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Honda CBX Carbs – Six To Clean

A simple summer day job turns into holy hell when old fuel is discovered in the CBX carbs — all six of them.

Summer being about over I decided to at least attempt one of my holiday goals— starting the 1979 Honda CBX known as “Larry’s Bike.” I should explain. The bike had been hot-rodded more than 30 years ago by yes, Larry. It was raced at Calgary’s former Race City Motorsport and prowled the streets of Cowtown as probably the baddest X in the city. Everywhere I went I heard, “Hey, there’s Larry’s bike.” Eventually the realization set in it would always be Larry’s bike, no matter who owned it. There were not many nitrous and air-shift equipped 1132cc (Ontario Mototech big bore) six cylinder street bikes back then. For the track it had wheelie bars and a slick. Now it lives in street bike mode.

The dual gas taps feeding the beast always leaked when the levers were turned so I figured I would start there. To my surprise and horror there was gas in the tank! Never ever does anybody want six gummed up carbs to clean, never mind ones that are a nightmare to get on and off. 

Yeah, about six or seven years ago I rode it to a show ‘n’ shine. Guess I forgot to get the gas out, and now a simple summer day job just got nasty. There was good news. I had shut the gas off and ran the bike out of fuel so only the bottoms of the float bowls were gummy. The gas in the tank didn’t smell too good but at least it drained out clean. 

The bad news was that the level in at least one of the CBX carbs was high enough to cause a float to stick. That meant putting fresh fuel into the system with my external tank. What a mess. The sticking float caused an overflow and a big puddle of gas on the lift. Sometimes a good (not box store) fuel additive can save the day, but the bike needs to be a runner for this option to have a chance.

Removing the CBX carbs revealed one centre float bowl had been weeping. Looks like Larry had reused the original gaskets (with a dab of liquid gasket) and they were failing, 30 years later. Funny thing I guess, this job was going to be needed no matter what.

Using some Simple Green in my cheapo ultra sonic bath cleaned the bowls in about 10 minutes, three at a time. I was impressed so I also gave the K&N pods the same bath (don’t leave them in too long or the glue will melt). Blasting some lube through the jets can confirm they are not blocked, a couple of strokes with the K&L jet cleaning tool and we should be good. 

After reinstalling the bowls it was time to flip the carbs over. Removing the top caps revealed the metal diaphragms (no need to worry about pinholes on these guys) and the slides and needles. I like to use WD-40 to clean and lube the slides then wipe with a clean soft paper towel. 

The slides have to move in the bores with virtually no effort. I tested mine after putting them back together by sticking my finger in the carb throat and lifting them. Taking your finger out they should lightly snap closed. It’s also a good time to look for wear on the needles. Mine were good. Six carbs look intimidating, but the trick for me is to do one at a time so parts don’t get mixed up and wear patterns remain matched. 

I managed to order new gaskets and screws online. Removing the screws is best done with an impact driver. The Japanese Philips head screws don’t fit your standard imperial driver quite perfectly. Look for a driver that fits well.  Remember the screws are also very soft if they are chewed up; please replace them. Mine were mostly good but a complete new set is the way to go. Be very careful with the bowl gaskets. There are pinch points that hold them in place but they are not very trustworthy. I like to massage the gasket in, and then put the bowl on, lightly tightening the screws, then take it off again and make sure it’s seated.

Okay where was I? Oh yeah, fuel taps and a battery

by Rich Burgess Canadian Biker #317

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