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VM38 single

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VM38 single

PostAuthor: FenRider » Mon May 13, 2019 1:42 pm

Hey guys

Just got the bip single manifold and decided to go with a VM38 carb. The guy I got it from set it up as if it was for a big sportster, this is what he has set

main jet 330
pilot jet 30
needle jet 166 Q-2
jet needle 6DP1
throttle valve 2.5
main air jet 0.5

The bike wont idle at all but will go with throttle. The plugs went completely black. Obviously running too rich.

from some posts ive seen im guessing that main jet is way out?

My bike (1989 XV1100) has been off the road for over a month now ( mainly waiting for that bip intake to arrive from the states ) and im going crazy, I just want to get back on the road.

Any help is much much appreciated

Thanks
Matt

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Re: VM38 single

PostAuthor: nanno » Tue May 14, 2019 2:33 am

Just to give you an indication: I ran (dual) VM38s with a setup of 17.5 pilots and 175 mains and the air-screws approx 2 to 2.5 turns out. Depending on the rest of your setup, you should be somewhere in that ballpark. With the over lower airspeed in a 2in1 manifold, I'd say maybe one or two sizes up on the main and maybe #20 pilots, but this should definitely get you running.
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Re: VM38 single

PostAuthor: FenRider » Tue May 14, 2019 12:56 pm

The guy was nice enough to give me some spare bits, so i have a 340 and a 27.5 i could try ? or did you mean one or two sizes up from one of your carbs IE: 180-185?

I have seen some guy on the net use a VM30 with a 250 and a 40 which ran. is that simply the difference of a VM38 and a 30 ?
His bike was an XV1000

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Re: VM38 single

PostAuthor: nanno » Wed May 15, 2019 10:26 am

Up one or two sizes from my settings.

A bike will run with a lot of settings, and even though I wonder HOW it'll run with those settings (the VM30 being a massive choke-point and thus increasing air-speed a lot, which puts jetting in a completely different ballpark...)
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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1979 RD250/R5/DS7-hodgepodge (in bits)
Sex: Male

Re: VM38 single

PostAuthor: FenRider » Wed May 15, 2019 12:00 pm

Thanks. Jets should be with me tomorrow and will fit them Friday.

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Re: VM38 single

PostAuthor: FenRider » Sun May 19, 2019 1:06 pm

Little behind on the reply as I had that nasty 24 hour bug thats doing the rounds.

So got round to changing stuff up and it idles, needs tweaking but its nice to hear it run. Bit of my own lack of understanding involved with it not idling but its encouraged me to read and learn more.

New issue though. XV1100, push/pull cables, VM38 single cable, me/big idea, buy XV1000 cable modify end.......... too short

What throttle cables are people using ? im going to have to get a 90 degree carb top adjuster to have good clearance from the tank as well.

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Re: VM38 single

PostAuthor: nanno » Sun May 19, 2019 2:56 pm

I've been running twin VM38s and there's a readymade 2in1 cable for that. I'd say have a look at Guzzi cables, they will definitely work on the carb side and the length should be pretty good too. If nothing else, a throttle assembly from a Guzzi T3/T5, early LeMans/California should work. On my Turbo TR1 (back when using a VM44), I used a heavily modified XS750 throttle cable, where I shortened the outer sleeve and made the actual cable and nipples from scratch.
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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1979 RD250/R5/DS7-hodgepodge (in bits)
Sex: Male

Re: VM38 single

PostAuthor: FenRider » Wed Jun 05, 2019 3:23 pm

sorry another late reply.

soooooo...

I decided to adapt the xv1000 cable a bit more and got it to a good point. It did however frey and a friendly neighbor took it to a shop and they remade the cable to how I had modified it... but they did a proper job of it, lol.

Anyway, its a good fit and I have been out and ridden the bike....... WHOOP
however I noticed that when I pulled the clutch to change gear the revs didnt always drop. Checked the plugs and they confused me a little.

The side electrode is white, but the insulator tip is dark brown turning black. White = lean, black = rich.
Wont start with choke, but just a quick rev and its good ( I dont rev with the choke on ). Doesnt idle great admittedly but im not expecting great idling from this.

I havnt experienced any bangs or pops while riding or idling.

Thoughts, opinions...

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Re: VM38 single

PostAuthor: nanno » Thu Jun 06, 2019 8:55 am

That's usually a sign of a spark plug that is too cold (or oil-consumption). Are you running BP7ES or the stock B8ES?
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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1982 Yamaha TR1 Turbo
1977 XS 750 Sidecar
1984 XT500 4Valve (Austrian Tax saving edition)
1979 RD250/R5/DS7-hodgepodge (in bits)
Sex: Male

Re: VM38 single

PostAuthor: FenRider » Thu Jun 06, 2019 11:55 am

BP7ES

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Re: VM38 single

PostAuthor: FenRider » Sun Jun 16, 2019 1:05 pm

Went for a good ride and the bike wasnt running nice at all. I saw a post on here someone running with a 25 pilot and 230 main, e-clip to the top of the needle. So im on this setup now.
Now the bike runs much much nicer, however its very evident the front cylinder is very lean while the rear is very rich.
Im considering dropping the clip one position and putting a one hotter plug on the rear! thoughts and feelings about this or even a better alternative ?

Also having a think, any advice on setting the float ?

Thanks

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Re: VM38 single

PostAuthor: FenRider » Sun Jun 16, 2019 2:47 pm

And for the plugs they are BPR7ES not BP7ES

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