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Discussion Starter · #1 ·
I have a 2000 Yamaha Kodiak 400 that I have had since 2002. I have ridden lots of miles and done (I am sorry to say) virtually no maintenance to it. Late last fall (nearly 2 years ago), I was using it around the farm and it was running fine. After shutting it off for a few minutes, I went to start it and it backfired, blowing the boot off the carburetor (between the engine and carburetor). Try as I might, I could not get it to start after that.

Fast forward (past a shoulder surgery, and many months) and I have been trying to get it going again. I have replaced the carburetor (with a cheap ebay carb) and the spark plug. I have replaced the gas with brand new, super unleaded (non-ethanol). I changed the oil and took off the valve covers and they appeared to be working.

It turns over fine and the spark plug sparks when grounded to the frame or engine.

When I put my finger over the spark plug hole, it is pushing air out when I turn it over and it is pulling air through the carburetor. The carburetor is taking fuel, and (assumedly) injecting it into the engine. There is air (and gas smell) coming out the exhaust.

When I remove the plug, it is not very wet, and only faintly smells of gas (sometimes) and other times smells more like vanilla (yes, like a candle and I have had a friend verify this).

The connections between the carb and engine have been checked for leaks, cracks, holes and are tight.

I have tried pouring gas into the spark plug hole. I have tried spraying starting fluid into the plug hole and into the carburetor. I have tried the starter, for minutes at a time, with the choke on, or the choke off.

Nothing that I have done makes any difference at all.

The only exception to that is when I have sprayed a LOT of starting fluid either into the carburetor, or directly into the head (with the carb removed), after a couple minutes of turning over, it will finally ignite the starting fluid on top of the engine, or in the air cleaner box (depending on which way I did it). The engine never, pops or lets out exhaust smoke, not at all.


A google search suggested the following things:

Incorrect valve clearance "as the engine gets some hours on it, the valves may seat deeper in the valve seats and need adjusting".

The timing is off/the flywheel timing key is sheared. (I'm not even sure that it has one of these.)

So, any thoughts/suggestions?

Thank you so much!
 

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Step 1. Do a Leak Down check on it
Step 2. Check the valve clearances
Step 3 Take the jets out of the stock carb and put them in the Chinese one. They are rarely
jetted properly.
Step 4 check for a strong spark

Mad
 

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Discussion Starter · #3 ·
Step 1. Do a Leak Down check on it
Step 2. Check the valve clearances
Step 3 Take the jets out of the stock carb and put them in the Chinese one. They are rarely
jetted properly.
Step 4 check for a strong spark

Mad
Maddevill, thank you so much for your response and advice.

I am pretty novice at this stuff, so I have some questions. (I will also try searching for the info online.):

1. What is a Leak Down check? How do I do it?
2. How do I check the valve clearances? Can you recommend a good video, or instructions on how to do this?
3. It seems that the jets are an unlikely culprit, given that it was doing the same thing with the stock carb/jets. Do you disagree?
4. It seems to be sparking well (I think). How do I know if the spark is "strong"?

Thank you so much!
 

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Discussion Starter · #4 ·
Also, it seems like the jets are unlikely to be the problem because I am unable to get any "pop" with starter fluid or pouring gas directly into the cylinder. This ATV has always ran for a second or two on starter fluid when there was a problem (such as a clogged jet) in the past. Am I wrong about that?

Also, regarding the "strong spark", I tried two different new spark plugs as well as the "old" one. Or, is the "strong spark" generated elsewhere (like a coil)?
 

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Oofah. A lot of information to cover. Look on YouTube for videos of checking the valve clearances. It's not that hard.
Basically you remove the spark plug and set the engine up to Top Dead Center on the compression stroke, take the valve covers off and check with a feeler gauge. If you have screw adjusters it's easy to set them.
A leakdown test can tell you a lot about the health of your engine. First you need an air adapter that screws into
your spark plug hole. I found the house from the Harbour Freight compression tester works fine. Again set the motor
up on TDC but this time you'll need to remove the stator cover so you can have an assistant hold the crankshaft
from turning. Then introduce air into the spark plug hole. Not too much. About 40 psi should do.
Open the throttle. If you feel or hear air coming out of your air box it means your intake valve is either too tight
or hanging open. If you hear air coming out of the exhaust pipe it means exhaust valve too tight or possibly burned.
Remove the house that goes from the crankcase to the air box. If you hear air there it means your rings are not
sealing very well.
As for spark, when cranking, the spark at the spark plug electrode should be bright white or a bit blue. If
it's a dull orange it's weak. Clean all your ground connections and check your batteries health.

Mad
 

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Maddevill, thank you so much for your response and advice.

I am pretty novice at this stuff, so I have some questions. (I will also try searching for the info online.):

1. What is a Leak Down check? How do I do it?
2. How do I check the valve clearances? Can you recommend a good video, or instructions on how to do this?
3. It seems that the jets are an unlikely culprit, given that it was doing the same thing with the stock carb/jets. Do you disagree?
4. It seems to be sparking well (I think). How do I know if the spark is "strong"?

Thank you so much!
1. get a compression tester tool, Amazon.com: BETOOLL HW0130 8pcs Petrol Engine Cylinder Compression Tester Kit Automotive Tool Gauge: Industrial & Scientific

remove spark plug, install tool and crank the engine while holding the thumb throttle all the way in, your compression should be between 170-220

if its on the low side, add an oil cap full of oil to the cylinder through the spark plug hole, wait a min or so and do the compression test again, if numbers are higher you need to change your rings, possibly piston.

2. I do not have a video of the valve adjustment on a 400 yet, but this guy does a really good job. the intake valves should be at .0024-.0039in. and exhaust at .0063-.0079in.

3. Agree!

4. Remove the spark plug and install it in the spark plug cap. touch the engine (away from the spark plug hole) and crank the engine. you should see a bright blue almost white spark. Do it indoors away from the sun or outdoors once the sun goes down.

sub to our channel:)
 

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by the way, you dont have to pour gas down the cylinder to try and start it you can either soak the spark plug itself in gas or any flammable liquid and reinstall spark plug

or

buy something like a seafoam can and spray straight into the carb.

when you re-installed the new carb, how is the butterfly position in the carb, you have to make sure it is in the almost closed position, there should only be a tiny gap as thick as a piece of paper.

there should be about 2-5mm of free play in your throttle cable or else it may not start.
The throttle cable needs to be resting in A, end of it in B and it should be touching the idle control rod.

3719


looking forward to you reply
 

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I have a 2000 Yamaha Kodiak 400 that I have had since 2002. I have ridden lots of miles and done (I am sorry to say) virtually no maintenance to it. Late last fall (nearly 2 years ago), I was using it around the farm and it was running fine. After shutting it off for a few minutes, I went to start it and it backfired, blowing the boot off the carburetor (between the engine and carburetor). Try as I might, I could not get it to start after that.

Fast forward (past a shoulder surgery, and many months) and I have been trying to get it going again. I have replaced the carburetor (with a cheap ebay carb) and the spark plug. I have replaced the gas with brand new, super unleaded (non-ethanol). I changed the oil and took off the valve covers and they appeared to be working.

It turns over fine and the spark plug sparks when grounded to the frame or engine.

When I put my finger over the spark plug hole, it is pushing air out when I turn it over and it is pulling air through the carburetor. The carburetor is taking fuel, and (assumedly) injecting it into the engine. There is air (and gas smell) coming out the exhaust.

When I remove the plug, it is not very wet, and only faintly smells of gas (sometimes) and other times smells more like vanilla (yes, like a candle and I have had a friend verify this).

The connections between the carb and engine have been checked for leaks, cracks, holes and are tight.

I have tried pouring gas into the spark plug hole. I have tried spraying starting fluid into the plug hole and into the carburetor. I have tried the starter, for minutes at a time, with the choke on, or the choke off.

Nothing that I have done makes any difference at all.

The only exception to that is when I have sprayed a LOT of starting fluid either into the carburetor, or directly into the head (with the carb removed), after a couple minutes of turning over, it will finally ignite the starting fluid on top of the engine, or in the air cleaner box (depending on which way I did it). The engine never, pops or lets out exhaust smoke, not at all.


A google search suggested the following things:

Incorrect valve clearance "as the engine gets some hours on it, the valves may seat deeper in the valve seats and need adjusting".

The timing is off/the flywheel timing key is sheared. (I'm not even sure that it has one of these.)

So, any thoughts/suggestions?

Thank you so much!
Sounds to me like the timing is off. Usually, when it backfires out of the carb, the timing is off. You will still have spark, but, it will spark at the incorrect time. Download a manual and check the timing.
 
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