Bike Won't Start - TwoWheelForum: Motorcycle and Sportbike forums
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post #1 of 6 (permalink) Old 11-27-2005, 01:06 PM Thread Starter
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Bike Won't Start

If you ever go to a bike-specific site and look at the tech section, there will always be a thread where the bike won't start. Doesn't matter if it has carbs or FI, the rider will grind the starter until the battery's dead. Now he has a bike that won't turn over or start.

My CBR's been harder to start lately, and I thought it was the cooler weather. On Thursday, I pulled a cold plug and placed it on the valve cover. Had a nice blue spark. So I suspected the choke.

On Saturday, I pulled the carbs. I placed the carbs in my Black&Decker Workmate to hold it steady. There are 32 phillips-head screws that must be removed. The first picture shows the black diaphram/piston/jet needle. The paper towel shows how dirty the piston was, and just below is how dirty the piston walls were. The Vaseline will be explained later.

To clean the choke plunger, the carbs have to be removed from each other. Even No Worries doesn't want to do that. The second picture shows how to clean the choke plunger from inside the diaphram chamber. The red carb cleaner hose is shown in the choke bleed. This is a Keihin carb and the engine side of the carb is at the bottom. The synch tube is under the little black cap, a half inch below the cleaner hose, and the choke lever is the black plastic tab to the right.

To clean the choke passages, spray carb cleaner into the choke bleed. But first open the choke passages by opening the choke lever. If you don't open the lever, carb cleaner will spray into your face and eyes, so wear eye protection. Keep spraying until carb cleaner comes out the front and rear of the carb. Comes out brown then clear, that's when it's clean.

Now you have to put the diaphram/piston/needle into the chamber. But first refer to picture number three which shows a little Vaseline in the groove around the diaphram chamber (red hose). Don't force or bend the needle. Should slide right in.

The fourth picture shows the diaphram with the edge securely in the groove with the Vaseline. Make sure the little rubber ring on the edge is around the air bleed on the bottom of the groove. That orients the piston so the front is facing the inlet. Also make sure there are no tears in the diaphram. Put the top on and make sure you don't forget the spring.

I also cleaned out the idle jet on the float chamber side, but they weren't clogged. I put it all together, added some fuel and it started on the first stab of the starter. Boy is that a relief. And with the clean piston slides, the bike has a real "snap" to the throttle. Too bad the cold weather came today, but there will be plenty of days to ride this winter. Next spring I am going to replace the 32 phillips head screws with allen screws. Mine take 4x0.7 by 10mm long.
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post #2 of 6 (permalink) Old 11-27-2005, 04:00 PM
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Very informative!! Great write up!

aka Gas Man

Was: 2002 Kaw ZX-9R

is me till the
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post #3 of 6 (permalink) Old 11-27-2005, 08:55 PM
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Originally Posted by Gas Man
Very informative!! Great write up!
Glad you kept it short and to the point.

Submit your ride for the TWF Bike of the Month here

Currently ride 1987 GSXR 50, 1996 Ducati M900, 2005 GSXR 1000
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post #4 of 6 (permalink) Old 11-28-2005, 07:49 AM
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Hey!! wadda ya tryin' ta do...Take my Job???

Great article though...
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post #5 of 6 (permalink) Old 11-28-2005, 09:24 AM
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Definitely a good reference!!!
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post #6 of 6 (permalink) Old 11-28-2005, 10:44 AM Thread Starter
Join Date: Aug 2004
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Glad you like it. I just wanted to show that the choke system could be cleaned without taking the carbs apart from each other. So by just taking the vacuum chamber covers off, you can clean the chokes and the piston slides.

Plus, there are only 16 screws to strip instead of dozens more. After I rounded off the phillip's head on some of those little SOB's, I've used vise grips, and on two of 'em I had to hacksaw a groove for a common screwdriver. When I get those Allen head screws, it'll be even easier.
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