Performance Carb Suggestions

grizld1 · Posted: August 9, 2007, 9:20 am Post subject: Re: Performance Carb Suggestions

Yes, Brother Roy! PREACH it! On the high-powered iron the dyno's a must; how fast would you have to go on a big carbureted sport bike to run an accurate chop on the main circuit, and how many times would you have to do it? Maybe a dozen 160 mph romps down the Interstate? Hell, even a quick 600-class sport bike is gonna force absolute insanity to dial it in optimally. If the machine runs EFI, forget about trying to tweak the fuel mapping without a dyno.

The good news is that the XS650 can be correctly tuned by function without getting suicidal, if a person takes the trouble to learn the process and stops looking for the product. As far as paying somebody to tune 'em without a dyno, forget it--if Mr. Customer could find somebody competent to do it, he wouldn't want to pay what it would cost to do it right: it would cost more than a pair of VM bodies, for sure, say 5 hours or so at 50 or 60 bucks an hour if the tuner knows his stuff and works really fast? And then there's the cost to put everything else right before touching the carbs, because you can bet Mr. C. hasn't been through it first.

But as they say down here, them as won't hear it's gonna feel it.

Glyn

First post on the site and it is a question about jetting of the VM's commonly put onto the 650's. Sad to say I sold my XS a while ago but have kept Loyal to Yamaha (XZ550's) and twins in general (Honda CX 500 also).

I got a couple of VM's off E Bay which I have put onto my CX. I just can't get it to run right and thought if I copied exactly the specs for VM 34's with mesh filters for the XS 650 it would be a good start.

Could anyone tell me the size/codes of all jets/ slides/ needle's etc to get me going? Also can anyone recommend a good international supplier for the parts.

PS can anyone recognise this model of Mikuni, it seems slightly different to those I have seen advertised?

yamaman

You've read this post?

650rider.com/index.php...8060#48060

Glyn

Many thanks for that link. That's a really good starting point. Since the CX is quite a different motor to the XS I'm sure I'll have to try a few jet combinations from the standard suggested settings. I've read that the jet needle dimensions/taper are more critical than the needle jet size when getting the midrange correct? I havn't checked the coding on my carbs yet. Is the needle jet situated below the main jet? Also should there be a code stamped onto the jet needle somewhere so I can check mine? Thanks again. Glyn

Glyn

Just took the top of the carb off and have discovered the following;

1. Slide diameter is 35mm, code stamped on underside of the slide is "2.5"

2. Jet needle has the code 6DH4 on it.

I have not pulled the needle jet yet. I'm thinking it will be a lean one.

I've also got 180 mains in there and size 35 piot jets.

In the link on this site Grizz stated the slide should state 2.0.
Looking at the Suduco Mikuni Guide book, a 2.5 slide will be leaner than a 2.0 slide. My needle is also alot leaner than a 6DP1or a 6DH2. I'm also running mesh filters. It would seem that I have a really lean condition?
This wouldn't really be improved with a larger main jet since this onlt really comes i at 75% throttle and above?

Perhaps if I go with a richer needle, eg a 6F4 I would still be able to use the 2.5 slides ie one would compensate for the other? Or maybe just a richer needle jet would compensate? Any advice welcome, this is pretty confusing.

woodman · Full Member Joined: Oct 12, 2008 Posts: 256

Thats good advise about getting the bike dyno tuned. However here in Montana there are on Harley shop dynos & if it aint a Harley with & SS carb and drag pipes they would be dead in the water as far as any tuning skills are concerned. Not to mention that they would laugh you right out the door

woodman · Full Member Joined: Oct 12, 2008 Posts: 256

deleted, Ill keep my opinions to myself

JVM650 · Full Member Joined: Jun 23, 2008 Posts: 19

I have gotten my stock 81 up to 8000 +

Sledhooligan · Full Member Joined: May 04, 2009 Posts: 12

So you want big carbs check these out. Cutler Performance 44 and 48.
www.cpcracing.com/site...age/190735
I'm going to try to use the older 48 round bore on my build.

jayel · Posted: May 6, 2009, 3:38 pm Post subject: Re: Performance Carb Suggestions

putting big carbs on a stock engine is a waste of time, the engine can't use the extra flow, the cx500 probably should run a leaner setup than the 650, 250cc per cylinder rather than 325cc, end of the extent of my cx500 knowledge

dwyatt · Posted: May 9, 2009, 1:11 pm Post subject: Re: Performance Carb Suggestions

I sidestepped the whole arguement and went with 36mm flatslides.

jbrasel · Posted: May 21, 2009, 9:05 am Post subject: Re: Performance Carb Suggestions

An easy drilling of the slide, improved needle, bigger pilot and main jets, and pod filters and my stock BS34s flow just fine. No noseplant at 6 grand.

Do you really think that hitting 7k regularly is doing that much damage?

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

I used to twist my '79 right on up to redline six or eight times a day. If you don't hold it there for an hour or two, it shouldn't do any harm. The 650 is built to take it, if you can stand the vibes. In fact, the noise and the vibes are so bad that you'll probably get tired of the abuse before your 650 does.

I would go so far as to say that if you twist it up to redline in fourth or fifth gear and hold that speed for five minutes and the thing comes apart, there was something wrong with it to begin with. I wouldn't call it the rider's fault. It gets to be the rider's fault when he decides to beat the p*ss out of the machine all day every day just to see how much it will take. This latter form of abuse is most common among rich people and among spoiled children whose daddy pays the bills.

xsjohn · Posted: May 21, 2009, 11:32 am Post subject: Re: Performance Carb Suggestions

After 40 years of Yamahas I wouldn't know much about it ...........5500 is a lot for a imperfect (non 0 runout) out of balance pressed crank......I say no more....

xsjohn

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

xsjohn wrote:

After 40 years of Yamahas I wouldn't know much about it ...........5500 is a lot for a imperfect (non 0 runout) out of balance pressed crank......I say no more....xsjohn

I find an engine suffers far less from high revs if it's pulling hard. Wind it to redline in first, second, third, it'll come apart a lot sooner than it will if it's pulling hard. Light loads permit lash in the bottom end and the effects of that lash are often disastrous. Keep it under a nice steady pull, she'll take a lot more than if you got her running free and loose.

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

jimmythetrucker wrote:

xsjohn wrote:

After 40 years of Yamahas I wouldn't know much about it ...........5500 is a lot for a imperfect (non 0 runout) out of balance pressed crank......I say no more....xsjohn

I find an engine suffers far less from high revs if it's pulling hard. Wind it to redline in first, second, third, it'll come apart a lot sooner than it will if it's pulling hard. Light loads permit lash in the bottom end and the effects of that lash are often disastrous. Keep it under a nice steady pull, she'll take a lot more than if you got her running free and loose.

The main problem with the 270/77 rephrase is the engine will rev freely past the 7500 red line causing the pressed on crank to separate. That is why people who race with the 270/77 rephrase weld the crank. Vibration =stress. I agree with XSJohn these cranks are not balanced and are pressed on =vibration=stress +over revving= separation of crank. I want to keep my engine and money

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

Skull sez -- "That is why people who race with the 270/77 rephrase weld the crank. Vibration =stress. I agree with XSJohn these cranks are not balanced and are pressed on =vibration=stress +over revving= separation of crank. I want to keep my engine and money."

Jimmy sez -- I want to keep my engine and my money, too. That's why you'll never see me sitting at a stop light, in neutral, redlining the tach just to make noise. When I redline the tach, I'm always pulling a load (i.e.: I'm in one of the two tallest gears), and I don't hold it there for an hour or two at a time. The Japanese motorcycle is built to take it. If the engineers claim it'll rap eight, nine, ten grand, it'll take eight, nine, ten grand, and it'll hold together if it isn't abused. They didn't sell hundreds of millions of motorcycles because they build their engines in Milwaukee.

I can't imagine anyone who spent the money to rephase a crank wouldn't spend the additional money to have that crank welded and balanced. That kind of foolishness is born of an attempt to achieve Dom Perignon performance with a Pink Ripple brain. It's primary worth is that it's a learning experience. It's the kind of thing that most often happens to those who most deserve it.

At cards, when there was real money on the table, in the Marines we always said "Go big or stay at home." If I was afraid my 650 twin would turn into a bomb when I twist it above 5500 revs, I'd sell the sumbitch and buy a Harley. And I damn sure wouldn't be telling anybody else (as I DO tell others) that the XS650 is a great piece of machinery.

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

Jimmy, It's an opinion not a who has the last say bough beating someone else's opinion into submission. Gets boring and goes off track

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

Skull -- What I wrote is my opinion. It wasn't an attempt to have the last say. It's the way I truly feel. Honest. No s***. So if you disagree, by all means say so.

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

650skull wrote:

Jimmy, It's an opinion not a who has the last say bough beating someone else's opinion into submission. Gets boring and goes off track

Everything_To_Xs · Posted: May 21, 2009, 6:15 pm Post subject: Re: Performance Carb Suggestions

Bloody hell what started off as a simple question turned into a little brawl lol. Im gonna go grab some popcorn Smile

Tell you what, Mikuni VM 34's are pretty damn good no doubt about it, this is what i intend to buy for my xs, but my chop is running EZ carbs and runs great.

y spair engine that i am building will have a set of AMAL 34mm Concentric 930 carbs which ive heard good things about.

Going off the subject a bit, anyone here run an XS with a set of Victor 441 pots?

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

650skull wrote:

Jimmy, It's an opinion not a who has the last say bough beating someone else's opinion into submission. Gets boring and goes off track

It's impossible to beat an opinion into submission. An opinion is NOT a person. If you think an attack upon your opinion is an attack upon you, that's what's called, "a personal problem." It is in fact a SERIOUS personal problem because it renders you incapable of functioning in groups. Think about it.

On the other hand, it is a fact that all opinions are NOT created equal. If you persist in stating opinions that have no basis in fact, then you can expect those opinions will take a beating. And if, again, you decide to personalize what happens to your opinions, that is just another of those things we call "personal problems."

The bottom line is: If you can't stand to argue, don't voice your opinions in public.

Everything_To_Xs · Posted: May 21, 2009, 7:09 pm Post subject: Re: Performance Carb Suggestions

Who exactly was that pin pointed at?

xs1961 · Posted: May 22, 2009, 3:37 am Post subject: Re: Performance Carb Suggestions

God, I love reading this banter... Smile

Anyway, back to carbs .. best thing I ever did was junk my CV's for the umpteenth & final time for the 34mm VM's, goes like s*** off a shovel again now ..true shes a bit thirstier on the juice & I may have spend 3 minutes re-balancing them every 10 days or so but that beats the asthmatic qualities of the originals & their up n down erratic idle & strangled top-end (non)performance.. Wink

Take note of Everythings_gonewrongwivmy_XS carb tip - GPZ500/ER5 , best discovery I never made Wink

..Im selling all my stock carbs for a few of these..

What Happened to 650rider.com?

Yamaha xs650