Yamaha RT100 Carb Rebuild/ Cleaning

Heres a vid of me rebuildin my rt100 carb...

Carb jet and circuit info:

Most Quad and MotorCycle carburetor circuits are governed by throttle position and not by engine speed.There are five main metering systems inside most motorcycle carburetors. These metering circuits overlap each other and they are:

* pilot circuit
* throttle valve
* needle jet and jet needle
* main jet
* choke circuit

The pilot circuit has two adjustable parts. The pilot air screw and pilot jet. The air screw can be located either near the back side of the carburetor or near the front of the carburetor. If the screw is located near the back, it regulates how much air enters the circuit. If the screw is turned in, it reduces the amount of air and richens the mixture. If it is turned out, it opens the passage more and allows more air into the circuit which results in a lean mixture. If the screw is located near the front, it regulated fuel. The mixture will be leaner if it is screwed in and richer if screwed out. If the air screw has to be turned more than 2 turns out for best idling, the next smaller size pilot jet will be needed.

The pilot jet is the part which supplies most of the fuel at low throttle openings. It has a small hole in it which restricts fuel flow though it. Both the pilot air screw and pilot jet affects carburetion from idle to around 1/4 throttle.

The slide valve affects carburetion between 1/8 thru 1/2 throttle. It especially affects it between 1/8 and 1/4 and has a lesser affect up to 1/2. The slides come in various sizes and the size is determined by how much is cutaway from the backside of it. The larger the cutaway, the leaner the mixture (since more air is allowed through it) and the smaller the cutaway, the richer the mixture will be. Throttle valves have numbers on them that explains how much the cutaway is. If there is a 3 stamped into the slide, it has a 3.0mm cutaway, while a 1 will have a 1.0mm cutaway (which will be richer than a 3).

The jet needle and needle jet affects carburetion from 1/4 thru 3/4 throttle. The jet needle is a long tapered rod that controls how much fuel can be drawn into the carburetor venturi. The thinner the taper, the richer the mixture. The thicker the taper, the leaner the mixture since the thicker taper will not allow as much fuel into the venturi as a leaner one. The tapers are designed very precisely to give different mixtures at different throttle openings. Jet needles have grooves cut into the top. A clip goes into one of these grooves and holds it from falling or moving from the slide. The clip position can be changed to make an engine run richer or leaner. If the engine needs to run leaner, the clip would be moved higher. This will drop the needle farther down into the needle jet and cause less fuel to flow past it. If the clip is lowered, the jet needle is raised and the mixture will be richer.

The needle jet is where the jet needle slides into. Depending on the inside diameter of the needle jet, it will affect the jet needle. The needle jet and jet needle work together to control the fuel flow between the 1/8 thru 3/4 range. Most of the tuning for this range is done to the jet needle, and not the needle jet.

The main jet controls fuel flow from 3/4 thru full throttle. Once the throttle is opened far enough, the jet needle is pulled high enough out of the needle jet and the size of the hole in the main jet begins to regulate fuel flow. Main jets have different size holes in them and the bigger the hole, the more fuel that will flow (and the richer the mixture). The higher the number on the mainjet, the more fuel that can flow through it and the richer the mixture.

The choke system is used to start cold engines. Since the fuel in a cold engine is sticking to the cylinder walls due to condensation, the mixture is too lean for the engine to start. The choke system will add fuel to the engine to compensate for the fuel that is stuck to the cylinder walls. Once the engine is warmed up, condensation is not a problem, and the choke is not needed.

The air/fuel mixture must be changes to meet the demands of the needs of the engine. The ideal air/fuel ratio is 14.7 grams of air to 1 gram of fuel. This ideal ratio is only achieved for a very short period while the engine is running. Due to the incomplete vaporization of fuel at slow speeds or the additional fuel required at high speeds, the actual operational air/fuel ratio is usually richer.

Category:

Autos & Vehicles

Tags:

• yamaha
• rt
• 100
• rt100
• motocross
• wheelies
• wheelie
• wheely
• carburetor
• carb
• carburator
• cleaning
• rebuild

[dustinwaller87]

hey i have the same carb.. but the slide wont move.. its stuck any solutions to get it unstuck.. everything else works great on the carb but the slide..??

[atomicsaladbowl]

pb blaster and any penetrating lube, let it sit for a lil while, and put sum pressure on it

[randobad]

The frisbee is the best idea ever!!!

[atomicsaladbowl]

damn right!! i clean all my carbs in frisbees, contains the mess

[lazzer408]

1:20 "main jet" that is incorrect. That is the valve seat for the float needle valve.

[atomicsaladbowl]

wow i missed that in editing, thanks you are right

[MitchuII]

My 97 Rt100 runs fine until you stop. Whether it's in neutral or the clutch is engaged, the sonofabitch will just rev on it's own to the limit. If I let off the clutch a bit, it'll go back down but sitting still, it goes off the chart. Also, if you take it down the road wide open, it will die suddenly. Only when it's at full speed/ throttle, though.

[doffshore1]

@atomicsaladbowl Lol Frisbees your braggin about, haha man I use a nice big clean oil pan works pretty darn good but every body has there special way hahaha and thanks man I just picked up a 1991 rt 100 and rebuilding the carb Is the needle for the float suppose to hang on to the float I found it very weird because all the carbs I usaully do when I pull the float out the needle comes with it... any help appreciated thanks bro

[motoxrider713]

haha nice cleaning tray! haha! but anyways good job man!

[ib6ub9babe]

can u send me pic of that carb i need one and need pic to show wreckers

[ib6ub9babe]

do u have a spare rt100 carb that u want to sell ? if so how much

[joshwaggoner14]

how do i know where the jets are on my suzuki rm 125?

[11wesley11]

i need help. this guy figured out my yamaha beartracker the slider wasn't moving up when you went full throttle and he fixed it but now when your riding at about 1/2 throttle it suptters and wont go. i looked and the slider doesn't go up the whole way because he put bolts and nuts around the diaphram or however you spell it and its too heavy and i dont know how to fix it helpp

[admillnx6]

i like the way he undoes the main jet with a pair of pliers,he must have apprenticed down my local bike shop.

[admillnx6]

this sounds like a partially blocked main jet and(more likely)main jet holder,make sure their clean and if youre running a aftermarket pipe/filter combination,then return to stock.

[11wesley11]

hi can anyone help me with what i think is a carb problem i own a 2003 yamaha beartracker and its starts and idles no problem its when u give it gas is the problem no matter how little or how much gas u give it it sputters and doesnt want to go at first but when it finally gets there and is reved up its runs fine i think its no getting the right fuel air mixture but idk can someone help?