jetting a blue plate flathead on meth

There's only a 7.5% difference between a 54 and a 56. If I was going into it blind like you are, I would error on the large size. You can always go smaller if it's too rich, with no harm, unlike if your too leaning where you could hurt the engine.
Knowing what jet you're running with gas would help. You need to know where you're at before you can figure out where you're going. Knowing where, (what part of the country) your running might help. And, like a broken record, knowing the air density would help.
 
.056" jet. Unless you can have the engine tuned on a dyno, or at least check your air/fuel ratio -- you're just guessing anyway. Air density is a great piece of data, but pretty much worthless without knowing that the engine was tuned and jetted correctly at a specific AD, you've got no baseline to go off of.

Put a 56 in it -- if it wet fouls the plug at peak rpm, then go down .002" at a time until it clears up. Forget about egt and cht for the most part. They will be very cold on a small plate engine. Tape the blower housing completely up you still won't have temp issues.

Also, if you know who built the engine, call them and ask them. Most, like myself, keep good records of each engine they've built. This would include what jetting the engine had on their dyno, as well as other information that might weight into your decision on jetting: ignition timing, exhaust choice, throttle shaft offset, fuel signal at the short stem, peak torque, suggested peak rpm, and a whole lot more. I recommend always asking the builder first. He would want this, I'm sure. :)


--
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
 
CarlsonMotorsports said:
Put a 56 in it -- if it wet fouls the plug at peak rpm, then go down .002" at a time until it clears up. Forget about egt and cht for the most part. They will be very cold on a small plate engine. Tape the blower housing completely up you still won't have temp issues.
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a .054" jet is 7.55% smaller than a .056" jet, and a .052" jet is 15.98% smaller than a .056" jet. That's in area, not diameter.
Knowing these numbers, do you still feel it's wise to make such big changes?
When the mixture is right, the EGT will tell you, unlike that CHT, which only tells you the temperature under the plug.
And don't forget, the low-speed jet needs to be bigger too.
 
Al,
I am certain we have had this discussion before.

"When the mixture is right, the EGT will tell you,"
Click to expand...

What EGT are you looking for?

I can tell you beyond a doubt that if you try to tune a small plate flathead by "optimum" EGT, you'll be way lean and real sorry you did. You'll flat kill the power. These things make more power with fuel dripping out of the end of the exhaust than with a nice and hot egt. I can supply the dyno data to reinforce this.

I most certainly would recommend going down .002" at a time on the jet until the engine stops wet fouling the plug at peak rpm. It's not only wise, it's critical...Just as I wrote above.


And don't forget, the low-speed jet needs to be bigger too.
Click to expand...

Al, forgive me, but where is this low-speed jet? ;)
 
CarlsonMotorsports said:
What EGT are you looking for?

The maximum possible.

I can tell you beyond a doubt that if you try to tune a small plate flathead by "optimum" EGT, you'll be way lean and real sorry you did. You'll flat kill the power. These things make more power with fuel dripping out of the end of the exhaust than with a nice and hot egt. I can supply the dyno data to reinforce this.

I would love to see that data, I love to learn new things.

I most certainly would recommend going down .002" at a time on the jet until the engine stops wet fouling the plug at peak rpm. It's not only wise, it's critical...Just as I wrote above.

You know better than me. "Critical?" Sure is contrary to everything I know.


Al, forgive me, but where is this low-speed jet?
lol they keep changing carburetors on me. You're forgiven, even for the gracious way you put it.
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Forget what you thought you new about air/fuel ratio with the small restrictor plate engines ! Run those little restrictor plate engines really rich the unburned fuel actually aids in compression ! Also EGT setups are illegal in these classes. Back in the day I welded bungs for the EGT probe in my most popular pipes for each class for dyno tuning purposes .and then once I found what jet, timing and pipe I would replace the EGT pipe with a new copy of said chosen pipe that the engine liked. The probe I believe restricted the pipe which had me falsely tuning the engine so I had to quit using the EGT probe during fine tuning for customers. Most pipes ID were under 1.000" most .930 to .960 range which I believe is to small to farther restrict / impede exhaust waves. I also notice with flathead engines and (my dyno) it will take at least a minimum of .001 and most the time a .002 jet change in either direction to show a measurable difference regardless of percentage of area "forget that" . You would probably need a million dollar dyno way more elaborate than what karting has to offer , to show way less margin of error within the error of dyno to close the gap on tuning with changes less than .001 . OMHO
 
There have been no changes on carburetors. Nobody changed carburetors on you, Al. :)
The flathead Pulsa-jet carb used in karting (even back to the old pull choke carbs of the 70's - before the Briggs got popular in karting) NEVER had a low-speed jet, nor did they get a design change dating back to the '50s when the Briggs series 13 flathead was first introduced.

Al, you have to be willing to learn too. If I needed help tuning a Mac or West Bend, I'd be sure to consider your advice. With God's grace, these little flatheads have put bread on my family's table for over 25 years now. I do know a thing or two about them, but still learn something new from time to time. :)
 
Can someone take Al to a race track? He needs an education in present day karting. I'd be willing to chip in some loot for petrol.
 
Ill take him, I know the current trend in karting well, i agree with most, But i allways look at and question is it right, Will it work, If so what can be done to make it better,
All jokeing aside the guy is here to help, Spread sheat for the petrol Al ! , us see my s10 gets 40 mpg ohio to tx is ? if i average 65mph & leave 5 today ill be there at ?
How mutch loot 3.75.9
He'l figure this in his head before i can think about how to calculate it.

Donn
 
False information needs addressed. There is so much good information on here that a lot of folks start to believe everything they read on here. That's a dangerous attitude, when there is a little bit of dis-information strewn in as well.
Al, if you feel I "dressed you down," I am sorry. I am sure you simply want to help, but it's not helpful to say something that's simply not true. Yes, I'm going to correct that. If I didn't, it would show that I don't care for all the people that are reading this very forum.
I make mistakes too and welcome rebuke and correction - It shows love just as a father corrects his son.

Glad you enjoyed carburetors 101 -- when you're ready for 102, just ask. :) <-- I am kidding, Al. Notice the smiley face.
 
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