TRX300 Carb Rebuild - Page 2 - Honda ATV Forum
Honda FourTrax Discussions for the FourTrax Rincon, Foreman, Rancher, Recon

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post #11 of 37 (permalink) Old 03-17-2018, 03:57 PM
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I think goober is referring the the ‘needle jet’ operated via the diaphragm. The pilot adjusts air/fuel mixture.
Pretty sure I’m right, I’ll happily stand corrected though lol

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post #12 of 37 (permalink) Old 03-17-2018, 04:18 PM
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Congrats Goober, that $24 carb turned out to be a very useful bargain! Great work!
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post #13 of 37 (permalink) Old 03-19-2018, 12:54 AM
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Something that caught my attention...

I see some of the guys that are mad into tuning and mudding are drilling the slide in the carb, a 1/8” hole, I don’t know where, I have asked the question though. @retro I’m sure you may know the answer to this?

They say it improves throttle response and 90% of the guys who are doing this donit when snorkelling.
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post #14 of 37 (permalink) Old 03-19-2018, 01:18 AM
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Oh my, its been quite a while since I seen that done! Thats an old-school mod that helps old hollow slide Mikuni carbs respond off-idle when giving it the throttle. They used to drill a tiny hole just above the bottom edge of the slide, centered on the inside wall of the slide. The reason for that was those old slides were hollow. The wedge shaped cutout (on the atmospheric pressure side of the slide) was very shallowly cut at the factory. Folks tried cutting them at different angles and achieved some small power gains at WOT, but in doing so the bottom end off-idle response suffered due to loss of a strong pressure/velocity signal that those factory shallowly cut wedge angles provided. So they drilled small holes in the back wall of the slide to help compensate for velocity losses. It served to mix & atomize fuel a bit better at low RPMs perhaps, but other than that it was just a bandaid. Later on Mikuni started providing flat-slide carbs for factory racing bikes and those hollow slide mods disappeared.

EDIT:
Basically what they were doing was modifying the venturi shape (provided by the cutout angle in the slide) for maximum flow, then when they noticed the bottom end wasn't working they drilled a hole to provide for a "leaky" venturi. I think the idea was based on the assumption that once a small column of air is set in motion it takes less time and energy to accelerate it as the venturi volume is expanded by throttle opening. Something like that... :-)
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Last edited by retro; 03-19-2018 at 01:32 AM.
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post #15 of 37 (permalink) Old 03-19-2018, 02:04 AM
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Snorkeling is a science all by itself. A design project unique to every application. Four-strokes are much more sensitive and more vulnerable to sudden changes in air mass density and velocity in a confined length of pipe than a two-stroke is, because the intake stroke happens only once every two revolutions of the crank. A single cylinder four-stroke is the worst possible candidate for a snorkel that I can think of. I'd avoid them wherever possible. If not possible to avoid, then make them as short as possible.

A snorkel can be used to provide great advantage if carefully designed and refined, but in general practice they commonly aren't. I'm sure most Honda ATVs that receive snorkels suffer through most of the RPM range, with a few rare exceptions scattered here and there. It sure would be nice if one of you guys would write some software to help everyone begin with a sound baseline snorkel design... start a thread. :-)
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post #16 of 37 (permalink) Old 03-19-2018, 03:03 AM
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Retro , hit the nail on the head about snorkels , they do effect the performance , some makes and models more than others , Yamaha seems to me the hardest to fine tune after snorkeling --------personally I feel lucky as I have 5 atv's with snorkels , 4 300's and a 450 and all were no real problem

I remember when I tried to snorkel my Bronco , that didn't work out too good for me at all , first I ran 4 inch pvc pipe up along the window post to the roof , drilled holes for screws for the clamps into the post and cut a hole thru my fender , stupid is as stupid does , it effected performance bad and I never could get it right , then someone tells me to run the tubing into the cab , that was a mistake , even though it ran better with a shorter tube , I was getting gas fumes in the truck and your eyes would burn
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post #17 of 37 (permalink) Old 03-19-2018, 05:37 AM
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Quote:
Originally Posted by retro View Post
Snorkeling is a science all by itself. A design project unique to every application. Four-strokes are much more sensitive and more vulnerable to sudden changes in air mass density and velocity in a confined length of pipe than a two-stroke is, because the intake stroke happens only once every two revolutions of the crank. A single cylinder four-stroke is the worst possible candidate for a snorkel that I can think of. I'd avoid them wherever possible. If not possible to avoid, then make them as short as possible.

A snorkel can be used to provide great advantage if carefully designed and refined, but in general practice they commonly aren't. I'm sure most Honda ATVs that receive snorkels suffer through most of the RPM range, with a few rare exceptions scattered here and there. It sure would be nice if one of you guys would write some software to help everyone begin with a sound baseline snorkel design... start a thread. :-)

So Im your opinion drilling a hole in the slide will have little affect if any at all?

I may just do a thread on snorkelling, not until I have mine set up/fuelling properly though. Be a couple of months Id have thought.
I plan on making an airbox at some point to, seems the hardest part to keep sealed is the joint to the airbox, if I can make a steel airbox I can jubilee clip the hose directly to it and eliminate the weak link.
As far as I know I just need to cut the airflow slightly, I have a 1 1/2 to 1 1/4 reducer I plan on trying in the end of the snorkel, Im sure it only needs the slightest amount, Im really close.
Have to wait and see!

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post #18 of 37 (permalink) Old 03-19-2018, 01:14 PM
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Sam , you have a 300 , are you sure the snorkel is your problem , did you ever try a new OEM carb on your bike ? ----------------- on my 300's , all 4 that are snorkeled run 1 1/2 pipe , no reduction in pipe size , except for going in the air box , there at the air box it is a 1 1/4 piece of pipe , they all run great and I never have all the swopping jets or tampering with orifices in the air tubes -------- if you seal the top of the air box lid with aquarium grade clear silicone and let it dry over night before you snap the lid down , it does a very good job of sealing out the water , if after opening and closing the box 6 or 8 or a dozen times the silicone starts getting messed up , then that silicone comes off easy and do it again , leaning it over too far or flipping it , is the way water gets into mine
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post #19 of 37 (permalink) Old 03-19-2018, 03:31 PM
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I’ve considered swapping the carbs over but they just cost so much this side of the pond, hence me persevering with the one I have. I do have 5 to 6 inches of the 1 1/4 pipe from the airbox then straight into 1 1/2” all the way.
Making an airbox was just something to do if I’m honest, I enjoy engineering projects, I haven’t had a leak myself as yet (fingers crossed) and I’ve beem that deep I lost sight of the handle bars!
What kind of prices are OEM carbs over your way?

98 300 Fourtrax 4x4

Custom built mud bike - Now sold.

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Fully overhauled (nut & bolt rebuild), 2 lift kit, 28 mega mayhems, ITP delta rims, ES floorboards, 22 LED lightbar, Pyle Bluetooth sound system.
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post #20 of 37 (permalink) Old 03-19-2018, 03:36 PM
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