Carb tuning question (main jet sizing)

[86FJNJ]

Looking for some help to fine tune my carbs.

1986 FJ1200 1TX
Unipod filters
Stock headers and collector
Cobra F1r mufflers (straight through)

40.0 pilots
155 Air Bleed
Needles shimmed

I was running 115 main jets for a couple hundred miles and have just switched to 117.5 mains. Feels like it has more power now 5k-6500rpm when doing a quick twist of throttle, bike jump a bit more. But when going WOT from 5k rpm in 4th and 5th there is a slight lag of about a second and then all of a sudden the power kicks in and bikes gets power.


Is this lag indicative of main jets being too small or too large?

[Pat Conlon]

Go to 160 air bleeds...see if that makes the bog go away.

[86FJNJ]

I'll try it. Is there a chance that leans out the pilot circuit? I'm already 3 turns out on fuel mixture with the 40.0 pilots

[86FJNJ]

Ok chat gpt says air bleed mainly effects mid range and top end, I'll try it out but I feel like the mid range is perfect with the needles shimmed so my guess is it would lean mid range out too much

[86FJNJ]

Is it possible I'm not getting enough fuel at peak throttle/rpm?

[Pat Conlon]

Is it possible I'm not getting enough fuel at peak throttle/rpm?

Could be.... Then again, with the big mains and shimmed needles you could be getting a rich slug of fuel causing the bog.

Air bleeds are easy to get to for changing....

A bit of history: Dynojet kits for our FJ's popular in the '80's and '90's used proprietary sized jets and needles (non Mikuni) in addition the kits included a softer spring for the slides. These soft springs enhanced throttle response by allowing the slides to raise up quicker in the carbs and counteracting a mid range bog our bikes often had when rejetted with fatter jets.

Cheers

[86FJNJ]

Pat, so interesting.... many months back when I started my FJ journey I didn't know exactly what I would need and came across this jetkit on ebay so I purchased it but haven't used it. Are these the softer springs you mention?

I could easily swap out the springs with the carbs on the bike if these springs are worth considering.

[Pat Conlon]

Yes, those are the soft springs....remember, they were designed to be used with the proprietary sized Dynojet needles and jets....

Caution:  IIRC the Dynojet instructions calls out for you to drill out the holes in your slides, DO NOT do this...

You already have the springs, so go ahead and try them, why not?
 You can easily change them back...(like the air bleeds)

However, Stay with the tried and true oem Mikuni needles and jets.

You are in the fine tuning stage on your carbs, try different things, it's part of the rite of passage to the kookaloo zone.

IIRC you have a stock engine (bore, cams, timing) with RPM UniPods and a stock exhaust with slip ons, correct?
If so, remember that your engine is flowing only slightly more air than stock, and not by much.
The real improvement in volumetric air flow efficiency happens when you install an aftermarket 4-1 or 4-2-1 header.
Look at the Stage 1 Dyno jet instructions....Stage 3 is not what you should use.

Have fun

[86FJNJ]

yeah def not drilling anything! haha thanks for the advise as always. I may put a few more miles on it as is and then play around with 160 air bleeds and springs etc..Overall bike is running great and I may need to expect to only get it 95%, I suppose the last 5% would only be possible with a dyno tune which I won't be doing....just happy to cruise the back country roads by me and just want to make sure it's not running to lean and blows up or overheats or too rich