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Need Help with an 87 TRX70 - Carb and Choke problem

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Hi guys,

My first post here.

I picked up a trx 70 for my kids a few years back for $300. Just got around to playing with it. Its in great shape however I have a couple problems.

1. It runs fine with the choke on (up position) but when I push it down and adjust the pilot screw and throttle stop screw for a nice idle it has no power when I give it gas. It stutters and wants to stall unless i let off the gas and just feather the throttle. If I put the choke up and adjust the screws for a steady idle it runs fine and has plenty of power when riding. Obviosuly this isnt right and I want to fix it.

I took the carb off, disassembled it entirely, cleaned it with carb cleaner and air from my pancake air compressor. I made sure all those little holes in the jets were clean and I could see light through them when I held them up to the lights. I also replaced all the gaskets with oem honda gaskets and the little fuel strainer too. I believe I did a good job. I didnt take apart the throttle valve assembly. The piece that goes into the top of the carb which is attached to the throttle cable. I think I read somewhere that the needle clip might need to be adjusted 1 notch up or down. Can anyone confirm that? Would this make a difference on the choke being screwed up or does it sound like I need to take the carb apart again and poke a piece of wire through the main jet? The choke issue is definetly related to carb right?

2. I replaced gasket inbetween the intake pipe and carb. There was no plastic insulator. I ordered an oem honda insulator and oem gasket and installed them. Now when the bike is running i have an annoying whistle coming from that area. Its almost like the insulator is 1/8 of an inch small and left a tiny little hole for air to escape. I have the insulator facing the right way and tried turning it in both directions to make sure I didnt install it wrong. I am left with tiny gap either way. Its driving me crazy. The previous owner cut and installed his own gasket and made it a little larger to cover up the entire face of the carb where the intake pipe bolts to. I dont understand what is causing it and Id prefer to keep the bike 100% stock. I'm not a hacker. Here is a photo so you guys know what I mean.


Any help would be greatly appreciated. Im new to wrenching quads but I learn quick and I've been taking things apart and putting them back together sucessfully since I was 5 years old. I'm 36 now. We have great running 86 suzuki lt50 and my kids are driving me nuts to get this 87 trx 70 going so they can ride together.

thanks guys!


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You don't want any gaps between the carb and intake check all your fuel lines for holes or cracks. If your sucking in air your not getting enough fuel. When you use the choke it is letting the carb get more fuel. I dont know the fix 100% but if you have a gap between the carb and intake you might could double up and try 2 gaskets. If your sucking in air you don't want to keep running it like that. Have you checked the intake and carb mounting serfaces to make sure their flat. Until you find the problem your not going to be able to adjust the carb. Once you get it fixed find the factory settings for your air fuel mixture screw and set it. From there you will need to adjust your idle. I hope this helps.

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Thanks for the advice. I took the carb off with the intake pipe still attached. Then i took it apart. It looks like the surface of the pipe or the carb might be slightly warped which is allowing the air to escape. I just reversed the insulator and gasket to the parts order diagram and it sems to cover the area it hadnt before. The previous owner had to homemade gaskets inbetween the pipe and carb. Maybe for this reason.

I also took the carb all apart again. I cleaned every hole and jet with a thin piece of copper wire, carb cleaner and compressed air. All passages appear to be perfectly clear including that little tiny tiny one on one of the jets.

Only thing i didnt do yet is take apart the throttle cable needle and clip. I am going to do that tomorrow nite or friday nite. Someone said might have to readjust a notch up or down?

I guess I will go from there unless someone else has a suggestion.

thanks again for the reply.

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I feel it's going to be the gap between the intake & carb. Even if you put a brand new carb on there if it had the gap it would still not run right. It sounds like you crossed all of your t's & dotted all your I's with the carb it's self. Did or do you have any popping back thru the carb?

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can anyone help me with the choke problem??? Its driving me crazy!!!!!!!!:aargh::aargh::aargh:

I took the carb off again. All jets are 100% clean, the carb is clean, I removed w clip and throttle needle, the C clip was on the top notch. I moved it to the middle notch (factory setting) and once again made sure the entire inside of the carb was clean, float moves freely. Assembled again and the bike will start on the first pull but it only runs perfect with the choke on (in the upward position). If I move it down I have to adjust the 2 screws, I can ride it but when I give it a good amount of gas on the throttle it bogs down. It especially loses power when I go up a hill. If I ride it with the choke on it runs great.

Could this be a valve issue or does the symptom directly point to the carb???

Someone please help me before I go insane.

I havent ordered a carb rebuild kit with the jets but i did replace all the rubber gaskets/o-rings. All of the jets are clean and not blocked up with anything.

Could my problem be related to anything else other than the carb? The fact the bike runs perfect with the choke on leads me to believe my problem is carb related. Anyone located in Connecticut on this board? Id be more than happy to buy you a case of beer if you took a look at it with me. :yes::yes::yes:

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Did you look at the fuel lines and make sure theirs no cracking also did you check the fuel cut off & make sure the fuel flows good. When you have to run it with choke that means you are running on the rich side. Did you end up getting a good seal between the carb & intake? Does it seem like it's running out of gas when you try and ride with out the choke on? When you say the 2 screws would it be the idle screw & fuel air mixture screw? Is the air filter clean. Has it got the stock exhuast pipe & airfilter? My daughters quad would run and die it has an electric choke but once it died it would not start unless I removed the air filter and hold my hand over the carb for choke. Found out a vacum cap had come off the carb. after i repulld the carb and took it all apart and put it back togather I remember it had a vacum cap that was now missing that was the problem. So look close at the carb.

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