Awful gas mileage


Information and questions on GL1100 Goldwings (1980-1983)
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figdog
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Location: modesto, ca
Motorcycle: 1983 aspencade

Awful gas mileage

Postby figdog » Thu Dec 18, 2014 10:08 am



I posted earlier regarding starting issues during world tour, but created another post because I've solved the starting problem, but now have a mpg problem

At the same time the heavy rains caused starting issues, I noticed a severe drop in my mpg. I used to get 40 no matter what, now I get between 25-30

I had my carbtune tool shipped to me, and when using it to sync carbs, I noticed something disturbing. All four carbs are even near 30 hgcm ....however .... The number 4 carb is acting very funny. Unlike the other carbs, the guage doesnt oscillate. It stays flat at 30 ... Then at regular intervals it shoots down to 0 .... Stays there for a bit, shoots back up to 30 .... Freezes ... Then back down to 0 again. The other gauges oscillate as expected between 32-29ish ... What does this carb 4 behavior mean?


I noticed some time ago that the rubber line from the number 3 carb to the rear case (vacuum / pulse generator?) had a hole in it. I have since fixed that, but my nightmare is that this somehow threw off the timing, which led to a bent valve and hence the weird vacuum reading ... Or am I just being paranoid?



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WingAdmin
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Re: Awful gas mileage

Postby WingAdmin » Thu Dec 18, 2014 10:30 am

Have you checked your electricals? Particularly the spark plug wires? They are usually responsible when water (i.e. rain) causes a decrease in performance.

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ct1500
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Re: Awful gas mileage

Postby ct1500 » Thu Dec 18, 2014 11:44 am

Faulty ign timing will not bend a valve. During these rains if water was getting into the intake with bike parked on side stand it would most likely make its way to the no. 4 cyl. and a hydro-lock/damage could have occurred while starting.

You need to do a compression test of motor as it sounds like it is running on three cyls only.
Last edited by ct1500 on Thu Dec 18, 2014 2:12 pm, edited 1 time in total.
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virgilmobile
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Re: Awful gas mileage

Postby virgilmobile » Thu Dec 18, 2014 12:51 pm

The only way the one vacuum suddenly drops to zero and then goes back up is that cylinder is drawing air past the throttle plate...When the throttle plate opens,the vacuum drops...Close the plate and the vacuum goes up

Either you have unusual vacuum leak(doubtful)or the throttle plate is no longer securely coupled to the rest of the carbs...

Also the vacuum line that you repaired...It would not cause this...This line actually does not have a vacuum on it at a idle...The vacuum shows during acceleration or as the RPM increases....

I would first inspect the linkage then,if necessary,loosen/remove that one coupler tube and look at the throttle plate...Operate the throttle and be sure the plate moves securely with it.

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WingAdmin
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Re: Awful gas mileage

Postby WingAdmin » Thu Dec 18, 2014 1:28 pm

virgilmobile wrote:The only way the one vacuum suddenly drops to zero and then goes back up is that cylinder is drawing air past the throttle plate...When the throttle plate opens,the vacuum drops...Close the plate and the vacuum goes up.


Or a broken intake valve that isn't opening up.

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Steve F
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Re: Awful gas mileage

Postby Steve F » Tue Dec 23, 2014 6:14 am

Have you tried swapping the gauges around to see if the gauge is at fault? Sounds like you may have debris in the damping valve in the gauge vacuum line.
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figdog
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Joined: Tue Mar 08, 2011 12:12 pm
Location: modesto, ca
Motorcycle: 1983 aspencade

Re: Awful gas mileage

Postby figdog » Tue Dec 30, 2014 2:28 am

What a difference new spark plugs make ... Thanks for the help everyone!




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