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Discussion Starter · #1 ·
Hi. I recently got my 1973 Honda CL350K5 to start after sitting for 34ish years. My new problem to tackle is that when I start it, It idles at around 2000rpm which I understand to be a little high, but then it revs itself up to 5000 or 6000rpm. I ha ve tried adjusting the fuel mixture screw both directions which only makes it rev highier. I also reset the butterfly stop point and made sure the throttle cable was not stuck. Here are a few videos to help show what I mean. Thanks in advance!

https://photos.app.goo.gl/9bwmk4xsBzYyokMP8

https://photos.app.goo.gl/KpZWsskMqRKqwoxC7
 

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Discussion Starter · #3 ·
Sorry, I was half asleep when I wrote this. I should clarify what I have already done. Both carbs have been cleaned and the jets and other parts inside have been replaced. I also cleaned the gas tank and got new fuel lines. Also, I didn't have a battery for it when I tried to start it so I was using just a Stanley car jump starter. New spark plugs are installed and I think that is all I have replaced.
 

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I have similar problems on a '73 CL350 that spent the last 30 years in my brother's barn. I've got mine totally cleaned, rebuilt, etc. aside from engine noise and idle speed issues that you've mentioned. Here is my thought, but keep in mind I am still a novice at this. Normally, you need to close the choke 90 degrees to start the bike, and as it warms up and starts running faster, you return the choke to the open position. Is it possible that you are not using the choke to start, and the idle is truly set too fast?
 

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Whenever that happens on mine, it's because the throttle cable on one side didn't seat properly, sitting on an edge instead of in the cup. If the carbs aren't synced for whatever reason, my idle races. I've also read airleaks do this too, but thank god with 99 problems, an air leak hasn't been one. Yet.

Check carb sync and for airleaks.
 

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It sure sounds like you have a vacuum leak. I use starting fluid to find them. Just give little sprays around the carb and intake boot by the head and I am sure you will find them. Be sure to check at the throttle shafts at both sides of the carbs to.
TOOLS
 

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Discussion Starter · #8 ·
Ok, Sorry for the kinda late response. I tried the things you suggested to no avail. I sprayed both the carb intake boots and the idle didn't change, the only thing that brought the idle down was adjusting the idle stop screw to close the butterfly more. This brought the high idle down to about 3000-4000. But doing this made it not able to start without the throttle rolled on a bit. A friend told me that these older bikes were designed to run with lead in the gas so I need to give the engine more gas through the carbs and I should turn the screw 3 times. I'm guessing he meant the mixture screw so I'm going to try that next weekend. Any other suggestions would be appreciated. I really want to get this thing road ready! :)
 

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I hope you changed the oil before you started it

Go through this list. Replace those ancient carb boots.

Stock CB350 Tuning Checklist


Check throttle cable for smooth operation and crisp return action. Throttle should snap back vigorously to full close with just a little free play through the full swing of the handle bars.
If it doesn’t; lube and adjust all 3 cables and ensure proper routing

Engine Compression should be at least 160 PSI on both cylinders with a warm engine and the throttle completely open with the choke off. If it isn’t then no amount of carb or ignition adjustments will make it right
check and adjust valve clearance. If the valves were out of spec then redo the compression test after properly adjusted
adjust cam chain tensioner. If the engine has recently been apart you should also check to ensure that the cam chain and sprocket are properly indexed with the cam and crank. This is also a good to check if the engine has more than 20,000 miles or you have other reasons to suspect the cam chain or tensioner to be out of spec.
replace and gap the spark plugs; they are cheap
high tension leads and spark plug caps should be checked for cracking and replaced. I also will trim about 1/8” back from the high tension lead and re/install the spark plug cap to ensure a good clean connection.
spark check make sure you are getting a good spark from both plugs. If not there are lots of electrical checks that will need to be made which I won’t go into here
Battery check ; Make sure you have a good battery with a full charge and your stator/regulator/rectifier are charging at between 13.8 to 14.8 volts with the engine running at 3,500 rpms.
ignition check; time your points or your electronic ignition to spec
Exhaust system check; are there any leaks from your exhaust?
air filter check; is your air filter clean and properly installed
rubber intake grommets; with the engine warmed up and idling, spray some WD-40 all around the rubber intake grommets and listen to the engine idle…if the engine idle changes then you have an air intake leak.
fuel supply; do you have a tank full of fresh high test gas? Have you checked the petcock bowl screen for clogging? Are the fuel lines clean and unobstructed with any inline fuel filters of the proper size and clean?
after everything above is done, now you are ready to begin with the carbs;
begin by completely disassembling both carbs and I mean everything
remove top of carb and withdraw the slide and inspect for any holes or tears in the slide diaphragm. Clean any gunk from the slide so it’s operating room clean. Remove the needle and clean it in carb cleaner
remove the float bowl, float bowl gasket, 2 main jets and pilot jet, rubber passage plug, brass floats, and fuel inlet valve, inspect and replace rubber o-rings on the two main jets, fuel inlet valve, rubber passage plug and float bowl.
Remove the screws, butterfly, seals, and spindle for the choke
Remove the linkage, spring, screws and butterfly, seals and spindle for the throttle plate
With a wooden dowel gently tap out the two brass emulsion tubes from the main body of the carbs. You insert the dowel from the top of the carb where the slide goes and they will both pop out of the bottom from each of the main jet holes in the carb body.
Thoroughly clean the carb bodies and all brass parts in a carb cleaner like Berrymans, etc.
Wash and dry all jets and blow out all openings in the carb body and jets with compressed air. Visually inspect all holes to ensure they are all clean and clear of all debris. Pay special attention to the holes in the pilot jet and the emulsion tubes. If you cannot clean any of the holes then you’ll need to replace that piece. Keep in mind that brass is a soft metal, so anything you use to try to scrape out the holes will leave burs on the metal and likely change the opening size and fuel metering characteristics of the jet.
Inspect the floats to make sure they float, are not crushed, and don’t have any pin holes in them (I always hold them under water and look for bubbles)
Install the throttle and choke butterflies with a light coating of grease on the spindle. Be sure to look at the taper on the upper and lower edges of the butterfly plate to ensure you don’t install them backwards.
Install the two long brass emulsion tubes. Be sure to install the secondary one (smaller with a slotted end on it) with the screwdriver slot aligned with the small crossover hole from the primary tube so as not to restrict the crossover tube with the crown of the screwdriver slot.
Install the fuel inlet valve with new o-ring (lightly coat the o-ring in grease) and float. Float height should be set to 26mm on the 350k4s.
Install the pilot jet and two main jets with new o-rings (lightly coat the o-rings in grease), install he rubber passage plug
Install the new bowl gasket and spring jet holder.
Install the needle and clip into the slide then the slide into the carb.
Install the pilot air mixture screw with new oring and do not overtighten…set both to 1.25 turn out
Adjust carb throttle cables with the carb mounted to the bike
Set both of the idle screws so that they just barely contact their stops without opening the throttle butterfly
Adjust cables so that the throttle butterflies begin opening at exactly the same time (you can hear it when you open and close the throttles…it sounds like one click instead of two when they are in synch)
Make sure there is proper throttle cable play at the throttle on the handlebar with no binding
Warm up the engine to full operating temperature
Adjust the idle screws (not the air mixture screws) in equal turns for both carbs till the engine idles properly.
Set the idle air mixture screws per the manual
 

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If, after you check all the stuff Doode mentioned, it still does it... check the ignition advance unit to see that the springs are tight and return the weights fully. Engines with older advance units that are sloppy in function sometimes like to stay advanced once the revs go up and it can make it come back to idle slowly
 

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Discussion Starter · #11 ·
Sorry, it has been a while again. What ended up solving my issue was getting a battery for the bike. I was using my jumpstarter for my car to just see if the bike would even turn over. Once I put the new battery in, it runs and idles perfectly! I also turned the idle mixture screws out 3 turns. That also seemed to help.
 
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