Fuel Economy

Well BL, At least you have done one impossible thing in your life BWHAHAHAHAHA If your mileage is as bad as you say, I would consider buying some new jet needles and needle jets (if you can find some). If either are badly worn, then your mileage will go downhill fast. One of the things that will wear needle jets is using aftermarket jet needles. These are longer and have less taper and are skinnier than stock usually and tend to wiggle around in the needle jets and tend to wear the needle jets RAPIDLY because the needle jets are soft brass. You can't really see wear since the hole is recessed and chamfered and pretty small (at least I can't; maybe somebody with better eyes could). Unfortunately, the needle jets are getting hard to find for VM series carbs, and I steal sets from parts carburetors when I need to swap them out. There is a "BADGE" number on the side of the needle jet. Once you get it out (it is press fit), the badge number is on the side and for your carbs, I think it is a 258 series and the marking will be something like:
258 0-3

The 0-3 is the size with the "OH" being the range where an OH needle jet is smaller than a "P" range. There are 10 sizes in each range. An 0-6 is ten sizes smaller than a P-6. Almost all post 74 VM carbs on 900/1000 are 0-2 to 0-6 sized. Going up or down a size on the needle jet won't affect your performance as the size increments are VERY tiny. Just make sure you get the correct BADGE number as there are many different styles of needle jet and getting the badge number correct ensures that it will be the correct length to match the main jet holder tube. You can try z1enterprises.com and see if they can get needle jets CLOSE to what you need. You MAY also be able to get new jet needles via carb kits, if the jet needles are needed. This are easier to spot problems as the stockers are gold (perhaps anodized?) and the gold will be worn off worn and unusable jet needles.

when I rejetted my carbs I did open up the top of the carb and check out the needle jets. The gasket at the very top of the needle assembly was not seated in its channel at all. I will open them up again and inspect the needle jets themselves, but could THIS be a big problem? I squeezed the gasket in as well as I could, but it certainly wasn't sitting tightly where it needed to be.
By the way. THANK YOU everyone who has posted their ideas and help to my problem so far....PLEASE keep it coming. When I open up the carbs again, I'll shoot some photos to see what you guys think.
OH and they are mikuni carbs...not sure if that is an important point to make

Post edited by: Bicycle Lee, at: 2007/05/02 10:58

You should have some sort of VM26 carb assembly with mechanical slides. Not sure about " a gasket at the very top of the needle assembly" not being seated. I suspect it is time to take some pics as we might not be talking about VM26s.

The needle jet is about 1/4" long and press fit and inserted from the underside (bowl). The main jet holder tube keeps it in place. The jet needle is the long skinny "knitting needle" piece that comes out the bottom of the slide.

I think we are talking about the same things, but I will supplement with pics when I take them.

On another note....can anyone recommend a good motorcycle mechanic in the salt lake city area?:laugh:

you should click the link in wg's sig, he has a great site, very informative

SO!!!! Ok, I just went for a nice short little ride after a couple days of horrible riding weather and when I pulled back into my garage I left the motor running and got off to check things out. It IS leaking fuel from where the exhaust leaves the head.#2 is ESPECIALLY bad. So fuel ISN'T being burned in the carb and is being expelled out into the exhaust and/or crankcase....
So now what do I do?

Dump the oil and check it out... I had so much gas in mine, it filled the case past the oil window. When I dumped the oil it was full of gas.. very bad for your motor and milage. Ended up beaing bad needle and seats, plus my pet cock was leaking.



2bskor wrote:

I have a 79 kz1000st and it also gets real bad mileage.
I am now wondering if it is going in my crankcase as my sight glass is frothy almost like there is water in the oil. I changed the oil and the filter even took the cover off and cleaned the window:S

Sorry to hijack you problem but if the fuel is going into my crankcase would it burn off or how would I tell and how is it getting there.

My tank takes roughly 15 litres or 4 gallons and I'm lucky to get 100 kms or 45 miles.

the carb bowls drip a bit but never that much and there is no other visible fuel leak.

The only way for fuel to get into the motor is through the carbs. Needle and seats, float level, petcock. I'm not sure how it would leak from the exhuast though. :blink: It could be in your crankcase but I don't know how raw fuel can just come out of the exhaust. The only way for it to get into the exhaust is through the exhaust valve, which would mean you are burning it. Your plugs would be black, you might even have black smoke coming from the exhaust from unburned fuel.

Bicycle Lee wrote:

SO!!!! Ok, I just went for a nice short little ride after a couple days of horrible riding weather and when I pulled back into my garage I left the motor running and got off to check things out. It IS leaking fuel from where the exhaust leaves the head.#2 is ESPECIALLY bad. So fuel ISN'T being burned in the carb and is being expelled out into the exhaust and/or crankcase....
So now what do I do?

I meant right where the pipes come out of the head....not the actual exhaust itself...on the front of the motor where the pipes come out, that flange was dripping fuel....

You mean the exhaust side of the motor? Gas must be leaking and running down the cooling fins to the front of the bike? There is no wqy fuel can get to the front of the bike. It has to be dripping onto the cylinder block from the tank or carbs... :blink: I dunno, sounds very strange to me BL...

hey, that just makes TWO impossible things this bike is doing! :laugh:
I am just saying what it LOOKS like my bike is doing....where the exhaust comes out of the head is dripping gas...and I am 99.99999999998% sure that it isn't the tank that is leaking.

If I was you BL, I wouldn't ride that bike until you find the leak. If what you say is true, that gas is leaking onto your hot header....:blink: :blink: :blink: BL go BOOOOM!!! Seriously.... Find the leak. Pull the tank off of the bike you might have a pinhole or something underneath it. If it's not the tank, how about the fuel line? Look at the carbs, if gas is leaking out of the carbs, I would say the #1 or #4 carb and running to the front of the motor off of the cooling fins. Gas only comes from one place, the tank... Follow the gas trail and find out where it's coming from. Follow the drip backwards.. Don't ride it until you do though, you could blow yourself up man!:ohmy: