Update on the shifter kart

[Kaptain Krunch]

So, spring is here and i need to finish my KZ400 kart, its almost there, just needs the finishing touches, brakes, a little tweaking on the clutch linkage, paint, and a little engine work. Today i made a gas tank for her, out of a fire extinguisher.

Over april break i'll be getting a buncha parts from my dads cars, i need a master cyl, some switches, a starter motor for reverse (possibly), and probably some other stuff. Then i should be able to bring it into the shop at school, and do a buncha little stuff on it, im planning on junking these CV carbs, for a 34mm mikuni roundslide, then i need to do tune up the engine, adjust valve lash, chain tension, new plugs, oil change, etc.

Anyways, heres some pictures of the tank, came out alright, i used a threaded end from some gas pipe as a inlet/cap. For the output i just welded a bolt on that fit a on/off petcock i had.

 

[KieranM]

nice welds. could be just the way im looking at it but is it kinda small?

 

[anderkart]

Cool tank there Kaptain. You probably already know you'll need some sort of tank breather. The check valve in my karts old gas cap kept malfunctioning so I just installed a barbed fitting for 1/4" hose into the cap and ran a hose down to an old fuel filter to help keep it from drawing dust in. I also installed a little mini PVC valve to hopefully act as a check valve and keep gas from spilling if I ever rolled it.

 

[Kaptain Krunch]

nice welds. could be just the way im looking at it but is it kinda small?

Thanks, it is pretty small, i built this thing, with plans for a roll cage, but decided against it, i was planning on putting the gas tank up on the roll cage, so without it i have hardly any room for a gas tank, hence it being to small. This thing sips gas though, so i should have no problems.

AK, i was planning on putting a barb w/hose on the gas cap, like dirt bikes.

 

[Doc Sprocket]

Right on! I was thinking about using a pair of extinguishers fow twin tanks on my XV250...'Till I killed the bike in favour of using the engine to power my next project!

 

[SpyGuy]

Nice work on using the fire extinguisher! A threaded gas pipe and inlet cap ..... good thinking! I've seen a couple of guys thread barbs into the tank bottom, and another guy threaded his barb into the original fire extinguisher endcap.

Now I gotta try this .... I've been trying to figure out how to do the neck for a gas tank, and now I know!

 

[Kaptain Krunch]

Nice work on using the fire extinguisher! A threaded gas pipe and inlet cap ..... good thinking! I've seen a couple of guys thread barbs into the tank bottom, and another guy threaded his barb into the original fire extinguisher endcap.

Now I gotta try this .... I've been trying to figure out how to do the neck for a gas tank, and now I know!

Yea, it came out pretty good, i wish it was a little bigger though.

I set up my fuel lines, got it all ready, and guess what? those little diaphragm mikuni pumps arent powerful enough...I think they are meant to push the fuel rather than pull it, but either way i need something much more powerful. I have a feeling a automotive fuel pump might be a bit much, anyone else have a solution?pressurized fuel tank maybe? that could get complicated though.

 

[crazycart]

One of these? It should pump just fine....you may not be getting enough vacuum from the engine.

 

[Kaptain Krunch]

I tried both square and round, round ones are more powerful i believe. im getting my vacuum from the intake, it was already tapped for a diaphragm petcock. I have about 5-6ft of fuel line, mostly flat with one big up hill, you sure it should be powerful enough?

I went and tested again, and god **** these things have no pumping power at all, i brought the fuel pump level with the gas tank, started the engine on a bottle, and it didnt pump 1 drop, not at idle, not at half throttle...Do i need to use the pulse from the crank case?

 

[anderkart]

Hey kap, I usually hesitate to give you advice cause you typically know a lot more about this stuff than me. But just in case, most kart racers install their pulse pumps on the top of the engine and as close to the carb as possible for a couple reasons. You want to keep your pulse line run short cause it tends to expand/contract the line and diminish your signal. And secondly these pumps tend to have more drawing power than pushing.

My experiences have also been that intake pulse fittings usually give a much stronger signal than crankcase fittings. Also Its not uncommon for older pulse pumps to develop diaphragm leaks or become saturated with oil/sludge from use with crankcase fed pulse signals. Also make sure you use some type of hose clamps on your pulse-signal line ends.

 

[crazycart]

Do i need to use the pulse from the crank case?

Yes...which will be hard considering its a 4 stroke.....

 

[Kaptain Krunch]

Hey kap, I usually hesitate to give you advice cause you typically know a lot more about this stuff than me. But just in case, most kart racers install their pulse pumps on the top of the engine and as close to the carb as possible for a couple reasons. You want to keep your pulse line run short cause it tends to expand/contract the line and diminish your signal. And secondly these pumps tend to have more drawing power than pushing.

My experiences have also been that intake pulse fittings usually give a much stronger signal than crankcase fittings. Also Its not uncommon for older pulse pumps to develop diaphragm leaks or become saturated with oil/sludge from use with crankcase fed pulse signals. Also make sure you use some type of hose clamps on your pulse-signal line ends.

The pumps i have been using are known to work, so i can rule that out. One came off the sled i used all this winter, and the other one i had as a spare, which i did test on the sled and it was actually TOO powerful, and pushed the gas right past the needle and flooded the engine out.

The intake pulse feels ok, but what im thinking, is these were meant for two stroke sleds, and had constant pulses from the crank case, with this four stroke, im getting one pulse (positive) once every 4 revolutions. i read somewhere that these things run off the negative pulses, could be false though.

However, i did try running this thing off the crank breather, and sure enough it pumped perfectly, which is great and all, but i assume blocking the crank vent and using it as a pulse line is a bad idea. So im stuck...

 

[crazycart]

You can probly get a cheap electric pump at an auto parts store

 

[Kaptain Krunch]

I have some parts cars i can get it off mid april, guess i just have to wait. Would an automotive one be too powerful though? i mean i would imagine it would just force the gas right past the needle.

 

[anderkart]

Have you already tried T-ing off both your cylinders intake pulse fittings?

 

[modelengineer]

Are you sure you are getting the pulse from between the butterfly and the engine?

Also, tee-ing off both cylinders is not a good idea. The pulses will be stronger on just one cylinder.

 

[Kaptain Krunch]

About 90% sure its past the butterfly, and no i didnt try teeing off the cylinders for the reason andrew gave. At this point it sitting in the middle of our back yard and i have no clue what im gonna do for a fuel pump. I did a little more research, and it says these things are compatible with both 2 and 4 stroke engines, Maybe ill try tapping the crank case.

 

[modelengineer]

If it's like my twin then there shouldn't be any pulses from the crank case, one piston goes up while the other goes down. Some engines have both movie in sync, tho.

I'd check to make absolutely sure it's past the butterfly, because if it's not then you won't get any vacuum or pulses and it won't work.
Usually those pumps are great, but you have to prime them with fuel (AFAIK).

 

[sideways]

If it's like my twin then there shouldn't be any pulses from the crank case, one piston goes up while the other goes down. Some engines have both movie in sync, tho.

4 stroke inline twins usually have both pistons going up at the same time with one on compression and one on exhaust. One like yours is quite unusual?

Hayden

 

[anderkart]

Are you sure you are getting the pulse from between the butterfly and the engine?
Also, tee-ing off both cylinders is not a good idea. The pulses will be stronger on just one cylinder.

Everyone's had good suggestions but I'm kinda thinking modelengineer might be on to something here. I looked at all your build thread pics and couldn't see any fittings located in your intake manifolds, so I'm assuming yours are in the carbs. Maybe your carbs fittings are ported vacuum instead of a true pulse signal. I've got a vacuum gauge that also reads pressure. If you've got access to one of these you could test and find out what you've got there for sure.

Looks like your intake manifold might have room to somehow install a 1/4" pulse fitting. (or if not maybe you could extend them a bit to get a fitting in there)

I was kinda thinking along the same lines as you 2 about T-ing off both your carbs pulse fittings but It'd only take a couple seconds to at least try, you never know...

Another option I've been thinking about:
Your build thread showed a pic of a large breather hose coming off your valve covers. My Star engine has a similar sized breather hose tapped in right next to my crankcase pulse fitting. They're located so close to each other I have to run a functioning automotive PVC valve in the breather or I wont get a strong enough pulse signal to drive my pulse pump.

I was thinking it might just work on yours to T a pulse fitting right near your valve cover and then install a PVC valve on down the same breather line. (maybe several feet on down the line if necessary) The PVC valve would need to be installed in the direction it'd still allow crankcase pressures to exit, but check any inward flow. You'd just need to mount the PVC valve in the upright position so gravity helps the ball valve make its seal.

My pulse pump works great like this and you'd basically be doing the same thing.