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Jared Langenfeld
Joined: 06 Apr 2011
Posts: 65
Location: United States, Kansas, Kansas City
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 Posted: Mon Jun 04, 2012 9:31 am Post subject: Fuel Line Routing |
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I have been having problems with my pump-around PWM carb and I decided to just start all over and now I will be running a PWK carb with no pump-around. So I bought a brand new PWK carb and a brand new Mikuni fuel pump.
So my question is what to do with the two outlets of the pump. I have read several different solutions:
1) Plug one of the outlets, put a y-connector between the other outlet and carb and split to the carb and fuel tank
2) Connect both outlets with a y-connector and then use another y-connector to split to the carb and fuel tank
3) Route one outlet to the carb and one outlet to the fuel tank
Personally, I feel solution 3 would work the best, *IF* the pump works how I think it works. Both of the outlets take fuel from the same chamber inside the pump, right? So there shouldn't be a difference between having a y-connector outside the pump or use the two outlets as a figurative y-connector?
Any help would be appreciated!
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2008 Mike Wilson with Honda CR125 shifter |
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Jason Vehige
Joined: 21 Apr 2006
Posts: 282
Location: United States, Tennessee, Nashville
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| Posted: Mon Jun 04, 2012 11:29 am Post subject: |
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On my ICC I use a t fitting to "combine" the 2 outlets... Second t with one line return to the tank and one to the carb. Like your option 2....YMMV
Trying the Dellorto pump currently.
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Jason Vehige
08 Gillard Charlotte / SGM sl204
05 Vanspeed Sirio / SGM sl204 |
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Joe Ricard
Joined: 23 Jun 2009
Posts: 882
Location: United States, Mississippi,
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| Posted: Mon Jun 04, 2012 11:39 am Post subject: |
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Jason did mine at Nats a couple years ago and obviously is like #2
Works Great!!!!!!!!
Rather have all the fuel available at the carb inlet. and route the return line "T" so it has to travel up hill for a ways. keeps a nice static head on the inlet supply to the carb.
Some people put a restrictor at the tank return fitting .040 or some sort. I guess to control the fuel flow from taking the path of least resistance.
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Arrow AX-8/ Rotax Sr. |
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Chris M Johnson
Joined: 14 Oct 2005
Posts: 568
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| Posted: Mon Jun 04, 2012 3:25 pm Post subject: Re: Fuel Line Routing |
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| Jared Langenfeld wrote: | I have been having problems with my pump-around PWM carb and I decided to just start all over and now I will be running a PWK carb with no pump-around. So I bought a brand new PWK carb and a brand new Mikuni fuel pump.
So my question is what to do with the two outlets of the pump. I have read several different solutions:
1) Plug one of the outlets, put a y-connector between the other outlet and carb and split to the carb and fuel tank
2) Connect both outlets with a y-connector and then use another y-connector to split to the carb and fuel tank
3) Route one outlet to the carb and one outlet to the fuel tank
Personally, I feel solution 3 would work the best, *IF* the pump works how I think it works. Both of the outlets take fuel from the same chamber inside the pump, right? So there shouldn't be a difference between having a y-connector outside the pump or use the two outlets as a figurative y-connector?
Any help would be appreciated! |
Jared,
CR125 carbs are different than ICC. ICCs are designed to work without pumparound, with hondas it is almost a necessity. Karts do not lean in the turns like bikes so the CR125 motor will tend to fuel starve in long turns. You can run without a pumparound, but it can be a headache.
I have run both pwk and pwm and the slide/needle and pilot jet have a much larger effect than the style of carb. They both work great. I slightly prefer the air screw adjustment on the PWM. I much prefer the screw top on the PWK for changing needles.
Carbs are pretty much bulletproof, but the fuel pumps and fuel lines are what will cause problems. Also the pulse line can cause problems. Make sure it is pulse line material, thicker than fuel line, and keep it as straight and as short as possible.
Now that you have a new fuel pump, I would ask you to consider trying to get the pumparound working.
If you buy see-thru fuel line, you can actually see the fuel moving through the system and diagnose any problems. The standard mikuni fuel pumps have arrows showing the direction of flow.
The routing should be tank -> fuel filter -> input pump (arrow in) -> output pump (arrow out) -> carb bowl (side of bowl)
Then on the output side:
Carb relief tube (custom machined on top) -> input second pump (arrow in) -> pump output (arrow out) -> fuel tank.
You may have to plug the fuel relief tube on the bottom side of the pumparound if that has not been done.
I usually think simple is better, but in the case of carbs on a honda, the pumparound is proven tech. If the carb really is broken, you can have your new pwk converted (for about $150) or you can get a kit to do it yourself.
Good luck. |
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Jason Vehige
Joined: 21 Apr 2006
Posts: 282
Location: United States, Tennessee, Nashville
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| Posted: Mon Jun 04, 2012 3:34 pm Post subject: |
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If a pump around works for you great, but they sure as hell were not designed to use them....
I know of more than 1 autocrosser running floats in their Moto with no issues 
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Jason Vehige
08 Gillard Charlotte / SGM sl204
05 Vanspeed Sirio / SGM sl204 |
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Chris M Johnson
Joined: 14 Oct 2005
Posts: 568
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| Posted: Mon Jun 04, 2012 3:40 pm Post subject: |
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| Jason Vehige wrote: | If a pump around works for you great, but they sure as hell were not designed to use them....
I know of more than 1 autocrosser running floats in their Moto with no issues |
I just gave him the advice because I saw two ICC guys had responded and thats a different system. You can run without on moto, but I have seen a bunch of threads over the past five years of guys having float and starvation issues. The cr125 was not designed to run on karts. Majority are on pumparound. Since hes got the pumparound it makes sense to give it another go now that he has a new fuel pump. |
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Jared Langenfeld
Joined: 06 Apr 2011
Posts: 65
Location: United States, Kansas, Kansas City
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| Posted: Mon Jun 04, 2012 3:46 pm Post subject: Re: Fuel Line Routing |
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| Chris M wrote: | | Jared Langenfeld wrote: | I have been having problems with my pump-around PWM carb and I decided to just start all over and now I will be running a PWK carb with no pump-around. So I bought a brand new PWK carb and a brand new Mikuni fuel pump.
So my question is what to do with the two outlets of the pump. I have read several different solutions:
1) Plug one of the outlets, put a y-connector between the other outlet and carb and split to the carb and fuel tank
2) Connect both outlets with a y-connector and then use another y-connector to split to the carb and fuel tank
3) Route one outlet to the carb and one outlet to the fuel tank
Personally, I feel solution 3 would work the best, *IF* the pump works how I think it works. Both of the outlets take fuel from the same chamber inside the pump, right? So there shouldn't be a difference between having a y-connector outside the pump or use the two outlets as a figurative y-connector?
Any help would be appreciated! |
Jared,
CR125 carbs are different than ICC. ICCs are designed to work without pumparound, with hondas it is almost a necessity. Karts do not lean in the turns like bikes so the CR125 motor will tend to fuel starve in long turns. You can run without a pumparound, but it can be a headache.
I have run both pwk and pwm and the slide/needle and pilot jet have a much larger effect than the style of carb. They both work great. I slightly prefer the air screw adjustment on the PWM. I much prefer the screw top on the PWK for changing needles.
Carbs are pretty much bulletproof, but the fuel pumps and fuel lines are what will cause problems. Also the pulse line can cause problems. Make sure it is pulse line material, thicker than fuel line, and keep it as straight and as short as possible.
Now that you have a new fuel pump, I would ask you to consider trying to get the pumparound working.
If you buy see-thru fuel line, you can actually see the fuel moving through the system and diagnose any problems. The standard mikuni fuel pumps have arrows showing the direction of flow.
The routing should be tank -> fuel filter -> input pump (arrow in) -> output pump (arrow out) -> carb bowl (side of bowl)
Then on the output side:
Carb relief tube (custom machined on top) -> input second pump (arrow in) -> pump output (arrow out) -> fuel tank.
You may have to plug the fuel relief tube on the bottom side of the pumparound if that has not been done.
I usually think simple is better, but in the case of carbs on a honda, the pumparound is proven tech. If the carb really is broken, you can have your new pwk converted (for about $150) or you can get a kit to do it yourself.
Good luck. |
Thank you very much for the input. I have spent this whole season trying to diagnose why my engine is hesitating in long and high-load corners. When I am in a high-load corner and start rolling back into the throttle, the engine will hesitate and I will have no power until I get out of the corner.
Over the course of this season, I have replaced and re-routed all the fuel lines and I have rebuilt the fuel pumps and the problem has not gone away. In a straight-line, the motor pulls strong and in slower and shorter corners, the motor pulls strong. Only when I am in a long and high-load corner does it hesitate and lose power. I have also played around with adjusting the pilot jet and main jet. So the only thing I haven't touched is the carb itself.
There are several other moto guys that I know who run a non-pump around system and have excellent results. My close friend, Shawn, runs a non-pump around PWK on his mod-moto and has one of the strongest moto engines I have seen. I co-drove it all last season and had zero issues. So I have decided to try a non-pump around PWK on my kart.
Again, I appreciate your input, thanks.
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2008 Mike Wilson with Honda CR125 shifter |
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Chris M Johnson
Joined: 14 Oct 2005
Posts: 568
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| Posted: Mon Jun 04, 2012 4:04 pm Post subject: |
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It sounds like you are on top of it. Hopefully the new carb works for you. Its hard to tell how much experience someone has online so I gave as much infomation as I had to help you with the PA. Good luck.
I just read your thread again, and while it may sound unlikely, really bad jetting could have this effect. If the motor is peaky to begin with (say the timing is not advanced), the pilot and needle are wrong, and the main jet is 4 sizes too big, it can do that. Every motor is different but a si-mod at the peak of summer will take a ~170 main jet. If the motor is too rich on top you will find it doesnt always clear out and will intermittently have problems part throttle. The reason your friends motor is strong is because it is tuned/built well, not because it has a standard carb.
Just some more baseline advice, but try a DGJ needle, 55 pilot, and 172 main. If you are anywhere above 178 on a hot summer day that will start to cause drivabiltiy issues. Good luck. |
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Tom Barth
Joined: 22 Oct 2001
Posts: 1400
Location: United States, Michigan, Waterford
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| Posted: Wed Jun 06, 2012 5:04 pm Post subject: |
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Needle carb 101:
Both PWM, PWK and Dellorto are classified as needle carbs, meaning that the fuel is metered by a tapered needle attached to the throttle valve. As the throttle valve is lifted and the vacuum strengthens the tapered needle allows more fuel to engine. OK, what does this have to do with the fuel supply? Nothing, just thought I'd mention it.
But, both carbs have a needle valve that lets fuel into the float chamber as needed by engine. Normally the needle valve size is large enough to allow fuel to be fed to bowl by gravity. The PWM/PWK has needle that is probably about .3 to .4 mm in flow I.D. This size is too large when switching from gravity to pressure i.e kart engine with fuel pump. If the fuel line to carb is direct from pump the the large I.D. allows too much fuel in the bowl and overflow out the vent tubes occurs. This condition can be corrected by putting tee in line from pump to carb and back to tank. Most Dellorto's use this method. Note: Rotax chooses to use smaller needle valve and match fuel pressure with engine usage.
I personally prefer to use the tee to ensure maximum fuel to carb. Needle valve size should be at least 20/30% larger than largest main jet. Unfortunately there is not a large selection of needle valve sizes available for the PWK/PWM.
But....using the tee is the correct way to supply fuel to the PWM/PWK carb.
I really can't see any advantage to the pump around. They are expensive & troublesome.
Try it, you'll like it. 
_________________
Tom Barth
http://www.greenflagkarting.com/
Power is good...more power is better... too much power is just right! |
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Robert Lawson
Joined: 10 Nov 2001
Posts: 2227
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| Posted: Thu Jun 07, 2012 11:54 am Post subject: |
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Jared,
It seems you replaced everything but did you replace the pick-up tube inside the tank?
Too many guys overlook this, if it's more than a season old it has probably gotten pretty hard (barring Tygon). If the tube can't freely swing with the fuel load it may cause problems, especially in long fast corners. Take a look, it's a cheap test!
I ran a standard PWM on an RS 125 enduro kart for 15 years. I also use the free swinging pick-up like a CIK tank with a Mikuni dual pump. On that kart we ran the feed line to the pump, one outlet to the the carb (no T's or Y's or main jets in the line) and the other also unrestricted back to the top of the tank. It has worked fine (brother is still on it!) in long fast corners like the carosell at Road America. I'm now on an ICC and use the set-up that most all Delorto guys use (Y's then T's, etc.) and it works fine too. Never had to use that on the PWM though.
Float level is critical on the std. Keihin carb. You will have to check/adjust it often to keep it in the happy spot. As long as it's right the direct plumbing works good.
Never bought a pump-o-round but we did alter a carb ourselves. It worked, it didn't work, then it worked.......and then it didn't!
Hey, guys swore by the Track Magic "Magic Can" too......
Whatever works for you, take a look at that fuel line in the tank and let us know the result.
Good Luck,
RPM |
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Chris M Johnson
Joined: 14 Oct 2005
Posts: 568
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