Poor Fuel Economy... 26mpg! HELP!

I've had my bike, 97 VFR750F, for a month and a day now with 350 miles since, it's been a blast! However I've been going through as much gas on the bike as I do in my car (granted it's not as fun )! I'm a big guy at 280lbs, so my weight could be part of the cause, but the previous owner was taller and maybe just as heavy as me. However, he said he was averaging 35mpgs. I've been averaging about 25-27mpgs!!!! Yesterday, my gauge was getting near the E, my tripmeter read 112mi (I reset it every fill up), I filled 4.28 gallons... 26MPG.

Most of my riding during the week is about 2 miles to work, with me shifting at about 3.5k-4K rpms. When I'm steadily going I'm riding in 4th or 5th gear at about 3500-3250krpm (~35mph). When I'm not riding to work, it's just for fun with friends. Admittedly, it's not as laid back as my riding to work... at times I only accelerate to about 10-15mph past the posted speed.

This is what I gather to be done by the previous owner of the bike:
Racetech front springs with gold valves
Rear shock set to a stiffer setting
Front sprocket down a tooth (OEM sprocket given to me)
Airfilter is K&N lifetime filter
The jets where returned to stock and a stock pipe was placed on the bike (Feb08)
Plugs are new this year (Feb08)
Antifreeze is fresh this year
Castrol Synthetic 5-40 (filter is new at time of sale)
Newer Pirelli Diablo tires (F:36psi, B:42psi)
SS brake lines and HH EBC Pads and new fluid.
Seargant seat

The bike starts right up and have no trouble with the bike while running. The choke (enrichening circuit?) works but only idles up to about 1750-2000rpm when I start the bike initially. I figured it was something worth mentioning since all of the previous bikes that I have owned (83 Honda Shadow 750, 96 Honda Manga & 88 Honda Hawk GT) idled up much higher with the choke fully activated. I don't have to use the choke to start the bike (yet?), but I do it anyway (on cool mornings) for good measure.

Are these MPG's to be expected with the mods above? Should I replace the spark plugs and clean the air filter? What else should I check? Any input would be greatly appreciated!

 

Hi,
If the bike ever sat without being ridden for a few months you could have some very clogged jets. I let my '93 sit for a while (3 months), saving the tires for a riding school. When it finally came time to go I was getting about 25mpg on the highway. I used up a bunch of gas that weekend!
No amount of carb cleaner helped my '93, but it may help in your case. I also think you're shifting a little early, but that's just me.
For what it's worth, my mpg on my '95 is about 42 in town, close to 50 on the highway.
Cheers! :smile:
Craig

 

I'm doing about 35/gallon too.

 

Try trading out that front sprocket. If jets are stock and you're not down on power, I'd suspect the gearing you mentioned. I have a 97 and I don't baby it and I've got a Staintune (sp) pipe and I get between 37 and 40 and I weigh 240 at 6'-6".

 

I sure do hope it's not a leak!!! That would really suck. I dont really smell any gas when coming into the garage after leaving it there overnight. Hopefully nothing comes up and I can get into the bike tonight to check the plugs and the filter.

I'm not sure if the bike sat... based on the title the bike was always owned by one owner, who owned 12 other bikes!! It very well may have if he really had 12 bikes (10 were already sold when I wen to pick up the VFR). Do you think running seafoam through the carbs will help clear the carbs up? I assume it didn't sit very long since I've had not trouble with the bike starting or idling. I havent experienced any hesitation either.

No the power delivery is great, the bike pulls hard after about 7krpm. It's fine at low speed.

... not me

The PO said that he was averaging 35mpg with the current sprocket and about 40mpg with the OEM sprocket, but changing it up can't hurt either way.


So to do list for this weekend,
-Check plugs
-Clean filter
-Swap front sprocket
-Check for leaks!
-Try seafoam in the tank?

 

Carbs could be leaking, due to a poor seal, or maybe the float valves are stuck, causing wasted gas to run down the overflow tube.

Sounds like it has had carb work. Pull the left fairing off the bike, and run the bike. You might notice leaking in the carbs or floats themselves. If new seals and orings were not used when sealing them back up, it would cause a small leak. You should be able to smell gas though, just by poking your nose in there.

Also with the bike still running, look on the ground behind the front tire. Might see fuel spots.

I get anywhere between 35 and 48 mpg, depending on how I ride, and I weigh about 220.

 

I also suspec that some carb work is in order. Your comment about the bike not "idling" above 1750 when the choke is engaged is kind of telling, since my '96 will sing happily at 3500 once she's warmed up fully with the choke on.

I have stock jets, a TBR pipe, and a heavy throttle hand, and I usually get around 40 mpg. 50 mpg is totally attainable if you are gentle.

 

This is exactly what the owner told me when I asked him if he had ever done anything to the carbs:
"Carburetors where jetted fat for a aftermarket pipe and a Factory needle jet was added. This last February the jets where returned to stock and a stock pipe was placed on the bike."

I will remove the cover tonight and look/smell for leaks... hopefully this isn't the case... removing those 4 carbs doesn't look fun. Removing the 2 carbs from my v-twin cruiser was a PITA, hopefully things have changed since 1983!

Well that's the funny thing about the choke. Initially it will have a low idle and then over time it will rise to over 3.5k rpm. I'm not sure if that is normal for this bike. The Magna that I had (same engine pretty much) also had a touchy choke, but that bike definitely needed carb work... never got that done though, since it got totaled before I could.

Worst case scenarion I will need to regasket the carbs, clean out the choke system and/or rejet the carbs? looks like I better print out the service manual for the bike just in case!

 

I'm getting about 42 out of my 92. It's not idling the greatest so i'm guessing my carbs need some attention.

But i'm not doing anything with it till it's too cold or snowy to ride.

 

I changed the plugs and cleaned the K&N air filter as best as I could with the air compressor. The old plugs looked okay, they were gapped at .034... as were the new ones. I did find some oil on the plugs, I'll be ordering new valve cover gaskets ASAP.

I did run the bike and could not see or smell any leaks. There is a rubber looking gasket on one of the carburators that does not seem to be seating properly. It'll be raining next Monday so hopefully I can pull the carbs off to clean them and reseat the gaskets.

I have yet to change the front sprocket... maybe I'll do that tomorrow!

 

Reading your posts I am assuming that the PO installed a Factory Pro needle in the carbs with the aftermarket pipe. If the needles are still in the carbs that very well could be your problem. I did some mods to the Triumph this spring and had to rejet with a larger main jet and installed a Factory Pro needle (it is tapered more than stock). My fuel economy was poor (31). Reinstalled the stock needles and fuel economy jumped to mid 40's with more power. Check it out, this may be your issue......

 

I agree with MarkBartels. You might also want to check when the last time the valves where checked and the carbs sync.

cheers

 

Opps missed this one, Sorry late to the party I see.
Okay here's the deal, but first is this a 49 state model? Ca. ones have a bunch of emission stuff that could play into this. Not sure but anything that messes with the carbs has me going WTF. ok on a side note but shouldn't make that much difference stock gearing will give you the best bang, But I'm thinking the choke system is off, best take it to a service tech. Mine will if left alone will on choke climb past 5Krpms in only a couple minutes and other VFRs that are in tune will also, not that this plays into the fuel use, just is curious as to why some will and won't here.
Ok try this, and if you don't believe me ask Powder what he thinks Try premium fuel and go full synthetic Amsoil. I have a KN with a Staintune snubber out with stock carbs. I have had it on the dyno too to make sure she's as good as it can get as I was looking for more HP and thought for sure we could tune the carbs even more, Nope. oh if someone has messed with the carbs, god knows whats a sque, as Noted by Mike Valsco aka probably the best VFR tuner period. He states it would be really hard to get mine running any better. On a side note from Mike, If I want more Zip he says run higher octane fuel. Race gas would bring in 3-5 Hps. and todays carb kits are a joke, less an HRC one from the days.
I have the stock 16 tooth counter shaft sprocket, I'll see any where from 48-52 on a regular bases, I even got 59 on an all freeway 120 mile trip and I've seen 38 on a blast on my favorite mountain rd too. but over all it's in the 48-52 range all the time. So, If it were me I'd take it in, something is a miss.

 

Hi, Sorry to hear about the trouble, But dont for get to oil the K&N filter and where was the oil on the plugs because that may not be a valve cover.

 

I was using premium fuel since I got the bike... but switched to using regular after a month of 26mpg. The PO was using Castrol Synthetic 5w-40. I was going to plan on using Mobil1 Synthetic (motorcycle specific) 10w-40 oil. I did not oil the air filter... I didn't know you had to. I will look for instructions to properly clean the filter. I do not know if this is a CA model, I assume not since the PO was the original owner and the owners manual doesn’t state anything about it being a CA model.

I like the way power is delivered currently with the smaller front sprocket, will there be much difference if/when I change to the oem sprocket? I was going to use the old sprocket but I may get new sprockets and chain since I'm nearing the chains limit… I’ll look into doing this at the beginning of next season.

The choke is more than likely a problem since it takes a while before the bike idle will increase over 2500rpm. I have downloaded the oem service manual but I can’t find where they cover on cleaning or adjusting the choke. Maybe the clymers manual covers this information?

I hope to be able to pull the carbs off soon. Should I wait until I can get the oem needle jets? Anybody know the part numbers?

I do want to have the carbs synched once I have the MPG problem sorted, but no local shop will work on a bike that is over 10yrs old.

Most of the residual oil was below the lower part of the threads near the sealing washer. Here are some pics of the plugs, you can still make out where the oil was:
FR plug --- FL plug
RR plug --- RL plug

What else could cause oil to be on the plugs?

 

Hmm, something tells me it's not oil? more like over rich, just guessing of coarse, but with the symptoms your describing I'm leaning on an over rich condition. now as far as what is causing this? Curious, what makes you believe you have different needles? as most jet kits where just that jets.

 

well i must admit I'm a newb when it comes to carburated engines. I was under the impression that needle jets were what helped inject more fuel into the carburators- causing a rich condition? What would you suggest I order to set the carbs back to stock?

 

This is going to be tricky, as one your not sure in whats been done if anything. so to really know, one, you'd have to talk to the PO and find out for sure whats what, second, if not the next step is looking at the carbs an get numbers. then you'd know what was next. I'm not seeing any part# in the service manual and it looks like the needles can be removed from the top of the carb from the vacuum can. Best get your hands on a 4th gen Honda service manual if you are going to tackle this one, then from there you'll have to find a Honda tech that knows what he's talking about and go the distance in finding the numbers so they can tell you what you are looking for to tell if it's stock or not. I'm thinking it is stock as jet kits even back then weren't all that popular, but still, to be sure there's some investigating to be done. Hmm any one have a spare set of carbs for the fellow? Might be easier just to replace with a set that one knows they haven't been messed with.