Carb "Pilot Screws"

[Harmonicashawn]

I know this subject has been beaten to death, but I would like to add my thoughts (feel free to correct me). My bike idles great and runs great through the entire range, but just off idle--it goes lean and backfires slightly (this seems common). I decided to richen-up the "pilot screws". I agree with several of the other members who err on the rich side (milage will not be affected much). The "pilot screws" adjust the idle mixture. The Main jet size controls the main circuit mixture. What I usually do on a muscle car is adjust the screws until the highest vacuum reading is attained. What I found with my bike is that No amount of adjustment made any difference at all! That tells me that the entire "idle Circuit" is plugged or otherwise non-functional. The reason the bike idles fine is because the throttles are probably opened-up enough to draw from the main circuit. It's time for a chemical dip.

[Prairiehammer]

V-Boost! Is it functional?

Nothing to do with your pilot screw issues, just noticed that your Venture has V-Max V-Boost.

Did you put it on?

[Harmonicashawn]

No--Previous Owner did. I think it works (gets crappy milage--LOL)

[dingy]

Something you might want to keep an eye on with your VBoost can be seen in your 2nd picture. The throttle cable bracket has been tweaked on the pull cable to angle it outboard. This is in order to get it to clear the frame. What this does is puts the full pressure of the thin cable on the white nylon bushing just under where the cable enters the curved part of the bracket.

 

I was going to do this with mine, but I was concerned about the cable wearing through the nylon and becoming frayed. I elected to do some McGyvering to the bracket and inlet tube to keep the straight up pull.

 

This relocation of the cable is needed due to the VBoost intakes raising the carb rack right up to the frame.

 

What kind of mileage are you getting? I have a 1300 block with VMax jetted carbs, Vboost, VMax rear end & VMax rear wheel, to mention a few items. If I ride it very conservatively I have gotten 37mpg. If I am using it for what it was built for, I have seen 25 MPG, but that comes with a large grin factor also.

 

Also looks like you are doing a carb sync. The VBoost butterflies also have a separate sync procedure on them, if they are out of adjustment, syncing main butterflies will be about impossible.

 

I also see from your 1st picture that you have filter pods on. These are usually only used with a Stage 7 kit. With this, the VBoost is held wide open all the time. When you turn the key on do you hear the VBoost cycle through from closed to full open then back to closed. Do you have the power surge on a medium power take off at 6,000 RPM?

 

Gary

[bkuhr]

What I usually do on a muscle car is adjust the screws until the highest vacuum reading is attained. What I found with my bike is that No amount of adjustment made any difference at all! .

 

I have found that it seems to work better to adjust for the highest RPM, but only adjusting for changes of 50-100 rpm, so digital tach is manditory. I suspect the displacement/cylinder is so small, not sure if change in vacum would be noticable.

 

That being said, I have 2 carbs clogged as yours, and two that idle screws work on. Big difference when the adjustment does work.

[Harmonicashawn]

as far as the V-Boost is concerned---I am not familiar with this setup at all. I did not install it and am not sure if it works properly! This bike does have individual K&N filters. I have done some sparkplug reading and the mixture seems to be a little rich---so I'm not concerned about melting a piston or something. The bike runs very well overall, but does need some tweaking! Any tips on the V-Boost tuning would be appreciated! I was getting about 25Mpg until I removed the V-Max rear in favor of a stock one (now I'm getting 35Mpg).

[KIC]

Something you might want to keep an eye on with your VBoost can be seen in your 2nd picture. The throttle cable bracket has been tweaked on the pull cable to angle it outboard. This is in order to get it to clear the frame. What this does is puts the full pressure of the thin cable on the white nylon bushing just under where the cable enters the curved part of the bracket.

 

I was going to do this with mine, but I was concerned about the cable wearing through the nylon and becoming frayed. I elected to do some McGyvering to the bracket and inlet tube to keep the straight up pull.

 

This relocation of the cable is needed due to the VBoost intakes raising the carb rack right up to the frame.

 

What kind of mileage are you getting? I have a 1300 block with VMax jetted carbs, Vboost, VMax rear end & VMax rear wheel, to mention a few items. If I ride it very conservatively I have gotten 37mpg. If I am using it for what it was built for, I have seen 25 MPG, but that comes with a large grin factor also.

 

Also looks like you are doing a carb sync. The VBoost butterflies also have a separate sync procedure on them, if they are out of adjustment, syncing main butterflies will be about impossible.

 

I also see from your 1st picture that you have filter pods on. These are usually only used with a Stage 7 kit. With this, the VBoost is held wide open all the time. When you turn the key on do you hear the VBoost cycle through from closed to full open then back to closed. Do you have the power surge on a medium power take off at 6,000 RPM?

 

Gary

 

I don't have a clue to what all this means and what you are saying, but it sure sounds like GREAT information !!

 

I don't have a V-boost or anything like it.....

[Harmonicashawn]

I do hear "something" cycle when I turn on the ignition! I never bothered to find out how this works---should I just disable it? I didn't realize it was servo controlled (kinda thought it might be like a Carter AVS carb--counterweighted--pressure differential type deal). I should state that I am splitting hairs because this thing runs great with minimal issues (but I like my crap to be perfect).

[dingy]

I do hear "something" cycle when I turn on the ignition! I never bothered to find out how this works---should I just disable it? I didn't realize it was servo controlled (kinda thought it might be like a Carter AVS carb--counterweighted--pressure differential type deal). I should state that I am splitting hairs because this thing runs great with minimal issues (but I like my crap to be perfect).

If you hear a 'whirring' for about 3-5 secs when key is turned on, coming from over the top front cylinder bank, the VBoost is operating as it should. This is a self check, so the electronics knows what the position of the motor that operates the butterflies between the front & rear carbs.

 

There is a separate electroic controller that operates the vboost, it kicks in at about 5700 rpm & opens the 5 & 6 butterflies. Works off an input from #2 coil for its rpm signal.

 

This is what made the VMax's reputation what it was & is.

 

If you ever want to help it more, by a bunch, your next step would be a set of VMax heads. 85~07 will fit with minor changes, main thing is the 'freeze' plug covers on side of cylinders are shorter with the VMax heads.

 

Gary

[Harmonicashawn]

Update!

I discovered what the P.O. did when installing these carbs. They are linked ALL the time! They gutted the v-boost butterflies and linkage and pooped on some epoxy to seal the linking mainifolds. I'm kinda thinking that I'm losing about 10 horse in the low and midrange as a result. I need to either get a working butterfly setup or block off the manifolds. It must be jetted pretty well (a little rich) as evidence by the spark plugs. "Sydoc"---once again I defer to you for your expertise! BTW--what I heard when turning on the key is radio static or feedback or something.

Edited July 12, 2012 by Harmonicashawn