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Perhaps this has been covered previously, but allow me to ask if this sounds right for a Pinto powered FC. I realize other factors come in to play, but this is what I'm looking at as I rebuild this carb.
Main jets primary 160 secondary 145?
Air correction jets 160, secondary 165?
I haven't prepped a car with a carb(s) in over 40 years.
Thanks,
Jim Gustafson
Does Pegasus have the generic jets on their 2 liter Pinto data page?
I've got dyno sheets going back to 2001 Ivey & Elite with these values.
Main: Pri 155 / Sec 165 Air Corr: Pri 165 / Sec 160
Main: Pri 155 / Sec 170 Air Corr: Pri 165 / Sec 160
Main: Pri 140 / Sec 165 Air Corr: Pri 165 / Sec 160
Main: Pri 150 / Sec 190 Air Corr: Pri 165 / Sec 160
Main: Pri 155 / Sec 170 Air Corr: Pri 180 / Sec 160
I was surprised when I found the main primary jet 160 and the secondary only 145. I wondered if someone installed these incorrectly?
Jim Gustafson
Carb Jets:
The secondaries should be mechanically operated. This means that any time you are at full throttle (and this will be 95% of the time), both the primary and secondary will be open. If you are seeing a discontinuity in the EGT's, that may be due to the auxiliary enrichment tubes (put in by various engine builders to modify the fuel distribution) starting their flow with a slight delay - this is normal.
The main jets are located in the bottom of the float bowl. To change them you remove the top of the carb (6 screws) -- if you are careful not to tear the gasket, it can be reused. You will probably have different jets for the primary & secondary venturi -- so be careful to note what size is currently used for each one. A "one jet leaner" usually mean a differnence of 5 (i.e. change a 175 to a 170 - smaller numbers are leaner).
Your carb also has air corrector jets (aka A/C) -- you also remove the carb top to access these -- but they are located on the upward face of the carb body. Again, primary and secondary values may be different. The air correctors adjust the mixture just at the high flows (i.e. high RPMs) -- three steps of A/C jets is about the same as one step of main jets. A larger A/C jet will make the mixture leaner, and a smaller one will make it richer.
Finally, you will find idle jets on the side of the carbs in the main body, just below the top. You unscrew the holder, and the jet sits in that. Watch out not to lose the rubber o-ring under the jet holder. Idle jets are hardly ever changed, but you should pull them out to make sure a piece of debris hasn't clogged the very small orifice.
The mixture screw located near the base of the carb will adjust the mixture at idle. With the engine running at idle (usually 900 - 1000 RPMs), screw it in until the engine starts to run rough, then back it out again until the engine again begins to sound a bit rough -- at that point, screw it back in 1/4 to 1/2 turn and you're all set -- a smooth running engine.
DaveW’s jets at one time when he had a Pinto were:
JET PRI SEC
AIR 200 140
FUEL 135 165
(FOR AVGAS, ~55F)
Rollin Butler’s starting point.:
JET PRI SEC
Air 175 160
Fuel 145 155
Primary air is always bigger.
Secondary fuel is always bigger.
From: Dave Weitzenhof
1. The primary jets have more effect on cyl 2 & 3 than on cyl 1 & 4. The secondaries have more effect on 1 & 4 than on 2 & 3. Therefore, if 2 & 3 are rich compared to 1 & 4 (plug check after clean-cut, etc.), lean primaries or richen secondaries, and vice-versa.
2. A long time ago, before the widespread use of EGT sensors, I very successfully used a seat-of-the-pants trackside method of setting the over-all degree of richness. I would warm up the engine to operating temp, and then immediately run it to ~3000 rpm, let the rpm stabilize, and then open the throttle wide open for ~1 second. If the engine died or hesitated for more than ~1/2 second, the jets were too lean and needed to be richened. If the engine just barely hesitated and then revved cleanly, the jets were just right. If it picked up smoothly with no hesitation, the jets were too rich. All of this assumes no major carb or other engine problems. This really did work quite well.
Just something else to keep in mind. Jets can have a significant size tolerance. I measured all my jets one day, and found that they varied .06mm across the nominal size. That is, a 140 jet can be from 1.37mm to 1.43mm.
It's little tid bits of information like this the make me dream of the good 'ole days plugging in a laptop and set my fuel and timing tables...:ha:Quote:
Originally Posted by Hawke
0,06mm is about two and a half thousandths. That is pretty darn close but it all depends on how precise you want to be.
Thank you all, for the information. It's pretty clear this carb was jetted incorrectly, and the jets were reversed.
Primary fuel was 160, secondary was 145.
Jim Gustafson