My KB125 Rebuild - Page 20 - xBhp.com : The Global Indian Biking Community

rookieraj · 02-04-2012, 01:11 AM

For those of you who have been following this thread...my sincere thanks.

Now the disappointing part - the bike is still not a runner. I need help in the form of advice.

After rebuilding the engine and installing it on the frame, I decided to start the engine before proceeding further. I kicked it a few times and what I noticed was that the engine is backfiring through the venturi of the carb. A few phone calls to a few trusted mentors - KB100, Muthu Anna and some research on the internet has given me the impression that the air-fuel mixture is extremely lean and the engine is firing too much in advance. This means that either the fuel supply is restricted or that there is a massive air leak somewhere.

I changed the CDI but to no avail; so the problem is not in the electricals. I'm getting a good fat blue spark - so that is not the problem either. I've changed the pilot jet but the problem persists. I've checked the position of the disc valve - its exactly as the workshop manual says it should be ie the window on the valve should open when the piston is in the compression stroke and it should close a little after TDC.

Let me also tell you the different combinations of starting techniques that I have tried.

Choke open + no throttle - engine backfires through the carb after every third or fourth kick. Kicking is extremely hard.

Choke open + one-fourth throttle - absolutely nothing.

No choke + no throttle - absolutely nothing.

No choke + one-fourth throttle - absolutely nothing; kicking is relatively easier.

So that leaves only the air leak to be checked. What complicates matters is that I have no way of checking the compression. Will see what I can do tomorrow. Will look forward to your comments.

Meanwhile, Muthu Anna has sent me a mail and I'll check everything he has asked me to.

All dressed up and nowhere to go...now who said that? hmmm...

kb100 · 02-04-2012, 07:03 AM

fouled plug......maybe

yamdoot · 02-04-2012, 12:12 PM

Finally we get to know the update Rookie. If the rotor position has not been tampered with, there is no question of the timing being off. Im sure Muthu sir and Sarin will diagnose the exact problem.

kb100 · 02-04-2012, 06:58 PM

what plugs are you running the kb uses bosch W5DC plugs the threaded portion will be longer ,

rookieraj · 02-04-2012, 09:13 PM

Quote:

Originally Posted by kb100

what plugs are you running the kb uses bosch W5DC plugs the threaded portion will be longer ,

I have the W8DC. I know its hotter than what is recommended but the W5 is not available in my area. Will head to Karol Bagh tomorrow to hunt for the plug.

rohitsapru · 02-04-2012, 10:45 PM

Quote:

Originally Posted by rookieraj

...the air-fuel mixture is extremely lean and the engine is firing too much in advance. This means that either the fuel supply is restricted or that there is a massive air leak somewhere.

If you suspect an air leak, you should do a leak-down test.

Here are couple of links that I found from Google:
http://www.duncanracing.com/TechCent..._presstest.pdf
Pressure Testing Two Stroke Engines

Quote:

Originally Posted by rookieraj

So that leaves only the air leak to be checked. What complicates matters is that I have no way of checking the compression.

Why do you say that you don't have any way of checking compression? You just need to buy (or borrow) a compression gauge. It will cost around 650 bucks.

Hope you are able to find the problem.
cheers!
Rohit.

psr · 02-04-2012, 10:52 PM

Quote:

Originally Posted by rookieraj

I have the W8DC. I know its hotter than what is recommended but the W5 is not available in my area. Will head to Karol Bagh tomorrow to hunt for the plug.

Recommended is NGK with 5 or 6 grade plugs(BP5ES or 6ES)...Do not use resistor plugs,and check plug cap for bad connection or break inside..by changing with new plug cap.
Hope you had fitted the Rotary Disk Valve in correct orientation.

I am now re-painting/rebuilding my KB for RTO inspection next week..She will be completing 25 yrs with me..

kb100 · 02-05-2012, 06:39 AM

Quote:

Originally Posted by rohitsapru

If you suspect an air leak, you should do a leak-down test.

Here are couple of links that I found from Google:
http://www.duncanracing.com/TechCent..._presstest.pdf
Pressure Testing Two Stroke Engines

Why do you say that you don't have any way of checking compression? You just need to buy (or borrow) a compression gauge. It will cost around 650 bucks.

Hope you are able to find the problem.
cheers!
Rohit.

do you own a compression gauge

rohitsapru · 02-05-2012, 01:57 PM

Quote:

Originally Posted by kb100

do you own a compression gauge

Yes I do. I think its a Taiwan make.

psr · 02-08-2012, 10:57 AM

My 25 year old KB100 recently re-painted by me (personally) for RC renewal.

02-04-2012, 01:11 AM	#191 (permalink)
rookieraj Senior Member Join Date: Feb 2011 Location: New Delhi Posts: 128	Help... For those of you who have been following this thread...my sincere thanks. Now the disappointing part - the bike is still not a runner. I need help in the form of advice. After rebuilding the engine and installing it on the frame, I decided to start the engine before proceeding further. I kicked it a few times and what I noticed was that the engine is backfiring through the venturi of the carb. A few phone calls to a few trusted mentors - KB100, Muthu Anna and some research on the internet has given me the impression that the air-fuel mixture is extremely lean and the engine is firing too much in advance. This means that either the fuel supply is restricted or that there is a massive air leak somewhere. I changed the CDI but to no avail; so the problem is not in the electricals. I'm getting a good fat blue spark - so that is not the problem either. I've changed the pilot jet but the problem persists. I've checked the position of the disc valve - its exactly as the workshop manual says it should be ie the window on the valve should open when the piston is in the compression stroke and it should close a little after TDC. Let me also tell you the different combinations of starting techniques that I have tried. Choke open + no throttle - engine backfires through the carb after every third or fourth kick. Kicking is extremely hard. Choke open + one-fourth throttle - absolutely nothing. No choke + no throttle - absolutely nothing. No choke + one-fourth throttle - absolutely nothing; kicking is relatively easier. So that leaves only the air leak to be checked. What complicates matters is that I have no way of checking the compression. Will see what I can do tomorrow. Will look forward to your comments. Meanwhile, Muthu Anna has sent me a mail and I'll check everything he has asked me to. *All dressed up and nowhere to go...now who said that? hmmm...*

02-04-2012, 07:03 AM	#192 (permalink)
kb100 Senior Member Join Date: Jan 2010 Location: KL-2 Posts: 678	fouled plug......maybe __________________ Kawasaki KB100/enduro/125 substitute parts list http://www.xbhp.com/talkies/508615-post105.html

02-04-2012, 12:12 PM	#193 (permalink)
yamdoot Senior Member Join Date: Nov 2004 Location: Indore/ Mumbai, India. Posts: 918	Finally we get to know the update Rookie. If the rotor position has not been tampered with, there is no question of the timing being off. Im sure Muthu sir and Sarin will diagnose the exact problem. __________________ 1985 Yamaha RD350 HT 1989 Race winner Ki-Honda 110 1994 Suzuki Shogun Rally prep. 1997 Yamaha RXG stock 2008 Yamaha FZ No Cams, No Valves, No Headaches.

02-04-2012, 06:58 PM	#194 (permalink)
kb100 Senior Member Join Date: Jan 2010 Location: KL-2 Posts: 678	what plugs are you running the kb uses bosch W5DC plugs the threaded portion will be longer , __________________ Kawasaki KB100/enduro/125 substitute parts list http://www.xbhp.com/talkies/508615-post105.html

02-08-2012, 10:57 AM	#200 (permalink)
psr Senior Member Join Date: Aug 2010 Location: CHENNAI , TAMILNADU Posts: 3,245	My 25 year old KB100 recently re-painted by me (personally) for RC renewal. __________________ When Was The Last Time,You Did Something For The First Time. http://www.codewins.com/motorcycles/...alveclearance/.( D I Y Valve clearance setting.. )

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