Carb Tuning at altitude

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Can I do the same test in 4th gear? My 5th is the OD that Morely sells, I'd be doing ~75 mph at 4k and it doesn't accelerate well in that gear to begin with.


Here is something that is a bit more Vmax orientated. It was originally posted by Maleko89 (Mark) one helluva tuner. Its also a sticky in the carb section

Originally Posted by maleko89
You should probably be able to accept WOT in any gear above 2K w/o any bucking or complaint.

Do the following tests.

1) Cruise at 4K in 5th gear .. hold RPM steady (count to 5) and then whack it WOT as quickly as you can. You shouldn't feel the slightest delay or hesitation. If you do, too rich. This does not work at 3.5K or 4.5K, only at 4K because the slides will start to retract at 4.5K even at the lightest throttle angle. 4K sets us up on the threshold and gives us a big jump when we whack it. there is no other RPM to do this where you will get as big a slide jump when rapidly moving to WOT.
This tests for too rich of needle.

2) Verify that starting cold .. that the engine is weak .. and will complain if you try to hold the RPM at 1800 rpms. Within 1-2 min or no later than when the temp needle touches the first mark you should be able to hold the engine between 1500 and 2K w/o complaint or popping back through the carbs. At the least you should be able to do this by the time the engine is fully warmed up but if you are more than 1/2 way between the dot and cold on the temp gauge your pilots are plugged or too lean... (clean or reduce the PAJ2). If you can hold 1.5-2K as soon as you start cold then your pilots are set too rich and you will suffer rich symptoms when it comes to operating temp (clean or enlarge the PAJ2). Only change PAJ2 bigger/smaller if you mixture screws are out or in too far already.
This is how you set your pilot mixture.

3) Do a hard WOT pull in 2nd or 3rd gear from below 3K. Look for a smooth pull all the way up. If it seems to lag in the 4-5K range then too much needle. If we sputter going past 4.5K you don't have enough needle.
This tests for needle richness and leanness.

4) Verify you can cruise "nice and deliberate" at 5K .. if you stumble around and are OK everywhere else you don't have enough pilot.
Another pilot mixture test.

As for your mains, I'd at least go to 147.5's. General rule is to subtract main jet size by 1% for every 1000 feet above sea level. So, need to decrease main jet size of 152.5 by 4.5%. 95.5% times 152.5 = 145.6. I'm thinking 145's would work best at 4500 feet above sea level.
 
Can I do the same test in 4th gear? My 5th is the OD that Morely sells, I'd be doing ~75 mph at 4k and it doesn't accelerate well in that gear to begin with.
You should be able to. Now the fuel requirements are a little different in the higher gears....but it should be close. Was it a vmax that your friend toasted? It's tough to make them run too lean.

Sent from my SCH-R890 using Tapatalk
 
No idea about bandameir I have an OD 5th so I kind of killed the notion of racing her...

My friend with a similar setup jetted his according to the information I posted. It was too lean and cooked his engine.

Bandimere has test and tune days on the weekdays- you would never even get out of 3rd gear in 1000ft.
Cooked engine meaning what? If he ran it lean it would burn holes in the pistons or prematurely wear out.
Bandimere test and tune nights are on wednesday. Lots of good people and good info there too.
http://www.bandimere.com/tickets-sc...ult-calendar/csp-responsible-speed-test-night
 
Yes, he jetted it the same as my initial post, ran way too lean, cooked the engine. He ended up getting a new one from PCW

You should be able to. Now the fuel requirements are a little different in the higher gears....but it should be close. Was it a vmax that your friend toasted? It's tough to make them run too lean.

Sent from my SCH-R890 using Tapatalk
 

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