'78 Honda Express NC50 carb swap info needed By rapidrob (Read 1,879 times)

[rapidrob]

There are many options posted on the web. With the Troll replies it is a challenge to find the truth about them and which ones work well.
I'd like to keep the original throttle and choke cables if possible.  I know some sort of intake adapter will be needed as well.
I live at 7,000 feet ASL and would need the correct jet size.
Any helpful info would be appreciated.
Thanks.

[rapidrob]

I was looking at this carb Dellorto SHA 15.15 carburetor. It comes with a lever choke or a cable choke.
Have you tried this carb and what choke did you use and why?
Thanks.

[greginisn]

Rob,

Maybe this will help

scootdawg.proboards.com/thread/51675/high-altitude-gy6-advice-colorado

I'm at 2000' so no jetting advise for you.

Greg

[rapidrob]

I'm told the carb comes with a 68 jet. A guy on Youtube did a vid on his Express and he had put in a 62 which was still too rich at 5,000 feet ASL. I ordered a 58 jet for my 7,500 feet ASL home.
I'm not sure if running too lean is a major problem or not. My automatic oil injector is not adjustable but my pyrometer and spark plug can tell me if the engine is running too hot.
If it turns out that the engine is not getting enough oil I can always augment with a pre-mix as well.

[rapidrob]

I installed the new Dellerto SHA 15.15 today. I have three jets. a 58,61 and the 68 it came with. I made a cork gasket for the carb adapter plate and also used an "O" ring to make sure I have no vacuum leaks at the carb throat.

I test drove the bike and found I have a reoccurring problem.

The engine 4-strokes at high RPM.

The 58 jet allowed me to go 25 mph and then 4-stroked until I went uphill a little. Very slow acceleration.

The 61 jet allowed me to go 20 MPH and then 4-stroked. Pretty good acceleration.

The 68 jet 4-stroked at 18 MPH and stayed that way until I went below 15 MPH for a good distance. Very good acceleration.

I'm told 4-stroking is too much fuel? Or is it too much air? I'm at 7,000 feet.

Could the crank shaft seals be causing this?

The new carb idles very well and adjust as you'd expect it to.

My bike has:

530 original miles on it. It sat for 25 years. Fuel system was flushed out and is like new inside of the tank. New external fuel filter and it flows very well.

Original muffler

Original piston and rings

New spark plug

Timing is a little advanced by using a timing light at the "T"

Oilier is working as it should

Gas is regular and fresh,no alcohol.

Any ideas?

[rapidrob]

I ran the bike today to get the mail. Using the 58 jet I was able to go 25 mph with no 4-stroking. A lot of goo blew out of the muffler and onto the rear tire. The muffler has not been cut and modified. The bike is at its max mph now due to my body weight and the engine still at 49 cc's.
I may have to do the 60 or 70 cc upgrade to climb hills here.

[rapidrob]

Here is an update as of today.
Thinking about what has been said about the muffler being too restrictive got me thinking. If I ran the engine lean,keeping the oil rich enough to prevent seizing,could I clean out the deposits that are in the muffler?
I did just that today. Using the #58 jet and restricting the fuel to the carb I was able to run the engine leaner than normal. I checked the head temperature under full load using a pyrometer and made sure the cylinder never went hotter than 360F,and it didn't.
I drove the bike for several miles and sure enough all sorts of crap blew out all over the rear tire rim. The harder I drove the bike,the better the engine started to run. No more 4-stroking,not even a hint.
I returned home and set the fuel back to normal flow,checked the spark plug and topped off the gas tank and oil.
I drove the bike for about hour at full throttle which was just over 25 mph. The bike pulled as well as the engine could for its size and my weight and my location elevation.
The new carb really makes a difference and If I do the larger bore conversion I'm sure the bike will run well.

[cyborg]

Great!!!!