Motorcycle Forum banner
1 - 16 of 16 Posts

·
Registered
Joined
·
11 Posts
Discussion Starter · #1 ·
My 69 Honda S90 starts fine and seems to run great, however, sometimes when I turn it off or come to a stop, gas is seen leaking out of the overflow tube onto the ground and then the bike won't start again unless I let it sit for about 30 minutes. Is this most likely a carburetor float or float valve issue, or something else? Thanks
 

·
Premium Member
Joined
·
6,080 Posts
Well, since the float and float valve are supposed to prevent that very thing, yes, it is a float level problem. It could be as simple as needing a level adjustment. Worse, it could be the valve needle is worn to the point it doesn't seal well, or a pinhole in the float allowing fuel into it. The valve needle has a polished conical tip, that fits into a matching seat, and a ring wears into it, causing it to bind or just not seat well.
 

·
Premium Member
Joined
·
6,080 Posts
If you don't have one, try to find a service manual, so you can set the level correctly - it will run a lot better.
 
  • Like
Reactions: -Nate

·
Registered
Joined
·
11 Posts
Discussion Starter · #5 ·
I have the original shop manual that came with the bike. It says 16.5 mm as float tang just touches the float needle. Not sure exactly what to use to measure that, but I will think of something - maybe some calipers.
 

·
Premium Member
Joined
·
6,080 Posts
The manual may or may not give the complete procedure. Holding the carb body so the float just rests against the needle - bowl seat vertical - use the float to gently press the needle against the seat, then lift the float away from the needle and then let it rest against the needle. Also, 16.5mm is a hair over 41.5/64, or 0.649606", in case you only have an SAE scale. That's way more precision than you need, though - usually Honda carbs are spec'd to the nearest mm, so +/- .5mm (.02").
 
  • Like
Reactions: -Nate

·
Registered
Joined
·
11 Posts
Discussion Starter · #7 ·
Thanks Rick, that helps. And yes, the manual leaves a bit to be desired. I was hoping it would describe in some detail how to actually remove the carburetor, but instead, it simply says, "remove the carburetor".
 

·
Premium Member
Joined
·
6,080 Posts
Is that a Honda manual, or some after-market one? Either way, some of the Honda manuals assumed their mechanics remembered their training.
 
  • Like
Reactions: -Nate

·
Registered
Joined
·
11 Posts
Discussion Starter · #9 ·
The bike came with the original Honda shop manual, but lacking any detail on how to remove the carb, I also purchased a Clymer Honda Service Repair Handbook hoping it would be better - it offered no more than the Honda shop manual. So yes, I guess they assume removing a carb can be done in one's sleep for a decent mechanic, which I am not. I purchased this bike - the first motorcycle I ever owned back in 1967 - and then spent 54 years not being on one until I got a wild hair and bought this one last year, so I'm basically starting all over. Got my motorcycle license and riding equipment, and only plan to ride it around my neighborhood and maybe some country roads around my small town.
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #10 ·
I did get this information in the vintage section of the forum:

"As far as removing the carburetor, just turn off the petcock and then just remove the two air cleaner mounting bolts, this should give you enough room moving the assembly back to get the carburetor off of the filter. Remove the intake tube from the head instead of the carburetor first also. Tilt carburetor and then unscrew the cap and pull the throttle slide out next. No need to remove the tank or crossover tube."

and will follow it for lack of any other instructions. I'm more of a visual learner and that's why I was hoping the manual would explain the process with pics, or I could find a YouTube video. Anyway, a guy down the street who has 50+ years of car/motorcycle maintenance/repair history is going to help me, so I should be good.
 

·
Premium Member
Joined
·
6,080 Posts
So, where abouts is 'down the road'? Anywhere near me? I used to own and work on one of these about 50 years ago, and still remember how the parts attach, and could also lend a hand.
 
  • Like
Reactions: -Nate

·
Premium Member
Joined
·
6,080 Posts
Looks like it was kept in a vacuum-sealed jar all these years!
I used to take mine off road, and found the CT90 handlebar and rider's pegs held up a lot better against the branches and small stumps hidden in long grass. The bar had a cross brace, and the pegs flipped up on springs; discovered this after replacing both a few times, and the shop didn't have them in stock, so recommended the CT version. Never needed another set.
 
  • Like
Reactions: -Nate

·
Registered
Honda Tiderls, Ural Solos & BMW R60/6
Joined
·
893 Posts
Nice bike ! .

90 % of the time there's a tiny bit of rust from the inside of the fuel tank or in the gasoline, it can be nearly invisible yet cause this flooding whilst still allowing the bike to run .

Thr fuel tap has a -delicate- fuel debris collection bowl on the bottom of it, use only
a 6 pointed box end wrench or socket to remove it as it's made of very soft pot metal .

Expect o see some dirt or rust n there, clean it out well and add a paper element fuel filter, easy to find in the lawn mower section of your local F.L.A.P.S. .

These are very find bikes indeed, ride well and have fun, don't forget to
hot change the oil every 1,000 miles .
 
1 - 16 of 16 Posts
Top