Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties Mikuni

Mikuni

Post Mon Jul 29, 2013 9:15 pm

Posts: 35
a few years back i strokeed the motor in my Servicar. it runs great but doesn't like to hold an idle. i used the same Mikuni on it b4 the stroking and idle was not an issue. should i have gone bigger on the jets as part of the build?

Post Tue Jul 30, 2013 2:17 am

Posts: 16
Be more specific!
on wath carb, jet size ect..

Post Wed Jul 31, 2013 4:27 pm
GuS

Posts: 369
Location: Bergen, Norway
I have a 36 millimeter Mikuni on my stroked 45. Idling is no issue but it took me some trial and error jetting before I got there. What size carb do you got and how is it set up?

Good scource to learn the VM carb is Panics booklet and the Mikuni Manual.

http://victorylibrary.com/books1.htm
http://www.mikuni.com/pdf/vmmanual.pdf


GuS

Post Thu Aug 01, 2013 10:20 pm

Posts: 35
i don't have the specs off the top of my head. i did get the Mikuni as a kit for a stock 45. it worked great as such. since then i've stroked it to approx 55"and left the jets alone. it runs great at speed but is a guessing game with the throttle to keep it running at a stop lite.i'll try to get details on the specs over the weekend.

Post Fri Aug 02, 2013 5:45 pm

Posts: 202
Location: Middle England UK
The normal kit supplied for a 45 is a VM34.

Post Sun Aug 04, 2013 12:45 pm

Posts: 35
ok, i got into it with mixed results. i see no markings as to what model it is, but the throught of it that mates to the intake manifold measures a 34mm ID. took the jets out. found no markings at all on the pilot jet. the marks on the main were dirty, and garbles and unreadable. i tried to file off the burrs around the egdes and the marking got les readable. so i'm at a loss to get the info u asked for.

thinking to contact Sudco and see if they can tell me how they set up the kits for stock 45's.

Post Thu Aug 08, 2013 5:06 pm

Posts: 35
called Sudco. they tell me they don't offer kits for 45's anymore and, as such, they don't have any info on the kits they used to sell.
anybody have any ideas how else to figure what size jets i have ?

Post Fri Aug 09, 2013 7:07 am
Pa Site Admin

Posts: 5843
Location: Ohio USA

Try measuring them with pin gauges or number and letter size drill bits... if you have room to take those measurements.

Post Sat Aug 10, 2013 1:32 am
GuS

Posts: 369
Location: Bergen, Norway
Servitrike
A magnifying glass is only way to see the numbers on the jets. Don’t poke anything sharp into the jets, it will only mess up the metering device the jet is supposed to be.
Back to your original question: Stroking will create a stronger vacuum in the carb. My best guess is that you need to go leaner on the jets if anything.
You state only idling is a problem. Assuming you plugs come out with a good colour after high speed driving, it suggest leaving the high-speed jets/items as is. Idling is controlled by the pilot jet, idling screw and the air screw. Did you try to adjust the idling and air screw after stroking?
What is your air screw setting? How many turns out. Carefully turn it in with a flat screwdriver till it closes fully. Don’t tighten. Count the turns.
What is you idle screw setting? How many turns in? With slide fully installed with its spring, air filter removed to see the slide, turn the knurled screw out with hand or a flat screwdriver until the slide bottoms. Count the turns.

GuS
Last edited by GuS on Sat Aug 10, 2013 2:53 pm, edited 1 time in total.

Post Sat Aug 10, 2013 8:09 am

Posts: 19
Location: Canada
Anyone know what the jet sizes were on the standard VM34 carb package supplied for a stock 45?

Post Sun Aug 11, 2013 12:06 pm
Pa Site Admin

Posts: 5843
Location: Ohio USA

GuS wrote:
Servitrike
A magnifying glass is only way to see the numbers on the jets. Don’t poke anything sharp into the jets, it will only mess up the metering device the jet is supposed to be.
Back to your original question: Stroking will create a stronger vacuum in the carb. My best guess is that you need to go leaner on the jets if anything.
You state only idling is a problem. Assuming you plugs come out with a good colour after high speed driving, it suggest leaving the high-speed jets/items as is. Idling is controlled by the pilot jet, idling screw and the air screw. Did you try to adjust the idling and air screw after stroking?
What is your air screw setting? How many turns out. Carefully turn it in with a flat screwdriver till it closes fully. Don’t tighten. Count the turns.
What is you idle screw setting? How many turns in? With slide fully installed with its spring, air filter removed to see the slide, turn the knurled screw out with hand or a flat screwdriver until the slide bottoms. Count the turns.

GuS


You don't use the drill flute end of the drill bits to measure. You use the shank end.

Post Sun Aug 11, 2013 11:02 pm

Posts: 35
magnifying glass i tried. that, my glasses, AND an LED flashlite. i guess my eyes ain't what they used to be. i haven't counted the idle screw turns. i'll need to get back to u on that.

Post Sun Aug 11, 2013 11:06 pm

Posts: 35
@ Gus. . .i understand the concept of the increased vacuum, but then u lost me. wouldn't an increase in vacuum mean an increase in air volume, thereby requiring an increase in fuel volume? how did u arrive at needing to downsize the jets? is that a high altitude thing? i'm down in LA @ almost sea level.

Post Sun Aug 11, 2013 11:10 pm

Posts: 35
Pelee Islander. . .

"mikuni comes from 45 restro with 280 main 20pilot and 3 metering jets"

that is a quote from a member of a yahoo group i'm in. i asked the same question and got this answer.

Post Mon Aug 12, 2013 2:12 pm
GuS

Posts: 369
Location: Bergen, Norway
Servitike
Stroking increases the air volume and the velocity in the cab increases. Increased velocity reduces the pressure (increased vacume or suction). The increased vacume will pull more gas through the jets. You would have the same effect if you changed to a smaller carb. The vacume would increase, pulling more gas and enrichen the mixture. To compensate you would need to put in leaner jets..
If the increased demand is compensated by the increased gas, meaning the exact ratio the motor need is maintained after stoking, there would be no need to adjust the carb. It seem as that would be the case for your high speed circuits. As stated in the previous post my best guess would be that your low speed circuits would get to much gas. My guess is based on idling the demand for gas is less then the demand on higher speed, and your high speed mixture seems to be ok . My guess that the low speed mixtue is to rich would of cource have to be tested.
Good indication would be if you plugs came out fouled by soot after city driving, idling on red light etc. Solution would be to go leaner....

I see that W&W cycle in Germany offer a 34 mm. They only inform on the main jet. No info of the other jetting.

I bought my 36mm from Topham in Germany. He jetted the carb based on my info on motor specification with a clear warning I had to test and try.
I started with 40 and ended with a 35 Pilot.

Pilots are inexpesive and you should get yourselves some to test with.
Example
http://www.ebay.com/itm/Mikuni-VM22-210 ... 2b&vxp=mtr

Again i strongly reccomed Panics booklet. He sells it as PDF, and you will have it today in your mail if you order it.
http://victorylibrary.com/MIK-HD.htm

GuS

Post Mon Aug 19, 2013 9:15 pm

Posts: 35
thx for the explanation Gus. i now have a few on the way to me to experiment. i will check on Panic's book soon.

Post Mon Sep 16, 2013 9:05 am

Posts: 3
Hi Limey_Dave and all

I saw you replied to this post about a VM34 mm Mikuni kit on a 45 WL. I have one of these carbs on my 45 chop and it has a 210 main jet (seems too small?) and a Q-2 needle jet (seems too big?), a 35 pilot jet (seems about right?), slide is 2.5 (should be OK), air jet is a 2.0 (should be OK?) Needle is a 6DH4 (everyone seems to use this one!?)

Any ideas at all?
or do you know anyone in UK (a lot of armchair riders on forums seem to want to keep their settings secret!) who is running a 34VM on a 45 please?

thanks

Slim

Post Thu Sep 19, 2013 7:10 pm

Posts: 202
Location: Middle England UK
Slim
I think your best bet is to phone these guys,they're about the top people in the UK for Mikuni info.

http://www.allensperformance.co.uk/

Post Wed Oct 16, 2013 6:01 pm

Posts: 19
Location: Canada
Servitike.........thanks for the info.

Post Fri Oct 18, 2013 6:26 am

Posts: 35
i bought jets from "jetsrus.com". i got to the point of running 2 sizes larger and it was starting to feel real good. the rear plug was looking just about perfect and the idle was getting almost where i wanted it. then i discovered a compression problem in the front cylinder. i'm hoping that it is just a leaking head gasket but haven't gotten it sorted out yet.

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