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Discussion Starter #1
Hows it going everyone? My name is Andrew, I just purchased a 450r from a "friend".. he told me it ran when he last used it over a year ago but that he had noticed some scourning in the carb causing idle issues and that he would have to constantly manipulate the throttle with the adjustment knob. His theory was to much air bypassing the plunger due to scouring, anyone ever had to replace a carb due to "scouring"??

So since I purchased the bike I have been able to fire it like 4-5 times, every time it died when I let it idle expect ones it fired and idled for a few seconds then I revved it and let it go back to idle and died. I have removed, disassembled, soaked and cleaned the carb twice. Just to be clear I didnt soak the carb itself just cleaned it the best I could.

Now my main issue isn't that it wont idle but that it never actually wants to fire, the 4-5 times its fired had 100s of kicks in between, I found plug to be soutted up black with wet fuel on it. I have checked the petcock to make sure carb is getting fuel, I did drain the original fuel and put new 92octane in it. I found the gaskets and orings in the carb to be old and some cracked but no fuel leaking externally. Have adjusted the air/fuel screw to 2.5 turns out and turned it one-out from there trying to get it to start. Removed the fuel tank and tried to start it and it actually started twice in a row but once trying with carb cleaner or with the tank nothing. Not sure if it was a coincidence or if I'n maybe getting way to fuel. Makes sence with the fouled plug. Can anyone give me some direction here? I'm a certified automotive mechanic but have never felt with carbs before and I feel lost ? have done a ton of research but nothing seems helpful! I will try to attach some photos of the "scouring". Although I really dont think that my issue.
 

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I would like to first point out that I did notice right off the bat in the Picture is the carburetor slide is in the UP position and the butterfly valve is closed... Were you lifting up on the Carburetor Slide when you took that picture? Or is that just what it looks like inside the carburetor when you took that picture? Also when you "Pump The Throttle" you wanna see the slide move up and the butterfly open at the exact same... during that process you also wanna see fuel squirt past the butterfly valve and slide and the slide should drop back down when yo let off the throttle so basically 3 things should happen at the same time Slide, Butterfly and Squirt of fuel when you pump the throttle.

As for the Air/Fuel Mixture needle (seen in the 2nd picture). The broken O-Ring, that it should still operate fine like that, mainly that O-Ring just keeps tension to keep the adjustment needle tight from moving around and loosing adjustment. Now at the tip of that needle there should be a Spring, Metal washer and then small O-Ring in that order.

Now is the best time to take the carb bowl off, take out all the jets, remove the Air Cut Valve and use compressed air to blow out all the orifice circuits (I'm sure you already did). The bowl will have some circuits as well, take the Accelerator pump diagram apart (will have a small spring in it as well so be careful when removing the 3 screws on the bottom of the bowl) that also will be a good time to check the Diaphragm to make sure it's not ripped or anything.



As for the Spark plug make sure you're running an Iridium IFR7L11 or a IFR811



If that is all good then lets move onto the Valves.

Identifying if the valves are the issue. There are a couple of ways to pin point if your valves are causing the hard to start problem
1. Pull the quad with another quad or vehicle while in 4th gear holding the clutch and let go of the clutch and see if it fires up.

2. Leak Down Tester. The Leak Down Tester This is the quickest way to check if the valves are to tight in my opinion. Now setting the Engine to Top Dead Center hook up your Leak Down tester, you wanna slowly turn the air pressure up on the tester, you should only hear a small amount of air escaping FROM THE EXHAUST VALVES ONLY or noise of air from the exhaust. If you hear air coming from the Carburetor/Air filter. That means the the intake valves are to tight and need to be re shimmed.
 

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Discussion Starter #6
So I took that photo with the throttle assembly held open with the carb out of the bike, I noticed that with the carb installed when I pull the throttle I see no fuel spraying in the carb which is kind of weird because after a few kicks I find the sparkplug to be covered in fuel. Either way where should the fuel spray out of the little copper piece at the bottom front of the carb(airboxside)?
What would starting it in 4th show?
Also I dont have shop air at my house or my compression set, can it be checked with just feeler gauges and if so do you know the specs?
 

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Good points Ryan, but just want to clarify that the plug is an IFR8H11.
why that one? i just use the reg one that pepboys/autozone gives you when you tell them the model..
 

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Discussion Starter #8
Going to check the valve clearances tomorrow but today was fidgeting with the carb, got it running with carb cleaner then kept it running by giving it throttle. Noticed that a **** ton of gas is coming out of the carb theough the intake side(obviously I have no intake on it) also noticed that if I rev near redline itll pop flames everytime. Seems like wayyyyyyyy to much fuel. Any incite?
 

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@Touge450r
Are you getting spark?

If the Carb bowl is full of fuel it will take a few pumps of the throttle to prime the Accelerator pump and yes you should see some fuel squirt out of the copper looking thing at the bottom of the carburetor on the air box side.


As for checking the Valves... YES, you can also use a Feeler Gauge. After removing the three 10mm Valve Cover Bolts, and setting the engine to TDC... Both of the intake valves should be a .006" (Thousandths) and both of the Exhaust should be at .011" (Thousandths).


As for pull starting it in 4th gear... the reason I say you can try this is because these engines have whats called an Auto Decompression Mechanism and it has a weighted wing that flings out, now that wing that is spring loaded and only activated with centrifugal force lets say like 800 or more RPMS it's got a small "Bump" connected to it if we may call it that, and that small "bump" is shaped like a capital D that is Timed at TDC and what that bump "capital letter D" does is it pushes on a little rocker arm that is just above the exhaust rocker arm, it is designed to slightly open the exhaust valves only at TDC. (almost like a mini exhaust cam lop that goes away when the engine starts up) Now when that wing Flings Out due to centrifugal force that "Capital D" is now flipped upside down and not pushing up on the Rocker Arm no more because the flat side of the "Letter D" is now flipped over and now giving it full compression, or well possibly in this case More compression if the Intake Valves are to tight. Hopefully you understand that I'm trying my best to explain it.

@El Mamito USMC
These bikes require an Iridium Plug from factory, it's just best too run what the service manual tells you to run. From what I know it's a plug that will last a bit longer probably more resistant to heat. I know that Iridium plugs are a much more reliable plug. Less of a chance of it fouling out on you. I mean it is going into a a Machine that a lot of people depend on getting them back home or to their camp sites when on trail rides that are miles long and I think manufacturers would rather not have complaints that bikes are loosing spark 20 miles out in a trail left and right due to cheap plugs.
 

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Discussion Starter #10
@Touge450r
Are you getting spark?

If the Carb bowl is full of fuel it will take a few pumps of the throttle to prime the Accelerator pump and yes you should see some fuel squirt out of the copper looking thing at the bottom of the carburetor on the air box side.


As for checking the Valves... YES, you can also use a Feeler Gauge. After removing the three 10mm Valve Cover Bolts, and setting the engine to TDC... Both of the intake valves should be a .006" (Thousandths) and both of the Exhaust should be at .011" (Thousandths).


As for pull starting it in 4th gear... the reason I say you can try this is because these engines have whats called an Auto Decompression Mechanism and it has a weighted wing that flings out, now that wing that is spring loaded and only activated with centrifugal force lets say like 800 or more RPMS it's got a small "Bump" connected to it if we may call it that, and that small "bump" is shaped like a capital D that is Timed at TDC and what that bump "capital letter D" does is it pushes on a little rocker arm that is just above the exhaust rocker arm, it is designed to slightly open the exhaust valves only at TDC. (almost like a mini exhaust cam lop that goes away when the engine starts up) Now when that wing Flings Out due to centrifugal force that "Capital D" is now flipped upside down and not pushing up on the Rocker Arm no more because the flat side of the "Letter D" is now flipped over and now giving it full compression, or well possibly in this case More compression if the Intake Valves are to tight. Hopefully you understand that I'm trying my best to explain it.
I do have spark, and i havnt seen any fuel come out of the copper nipple at the front of the carb. I can get the bike to start with carb cleaner then it seems to run really rich till it dies then wont start again even with the carb cleaner, I'm guessing it's fouling the plug with all the fuel. When I get it running with the airbox intake off I can literally watch it dump fuel into the venturi out of the main jets' circuit and the needle vibrates like crazy just dumping excess fuel at any throttle opening.. I'm assuming this isn't normal? A ton of Fuel vapor shoots out the intake side of the carb, does not seem efficient or normal haha
What in the carb would cause this?
And yes I do understand your explanation of the decompressor, pretty good explanation actually. And if it started fine in 4th then your theory is it's not making enough compression while kicking it over? Foes the deconpressor have a spec I can measure with the feeler? About to pup the valve cover off and check my valves now.
 

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Yes the Decompressor does have a measurement, sorry I should have mentioned in my previous reply. But anyways that should be also set at .011" thousandths. A lot of guys set them by using a leak down tester and set them usually at like 50 or so PSI psi if I remember correctly. YES you can do it too with a Feeler Gauge as well, set it to .021" thousandths and should work fine.

As for the 4th gear theory that is correct, it's not making enough compression from just kicking it over.

Intake Valves = .006" Thousandths
Exhaust Valves = .011" Thousandths
Decompressor Rocker Arm = .021" Thousandths


As for you seeing fuel coming out the intake side of the carburetor... if you have the air box off is pretty much expected.
 

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When you say the needle bounces around, you mean the whole slide jumps up and down or just the needle? If it is just the needle then you need to look under the top lid and make sure it is clamped down like it is supposed to be as the needle should only move with the slide. Also, you mentioned some seals in the carb were cracked like the one pictured, I would get a rebuild kit and replace all of those just to eliminate them. As has been mentioned I would look at the valves next. As far as the copper jet at the front that is the accelerator jet and it will only squirt fuel when you jam the throttle fast. It is just extra fuel to help prevent a stutter in acceleration, if it does not shoot fuel when you jam the throttle quickly, while running or not, that is another issue that needs to be addressed. Do you know what size jets are in the carb?
 

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Discussion Starter #13
Alright finally she starts every kick, backfires q little and idles high but hopefully I can just adjust the air/fuel and get that sorted our, I also want to put all new gaskets and orings I'm the carb but for now at least it's running. Found a few issues, the accelerator jet had a clogged passage, I spent a little time figuring out where the passages go through the carb and the cap that holds down the spring for the diaphragm and really cleanes out those passages with compressed air and carb cleaner and was able to get that working. While I had it disassembled I realized I was missing a small round part that sits in the vinturi around the needle of the slide where the excessive fuel was coming out, I scoured my shop floor and ended up finding it in a oil bucket that I so happened to drain while looking and bam there it was at the bottom!
I think the main issue was the valves though, mainly the intake valves. I couldn't get my smallest feeler gauge in between them which is .002.. so after a few trips to my local shop I got the correct shims installed and they are now right about .006 and exhaust .011-.012.
Also changed the oil(so much fuel In it it was like water downed milk), filter and plug. Thanks for the advise guys, really happy this thing starts and runs great now!
 
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