|Posted on Monday, August 24, 2020 - 09:20 am: ||
Working on a project for a buddy's son - 1973 Honda 350 4-cylinder. This will be my first foray into the world of quad carburetors - anyone have any tips? Bike was running 3 years ago when parked, so I'm guessing carb cleaning and the usual tuneup stuff...but I'm concerned about "syncing" the carbs afterwards?
Anyone whe's been down this rabbit hole before, please chime in And, if anyone wants to buy a bike...that's the plan for after it's running again.
|Posted on Monday, August 24, 2020 - 09:51 am: ||
As an Internet acquaintance of mine says: carburetor is a French word that means ďleave it alone.Ē
From my experience, Honda carbs rarely need rebuilding. I have a 1983 Honda VT500FT Ascot and Iíve let it sit up for long periods. Sometimes itíll run rough after a long storage period, but it always clears up within a few miles of riding. The only time Iíve had to rebuild the carbs was when the float bowl gaskets deteriorated to the point that they constantly leaked.
Iíd put fresh, non-ethanol gas in it with a healthy dose of your preferred fuel system cleaner (Seafoam, Techron, etc.) and see if itíll run. If it will run, run a whole tank of gas through it and odds are good youíll be good to go. Thatíll save you a whole lot of grief.
DO NOT spray carb cleaner down the throats of the carburetors because it can get on the diaphragms that actuate the slides. They will deteriorate and soon tear and then youíll have to replace those.
|Posted on Monday, August 24, 2020 - 10:11 am: ||
What Hugh said.
I bought a Honda CB-360 from a boneyard, back in the 80s. The owner told me that he would get bikes in that wouldn't run for shit. He'd drain all the old gas and put in a gallon of premium and half a bottle of Gumout. He'd get the bike to start and would screw the idle screw in until the bike would idle. Then he'd leave the bike running and go on to another project. After about 10 or 15 minutes, the idle would soar to about 5,000 RPM. He'd then readjust the idle screw and the bike would run fine.
The bike I bought was one of those, and it would pull redline just fine and it ran well. A friend of mine rode it for almost 100 miles on the Interstate at maximum throttle (he was trying to kill it - he hated that bike) and the bike handled the abuse flawlessly.
I have another Gumout story, as well, but I think that if you try it, the worst thing that will happen will be that you'll be out less than 10 bucks.
|Posted on Monday, August 24, 2020 - 10:31 am: ||
Joe I had several IL4 Suzukis.
If the carbs are Vacuum, sinking may not be a problem, if not don't move any of the actuating shaft fasteners or hardware
I presume that the carbs are mounted to some sort of "bar" if so consider removal as a unit. It would be tough but easier to work with. ( assuming the rubber spigots are in good shape )
If sinking is a standard procedure I expect that you would find connections for the Vacuum gages / manometer on each inlet spigot on the head ( my GS had tapped holes in the inlets. )
Suzuki had the two inner cylinders at slightly less vacuum than the outer ones
about 1" of vacuum and unless its grossly off its not a huge thing.
I would avoid gumout spray and try the gas and cleaner first a lot of carbs from that time had various plastic bits in them.
Then bowl disassembly may be doable in place (possibly) BTW 350?
I know they had a 400 - four ( I lusted for one when I was young )
|Posted on Monday, August 24, 2020 - 10:31 am: ||
Multi carbs are always a pain but definitely doable. The most common problem after sitting is a clogged slow speed jet. As the others mentioned, fresh gas and a cleaner may do the job. Revving it and covering the intake sometimes will clear a clogged jet. With my luck I have to take the carbs off and clean out the float bowl and pull the jets and clean them. Make sure they are nice and round holes. Running lean on one cylinder will lead to major trouble. Syncing is best performed with a carb stick. Mercury filled tubes with rubber hoses. Dialing them in this way will make it run the best. I've done many over the years including Yamaha inline 4's and even a V-max. I even put ports in the intake of our 4 banger race motor to dial in the dual side draft Webers. You can also use the carb stick to set your idle mixture screws. In fact I go back and forth between syncing and idle mixture till all is correct. It's tedious but worth it. I'm hoping a simple cleaning will make it work.
|Posted on Monday, August 24, 2020 - 11:26 am: ||
I recently finished a refresh of my father in-law's 73 CB 500 K. I thought it would be nice to get it running for him before he is too old to ride it again, and I knew he would never do it himself.
The bike ad been sitting since 1992 with fuel (or what was left of it) in the bike. The inside of the tank looked like it had been foamed to prevent sloshing, and ALL of the screws on the carbs were so gummed they would not turn. Before I committed any serious money to the project, I wanted to confirm it at least ran with no major clunks or grinding. By luck I found a "better" condition set of carbs on CL for all of 25 bucks, and between the two sets was able to get one good set together. After I got it running, I asked a SAE powersports mechanic buddy (and owner of a nice 72 CB 350 four) to come over and sync the carbs. He did a quick compression check beforehand. They weren't horrible numbers, but not as consistent as they should be. He suggested I pop the jugs off and inspect the rings telling me "they may only be stuck".
A few weeks later when I finally got around to it I found the rings to be just fine, but a bit worn after 30,000 miles. I told my friend, and "I know" was his answer. I asked him if he knew, why didn't he tell me. His reply was classic. "If I told you it needed rings would you have done them?" he asked. "Probably not" was my answer. " Well, you already bought the gasket set to inspect them, the rings are only another 50 bucks, and your already in there, and the bike has no value in pieces, so keep going."
|Posted on Monday, August 24, 2020 - 12:27 pm: ||
You will need manifold adapters and a set of vacuum gauges to sync the carbs... if that is even needed.
Make sure compression and/or cylinder leakdown test is less than 10% between cylinders before even thinking about carb sync.
(Message edited by teeps on August 24, 2020)
|Posted on Monday, August 24, 2020 - 01:15 pm: ||
My only advise is to be careful not to suck the fluid out of the manometer. Itís easy to do.