Carb Jet Question

[Herman]

I got a 97 magna a few weeks ago (my first bike) with just shy of 3,900 mi on it.  It's got cobra exhaust, but I'm not sure if it has ben rejeted or not.  Is there a way I can tell since I don't have anything to compare it to?  It seems to run smooth and the MPG is pretty good.  about 115 on 2.270 gallons, so about 50.66 MPG.  RPM's are about 5k at 75mph (read on the MRA forum that a guy's rpm changed after new jets).  Any thoughts or ideas?

[Curtis_Valk]

If it is not stumbling or having lean surge in the midrange, don't worry about it.  Your mileage is good.  I don't know how to tell really, but I don't think you have the cobra jet kit because of all the problems most folks have had with it.  The cobra kit involves drilling the slides and is not easily reversable if it proves problematic.  Stay far, far away from that one and consider the Dave Dodge jet and shim kit.  This is based on what I have learned on the MRF forum over the last year or so, not personal experience.

Also RPMs are no indicator of anything to do with carburation.  Since there is no slip in the mechanical link (drive line) between the pavement and the engine, there is nothing that will influence or change RPMs except tire or sprocket changes (assuming the clutch is not bad and slipping).  Any perceived change in the RPMs after a jet change just means you can't trust the butt dyno.

Sorry I'm not more help with your specific question (how to know if your bike has been re-jetted).  I am not afraid to say I don't know, it just takes me lots of words to get there LOL!!!  

Curtis

[Herman]

Yea, I can't decide if I want to leave it alone and go with it, or try out the DRP jet kit  for $40 plus paying to sinc. the carbs.  I'm not sure if it's worth the $$ to know for sure it's re-jeted.
Thanks for the input.  Little input is petter than none at all.

[Greg Cothern]

Not much of a way to tell if it does not have the lean surge dead spot around the late 3k RPM range, except to open up a carb.
I must say I am not a fan at all on the carb sync'ing as in most cases it is a waste of money.  I have sync'ed a few and cant tell a bit of difference in them at all.  When sync'ing a carb all  you are doing is setting the butterflys the same.  Unless the carbs are completely CNC built they are going to be a little different anyways and you will never get them the same.
The idle drop procedure is a more worthy task to tackle.

[Charles S Otwell]

Just my two cents worth, If it runs good,rides good and looks good ,ride it. The more you ride it the more you'll know what it needs. Sounds like you've got a nice bike enjoy it !


Charles
#279

[Greg Cothern]

Well said Charles!

[chrislarue]

Ok, a question playing off of this thread:

My '96 "supposedly" has a jet kit according to the previous owner - not sure what kind, Cobra or other (does K&N make a jet kit?) - but I have heard about this 3k dead spot and have been unable to fully understand what it means.

I do know it almost feels like a turbo charger kicks in at about 6k rpm. Is that part of the jet kit dead spot issue?!?

And, just to be sure, does Dave Dodge's jet and shim kit fix all these jet kit issues that other brands seem to have?

If so, do I need the stock jets (because you know I don't have them)?

Thanks for continuing to education the ignorant...