Carburetor #1 vs. Carburetor #4 after dipping in Berryman’s Chem-Dip Carb Cleaner for 2 hours. Small parts and jets to be done next.
Finally getting started on the carburetor rebuild. The plan is to tear down each of the carburetors, put all of the metal bits into a carburetor cleaning bath, make sure all of the jets and body orifices are clear, and replace all of the o-rings within the carburetors and the intake boots with an o-ring kit from http://cycleorings.com/.
The carburetors on this motorcycle are Mikuni BS32SS which are very common to this generation of motorcycle. A couple of nice reference documents are available online to supplement the information in the service manual and parts diagrams. http://zeus.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf and http://zeus.mtsac.edu/~cliff/storage/gs/mc_maint/GS_CV_Carb_Cleaning_Series.pdf.
Here are the carburetors as removed from the motorcycle:
Carburetors removed from the rails and pulled apart:
It is fairly straightforward to breakdown the carburetors. The most important advice is to have properly fitting screwdrivers. The screws that appear to be Philips head are actually Japanese Industrial Standard (JIS). I have a good set of JIS screw drivers and impact driver bits that you can find here, http://www.vesseltools.com/. The jets require slotted screw drivers that must also fit well. For the main jet, I filed down a 5/16″ screw driver blade until it fit just right as you can see in the photo below.
The red circle above is the only screw that gave me much trouble on Carburetor #1. This screw holds the plate which retains the needle valve. Quite a bit of corrosion there. I tried carb cleaner and penetrating fluid until I was afraid that I would strip the screw head. Turns out a couple of taps on an impact driver with the JIS #2 bit loosened it right up.
Here is Carburetor #1 broken down and ready for dipping. Quite a few small parts to manage.
Doesn’t look too bad, but there are clogs that you can find when you try to spray carb cleaner into an opening and the spray does not come out where it is supposed to… I am going to try an initial bath of 2 hours, put this carburetor back together with the new o-rings and gaskets, and then continue with the other carburetors one by one.
Final valve clearance numbers after the shim replacements/shuffle:
Initially I ordered 4 new shims form Z1 Enterprises and rearranged 4 existing shims, but it turned out that Exhaust #1 and Intake #4 were tighter than the assumed 0.02mm since I could only measure 0.03mm and above. Both would still be in spec at 0.04mm, but at the opposite end of the desired clearance range than the other valves.
On Intake #4 I had a shim left over that improved the clearance to 0.09mm, but I had to order one more shim to improve the Exhaust #1 clearance to 0.09mm. Both ended up dropping two shim sizes while everything else dropped one shim size.
I like how the final numbers came out. All right around 0.08mm with a few at 0.10mm.
Even though the 1981 Suzuki GS650L is still in no condition to run and a compression test should be run on a warm engine, it is still a good idea to determine what kind of compression the engine has before spending time working on other components of the engine. If the compression is low on one or more cylinders, there are bigger and more costly issues to be solved first.
In a warm engine compression test for this engine, each cylinder should have a compression reading between 142 psi and 199 psi and no more than a 28 psi differential across the compression readings.
I pulled the four spark plugs to perform the compression test and also thought that they would give a good indication of how the engine was running in the past. Doesn’t look like it has been run much at all with these spark plugs.
Next I had to get the engine to turn over. I installed a Yuasa YUAM62H4L YTX14AHL-BS Maintenance Free Battery instead of the original equipment Yuasa YUAM2214Y YB14L-A2 Battery which obviously requires maintenance, breather hoses, and puts out corrosive gases. I don’t think I have ever had to add electrolyte to a battery.
With the keys obtained from Hawaii, the battery installed, plugs removed, and a compression gauge (OTC Tools – http://bit.ly/RmjM8y) connected it was time to crank over the engine. Here are the results:
- Cylinder 1 – 168 psi
- Cylinder 2 – 180 psi
- Cylinder 3 – 150 psi
- Cylinder 4 – 180 psi
Everything was within spec, even when cold. I sprayed some PB Blaster in Cylinder 3 and it came up to 165 psi. Very satisfied with these results on a cold engine.
Next will be the biggest challenge for me, I hope, rebuilding four carburetors…
Back from vacation and ready to get going again on getting the 1981 Suzuki GS650L back running again. The previous owner had already removed the valve cover, so it made sense to check the valve clearances next so that I can get the top of the engine closed up.
The valve clearance needs to be checked with a cold engine, no problem there when the bike hasn’t run for three years. Specified valve clearance is 0.03mm to 0.08mm and clearances tend to get tighter the longer the engine goes without a valve adjustment. There are a few tools that you will need to check the clearances.
From left to right: 19mm wrench to turn the crank to each valve position, tweezers for removing the valve shims from the tappet, tappet depressor tool to push down the tappet and remove or insert the shim, and a metric feeler gauge.
As noted above the valve clearances are very small numbers and many feeler gauges that you see in auto parts stores don’t have the necessary increments. The one pictured is from Starrett Tools, http://bit.ly/1iNUcFh, and is a bit more expensive than others, but has all of the 0.01mm increments in the specified range and Starrett has a great reputation for measurement tools across many industries. The valve shim tool is from Motion Pro, http://bit.ly/1fIfGD9.
It is important to follow the steps in the manual for checking the clearances or you may got false readings with the springs of adjacent valves affecting each other. It is four positions to check the eight valves. Exhaust 1 and 2 first, then Intake 1 and 2, then Exhaust 3 and 4, and finally Intake 3 and 4. The crankshaft is turned 180 degrees between each valve pair clearance check. The following picture shows Exhaust 1 and 2 ready to be checked with the cam lobe of cylinder 1 pointing forward and the cam lobe of cylinder 2 pointing up.
Another photo with the valve shim tool in place to depress the tappet and remove the shim to determine its thickness. Make sure the valve shim size faces down so that it doesn’t get worn off. This one was a 2.75mm thick shim.
Looks like the valves haven’t been adjusted for a while and are getting pretty tight. The shims shown with x mm are slightly thicker than standard, but I don’t have a micrometer to determine how much thicker. I will be reusing one of the 2.60x mm shims on Intake 2, so that should be slightly less than 0.10mm for the new clearance. Not sure what I am going to do yet on cylinder number 3 since I have not found x shims available for purchase yet. A popular source online for shims is Z1 Enterprises, http://bit.ly/RiF3jv.