Nobody rides until I've got my turns out of it
Gus probably break it.. Lol I break everything
When it rains it pours!
- Thread starter sicivicdude
- Start date
- Status
Gus probably break it.. Lol I break everything
Tiniest of tiny updates, I took the pressure valve out of the return line and replaced it with a piece of 1/4" fuel line. I figure that the "pressure" generated by the pump even with a straight bypass off of it will provide pressure to the carburetor enough to keep that bowl full. Need to take it over to twostroker99's and test this theory out, really.
I also picked up some AMA pro stickers yesterday. Tiny victory but basically everywhere you race you have to have a 2-3 digit number highly visible on the quad so they'll know who ran what race.
I also picked up some AMA pro stickers yesterday. Tiny victory but basically everywhere you race you have to have a 2-3 digit number highly visible on the quad so they'll know who ran what race.
Yeah, I think you cannot have more than 1.5 psi for a bike carb so the 1/4" return is probably enough.
Keep it coming!
Keep it coming!
Well, this carburetor is designed to be a gravity feed off a fuel tank. The fuel tank on a regular dirtbike/quad is usually not more than 1 foot over the carburetor. With a full tank of fuel there is less than half a psi (~.44 psi per foot roughly) on the fuel inlet valve HOWEVER this PJ38's float valve is only designed to flow enough fuel to feed a gasoline fueled engine at ~.4 psi of pressure. Considering I figured a consumption rate of basically 3 times as much but the fuel inlet is probably oversized by an engineering "safety factor" of MAYBE 25%, I need to push approximately 2 times the volume through it than it's safely designed for 
I figure "pushing it" to about 1 psi will still be low enough that the float valve can close properly but high enough that when the valve is open (during high rpm and fuel consumption) it'll have fuel blasting through there like a damn with a pinhole in it!
I figure "pushing it" to about 1 psi will still be low enough that the float valve can close properly but high enough that when the valve is open (during high rpm and fuel consumption) it'll have fuel blasting through there like a damn with a pinhole in it!
Sorry I forgot & to lazy to reread this whole thread but ... are you running a power jet on that PJ38? Just wonderin what your flow potential is with your main jet + power jet if you have one ... compared to float valve size.
I'm running a Mikuni powerjet with a 100 powerjet, a 170 main and a seriously shaved needle. Of course, none of those are an actual number but the carburetor isn't designed for anything but a large main jet and regular needle... I figured they put in a "safety factor" on that float needle and that still may not be enough.
Just got back from test running! As with everything it had it's ups and downs....
I loaded it in the back of the truck and took it over to a buddies house that has a farm plot behind his house. The path going around the field is relatively smooth (not washed out or anything), level, and most importantly, available. I loaded it in the truck and threw some Duro "balloonies" in the truck to carry with me. I started taking the lugnuts off the rear wheels when I got there and immediately remembered that the haulers are on banshee hubs and the duro's are on blaster pattern! Bad start already.... Good news is that I put about .4 gallons in the tank and prime with a splash of premix and she fired on the second kick.
Most bad news:
I lost the cap to my mechanical caliper so I lost brakes on the first "run" LOL! There isn't a whole lot of space to shut down but I managed.
The top bracket on my in bumper fuel cell broke. That's the one I had to rebend like 5 times to get to fit right so it finally stress fatigued enough and broke on a hard bump (dirt path with no suspension).
2nd gear launch with no bar on a 8" extended swingarm on hardpack lifted the front end off the ground. That may have actually been what broke the fuel cell because it slammed back down. It felt RIGHT like it was DOING THE DAMN THING.
When I shifted to third, about halfway through third gear it just DIED each time. Once I actually felt fuel spray out of the carb vent onto my leg and there was copious amounts of splooge running out of the silencer. This was a better run than at busco in April when it was shooting liquid fuel out of the pipe tip but still not right. It runs right until the pump "comes on line" and then just spits and sputters.
Considering that this pump setup is straight bypass and I broke the fuel cell, I think it's time to consider a gravity feed system fuel cell..... I'm going to mount the duro's on the quad (I don't want to run the blades on hardpack but didn't have a choice tonight!) and see about putting a gravity feed cell on it and go back and try again. I was SOOO excited that first launch that it pulled like it was supposed to and then so crushed when it just started spitting and sputtering again....
I loaded it in the back of the truck and took it over to a buddies house that has a farm plot behind his house. The path going around the field is relatively smooth (not washed out or anything), level, and most importantly, available. I loaded it in the truck and threw some Duro "balloonies" in the truck to carry with me. I started taking the lugnuts off the rear wheels when I got there and immediately remembered that the haulers are on banshee hubs and the duro's are on blaster pattern! Bad start already.... Good news is that I put about .4 gallons in the tank and prime with a splash of premix and she fired on the second kick.
Most bad news:
I lost the cap to my mechanical caliper so I lost brakes on the first "run" LOL! There isn't a whole lot of space to shut down but I managed.
The top bracket on my in bumper fuel cell broke. That's the one I had to rebend like 5 times to get to fit right so it finally stress fatigued enough and broke on a hard bump (dirt path with no suspension).
2nd gear launch with no bar on a 8" extended swingarm on hardpack lifted the front end off the ground. That may have actually been what broke the fuel cell because it slammed back down. It felt RIGHT like it was DOING THE DAMN THING.
When I shifted to third, about halfway through third gear it just DIED each time. Once I actually felt fuel spray out of the carb vent onto my leg and there was copious amounts of splooge running out of the silencer. This was a better run than at busco in April when it was shooting liquid fuel out of the pipe tip but still not right. It runs right until the pump "comes on line" and then just spits and sputters.
Considering that this pump setup is straight bypass and I broke the fuel cell, I think it's time to consider a gravity feed system fuel cell..... I'm going to mount the duro's on the quad (I don't want to run the blades on hardpack but didn't have a choice tonight!) and see about putting a gravity feed cell on it and go back and try again. I was SOOO excited that first launch that it pulled like it was supposed to and then so crushed when it just started spitting and sputtering again....
Removing a float once it's on gravity feed? Will the "float" still float with one half gone?
Darn not having a milling machine to mill a solid billet oversized bowl!
Darn not having a milling machine to mill a solid billet oversized bowl!
Nice looking head! I've been running an o-ring on my head since it was put together and haven't had any issues with it. Definately better then the stock gasket imo
thats good to hear you got some seat time James but also sucks about the pump. gravity feed it up and see what happens
i dont wanna see you fry it.
IMO it needs at least 200% stock capicity to feed an alky nitro blend. then i would still be cautious not to run it dry for the first few passes till your sure.
sounds like you are getting there on tuning, hope to see it run in sept.
IMO it needs at least 200% stock capicity to feed an alky nitro blend. then i would still be cautious not to run it dry for the first few passes till your sure.
sounds like you are getting there on tuning, hope to see it run in sept.
Well, this is a PJ38 with a stock sized bowl on it. It's already twice the fuel capacity as a stock carb! LOL
That was the idea behind the low pressure fuel pump, it was supposed to supply a slight positive pressure behind the needle to make sure that there would be adequate fuel flow into the bowl. Unfortunately there's more than adequate fuel flow into the bowl!
I'm going to do a few test passes to make SURE that a gravity feed system is going to fix the flooding issue. Once I can get through third, I'll worry about running out! LOL!
That was the idea behind the low pressure fuel pump, it was supposed to supply a slight positive pressure behind the needle to make sure that there would be adequate fuel flow into the bowl. Unfortunately there's more than adequate fuel flow into the bowl!
I'm going to do a few test passes to make SURE that a gravity feed system is going to fix the flooding issue. Once I can get through third, I'll worry about running out! LOL!
Well, this is a PJ38 with a stock sized bowl on it. It's already twice the fuel capacity as a stock carb! LOL
That was the idea behind the low pressure fuel pump, it was supposed to supply a slight positive pressure behind the needle to make sure that there would be adequate fuel flow into the bowl. Unfortunately there's more than adequate fuel flow into the bowl!
I'm going to do a few test passes to make SURE that a gravity feed system is going to fix the flooding issue. Once I can get through third, I'll worry about running out! LOL!
guess its been a while since i looked at a stock carb.
I guess I could actually build a SCD racing custom alky bowl too.....
thats probably what you will do. you have a some good tig skills and imagination, put them to use. you could have it done rough in 20 minutes if you have the material there.
I want to try it with just a gravity feed system to make sure it will actually fix my problem first but I may do that....
I don't know about 20 minutes, when was the last time that you fabbed something from scratch and it only took twenty minutes? Hot pockets in the microwave don't count!
I don't know about 20 minutes, when was the last time that you fabbed something from scratch and it only took twenty minutes? Hot pockets in the microwave don't count!
if you are just modding the stock bowl there wont be much to it. in a hurry im sure you could hammer it out with everything laid out in front of you. yum! hot pockets!
- Status
