poor mpg

[tvmax]

I pulled my carbs expecting to find high float levels due to the poor mileage and rich smell. I found the floats about 4mm on the low side. Now I have also had a problem with the bike breaking up at high rpm. Sometimes it will go thru first and second before breaking up. I think the low float setting may be that cause. But what else can cause the rich mixture? I am sure the chokes are all off. I did find a slide diaphram with a hole. I expected that because I could feel it cut in on partial throttle. Could this be the culprit? I am running stock jets except for the main which is a 150.

Thanks
Jim

 

[maleko89]

Jim, how did you measure your fuel levels?

If you left them as-is the bike would probably cut out at higher rpms because the bowls are running dry.

I would fix the slide and make sure the others are okay as well.

Other causes of poor mpg are valve adjustment, premium gas, dirty air filter, mixture screw adjustment, ignition problems.

 

[tvmax]

Mark,
I didnt actually measure these carb float levels yet. I did another set I have as per desctibed here on float level setting. I also noted another mark on how to set dry in the postings.
This set is so far off you don't need to measure. I will before I change them just to see how far off they are. But the floats are like so far off from the other corectly set ones it isnt even funny. I will post the measurement soon.
I assumed when I saw the float levels I was fuel starving at high rpm's. Which is good to find out what may be one problem. I know I need a valve adjustment. I will be doing that tomorrow. I will install the spare carbs I have with previously set floats. Do a good sync and see how it runs. I do alot of city driving and traffic so with a bad diaphram and heavy throttle hand in traffic may be another cause of bad MPG. I just figured that it would have been very lean. I will see what the mixture screws are at but I am pretty sure they were in the 2 to 3 turn range.
I will have to take it out of town for a long run to see what mpg I get. I may be killing alot being in town all the time. On and off throttle in this traffic is like playing a video game.

Thanks
Jim

 

[Thevmaxrider]

You will run into MPG issues in town anyway, but also if you are doing a bunch of short trips you may see a more pronounced effect. I will lay odds that if you are doing short hops only that is a big part of the issue. The Vmax engine has a cold combustion chamber, darn Yamaha engineers made the cooling system too efficient in the heads, which tends to cause carbon issues if the engine isnt run long enough to completely get up to temp. One thing I make it a point to do if I am just running around town etc. in short duration trips, which doesnt happen ofter:biglaugh:, I make it a point to open Snowmax up when I get out on the open road. Carbon is an efficiency killer!

 

[tvmax]

The floats measured at 1.26" as measured in dry float level setting thread. Putting them to 1.125 and see what happens.
I saw where you can get replacement diaphrams and not the entire slide. Has anyone used those? How hard are they to install?

Jim

 

[Firewrench]

The floats measured at 1.26" as measured in dry float level setting thread. Putting them to 1.125 and see what happens.
I saw where you can get replacement diaphrams and not the entire slide. Has anyone used those? How hard are they to install?

Jim

Where did you see replacement diaphrams? I could probably use a couple myself.

 

[tvmax]

Ebay item number 270355878383
I need 2 or 3 sets LOL

 

[maleko89]

They are about $70 from Gary McCoy's Yamaha.

 

[tvmax]

I put the carbs on after resetting my float levels. The bike actually needed a bit of choke to start! That had never happened even when cold. After a quick sync and mixture adjust you could tell they were much crisper. I have no had the chance to do a full rpm test yet. I had to get to work but look forward to that tomorrow. You can hear the diference in how it is running.
Cant wait to get a few more adjustments and see what the MPG is on a hiway run.

Jim

 

[tvmax]

After adjusting the floats and syncing the carbs it runs fine riding arround at rpm's under 4k. If I use full throttle it breaks up. It also wants to break up over 6k especially using full throttle. I am thinking I may have an ignition problem. I bought some of the COP coils described on another thread. Once they arrive I will install them and go from there. I just hope it isn't the black box.

Thanks
Jim

 

[lankeeyankee]

I pulled my carbs expecting to find high float levels due to the poor mileage and rich smell. I found the floats about 4mm on the low side. Now I have also had a problem with the bike breaking up at high rpm. Sometimes it will go thru first and second before breaking up. I think the low float setting may be that cause. But what else can cause the rich mixture? I am sure the chokes are all off. I did find a slide diaphram with a hole. I expected that because I could feel it cut in on partial throttle. Could this be the culprit? I am running stock jets except for the main which is a 150.

Thanks
Jim

Hey Jim
I know I am off subject here but your in great hands with the Grand Master Float Adjuster Mark, this guy is the bestest of all best when it comes to float adjustments..

Anyways I see your other bike is a 1500 Trakdynamic Pro Stock.. Ya wanna trade for my fortune Cookie Scooter.. its fast speed GPS'd at 62MPH dont let that scare she is timid

 

[tvmax]

I have actually thought about selling it. I havent had the chance to race for years. I just had everything refreshed and still need to shim the cylinders for 0 deck. Have a new 1 2 3 auto to install. I have a crack in the body to fix. It got damaged when I was coming back from Australia. It is a very consistent bracket bike. Big motor mild cams and very light. All titanium, billet or chromoly. MTC Auto clutch, MSD ignition, FBG lectrons, Carl Nieberg head, ect.
I got into off road racing and didnt have time to play with it. It is just a nice conversation piece in my uncle's basement bar now. I have so many toys that I don't have time for anymore. I need to have a fire sale. LOL

 

[tvmax]

Well I have thought that my problems are not just one thing. Today I did the COP mod. Cured alot of my problems.
Now the bike still breaks up but only in the 7000+ rpm ramge. It sometimes pulls thru to redline. It will go thru the first two gears but then in third it breaks up. I have a 150 main in with a early Hindle exhaust. Is it possible I need to step up to a 152.5 main?
That is probably my next step.

Thanks
Jim

 

[jfeagins]

Just had to ask: Are you SURE your fuel pump is delivering enough gas and not running low at higher RPMs?

 

[lankeeyankee]

Just a simple question.. Have you removed the Y piece from your airbox:ummm:

I know during my tuning days my bike wouldnt run worth a shit when I removed the Y piece it would crap out around 9K.. stumble cough and choke with a handful of throttle in the mid

 

[veebooster]

Stock air box?
When I was tuning my Morley kit it would break up @7000 rpm. Worse on colder days....upped the main size. Good now.

Dale #2592

 

[tvmax]

Stock airbox. How do I tell on the fuel pump? If I inplug the line and turn on the key should I get a steady stream or what?

 

[veebooster]

I would think yes cause there's no back pressure....but don't know for sure.

Dale #2592

 

[maleko89]

The fuel pump should shut off after a few seconds. It's a safety feature. When the pump relay picks up ignition signals when the bike is running it will only shutoff when bowls are full.

 

[tvmax]

Put new plugs in today. The old ones were light tan with a little white. Slightly lean. It it because of main jet (150) or fuel pump output? I am leaning to pump or fuel filter. I took it for a ride with the new plugs and it runs noticably better. I can run thru first, second and got almost to top of third and it started breaking up. If I then slow up and down shift it breaks up in all gears after that. If I let it idle then hit it it goes to redline again untill fuel runs out. I am hoping the filter. I will try to source one here. Either way the bike is running better every little thing I do. Does anyone have a test for the fuel pump output? Like how much it should pump in 30 sec?
Does it hurt to run the 10% alcohol blend fuel in the vmax? It would lean it out a bit if I am thinking right.
Oh I know the carbs are closer because I have to use a little choke this morning. It got down into the 70's. Brrrr

Thanks Jim