Craigslist Project Bike: Tear Down and Carb Cleaning

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Categories: Hell For Leather, How To

We asked readers how we should build our latest Craigslist project, a 1981 Suzuki GS750. It came with a killer front fairing and loads of extra parts like shorty exhaust, dual-disc front end and wheel, and chrome fender. We payed $200 and decided to have fun building it into something unique.

We received a wide variety of responses. If you remember the first article posted, we listed a couple viable options: complete original restoration, cheap café, traditional café, flat tracker or flip it and find something else a little more interesting. There were many custom-bike suggestions from the dual-purpose rat bike idea to the low-seat, cutdown version, but we wanted to take a big bite of this project and pray we could swallow it.

We hinted at the idea of competing in the Dirt Bag Challenge: 30 days, $1,000, build a bike and compete on a 60-mile ride. Most of the winners built outlandish, unrideable bikes. To put some of your minds at ease we won’t be competing and don’t plan on building an unridable piece of "art".

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We decided to build a bike that's meant to be ridden, simple as that. Most upgrades we perform will be for the benefit of the rider, with some cosmetics thrown in for our own cool-measure.

We aren’t exactly sure what the final product will be, but we have a few goals and ideas:

  • Keep it cheap
  • Keep it simple
  • Modern touch
  • Don’t be scared

I’m not a huge believer in sketches and hard-fast planes as that can get in the way of progress and expense. We do, however, have a few visuals we want:

  • Black tank
  • Black frame
  • Gold accents
  • Traditional gold strips
  • No fenders
  • Only necessities

Get the Bike Running Right 

Before we can do anything, we have to make sure the bike is tip top. I learned this as an appurtenance at a hot rod shop in North Carolina. You must check the operation and functionality of every moving part, before tear down. During reassembly, this can save you days of headaches and work.

We already knew the bike would run and idle, but we had a slight tuning issue. Under load the bike bogged hard and didn’t recover. The pop-on air cleaners let in a tremendous amount of more air than the stock air box and are notorious for creating lean conditions. We started covering parts of the air cleaners to temporarily force the bike to richen up. This seemed to help.

One test to indicate a lean bike, was pulling the choke. Please do not try this at home. Driving down an empty road at a steady 20mph, we slowly pulled the choke. The bike sped up, telling us it was screaming for more fuel.

When the bike became hot, it started with the infamous ghost idle, where the bike would rev up slowly and when we turned down the idle, it would cut off.

First we checked for an intake leak and then disassembled the carbs using instructions we found online and in our Suzuki service manual. Luckily someone had rebuilt the carbs not that long ago, so the gaskets were in pristine shape.

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We noticed our intake tubes were fairly new, so we lubed them and replaced our bottomed-out factory clamps with radiator hose clamps (not the cheap ones). During all of this another problem arose: While leaned over on the kickstand the carbs began leaking gas at a tremendous rate.

After cleaning out dirt and replacing the inline filter a couple times we decided to bring the carbs back to factory specs. We first set the float bowl level, which had been way too high and might have caused our overflowing problem.With the carbs upside down we slowly and carefully bent the float's ears so the body of the float rested between .84 and .92 inch above the body of the carb (while it's upside down), using the bottom of our calipers to measure.

After the carbs were on and off a few more times we finally decided to raise the needle, as the bike still requested more fuel. Raising the needle is common when installing less-restrictive air cleaners and open exhaust. Our Mikunis were unlike a traditional CB750 carb. We had a spring that held the needle up inside the slide. We had to replace the top plastic washer with smaller washers, physically raising the needle into the slide.

With two small washers on top, our under-load bog disappeared, but we still had an erratic idle. After doing some Internet search and with the help of reader Armando Domingos [Edit Note: and Innis O'Rourke], we ventured to GSResources.com and discovered we made a silly mistake. While setting the carbs back to factory settings, we mistakenly put our air screws too lean with 2 turn out from bottom. The factory requires 2.5 turns out. 

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