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1981 gs 650 gas mileage problem

  • Thread starter Thread starter johne
  • Start date Start date
J

johne

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I have a 1981 gs 650. shaft drive, 18.160 miles and just had it tuned up. It has a little bit of light backfiring when it first starts it but then it runs smooth. I burnt 3/4 of a tank while driving a 30 mile highway stretch and I kept it under 60 MPH. I installed new plugs wires, changed the oil and filter, air filter and tried sea foam, and it made no difference. Any ideas would be appreciated.......Please advise. Thx
 
30 miles on 3/4 tank? Test the obvious... Maybe your fuel gauge is broken. Maybe your petcock is leaking into your oil sump.(smell the oil!) and No smoking-this bike must stink of gas....Maybe there's a pool of gas under your bike :) kidding, I'm sure you'd notice but that's really record-breaking bad mileage.

the startup backfiring might be the engine choking on gas due to stuck floats in the carb bowls.... I wonder if you need choke/enricher to start this bike? That'd be a clue per stuck floats, bad float needle..
 
The backfiring does sound like excess fuel being dumped into exhaust

Was the tune up intended to correct this problem? Is this a new to you bike?
driving modestly, this model will get 50 mpg easily
 
the original oil i changed didn't smell of gas and there is no gas leaking and i have had several bikes in the past and never encountered this. Is there a ? adjustment screw i can try the make it more lean than rich.
 
Is there a adjustment screw i can use to the make it more lean than rich if I'm getting to much fuel?
 
Do you understand proper use of this style petcock? I'll ask again... Is this a new to you bike? If so , it might need more than a tune up and seafoam... Previous owners can be very creative with maintenance.
 
its very new to me, can you tell me about the style of this petcock? and if i need to do a rebuild on it. Any ideas would help.thx
 
Assuming it's still the stock petcock...... This has 3 positions: "pr ", "on " ,"res" : in "on" and a "res" ,fuel should only flow when engine is running (engine vacuum is applied to the petcock letting fuel flow). The "pr" spot lets fuel flow at all times - this is used after bike has sat idle and fuel has evaporated from carbs this spot quickly refills carb. But you don't want to leave it in " pr" when bike is not running,as carbs will likely overfill - if this happens, fuel will run into crankcase diluting the oil.

Test the petcock to make sure it is working correctly.
 
I looked at a few clips on how to check the petcock valve and I'm going do it asap. Thanks for the heads up on this.
 
Is the bike stock? Detail all the maintenance you have done? Valve adjustment? Full carb tear down and replacement of all the O-rings?
 
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