Am I supposed to go up on pilot (richen) or down (lean) when going down on mains?

My baby was running at 140/142/142/140 at 5k altitude, and I dropped the mains down to 132/135/135/132 to try to bring her back to normal altitude jetting and she wouldn't idle anymore? 😔

I messed with the mixture screws but it made very little difference.

I've gotten different answers from every single person I've asked saying mains don't affect pilot circuit, mains enrichen it, and mains lean it out.

 

Pilot air screw inwards will richen. If it is more than 2 turns out for nice idle then a smaller size pilot jet is required. Carb' metering systems (pilot jet,throttle valve, needle jet-jet needle, main jet, choke circut) overlap each other so to get her to run right all circuits must all be able to work together seemlessly. If it doesn't, somewhere on your throttle you'll notice it.
Thankfully here in U.K, I never have this issue. Bet it's a pain in the rs ! Hope you get it sorted mate.

 

^^^^

 

Why did you lean it out to ride at a lower elevation? And why are you running smaller than stock oem jets?

I usually run a slightly smaller pilot jet when I up the main jet size. But again, it's because of the overall mixture. I can then run a few turns out on my mixture screws without hurting my idle and can keep some of the fuel mileage without having to run a bigger main jet.

But there's been times I've upped both as well, it depends on how much larger of a main I went with, if I changed needles, etc.

 

So, you've gone both up *and* down on pilots when going up on mains? That's where my confusion lies.

Also, I'm in Denver so I'm leaning it out slightly from stock. I forgot to specify.

 

Ah, okay, Denver is still pretty high up. But why were 142s and 140s in the carb? That's a pretty big jet for the f3 period, let alone that high up. Did you loosen the mixture screws? What slow jet is in there now?

 

In this LINK there is a calculator at the bottom. If you plug in all factory set-up at 5,000 feet it says stock jetting. It suggest 140,145,145,140 with 2 shims each.

Then use the 'D' shaped tool to turn the pilots out 2 1/2 turns.

If I plug in K&N air filter, it says same jetting but only one shim.

It would seam that 132/135/135/132 is to lean. Also any time you play with jetting you should re sync the carbs.

 

So for example, on my f3, I bought a jet kit. Things were great when I was hard on the throttle, but I felt this slight surge when cruising. It took a 3/4 turn on my mixture screws to get rid of it, and my mileage went down and I didn't think my wot was great anymore either. I went to jets R us and went up one size on my pilots. It worked great.


Then on the Bandit, I put pods on it and deleted the air box. It's a crazy jet change. 102.5 to 150!!! So because of that, I went down on the pilots, 35 to 32.5, IIRC. It was fueled okay, but my mileage was in the 20's per gallon. So I put in a more tapered air needle for the pods, went down from a 150 main to a 140 and went back to my 35 pilot. It really allowed the mixture screws to go back to about 2.5 turns out and my mileage went back into the mid upper 30's. Same power


It just depends. I've also just done jet kits with needles that have worked great without replacing pilot jets, and I've also done just jets with great success.

 

WOW, that's some kind of crazy jump.

A restrictive box acts like a choke so you can go smaller. I remember my older brother took the air box out of his '72 CB750 and it wouldn't run. Already to lean from factory.

A mod on my DRz400 was call the 3x3 mod. You cut a 3X3 inch opening at the top of the air box and go with a bigger jet and pilot. I did get a cruising surge but bigger power otherwise. Any bigger in the opening and it sounds like a wrecking ball hitting the bottom of the engine. Not mine but my son-in-law's. Some duct tape was a quick fix.

Jetting has a lot to do with box design and air flow. Best to keep things as stock as possible. The older I get the more I go that way.

On my 1kF I went up from the carbjetkit from the link above. I had a TB slip-on, K&N filter and wanted to make up for the ethanol as well. I went up 1 more from what they suggested for TB and K&N. I don't have the TB anymore but kept the jetting the same and it runs great. I'm up 3 from factory with just the K&N.

 

Yeah, the stock needles made it impossible to fuel right. There was no taper to it whatsoever. Once I changed the needles and went down on the jets, it really changed the bike. Luckily, I was able to piece everything together for about $80, which gave me 3 sets of needles to try, 5 sets of main jets, and 2 sets of slow jets.

I like tinkering, so it was a fun month or so of trying different setups.