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Post by stretchelite on Nov 19, 2012 1:29:21 GMT -5
I have a 1e40qmb with a 72cc kit and pipe with stock carb, it runs rich until it gets up top then goes lean sputters and dies when you let off the gas. I have good flow to the carb, but I can't seem to get fuel into the bowl fast enough to compensate for how fast its leaving and/or I'm getting too much back flow and the pressure is pushing the fuel back out?  any ideas on how to fix this? I've cleaned the carb 1000 times it is SPOTLESS, replaced the float, pin, and the piece the pin sits in, adjusted the float way high to try and compensate then returned it to spec when the carb leaked all over. Thanks for any help |
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Post by reveeen on Nov 19, 2012 2:49:43 GMT -5
I *think* we have had this discussion before........
Vacuum petcock+ WOT (no vacuum)= no fuel
maybe try another petcock?
After wasting the money here, for an assortment of vacuum petcocks (both OEM and aftermarket), I am firmly convinced a manual petcock is the way to go.
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Post by stretchelite on Nov 19, 2012 16:43:06 GMT -5
I have no petcock, I removed it and ran fuel line straight to carb to rule it out. Can I get a larger pin and seat to allow more flow??
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Post by 90GTVert on Nov 19, 2012 22:02:04 GMT -5
Make sure the in tank filter is clean, if so equipped.
There should be no need to alter the float setup, other than getting it set wherever it needs to be. It's usually not that picky though. Seems more likely to be a tuning problem or an air leak.
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Post by skuttadawg on Nov 20, 2012 1:03:58 GMT -5
Are you using the jets that came with it ? With a BBK you will need a larger idle jet and main jet . Cleaned the airfilter ? Here is a link about carbs that may help you www.iwt.com.au/mikunicarb.htm . Run it at WOT in front of your house then hit the kill switch . Then remove the sparkplug and compare it to this chart www.4secondsflat.com/plug_chart.html . My 2T came with a 19mm TK where many have a 17.5mm or smaller , where the 2T power kits come with a 21mm PWK carb . My carb uses Mikuni VM11/22 size jets and here is where I found them the cheapest price www.power-barn.com/servlet/the-1344/Mikuni-VM11-fdsh-22-Large-Round/Detail . I would get a caliper to measure the jet dimensions before buying any . Does it bog any ? Airbox or Uni airfilter ? I tried some jets that were too large at first and it would flood it with too much gas . Check the fuel/air screw and position of the needle on the clip . If it sputters when you let up off of the throttle it could be a lean misfire . Running too lean will burn up the piston and have it soft seize . Premix or oil injection ? A new sparkplug can often do wonders . I use NGK BR8HIX which is the iridium type |
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Post by stretchelite on Nov 20, 2012 13:07:48 GMT -5
Sorry I know the idea running through everyones head is that I don't know what I'm talking about, lol and at times I forget that not everyone has seen my other threads. I have jetted and plug chopped ALOT I have the 17.5 mikuni (possibly 16mm?) no filter with velocity stack (because I had one laying around and it actually made quite a difference. I am RICH from idle until my cvt has cycled then I go REALLY lean at higher rpms once the cvt has cycled and the rpms steadily increase. I let off the gas and have to choke it to keep it running until it refills the fuel bowl. I removed the in-tank filter and the inline filter is 1 day old I drained the tank and refilled with fresh premium that I strained as it went into the tank 32:1 premix with castor 927.
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Post by 90GTVert on Nov 20, 2012 14:00:43 GMT -5
Fuel tank venting issue? Can you tell any difference in how fast fuel will run through the hose with the cap on or off?
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Post by stretchelite on Nov 20, 2012 16:22:59 GMT -5
nope none at all I JUST drained the tank AGAIN ): sad seeing that money pour into my drain bucket. Moved the tank up 2 inches made no difference, I notice ALOT of fuel coming OUT of the carb at higher rpms I'm fairly certain its blowing pressure into the fuel bowl and causing the flow to stop... Will cf reeds close faster than he stockers? or is there a higher tension set/ can I double up on them or something to help?
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Post by 90GTVert on Nov 20, 2012 22:21:51 GMT -5
Have you checked the stock reeds to see if there's any sort of gap or anything that doesn't look right?
CF reeds may help, but stock SS reeds in good condition should perform to a reasonably high RPM.
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Post by stretchelite on Nov 20, 2012 23:28:18 GMT -5
no gaps at all just replaced them the other day. I can run up to around 38 mph before it starts spitting and sputtering fuel all over the place. It dies even at 3/4 throttle it'll run fine then die out of nowhere let it idle for a few seconds or shove my hand over the carb it picks right back up.
I don't know what else to look at if it's not the reeds causing the back flow /:
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Blowin Smoke
Scoot Enthusiast
Posts: 289
Location: Port Orange, Fl
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Post by Blowin Smoke on Dec 1, 2012 12:08:02 GMT -5
Put an air box on it and down jet until you get good top speed. Then work on the pilot circuit.
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Post by prodigit on Dec 1, 2012 15:54:07 GMT -5
I have a vacuum petcock, and don't suffer from this.
however perhaps you need to increase your main jet, and decrease your pilot jet, or perhaps increase both, and adjust your idle rpms screw.
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Post by stretchelite on Dec 6, 2012 2:48:05 GMT -5
gonna get some fiberglass reeds maybe tomorrow. It is 100% sure NOT a jetting issue I have a BIG jet in it, same size some of the 125 dirtbike guys run. I run RICH RICH RICH at low RPM then mid-high RPM I run LEAN, it spits fuel all over the frame. It HAS to be an issue with how the reeds can't close fast enough to compensate for the backflow of pressure coming from the cyl. If I choke it a little to get past the bad rpm range to the point that the reeds become for lack of a better word useless it runs fine. I'm not sure f the spring rate on them is too low or if at that high of a speed they are too heavy to keep up, but I've done EVERYTHING imaginable short of a new carb and the lighter reeds, I can now drain my entire tank using my fuel drain from the carb very quickly, so the fuel flow is fine. The float is perfect, the jet is HUGE I CAN NOT run an air box witout spending ALOT of time redesigning my frame layout or fabbing up a new intake to reposition my carb, but even then I have never once owned a scoot 4 wheeler or gokart that had a stock airbox on it so that is not my problem, even with an airbox on it it would still backflow through the carb, it would just soak the filter instead. Thanks for the help, but I'm pretty convinced this issue won't be solved through explanation online unless I video chat someone that is EXTREMELY knowledgeable in 2T engines showing what its doing step by step. If the reeds don't work I'll sell off the engine at a low price cut my losses and go 4T so I know it will be reliable and give me no issues.
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any ideas on how to fix this? I've cleaned the carb 1000 times it is SPOTLESS, replaced the float, pin, and the piece the pin sits in, adjusted the float way high to try and compensate then returned it to spec when the carb leaked all over. Thanks for any help
