Fluid dynamics mixture problem

[pablohoney]

Hi fellas,
I just finished rebuilding my 79 xs650 special and it runs great except for one issue. When I am on the freeway it runs great but I when I stop from the freeway it either dies or when I rev it, it take a while for the rpms to come down. It will start right back up, but same issue with the slow rpm drop. Seems like lean mixture. However, when I am riding at 40+ and pull the clutch and rev it they come down fast. What seems to be happening is that when the bike is stopped the mixture is lean and when moving it is fine. I think it is due to my air filters creating a low pressure zone at the intake at speed, and when stopped, it is the pressure is normal. A venturi action at the intake. Does this seem likely? Want to know before I buy new filters. Will I have the same problem with pods? Thanks a bunch!


Taylor

 

[5twins]

That's one strange looking intake set-up. Pull it off and take a test ride to see if the problem goes away. If it does and you want pods, get some UNIs. They don't cause problems like you're having now.

 

[xjwmx]

Yes, I would see what happens with it off. Also, use neutral instead of the clutch to see if friction through the clutch is dragging it down. You know how it's easier to push in neutral. CV carbs like you have are supposed to be insensitive to ambient pressure, which would be equivalent to pressure change at the intake only, seems to me.

 

[pablohoney]

Well, I ran it with no filter and it ran for crap. Idle was all over the place. When I would come down from speed it would idle real high the super low. Also clutch vs. neutral didn't seem to be a factor. So does pods and retune seem like it will fix it? i sure hope so...


P.S. They are BS38 carbs if that makes any difference.

 

[pablohoney]

BTW will I just end up boning myself if I get these: http://cgi.ebay.com/ebaymotors/2-PO...torcyclesQ5fPartsQ5fAccessories#ht_1826wt_939
or do I need to get much more expensive air filters?

 

[pablohoney]

Nevermind, I will go with expensive ones.

 

[5twins]

You don't need expensive ones, the UNIs are only about $15 each. Absolutely DO NOT get those eBay ones. Those are the shit cheapos that cause all sorts of tuning problems. About all they're good for are pencil holders on your desk, lol.

The way your bike is acting, I think it needs more tuning regardless of what intake system you have.

 

[pablohoney]

I got the ones from mikesxs, $17.50, not too bad. Will probably need a bit more tuning, but hopefully not too much. Lets see if that does it! Thanks for the assistance.

 

[sgallaty]

test to see if your advance is sticking, too.

 

[pablohoney]

Thanks I did, but it is fine. Just put in the new filters, seems to run great. Much nicer than before! Btw, there is/has been for a while a slight metallic tapping when I let off the gas, only at certain rpms. Valves?