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Discussion Starter · #1 ·
Hello!

Looking for some input on where to look next.

Bike sat up for 2 years with unstabilized gas. Doesn't start.

Pulled carb, found jets clogged, green gunk, etc...

Cleaned entire carb, jets, etc.. with carb cleaner. Sprayed in every orifice I could find. Blew out with air compressor.

Drained most of the old gas from the tank, cleaned the petcock, replaced the fuel line and inline filter. Added 2 gallons or so of fresh gas.

Cranked right up. Ran mostly ok for about 10-15 minutes. Stopped to adjust idle screw then nothing.

Pulled carb and cleaned again. This time gave it an hour in an ultrasonic with water and dawn. This time engine would idle fine but bog down when throttled up.

Pulled carb. Cleaned again. Nothing. Won't start. Picked up rebuild kit.

Installed kit, reinstalled and still nothing.

Checked spark and it's sparking. A little off but not too bad. Gave it a shot of carb cleaner in the plug hole for good measure. Still nothing.

Pulled again to double check the install. The kit came with a 125, 40, 85, and 90 jets. I swapped the 85 with the 90 for good measure. Still nothing.

After hitting the plug with carb cleaner, it looks like some soot is blowing out of the piston back into the butterfly, but the gas in the bowl looks clean and the jets are clear.

Spraying carb cleaner straight into the carb from the air filter doesn't help.

I Pulled the inspection adjustment ports off the head and confirmed that the two valves are at least moving up and down.

Any suggestions on what to try before I drag this thing to the shop?

Thanks!
 

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Carb could still be dirty, or maybe need new choke valve.
Set the valves. PO might’ve improperly set them.
Got a battery in it?
 

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Discussion Starter · #3 ·
Carb could still be dirty, or maybe need new choke valve.
Set the valves. PO might’ve improperly set them.
Got a battery in it?
Thanks for the quick reply!

Choke cable and valve seem good to me. I can feel the pressure difference at the air box when the choke is engaged. Is that an ok-enough test?

I also replaced the spark plug for good measure.

I'll pull it and clean again and gauge the valves. From what I've seen, is .006 the proper adjustment? Also going to borrow a pressure gauge and check the compression.

Do I need to be concerned about the carbon blowback into the carb at this point? There wasn't any until I sprayed a shot of cleaner into the chamber to see if I could get it to pop.

Thanks again for the input. This site has been a very useful resource for me researching this bike. I feel like a noob posting basic questions that have already been covered but I'm hoping someone will recognize something and set me straight on a hidden passageway or something else obvious that I'm just not aware of. I'm not a mechanic but I've toyed with bikes, small engines, etc.. over the years.
 

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Download the service manual from the link in my signature block below

the 96 TRX300 had faulty CDI so I would consider replacing it. Here’s something to try:

heat the CDI in an oven, connector side up, no more than 200F. For at least three hours. Let cool completely before you reinstall
 

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Discussion Starter · #5 ·
Download the service manual from the link in my signature block below

the 96 TRX300 had faulty CDI so I would consider replacing it. Here’s something to try:

heat the CDI in an oven, connector side up, no more than 200F. For at least three hours. Let cool completely before you reinstall
I think I've read the entire service manual front to back twice by now. Thanks for that!

To follow up on this, I hooked up the compression tester. I'm getting somewhere around 15 PSI (tester is good - my riding mower gets 120-125).

I think I found my (latest) problem. Now to read up on valve jobs.... Pointers to any specific posts / videos appreciated.

Thanks!
 

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Do a compression test on it. The timing chain jumped loos on my brothers 1993 TRX300FW. They are an interference engine, so the valves will hit the piston if the timing isn't correct.
 

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Discussion Starter · #9 ·
Maybe timing chain loose and jumped off?
Checking the timing chain from the valve adjustment port seemed to not be loose or completely jumped. I plan on taking the head off this weekend. I'm expecting to find a blown intake valve seal. Not sure why I'm expecting that, but that's what my gut is telling me. I'm probably 100% wrong. :)
 

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Discussion Starter · #10 ·
Depending on how wore out it is, it should have 140-200 lbs of compression.
I'm getting 30 max. Hoping it's just a valve... If it looks like much more than that I'll get a estimate from a mechanic. I don't want to put more into this than it's worth.

Thanks for the reply! I'll post back when I get more info.
 

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If it smoked on start up, and cleared up when warm, that indicates to me a valve seal. But considering you only have 30 lbs of compression, I think it probably ate a ring.
 

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Discussion Starter · #14 ·
Thanks for the continued support!

Honey dos ate my weekend, so I'm hoping to get a few hours to crack it open and take a peek. I tried pouring a cap full of oil in the cylinder. No significant increase in compression.

I'll update when I know more, but I'm sure whatever it is won't surprise anyone. :)

Thanks again!
 
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