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Yet another pods/re jet thread...

  • Thread starter Thread starter Monkeyking
  • Start date Start date
M

Monkeyking

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Howdy, I'm a new member of the forum and a new owner of a 1978 GS750. I bought the thing in what appears to be pretty good condition with stock exhaust and Uni pods. The PO re jetted from (according to info found here) a pilot of 15 to 17.5 and a main of 100 to 117.5. On top of that I live 4000 feet higher than he did, so it's running WAY too rich (I think he may have had it too rich already).

So I want to go to K&N's (those Uni's are looking a little old anyway). According to info found here I figure that I should drop to a pilot of 15 (so back to stock) and a main of 95, which is leaner than stock. I'm just looking for criticism of my thinking before I order a bracket of jets between 92.5 and 97.5, do these numbers sound about right?

I recognize that changes in carbs are predicated by ensuring valves are tuned etc...all of which is in the works.

Thanks in advance!
 
Monkeyking said:
Howdy, I'm a new member of the forum and a new owner of a 1978 GS750. I bought the thing in what appears to be pretty good condition with stock exhaust and Uni pods. The PO re jetted from (according to info found here) a pilot of 15 to 17.5 and a main of 100 to 117.5. On top of that I live 4000 feet higher than he did, so it's running WAY too rich (I think he may have had it too rich already).

So I want to go to K&N's (those Uni's are looking a little old anyway). According to info found here I figure that I should drop to a pilot of 15 (so back to stock) and a main of 95, which is leaner than stock. I'm just looking for criticism of my thinking before I order a bracket of jets between 92.5 and 97.5, do these numbers sound about right?

I recognize that changes in carbs are predicated by ensuring valves are tuned etc...all of which is in the works.

Thanks in advance!
Click to expand...

First off you have a 35 yr old bike which likely has never had the carbs cleaned properly. They need to be stripped and dipped. The o-rings will also need replacing.
I would go back to the 15 pilot and leave the main alone. You will be able to adjust for altitude using the adjustments of the jets (air/fuel). It's trial and error from there. Good luck and welcome to the nuthouse!
 
Read up on this thread after you've gone through the carbs and valves, properly:

http://www.motorcyclecarbs.com/Motorcycle_Carburetor_Jetting__W7C240.cfm

Off the bat, sounds like things are mismatched with the pods and stock exhaust. Plus your jets seem a ways off. I also have a 78 gs750 , and the stock jets were 102.5s. For emissions purposes, these bikes seemed a tad lean from the start. Just taking a guessing, but I'm thinking 105sUPMC might be more appropriate in your case. Again, AFTER you go through the carbs and adjust the valves. Right now, you don't know what you're facing and all the screwing with jets is futile unless everything else is healthy. Good luck.
 
Thanks guys, just for the record I guess I wasn't clear enough: I know that I need to give the whole system a tune up (valves, carb cleaning etc...), but I wanted an idea of where to go with the jets as they are obviously not right. And if I'm going to order carb parts anyway, I may as well put some jets in that order...

allojohn, what would the rational be behind leaving the main so large? I felt that my estimation of leaner than stock sounded off, but isn't 117.5 pretty rich?

Anyway, thanks a lot.
 
Monkeyking said:
allojohn, what would the rational be behind leaving the main so large? I felt that my estimation of leaner than stock sounded off, but isn't 117.5 pretty rich?

Anyway, thanks a lot.
Click to expand...

The main jet is used from about 2/3 to full throttle and with K&N pods on you're sucking in a ton of air so you'll be needing plenty of fuel. It could still be rich but maybe not. Back off the pilot to 15 and see how it runs.

Unfortunately, when you use pods it's not easy to get things right quickly. K&N's will give you the best chance, but there's no easy fix, you've just got to work at it.
 
From Eric.................



With pods and stock exhaust, at that altitude, all he needs is stock pilot jets and 107.5 or possibly even 110 main jets.
He should then be "golden" except for the usual fine tuning with the air and fuel screws.


Eric
 
Hm, well lots to think about. I knew that I was in for some fun time in the garage when I bought this thing, but I've got a thing for those UJM's....honestly I wish PO had left the stock airbox on, but going back now I'd still have to play with the jets, so I guess I'll just see what I can do.

Suppose I'll be back with more questions. Thanks guys.
 
you could find a stock airbox
check the Parts for sale forum
 
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