Stock carb mod

[carpediemi24]

Thanks Egor and Mdlee! I have moved the needle but have not tested due to snow and my bike is clean. I still am trying to wrap my head around going smaller port hole. Seems like it would get less gas and thus slower top end!? I am going to order some spare brass stems to play with as a back up. About to build a new bike next week with all premium parts and upgrades and this has been my only glitch to figure out thus far. I started from scratch on this build but was an older frame I rebuilt 98% of it.

Merry Christmas!!
Buck

 

[Egor]

Some times it is hard to comprehend. But what you have to consider is that at your altitude you have less air and so the engine needs less fuel in the less air. You can get a piece of wire and find one that will just fit and then measure the size with a micrometer. One thing I have done with a jet that is too big. I take a wisker of wire out of an old extension cord and bend a 90 in about 1/2" of wire and put it in the jet. This will change the size of the jet. it is a quick way to find if it is too big. And you still have to try and shut off the fuel and see if it leans out and runs correct. If you can at the wide open throttle just reach down and turn off the fuel. Have fun, Dave

PS: Snow. I just got new our new house in Utah closed today, I guess I will now know what SNOW is.

 

[michaelgrav]

I am gonna give your idea a chance before spending money on a Mikuni 18mm, God knows I have invested in so many upgrades but the bike does haul ASS!. I have a little top end faltering hope this works!

 

[carpediemi24]

Thanks Egor! Its been a couple weeks. Did try and move the needle notch by notch up..top notch slowed down the bike at top end for sure. I moved the needle to the middle position and nice top end, barely bogs. I did, by accident ride with the gas off and it just, I believe, it only sputtered and died. I only got to ride it that day, recovering from lower back out, but a day or two more and will play some more. http://motorbicycling.com/images/smilies/brnot.gif

Building a new build from Dax F80 (I believe 69CC !?) soon as bike arrives. Will chrome out the covers of the motor and some other goodies This is too fun for a tinker like me.

Peace everyone!

 

[chopperjoe]

Re: Stock carb mod...

Giving a little context first. OK, just read the 18 pages here. Been reading these 2 motorbike forums and feel like my diploma should be in the mail soon

Egor, man I so would Love your opinion here. I really want to build these bikes here in CO as a hobby/job...I just so enjoy this.

Ok, my question and whats going on. I have the Starfire Gen-II-A 50cc (sticker/metal id says) and the NT carb (pic below). I live in Boulder CO which I believe is 5400ft-ish above sea level. I believe I have about 100miles or less on motor. The bottom of the main case is leaking a few drops after a 5 mile run or so. It seems to have a gray silicon like (want-a-be) gasket that is crumbling out at the bottom. So I would of course assume leaks compression a little.

Next, I keep the bike inside and temp is around 68 degrees and the outside temp here mainly now is 25-50 degrees (if this helps). I put the choke all the way up when I am about to start. Then slowly over 5-ish minutes I drop it down to idle/rev lower. It does idle I guess pretty well once warmed up...meaning it usually does not die after warmed up.
I do have to peddle a few feet before letting out clutch (85lb bike I believe with 44t front and 18t back sprocket).

Where I would LOVE and be so grateful to learn and know is, once warmed up, and going full throttle, the engine seems to bog at the top end, I let of the throttle a second or so then back to full, then bogs a few seconds later and repeat the same.

OK, I am listening, what would you experts do to the carb/engine,etc as a modification???

I am pretty handy just not sure which mod to do.

Oh, the spark plug right now is more darker chocolate than tan (richer). Stock spark plug. 91 octane fuel. 100% synthetic oil. Around 240lbs with me on bike.

I hope I listed what you need to hear to make some suggestions!?

Again, Thanks so much for your time and input.

Buck

like that rubber mount setup, great idea

 

[Dontwannawalk]

Re: can you guys seee this?

I hope I have my attachment on this, or my post isn't going to make any sense. any & all help is appreciated

Norm

On yes, polishint is suppose to be "polishing"on the thumbnail

 

[PaulFlorida]

Dontwannawalk: Yep that will increase airflow if you smooth the transition and polish the bore. I also bored out the carb until it was about 1.5mm smaller than the slide width. Never bore a carb larger than the slide width.

 

[karma1968]

Respuesta: Stock carb mod

heh that's the motor i just sold . and yes it did help.

 

[YPEDAL]

Egor, Hello. I have a question for you regarding your carb modification. You stated the drill bit is a .040 in I don't know terms is that like a 1/16 drill bit size. Thanks, YPEDAL

 

[Egor]

Y Pedal - the drill .040 is a number #60 or 1.02mm, there is no fraction to .040. The closest is a 3/64 .0469 and that should be ok. Hope this helps, I think you will like the way it will idle. Have fun, Dave

PS: I think if you can find some felt and make a donut that will fit tight around the center post to the main jet, it would work better than the cotton and wire. Just keep it away from the float. You are trying to replicate the missing idle circuit.

 

[Dontwannawalk]

Hi J, 1/64th is WAY too big. E-bay has a set of micro bits with a .039 bit that will work, Search Item number: 260288126783. What part are you needing to torque? Head bolts are 10 to 12 ft lbs. Hope this helps.

Here is another set of bits on e-bay. This is the set I have. Search Item number: 300259348928

Is there an update on where to find this set of drill bits? I've been hunting e-Bay and other sources to these tiny bits & have found none!! The smallest I have is a 1/32" .

Norm

 

[ken murphy]

Is there an update on where to find this set of drill bits? I've been hunting e-Bay and other sources to these tiny bits & have found none!! The smallest I have is a 1/32" .

Norm

I got mine at ace you can also try a hobby shop

 

[Masterm222]

I have a set from a Hobby store but I also saw them at Harbor Freight. A set of Oxy/acetalene torch tip cleaners work great for sizing jets.

 

[ken murphy]

I dont mess w/those stock carbs much,except drilling the throat Egors way to idle.I put Mic.carbs on.

 

[Neptunati]

Is there an update on where to find this set of drill bits? I've been hunting e-Bay and other sources to these tiny bits & have found none!! The smallest I have is a 1/32" .

Norm

Go to Harbor freight. I bought part #44924-aaa there. Its 20 bits but theres a #68.5, and a #71.5(ish) and 70.5 . I say .5 because there just a lil bigger. Also bought part #91682 it has a true #68 and 70 in it. but not labeled, which is stupid.

 

[ken murphy]

Here's the new 1

 

[shearbf]

Got a drillbit and did one carb last night. The job does require some skill to do free hand.
I'm happy to have got it right on! you must be a lefty, you drilled left of center down to the right and foward 45deg. I drilled right of center down & forward. and I figured this gets the vaper coming from further away from the bowl's fresh air intake. Of corse I'm a righty-tighty.
I will do your piston skirt mod. on one of the bikes soon. Can I just take the head & jug off and get the piston out & back in? If-when I split the cases on one of these, should I have new gaskets on hand? Hope to go putting with the new carb today.

 

[shearbf]

Small drills are bought one at a time at industrial tool supplies. I bought a .040 ( #60 drill) for under 2 bucks. Also should be available at an old time COMPLETE auto parts store. Don't even go to a nice new building auto parts.

 

[ken murphy]

Small drills are bought one at a time at industrial tool supplies. I bought a .040 ( #60 drill) for under 2 bucks. Also should be available at an old time COMPLETE auto parts store. Don't even go to a nice new building auto parts.

gaskets are key to these lil china girls two,I myself do the modifacation to the slide but I go alil further n put three lil slots in yhe bak and grind the angle flat,I will post a picture later if you want.
I've come up with my own gaskets for the intake and exhuast,the base of the cylinder and the head gasket
I would order gaskets for sure,these are leaky lil girls--------ya gota seal em up as good as possible.
happy trails

 

[Dontwannawalk]

UPDATE:

its running pretty well now, i kept the .0625 hole because the solder wouldn't stick, and i melted i tickler, (if you solder a hole in your carb you need to remove the tickler! idk how tho) i tapered my needle and i have the clip second from top. and air filter off, the plug is brown, a little too dark, but close enough. im topping out at probably 34 mph with a 44 tooth, low end isn't TOO amazing. but good enough to keep me from fiddling with it. my low end suffers from my poor compression probably, which comes from small scratches in the cylinder.

I've replaced the head gasket with a normal rubberized gasket. working better than original after i had the scratches, but original was better before the scratches.

I need a little carb talk education here, What is meant when you say "I have the clip second from the top." I've been working on getting mine to lean out some with no luck so far, I drilled the hole. bent the tabs and still have a black burning plug, I'm estimating that Ive got about 60 mpg so far. Perhaps I need bend the tabs some more and sink the float down more??? I also have taken the intake end of the carb and taken the lip off and tapered it. The choke is completely out at this time but I haven't used it from the get go. I may have to put it back in if I ever get it to lean out some. Top speed so far is 23 MPH. I have about 150 miles on it. Any input will be appreciated.

Norm