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88 fourtrax 300 4x4 starting/carb/throttle issues

2308 Views 11 Replies 4 Participants Last post by  Blueniner9
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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Update: I’m pretty sure my issue could be related to the choke. I replaced the cable and I’m wondering if I got the wrong one and maybe that could be causing my issue? When I choke the bike after warm up it sputters and it dies immediately. It does not idle up like I thought it should. Thoughts?
Vacuum piston is good. I even checked it with a super bright light for pin holes. I did order a new choke valve as I’m still using the old one. It ran great today, but it seems to be intermittent between barely able to idle and then runs like a top. Thanks for the advice- I’ll definitely be changing the choke.
I’ve been traveling for work, but here is my update:
Ordered new choke just to be sure, replaced that and rebuilt the carb again. Verified I have good spark, but ordered a new CDI/coil as well.

Put everything back together and she started and idled great, throttle worked as it should, etc. let her warm up so I could do fine tuning and she started to idle a little erratically, then when I went to tap the throttle it died. Started her back up and she idles with a very slow hesitation and as soon as you try to give her throttle she gets even worse. I have a video of it but haven’t figured out how to post that yet.
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.
Thought I’d give a final update and thanks to those who helped. It ended up being the CDI. I got so frustrated, I took it to a dealer, who was certain it was the stator. I put a new stator/pick up coil in it and had the same problem. Snagged an OEM CDI box from HoT and boom, she runs like new! Thrilled to have this machine up and running again. Will rehab the plastics and repaint the frame/racks this summer. Also, scored a 85 TRX 250 utility the other week that was Stuck in reverse for $80. Pulled left side case and it needs a new shift drum center. Parts ordered. Hoping to post a few pics of my machines when I get a chance. Thanks again all!
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