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General Category >> Rubber Side Down! >> Mikuni VM 38 Tuning *VIDEO*
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Message started by jandaso on 03/27/11 at 10:07:14

Title: Mikuni VM 38 Tuning *VIDEO*
Post by jandaso on 03/27/11 at 10:07:14

I been reading everything I can for the tuning of the carburetor and I have come out with a staring main jet (185), needle is of the second slot
From top to bottom. Pilot jet ?????? I don't even know where to Start. I have a UFO and a Dial-A-jet on the carb plus a cone filter. Currently I have in hand a 10,12.5,15,17.5,20 and 30 pilot jet sizes. I just need some
enlightenment to figure out on what to Start. I plan to run the bike today and see how it Will do but I just need a setup to start playing with it. Current mods Is a Dyna muffler, Verslavy and a Barnett clutch.

I know lancer (hope he gets well soon) is the guy to talk to for these questions but he's not being active and there should be people out there who can point me to the right direction. Thanks

Title: Re: Mikuni VM 38 Tuning
Post by verslagen1 on 03/27/11 at 10:21:08

start in the middle and let the bike tell which way to go.

Title: Re: Mikuni VM 38 Tuning
Post by jandaso on 03/27/11 at 10:53:13

I will post how the bike runs to see what adjustment I can make. Thanks again

Title: Re: Mikuni VM 38 Tuning
Post by jandaso on 03/27/11 at 14:23:32

Cant get her started with dial a jet on. Idle rought and a lot of black smoke. Wujuuu problems !

Title: Re: Mikuni VM 38 Tuning
Post by BurnPgh on 03/27/11 at 16:05:23

with the UFO a pilot jet generally isnt necessary. Lancer generally include a pilot jet that has been soldered shut for use with the UFO/DAJ set up. For me...the soldered jet was a bit too lean, and the 10 pilot is a bit rich. I stuck with the #10 and diddled with the air adjustment and idle screws to get a good running.

Title: Re: Mikuni VM 38 Tuning
Post by jandaso on 03/27/11 at 17:12:08

I will deal with it tomorrow. Now the bike won't even start. :'(

Title: Re: Mikuni VM 38 Tuning
Post by justin_o_guy2 on 03/27/11 at 18:52:26

7A717E7471637F100 wrote:

I will deal with it tomorrow. Now the bike won't even start. :'(

& the upside is

No new riding gear is needed..

Title: Re: Mikuni VM 38 Tuning
Post by Boule’tard on 03/27/11 at 19:06:42

The UFO is more trouble than it's worth, IMO. But it can be made to work (and still have a small pilot jet) by enlarging the hole in the UFO (that the needle goes through) with a 5/16" drill bit. Also, there is the optional air bleed, outlined in the UFO instructions, that will lean out the idle mixture. It is an approximately 1/16" hole in the brass shroud just upstream of the needle. Drill it just above the "floor" of the throat. Those two mods should get the mixture in range to where you can control it with the air screw.

Title: Re: Mikuni VM 38 Tuning
Post by jandaso on 03/27/11 at 19:21:44

I soldered The pilot jet shut and nothing. The bike just turns but won't start. I just smell gas and hear the filter sucking air.

Title: Re: Mikuni VM 38 Tuning
Post by justin_o_guy2 on 03/27/11 at 20:05:24

I just smell gas and hear the filter sucking air.

& how many plates of beans & onions did you have b4 bed last nite?

Title: Re: Mikuni VM 38 Tuning
Post by jandaso on 03/27/11 at 20:16:11

haha. I had to use my car to jump the battery since it was weak. The bike really just turns and it seems it flooded. The bike is not giving me any signs of firing up. Im getting frustrated after trying for a couple of minutes there is a really strong smell of gas. Tomorrow i will change the Sparkplug for the iridium one (not hoping this to be the fix but i was going to do it anyways)

Title: Re: Mikuni VM 38 Tuning
Post by LANCER on 03/28/11 at 11:21:03

If you have a good smooth UFO installation on the slide and soldering the pilot jet closed, it "should start for you".
The ones I have assembled worked for me so I'm not sure what to tell you now, except to recheck your work.
Call Thunder Products and talk to Lonn, he is the owner and knows the UFO better than anyone...he might have some guidance for you.

Title: Re: Mikuni VM 38 Tuning
Post by jandaso on 03/28/11 at 11:38:51

Everthing went smooth with the UFO now i need to wait for a washer that went missing for the Dial-A-Jet. I took the air box out and there is a hose that I left open. I bought a small cone filter to use it for it. Would that work ?? the hose just blows air. I just need to find a spark plug remover tool since i dont have one. Called all the motorcycles around my area and they dont have it in stock.

it would help if somebody can help me with an alternative: a deep 18mm socket wont fit, I already tried that.

P.S. Lancer let me know when your ready for a nice talk on what i want to do and how your cams can help me achieved my goals and thanks for the response. I hope your getting better.

Title: Re: Mikuni VM 38 Tuning
Post by verslagen1 on 03/28/11 at 11:48:38

Try a lawn mower shop for the sparkplug wrench.
You might take a used plug with you to a pawn shop or yard sales.
I have a well worn 11/16" deep socket that fits.

Title: Re: Mikuni VM 38 Tuning
Post by jandaso on 03/30/11 at 14:52:35

Changed The spark plug and after all the bike started with a little hesitation (my guess: bike was flooded or the old spark plug went bad) The bike idles fine but when I pull down the throttle the bikes dies. The only way I can keep her from not dying is pulling really slow on the throttle plus the bike is backfiring when letting go of the throttle.

Any help on what can be causing this?

Title: Re: Mikuni VM 38 Tuning
Post by BurnPgh on 03/30/11 at 19:25:22

4F42584148594C5F492D0 wrote:

Prepare to curse, jan. Tuning is very very tedious. I had forgotten that I had at first, a very lean spot right off idle. I didnt enlarge the hole the needle went through but I did do the air bleed and it helped a lot. It helped enough that I could tune from that point. Start with a very small size and enlarge it one size at a time, and test it each time. You'll find that the popping and hesitation will lessen. Just for kick though, before you go drilling the needle jet...try a #10 pilot, needle on the 3rd slot, #200 main, airscrew out 2 turns. Thats where I'm at after a long tuning process last spring and should put you in the general ball park. You'll Probably be running rich as I have a more open muffler but give it a shot.
And you'll never be able to crack open the throttle from idle to main without it stalling. I dont know how to explain it well but someone will chime in.
PS - the off idle hesitation is far less pronounced under load. Even now, tuned as well as Im going to get without continuous dyno acess, if i crack the throttle wide open from idle while in nuetral if i try hard i can get it to stall. If im actually taking off in 1st and crack the throttle the same way I get a split second of slight hesitation and then I get launched forward like a rocket.

Title: Re: Mikuni VM 38 Tuning
Post by jandaso on 03/31/11 at 07:44:02

4275726E506768000 wrote:

[quote author=4F42584148594C5F492D0 link=1301245635/0#7 date=1301278002]The UFO is more trouble than it's worth, IMO. But it can be made to work (and still have a small pilot jet) by enlarging the hole in the UFO (that the needle goes through) with a 5/16" drill bit. Also, there is the optional air bleed, outlined in the UFO instructions, that will lean out the idle mixture. It is an approximately 1/16" hole in the brass shroud just upstream of the needle. Drill it just above the "floor" of the throat. Those two mods should get the mixture in range to where you can control it with the air screw.

Title: Re: Mikuni VM 38 Tuning
Post by BurnPgh on 03/31/11 at 13:51:42

no DAJ

Title: Re: Mikuni VM 38 Tuning
Post by jandaso on 03/31/11 at 14:16:30

Well, I will try moving the needle up and down to see where I get the best overall performance and later work my way to the pilot jet #10. I will keep the main jet 185 since I have a DAJ. Another thing that I'm doing is making the hole of the UFO bigger with a 5/16" drill bit (Lonn owner of thunderproducts recommended me this.) Will see what happens and I will post the updates.

Title: Re: Mikuni VM 38 Tuning
Post by jandaso on 04/01/11 at 15:01:11

[media]http://www.youtube.com/watch?v=iXZLOPCCnws[/media]

Here is the bike with the Mikuni 38, UFO, DAJ, Pilot Jet #10, Needle Jet 6DP1 with the setting on the first slot (tried first, second and third slot and didnt do any different)

Later I drilled the UFO with a 5/16", tried the pilot jet 10 and changed the needle for a 6D8H. The different was huge (not perfect), but I will be testing with the soldered pilot to see if it gets better;if not, a will also try a thicker Needle.
[media]http://www.youtube.com/watch?v=EsJ2ZCzS8fw[/media]

Thanks for the help everybody. Now i will run more test and wait till i get a bigger needle online