Poor Fuel Economy... 26mpg! HELP!

Well,...I know that it's been quite awhile since anyone has contributed to Gsus fuel mileage problem, but unfortunately I am in the exact same boat. After searching near and far for over 4 years, I finally found a VFR750F that was 2-1/2 hours from my home. So, I didn't have to ship it from the coastal areas...and was able to ride it home. The bike was immaculate, and 100% stock. Nothing had ever been done to it mod-wise. The 1st & 2nd owners together put a total of 5K on the bike, and the 3rd owner (seller) put 23K miles over the course of 8 years. I bought the bike from him about 3 weeks ago. My trip was 2-1/2 hours total, but after 1-1/4 hours I had already used 2/3rds of the tank. I stopped in Emporia and filled the tank to the brim for the 2nd half of trip. 1-1/4 hours later I was pulling into my hometown, and again I had used 2/3rds of a tank. Calculating both fillups, I got right at 25mpg on both rides. Since then I have run 3 full tanks thru the engine, and got exactly the same results. The bike fires right up with the choke, and idles smoothly after a few minutes. It has plenty of power off the line, with strong acceleration thru out all the gears. First suggestions locally were to check out the air intake filter and routings for possible blockage or obstruction. I removed the tank and filter. It had been changed only 1500 miles previously, and outside of just a little dust it was practically new. Also, the air box housing was completely clean, as well as the snorkel portion that rises out of the front edge of the lid and then curves down in front of the air box housing. No blockage at all. The seller said he rode it to work and back each day, requiring him to refill the tank every 3 days or so. He averaged 45-48 mpg. About 2 years ago, he basically stopped riding the bike, but would go out and startup the bike and let it run until the fan kicked in every 3 to 4 weeks. My gut feeling is that the same fuel sat in the tank for the entire 2 years,....only the gas used in the periodic startups and warmups was being used. I have an awful feeling that this means the carbs are going to have to come off and disassembled for a thorough cleaning, which makes me sick to my stomach. As it is, I overpaid about $500 for the bike since it was literally a 9+ on 1-10 scale. Local shops want between $350-500 to pull the carbs and go thru them. I'd also like to know if running several cans of Seafoam thru the carbs (mixed appropriately in several tanks of gas) might eventually clean out the carbs. Since the bike idles so smoothly, starts up without hesitation and has ample power thru out the entire powerband....that tells me that there is at least fuel flowing thru each of the needles and jets. If fuel can flow thru these small components,...then fuel containing detergents might eventually clean out the residue that has piled up. What about possible stuck floats? Could that be resolved with enough Seafoam moved thru the carbs? With what I paid for the bike, plus insurance for a year and titling/registration.....I really can't afford to drop 3-5 benjamins on carb work. I'm afraid my only option would be to ride the bike locally in the early Spring next year, and then sell it going into the summer. I can't tell you all how bummed I am about this. I've wanted this bike so badly I would dream about it at night. Another issue I have with having the carb work done is in finding a mechanic truly qualified to do the work and get it all back together correctly. For any of us who have looked at how crammed those carbs are on this bike, it's a major puzzle just getting them out and back in,...not to mention the complexity of tearing them apart for cleaning and the reassembling. I wish some of you gurus lived closer to the Kansas City area. Any help would be greatly appreciated. Ron

 

Oh,....btw,...I also looked extensively for a possible gas leak when I had the tank off and air filter media out. Considering the fact that the '93 tank holds 5.02 US gallons...and the average mpg for most VFR riders coming in at 42mpg....a full tank would give about 211 riding miles. Gsus and I are getting right at 25mpg, which equates to a riding max distance of about 125 miles. The difference is roughly 85 lost miles per tank fill. Dividing that by the average mpg of 42, reveals that Gsus and I would have to be leaking about 2.0 gallons of gas out of each tank fill (assuming the "leak" is the culprit). That's a lot of gas to be leaking out of the tank-to-carbs-to-engine setup. With that much fuel loss, we'd both be smelling gas and seeing evidence of gas leakage on the floor of our garages. I read that Gsus had no such smells or evidence, and neither do I. Although my bike is 100% stock with no carb work ever done, I really don't see how an after market sprocket change (other then stock # of teeth) could account for this huge difference in gas mileage. Considering that several members have chimed in with max mileages of approximately 50mpg, Gsus and I are getting half what they are. HALF!!! That's just way too much fuel loss. For those who think I'll need carb work,....and I decided to keep the bike and have the work done.....do any of you know of a qualified mechanic in the Kansas CIty area that could do it properly? Btw,...I forget to mention what else was done 1500 miles ago. I mentioned the air filter was replaced. Also, the spark plugs were, the front and rear sprockets and chain were, both front and rear tires were and the battery. That's probably the biggest reason I couldn't get the seller to budge on his price. I paid $3500 for the bike with 28K miles on it,....and creeping up on 20 years old. I saw a lot of bikes on the east and west coasts that were selling at around $3000, but then I'd have to pay $500-600 to get the bike shipped to me. That being the case, I wanted to get a bike locally that I could actually see and check out rather then buying over the internet. That really paid off for me.....didn't it! :-( Thanks ahead of time for any assistance you all might throw in my direction. My tank is still off the bike if there's anything else you think I should check in that scenario.

 

After looking at other suggestions on this forum, here are some more details. I have only been riding single, and I'm a slender guy at 160 lbs. I've tested the bike for brake drag, and it rolls fairly easy considering it's a 500 lbs bike. I certainly don't feel any drag or hear any drag. I've used only the high 92 octane fuel....and all of the miles have been on the highway (no real stop-and-go riding). With the tank off, I was able to check out the movement of the choke cable where it connects in front of the air box housing. The cable moves easily in both directions, and when moving the choke lever to full disengage it, the cable pushes it's connector all the way to the left side of air box housing. I couldn't move it any further even if the cable was disconnected at this point. So, I really don't think it has to do with the choke mechanism. When starting cold bikes, I've always used the choke at full just to start the bike, and run it for maybe 1 min if really cold. Then I completely disengage the choke and raise the rpms by pulling back on the throtle a little....getting the rpms up to around 1500. I hold the throttle there for about 1 min, and then let it go back to a resting position. My bikes have always idled smoothly at that point around 1200 rpm. In the time it takes to get my riding gear on, gloves, helmet, com system, etc., the bike is warmed up enough that I'm able to take right off. I've always heard it was best to get the bike off of choke as soon as possible after starting a cold engine. I think that's it. The bike is really clean with zero damage anywhere. I thinking sitting for 2 years did in the carbs. This sucks!

 

My bike set alot too, I did an half ass carb clean on mine to get threw till winter whn I can do it proper. What I did is disconnect the fuel line from the tank (turn off the pet cock) and ran a fuel additive (Octiplus, simular product to seafoam) directly into the fuel line while running the bike at 5k rpms. Ran12 ozs threw, reassemble, then rode the bike for 10 miles at high rpms, once all the additive had run threw, bike ran noticalby better. Performing this method also helps clean the combustion chambers and valve seats.

 

i suggest you start a new thread in either the mechanics garage or the 3-4 gen section.

If the bike sat up then the pilot jets are clogged and will need to be cleaned, either ultrasonic or mechanically with a #12 electric guitar string.

With the tank off you can look down into the intake and raise the slides with a chopstick--are the throttle butterfly valves fully closed or is there a open gap? The gap is controlled with the idle speed adjustment screw. Many times the idle screw will be opened up when the pilots are clogged in order to get the bike to run, in which case it is running very rich all the time. The butterfly valves should normally be closed with no gap.

The fact that it will cold start without the choke indicates a rich mixture, as does your mpg.

No over-the-counter chemicals that you can buy will solve this problem.

Tinkerin is in colorado and the squirrelman knows how to clean carbs.

 

That ^^ is correct.

Mr. McD, instead fo paying a shop up to $500 for the work, you could get the job done for way less than 1/2 that amount, but you'd need to do the carb removal/replacement on your own or get a friend there to help you. PM me for details.

For God's sake, please remove the carb set as a unit, and do not seperate the alloy airbox base from the set !!

Have you determined whether you do or do not have a jet kit installed ??

 

Thanks for the replies, guys. To squirrelman....the bike is 100% stock. All 3 previous owners all live in the same small Kansas town, and all work at the same factory. Owners 1 & 2 combined put 5K miles on the bike. I think the first owner only put 1100 miles on it. The 3rd owner, who I bought the bike from, rode it the next 8-9 years, and put 23K miles on the bike. He rode it daily to work and back, requiring him to fill the tank every 3 days or so. All 3 were in their late 40s to early 50s, so the bike was ridden gently if anything, and no mods were made of any kind. To Kenny Bobby, I DO need to use the choke in order to start the bike when the engine is cold. I've always heard that it's bad for a bike to run it too long with the enrichment you get when the choke is engaged. So, I've always used the choke to get the bike started,...but after 30 seconds or so I completely disengage the choke and simply increase the rpms with the throttle. I run the engine at approx 1800 rpm for maybe 2 minutes, and then let it go back to it's resting position. The bike is then idling around 1000 rpm with the choke off and my hand off the throttle. Bikeman.....I've heard of using your method of cleaning out the carbs by running straight detergent thru the carbs. From what I've read, it can be very effective. I might try that tomorrow,...as well as pulling the slides out of the way and looking at the butterfly valves for full closure. Thanks for those tips. In all honesty, I wanted to start a completely new post,....but couldn't figure out how to do it. I just can't seem to find the option in the menu system and various hot links to allow me to create a new post. Sorry about that.

 

I'm really thinking about trying your technique for a quick cleanout of the carbs. I read a similar procedure in another forum, and the guy ranted and raved at how well it work. So,...just a few specific questions for you:

1. What kind of setup did you use to funnel the fuel detergent into the fuel hose and down into the carbs?
2. Were you concerned at all about what affect full-concentrated fuel detergent might have on the softer rubber parts
inside of the carbs?
3. Several VFR suggestions centered around either my floats being stuck, or the carbs being flooded. Do you think
your technique might resolve either one of those scenarios?

 

I removed the fuel hose that connects to the fuel tank petcock, installed a small funnel, slowly poored in the additive. The fuel pump will spit fuel back out so have some towels handy. Keep in mind that once you run it all in and have reinstalled the fuel line, the pump, filter, hoses and carb are still filled with the additive and the engine needs to run until its all out. I ran mine for 10 minutes in the garage and then took it out on he road. Ran crappy till it all passed.

On mine (gen4) I had remove the seat and loosen the rear tall plastics to access to the fuel line.

I was not concerned about the seals and what not down in the carbs, its only in there for a brief time. I have not any issues since.

I suppose if a float was stuck down due to "gum" in the bowl it could free it up. If it were me I give it a try. Regardless, 26mpg is bad, something is going to have to be done. Like the guys have said if the jets are clogged will need to be removed by compressed air or a wire.

 

Let's see photos of your sparkplugs. If you find one noticably darker than the others or they're all dark, you'll know more about what's going on.

Ideal plug color is a tan light brown. Darker plugs suggest an over-rich A/F ratio, wasting fuel. Possible causes are varied, anything from improper float level settings to pluged air filter, dirty mainjet holder tubes, wrong jets installed, leaky float needles, etc.

 

I don't know if you have found the problem with the original issue but I had the exact same issue with a 2000 Suzuki 600 Bandit. I should have been getting in the high 30s and instead was getting in the low to mid 20 MPG. It started fine but ran just OK. You could ride it, and I did, but it just felt sluggish. It seemed to clear out and come on once on the main circuit over 8K. It smelled rich when running and started with no choke. I knew the PO had been through the carbs so I pulled em and had a go. I found that #4 needle jet was missing. Gone. This was the jet and not the needle. I replaced that with a new one and that fixed everything. The mileage increased, it became a bit cold natured (which they are prone to be) and it had a smooth power band. Strange things happen in the hands of previous owners.

 

Big_Jim.....your "discovery" of the missing jet in one of your Suzuki Bandit's carbs is exactly why I am so hesitant about bringing the bike into just any shop to have the carbs pulled and gone thru. I've never been afraid to jump in and wrench to learn, but have to admit that tearing apart my carbs myself is something that has me very nervous. I'd do it,...if I had one of you carb gurus next to me.

I did follow up on checking underneath the sliding floats for evidence of full butterfly valve closure. No problem there at all. All 4 respective butterfly valves closed fully, and I could also hear the click on closure for each one...outside of actually seeing full closure as well. Everything looked very clean on the inside as well. One thing I did notice, however, was a rattling sound on the 2 left side carbs whenever I'd pull the float up and then let it go. It almost sounded like there was a completely loose and free spring inside or below the float. Both right side carb floats made no noise at all when I lifted them and then let them pop back down.

Tomorrow I'll pull the plugs and then take pics of their condition/color....as well as some pics of the butterfly valves closed. Obviously the 2 back plugs are easy to get at and remove.....but what about the 2 plugs toward the front? Any tips at getting to them?

 

The problem with carbs is not really looking. (like I did) I made assumptions that I couldn't make. You have to be able to trace every circuit, know where every jet is and its size and you have to make sure each carb is assembled exactly the same. Carbs are not hard but they do take a clean, well lit work area and, as the Zen master says, "great peace of mind." Go SLOW and build one at a time. Examine every detail. Examine the carb exploded view in the book. Most carb problems come from being plugged up. If you are getting crappy gas mileage then there is a hole that gas is spewing out of some place. The carbs on my VF500F drove me nuts because one of my air screws was stuck. I could have tried to drill it out but in the end I just let it be. I had three other carbs and it only effected the idle circuit. Ya have to know when to punt and when to swing for the trees (if I may mix my metaphors.) Another thing. I also found that the choke rack on the Bandit had been assembled wrong. The plunger on the last carb was on the wrong side of the rack causing the other three to be open slightly. I found this early, before riding it, and it should have been a harbinger of things to come.

 

What size sprockets and tires have been put on that thing--that might explain part of the low fuel mileage. The speedometer is reading off the front sprocket to calculate mileage.

Dark fluffy spark plugs will tell you whether or not it is running rich.

Inspect the crankcase oil level and see if it smells like fuel.

What type of fuel are you using--E10, E15, E85, pure gasoline?

So it starts using the choke, then idles down around 1000 after warmup-- sounds normal there.

Are the caps on the pilot mixture screws present or are they missing? You can check the setting of the mixture screws without removing the carbs. They should be about 1-7/8 turns open. If the screws were adjusted and opened up then this could explain your poor fuel mileage.

Since you verified that the throttle butterfly is closed, it's not likely that you could be pulling from the transition ports or the mains or the choke circuit--otherwise your idle would be off.

Don't know how the slide springs could break on two carbs, but it would be easy to check without pulling the carbs. Do the slides seem to have springs pushing them back down to the closed position or do they hang when you pull them up? A weak spring(s) would let the slides run higher than normal and dump a bunch of fuel from the main circuit.

http://vfrworld.com/forums/1st-2nd-...r-circuit-identification-porn.html?highlight=

 

Hello guys. Sorry it has taken me so long to get back to you on this problem....but domestic and work chores had me busy beyond belief. To answer some of KennyBobby questions,.....The front and rear sprockets.....and chain were all replaced 1500 miles ago with stock number of teeth. I got that directly from the seller. Hopefully, I'll get to pulling the plugs tomorrow to examine their color and condition. I'll also check for the presence of the caps on the pilot screws. As far as fuel is concerned, I've always used the top 91 octance,...and it was pure gasoline with no ethanol added. The four slides also appeared to function properly. I'd elevate each one to the top of it's run, and then let them go. All 4 immediately popped back down. The only thing I noticed, which I mentioned before, is that the 2 slides on the right side carbs made no abnormal noise upon release. The 2 slides on the left side carbs, however, had kind of a rattle sound when released. It sounded like either a spring was freely loose inside, or possibly broken. In any case, they moved up and down just like the right side slides,....and closed quickly with a snap just like the right side slides. I'll get back to you all with my other findings tomorrow. Thanks guys.

 

Let me start a new thread for you over in the 3-4 gen forum to get some focus on your issue--here is the link:
http://vfrworld.com/forums/3rd-4th-...ddys-poor-fuel-mileage-thread.html#post379548

 

Reg,

Does you bike use an O2 sensor for closed loop control of mixture? If so then when was it last changed out--they are a consumable item that wears out over time and miles. As they degrade their voltage signal causes the mixture to progressively get richer and richer.

 

Now that the cold, snowy Winter weather has moved on in the Kansas City area (except for today that is), I decided it was time to get the VFR out of the garage and fire that bad boy up. Here's an update to my bad gas mileage saga. Those reading may want to grab a cold beer,.....and some tissues to wipe away the ensuing tears that will no doubt roll down your cheeks. Having followed up on any and all suggestions made by those members following my thread, and the few other threads out there concerning poor gas mileage,.....I decided to replicate a technique provided to me from one of our fellow VFRWorld warriors. This technique for power cleaning out the inside of the carbs is as follows:

The forum member had suggested using Sea Foam as a gas-additive cleaner....and told me about a setup he used to power clean the inside of his carbs. Basically, he just removed the tank, and then connected a large funnel w/ attached gas hose. He then used adapters to connect this setup to the gas hose that connects to the bottom of the tank. With this setup, the tank is gone....but he could run straight gas or any mixture of gas and cleaner in the funnel....and then startup the bike and run it for 15-20 mins. Then he put in straight gas and ran for another 20 mins to flush out the Sea Foam. At that point, the funnel setup was removed and the tank reinstalled....and then out on the road for a 30 min ride at high rpms. He said it worked like a charm. Initially, the exhaust pipe expelled a lot of blackish smoke as he tooled down the road, and idled a little rough. However, after 15 mins on the road....the exhaust stream cleaned up, and the bike idled smoothly again. His mileage then rose up to a respectful 40-45 mpg.

I tried to replicate his setup w/ supplies from the local Ace Hardware. I removed the tank and connected the funnel/gas hose in it's place. I mixed up a 50/50 mix of gas and Sea Foam....and then started up the bike. It ran fine for about 15 mins. Most of that running time was at idle speed, but here and there I would raise the engine speed up to around 3K for a few seconds...and then back down to idle speed. I also revved up the engine several times. Around 20 mins into this scenario, the engine just sputtered and died. Since the funnel was almost empty, I figured it was just a lack of pressure since it was an open system with maybe an inch of gas at the bottom of the funnel. I emptied the 50/50 mix from the funnel, and replaced it w/ 100% gas. Then I tried countless times to fire the bike back up so that I could at least flush out the Sea Foam that was still inside the carbs. However, the engine just wouldn't start again. It was almost December, so I wrapped everything up tight to keep debris out of the tank and gas hose. I also put a battery tender on the battery, trickling power in over the Winter months to keep it fully charged and fresh.

Two days ago I hooked the tank back up, and tried to fire up the bike. Nothing. I tried and tried and tried,....but it just wouldn't start. Usually when you try to start a bike that many times, you end up flooding the carbs....but it had no smell of excess gas at all. So, my guess is that the carbs are not getting any fuel at all....or at least not enough to fire up the engine. Not really sure what to do at this point in time. Maybe the carbs are literally gummed shut inside, and that's why they can't get enough fuel to startup the bike. The engine turns over without issue, and the battery is new. The plugs are all getting adequate spark, so ignition system is okay. It's my understanding that the fuel filter is actually inside the gas tank...mounted to the very top of the fuel petcock assembly that inserts up into the tank from the bottom. Perhaps the fuel filter is fully plugged. I checked all the obvious things,...such as fuel valve was in "On" position. The Run/Stop switch was in the Run position. The bike was in neutral, and I even sat on the bike with the side stand up to ensure that wasn't the problem. All those were ok. In looking at the service manual for 90-93, I was never able to see exactly where the fuel pump was located. Suggestions as to where to look for that? Any ideas at all on what I can try to get the bike to at least fire up again.....before I end up pulling the carb assembly for professional cleaning? Another idea that's actually cheaper is to buy a complete carb assembly off of Ebay. I found one from a 93 that only had 5275 miles on it. The assembly looks in great condition, and very clean. Price tag is around $195 plus $30 S/H. That's definitely cheaper then having the carbs disassembled and cleaned. I'm open to trying anything that you all can come up with. At this point, I having nothing to loose....and everything to gain. Thanks everyone for your dedicated input. Ron

 

You can't buy ebay carbs without rebuilding them or you will trade one problem for another.

Are you sure you are getting gas through the line from the tank? Have you actually seen gas running out of the line to the carbs?

I would pull the air cleaner and hit one or two carb intakes with a bit of carb cleaner spray and then try to start it. If it pops or tries to start you know that your not getting fuel. Does the tank have a vacuum petcock?