TOPIC:

where is the accelerator pump diaphragm? I DO have a vacuum petcock....should I switch it?

on the bottom side of #2 carb dunno what carbs i got my bike is a 650 ltd not sure if you got same set up or not tho

Bicycle Lee wrote:

where is the accelerator pump diaphragm? I DO have a vacuum petcock....should I switch it?

Does it allow fuel to flow when the engine isn't running? If not, then no.

Your bike doesn't have a accelerator pump. As for link's suggestion of a torn diaphragm inside the carbs, if there are any in those model carbs. Also fuel just might be running into the crankcase. My 650 was like that. When I took off the head, there was this trail of fuel going down from the valve and no.2 and that spark plug was always wet. I had this carb cleaner that would clean the valves also, and it was slightly oily so I didn't loose any rings or get a wear pattern from it. Also if your bike jumps in the engine section and has hissing/ spitting noises coming out of the exhaust, that could be your problem.

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.

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.

no sweat on asking a related question...
My bike IS a little jumpy and makes hissing/spitting noises out of the exhaust sometimes...I need to change my oil very soon anyway, since it's heating up so fast here. So what am I really looking for?

you should be getting a lot better gas mileage than that. heck my bike even gets about 25-30mpg riding hard. something is defently wrong. if tou say the bike is spitting and poping out of the header you more than likely need to go back in the carbs and check everthing over agian. did you completely rebuild the carbs when you changed the jeting. you need to check the needles and the float levels.

have you checked the plugs. there are a good tell tell sing if you are running way to rich or not.

have you checked the petcock. if the gas dose not shut off it will fill the cabrs up with gas and can dump into the motor and run down to the crankcase and mix with the oil. i have been trough this one my self.

best person with carbs on this sit from what i have seen is a member that goes by wiredgeorge. he can set you straight if anyone can.

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?