Less than 20mpg!!!!! whats happening


Information and questions on GL1500 Goldwings (1988-2000)
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crimbo79
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1996 ST1100 Pan European

Less than 20mpg!!!!! whats happening

Postby crimbo79 » Mon Feb 16, 2015 3:14 pm



Hi all I'm a long time reader/lurker but this is my first post and guess what its a plea for help.

I have a 1990 GL1500 and my fuel economy has been slowly getting worse I purchased it almost a year ago with 62,000 miles on the clock and it was good for about 34-38mpg. Its now at 68,000 and at last check it was hitting 14-18mpg (from full tank to fuel light in 64miles!) So I checked all fuel lines (all good), vacuum lines (had to replace the line from the manifold as it had perished), cleaned and oiled the K and N air filter, checked the petcock (fine) stripped the carbs, set the floats and cleaned them and fitted new plugs.

I'm now scratching my head as I was hoping it would be something simple like a fuel leak wasting the gas but there was no sign of any leaks and it is still the same since rebuild.

I ride it smoothly keeping the revs low at around a max of 3-3.5k so its not a heavy right fist and it runs great right from start up.

I have seen all the posts on here about poor economy at the low 30s which makes me even more concerned.

Any ideas?



dennislp
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Re: Less than 20mpg!!!!! whats happening

Postby dennislp » Mon Feb 16, 2015 3:29 pm

check choke pistons and petcock for leak into vacuum line . is it running bad or just using fuel. good luck

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roadwanderer2
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Location: sweetwater, Tennessee
Motorcycle: 83 GL1100A aspencade, previously owned, 1981 honda GL500i silverwing interstate, 1974 yamaha xs400, 1974 Honda cb450 twin cam, 1983 honda vt30, 1982 honda 700 shadow, 1972 cb750four, and my first bike, a brand new 1982 honda CM400e. and a new to me 1986 GL1200 aspencade SEi
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Re: Less than 20mpg!!!!! whats happening

Postby roadwanderer2 » Mon Feb 16, 2015 3:43 pm

according to my manual, for the GL1100, the problem can be either a clogged air filter, ignition malfunction, or a faulty accelerator pump. not sure all this applies to the GL1500, but its some places you might want to check. is it backfiring at all? if it is, it could also be a faulty air cutoff valve.

hope this helps ya,

stuart.

crimbo79
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1982 GL500 Silverwing (café style)
1996 ST1100 Pan European

Re: Less than 20mpg!!!!! whats happening

Postby crimbo79 » Mon Feb 16, 2015 3:51 pm

Hey thanks for the replies, it runs fine, pulls happily through the gears all the way to the red line if I need it to. I thought possibly the choke but when I did the carb rebuild I checked the choke system and all seems good, I checked the vacuum pipe on the petcock after riding today and there was no sign of fuel leaking into it.

The accelerator pump seems to be functioning properly and there are no backfires.

Someone at my local garage said the fuel could be leaking into the sump but there is no sign of fuel in the oil.

Chris

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Mh434
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1981 GL1100I
1989 Kawasaki Concours

Re: Less than 20mpg!!!!! whats happening

Postby Mh434 » Mon Feb 16, 2015 4:11 pm

My first thought would be the K&N filter. I've used them before, and always had gas mileage suffer (as opposed to improve, as claimed). Just a thought...

crimbo79
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1982 GL500 Silverwing (café style)
1996 ST1100 Pan European

Re: Less than 20mpg!!!!! whats happening

Postby crimbo79 » Mon Feb 16, 2015 4:29 pm

Could it drop it by that much? its had the K and N fitted since I brought the bike but its worth considering, I will try and pic up an original air filter at the weekend and see if that helps.

dennislp
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Re: Less than 20mpg!!!!! whats happening

Postby dennislp » Mon Feb 16, 2015 4:48 pm

check needle jets and seats in slide they can cause problems

crimbo79
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1982 GL500 Silverwing (café style)
1996 ST1100 Pan European

Re: Less than 20mpg!!!!! whats happening

Postby crimbo79 » Mon Feb 16, 2015 4:57 pm

I think I will be re stripping the carbs again, I can't think where else the problem can be.

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roadwanderer2
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Location: sweetwater, Tennessee
Motorcycle: 83 GL1100A aspencade, previously owned, 1981 honda GL500i silverwing interstate, 1974 yamaha xs400, 1974 Honda cb450 twin cam, 1983 honda vt30, 1982 honda 700 shadow, 1972 cb750four, and my first bike, a brand new 1982 honda CM400e. and a new to me 1986 GL1200 aspencade SEi
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Re: Less than 20mpg!!!!! whats happening

Postby roadwanderer2 » Mon Feb 16, 2015 5:07 pm

I would go back into the carbs, re check the needles for clogging, check the needle seats, and do another carb sync. if your mileage has dropped that considerably, there's something definitely wrong somewhere. have you done a compression test? is it possible you might have a weak cylinder? all vacuum lines good? fuel pump pressure good? clean fuel filter? even though you have good throttle response, there's a problem somewhere.

stuart.

crimbo79
Posts: 62
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1982 GL500 Silverwing (café style)
1996 ST1100 Pan European

Re: Less than 20mpg!!!!! whats happening

Postby crimbo79 » Mon Feb 16, 2015 5:26 pm

I'm waiting for valve stem seals as I'm planning on replacing them all as when I had the head cover off a few days ago I noticed a couple were starting to split. I will do a compression test once they are all replaced, I'm going to check the condition of the valve seats and do some valve grinding/lapping as needed at the same time.

The fuel pump and the vacuum petcock pumps and cuts the fuel off as it shouldo.

Could the timing belts be a cause? could that cause the mpg to drop, I have limited history with the bike so no idea if and when they have been replaced.

Just a side note it cruises smoothly at around 65mph at 3k rpm in O/D

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roadwanderer2
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Location: sweetwater, Tennessee
Motorcycle: 83 GL1100A aspencade, previously owned, 1981 honda GL500i silverwing interstate, 1974 yamaha xs400, 1974 Honda cb450 twin cam, 1983 honda vt30, 1982 honda 700 shadow, 1972 cb750four, and my first bike, a brand new 1982 honda CM400e. and a new to me 1986 GL1200 aspencade SEi
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Re: Less than 20mpg!!!!! whats happening

Postby roadwanderer2 » Mon Feb 16, 2015 5:54 pm

let me do a little research on the timing belts to see if that would have any affect on the fuel mileage and I'll brb. this should only take me a few minutes.

stuart.
Last edited by roadwanderer2 on Mon Feb 16, 2015 6:13 pm, edited 1 time in total.

gman1
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Re: Less than 20mpg!!!!! whats happening

Postby gman1 » Mon Feb 16, 2015 6:11 pm

I would do a vac. test on fuel cutoff valve.If it holds vac. you got me.wish you well.

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roadwanderer2
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Location: sweetwater, Tennessee
Motorcycle: 83 GL1100A aspencade, previously owned, 1981 honda GL500i silverwing interstate, 1974 yamaha xs400, 1974 Honda cb450 twin cam, 1983 honda vt30, 1982 honda 700 shadow, 1972 cb750four, and my first bike, a brand new 1982 honda CM400e. and a new to me 1986 GL1200 aspencade SEi
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Re: Less than 20mpg!!!!! whats happening

Postby roadwanderer2 » Mon Feb 16, 2015 6:21 pm

hey crimbo:

I checked my manual, (GL1100, I don't have a manual for the GL1500's), and it shows nothing about the timing belts having anything to do with poor fuel mileage. everything comes back to the fuel system and the carbs. right at this point, if it were me, I would ask wingadmin his opinion on what and where the problem may be. for all intent and purposes, assuming everything is correct, you should be getting somewhere around 30-40mpg from your bike. sorry I cant be of better help. hope its an easy fix for ya, good luck, but don't hesitate to ask any more questions.

I have a question for you......you said you got the bike used? are you certain that the carb jets that are in it are the correct ones to begin with? the PO might have changed them before you got it and installed or had the wrong ones put in. is this a possibility?

stuart.

dennislp
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Re: Less than 20mpg!!!!! whats happening

Postby dennislp » Mon Feb 16, 2015 6:35 pm

check the air cut valves under fairing right side if the filter rotted it can get in valves and cause rich problems make sure they are cycle

crimbo79
Posts: 62
Joined: Mon Feb 16, 2015 2:43 pm
Location: sussex, uk
Motorcycle: 1990 GL1500 flying banana
Previous
1982 GL500 Silverwing (café style)
1996 ST1100 Pan European

Re: Less than 20mpg!!!!! whats happening

Postby crimbo79 » Mon Feb 16, 2015 6:53 pm

Air cut off valves, why didn't I think of that?! Will add that to the list for the weekend.

1. Air cut off valves.
2. Check jet sizes against original specifications.
3. Check needles and seats.
4. Rebalance carbs.
5. Recheck petcock vacuum.
6. Replace air filter with standard (if I can find one and have the cash)
7. Valve stem seals and valve lapping (if the seals arrive by then)

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ct1500
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Re: Less than 20mpg!!!!! whats happening

Postby ct1500 » Mon Feb 16, 2015 7:20 pm

What is the engine doing that it needs internal work at 68K miles. And valve seals have nothing to do with compression.
This is what I do
Local and need repair help with your 1500, Valkyrie or ST please PM

crimbo79
Posts: 62
Joined: Mon Feb 16, 2015 2:43 pm
Location: sussex, uk
Motorcycle: 1990 GL1500 flying banana
Previous
1982 GL500 Silverwing (café style)
1996 ST1100 Pan European

Re: Less than 20mpg!!!!! whats happening

Postby crimbo79 » Mon Feb 16, 2015 7:29 pm

The engine is running fine, I am just replacing the stem seals as a couple are starting to split which I noticed when I replaced the head cover seal that had a slight oil weep the other week so I thought I would replace them all and whilst the heads are off I'm going to lap the valves if they need it. I'm not doing for the sake of compression.

dennislp
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Re: Less than 20mpg!!!!! whats happening

Postby dennislp » Mon Feb 16, 2015 7:36 pm

check fuel pump pressure could be to high . would be very uncommon but possible

crimbo79
Posts: 62
Joined: Mon Feb 16, 2015 2:43 pm
Location: sussex, uk
Motorcycle: 1990 GL1500 flying banana
Previous
1982 GL500 Silverwing (café style)
1996 ST1100 Pan European

Re: Less than 20mpg!!!!! whats happening

Postby crimbo79 » Mon Feb 16, 2015 7:42 pm

Thanks Dennis, any idea what pressure it should be and how to adjust it if it can be adjusted?

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roadwanderer2
Posts: 4111
Joined: Thu Aug 08, 2013 4:03 am
Location: sweetwater, Tennessee
Motorcycle: 83 GL1100A aspencade, previously owned, 1981 honda GL500i silverwing interstate, 1974 yamaha xs400, 1974 Honda cb450 twin cam, 1983 honda vt30, 1982 honda 700 shadow, 1972 cb750four, and my first bike, a brand new 1982 honda CM400e. and a new to me 1986 GL1200 aspencade SEi
Contact:

Re: Less than 20mpg!!!!! whats happening

Postby roadwanderer2 » Mon Feb 16, 2015 7:56 pm

I mentioned checking the air cut off valve and the fuel pump pressure in an earlier posting..........as for the air filter, you might find one on the uk eBay for a reasonable price. 98% of the parts I get for my GL1100 I get from eBay and I've never had any problems with them. do the research, don't buy the first part you look at, look at ALL of them carefully then make your decision as to which one you want to purchase especially if your going for "add-on goodies".

fuel pump pressure for the 80-83 GL1100 is 0.17 kg/cm2@cranking speed, 0.16kg/cm2@1100rpm and 0.14kg/cm2@5000rpm. not sure if its the same for yours, but this is what my manual states for testing the fuel pump pressure.

im sure there's a "how-to" article in here somewhere on how to test your bike's fuel pump pressure.

stuart.

dennislp
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Re: Less than 20mpg!!!!! whats happening

Postby dennislp » Mon Feb 16, 2015 8:18 pm

the specs just give flow rate but most of the time 2.5 to 3 psi on a elect. pump

dennislp
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Re: Less than 20mpg!!!!! whats happening

Postby dennislp » Mon Feb 16, 2015 8:30 pm

check spark adv with a timing light pull the little cover over crank on timing belt cover a 6cyl eng will still run smooth if off just use a lot more fuel. check vacume at ecm

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robb
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Re: Less than 20mpg!!!!! whats happening

Postby robb » Mon Feb 16, 2015 9:11 pm

from full tank to fuel light in 64miles

Out of curiosity did you refill the tank before determining bad mileage. Could it be a fuel level sensor gone bad.

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virgilmobile
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78 GL1000
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83 GL1100 standard
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Re: Less than 20mpg!!!!! whats happening

Postby virgilmobile » Mon Feb 16, 2015 9:18 pm

When you replaced the plugs,what did the old ones look like.?

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Bluewaterhooker0
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Re: Less than 20mpg!!!!! whats happening

Postby Bluewaterhooker0 » Mon Feb 16, 2015 9:56 pm

Everyone seems to have the mechanical engine aspects covered. How about sticking calipers on the front or rear brakes ? I would think that would show itself in other ways, but then, I would think the engine issues would show with other problems, as well.
Since all seems to run well, I would think possibly the enricher/choke could cause fuel consumption issues. I know, when I spend more time starting my bike than riding, my mileage goes down the tubes. That enricher, apparently really throws the fuel into the carbs. So, I would think, even a slightly active enricher/choke might not effect performance much, but seriously effect MPG.
Since you indicate it used to work properly, I would look to things that could easily go askew.




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