[Bigazzsnaz]

Hi all,
I've just connected to the forum site as I'm having trouble with my Honda trx 350fm 2003 I think. I'm from Australia so not sure if you have them over in the US. Basically it runs fine on idle. But when you push the accelerator it just doesn't want to rev up at all, thought it might be a carburettor issue. So I pulled the carb out and cleaned all the jets etc until it was completely spotless. Put it all back together and it still did the same thing. So I pulled out the fuel tank and cleaned the fuel filter and put fresh fuel into the tank as well as blowing out the fuel line. Connected it all back up and it's doing the same thing, next I cleaned out the air filter and re oiled it. Still did the same thing. So I thought it might be a carby issue still. So I bought a brand new carb genuine Honda which was quite expensive. Connected everything back up and yes still not working. And I've checked the compression which is meeting the guidelines on the Honda workshop manual for the TRX 350fm
I'm getting 80psi without throttle, and 120psi with throttle open. I feel like I've tried everything and it still isn't working. Do any of you guys have any idea what the issue is? And any tips or tricks that could fix this issue.
Any advice will be much appreciated thanks a lot

Here is a link to the workshop manual for my model: https://www.manualslib.com/manual/804553/Honda-Trx350tm.html?page=84#manual


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[Bigazzsnaz]

When running can you try giving it a little choke and see if it will rev up? Also, have you examined the hoses for kinks, leaks, etc?

Hi mate, yes I've played around with the choke, and I've examined all the hoses for kinks and twists. I've also cleaned them out with a compressed gun. Thanks for your reply appreciate it.


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[Bigazzsnaz]

It doesn't have any holes in the vacuums line as I replaced it and tested the small black vacuum part on the side of the carb, doesn't make sense? Thought it would be a carb issue and replacing the carb would fix this? Any other ideas? Doesn't seem like a mainstream problem


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[Bigazzsnaz]

Yeah okay, seems like a good idea, I've been running the carb without the air box and filter even on, just open as it's in a very clean shed so I know no dirt will get sucked into the intake. May have to pull down the carb and inspect further. Also what plug are you talking about?

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[Bigazzsnaz]

Okay, thanks heaps for all your advice I'll be back in the next couple of days with the results!


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[Bigazzsnaz]

Many carb problems turn out to be electrical in nature rather than carburetion.

Do you own a good 35 dollar Aussie multimeter?

Rick

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Hi Rick
Yes I do have a good old 35$ multimeter, any specific wires I need to test? What's the go? I've only got basic electrical skills.
Cheers


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[Bigazzsnaz]

my concern: have you checked the timing ???. the trx350 ranchers are prone to stretching the cam chains, and when this takes place ?, they don't run very well. another thing, the c.d.i, or the reg/rec, stator can cause your issue. but start by checking the timing, and valves for adjustment .

Cheers mate, I'll look into it, could be the timing chain possibly, seems kinda weird that it idles like new. Could this still be a valves issue?


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[Bigazzsnaz]

my concern: have you checked the timing ???. the trx350 ranchers are prone to stretching the cam chains, and when this takes place ?, they don't run very well. another thing, the c.d.i, or the reg/rec, stator can cause your issue. but start by checking the timing, and valves for adjustment .

Cheers mate, I'll look into it, could be the timing chain possibly, seems kinda weird that it idles like new. Could this still be a valves issue?





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very well could be a valve issue ?. if the valves are not set right ?, you lose compression ?. in other words, if the intake or exhaust valve is not right ?, you may not be '' sucking in '' enough fuel to make the motor top out like you want.

I've done a compression test and got 80psi without throttle open and 120psi with throttle open seems like enough pressure ?


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[Bigazzsnaz]

I'll tighten the chain and see what that does to the equation ?


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[Bigazzsnaz]

I'll tighten the chain and see what that does to the equation ?





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you can't tighten the cam chain bro !, it has an automatic cam chain tensioner built into the back side of the engine case. you have to remove the back engine cases in order to change the cam chain, which means, the starter has to come off, pull starter removed, stator case removed, flywheel removed, then you can replace the cam chain. you will need to drop the rear swing arm in order to get the rear engine case off. and you will need a flywheel puller tool to pop the flywheel off.

Ahh rightio, saw something about the chain tensioner in the manual obviously it's not adjustable, excuse my lack of mechanical knowledge this is my first proper ATV project


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[Bigazzsnaz]

also, YOU MUST PULL THE TOP END OFF AS WELL !. reason : the cam followers will drop down in the lower engine if you pull the cam out to replace the chain. you can how ever, unbolt the cam chain sprocket from the cam, and replace the cam chain that way ?, but I always pull the cam out, cuz I want to inspect the cam lobes. tip: the cam sprocket has punch marks stamped on it, they should have 250, and 350 stamped on it ?, YOU WANT THE 350 MARKS TIMED TO THE INDEX ON THE CASE, NOT THE 250 !..LOL.

Ahhh okay sweet, handy tip right there


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[Bigazzsnaz]

Hi all, just a general question, is there a specific wire to do with the CDI or something out that cuts the throttle control?



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[Bigazzsnaz]

Hi all, just a general question, is there a specific wire to do with the CDI or something out that cuts the throttle control?







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no, c.d.i either works , or doesn't ?. has nothing to do with how the motor rev's, for the most part anyway. in other words, has no control over the carb.

Thanks for the confirmation mate


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[Bigazzsnaz]

Start the bike with the multimeter connected to the bike battery. What do you see for AC and DC voltages at about half throttle?

Rick

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Hi Rick
Here are my results
Battery without any connections 13.05v
Ignition on : 12.92v
Idle: 14.44v (bouncing up and down)
Throttle no change?? Still 14.44v

Idle on AC .009
Half throttle .009

Hope this give you a more clear idea of what's going on?


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[Bigazzsnaz]

Those voltage numbers indicate that your voltage regulator / rectifier are healthy and you can look elsewhere for problems. I'm thinking timing chain problems or maybe a sick CDI.

Rick

Thanks Rick


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[Bigazzsnaz]

How many km or hours on this engine?

10,000km


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[Bigazzsnaz]

Hi all, is there anyway to check to see if when you give the bike throttle the spark is becoming more frequent? Leaning toward a spark issues after replacing the timing chain at my Honda dealer. Any ideas, or should I just go new spark plug? Plz note I have cleaned the plug and no improvement.


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