Gas Mileage 81 Xj550 Seca?

I am currently restoring an 81 Yamaha xj550 Seca. It's in mediocre shape but is still able to turn on and ride...with a little finesse. Anyway, I recently filled the tank and at almost 45 miles the fuel gauge is already at half empty. It's only been in city driving. I'm curious of other Seca 550 owners gas mileage. Have you found a way to improve it? Thanks. Josh

 

First question , are you running pods? Is jetting stock or been opened up to larger jets? This also goes down to riding style can effect this . The other variable is the gauge maybe off , when you fill up tank most of us don't fill to the brim anyway ( think thermal expansion on a hot day, will leak fuel out cap vent) so it may say full . Actually 45 mpg is about normal , I used to own a Buell Blast 500 thumper was supposed to get 70 mpg but only had 2.8 gallon tank and no gauge you rode till it sputtered and then switched to reserve. Most of the bikes I've owned have never had a fuel gauge. I think the 550 has 3.5 gallon tank as I recall now that i think about it.

 

Thanks Jetfixer. I may have not been clear but I didn't mean I'm running 45mpg. I mean I have only driven 45 miles total and the tank is half empty...according to the fuel gauge. I'm not using pods and as far as I know all the jetting is stock. The tank is a 3.9 gallon tank. I rode the bike once until it ran out of fuel and if I recall correctly I got a total of 96 miles....all city driving. It just seems to me that that is incredibly low.

 

The fuel gauge says half a tank, but is the tank actually at half? The Seca tank is 4.2 gallons, with the last .9 gallons being considered reserve. My Seca gets about 43 city and between 50-55 hwy, but I ride on the slow side. I ignore the gas gauge and go by the trip odometer, which gets set to zero whenever the tank gets filled. You'll get an idea of your mpg after a few tankfulls of mixed driving.

 

your 550 seca should get 45 to 50 mpg. your tank holds 4.2 gallons with .9 reserve.
if your petcock is set to run you should get 150 miles before switching to reserve. then you will have about 40 miles of fuel left.
you can never run all the fuel out of the tank.
do not rely on fuel guage to be accurate use trip meter to get a feel for the guage indicator.
when you got 96 miles how much gas did you need to fill tank? and by ran out of fuel you meen bike stopped running?

the gas milage comes from 6th gear and rolling. if you stop a lot in traffic or never get to the 5th or 6th gear range in the city your gas milage will suck.
have you color tuned and synced the carbs?

what rpms are you shifting at?

what do your spark plugs look like?

 

I've been regularly getting to around 130 miles, then putting 2.5 gallons in the tank. Why? Because my fuel gauge says nearly empty at that point. I probably worry too much.

 

between 147 and 150 miles my 550 starts the sputter stumble to remind me to go to reserve

 

Talking from experience here, make sure the choke is operating properly. If it's not, your fuel mileage will drop and the excess gas will do damage to the motor.

 

Thank you. I'm actually in the process of doing a carb clean and noticed my choke plungers were not functioning very well so I'll be very aware of that.

 

Not sure what rpm I'm shifting at maybe somewhere between 4k and 5k. I try to keep the bike below 4ooo when I commute and avoid highways. Having said all this, I really don't know.l

 

Thanks everyone for your replies. I decided to do a carb clean just to get the experience of doing one. I noticed that the previous owner replaced the original 112.5 main jets with 115's. What's the purpose of putting bigger jets on a bike? It's weird because when I compared the size between 112.5 and 115 to the naked eye they look virtually the same. I know some people do this to accommodate a different exhaust and the mufflers on my particular XJ550 Seca are not the original. I also know some people re-jet to accommodate higher altitudes and the previous owner did live at a higher altitude. I currently live at sea level.

 

Jets may look the same , but these bikes were jetted slightly lean for mpg and EPA purposes , larger jets can be used to compensate for a free flowing exhaust ,but this can effect mpg slightly . If your choke plungers are not closing fully then yes this can cause more fuel consumption. Plug color can tell you this , if plugs are black and sooty looking ...rich...white...lean ...if plugs are brown this is ideal . Carefully remove your mixture screws make sure they are not damaged and check the condition of the small O ring .

 

Are you saying to keep the 115's or should I go back to the 112.5?

 

I was running 124 mains in my 750 Seca , switched back to 120 ...ran better and gas mileage was better...so you could try it.

 

The gas gauge on the Seca 550 is a fourm of entertainment while riding. Keep an eye on the trip meter.

 

mikuni jets sizes are a measurement of the amount of fuel that flows through it.


it is not a drill size like the hatachi carbs

 

Ha! It is kind of cool that it turns on. I actually had to repair mine. Interesting piece of equipment.

 

Guys, I just rebuilt my carbs and it took me two whole days!!!!!! Does anybody have advice on how to get the rear carburetor boots back on. Those things are a bitch. The front the carbs easily slipped into the front intake manifold but those rear boots are no joke. Any help would be gladly appreciated.

 

Easy spray a little wd40 do the inner boots first, roll a corner in first , a 90 degree pitch help guide it into place the other thing pull the top of the airbox remove filter if your had is small enough you can reach in and move the boot into place.

 

When I was doing this, I also heard, use a hair-dryer to warm them up. That did help with softening them and made it a little easier. I did have my daughter reach way into the tight part of the airbox while I worked on the carb-side.

 

This may be very off topic but it sounds like you have all original air box? I am currently rebuilding a 1981 550 Seca and unfortunately I am missing the air box cover. So very hesitantly I’ve decided to fiberglass one since it’s nearly impossible to find one to buy. The problem I’m having is that I have no idea what this thing looks like. I really wanted to know what the inside looks like so I can make it work with a stock filter. If you could post some pictures of it I would really appreciate it!

 

the seca cover and maxim cover are the same part
this link lists ehe bikes you can use a cover from

https://www.partzilla.com/product/y...?ref=2bf15fd226c61243fdc51998ec8be809aa681a10

 

I am so sorry I did not respond to this earlier. I will try and get to it tomorrow.

 

Thank you so much

 

So, I took the carbs out and everything actually seemed fine. Only bad part was the rust like substance collected at the bottom of the float bowls. But all the orifices were clear and what not. I put them back on, bike runs. I was nearly empty in the tank so I put 1.5 gallons of premium in there. After a couple days of riding the tank started to sputter and the odometer reads that I went thirty seven miles. Does this sound right to anyone?

 

I don't recall you mentioning, but have you serviced the petcock? Do you know if the screens are clean? I'm just thinking of stuff that would prevent you from going the 125-150 on a tank (before reserve).

On another note, I always put 87 or whatever the lower octane gas is. From what I can tell, these engines won't benefit from high octane.

 

Yes, I did actually service the petcock. Works fine. A friend of mine said you might need new clutch plates. Faulty clutch plates require more gas I guess so the engine isn't running as well. It's either that or I am running extremely rich and need to tune the carbs better.

 

You might know if the clutch is slipping. I'm not sure if there are other failure modes that degrade performance.
About running rich, I would pull the plugs, 1 at a time. If dark, adjust mixture screw 1/4 turn at a time. Less if it seems closer to the right tan/brown color. I did this a lot when I first got my carbs back in.

 

your tank holds 4.2 gallons with .9 reserve. if you are using an oem petcock and it was set to run sputtering at 37 miles is about right.

1.5 gallons into an empty tank would have given you around .6 gallon to run with petcock on run. because your reserve is .9 gallon. did you turn the petcock to reserve ?

with out knowing how much fuel was actualy in tank above statment is a rough guess.

so go to the gas station and FILL UP the tank to bottom of filler neck inside the tank. Ride 50 miles and fill the tank again. this is the only way to determine your fuel mileage.

 

Yes, I did turn to reserve and then I turned it too PRI and I still couldn't get anything. It pretty much wouldn't start after 37 miles. I walked it to the gas station and put another gallon in there and bike started instantaneously.

 

it sounds like your petcock is not working correctly

 

I think I'm getting around about 45 miles to an imperial gallon with my Radian motor'd 550 seca which is about 36/37 to a US.
Not sure how that helps but it's another reference point.

 

Joshua, are you still going to get some pictures of the air box cover?

 

Awesome thanks

 

https://postimg.cc/gallery/1tbjzd61m/

 

Sorry about that. Looks like XJ550h beat me to it.