you might be able to hold off a little on the fuel increase. A leaner mixture is going to burn hotter and, with more cooling, you might be able to get away with it.

It's a balancing act. Cold air more fuel, more cooling less fuel. This scenario is a perfect example of the benefits you get with the EGT gauge. (Exhaust Gas Temperature) You adjust the mixture until you get the highest EGT readings you can. Heat is power. If you go too far, the EGT will drop.

.062" to a .063" jet is a 3.25% increase in area. If you had an air density gauge, the decision on what jet to run would be infinitely easier.

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
 
The OP is talking about a purple plate jr 1, Al. .425" restrictor.
Put as much fuel through it as you can. DO NOT try to build temp by leaning these small plate engines.
DO NOT adjust/decrease fuel to increase egt (or cht which you likely use). It will flat KILL the power.

Al, I've tried to tell you this before, but yet you keep giving misinformation (specifically on small plate flatheads.)
Please stick to your area of expertise.
 
Thanks for the PM, Al.

You are wrong on this, accept it.
If you perceive correction as "condescending", then you need to re-evaluate the value of correction.
I've given the data to prove the theory and you still refuse to accept it. Worse yet, you give bad advice on how to tune a small plate flathead engine to others that may not know the truth. Build one, test it, then report back to us, please.
 
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tape up your sidecover [if the rules allow] to get as close to your normal head temp as possible.this will minimize the changes you will have to make and enable you to stick close to your normal "tune up".
 
Leave the jet alone if its been running good , My purples liked .059 -.060 - .061 jets . Tape it up tight and crank it up early ! You can let it warm up some in the pits, before going to the grid then re- crank early in the grid and don't blip the throttle let it idle a long time. Listen to Carlson he is correct!
 
CarlsonMotorsports said:
Thanks for the PM, Al.

You are wrong on this, accept it.
If you perceive correction as "condescending", then you need to re-evaluate the value of correction.
I've given the data to prove the theory and you still refuse to accept it. Worse yet, you give bad advice on how to tune a small plate flathead engine to others that may not know the truth. Build one, test it, then report back to us, please.
Click to expand...

LOL Brian is dead on with his advice, and has built more plate flatheads than Al will ever see, Al is a 2smoker guy and has ZERO experience with a flathead
 
flattop1 said:
Anything you print, send or say is subject to being repeated.
Click to expand...

and of course you are absolutely right, and I know that, but I thought the people on this board where little more civil. Especially the better-known people here. I guess I was wrong.

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
 
I will just say that when my boys started out racing karts, we ran Purple Plate Flathead for around 10 years ( 3 sons ). What Brian has said is absolutely correct. I always started out "rich" as Brian said, and leaned it down if it cut out at the end of the longest straight. But generally, somewhere in the .060" jet size is correct. Tape up the blower housing, don't try to over-rev it if possible. I never had much luck doing that.

Al, the reason for the big jet size is that with the small Purple Plate ( .425" hole size ), the engine does not create enough vacuum to pull fuel from the small fuel cup as it would with either a Gold Plate ( .575" hole size ), or unrestricted Stocker. For that reason, the jet has to be bigger to just get enough fuel to run. Don't debate ............... Just accept. :D

Dave E.
 
I know Brian, but if the motion of the piston didn't create the Low pressure in the cylinder ( which I will call "Vacuum" ), the High pressure would not be higher than inside the cylinder, and the fuel / air mixture would not move toward it. LOL I know it is a crude explanation, but it really is basically what happens.

Al ............. one time, at a Sprint Track, I was changing the jet in a Purple Plate Flattie. someone was talking to me ( bad mistake ), and I forgot to put the jet back in, but did put the needle assy in. It ran fine except for the top end RPM it would fall on it's face. I was amazed it even ran ....

Dave E.
 
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