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56.7 miles to the Tank???

  • Thread starter Thread starter Rockgs1000
  • Start date Start date
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Rockgs1000

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I have vacuum tuned the carbs and set for idle. I have yet to do the fuel mixture screw plug color set. But should have gotten way better fuel mileage than that. I checked for leaks into the crank case only oil in there. No drips from air filtersor any other engine leaks. Do they get that bad of mileage? 1979 gs1000l with VM carbs
 
They do not. Expect to get somewhere in the neighborhood of 35~40 mpg out of it.
 
I figured I have problems asking where I should start looking. My vacuum tune is straight across the board the two inside maybe a fraction lower in vacuum. The idle set is at around 1000 to 1200 don't have an analog tach but digital and doesn't have tick marks that low. Bike doesn't flood nor hard to start.
 
Check the valves adjustment, recheck the float hts, recheck the timing, be sure to be using at least as BS8E plug..hotter one may be needed in your bike, set the bottom ( pilot screws) at 3/4 out, set the side ( Mixture Screws) at 1 3/4 . I would also remove the pilots and the needle jets and repoke all the holes and flush with carb spray. Pay attention to the little hole at the tips of the pilot jets also..be sure its clear.

If the bike is stock, set the clips on the needles in the 3rd ( center ) groove. Check to see what size main and pilot jets you have.
 
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Click on the STICKY at the top of this section and look for the stock jetting sizes for the bike.
 
How do your plugs look?
With mileage that bad I would be think they should be heavily carboned up.
 
Check the carb vent tubes. If they are routed incorrectly into the airstream or below the float level, fuel can be sucked out.
 
Ok I have 257 miles on my valve adjustment, brand new bs8e plugs, I will check the pilot and air mixture screws to their settings. I haven't checked the timing will do that as well and check my plugs tonight . My carbs are vented to air with no vacuum lines on the nipples. The jets are stock both pilot and main with the clip set on 3rd one down. Carbs been rebuilt with new O-rings , no vacuum leaks around boots. Here is a thought wen I went to do the vacuum tune on the carbs the boots I have already have the line nipples on them, when I took the caps off there was a very small amount of fuel in the bottom of the cap since the nipples are on the bottom of the boot.
 
Yes theres fuel in them because its sucking too much raw fuel and its settling in the tubes. I would take the carbs off and recheck everything twice.

Take some tubing and blow ( with your mouth ) some air into the vents on 2 and 4. Some fuel may come out the throats so dont worry about that. Thing is to physically verify that the vents are actually allowing atmosphere air to get to the bowls.
 
Ok will check all again on the settings and jet numbers as well as clip height and plug color. Reset the fuel pilot screw and air pilot and get back most likely Thursday since that's my next day off to check it all . Thanks for the help
 
You are using about three times the normal amount of fuel, you don't have a minor tuning issue, you have fuel DUMPING out of or through the bike someplace, at least some of the time. One possibility is the petcock diaphragm is holed, all that missing fuel is being sucked into the #3 cylinder, this is enough extra fuel to ruin the rings quickly. Check the plug on #3, if it's much richer than the others this could be it. Another possibility is a float sticking at times, letting the float bowl overflow which you would not notice while you are riding. I have had both of these problems at times, they can waste a LOT of fuel.

There are numerous other possibilities, these are just the ones that popped into my head.
 
I am using the dreaded 80 year tank and pet cock may very well be right on the #3 carb getting it all. I am not getting any white smoke out the exhaust though
 
White or bluish white is an oil indication...greyish or nearly black is a over rich look..gun the throttle and watch the pipes..see if they belch thick blackish smoke.
 
Ok started it up and twisted the throttle, blackish grey smoke rolled out. So I took the vacuum off the third carb and sucked on it to create the vacuum and got no gas coming from the vacuum hose that would go into the third carb. None would, Nextel I checked the setting on the fuel pilot screw it was at 2.5 out on all carbs I readjusted to 3/4 out. Thing ran much different and responded much quicker, also repeated the throttle twist and got no smoke from the exhaust. It's raining cats and dogs right now but will check plugs when it stops.
 
Ok...Now set the side mixture screws at around 1 3/4 to 2 out. These are good baseline settings for the pilot and mixture screws. By "fuel pilot screws" you do mean the ones on the bottom...right? Yes those should be at 3/4 to 7/8 out.

Timing will also effect gas mileage ..also so will tire pressures. Check both.

If you have a spark plug cleaner, clean the chit out of them and then see how well the milage increases. bet youll now be around 35 MPG or so.


I have the General Pneumatics spark plug cleaner...cheap and very useful.

http://www.harborfreight.com/pneumatic-spark-plug-cleaner-32860.html
 
Thanks will ha e the wife pick one up for me, yes I meant the bottom screws I turned to 3/4 . I have already adjusted for idle on the side screws but never hurts to try it again.
 
Remember the saying..you tune VMs from the bottom up..In other words, to richen it up a little from idle to about 1/4 throttle you will open the pilot screws a little..1/8 turns and retest the performance is the general rule of thumb. Once you get it really good you can fine tune the mixture with the side mixture screws.
 
Thanks for the tip first time with an old bike didn't know how to tune the carbs for adjustment . I read some disassemble and assemble post and bass cliff not sure where I got the 2.5 turns out on bottom screw but that's where I had em.
 
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