VM29 carb settings

[redscott33]

Hello and sorry to bother you all with what might appear to be silly questions.
I have been agonizing over the last couple of weeks due to a misfire and loss of power on my Katana. I found the problem (fuel tap not sending enough fuel) but while searching for the fault, I took the carb's off, gave the bottom end a bit of a clean and put them back on. The clean was really just getting any crud out of the jets and bowls. While the carbs were off I bought some pods and put them on while the airbox was out of the chasis. Now that I have remedied the fuel problem, I need to tune the carb's again. Here come the silly questions.

Dumb question number 1 -When adjusting the pilot air screw, everybody mentions 1½ turns out. I usually do this by ear on my single but with 4 carb's it a bit hard. The crux of the question is : is one turn flat to flat with a screwdriver (180°) or is it two turns flat to flat (360°). See, I told you it would sound dumb!

Dumb question number 2 - There is a visible screw underneith the carb near the inlet manifold boot. What is a good starting point for this screw. Is it a fuel screw? I have looked at the diagram on the Sudco site for the VM29 carb and I can't find the said screw. I see the main jet, then the pilot jet but I would expect to see another behind them and that one is exposed outside of the float bowl for adjustment.

Dumb question number 3 - The SUDCO site says the main jet size for the Suzuki 1000cc engines is #115. I noted the size of my mains while the carbs were apart and mine are 110.5. The bike has 4 into 1 exhaust and pod filters. Should I do any work with the mains? That being said, I did not have any problems with the 110.5's before cleaning the carb's but I did not know if I could unleash any potential power with a main jet swap.

Dumb question number 4 - I would like to get my float levels spot on. How do I measure the gap for the floats. I have seen measurments given on other threads but from where to where are the measurement taken?

For those of you who have not slashed your wrists while reading these questions, any input would be greatly appreciated.

All the best,
Scott.

[Nessism]

1. 360 degrees is one turn

2. Screw on bottom is the fuel screw (assuming the VM29's are similar to the other VM's). Typical starting point for this screw is 1 turn.

3. I'm not sure what main jet you need but I do know that when you installed the pods the jetting requirements change significantly.

4. Measurement for the float height is done without a gasket installed - measure from the bottom of the gasket surface to the top of the float. Measure height just at the point where the tang on the float contacts the spring loaded float needle. 24mm comes to mind for this measurement but please double check me on this.

Hope this helps.

[trippivot]

29's do not have separate fuel and air mixture screws.

but VM s' are similar 26 28 kawa style air only adjustment suzu style have the fuel AND air adjustments.

float height 26 mm inside the carb body lip gasket removed
20 pilot jets
120 mains

2 turns=720 degrees on under fuel screw
2 turns on upper fuel screw

needle clip 1 under the middle groove

start there.

[redscott33]

Wow! That was fast!!!!!
Thanks very much for clearing up some issues I was having. Those adjustments sound pretty straight forward so I've got a great starting point thanks to you guys. If I need to change the pilots or mains, who should I get them from? Are SUDCO the best all round or should I try other places first?
Scott.

[trippivot]

K&L
Parts Unlimited
suzuki dealer
E bay
sudco
fast by gast
APE


5.00 each- no tax- for genuine Mikuni (pilot or mains) I'll ship for free.(in america) if you throw in enough for a 6 pack of tall boy budweisers.

[redscott33]

I'd be jumping at the chance to buy from you trippivot as you helped me out with the settings, but I'm afraid I'm not in the US so I will have to look for someone a bit more local. In fact, I'm on the other side of the world in Western Australia but thanks very much for the offer. It would of made life too easy for me if you lived in the same country and offered to sell the parts. :-)
Thanks very much for the info and if I can't get hold of anywhere over here, would you be willing to send them (might cost a bit more than a six pack of tall boy budweisers!)

[redscott33]

I have managed to source some jets as suggested by trippivot. 120 mains and 20 pilots. I took the bike out and had to adjust the air screw in to stop it from hisitating and popping. The air jet is now probably 3/4 of a turn out and that seems to be the best position so far. I will still have to do some more tuning with it. I have the fuel screw out 2 turns which is probably too much. What effect does the fuel screw have? Does it only effect a certain range or is it all of the way through from idle to full open? The bike is still hesitating in the lower revs and if I open the throttle wide open it does not hessitate any more but it lacks power, as if the carb's are not syncronized. The exhaust note is also different than it used to be with a lower drone rather than a loud high pitched sound. Sorry if that sounds a bit confusing. I did not disassemble the carb's from each other and I kept the throttle linkage together. Could the carb's still be out of sync even though I kept all of the carbs together?
Thanks in advance,
Scott.

[trippivot]

since there is no accelerator pump the throttle needs to be a smooth opening motion.
just stabbing it to W.O.T. will have it falling on it's face until the intake velocity gets up to speed. you have get a feel and lead the vacuum with your wrist.

both the fuel and air combine to get it where you like it.. very adjustable (over kill)

my next suggestion might to go in 1 turn fuel and re adjust air screw again

go ride again.
a tuning trick I use when you cannot tell if it is rich or lean at a throttle position and or a specific rpm.. I open the enrichener/choke a bit.

if it picks up you need more gas - and if it is the same or no change lean it a bit.
check the plugs and follow what they say black less gas white more gas

chocolate with a gray tip stop

always start with getting a good steady idle and quick return to idle when a mild 4-5K rev is applied.

next go riding and there you are feeling Needle height position with 1/4 throttle to 1/2 throttle opening and running condition.
this is a kicker because it takes a lot of work to adjust the needles it takes a lot of determination and wrist grease. and a little danger riding pulling the choke.
stay with it you'll get there.

[redscott33]

Thanks again for the advice trippivot. You have opened my eyes to a load of tuning ideas I had not thought of before and it's all starting to make sense. At first I looked at carby tuning as a black art but I'm actually really enjoying the challenge. Every time I make some input, there will always be some coresponding output to base my next changes on.

These carbs really don't like to be snapped on at all do they. I get the best results winding the throttle on and listening to the exhaust note so I don’t over do it. I really want to make some more changes tonight, such as winding the fuel screw in but the kids are "Trick or Treating" tonight so I'll do some tuning tomorrow. That tip about easing the choke on a bit is a great idea! So simple and it will tell me straight away if I need more fuel or not. Excellent!

I've been pretty lucky with the idle and I've managed to get that nice and even. It returns back to idle after a few blips of the throttle and it does not go down below idle and even back up after a blip. It just revs up, drops down to idle and stays there. I went for a ride yesterday and did a plug chop. The plugs were reasonably sooty but they were starting to brown around the ring at the bottom of the plug. The tip of the electrode was also sooty but the very corners of the electrode were starting to grey up a bit. I did not do a thorough clean of the plugs before the test (I was not intending to do a plug chop before I left) and they were black before I left, so tomorrow I will clean the plugs and go for a ride. I know the settings are not spot on as I was getting some hesitation all of the way through the rev range on my last trip but it's getting closer.

Roll on tomorrow! :-)
Thanks again for all of your help,
Scott.