Hi all,
On my trusty CT1C, fuel just trickles into the carb. When I take the hose off, it pours out like it should.
When it running fuel just trickles down. I feel like it is starving for gas when I am riding with the throttle at mid in 4-5th. It will miss a little.
The petcock is a common side spout type. I am thinking about going to a vertical spout type like a YZ . I like the reserve though.
It is not clogged and flows great with the hose off...Cap does not seem to be an problem.

Float needle stuck closed?

Let me guess...  you have a clear fuel line?

 

  Seems that it’s just a small trickle coming into the float bowl area but never measured it.
 Opening the petcock with a hose connected to a can produces a pretty good stream.
 I could measure the flow on the CT here and report back.
 60 MPH at say 30 mile per gallon you’d need to flow what a gallon of gas in a half hour ? 
 
 

Thanks for the replies. Yes the hose is clear. I swapped out the filter for a straight piece of clear hose. No change. I don't think the float is stuck(?) it starts easy and runs great(?) Would it perform normally as long as it gets just enough? Good thought.

There is plenty of gas in the tank. With bike just sitting the fuel line will not fill up hardly at all. Running it starts to flow a little like it is being sucked out sightly. On my other bikes, I open the petcock and the fuel lines instantly fill up. On my Suzuki SP370 with a big Don Vesco 3 gallon tank I had a similar problem. I went to a YZ style petcock and that solved the problem.
I have the same side spout my MX360 that has a big tank on it but it flows very well.
Don't know what's going on but I like to see the fuel line full. I am going to try a YZ style petcock. They are about $10 and work well. No reserve though..
If that does not change things then I will look at the carb...again.
Thanks!
 

There's a reason they didn't use clear line.  If it's flowing fine with hose removed, you DO NOT have an issue with the petcock or tank vent.

The hose not filling up is extremely misleading.  It does not mean enough fuel isn't flowing. Fix is install a solid hose you can't see through. 

If you actually have a fuel flow issue, it could be the float needle and seat (they come in different sizes and sometimes are replaced with the wrong one). Float drop could be restricted. Or the vent hoses on the carb could be restricted or plugged. 

Easy test (that needs to be done outside away from any ignition source!) is to remove the carb and place it over a container with the main jet holder removed.  You will probably need a longer fuel line to connect to petcock.  Carb should be held fairly level like it is on the bike. 

The Yamaha performance chart show the BSFC is about 300 grams/HP/hour at max power around 7000 rpm...  that's about 10.5 lbs of fuel per hour.  Gas weighs about 6 pounds per gallon.  And you want a "safety factor".  So lets say with petcock on 2 gallons per hour should flow through carb which would be more than enough to deliver enough fuel for full throttle at redline. 

An hour is a long time.  So doing the math a quart of fuel should drain out of the main jet holder into your bucket in 7 minutes and 30 seconds or less.  That's with a generous safety factor.  Even if it took 10 minutes you'd likely be ok and that would be for sustained full throttle at max power!

 I removed the main jet holder out of the 1973 CT 175 carburetor and rigged up a steel trough to direct gas into measuring cup. Had to lean bike slightly to the left to get into container 
  Approximately one cup in one minute , at that rate 3.75 gallons an hour 
​​​​​​  But wait there’s more….
 75 Yamaha RS1 100 cc that is ugly / runs awesome .
  Tested that - such a tiny trickle into the cup lost interest
in measuring it.
 1974 DT 360- one cup per minute 
​​​​​​

DaveHunter,  I got fooled by a clear fuel line probably 20 years ago now.  I don't use it anymore.  It was a later model 175 with the plug in the bottom of the float bowl so I had to take off the carb for the test.  Good thinking on the metal trough for the CT carb!

Your results are similar to what I remember...  way more than enough fuel was actually flowing even though the clear line had a huge air bubble and made it look like it was only flowing a trickle. 

It is possible to have a flow issue though.  I've seen the vent hoses pinched or plugged.  And once someone had installed a float valve with the tiniest hole I'd ever seen.  I don't know if it was defective or just poor quality aftermarket?  It wasn't genuine Mikuni.  Installed a genuine Mikuni...  IIRC the original size was 2.0 or 2.5...  and it was fine. 

 

FWIW When I restored by 1971 RT1-B 360 and started riding the engine would starve for fuel in a mile or so. The original gasket was rock hard so I had made a new one out of Viton which sealed the gas cap and the tank.
Unscrew the gas cap and it would run fine.

Eventually took the gas cap apart by prying around and around the outer edge very gently.

The inside of the cap was full of varnish and wasn't letting any air into the tank.

23 lbs/hour
38 horsepower

fugettaboutit

cliff