Mikuni needle jet

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Something found,needle jet Q-5,needle 6DH3 third position and fourth gear 4000rpm:plugs was totally black.I even got 70mph on second gear.
 
Yeah,this summer is almost over and Mikuni does not working very well-but something found:someone wrote before that Mikuni VM is designed for two stroke engines,now i have working with needle jet and seems that it help.
I was last week on dyno and we got with one VM36 58 hp from rear wheel.
And settings in carburetor was not good but i hope that i am on right way.
 
rick in seattle said:
remove the bowl plug, place a measurement cup beneath the bowl, and turn on both petcocks for 30 seconds. Measure the fuel collected, multiply by 2, and obtain the flow rate in fluid oz per minute. You'll need upwards of 9-10 fluid oz per minute to allow for 50 HP or so, which is obtainable with dual carbs.
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You really need to do better than that;almost double.
At 50 bhp,the engine will consume about 10 US fluid oz./minute,or 300ml/minute.That part is true.

Look at how it's been measured at the drain plug/plugs.The float is fully down to open the needle fully.For that to happen with the engine running,the fuel level in the bowl would be very low.
What will happen is the fuel level in the bowl will be normal at low power output,but it will begin to drop drastically under power.If you keep the power on,the fuel level will soon be about 4mm lower and the mixture is getting leaner.If the mixture was right when you first opened the throttle,it will soon become lean.You could adjust the mixture rich for when you first open the throttle,to allow for it leaning off a few seconds later.The more power you make,the leaner it will get.

If you can get double what you need in the drain plug test,the fuel level will only drop 1/2 as much.The change in mixture won't be so noticable.For 50-60 bhp,I'd expect a total flow at the drain plugs of about 600ml/minute.

I'd always try running the engine with no main jet first.If the needle-jet is big enough,the engine will start 8-stroking between 1/2 throttle and 3/4 throttle and won't run well with more throttle.
 
There are 828 billion combinations of carb size/jetting/flow characteristics. Try a 34 flat slide if stymied.
 
MrNorton said:
I tryed R4 needle jet and it´s too big,even idle speed coming black smoke and it was very poor power when i was driving .Next step,i have ordered Q5 needle jet and time will tell what happens.
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Check the seal on the enrichener ("choke") plunger. If it's hardened, damaged or not seating for any reason, it will run rich, showing most at low/mid throttle (HIGH vacuum/LOW flow) settings.
The going flat on the top end can be too little fuel.... by virtue of too much carb, that is, you roll it open, not snap it open at low revs, correct? A VM (like ALL non-CV carbs) will give a lean bog if opened too quickly (vacuum goes away, fuel flow ceases or goes to nill).
 
I've had several single carb Triumphs in my lifetime. Fitting twin carbs never seemed to make them go much faster, regardless of how much tuning I did . The biggest performance increase always came from changing the standard cams for race cams.
 
+1 - but most claims of the "my stock bike is now way faster w/ two carbs" aren't backed up by any thing more than the owners "seat of my pants perception" - usually I suspect after pouring $$ into the set up and all the time involved its more of a mental thing to justify the switch :shock:

acotrel said:
I've had several single carb Triumphs in my lifetime. Fitting twin carbs never seemed to make them go much faster, regardless of how much tuning I did . The biggest performance increase always came from changing the standard cams for race cams.
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MrNorton said:
Hi again,has anyone single Mikuni VM36 on MK3?,what size should be needle jet.I have my own MK3 PW3 camshaft and ported cylinder head and seems that engine get not enough fuel over 5000rpm.
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Let me add something here.

I went through a time where after some ignition changes where my 40mm mik pumper would start to studder under WOT at 4500 to 5000rpm. It seemed to make so much sense to go up in the main jet. I had a 180 and went to 190 then 200 with no improvement. I had a 170 laying around so I put it in and had a slight improvement.

I got online and ordered a 165, 160 and a 155 from Jets R Us. The 165 showed more improvement and then the 160 was on the money.
Hope this helps.

After this, I felt compelled to reshelve the premiers and revert, once again, to the awesome TM40 (HS40).
 
Hi again,problems with Mikuni VM36 continue,has anyone bouht/installed JS Motorsport Keihin CRS carburetors on Norton?.
I am really tired to fighting with my carburetor,so i think i ask Jim if he has some idea for my Norton(ported cylinder head/standard valves PW3 cam).
If you have any experience that carburetor type,i like to hear your experience.
 
WHY do you say it's not getting enough fuel? A flat spot in power could be caused by a few things....
Tell us more.,,
Does it pick up for a breif moment if you apply the enrichener?
 
Because spark plugs are snow white,my speed record is 80 mp/h and this higest speed what i have never ever got with this bike.
Ignition timing seems correct,because it´s very easy to start,no kicking back and down pipes are still very nice crhome,not blue yellow colour.
With idling speed plugs are nice brown colour.
 
Maybe biggest reason founded with my Mikuni problems:2:1 manifold 4 screw was about 1mm too long,cutted now and working very well.
It was air leakage between manifold and cylinder head.
Next,if not raining here in Finland,i try go to dyno and try find optimal settings.
Thank you all everyone who are gave good tips seaching my Mikuni troubles.
 
MrNorton said:
Maybe biggest reason founded with my Mikuni problems:2:1 manifold 4 screw was about 1mm too long,cutted now and working very well.
It was air leakage between manifold and cylinder head.
Next,if not raining here in Finland,i try go to dyno and try find optimal settings.
Thank you all everyone who are gave good tips seaching my Mikuni troubles.
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Cool, I hope that sorts it for you.

But you may wish to keep further options open for the future.

The PW3 is a hot cam. As others have said, I very much doubt the Mik can deliver sufficient flow as required by that cam. So it will be the bottleneck.

But worse, that cam looses a lot of 'effective compression ratio' when running due the the longer duration. If your 850 is at 8:1 as most seem to be, its effective CR will be a lot lower.

I would imagine that a change to a standard cam would work best in single Mik form.

Or skim the head to boost the CR and then experiment with twin carbs.

I was once going to buy a restored Commando, single Mik, stock CR, PW3 cam. I didn't buy it cos I couldn't quite believe how gutless it was (of course, there could have been something else wrong with it).
 
I have faced the same challenges,I was running one of jim comstocks "breathed on heads " the motor is running a web cycle 13 cam and had Matts keihien twin flats life carb set up on it,long story short I went back to a stock head and. Single mikuni.... Yes the top end is somewhat limited but the machine
Is PERFECT for me as a 59 YO I'm not riding past 80
Mph for any length of time and to tell you the truth,I can live with the trade off.... Bottom line these machines are made to be played with and I always have fun farting around with it,that's the beauty of having soooo many great resources and vendors supplying so much great and varied gear for these bikes.... And soooo many brilliant and bright minds on this forum and elsewhere...more than willing to help.... Have fun.... Play with your toys.... Get dirty.... So on and so forth... At the end of the day I love the simplicity,consistency and reliability of the single
Mikuni !
 
zefer said:
I have faced the same challenges,I was running one of jim comstocks "breathed on heads " the motor is running a web cycle 13 cam and had Matts keihien twin flats life carb set up on it,long story short I went back to a stock head and. Single mikuni.... Yes the top end is somewhat limited but the machine
Is PERFECT for me as a 59 YO I'm not riding past 80
Mph for any length of time and to tell you the truth,I can live with the trade off.... Bottom line these machines are made to be played with and I always have fun farting around with it,that's the beauty of having soooo many great resources and vendors supplying so much great and varied gear for these bikes.... And soooo many brilliant and bright minds on this forum and elsewhere...more than willing to help.... Have fun.... Play with your toys.... Get dirty.... So on and so forth... At the end of the day I love the simplicity,consistency and reliability of the single
Mikuni ![/quote
Jeff, can I have your surpluss Jim Comstock 'breathed on' head??
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rick in seattle said:
MrNorton,

If you're looking for life above 5000 rpm, I'm afraid a single Mikuni won't deliver, whatever the jetting. My VM34 will flow only a maximum of 5-6 fluid oz per minute to the bowl, which limits the maximum horesepower of the 850 engine to 35 HP or so. I don't know the flow specs on your VM36, but you might want to run this quick test yourself: remove the bowl plug, place a measurement cup beneath the bowl, and turn on both petcocks for 30 seconds. Measure the fuel collected, multiply by 2, and obtain the flow rate in fluid oz per minute. You'll need upwards of 9-10 fluid oz per minute to allow for 50 HP or so, which is obtainable with dual carbs. At the lower flow rates of a single Mikuni, you'll have plenty of grunt and performance in the lower rpm range. The performance limitation will show up at the higher rpms, where the higher HP is developed. This is NOT a petcock limit, but rather a limit in the internal piping and valving of the Mikuni. Those of us enjoying the ease of adjustment and tuning of a single Mikuni have to pay this performance price.

Rick
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When I was selling 34mm single PWK flatslide kits I had to modify the needle seat and fuel passages so it would flow over 10 oz per min through the bowl. Otherwise it would starve for fuel at WOT. It got to be too much work. And too many customers had problems syncing the cables and balancing the twin flatslides. So I finally went to Keihin CRS smoothbore twinpack kits because they are pre-synced, precise and very easy to tune with a single choke lever and only one throttle cable - Kind of like the simplicity of a single but with twin high performance.
 
I was on dyno today,max power from rear wheel.45.05hp 5700rpm.Max torque 59,25Nm 5000rpm.One mikuni VM36 carburetor,enough for me.
The horse kick is missing(PW3 cam)...
 
A hot cam usually shifts the power band up and makes it more pronounced. Mufflers tend to kill that effect because the advantage of the hot cam comes from resonance in the exhaust and inlet tracts. Megaphone exhausts with a hot cam often make the bike more difficult to ride smoothly, and the midrange power can be poor especially if the inlet ports are too big. I've never found the carbs and inlet ports which are too small stifling the effect of the cam. I use twin carbs because theoretically the inlet tract and exhaust form one resonating pipe when the motor is revving hard. I cannot visualise how a branched manifold can be as effective as two separate inlet tracts. The only time I ever used a single carb on a twin was when I got desperate for more torque in a short stroke motor and moved towards using nitro.
 
jseng1 said:
So I finally went to Keihin CRS smoothbore twinpack kits because they are pre-synced, precise and very easy to tune with a single choke lever and only one throttle cable - Kind of like the simplicity of a single but with twin high performance.
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5 years and counting old thread. I know shoot me.

What is the Sudco part number for the 33mm Keihin CRS twinpack with close to 67mm center to center spacing people start with before making modifications for installation on the Norton?

Darn difficult to find a table on the interweb with Keihin CRS dual carburetor center to center spacing information in it. Well, hard for me anyway.
 
Schwany said:
5 years and counting old thread. I know shoot me.

What is the Sudco part number for the 33mm Keihin CRS twinpack with close to 67mm center to center spacing people start with before making modifications for installation on the Norton?

Darn difficult to find a table on the interweb with Keihin CRS dual carburetor center to center spacing information in it. Well, hard for me anyway.
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Sudco got back to me. 016-3234 is the Sudco part number for CRS twinpacks with 66mm center to center spacing. Close enough for me. Unfortunately, Keihin is a little behind on manufacturing apparently, and they aren't going to be available until mid-November.
 
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