Poor Fuel Mileage

[78yamahaman]

I have recently resurrected a 78e and a 79sf. I am getting around 37 mpg on the 78 but on my special I am getting 18. I cant figure it out for life of me. My 78 I even rejetted the carbs and put on pod filters and it has a 4 and 1 header pipe on it. I purchased the morgan carbtune and synched the carbs but the mileage is still very poor. If anyone has any idea I would greatly appreciate it.

[egleaves]

That doesn't sound good. I just went for a nice long ride last weekend and got 38 out of my special, and I'm pretty sure it's a little out of tune.

I don't know what kind of pod's you're running, but I had some trouble with mine blocking the ports on the carbs (throat of pods too small) not too long ago. It made my bike run like crap and fuel mileage suffered as a result.

[psycoreefer]

18 is real bad. Are you sure you don't have a fuel leak somewhere? Maybe running down into the crank case, rather then out onto the ground?

[powerram50]

have you done a compression test?i know my special is way out of tune and i just got it to 30 mpg,i am also very throttle happy.

[dbeardslee]

The best thing I ever did for my bike was redoing the heads. Cleaned, lapped, and adjusted the valves and replaced the leaky stem seals. Also cleaned the intake and exhaust ports. Afterwards it ran much smoother and mileage was improved.

[dbeardslee]

P.S. - A slipping clutch can kill your mileage too.

[jeffe]

Also ,are the brakes dragging?

[78yamahaman]

It might be the breaks. I dont hear any noises like they are hanging up or anything and it seems to be ok. I havent done a compression test yet but it seems like its running solid. I get a gas smell on occasion but I cant find a leak anywhere. I have looked several times. I guess I keep trying and hope I figure something out. I will do a compression test though for sure and maybe tear it down this winter to figure it out. 18 is still better then the 12 my truck gets. Thanks for the help and any more ideas would be apprecitated.

[fredintoon]

Hi 'man,
admittedly the Pumpkin is a sidecar rig and gets the same 28mpg as my Buick but half way to a rally a while back it started to run like crap, needed to have the throttle wide open to get 55mph and the fuel consumption went to an estimated 17mpg.
Turned out that #4 carb was bunged up with crud and the 1100 is a really bad 3 cylinder engine.
My best guess is your carbs are crudded up. After you've cleaned them, try a test run. If it still gobbles gas, pull the pods and try it running open throated. Note that you will be running lean and vulnerable to dust. Choose a damp day and be gentle.

[XSPastor]

That gas smell you are getting from time to time should tell you something. You may have one or more carbs leaking into the airbox or worse - into the crankcase. Check your oil - if the level keeps going up and it keeps getting thinner and smells like gas, you have your answer. I get about 36 in my 81 special.

[trbig]

First off... check your pipes to make sure they are all geting hot by spritzing them with water. Look for an equal "Sizzle" on each one. Second, check your plugs.

The rejetting statement has me concerned about what was done and with what parts.

Also... as egleaves stated. What kind of pod filters do you have? If the rubber boot of the filter goes over the bell of the carb, then narrows down to where the filter kind of slips on that... they aren't worth having and are blocking off your air ports on the intakes.

Keep an eye on your oil level to make sure it isn't increasing.. meaning fuel is going into the crankcase.

Tod

[skids]

A crappy exhaust system will cause that also.

[XSPastor]

You may have one or more carbs leaking into the airbox or worse - into the crankcase.

Oops. I missed the part where he said he had pod filters.

[78yamahaman]

Well its the 78 thats rejetted. The 79 is not and the 79 is the one with the poor mileage. It could very well be crud in the carbs. I dont have and air box on the bike. I have filters from partsnmore.com I have been looking for leaks but I havent seen any yet. The bike runs very strong. Lots of power and no missing or backfires or anything. With the individual filters I dont think gas is going into the crankcase but I aint a genious. Thanks again guys for all the help.

[DiverRay]

Gas CAN get into the crankcase with indy filters!! I would pull the carbs, replace the needle and seats on all four, check the float height, and CLEAN them one more time. Also check the clutch, cause if it slips, the mileage goes down hill FAST.