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carb gurus converge

2K views 33 replies 6 participants last post by  QuizzicalChimp 
#1 ·
Getting a little heat exhaustion thought I would take a break and think about my setup.

Big shots with quiet baffles.
Biddy box
Pair valve removed

Currently running.
215
2nd clip
58 2 turns out

She pulled great and besides a rich spot at 50 from 4th where it belches some smoke it felt good.

So I moved the clip to the first slot and backed my AF another half turn.

Now she's lean at idle and I can't get it off my street.

Questions.

1. If I'm on the first clip on my needle, should I be considering going down to a 210? I don't think the first clip will be enough to lean it out anyway.

2. How many turns out until I need to try going up in the pilot jet? She's super lean at 2.5, but if I move down to a 210 I can raise my needle some...
 
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#27 ·
#28 ·
It's my needle height I can't get right.

50 mph 4 the gear roll on and it stutters and plumes smoke and then the main takes over and it scoots. From 0 to half? Throttle it feels good.

I've got a D-tool on a screwdriver. Set it at 2ish turns and have not touched it.

I've been working on a hot motor and doing 15 mile hauls

your still a bit confused on what each part does. at 50 in fourth its still on the needle. in fourth gear your not using the main jet until about 80 mph
 
#29 ·
I can tell ya that some have had problems dialing it in with the Bitty box mod. I would lean out the a/f to 1-1 1/4 with that 58 and put the clip back on the fourth notch. Mine tuned out at only one turn with the 58, but still ran rich at idle with it. Mine works best with the 55 slow and the stock needle with one shim with a Factory pro main. You may have something else going on?
 
#31 ·
Greg-how much of that is pilot at 45-50 in 4th? My stutter ends and takes off.

Eazy, based on what Greg said I think you're right. Will give it a try tomorrow
depends on throttle position. if your cruising at 45 in fourth the the slow jet is providing most of the fuel. the more throttle you give it the more fuel is provided by the needle.
 
#33 ·
Reading thru this you are changing 2 or three things at a time. Settle out, it's a process. I'll admit I didn't read past the bottom of page one. . if you've figured it out, cool.

First off, read this (I'd even print a copy to keep in the garage while you are working) http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,lower_rpm_engines.html

Second, You can't rejet when the bike is cold. it has to be at operating temperature.

Third, the Biddy Box has been difficult for some folks to tune, much like the P4/Q5 intake. . it has to do with how the air flows and turbulates in the intake.


Jetting takes time, it takes work. But follow the instructions above and work each part IN ORDER. It sounds like you are trying to tune out a problem somewhere else with the needle height. That isn't how it works. Start from the start. Find the right main jet. Then find the right needle height. Low end will be from pilot jet, so if it's boggy on the bottom end. The photo below (click on it if it's real small) gives you a good handle on what each part of the carb does at various RPMS.


Blue Text Line Font Diagram
 
#34 ·
Got it.

Tried both a 205, 200, and the stock main. The 205 pulled the absolute hardest up top but some oddities led me to mess with the needle some with the 200 in and found I liked it.

I'm still a little rich when I first roll or blip the throttle. The behavior has me thinking the FP needle taper is too thin. Going to try the stock needle shimmed this weekend. Going to enjoy riding the rest of the week.

200 main
55 - 1.5 turns out
4th clip
 
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