SuzukiSavage.com - Print Page

SuzukiSavage.com
/cgi-bin/YaBB.pl
General Category >> Rubber Side Down! >> Tuning my VM36
/cgi-bin/YaBB.pl?num=1271444201

Message started by Moofed on 04/16/10 at 11:56:41

Title: Tuning my VM36
Post by Moofed on 04/16/10 at 11:56:41

Over the winter I picked up a new VM36 carb. I wanted to replace the CV for a few reasons: I've got a Raptor petcock so I don't need the vacuum port; the mix screw was mangled and jammed; and it was not starting in cold (<35F) temperatures.

I set it up according to Lancer's initial recommendations (http://suzukisavage.com/cgi-bin/YaBB.pl?num=1262724030): 20 pilot, 2nd needle position, and 185 main. I'm reasonably sure the other parts are correct. With those settings I could feel a lean spot at an off-idle throttle position, especially when not warmed up. I would expect this, except the choke was only usable for about 5 seconds after cold start up, even in chilly weather. So the pilot is obviously rich. Main jet seemed okay, but haven't tested too much. There was some nice steady crackle when engine braking, but no big pops. Expected since my Mac exhaust is pretty close to a drag pipe.

I am now trying out a 17.5 pilot (the smallest Lancer sent) and the needle on the 3rd notch. This seems to have made the pilot even richer than before since even with the mix screw fully turned in the idle speed did not peak. There is also some hesitation when throttling up from idle. The crackling has been replaced by loud pops and bangs. Unsurprisingly, the choke is generally unusable.

So I guess I'll put the needle back to the 2nd notch. I'm probably going to get a takeoff harley pipe sometime soon since the Mac's loudness has grown a bit old, plus I'm buying a house soon and would like to have the neighbors like us. :o

The other thing that concerns me is my mileage (http://www.fuelly.com/driver/moofed/savage-ls650) still sucks about the same as with the old carb. The 4/14 mpg numbers are mostly from the initial settings, so enriching the needle isn't going to help anything. Perhaps there is something else sapping my power. :(

One more thing: there are 3 tubes coming off the VM. Two are obviously vent tubes, and the third looks like it would be used for draining the bowl, except I cannot find any valve screw to open it. All three of them accumulate a little wetness over time, but I don't know why. Is this right? Hopefully it's not costing me too much gas.

Okay, I'm done rambling. Any thoughts?

Title: Re: Tuning my VM36
Post by Boule’tard on 04/16/10 at 19:36:34

Congratulations, that's a great little carb. As I recall the 185 was a bit rich on an uncorked bike (k&n filter, dyna muffler) so I backed off to 175.

Also, the air screw setting vs. backfiring was the opposite of what I expected.. opening the screw led to less backfiring for some reason.

Edit: If you are running that UFO thing you can do a couple of things to lean out the pilot circuit.. I think my pilot jet was 15 and it was still way too rich. I called Thunderproducts and they said to enlarge the hole in the UFO (that the needle goes through) with I think a 5/16" drill. After I did that, and also drilled the optional air bleed per the UFO instructions, the pilot mixture was in range.. I could then control it with the air screw.

Title: Re: Tuning my VM36
Post by JESPOKER4FUN on 04/16/10 at 20:10:57

sorry I was talking about stock carb.

Title: Re: Tuning my VM36
Post by LANCER on 04/17/10 at 02:58:08

Do you have the UFO installed on the slide ?
I cannot remember if you have one.
If you do have a UFO, then solder closed any size pilot jet (saving the new ones I sent you) and install the soldered jet. Then try adjusting the pilot screw. With the pilot soldered closed, the VM carb will work like an Edelbrock Quicksilver, and simply pull up the fuel needed, as needed, to meet the engine requirements. BUT you need to have the UFO in order to do that. Otherwise the vacuum will not be enough to pull the fuel properly.
If you do not have a UFO then get one and install it, it is the best $30 you will ever spend on a perfomance mod for your engine. It will produce 1 hp for each 100cc of engine volume...650cc = 6.5 hp increase for just $30 and a couple of hours time.
It makes the best power in the low-mid range, with max being at about 60% throttle where we ride most of the time, but will continue to wide open; maybe 3 extra hp at the top end.

Title: Re: Tuning my VM36
Post by Moofed on 04/17/10 at 09:17:00

The air filter is a drop in k&n, so I still have the air box. I guess I could take the door off and see how that changes things. I cleaned and reoiled it when I put the VM in, which was about 2 tanks ago.

I do not have a UFO, but I've considered it.

I was under the impression the needle position didn't affect the pilot circuit significantly. But... fig 13 in the vm manual on Mikuni's site shows each notch can still make 3-6% difference at 15% throttle.

Thanks Boule’tard for pointing that out about the screw. The fig 16 confirms it is backwards from the stock carb. Time for more experimenting!

Title: Re: Tuning my VM36
Post by dasch on 04/17/10 at 09:42:16

Mix screw fully turned in?? Didn't somebody here say CW turn RICHENS and CCW LEANS the mix on VM??? I might be wrong...

Title: Re: Tuning my VM36
Post by LANCER on 04/17/10 at 10:31:23

there is overlap in all fuel circuits.
the pilot system works from idle to wide open, its just that as you go beyond 1/4 throttle the % of its effect is decreasing

the pilot screw is OPPOSITE OF THE STOCK CARB...
CW = RICH............CCW=LEAN

Title: Re: Tuning my VM36
Post by dasch on 04/17/10 at 13:11:14

That's my point. Moofed clearly says: "even with the mix screw fully turned in the idle speed did not peak"

Moofed?? If you had the mix screw all the way in on VM- it's so rich you don't even need a pilot jet!

Title: Re: Tuning my VM36
Post by Moofed on 04/17/10 at 20:13:43

Yeah, I realize that now. :-[