ST1100 Gas Mileage Decreasing

As the title says, over the past few months, my '01 ST1100 gas mileage has decreased from ~49 to ~44 mpg. My riding style hasn't changed and I typically purchase 87 octane from the same 2-3 stations. I average about 50 miles/day, mostly commuting. Bike seems to be running the same (very well), tires are good and inflated. Bike has 42k on it.

Thoughts?



Sorry, can't seem to upload a larger pic of the graph.

Edit: During the course of creating this post, I added and deleted a few images but now the deleted images show up as "Attached Thumbnails" at the bottom. How did this happen and how do I delete the "attachments". I didn't see a way when editing the post.

Re: ST11 Gas Mileage Decreasing

My 01' mileage dropped off like that and a carb sync restored it to the usual 50 mpg.

Jim

Re: ST11 Gas Mileage Decreasing

Gas station change to 10% ethanol?

Re: ST11 Gas Mileage Decreasing

I gained 4 mpg changing plugs out........it had been awhile oops

Re: ST11 Gas Mileage Decreasing

Balance the carbs and make sure the brakes aren't dragging,run some seafoam through her as well.

Re: ST11 Gas Mileage Decreasing

paulcb said:

how do I delete the "attachments"

Click to expand...

To get rid of the attachments:
Edit the original post.
Go advanced.
Open manage attachments.
Scroll down and you'll find all the attachments listed with a remove button.

HTH,
Mark

Re: ST11 Gas Mileage Decreasing

Torn carb diaphragms will cause a drop in mpg.
I think I have read that a failing vacuum cutoff will too.
I'd route around the cutoff and see if that changes the mpg...

Mark

Re: ST11 Gas Mileage Decreasing

Talking about balancing / syncing the carbs, at what RPM should that be done at ??

Re: ST11 Gas Mileage Decreasing

Mark said:

To get rid of the attachments:
Edit the original post.
Go advanced.
Open manage attachments.
Scroll down and you'll find all the attachments listed with a remove button.

HTH,
Mark

Click to expand...

Thank you Mark.

Re: ST11 Gas Mileage Decreasing

John OoSTerhuis said:

Gas station change to 10% ethanol?

Click to expand...

Maybe? If so, wouldn't I see a more digital drop as opposed to a slow degradation?

Re: ST11 Gas Mileage Decreasing

Jim Van said:

Talking about balancing / syncing the carbs, at what RPM should that be done at ??

Click to expand...

idle.

That's the point where the butterfly valves are fully closed, so adjusting their position in very small amounts with the adjustment screws will balance out the vacuum levels in the 4 cylinders. Once the butterflys are open at higher RPMs, then any small differences are pretty much negligible.

Re: ST11 Gas Mileage Decreasing

Jim Van said:

Talking about balancing / syncing the carbs, at what RPM should that be done at ??

Click to expand...

At lowest RPM it'll run smoothly(6-800rpm)........done WITH all intake and airbox in place as it is normally ridden. Using a flow meter on the individual intake snorkels is NOT a carb sync, or even close

Re: ST11 Gas Mileage Decreasing

My guess on the lower mileage may simply be the air temperature? I've never been as specific as to graph my mileage, but I know the mileage drops with colder temperatures. Other factors most directly associated with reduced mileage would be how "spirited" you ride. Also if you did longer distance riding earlier, and more stop and go later, that would be quite influential with the end results.

Re: ST11 Gas Mileage Decreasing

Also a stuck choke/enricher actuation/cable comes to mind...

Re: ST11 Gas Mileage Decreasing

Well, I've not had time to do anything other than add some Seafoam today. I'll run a couple tanks through and see how it goes. Next step would be a carb sync.

Thanks for all the replies.

Re: ST11 Gas Mileage Decreasing

Brant said:

At lowest RPM it'll run smoothly(6-800rpm)........done WITH all intake and airbox in place as it is normally ridden. Using a flow meter on the individual intake snorkels is NOT a carb sync, or even close

Click to expand...

What is this "flow meter?" I've always used carb sticks.

Re: ST11 Gas Mileage Decreasing

figured a menmer that uses one would chime in. It's a flow meter set atop the velocity stack that measures vacuum Hg. Imagine no problem with the accuracy, but these bikes, and for the most part all multi-carbed bikes, the sync and idle mixtures are done like it is ridden, in other words with all intake in place. Now on the ST 11's, that makes it a real PITA accessing mixture screws and a bit more difficult accessing the sync screws. I watched a Honda tech friend of mine do my ST some eight years ago. He was specificly factory trained on the ST's, and he had his share of bad language through the sync/mixture adj. on mine. Aside from the frustration, he happens to be annal maticulate till he was satisfied. I personally use merc stixs on my other notorious classic muscle bike, but back then, was unfamiliar with the process on the Steed. Could not of learned the process from a better tech as he showed that during cool down wait(cannot have a proper idle mixture when cooling fan comes on as it creates electrical load on alt. pulling additional load on motor), to blip throttle several times to seat screw threads/stops on sync screws. Re-start and re-adjust sync. Repeat process a few times till merc. stabilizes across all four the same and stays that way.

On a related note, I just ordered the MorganCarbTune to take the place of my merc. stixs, as it uses stainless slides, so no spill't merc. as sources for mercury are becoming scarce.

Re: ST11 Gas Mileage Decreasing

OK, I'll chime in. I've used a Flowmeter to sync my carbs. It is simple and works very well. My bike runs smooth, no vibrations, nada. Great mileage too. There is no difficulty accessing the three sync screws at all, if one has a long handled screwdriver and a flashlight and know where to look. As for the pilot screws (mixture) those are factory set and shouldn't be touched anyway, unless you are overhauling the carbs. You also need a special tool for them.

So, you can be "annal maticulate", whatever that might mean, and spend a couple of hours watching mercury dancing in tubes, or you could employ a Flowmeter and have the job buttoned up in about 10 minutes.

Re: ST11 Gas Mileage Decreasing

Brant said:

as sources for mercury are becoming scarce.

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Do you know of any, if so let me know who they are.

I kicked over my CarbStix 8-10 years ago and couldn't find any replacement mercury for it. If I could get my hands on a little vial of it I'd buy it.

Re: ST11 Gas Mileage Decreasing

Hi Bush
Factory fuel mixture settings are NOT real world applications. With that said, carb sync IS affected by fuel mixtures. That has to set to an overall best for your location.....then sync the four carbs together. Double check the fuel mix setting and re-sync again. Any way you cut it, that IS proper multi carb tuning procedure.

Hi dwalby,
Haven't come across any recently. Guess you could look for some old thermometers and re-purpose the merc. out of them. Know others that have done that. My option, so I don't have to deal with that in the future was to order the MorganCarbTune. A good friend and factory trained on these and many other scoots that went off starting his own shop a couple yrs. back(and a following that has had him swamped since) has a substantual supply of mercury, just no stixs to put it in. When the MorganCarbTune comes in, gonna just donate my MotionPro merc. stixs to him as he's had more carb sync situations come up than expected. Plus' he has a decent supply of merc. if it were to spill.