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Motorcycle Forum / General / Yamaha / August 2007Takegawa TTR90 90cc to 110cc Kit Kehin PD Carb Issue
My son rides a 2000 Yamaha TTR90. He bought a Bolt-on aftermarket Takegawa 110 kit against my wishes. It included the Cylinder, Piston, Rings, Cam, Kehin PD carb w/Air Filter and Manifold ect.. I helped him install the components. It actually started but we are unsure how well it ran. Not knowing much about the carb and having no adjustment info. We decided to go back to the stock carb for now. It runs excellent. He's very happy. The new kit carb issue: The choke lever (Black plastic) seems confusing. I believe when it is pushed up (arrow direction), It is in choke position with the throttle plate closed. My son seems to think the opposite. The engine only runs in the down position (and he think it is choked). When up it stalls out. Normally the bike ran well (at high RPM) @ choke and when moved idled normally? Any input would be immensely appreciated >We decided to go back to the stock carb for now. It runs excellent. >He's very happy. The new kit carb issue: The choke lever (Black >plastic) seems confusing. I believe when it is pushed up (arrow >direction), It is in choke position with the throttle plate closed. http://houseofmotorcycles.bikebandit.com/partsbandit/ShowSchematic.aspx?deptId=2 396065&machineId=10100 This schematic shows a carburetor with a cable operated "choke". Some similiar Keihin carbs have a black plastic knob that you pull straight up to "choke" the carburetor. The carburetor shown in the schematic doesn't have a true "choke", it relies on the throttle slide being as fully CLOSED as will allow the engine to run at idle speed and the small starting enrichener valve below the #15 spring being open. This valve then allows air to bypass the throttle slide and the movement of air through that passage allows fuel to be sucked directly out of the float bowl. >My >son seems to think the opposite. The engine only runs in the down >position (and he think it is choked). When up it stalls out. Maybe the float valve is stuck or the fuel level in the float bowl is too high. You can sometimes clean out the float valve by draining the float bowl, then unhooking the fuel line and squirting Berryman B12 or other clear aerosol carb cleaner down the fuel spigot until the float bowl is full. B12 will clean the gum and varnish out of the carb quickly. You can start the engine with B12 in the carb and run it until gasoline refills the float bowl. > Normally >the bike ran well (at high RPM) @ choke and when moved idled >normally? Any input would be immensely appreciated When a carburetor has a bypass enrichener valve, it is hard to start unless the throttle slide (or butterfly) is almost fully closed. If the slide or butterfly is open a little bit, there isn't enough engine vacuum to suck fuel out of the float bowl with the enrichener valve open. If the engine starts on the "choke" and then quits when the "choke" is off, this indicates a dirty idle jet, clogged idle ports and passages, or that somebody has turned the pilot air scew (item #9) too far counterclockwise. Thanks for the reply Albrecht. After re-examination of all the components I realized the boot that goes over the throttle cable at the carb was not attached. I guess it was sucking air. It is re-installed and working almost flawlessly. My son says at full throttle it "bogs" a bit. I imagine that is a minor adjustment I'm not sure how to do yet. Still he is really thrilled at the difference in power between the 90cc vs the 110cc. He calls it "Scary fast". I'm surprised myself. Hopefully it will all hold together for a while. >Thanks for the reply Albrecht. >After re-examination of all the components I realized the boot that >goes over the throttle cable at the carb was not attached. I guess it >was sucking air. It is re-installed and working almost flawlessly. Sudco International buys Mikuni and Keihin carbs and makes up custom kits for various applications. They will probably have parts for a Keihin PD carb. http://www.sudco.com/ The PE20 & 36 hyperlink shows a starting enrichener that is operated by a lever that pivots on the end, lifting the air valve when it's pulled up. This drawing shows that the carb uses hexagonal shaped jets which are known as "hex" jets. If you had a #100 hex jet and you wanted to go 10% richer on the main mixture, you would install a #110 hex jet. Round jets what are installed with a screwdriver instead of a wrench don't work that way. If you went from a #100 main jet to a #110 main jet, the hole in the jet would have about 20% more area and it would flow 20% more fuel. > My >son says at full throttle it "bogs" a bit. I imagine that is a minor >adjustment I'm not sure how to do yet. Well, you will just have to study the problem by listening to the motor and reading the spark plugs. If the engine sounds like it's gargling on gasoline when it bogs at high RPM and you look at the spark plug and it's all covered with dry black soot, you know the main jet is too large (or that it has fallen out and is laying in the float bowl). OTOH if the main jet is too small, you might see little black specks that look like grains of pepper on the nose of the spark plug. This indicates the mixture is so lean it's pre-igniting, and if you let that continue, the top of the piston will start melting and you will see little balls of aluminum on the spark plug. I wish I could describe the groaning sound an engine makes when it's running too lean and overheats before it melts the piston top. The old standard for judging mixture richness used to be a light tan lead deposit on the spark plug, but that doesn't work with unleaded gas. Nowadays, tuners expect to see a narrow ring of black soot deep inside the spark plug when they look at it with their magnifying flashlight. |
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