OK, I know this has been brought up before on another thread but I can't find it. I want to install one of the spun alluminum fuel tanks on my FL 250. What exactly has to be done to the carb? Is there a complete different set of jets that need to be installed, float, etc? I am rebuilding the roll cage now also and once it is ready to go I plan on selling it. Thanks for all the help

I know someone has done this before. Does anyone have any info on what to do? Or do I have to do nothting to the carb. Just thought it would have problems if there was a gravity feed tank installed instead the original.

they say you need to change the float needle and seat but Odystable says he has done it without changing anything and it worked fine.

OMO

Yup, I have done it 4 times now without changing anything.

Some say you need to change the needle and seat, but my guess is you only need to do that because they were already worn, I have always taken care of ours and would usually replace those items whenever we aquired a new one.

I would think you need to use a bigger float needle and seat. I used to race gearbox or shifter karts with tuned 250 motocross Engine and carb, the carb is designed to be gravity fed so when the fuel is pumped in to the carb the big float needle can not hold back the pressure and the carb floods, so we replaced it with a smaller size float needle and seat.
You are doing the opposite and with a small float needle being gravity fed you may get short of fuel in the float bowl when flat out for a long time, run lean and seize the Engine or hole the piston.

Actually what everyone says before they changed their needle and seat was the exact opposite of what you're saying, the carb floods out all the overflows when they convert from the pump to gravity feed.

I believe that TurboTexas just left the stock pump setup with his gravity feed tank. I did the same to mine but have a cracked intake boot so I can't comment on how it works.

Here are pics of his setup http://pilotodyssey.com/PO/viewtopi ... avity+feed

Thanks for all of the help. I think I am going to try the carb in the stock configuration and see how it does. If it doesn't work well then I will make some adjustmets. Once I am finished with the rebuild I will post some pics. Hope fully I don't drink to much Fat Tire and screw up the welds on the roll cage. LOL LOL

Just shows I know Nothing .
I have seen lots of problems caused buy either not enough fuel makeing it run lean, or too much fuel to the extent of hydrolicking the Engine and bending the rod or knocking the crank out of alignment, but I am refereing to gearbox/ shifter kart racing where they pull big g forces on the bends which causes a lot of fuel problems. Fit fuel injection problem solved.

I installed one on brooks 350 and did not have to change anything to make it work. I was able to give it a much more precise carb tune which led to more power.

Hi King. I read your post and have some questions if you don't mind. I have never heard of that before being one for learning something new would you care to share some info and your thoughts on the effect you mention. I know a little about rate and delivery and whcih to add yours to that. How would the carb know the differerce between the pressure at which the fuel is in when in the bowl. When the neddle closes the fuel level is at a static presssure( weight of the fuel itself with gravity pulling againgt it at attliitude) What advantagre can be achieved. I think about it. What if you live in a hilly area where a lower float setting is necessary as not to flood Engine under lower opperation speed. Would the delevery rate at lower setting be increased as not to starve the bowl of fuel while under higer operating speed at a lower float setting. If so would the over flow tube if routed correctly and unrestricted take care of this. for those being "Green" route to a recovery bowl like on the 90 pilots and not let run out on the ground. Thanks for any input.

I always set the float level to its "normal" position. The only fuel line is from the tank, through a filter, and then to the carb inlet. Vent tubes are routed and vented to atmospher. They dangle below the Engine cases. There is no return fuel line to the tank or routing of the vent hoses back into the carb or air box. Never ever had a problem with bogging while trail riding or starting on hills. (and we have big hills) The gravity feed eliminated the running out of fuel problems we had with the stock tank and check valve assembly. It also allows for instant starts, no more cranking the Engine for a while, waiting for the fuel pump to fill the bowl. As soon as the shut vavle is opened the bowl is filled.
As long as the needle and seat are good there shouln't be any problems with fuel leakage. The floats are what push the needle and seat closed, so if you have a float sticking or leaking then you won't have as much closing pressure on the seat.
I have not checked the fuel pressure with a gravity set up, but I can't imagine it having any measurable psi vs. the fuel pump set up which needs to open the return spring valve/orifice to return back to the tank and or bypass the return and fill the carb, all of which is a restriction.
The negatives for the gravity feed are, don't forget to shut off your petcock when you are trailering. Bouncing around can cause fuel to dripple into the Engine flooding it or hydrolocking it. The tank can get bent/dented in a hard roll.
The positives, huge amounts of room for carb adjustments and service, no more air bubbles in your fuel delivery system, more fuel = longer rides, more consistant carb tuning, faster cold starts.

The quicker starts I could use. I never new about the air bubble in system I will put on clear hose and check. Thanks for the input.

Stock carb and stock fuel inlet size?

They make 2 different needle sizes for a reason, they make one for pressure feed like using a fuel pump and gravity feed for like on a motor (( Internal Combustion Engine ? )) cycle.

Is the after market tank vented as well as the factory tank, if it is not is the constant fuel agitation by sloshing and bouncing keeping pressure in the tank?

Yes, this was a bone stock carb on a 350. The fuel cap was internally vented to atmosphere. Automotive type gas cap. I am aware of there being two different needle and seats. Any specs on them? Is the angle of the seat different between the two?

If you run the clear fuel line and find bubbles in the fuel line, remove your gas cap and stick the fuel line into the tank, jam a rag around the fuel fill neck and run the Engine under load. If the air bubbles are gone, the problem is in the tank/pick up tubes which like to rott. If the air bubbles are still there look at the fuel pump and hoses.