Rejetting trouble spot

[tricky]

So last season I put on a Jardine full system, and K&N lunchbox. According to the wiki, I dropped in 20/65/145 jets. Didn't touch anything else in the carbs. It ran alright, but this year I was intent on dialing it in.

While my top end was alright, my low end had lean conditions.. popping once and a while when I blipped the throttle, numb feeling, low power, and a very slight surging around 6-7k RPM.

I cracked open the carbs last week, shimmed the needles 1.1 mm each (using the washer on the needle already, and a dynojet washer I had lying around), drilled out the brass plugs and set my mixture screws to 3 turns out.

Today I took it out, and while the low end is great, between 7-8k RPM the thing was acting like a pig, surging and hunting.. it felt like fuel starvation. Above 8k RPM, it felt alright... it was a windy day though, so I will have to wait to try it out again for a full report

WOT through that band shows no issues, I think.. add the fact that it wasn't misbehaving before and that means the main jets are innocent, right?

I'm confused, I thought surging was a lean condition. I enriched the mixture by shimming the needles, so why is this showing up now?

[Wagoneer]

Bogging isn't just because its too lean, could also be flooding the mixture by being too rich as well. Check the plugs, they'll tell the whole story. If they're wet it's rich, if they're white it's lean.

Have you tried swapping the plugs at all? Gapped properly?

[mitch79]

I'm running a similar set up to you, K&N lunchbox and Yoshi slip on. I've played around with the jetting a lot and had the same result as you with a 65 mid jet. Around 5.5-6K there was a lean dead spot. I'm now running 20-67.5-147.5, 2 3/4 turns out on the idle mix screws and floats dead on 13mm. The lean spot is gone. Doesn't matter how much I shimmed the needles, the 65 didn't flow enough fuel at the top end of the mid range before coming onto the main jet. Give a 67.5 mid jet a go

[tricky]

Bogging isn't just because its too lean, could also be flooding the mixture by being too rich as well. Check the plugs, they'll tell the whole story. If they're wet it's rich, if they're white it's lean.

Have you tried swapping the plugs at all? Gapped properly?

I'll check out the plugs tomorrow, and determine whether or not it's a lean or rich problem.

If it's rich, I will have to either unshim the needle a bit and increase pilot/mid jet sizing, or I will have to reduce main jet sizing I think.

If it's lean, I will take mitch's advice

Thanks!

[steezin_and_wheezin]

Subscribed!

Recently rejetted to 147.5/65/20 for my new jardine/lunchbox setup. Just need to get my brakes sorted and i'll be tuning her in. I'll be watching this for updates.

@ mitch - What is your elevation?

[tricky]

Subscribed!

Recently rejetted to 147.5/65/20 for my new jardine/lunchbox setup. Just need to get my brakes sorted and i'll be tuning her in. I'll be watching this for updates.

@ mitch - What is your elevation?

I'll do my best to forge a path for you! For reference, I'm in Toronto. 75m or 250ft elevation, the temperature is warming up here, so a typical day is mid 30's C or about 90 F. Summer can get up to mid 40 C, and fall will be in the teens, so I have a broad temp range to contend with.

Haven't checked my plugs yet, been busy with some school stuff. WOT through the range gives me no issues. I've ordered some new main and mid jet sizings, so they should be here within the next week or two.

I suspect it's a rich spot... before the needle shimming, there was no real issue. After shimming, that range went haywire. But, many people have suggested at least 147.5 mains for this setup, so I'm prepared for the possibility that it's lean up there.

I have 142.5, 147.5 and 150 mains, as well as 67.5 mids and 22.5 pilots on the way. I'm prepared to dial this in! 

[The Buddha]

Let me know too ... I have had to rely on feedback to get the jets right ... since I have not had a 04+ ...
Cool.
Buddha.

[The Buddha]

Bogging isn't just because its too lean, could also be flooding the mixture by being too rich as well. Check the plugs, they'll tell the whole story. If they're wet it's rich, if they're white it's lean.

Have you tried swapping the plugs at all? Gapped properly?

If you're bogging is @ 1/2 throttle, unless you do a under load 5 second run @ steady rpm with 1/2 throttle, hit the kill switch and pull the plugs, your plug pull is worthless. It only reads idle.

Cool.
Buddha.

[gsatterw]

just checking...

do you guys remove your carbs when changing jets, or is there a way to swap them without taking them off?

[Big Rich]

Should be possible once they have been off already. The first time cracking them open can give you some grief, so I like to have them on a work bench for that. Just swapping main jets? I leave them installed.