Topic: jetting vm30's for cb350 twin?

[Saml01]

saml01 states his jetting is 'right', but he hasn't taken the bike on any long runs (or high speeds), so...grain of salt.

 And if you trawl through the dross at DTT you'll find its 'broken' (running on one cyl) may be mechanical or electrical or something caused by carbs.
 Not sure where I posted it but I have been running bike on dyno with stock carbs as many people either can't afford or don't want to mess with Mikuni. I've been posting print out of F/A mixtures (although nothing new since last November/December) When I get Kei-Hin right I'll start again with Mikuni's

PJ

I figured out what the cause was before I got the right jets into the bike, and before I made the video showing the bike running on the street. I also posted about it at caferacer, not at DTT. If you care, go look up what the solution was because im not gonna bother posting it here.

The reason my bike is running right is because I can afford and have the persistence to mess with these carbs and my discipline paid off.

Btw. You have a insolent and contemptuous attitude and I have no idea how or why people listen to you. You have been on my ass throughout this whole process of sorting my bike out and not once did you stop to think that maybe you are wrong, and I am right.
 

saml01 states his jetting is 'right', but he hasn't taken the bike on any long runs (or high speeds), so...grain of salt.

Plugs will tell you if a bike is running right in 20 minutes.  Long distance or high speed has nothing to do with it, how many more times am I going to repeat this? Every site you read says you can run a bike in a quarter mile strip and determine exactly whats wrong with it. They dont say that for #$%*s and giggles, its fact.
You dont want to believe me, thats fine. Keep messing with your carbs while I go and enjoy whats left of this season.

[Saml01]

Now are your main jets the Long/large hex variety (4/042) or the large round (N100.604) I figure you are using the large round because the orifice size on the hex jets are tiny in comparison. This link elaborates:

http://www.ozebook.com/compendium/t500_files/mikuni.pdf

I'm actually running:
230 hex mains
37.5 pilots 1.5 out (which are wrong i know haha)
3.0 slide
2.0 air jet
159 Q6 needle jet
6DP17 needles.

I think I'm lean still (although the choke levers instantly kill the bike probably due to huge pilots). According to my link those 230 hexs are equivalent to 140 rounds. I need to mess with it a bit now that I have my wiring all but figured out... been chasing ghosts there so I haven't had time to focus on the fuel since the bike runs... just a little weak (probably from its lean nature). I'll be back to report my findings... I would love to come up with a definitive answer. This thread has seen enough hits that google points randoms like me here, it would be great to link a complete writeup to this thread for future info seekers. 

There shouldnt be an "I think i'm lean". You look at your plugs and theres your answer.

I read the link you posted about a month ago while gathering my information. I spoke to mikuni and sudco about this, and they both confirmed that the information is false. The jets flow what is stamped. They didnt elaborate on which way they performed the actual calibration.

Also the difference in jets is simple. The round jets are designated in orifice size, the hex jets are designated in CC/min.
The conversion chart is handy, but one does not flow more then the other or any better or any different. Just a different design for a different carb. Also confirmed by mikuni and sudco.

[johnspeck]

saml01, you're quoting three different posters, and insulting at least two....

my first impression of your video was "learn to ride".  nice job with that left turn at the very end.  creative editing!

riding season?  mine goes for another couple months at least, probably same as pj.

i've tried to be cool with you, but you come off like a tool.  your opinion should be fact?  go back to tuning cars or whatever you think you're good at, and everybody's happy!

i don't care what you do with your bike and your time.  just don't waste mine posting in this thread anymore.

[crazypj]

Btw. You have a insolent and contemptuous attitude and I have no idea how or why people listen to you.

 referring to me.  
 because I have 41yrs working on bikes and a few mistakes when I started taught me a lot about carburation, among other things
 Plus of course, re-building a lot of motors for people with patience and persistence. (and a lot of modified motors in various configurations in last 30+yrs)
 There is a major difference between a 1/4 mile drag and a long distance high rpm haul
 What produces max power for 10 seconds or less will probably burn valves or seize or hole pistons in a 3~4 hr run near max rpm (or even 20~30 mins on a racetrack).
 If you really think its right, put it on a dyno with a gas analyser
 If you come out at 12~16:1 F/A ratio I'll be first to admit I was wrong. (or at least admit there is an alternative  )  You need 12:1 for max power, 15~16:1 for 'cruise' 1/2~3/4 throttle.
 CB350 will make about 33~34bhp if everything is running right with stock cam and quiet exhaust, little bit more with cleaned up ports, bit extra with 'loud' exhaust and porting. (36~38bhp)
 'My' jetting frequently goes against conventional 'wisdom' but it has been shown to produce more power than anyone else (even if only 1~3bhp)  I have dyno charts to prove it - If I can remember where I put them  

PJ

John, my riding season is just about to start, I cant ride when its 90+ with 85~90%+ humidity, need truck with A.C.  

[w1sa]

Don't know if this has been mentioned or whether it is meaningful at this stage of your testing, but the specific gravity of fuel/gasoline is in the order of .72 (approx).
So, a litre weighs approx.   720g ......not 1kg

As an example, a jet with a fuel/gasoline flow rate of 150cc/min = 108g

[crazypj]

Yes, that makes a difference.
 It will only affect main jet size though, the 'wrong' needle jet will still be wrong.
 Thanks.
 PJ

[johnspeck]

update jan 15:

swapped #159 P5 needle jets for P4's.  raised the needles one clip setting (one slot above center, from top slot before).
re-installed 2.0 air correction jets.
swapped 25 pilots for 30's.  the 30's were too rich at optimum air/fuel mix screw settings.  25's back in, air/fuel screws at 1.25 turns out.
still using 150 mains.

have to do plug chops, but seat of the pants says i got my power back without feeling sluggish and over-rich.

then i get to do it all over again, as i'm fitting an old hooker 2-1 in the next couple weeks.

[Blucav85]

back from the dead what was your final jet setup for the k&n's and aftermarket mufflers? read your whole post but alot of numbers were tossed out through that process

[BigPadg]

  No one is saying much about the throttle slide which has a great effect on performance. Guess that's because replacements are expensive or modifying them takes more than turning a screwdriver. Speedmotoco sent me 3.0mm cutaway slides in my VM32's and I went crazy trying to jet "around" this problem. I hand filed mine down to 2.0mm and may go as low as 1.5 on the cutaway since this has gotten rid of the flat, lean spot coming off idle under load and the cruising "burbling, out-of-synch" sound with throttle held steady. Since VM32's are on the large side for a CB350, the 3.0 slides afford way too much air when slides are lifted and up into 1/4 throttle opening. I downed my PJ two sizes from the 30 I was using jetting "around" the 3.0 slides to 25. Better performance and gas mileage, yeah!

[coltar3000]

crazypj,

i've been chasing some interesting tuning problems with my carbs. You've consistently helped too many people get their bikes on the road to give them the smiles that Honda intended. im personally asking you to help me with mine. I have no idea how to work these damn forums/computers and this was the only way i could find a way to ask your opinion. through all of these searches, im getting completely mixed signals from where my bike currently stands.
bike: 73 cl350
Vm30 carbs
uni pod filters
high flow pipes with handbuilt baffles to quite it down
stock motor with fresh pistons and rings (not bored over)
carb specs:
slide 2.5
needle jet 176 p-4
needle 6f4
pilot 25
main all over the board
neddle clip on richest setting (bottom)

everyone with the same bike specs has been able to get there bikes running with these carbs and some trial and error. my bike on the other hand is running way too lean. but according to all the "brass" it should be way too rich. the bike fires first kick and idles perfectly. i specifically followed your directions to get everything to this point. motor is timed perfectly. carbs are synched. throttle cables are new and done perfectly. no air leaks on the intake.
for tuning the main jets i started with 145's   outcome (too lean) the bike dies when giving any throttle
put in 165 mains: bike allows around the same throttle but still way too lean. i could now at least ride the bike down the rode, but still couldnt give any throttle over 1/8 - 1/4 turn. the only time i can get more throttle on is if i turn the choke on.
i put in 210's assumming id finally get too rich. the bike runs the same-ish.
i then jumped to 420 main jets as an experiment. the bike now lets me give a bit more throttle, but still acts too lean. again, i can give way more throttle if i put the choke on. i cant do any "ride testing" because i cant open the throttle much at all. at this point, i must be doing something wrong. and by the way, this is only the info i could remember to tell you. i seriously dont want to bother you but i thought it wouldnt hurt to ask. i would really like to talk to you on the phone if possible. if this sounds like a challenge you want to take on, please call me. im in california if that matters. thanks! colton (916) 223-onethreesixone

[.RJ]

Back from the dead.....  I'm looking for some guidance on my 350 motor for a starting point for jetting.  I've got the motor just about ready to go back in the frame, and here are the changes:

- 66mm bore (Wiseco)
- Megacycle 123-30 cam
- New stock-sized valves, ti springs, ti retainers
- Ported head - Buff / THR did the work for me
- Hindle 2-1 exhaust
- Mikuni VM30 carbs w/ Uni filters

When the bike was stock, I had the VM30's setup with

- 150 main
- 25 pilot
- 2.5 slide
- P4 needle jet
- 6F04 needle. 

I dont have any notes on where I was with the clip position or idle/air screw settings, but, it all worked pretty well and plugs looked good.

It worked pretty well then, but I assume with my new setup I'm gonna need more fuel.... any recommendations on where to start here with the new parts? 

[scottly]

It worked pretty well then, but I assume with my new setup I'm gonna need more fuel.... any recommendations on where to start here with the new parts?

Since a carburetor adds fuel according to the amount of air flowing through it, you may not need to change anything.

[.RJ]

Back from the dead.....  I'm looking for some guidance on my 350 motor for a starting point for jetting.  I've got the motor just about ready to go back in the frame, and here are the changes:

- 66mm bore (Wiseco)
- Megacycle 123-30 cam
- New stock-sized valves, ti springs, ti retainers
- Ported head - Buff / THR did the work for me
- Hindle 2-1 exhaust
- Mikuni VM30 carbs w/ Uni filters

When the bike was stock, I had the VM30's setup with

- 150 main
- 25 pilot
- 2.5 slide
- P4 needle jet
- 6F04 needle. 

I dont have any notes on where I was with the clip position or idle/air screw settings, but, it all worked pretty well and plugs looked good.

It worked pretty well then, but I assume with my new setup I'm gonna need more fuel.... any recommendations on where to start here with the new parts? 

Well, here we are nearly a year later and I finally fired the motor up. 

I'm running through some of the same issues as the OP with this jetting, this is my starting point:

155 Main Jets
40 Pilot Jet
2.5 Slide cutaway
Jet Needle = 6F4
P-5 Needle Jet = 159 P-5 (primary type)
Fuel mix screw 1.5 turns out
2.0 Air Jet
3.3 Fuel inlet valve
25mm Float Height
Stock coils, charlie's place ignition

It starts well (kick only) with the choke, and quickly wants to come off the choke, was ~65 degrees yesterday and its got a nice steady idle.  Riding it up the road its got good response, and 1/4-1/2 throttle feels good but 3/4-full throttle its breaking up really bad, I didnt try flipping the choke on to see if it helps though.  There's a local shop with a dyno that has experience with these, I may punt and take it over there.  With all the different options of things to change, seems like its easy to spend a few hundred bucks on brass going in circles.

[.RJ]

Bringing this back to the top with some new frustrations - a few changes to the last setup -

- 66mm bore (Wiseco)
- Megacycle 123-30 cam
- New stock-sized valves, ti springs, ti retainers
- Ported head - Buff / THR did the work for me
- Hindle 2-1 exhaust
- Mikuni VM30 carbs w/ Uni filters

Carb setup -

140 Main Jets
30 Pilot Jet
2.5 Slide cutaway
Jet Needle = 6F4
P-5 Needle Jet = 159 P-4 (primary type)
Fuel mix screw 1.5 turns out
2.0 Air Jet
3.3 Fuel inlet valve
24mm Float Height
Stock coils, charlie's place ignition NGK non-resistor plugs w/ 5k ohm resistor caps

I had a few teething issues that I think I've sorted out, but its breaking up past 3/4 throttle and or over 8k rpm.  It feels like the ignition is breaking up and the plugs are showing a bit lean, although I dont have enough room to do a proper plug chop.  Lithium battery shows 13v off, and 14+ running.  I've run the bike with mains from 130 to 170 and no real change in the issue. 

Any thoughts here?  I'm really running out of ideas and my only thought is my coils arent getting it done, but they both measure ~4.5 ohm and it seems unlikely they'd crap out as they worked fine before I split the bike apart.

Pic for attention

[CBGBs]

Are you guys getting anywhere with the setup? I'm looking to put VM30's on my 350 and trying to get a feel for the pain in the ass I'm in for. Bike has a pro porting job with 1mm bigger intake valve and custom exhaust. I'm out for top speed and rideability.

[grcamna2]

Bringing this back to the top with some new frustrations - a few changes to the last setup -

- 66mm bore (Wiseco)
- Megacycle 123-30 cam
- New stock-sized valves, ti springs, ti retainers
- Ported head - Buff / THR did the work for me
- Hindle 2-1 exhaust
- Mikuni VM30 carbs w/ Uni filters

Carb setup -

140 Main Jets
30 Pilot Jet
2.5 Slide cutaway
Jet Needle = 6F4
P-5 Needle Jet = 159 P-4 (primary type)
Fuel mix screw 1.5 turns out
2.0 Air Jet
3.3 Fuel inlet valve
24mm Float Height
Stock coils, charlie's place ignition NGK non-resistor plugs w/ 5k ohm resistor caps

I had a few teething issues that I think I've sorted out, but its breaking up past 3/4 throttle and or over 8k rpm.  It feels like the ignition is breaking up and the plugs are showing a bit lean, although I dont have enough room to do a proper plug chop.  Lithium battery shows 13v off, and 14+ running.  I've run the bike with mains from 130 to 170 and no real change in the issue. 

Any thoughts here?  I'm really running out of ideas and my only thought is my coils arent getting it done, but they both measure ~4.5 ohm and it seems unlikely they'd crap out as they worked fine before I split the bike apart.

Pic for attention

Very nice looking frame finish ! 
Did you get it anodized or painted ?

[.RJ]

Are you guys getting anywhere with the setup? I'm looking to put VM30's on my 350 and trying to get a feel for the pain in the ass I'm in for. Bike has a pro porting job with 1mm bigger intake valve and custom exhaust. I'm out for top speed and rideability.

Not really.  I switched the coils to Dyna coils, which helped, but still not great on top end despite really good throttle response and power everywhere below 8k.  I've tried a bunch of different mains, needles and emulsion tubes and it seems like I'm chasing my tail, and its not quite responding the way I would expect.  I might pull out the air jet next and see if that helps. 

[crazypj]

As this thread started mid 2009 and was still going in 2022 I thought I would revive it again.
I don't have anything to add or anything new to say but was given a link on Reddit and realised I haven't even logged in for a long time