88 fourtrax 300 4x4 starting/carb/throttle issues

2318 Views 11 Replies 4 Participants Last post by Blueniner9, Jan 26, 2020

Blueniner9

Discussion Starter · Sep 26, 2019

Hi, this is my second post here, first one over in the intro section...

I’m working on getting my late dad’s fourtrax running. It sat for 12 years. I’ve rebuilt the factory carb. Soaked the carb body, blew out all the passages, installed new jets, replaced the choke cable, new air filter, plugs, and all new fluids (Honda spec’d), drained fuel, new fuel lines filter, battery. I think that’s about it.

Sometimes the quad will start and run absolutely fine. I can drive it around, take it for high speed runs, putt around the yard, let it idle forever. Then some times it starts fine, idles a little goofy, and the bogs down with an insane hesitation if I give it gas.

I have no idea where to go from here. I’ve torn the carb down multiple times and recleaned it, verified the slide diaphragm has no holes in it, but cannot get it to consistently run. Any help is appreciated. This bike means so much to me because of the great memories I have of it with my pop. Thanks in advance!

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Goober

· #3 · Sep 27, 2019

Did you replace the starter valve? It’s what the choke cable hooks to—that oring has to be pliable and conically shaped—pointing into the carb

If it’s rounded or brittle it’s done. New valve kit costs ~ $40

Also make sure your vacuum piston seal is seated well and no perforations

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Goober

· #8 · Oct 7, 2019 (Edited)

Do you have the manual?
Sounds like fuel flow problems—is tank clean?
Do the fuel flow test on the ON and RESERVE settings
If flow is slow then petcock could be clogged

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Goober

· #11 · Oct 26, 2019 (Edited)

Blueniner9 said:
I do have a factory service manual. I’ve tried with Petcock on reserve and on with no difference. Fuel flowing fine into carb and I have an in-line filter. Tank looks clean inside but I’ll try cleaning the petcock as well.

Well maybe it’s an ignition thing—i think there’s a diagnostics table you can use on page 20-4.
double check the overheat system Ohms check the oil temp sensor and see if it’s in spec.
Possible the CDI is giving you problems. Try this it won’t hurt anything. Dry out the CDI like you were making some oven jerky. Put in an oven (connector side up) and turn the oven on no higher than 200F. Let it dry out for at least three hours. Let the CDI cool down completely before you reinstall it.
Here’s a pic of my 93 carb VE90E this is after disassembly and before cleaning. See anything familiar? Remember to check the teeny port where the pilot jet screw (circled) comes up through the carb bore—make sure it’s clear and you can barely see the tip of the pilot jet screw. Make sure you’ve synchronized the carb/throttle cable.

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