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Again with the bad gas mileage
Poor fuel economy came up in our conversation the other day, thought I'd pass this along.
As most of us know, the air cutoff valve works on decel to prevent backfiring. These ports are normally open. Evidently, it's possible for the diaphragm to get get stuck in the closed position and cause the bike to run slightly rich. Not so rich as to run bad, but rich enough to drop gas mileage on the order of 5-7 mpg.
If you're only getting mileage in the low thirty's, this might be something to look into.
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#1 05-07-2009, 11:30 AM,
So, how does one check this?
1986 Honda GL1200 Interstate
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#2 05-11-2009, 01:04 PM,
Indeed, can it be checked?

I run my Wing mostly open road with very little city driving.

According to the on-board computer, I get about 42-43 mpg. That 'seems' about 5 mpg low to me.
'86 Apencade SEi
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#3 05-11-2009, 01:10 PM,
I found it realyy depeds on the speed the bike is driven that makes the biggest difference in milage... Yesterday I ran 50 miles at 4300 RPM (more or less constant)... I did not calulate the mileage, but I can tell it was down in the low 30's... I had filled up the tank and drove 20 miles prior to that... With the two trips (about 70 miles total) I burned up almost 1/2 a tank of fuel...
:mrgreen: :mrgreen: :mrgreen: :mrgreen:
Ed Zogg
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#4 05-11-2009, 06:16 PM,
With the engine at rest (not running), remove the vacuum hose from the #4 intake runner. Plug the nipple to prevent a vacuum leak. Using a vacuum pump installed on the HOSE you just removed, apply at least fifteen inches of vacuum to the hose. If the hoses, tee joint and vacuum diaphragms are intact, you will hold a constant vacuum. No further tests can be made unless the vacuum side is correct. If you have a vacuum leak, the carbs will need to be pulled for further inspection.
Notice I said vacuum diaphragm(s). There are two. One for the afterburn valve and one for the vacuum cut valve (slow air cutoff). If one is leaking, the other will not get proper vacuum or hold it for a proper length of time.
Bleed off the vacuum you have just applied. Since this vacuum line is subject to manifold vacuum, there will always be a certain amount of vacuum supplied to the diaphragms. It's only under decel, when manifold vacuum increases, that this vacuum overcomes spring tension on the diapragms, allowing operation.
Start the bike and bring it to operating temperature. Apply vacuum with the vacuum pump and verify a change in rpm. The engine should stumble/blubber since you are no longer supplying air to the air tubes. (It should decrease. If it increases, I would suspect you also may have a vacuum leak elsewhere.) If no change occurs, the valve/diaphragm is most likely stuck shut.

Jack.....take the 42-43 mpg and run!!! Very few of us consistantly get that kind of GOOD mileage.
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#5 05-11-2009, 06:27 PM,
glhonda Wrote:Jack.....take the 42-43 mpg and run!!! Very few of us consistantly get that kind of GOOD mileage.


My bad, ignore my ramblings!
'86 Apencade SEi
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#6 05-12-2009, 01:16 PM,


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