Planet Minis

fatcaaat · 03-09-2009, 11:01 AM

Here is a question for you folks out there on the strange runnings of my CT. I do have a GPX177V2 motor in here, but that is irrelavant...we're talking general CT70 fuel delivery stuff here I think.

I can cruise without issue. Low end...just fine. If I wrap this motor out for about 1/4-1/2 mile in the upper 8k's it runs just fine too...but after one of these high rpm bursts, the motor pretty much shuts off and I'll coast for about 100 feet and it will start running again. I did one of these high rpm runs and it quit when I left off the throttle...so I immediately pulled over and kicked and nothing. I waited all of about 15 seconds and kicked and purred away.

So I am 100% we're talking fuel delivery here. The question is:

Is it the float level in my carb not letting enough fuel into the bowl and restricting fuel flow in general, or...

Is my fuel hose routing too long...I run the hoses to a univeral 2-way petcock, then run about another 6 inches total line to accomodate my fuel filter...and I loose the momentum of the fuel coming from the tank.

FastMC · 03-09-2009, 11:13 AM

Almost sounds like a fuel tank venting issue. Try cracking open the float bowl drain and just let the fuel run for a while into a container and see what happens after a minute or so. If you have the type of carb that has a fuel drain tap at the bottom of the bowl you can hook a piece of clear hose up to it and make a loop to see exactly where the fuel height is in the bowl and adjust accordingly.

FastMC · 03-09-2009, 11:20 AM

It's also possible you need a higher rate float valve. That big of a motor at high speeds will use a lot of fuel.

fatcaaat · 03-09-2009, 11:30 AM

Quote:

Originally Posted by FastMC

Almost sounds like a fuel tank venting issue. Try cracking open the float bowl drain and just let the fuel run for a while into a container and see what happens after a minute or so. If you have the type of carb that has a fuel drain tap at the bottom of the bowl you can hook a piece of clear hose up to it and make a loop to see exactly where the fuel height is in the bowl and adjust accordingly.

Running a Mikuni VM26 606 on this. I don't think it is a fuel venting issue. Now that I think about it, it is the same fuel delivery system I had when I had my Jialing 157cc motor in the frame and it wasn't an issue with that motor.

I have to think its the float level now as people are running this setup in all their pitbikes and haven't had issues.

BTW...for anyone ever considering running a GPX177V2 motor in a CT70, I am geared at 17/31 with 120/90-10 tires and the gear is not tall enough. 18T won't fit on the front, so a 29 will be needed on the back along with a little bit of machine work to the hub.

FastMC · 03-09-2009, 11:36 AM

[quote=fatcaaat;1214598]

I have to think its the float level now as people are running this setup in all their pitbikes and haven't had issues.

quote]

That's true but probably not revving the motor like that for extended periods like on the street.

50rider340 · 03-09-2009, 11:39 AM

i had this exact problem on my c70. I could cruise half throttle all day (88 in this bike) but say a big hill comes and i wanna bottom out 55 on the speedo id get half way and it bog out. Let it sit for a hot sec and it would crank right over and then i could keep on going. I switched a complete points motor to a CDI setup (hole different carb etc) and got the same issue. Went to larger fuel lines and same thing. So now im gonna be drilling new holes so the lines stay above the carb and see what happens then. But im almost possitive its fuel delivery, from the tank to your carb.

nielspbr · 03-09-2009, 12:44 PM

Put a mikuni vacuum operated fuel pump in the fuel line. The low difference in fuel levels between tank and float needle is preventing the fuel to flow in a high enough flowrate to feed the engine.

I presume you checked if there are no air bubbles staying in the fuel line.

LoudFastUgly · 03-09-2009, 05:19 PM

Quote:

Originally Posted by nielspbr

Put a mikuni vacuum operated fuel pump in the fuel line. The low difference in fuel levels between tank and float needle is preventing the fuel to flow in a high enough flowrate to feed the engine.

I presume you checked if there are no air bubbles staying in the fuel line.

+1, most street bikes have a 'make up' pump for when the fuel supply is less than half in the tank to keep float levels consistant. Looping a clear fuel line under the carb and then to the input barb may help to isolate the fault.

Dan_Lorenze · 03-10-2009, 12:51 AM

I've been having the same exact problem with my CT70 GPX177 with an OKO 26... Bottom and Mid, fine.. Top end revs really nice but it often bogs down and stalls when I'm screaming the thing, I wait a few seconds and the power comes back. In fact, if you've seen my video here in the CT forums you'll see pull to the side of the road, I lost power... I've just thought my jetting has been off and need to rejet. I think it's considered Vapor Lock.. My gas cap vents are hogged out and the float level I believe is good.. I've just chaulked it up as a cheap carb, to hear this happening on other carbs makes me wonder.. Hmm...

cdoublejj · 03-10-2009, 01:05 AM

most performance car builds that i have seen usually in evolve and electric pump you can hear it buzz before they start the car.

BILLYBIGWIG · 03-10-2009, 02:03 PM

apart from fuel problems are your v2 engines still running well

fatcaaat · 03-10-2009, 02:05 PM

Quote:

Originally Posted by BILLYBIGWIG

apart from fuel problems are your v2 engines still running well

My GPX177V2 motor is stupid fast in my CT. I only have about 50 miles on it though.

BILLYBIGWIG · 03-10-2009, 02:12 PM

good just bought a v2 kit for my 160 in the dax and a s35 decomp

big pete · 03-10-2009, 02:29 PM

I'm guessing it's the gas tank vent. It's either clogged or not venting fast enough. My friend's R6 used to have the same problem until cleared the vent.

Dan_Lorenze · 03-12-2009, 09:37 AM

Quote:

Originally Posted by big pete

I'm guessing it's the gas tank vent. It's either clogged or not venting fast enough. My friend's R6 used to have the same problem until cleared the vent.

I opened up quite a bit.. But you could be right, I should go crazy with it....

gstegman · 03-12-2009, 09:54 AM

What about riding it hard until it sputters then shut the petcock off and check the float level?

boonacka · 03-12-2009, 10:18 AM

I too think it may be a venting issue. i had the same problem a while ago with the same symptoms and it turned out to be a clogged vent on the cap.

muxster · 03-12-2009, 11:09 AM

I think I may have had the same problem at some point running the 140cc Lifan
look at the Belgiun CT on Z's website.
The guy has a Mikuni fuel pump on it!

TankTheory · 03-12-2009, 09:18 PM

Quote:

Originally Posted by nielspbr

Put a mikuni vacuum operated fuel pump in the fuel line. The low difference in fuel levels between tank and float needle is preventing the fuel to flow in a high enough flowrate to feed the engine.

I presume you checked if there are no air bubbles staying in the fuel line.

Where do you get said Mikuni vacuum fuel pump..?

FastMC · 03-12-2009, 09:29 PM

Quote:

Originally Posted by TankTheory

Where do you get said Mikuni vacuum fuel pump..?

Should be able to get it from anyone that does snowmobile stuff.

Parts Unlimited has them. $21

03-09-2009, 11:01 AM	#1 (permalink)
fatcaaat 3rd Gear Member Join Date: Sep 2004 Location: Arlington, VA Posts: 3,778	strange running question...float? Here is a question for you folks out there on the strange runnings of my CT. I do have a GPX177V2 motor in here, but that is irrelavant...we're talking general CT70 fuel delivery stuff here I think. I can cruise without issue. Low end...just fine. If I wrap this motor out for about 1/4-1/2 mile in the upper 8k's it runs just fine too...but after one of these high rpm bursts, the motor pretty much shuts off and I'll coast for about 100 feet and it will start running again. I did one of these high rpm runs and it quit when I left off the throttle...so I immediately pulled over and kicked and nothing. I waited all of about 15 seconds and kicked and purred away. So I am 100% we're talking fuel delivery here. The question is: Is it the float level in my carb not letting enough fuel into the bowl and restricting fuel flow in general, or... Is my fuel hose routing too long...I run the hoses to a univeral 2-way petcock, then run about another 6 inches total line to accomodate my fuel filter...and I loose the momentum of the fuel coming from the tank.

03-09-2009, 11:13 AM	#2 (permalink)
FastMC Sporting the Merkin Join Date: Mar 2004 Location: boston area Posts: 5,072 My Mood:	Re: strange running question...float? Almost sounds like a fuel tank venting issue. Try cracking open the float bowl drain and just let the fuel run for a while into a container and see what happens after a minute or so. If you have the type of carb that has a fuel drain tap at the bottom of the bowl you can hook a piece of clear hose up to it and make a loop to see exactly where the fuel height is in the bowl and adjust accordingly.

03-09-2009, 11:20 AM	#3 (permalink)
FastMC Sporting the Merkin Join Date: Mar 2004 Location: boston area Posts: 5,072 My Mood:	Re: strange running question...float? It's also possible you need a higher rate float valve. That big of a motor at high speeds will use a lot of fuel.

03-09-2009, 11:36 AM	#5 (permalink)
FastMC Sporting the Merkin Join Date: Mar 2004 Location: boston area Posts: 5,072 My Mood:	Re: strange running question...float? [quote=fatcaaat;1214598] I have to think its the float level now as people are running this setup in all their pitbikes and haven't had issues. quote] That's true but probably not revving the motor like that for extended periods like on the street.

03-09-2009, 11:39 AM	#6 (permalink)
50rider340 3rd Gear Member Join Date: Mar 2004 Location: CT Posts: 3,083 My Mood:	Re: strange running question...float? i had this exact problem on my c70. I could cruise half throttle all day (88 in this bike) but say a big hill comes and i wanna bottom out 55 on the speedo id get half way and it bog out. Let it sit for a hot sec and it would crank right over and then i could keep on going. I switched a complete points motor to a CDI setup (hole different carb etc) and got the same issue. Went to larger fuel lines and same thing. So now im gonna be drilling new holes so the lines stay above the carb and see what happens then. But im almost possitive its fuel delivery, from the tank to your carb.

03-09-2009, 12:44 PM	#7 (permalink)
nielspbr Euro Seagull Join Date: Feb 2008 Location: Netherlands Posts: 463 My Mood:	Re: strange running question...float? Put a mikuni vacuum operated fuel pump in the fuel line. The low difference in fuel levels between tank and float needle is preventing the fuel to flow in a high enough flowrate to feed the engine. I presume you checked if there are no air bubbles staying in the fuel line.

03-10-2009, 12:51 AM	#9 (permalink)
Dan_Lorenze 2nd Gear Member Join Date: Mar 2006 Location: Moorpark CA Posts: 451	Re: strange running question...float? I've been having the same exact problem with my CT70 GPX177 with an OKO 26... Bottom and Mid, fine.. Top end revs really nice but it often bogs down and stalls when I'm screaming the thing, I wait a few seconds and the power comes back. In fact, if you've seen my video here in the CT forums you'll see pull to the side of the road, I lost power... I've just thought my jetting has been off and need to rejet. I think it's considered Vapor Lock.. My gas cap vents are hogged out and the float level I believe is good.. I've just chaulked it up as a cheap carb, to hear this happening on other carbs makes me wonder.. Hmm...

03-10-2009, 01:05 AM	#10 (permalink)
cdoublejj 3rd Gear Member Join Date: Oct 2008 Location: St.Joe MO Posts: 1,367 My Mood:	Re: strange running question...float? most performance car builds that i have seen usually in evolve and electric pump you can hear it buzz before they start the car.

03-10-2009, 02:03 PM	#11 (permalink)
BILLYBIGWIG 1st Gear Member Join Date: Dec 2004 Location: durham england Posts: 184 My Mood:	Re: strange running question...float? apart from fuel problems are your v2 engines still running well

03-10-2009, 02:12 PM	#13 (permalink)
BILLYBIGWIG 1st Gear Member Join Date: Dec 2004 Location: durham england Posts: 184 My Mood:	Re: strange running question...float? good just bought a v2 kit for my 160 in the dax and a s35 decomp

03-10-2009, 02:29 PM	#14 (permalink)
big pete 2nd Gear Member Join Date: Apr 2008 Location: Norcal Posts: 866	Re: strange running question...float? I'm guessing it's the gas tank vent. It's either clogged or not venting fast enough. My friend's R6 used to have the same problem until cleared the vent.

03-12-2009, 09:54 AM	#16 (permalink)
gstegman "The Steg" Join Date: Jan 2008 Location: Castro Valley, CA Posts: 983	Re: strange running question...float? What about riding it hard until it sputters then shut the petcock off and check the float level?

03-12-2009, 10:18 AM	#17 (permalink)
boonacka 3rd Gear Member Join Date: Mar 2006 Location: SolomonRacing.net Posts: 1,191 My Mood:	Re: strange running question...float? I too think it may be a venting issue. i had the same problem a while ago with the same symptoms and it turned out to be a clogged vent on the cap.

03-12-2009, 11:09 AM	#18 (permalink)
muxster 2nd Gear Member Join Date: Sep 2008 Location: Redondo Beach, Ca. Posts: 471 My Mood:	Re: strange running question...float? I think I may have had the same problem at some point running the 140cc Lifan look at the Belgiun CT on Z's website. The guy has a Mikuni fuel pump on it!

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