terrible gas milage


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sickradsean
Posts: 5
Joined: Tue May 08, 2018 10:28 pm
Location: portland, or
Motorcycle: 1977 GL1000

terrible gas milage

Post by sickradsean » Tue May 08, 2018 10:45 pm



hello all, new to this forum. i have a 1977 GL1000 with 50k miles. i had been having a problem with the carbs flooding (even to the point of vapor lock) last year and had them serviced by the local guy. after forever (4 months) i was told that mine were shot (which i had been told by another mechanic who is a former honda mechanic and i dont know why i didnt go to him in the first place) so instead of being able to rebuild them he swapped them with a set. this got the bike up and running again. i recently took my bike out of the garage and changed the oil, filter, and gas filter, filled up (topped off with sea foam) and rode all this week.

all this long story gets to my point. I RODE 55 MILES ON 3.75 GALLONS OF GAS!! that should be 112 miles!

i have noticed that carb #4 weeps a little (not a full "leak" but some discharge from the seal)

i try to run the carbs dry when i stop my bike (takes a while as im assuming gas is pouring into those things)

and its not the petcock because when i changed the fuel filter and disconnected the hose it did not drip on "off".

any ideas are welcome, i understand that this is a 40+ yr old bike and its not gonna run tops (i have an '80 CB750 that gets double this milage) but this is insane. thanks.



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smittyboy734
Posts: 31
Joined: Tue Apr 12, 2016 7:21 am
Location: trenton,mi.usa
Motorcycle: 1978 gl1000..owner 70 cl70 .previously owned 81cb750k,76 cb500T ,78 kz650,71 H1500

Re: terrible gas milage

Post by smittyboy734 » Wed May 09, 2018 6:12 am

hi there and welcome,you said you run the carbs dry when finished riding,yes it does take a long time to empty the carbs four carbs full of gas will run awhile just idling,did you pull your spark plugs after riding to see how the were firing,and did you have the carbs synced after you replaced them

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ekvh
Posts: 296
Joined: Thu Apr 29, 2010 9:52 am
Location: Grand Forks, ND
Motorcycle: 1977 gl1000

Re: terrible gas milage

Post by ekvh » Wed May 09, 2018 8:34 am

Either leaky float valves, leaky plenum gasket, or leaking carb-to-plenum seals. Failure to remedy can lead to a bent rod. Ask me how I know.

sickradsean
Posts: 5
Joined: Tue May 08, 2018 10:28 pm
Location: portland, or
Motorcycle: 1977 GL1000

Re: terrible gas milage

Post by sickradsean » Wed May 09, 2018 1:04 pm

smittyboy734 wrote:
Wed May 09, 2018 6:12 am
hi there and welcome,you said you run the carbs dry when finished riding,yes it does take a long time to empty the carbs four carbs full of gas will run awhile just idling,did you pull your spark plugs after riding to see how the were firing,and did you have the carbs synced after you replaced them
i dont run them completely dry, just a few extra mins with the petcock off so that they wont flood when im stqrting it. as far as i know the carbs were synched when they were recently put on. i can check the plugs next time i take it out. im looking for them to be wet ya?

sickradsean
Posts: 5
Joined: Tue May 08, 2018 10:28 pm
Location: portland, or
Motorcycle: 1977 GL1000

Re: terrible gas milage

Post by sickradsean » Wed May 09, 2018 1:05 pm

ekvh wrote:
Wed May 09, 2018 8:34 am
Either leaky float valves, leaky plenum gasket, or leaking carb-to-plenum seals. Failure to remedy can lead to a bent rod. Ask me how I know.
gonna assume one of those got you a bent rod. haha. what would be the best way to go about checking those? just break down the carbs?

kndw
Posts: 58
Joined: Sat Jun 19, 2010 2:56 am
Location: Driebergen, Utrecht
Motorcycle: 1976 GL1000 Plempbak

Re: terrible gas milage

Post by kndw » Wed May 09, 2018 1:49 pm

Before you pull the carbs, you can open the top tank lid, take out the basket, unscrew the top lid of the air filter housing, and peer inside when you start the bike. If there is an internal leak due to either of the mentioned seals failing or failing float valves, you will see gas pooling in the plenum. I will also smell like you're hanging over a bucket of fuel.
It is likely one of the above things. To fix it, you will need to take the carburettors out, open them up, clean them thoroughly and change the seals. Maybe your mechanic did a sloppy job. It sin't too hard to do, and there is plenty of info on how to do that available online. Get the parts from Randakk. This is simply the best quality you can get.

sickradsean
Posts: 5
Joined: Tue May 08, 2018 10:28 pm
Location: portland, or
Motorcycle: 1977 GL1000

Re: terrible gas milage

Post by sickradsean » Tue May 22, 2018 1:07 pm

kndw wrote:
Wed May 09, 2018 1:49 pm
Before you pull the carbs, you can open the top tank lid, take out the basket, unscrew the top lid of the air filter housing, and peer inside when you start the bike. If there is an internal leak due to either of the mentioned seals failing or failing float valves, you will see gas pooling in the plenum. I will also smell like you're hanging over a bucket of fuel.
It is likely one of the above things. To fix it, you will need to take the carburettors out, open them up, clean them thoroughly and change the seals. Maybe your mechanic did a sloppy job. It sin't too hard to do, and there is plenty of info on how to do that available online. Get the parts from Randakk. This is simply the best quality you can get.
i opened everything up when i started it and the plenum below the airbox was dry the whole time! i did notice a massive hole in the airbox itself tho, seems to be some sort of home made intake? so where to now?



kndw
Posts: 58
Joined: Sat Jun 19, 2010 2:56 am
Location: Driebergen, Utrecht
Motorcycle: 1976 GL1000 Plempbak

Re: terrible gas milage

Post by kndw » Tue May 22, 2018 1:53 pm

sickradsean wrote:
Tue May 22, 2018 1:07 pm
kndw wrote:
Wed May 09, 2018 1:49 pm
...
i opened everything up when i started it and the plenum below the airbox was dry the whole time! i did notice a massive hole in the airbox itself tho, seems to be some sort of home made intake? so where to now?IMG_8998.JPG
The hole is where normally the intake is. Seems like somebody cut it off. This is helpful if different coils are installed.

The lack of pooling doesn't exclude the possibility of a leak entirely, but other options are that the timing belts are off a teeth, or maybe ignition timining is off? Tire pressure much too low? Leaking fuel lines? Brakes sticking?

sickradsean
Posts: 5
Joined: Tue May 08, 2018 10:28 pm
Location: portland, or
Motorcycle: 1977 GL1000

Re: terrible gas milage

Post by sickradsean » Tue May 22, 2018 2:36 pm

i replaced the fuel filter recently thinking maybe that would help. all the lines are tight. the only leak i can find externally is a vague weeping off carb #4


and this is only after riding a while.

the timing belts were replaced when i first got the bike (2yrs?) and were done by a guy i trust. i was told the ignition timing was done when the carbs got swapped, but again i dont trust this guys work, so ill keep that in mind. i can check the tire pressure and for brake drag.

another thing ive noticed is that after a while itll idle around 2k (with the choke full off) which im assuming is high, on my 1980 the zone was 1100-1300. is there an idle screw that i can adjust. again on my 750 its under the carbs in the center (but thats a straight 4).

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Fred Camper
Posts: 1293
Joined: Sun Aug 16, 2009 9:15 pm
Location: Metro Detroit, MI
Motorcycle: 1977 GL1000, 1976 LTD GL1000

Re: terrible gas milage

Post by Fred Camper » Tue May 22, 2018 10:17 pm

There is a screw on the right side to adjust idle speed. It does not need a tool, as on mine I can turn it by hand,.

kndw
Posts: 58
Joined: Sat Jun 19, 2010 2:56 am
Location: Driebergen, Utrecht
Motorcycle: 1976 GL1000 Plempbak

Re: terrible gas milage

Post by kndw » Thu May 24, 2018 3:05 am

I also had the problem that the idle rose from ~1100 to 2000+ in somewhat 5 seconds. This turned out to be a sticking slide in one carb, which would apparently slowly convince the other slides to rise a bit too.

Obviously the vague weeping is also bot a good sign.

It won't hurt to check the other things too, but it seems you will have to pull the carbs, clean them ultrasonically and place new gaskets/seals.

When you pull them, also make sure they are the proper type for your bike. Early gl1000's had 32mm carburetors and later ones 31mm The camshafts were also different. I'm not sure about the '77, but if it is supposed to have 31mm and the local guy put on 32mm this will also affect fuel economy



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