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carbs 101 - troubleshooting

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hello all,


the reason why i started this thread was because of my lack of knowledge of caburators and an issue i ran into on the weekend. my buddy has a 1988 toyota corolla with a carbureted system and i told him i would check it out before he went out that night. i started the engine and at park it wouldnt idle rough almost like a sputtering put put. he said it still drove. i then took the air filter housing off and noticed a not so good looking air filter (that started deteriorating ). looked at the carb and nothing really out of the ordinary. i then put everything back and started it again. this time, in park, it would rev then over rev without pedal to gas or anything. off on off on and it kept doing it. so i drove it down the block and i realized my foot is dead on the brake to prevent hitting the car infron of me because it was all go and just kept reving high. got it back to my house and tried neutral start and park start (automatic tranny) and once on, this this would just rev like crazy.


so i then went to the auto store and picked up a fuel filter, air filter, and carb cleaner. got back and i just balsted the carb spraying that stuff around inside and out, opening the butterfly and everything. by this time my buddy was like "can i go now" but i told him to chill unless he wanted to take the bus the next day. started the car and the same thing, just high high reving. took to the net but nothing that would explain this and help fix the problem. so this carb clean and high revving continued for a while and then i told him he may need to get someone to take him where he needed to go. so while he was trying to find a ride he was calling his family of few that are mechanics but no one answered the phone (UFC fight night - go figure) all while i am dealing with his cars issue.


just stumped, i started to see if he had connections to the carb and he did, i think. with nothing else to go on, i sprayed the gunk off the connections and made sure they were connected. as he was getting close to getting his ride and me sitting in the drivers seat i started it up one more time.... it worked. cranked a few times to cough up the carb cleaner out and started fine, no put put, and a very smooth idle. stunned, my and my buddy drove it around the block and drove like an 88 corolla should have with the carb clean.



this is where i ask you what could have been the problem? i am new to automotive carbs (even gave mine to Charlie69 to rebuild for me so i could avoid the unknown issues) but have worked on johnson/evanrude boat engine carbs back in the military and as the same concept they may seem i feel they are totally different. being that i have a J15 with a carbureted system i wanted to know what troubleshooting steps i could look after so i can have a way to figure out what the problem is. my theory was a minute chunk of the air filter might have got caught or fell into the carb and created a restriction to make the engine think i am full throttling but i dont know. like i said, i repeated the steps of spray, check hose connections, and look around but nothing untill i sprayed some of the electrical connections.


anyone out there ever ran into this?... may have an idea what to look out for the next time this may happen?.... the saying holds true, you learn by the mistakes you make but i didnt want it to come at the cost of my friends corrolla. granted things are back to good but i am still baffled as to what the cause of that was.


any help? :blink: :)

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You said you opened the butterflies did you mean the choke butterflies? If so a stuck choke could cause your problem. When you cleaned the connectors you may have restored power to it and it opened. Or it just took time for the carb cleaner to eat away at the problem. Who knows late '80's carbs are a bit mysterious.

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