Vm 34mm roundslide probs

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

Hey guys... Ive been posting a little bit here and there...

y bobber project was down for a while because of the motor crapping out on me...

I got a new motor ('78)with great compression swapped in the other day... I set the timing started right up...

When i pulled the plugs they are pretty black and sooty... Im getting a pretty good spark... blue but not quite as fat as i would like but...

The bike will run pretty well... but i can see some black smoke coming out of the exhaust at idle... Im thinking one of the air jets in the carbs is clogged and in need of a cleaning? I bought the carbs through the 650 motorcycles.com site. So i am assuming they set them up right...

Then when the bike gets warmed up it runs worse and worse.... mostly at idle... i think its just getting too rich.... but at like part or half throttle and above it seems to run better.... but the idle will start falling when i come to a stop.... and then it will die...

any thoughts? im gonna try and hit them with some carb cleaner tonight... maybe check the float levels....

Also... the throttle cable barrel adjusters on the top of the carbs are just to get the slack out of the throttle cable right? They are not used to set the idle or anything right?

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

pilot jets are to big,should be in the neighborhood of 22s,what size is in them now. There's just now such thing as bolt on carbs out of the box,no matter who's setting the jetting up,maybe close but never perfect. What sizes are the main jets,needle jet and jet needle.
Correct on your last question.
What I have found over the years of tuning Mikuni's s tune them cold,that's where most lean conditions are most noticeable. I really have no explanation as to why the Mikunis react differently hot,maybe the fuel passages open up some or the incoming charge is pre-heat more,just don't know but you need to take that into account when dialing in the A/F ratio.

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

would i be able to lower/raise the needle (i forget which leans it out)to lean out the mixture? or is that just a band aid to the problem?

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

To lean out the mid range you raise the clip but you really need to find out what size pilots are in there.

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

Ah.... you raise the clip to lean.... which drops the needle down?

I am planning on taking the carbs off and cleaning them and ill check the float level and check out alll the jets etc....

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

I actually had another question too... Im arguing with this guy thats helping me with the bike... is the choke on when the lever is pushed down (towards the ground) or is it on when the lever is in the up position (when the lever looks horizontal)?

yamaman · Posted: August 5, 2009, 12:24 pm Post subject: Re: Vm 34mm roundslide probs

When you push the lever down (on), it lifts the enrichener valve up, allowing fuel to flow. Some VM's have a pull up button & others are cable operated.
Who won? Mr. Green

Did you check the vault. I just posted the VM Tuning manual, which can be quite handy. Cheers.

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

I won... haha... So down is choke on... up is choke off?

Ive been reading the vm tuning manual like a bible... heh... had printed it out a while back... but theres not really an explanation about the choke operation... but in most of the diagrams it shows the lever in the down position...

I have been experimenting with running with the choke on/off...

With the choke off it backfires and pops like a mofo... heh... but it actually ran pretty decent with the choke on... until it warmed up... then when i switch it off it would run a little pop some... then die...

yamaman · Posted: August 6, 2009, 8:28 am Post subject: Re: Vm 34mm roundslide probs

I threw a couple of links into the vault, you might find useful!

Seeing as the "choke" is not really a choke, but a enrichener. It allows more fuel to flow (only with a closed throttle though, it needs vacuum/ closed slide, for fuel to flow). So generally if it runs better with the enrichener on, then you have a lean condition on the pilot. So you need to check pilot for size & make sure it's clear & also check float height.

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

Is it a lean condition that causes a backfire? or rich? or both...? Ill have to check my pilots..

Before i swapped motors the bike started popping and backfiring like hell.... ran great for a month or two... see if a good carb cleaning helps...

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

alright... i got the bike running decent last night.. but to get it to run right i had to tighten my air bleed screw almost all the way in on the right carb... its only like a half turn out.... but its running pretty good like that... does that mean I need a bigger or smaller pilot?

then i tried to ride it to work this morning... and the nut that holds the advance mechanism came loose... and the bike died... luckily i had some tools in my bag... and used the hammer and punch to tighten the nut back up... but im not sure what the timing is set at now... but it seemed to run alright....

Limped it to work... now im just gonna check the timing at lunch and see what happens... whew!

yamaman · Posted: August 7, 2009, 9:07 am Post subject: Re: Vm 34mm roundslide probs

I think you really need to pull those carbs & see whats in there! Wink

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

I pulled the carbs last night... Cleaned them out.... everything looked great.... I wrote down all the jet sizes and stuff.... But i left the paper at home where i wrote them down... The carbs are pretty new...

I remember it has p-6 needle jets.... I think its gotta 200 main... and a 25 pilot... Dont have the internet at home....

I got it running pretty good .... the right side was popping like hell.... when i turned in the air screw to 1/2 turn out or so... the popping quit... just have to synch the carbs a bit.... and it would run even better...

I gotta check the cam chain tension and adjust the valves now and do it all over again....

Does turning the air screw in lean or richen the mixture?

yamaman · Posted: August 7, 2009, 10:53 am Post subject: Re: Vm 34mm roundslide probs

Ok, P6 should be fine, what jet needle? 6F9 would be cool!
200 main.......is at the upper end! Could try 190 or 180 if you wanted!
Pilot at upper end, if your going to buy jets, get some 22.5's perhaps.
Slide size? 2.0 or 2.5 would be ideal.
Air jets, are they there / what size?
Air screws, in to make it richer out for lean!

I wouldn't think it would be to lean with a 25 pilot, sure it's not getting air from somewhere else? Like a leak in a manifold????

Just re reading this thread, I really think you might have a vacuum leak somewhere, spray carb cleaner around the manifolds to find out. Wriggle the carbs around a bit while you do it!

You don't mention what air filters your running, can influence things......

Your on the right track, so don't give up Wink

Cheers

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

Im about at wits end with this thing...

Im running the uni pod filters... and i have head pipes with some small baffles at the end...

So maybe i need to go with a bigger pilot... When i run the bike... and then switch the choke on... it would rev up quite a bit... Seem like im running lean at idle...

then a few minutes ago it just died and wont start now... i think my advance mechanism slipped a little again...

You have any write ups on how to set up the advance mechanism with the cam?

I need to go electronic ignition though.... im sick of points... such a pain in the f-in ass...

jayel · Posted: August 7, 2009, 12:23 pm Post subject: Re: Vm 34mm roundslide probs

westonboege wrote:

Im about at wits end with this thing...

Im running the uni pod filters... and i have head pipes with some small baffles at the end...

So maybe i need to go with a bigger pilot... When i run the bike... and then switch the choke on... it would rev up quite a bit... Seem like im running lean at idle...

then a few minutes ago it just died and wont start now... i think my advance mechanism slipped a little again...You have any write ups on how to set up the advance mechanism with the cam?

I need to go electronic ignition though.... im sick of points... such a pain in the f-in ass...

why are you putting the choke on after it's running??? it's not really a choke it's an enrichener ( more fuel ) you've probably fouled the plugs (won't start now) the advance mechanism doesn't SLIP it either works or it doesn't..... it revs up when you flip on the choke because you're adding MORE FUEL....
"You have any write ups on how to set up the advance mechanism with the cam? " NO... the advance is pinned to the cam shaft it's either right or it's not ... this isn't to say your advance mechanism isn't foobared but you need to figure out what you're doing first before you start tearing things up

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

I checked the plugs.... they are almost white.... its running lean with the choke off.... when i opened the choke it reved up because its getting more fuel... youre right... which makes me think that its running lean....

Advance mechanism was just put in the bike last summer.... The advance mechanism is pinned to the cam shaft... but if you loosen the bolts that hold it to the points cam... you can spin the rod that connects the points cam and the advance mech... right?

yamaman · Posted: August 7, 2009, 12:37 pm Post subject: Re: Vm 34mm roundslide probs

Well yep, your going to need to get the advance sorted first, thank 5twins for this one:

xs650temp.proboards.co...hread=1372

yamaman · Posted: August 7, 2009, 12:52 pm Post subject: Re: Vm 34mm roundslide probs

yamaman wrote:

I wouldn't think it would be to lean with a 25 pilot, sure it's not getting air from somewhere else? Like a leak in a manifold????

Just re reading this thread, I really think you might have a vacuum leak somewhere, spray carb cleaner around the manifolds to find out. Wriggle the carbs around a bit while you do it!

Just thought I'd highlight this bit! Smile

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

The carbs have about 500 miles on them.... and the boots are as new as the carbs.... brand new caps on the vacuum barb on the boots... i can check again for leaks though...if i ever get the damn thing running....

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

When the motor is at tdc.... you line the pin for the points and advance cam at 12:00 right?

yamaman · Posted: August 7, 2009, 3:07 pm Post subject: Re: Vm 34mm roundslide probs

Check Pamcopetes site, has a section installing the advance mech:

www.yamahaxs650.com/

While your there, you might want to check out his system if you want to ditch the points!

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

Haha... Ordered that with a new coil.... Some new advance springs ... In case one got bent or something during the motor swap.... And some 27.5 and 30 pilots.... I'm sure my open exhaust isn't helping my lean condition ...

Finally getting rid of the points.....

westonboege · Full Member Joined: Jun 03, 2008 Posts: 30

Well... i read through my manual last night... and realized that the PO took out the pin that locates the advance mechanism to the cam.... Which is why i was asking how to orientate the cam to the rod.... So ill have to put that back in when my new ignition gets here tomorrow...

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