The Mini Crotch Rocket Gets 15" tires!!! - Part 9 

Both lean and rich engines can backfire. Try running it with an auxiliary tank and see if the engine is struggling for air. One of the easiest ways to test the A/F mix while running is to slightly close the choke and if the engine runs better (less incoming air) then you know the carburetors are not supplying enough fuel and the engine is very lean. If even slight choke stalls the engine or makes it bog worse than you know it isn’t getting enough air and that the engine is far too rich.

To fix the headlight hi low problem, place a diode in line between the two. When on low it will block back feeding the high beem.

Check the fuel/air mixture with the spark plug. black spark plug, lots of fuel. gray spark plug low fuel. candle brown best option

The cloth your using for filters is too restrictive. Use some screen to keep the stones or gravel out.

It definitely looks better...I think the size of the tank looks out of proportion...even if you just painted part of it black, to tie into the seat, would help imo.

If you can afford it pick up an air/fuel ratio gauge which is an O2 sensor with a gauge and that will tell you if you are rich or lean. You can use it on all your projects by buying or making bungs and plugs to put into the exhaust of them.

Yey it's Sunday,,it's RBW DAY 😁👍

Now that looks like something that can go over bumb with speed and still be comfortable

Now it looks better than a Hayabusa! Have you ever been thinking of putting turbo kit on it?

Your a great welder - cut a hole down the center of the tank and install a proper air filter. Put an air scoop over for a cover for the hole.

Run it without the fuel tank on, just a small on. Your problem is airflow because the gap between your tank and carbs. Do the airflow calculations you will be surprised how much air you need.

The best way to check if the engine is running lean or rich, in fact its the best way to see how the engine is performing in general. and that is by reading the spark plugs. the spark plugs will tell you everything you need to know. providing you know how to read them. I would likely guess that there are videos on the subject along with videos on carburetor tuning. one thing you can amost always figure on, is anytime you change something involving the exhaust you will probably have to do some carb. tuning. the larger tires are definitely an improvement. oh yes we know who that is.

Ike from cars and cameras might be able to help you out with your jetting questions there Chris, i know they've had to tinker with motorcycle carbs in the past, this looks like its going to be an absolute blast when you get the gremlins shot and everything worked out fully

Lowering the air pressure can have the opposite effect you're looking for. The pressure inside the tire also out on the sidewalls. That can keep the tire from expanding at high speed. Think top fuel drag cars, they run very low pressure.

For little tubeless tires, try cinching down a ratchet strap around the circumference, then fill with air.

Look at you, worrying about that back tire having clearance space lol. As if you aren't gonna get that thing all put together and throw it into a burnout that roasts an 8th inch off that tire. PS: the exhaust sounds great. :) Also like the duel headlight idea, have one facing forwards to throw light and one pointed a little downwards to throw directly in front of the wheel.

U need to put smaller jets in it because the original exhaust pipe was bigger. And u custum made an pipe with is smaller then original. And after u drilled it out, is getting to much fuel i think. And also because youre tank setup on the carbs they get lower air flow. Hope this helps.

I see everybody has thought the same as me not enough air mixing with fuel take and cut a air vent in the front of the tank you would lose a little fuel in tank but it would be like a ram air

Bigger tires look great! Maybe you can shorten the front of your gas tank to allow for a better intake/filter setup. Might look a little more to scale as well. I also think you could raise the handlebars a bit for looks, but if you like the way it feels as is, by all means, keep it.

The build is looking awesome!! The new 15’s - hell yeah! But… only rocking a front brake?? Yikes! Keep doing what you do!

Also a good guide to go by for tuning carbs. If it pops at wide open main jet is rich. If it bogs at wide open main jet is lean If it pops at half throttle the needle is too high. If it bogs at half throttle the needle is too low. If it pops at quarter throttle the idle jet or needle is too high. Idle rises and falls. Rich idle jet.

Chris>Look at your Plugs when testing.White is Lean.Dark is too Rich.Tan is what you want.The bike looks Awesome !

It’s definitely starved for air and there might also be a problem with there not being enough air velocity going into those carbs which is especially important with constant velocity carbs which is what you have there. The solution would be to put velocity stacks on the carbs or use the stock air box the original motorcycle came with.

If you add a relay, you can get both of the lights working. Painless Wiring made a kit for the older Chevy pickups to do just what you want to do. You can also look up a diagram online to see the proper way to wire it without the kit. One relay, one additional fuse and you are good to go.

All the amazing things you build and you use that contraption to break the bead i would love to see the tires machine you could come up with manual or power either way watching you machine the parts and see it take shape like all your projects very talented young man I enjoy all of your builds

I've been concerned from the start that the tight clearance under that tank might restrict the air flow to those carbs too much. 😕 Also, needle height just adjusts fuel flow, not air. If you were concerned about fuel I would have tried the needles before drilling jets. Honestly though, my theory is air flow.

This thing would be sick for a seasonal “run to town” bike! I could see myself riding all over the place on this bike.

PROTIP: When mounting tires, wrap a ratchet strap around the tire(around the circumference) and crank it down. It'll push the bead to the rim. Way easier to get it seated.

SO incredibly sick brother

Rather than struggling to get the tire to bead up try using a ratchet strap it works so good I've rebeaded tires on cars that have been flat forever dry rotted and stiff but when you need to move something across the yard and don't want to spend the money to replace them or simply don't have the money to.... it's definitely my go to

Go back to STOCK on needles, One size over on mains is fine, but the MOST important thing to do on carbs of this type, with Open exhaust and zero air box is to open up the PILOT jets- Doing like you are now is the way to go, figure out the size, go a bit higher, TEST IT, try one more size, TEST, etc, if you go too far you can swap for another jet drilled to the last "Working" size drilled, or Solder up the hole and re-drill to the size that last worked best.....

Try running it without the tank on and the filters you put on the carbs it seems to be very restricted on air.

1st thing i would do is lose the pipe, like a mower exhaust. Likey causing problems. Come back to edit since i saw the air filters 😅🤦‍♂️

Literally High and low headlight-beam ... Lol ... Now that's funny.

I own a small engine shop/motorcycle repair. So here are my thoughts thru some experience. There are many, many motorcycle carbs that will not run right without the air box or the intake tubes. The air box/tubes cause a venturi effect and the carbs themselves steal some of that in-flowing air and use it to emulsify the fuel before its drawn up thru the tube. Also the carbs on your bike use a diaphragm to move the slide up and down by the amount of throttle applied, it also uses that air as its pulled thru the carb to move that slide, I would bet that's where your problem starts, I've had engines refuse to run until i put the stock airbox or intake tubes back on.

I would also make sure to test the revving without the tank in place. Like run it on the street with some small makeshift tank, to troubleshoot the possible choking that the small clearance under the tank may cause. Then also make sure there is no problems with the ignition, like coils and wires. To be honest, I would like to see a new revision of the fuel tank, but that probably would be awful lot of work. The muffler "block off" I think could do with some sort of perforated baffling, if they'd fit inside. Then make more holes on the pipe in the center.

Its starving for air which caused a rich poor running condition. You then introduced mote fuel with jet drilling and lifting the main needle only making it worse. First remove the damn cloth restrictor gags from the carb openings then make sure your not suffocating it with too little clearance under the fuel tank. You get the intake air flowing freely and things will probably improve.

A carb is a balance between fuel jet restriction and airfilter restriction. For testing, modify the airfilter instead of the jet, much cheaper.

A wide ratchet strap around the tire cranked down a bit will seat way easier. I use that trick when one of my front tractor tires (stupid stiff sidewalls) breaks bead. Use grade 8 bolts

When you make carb changes make sure to change the plugs, doesn't matter what you do if your plugs are foiled it will never run correct plus it allows you to read the plugs to see where your air fuel is.

Telltale of lean is the popping on deceleration, but you are starving for air you need to open a path for air to those carbs. Also explains why it got worse as you added more fuel to the same lack of air.

Not enough air and fuel pressure. Once you've fixed these, those drilled out jets should work just fine. the needle valve is for fine tuning, higher needle, richer mix.

I'm not a fan of the headlights. Please try 1 round light and see if it looks better. I think it will.

Nice job, liked👍👍

where that carb is setting and the Fack he is using what he is using for a filter it is got to be starving for air it it was me and it had to be closed off like it is then I would have cut a3 inch hole in the top and bottom of the tank and run an tube thru it with a rubber connector from the carb to the tank tube and put the breather on the top of the tank

those filters you're using is choking your engine. Your gastank might also be too close to the intake

You can use a relay wired into the high beam to activate the low beam light if you want them both to be on for high beam.

yo id Daily the FriCin Life out thAt Cute aZZZ lil BeeeeCh lol good build broski

with tire expansion, you also have to figure in the weight after you get on the bike.

awesome build but no air flow bro almost guarantee that the issues for the most part

needs turn signals now and gotten ready for the road. and yes it looks awesome.

My favorite part of watching your builds is seeing you make parts by hand. This bike is bad ass BTW,once you get all the bugs out it’ll be like a GROM ,only one with balls!

Um would you be interested in selling that or anything like it

Youll get it brother and the tires are much better. Be safe :)

The tank is restricting air flow to the carbs ........

Wow, that looks SOOOOO much better.... I really want to take this for a ride, it's so cool and I love the idea of a big motor in a small frame. Awesome build.... Keep up the great work. 😁👍

what would be cool if you made the air ducked thru the tank

С этими тряпочками на карбюраторах ехать не будет!

Put that socks out the carbs. That's all the problem

I agree with Jeff. I think it is starving for air.

Tires look way better, jetting should be fine from factory?

The way to use your cheetah is to have your tire inflator on your tire and pushing air at the same time you release the cheetah so the air you shove it gets added to the air already going in and it won't pop back out. I like the bigger tires too, feels more like something street worthy than with the 13s.

I'm more of a cruiser these days, but that's nice work Chris...

You Just choose wrong engine buddy

Please ! 3 videos per week !!!!!

Air filters aren't good I think

Great build, but you need rear brakes.

the carburetor is way too close to the tank

That's a vacuum carb, check the flange for tears

Try fly screen for air filter.

Beautiful job 👍

Allsome stuff I love the new wheels . excellent work all-round.yip I got a 24 mm flatslide carby with spear jets but there was no numbers on them witch made it a little bit more trickyer haha 🤣 cool stuff allsome work from cruzermans inventions 😁🎉🌟

I love 💕 the bigger wheels way more safer 👌🎉😁🌟 allsome work from cruzermans inventions 😁🎉

I believe those carbs are CV (constant velocity) and if they don't have the correct back pressure, via it's airbox, they will not run correctly. ..tyically.

wat helps getting the tire to bead on the rim is tension a ratchetstrap around the circumference of the tire . that usually concaves the tread in the center and pushes the sides out against the beads having the tires not stacked on top of eachother at the tirecompany helps too as it flattens them about the jetting : just go ahead and drill them if it doesnt work put a drop of solder in there and drill them out smaller wat you could try with the new jetting is remove the cloth airfilters as for tuning carburators , it IS a guessing game mostly , do a change test it change sumting else makes it worse , go the other way , makes it better , go further that way makes it better etc , makes it worse change the first thing back the other way etc etc the needles usually gets changed to work with the filtertype or no filters the jetting is the main tuning , you can read the sparkplugs or listen to the engine to see if its too lean or rish or go by seat of pants on accelleration if its still chocking for air even with the cloth taken off or just doesnt make the rpm you expect it tom you might need bigger carburettors this is offcourse with assuming that the timing of the ignition and the cams are correct

Needles will not fix wide open throttle mixture. The needle is for metering fuel in between the low speed and whatever your jet size is. The needle is literally a tapered shaft that opens more of the jet as the slide is raised. It did sound rich to me... but with CV carbs, you're probably going to have to mess with filtration to get it right. CV carbs use vacuum to control the movement of the slide, and as such, increasing or decreasing flow into the carbs can (most of the time does) cause issues. If you continue to have issues, I would simply replace the carbs with something else that you are better able to tune. Even a single Mikuni would be better, if you're able to actually tune it.

As your angry neighbour drives past “agh not another one” haha. You definitely wouldn’t expect a bike this size from the sound of it, looking so good!

Seems like air starvation, you can get lean pops when the fuel air mix goes lean. As said in other comments open up the gap between the tank and the carbs, your tank is probably acting like a restrictor plate so on WOT the air gap between your tank and the carbs is smaller than the air gap in the Venturi. As others have also said run it with the tank raised and see what happens. Your not wrong to re-jet it for the exhaust or the lack of airbox that common practice. Take the time to learn the basics of it but then get stuck into actual practice, you only truly learn by doing as you already know from your engineering skill. Keep it though man enjoyed this build series, a real fun little project. A bit more fine tuning you'll be there dude 👍

1:22 That’s what she said…..

Your running issue is your makeshift air filters! remove that cloth and try to de-shroud the intakes and it will come to life. Tune the AFR by reading the plugs.

Dude these tires look 10 times better. Insane build, keep up the great work 👏🔥

On carb tuning, see if you can find a Gunsons Colortune, its a glass topped spark plug that lets you see what colour your combustion is, make its piss simple.

Yup...it looks WAY better with those wheels. Gonna look really cool all painted and finished. :)

Wow that was a good video

If you think the problem is the carbs...its the ignition. If you think the problem is the ignition...its the carbs. - Confucius ( I think)

You can make the low come on with the high beam using a diode between the positive of the high beam and positive of the low beam. Basically a one way valve for electricity. You will want to make sure that you have one that is rated for the wattage of the lights.

You could try adding a diode between the high and low beam power wires so the high beam wire will turn on both but low beam will just be the bottom one if you don't know a diode is basically a one way valve for electricity

Cv carbs and no airfilter can be tricky. You can make larger holes in the slides to make them react more to the lower vacuum.

Lol 😆 🤣,,,,we all know who that is ,,,,,your expression is priceless 🤣,,,,,keep up the good work 👍

dude, you dont DRIVE motorcycles, you RIDE them. Stop saying that already.

I suspect that the engine is running to rich to start with, and also - the steps you take to calibrate a carb should be SUPERSMALL! If it is reasonable close to running well to beguin with that is. And I think it was. I’m not sure it was to fat mixture to start with, but I think it was, slightly. My little box of jets have steps of (let’s see…) 95, 96, 97.5, 99, 100, 101.5 , 103, 104, 105… (yes, metric, I’m from the civilized world 😉) and some of those steps are to wide! Remember, the area is proportional to the diameter², and the flow resistance is somewhere between linear and to the power of 2… Basically - you need to change in steps of 1 to 1,5% in diameter, i.e. 2 to 3% in area. Your steps are 30%!!! 😳 -- PS. The bike looks much, MUCH better with the larger tires! 👍 PPS. Clean the spark plugs before you try again. They are hurt badly by super fat mixture!

Maybe look at putting an induction cowl through the top of you gas tank to supply more air for your carbs.

Fast mini motorcycles need to be a thing. The monkey/grom don’t count considering how slow they are. Amazing build I’ve always wanted to make a mini crotch rocket. Perfect size for me 5”3 108 pounds.

Great suggestions on here. Before you fool with your jetting, check your plugs. You want tan. Dark, wet, black-ish is rich and light tan , white-ish is lean. Stay away from lean and error to the rich side. Less harmful. Great video's!!

Hey Chris, check out jetting for the GT250R which is the street bike version of the Hyosung. From memory the stock main is a 95 I think, but you can go up to a 97.5 or 100 with a free flowing exhaust. Sure I've read that Mikuni jets fit. Love the new tyres BTW. The GT250R is used in the Hyosung Cup in NZ which is a race series, they look pretty good in corners 😁

Nice choice with the new taller tires. I think you need Mikuni carborators. Needs turnsignal indicators. Remember the new Dodge Hellcat color? Crome pearl gold.

Hey Chris Shane I’ve been reading some of your Comments your getting on this project of your’s… And have been watching it my self and will I’m 61 year’s old and have been doing what your doing for a great many of years …. Besides carsamdcamas and Red Breard. …. Your one of the best best fabricators of steel I have ever seen.. so with that being said, Man when I read your Comments and they talk about air flow to it .. you need to do this or that to get it running just right or this is wrong with it … Look keep doing what your doing @&$);…..Man I know for one on any off the HooK just out of the sky ideal to even Build a crazy project you have to be great at what you do &&&&& And I’m sure as good as you are with any Soul felt Vehicle you build there’s no plan, just the build…. Right!!!!!! Ok my point… Look young man your good. And I’m sure you you know on any new projects There is going to Be Bugs from the ground up like your comments have been saying trying to get air or what ever them bugs nothing else…. I’m sure by the time you’re done with that build the bugs 🐛 will be worked on to we’re it just gets better… I’d like to be there just to watch and learn from you Chris…. Anyway I hope you never stop what your doing because at my age I’m learning from you….Don’t Stop building kool and crazy things… Sincerely, Shane

I've been a motorcycle mechanic for 14 years I'm pretty sure that a lean mixture pops and backfires. A rich mixture will cause excessive smoke and that's pretty much it. Besides running like s*** it'll smoke like a dragon if it's rich.

your biggest problem is the red cloth on carburetors...The vacuum is sucked in, and splashing petrol soaked the cloth, and becomes impermeable...try it without the clothes and with drilled jets, it will be rocket :-) ps: sorry for English, i am from Czech republic 🙂

Hyosung engines are terrible. Mate had similar 250 engine in his supposedly sport bike and my little Suzuki GN125 Suzuki ran rings around it.