Modder here!This fourm!This going to help my build alot

Well, I checked. Float is working fine. Cuts off fuel as it should. No adjustment, of course, on this carb. But it's working.

Same results: Engine will run for a while while it's cold with the choke bypassed. Then just floods like a Niagara. Using the NT carb to get the engine hot then quickly swapping out gets me a little better result, presumably because I'm getting better combustion with a hot engine and a dry plug. Then, the spark plug looks like it's taken a swim regardless of which main jet I use, and again, at WOT with the smaller jets, it almost works.

Naturally, I'm not ruling out operator error. It's possible I broke something. It's also possible I just got a POS. Can't get the thing to work for love or money.

Speaking of the which, I've already wasted my money. Now, I am wasting no more time. Seriously, I am done with this carb.

Thanks, Jag, for your efforts. If, for scientific purposes, you are still curious, I'll even ship this carb to you at my expense, naturally, and you can check it out. Fixing it is beyond my current skills and admittedly limited patience.
 
My last ideas: restrictive air filter or pinhole in float permitting gas to enter it
 
jaguar said:
My last ideas: restrictive air filter or pinhole in float permitting gas to enter it
Click to expand...

This morning, I ran it without an air filter to rule that out. I also checked the float for a leak. No gas in it, all sealed.

Sometimes things are just weird. Time to move on! (I was serious about my offer to send you the carb.)
 
Time to get out your credit card and purchase the Rock Solid Engines reed valve intake and the Rock Solid Engines reed valve compatible Walbro style (diaphragm) carburettor.

No more air leaks, no more fuel leaks, no more mysterious carburation issues and no more spilling fuel everywhere, each time you pull the fuel bowl off to change the main jet.
The only thing you get is a reed valve intake which boosts low and midrange torque and reduces intake noise as well as a carburettor which works reliably and has easy external adjustment screws to adjust jetting if required.
 
Sounds like a voodoo carb since it has an unsolvable problem.
throw it away as far as you can. I don't want to waste my time on it.
What is your next step?
 
Could it be that the float needle is not sealing 100% and you let the bike sit with the fuel petcock on and the crankcase partially filled with gas?
 
jaguar said:
Could it be that the float needle is not sealing 100% and you let the bike sit with the fuel petcock on and the crankcase partially filled with gas?
Click to expand...

I see we are alike in that we do not like mysterious failures.

It's extremely rare that I let the bike sit with the petcock on. When I do, I notice it when I fire her up. I learned that lesson with my old Honda 350 way back before I could legally drink. This has not happened since the first couple of days. In this case, I had the carb off and bone dry while working on it.

Applying Ockham's razor, when you've sliced away at every possibility, whatever is left has to be the answer. Somehow, extra fuel is getting in when the engine is pulling air through the carb. In one of my tests, I even blew into the fuel line inlet while testing the plunger (if that's what you call it.). It seals so well that I couldn't get air through it. That also rules out an internal, invisible crack in that part.

But I am suspecting a casting defect or a crack somewhere. Somewhere I can't see, and I have looked!

The plus side here is that I got to know both carbs intimately. I'm not gonna write off this type of carb without another one to compare it to, but for now, c'est la vie.

And Fabian? I think my credit card, for the moment, is best used on things that make me money, as tempting as the setup you describe sounds.

Cheers,
Rick
 
Too bad there isn't a "good" carb available for less than $70. Going the reed valve and expansion chamber route is the last step to perfection but out of many peoples budget. I recommend the Mikuni 18mm, offset intake extension sold by JNMotors (with rubber hose added to make it longer), and making the header longer by 6". Most people would be thoroughly happy with that.
Here is what I would do if I were stuck with the crappy NT carb. (3 steps in correct order):
Rejet the main according to top speed.
Set the needle height according to best mid range power and acceleration.
Change the needle tip thickness according to what it needs at idle; make it thicker with solder if it needs to be leaner or make it leaner by using my rotary tool on it.
That is what I did actually to mine to get me by till I got the Dellorto in my hands.
 
jaguar said:
Here is what I would do if I were stuck with the crappy NT carb. (3 steps in correct order):
Rejet the main according to top speed.
Set the needle height according to best mid range power and acceleration.
Change the needle tip thickness according to what it needs at idle; make it thicker with solder if it needs to be leaner or make it leaner by using my rotary tool on it.
That is what I did actually to mine to get me by till I got the Dellorto in my hands.
Click to expand...

This is good advice. Besides my own sense of how engines sound and run with regard to the mix, I have been going by spark plug color--doing a "plug chop"; that is, starting with a clean plug and running the engine at below 3/4 throttle to test the needle's position and then running it fast to test the main jet. That got me pretty well dialed in. I have a nice, coffee-with-a-little-cream-colored, tan plug.

I notice you make no mention of plug color.

But I will revisit this again. You've gone out of your way, Jaguar, to debug this. I appreciate it.

Cheers,
Rick
 
Plug color is dependent on what type oil is used and at what ratio. The only guideline I go by is how it runs which is the whole point of it all anyway. If its very white or really black then that says its too lean or too rich but not in a way that can help you distinguish between a 60 and a 62 main.
 
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