Wit's End

[SomeOldGuy]

I'm real close to yanking the motor and using it for target practice.
Got fuel flow, got good spark, got good fuel venting, lapped the head, got new studs and hardware, got good gas at 20:1, I'm confident that there's no vacuum leaks, I adjusted the float level, I checked all the passages in the carb, I soldered and sealed all the electrics, I checked the kill switch with a meter. NGK plug gapped to .024,new plug boot. Good rings. Muffler's clear.
It starts hard, runs for a minute and then dies. the best result I had was putting the carb needle all the way up (rich). It seems that it's just starving itself dead, or something happens when it warms up.
Any suggestions?

 

[Kioshk]

Engine? Carb?

 

[SomeOldGuy]

NT carb. 66/80 motor of some undifferentiated chinese manufacture

 

[Kioshk]

Basics first: what, if anything are you doing with your choke?

 

[SomeOldGuy]

nothing--keeping it open

I had motorcycles since the '60s....I have a little insight with these things

 

[SomeOldGuy]

I should add- I'm at 7000' elevation.....the air cleaner may be restricting too much air up here

 

[Kioshk]

LOL, yes; I had just Googled your location...you're WAY up there!

http://motorbicycling.com/archive/index.php/t-39451.html

Check out that thread.
"It was mentioned above, "where you live" but to expound on that, your altitude above sea level plays a part in proper tuning (jet selection). The higher you are the smaller the main jet needs to be and conversely, lower altitudes will benefit from a fatter mix. At 6000' I solder up the stock NT jet and drill them to .024. It seems to be just the right blend of fuel to air for my altitude. Experimentation will get you where you need to be for best performance."

 

[SomeOldGuy]

Ok-- I have a 1955 H-D KH that I take down to the California desert in the winter. The elevation there is effectively 0 and in some places below sea level. I richen the idle and high speed needles down there and lean them out when I'm up here....a couple of clicks, no biggie.
The center needle adjustment in the NT should take care of most of that. In any case, it should start and keep running, maybe not well, but at least continue to run for more than a minute or so.
I'm wondering if the float is too low. I used the 21mm number to adjust the level. The valve looks good, I didn't see anything that would cause it not to work.
When it runs, it sounds OK. I'd just like to have it run long enough to get everything adjusted.

 

[2door]

There isn't much to "adjust" except the idle speed screw if you have an NT carburetor.
The clip position on the needle valve only controls fuel flow at or below 3/4 throttle. Above that the main jet determines the fuel to air mix.

Check your fuel tank cap for proper venting. Some don't vent well, or at all and fuel starvation results. If the engine starts but doesn't continue to run I'd take a good look at fuel delivery.
Did you clean the fuel tank before installation? Are you using a fuel filter? Have you confirmed fuel flow from the tank to the carb?

As was suggested you'll need to use a smaller main jet than comes in the stock NT carburetor. At your altitude go down to at least .025 but that isn't what is keeping the engine from running. Check all of your wiring connections to make sure nothing is grounding against the frame.
Just a thought, are you disengaging the clutch after the engine starts to allow it to warm for a few seconds? How slow are you trying to ride it with the clutch engaged?

Let us know what you find or if our suggestions don't help.

Tom

 

[SomeOldGuy]

Getting good fuel flow. Drilled hole in cap.Screen's clean, bowl's filling up. Wiring's good and insulated.
If it just didn't fire, that's one thing, but understand that I can get it started but it won't run for more than a minute or so. The throttle works like it should.
The fuel/oil mix is 20:1- is that about right?
Plug gap is .024.
The float is adjusted at 21mm.
The carb is level.
I'm going to try running it with the air cleaner screen removed and see if that has any effect.

 

[crassius]

if it revs up a bit just before it quits, then something may be causing your bowl to stop filling when it's running

could also be something weird like the choke plate stuck closed no matter where the lever is put

 

[SomeOldGuy]

Nope--it just bogs and dies. Choke plate is clear.
I'm replacing the fuel and the fuel line. I took the fuel valve apart and checked it for operation.....it's a pretty pathetic excuse for a valve, but it works. I'll clear anything left in the crankcase before I refuel it. The tank's clean and so is the screen.

 

[Kioshk]

I've lighted a candle for you.

 

[nightcruiser]

My first inclination would be to say it sounds like it runs until the bowl empties, pointing toward lack of proper fuel flow.... but it seems you've been up and down that road already....

What about a bum CDI? Perhaps it's failing once it is warmed up? I would also suggest you just disconnect the kill switch, maybe it measures ok with your multimeter but closes after the motor vibrates it for a while?

As I assume you already know, running without the air filter should lean out your mix. If you are running way rich due to the NT jet being a bit large to start with and also your elevation then running without the air filter (briefly) should net some improvement in that condition.

I feel for you with this situation, not sure if you are starting the motor and trying to adjust while she is dying or riding? If you have been focused on adjusting things I would suggest you just get on and ride and see if you can get past the dead zone with some momentum...

 

[SomeOldGuy]

Thanks. That was my first thought about the bowl emptying---but I would think it would lean out and the RPMs would spike if that would happen.
I spun the crank with an electric drill and checked the spark---looked very good.
I'll disconnect the kill wire and see if that has an effect.
But I'm thinking is fuel delivery...... I got a new fuel line, but I'm still stuck with that bogus valve (a penalty of living in the rural High Sierra's)
If I ever get that thing sorted out, I'm going to paint ' Mao's Revenge ' on the tank!

 

[nightcruiser]

Yah, the fuel valve is bogus... I got an upgrade valve from SickBikeParts.com that I really like. This valve doesn't have a filter in it, so you must run an inline filter (which is the best idea anyway). In fact, I would recommend you remove the filter from the kit fuel valve (that goes up into the tank) and run just an inline filter, specially if you suspect fuel flow may be your issue...

 

[SomeOldGuy]

Fresh gas 24:1, good fuel flow, no air filter......still the same. It WANTS to start. I think I'll check recheck the timing situation.....I might hone the cylinder as a last ditch effort. I'm wondering now if the rings never had a chance to seat properly. I didn't think to check if the cylinder had been honed from the factory.

 

[SomeOldGuy]

OK- that's it....still no-go. I figure I must have a bad motor. We'll see how it stands up to some .308 FMJ at 50 yards.
Any good sources for a quality 66/80 powerplant?

 

[nightcruiser]

Maybe pull the head off and inspect the rings, see if they are both there and in 1 piece, try a different spark plug, perhaps swap the CDI... Check the position of the magnet, make sure the woodruff key is in there, make sure it is not installed upside down. (slot on magnet should be at about 1 o'clock when at TDC)

 

[SomeOldGuy]

did all of that--several times. I've been putting motors together since LBJ was president----this motor/kit is low grade trash. 3 orders for extra parts,a dozen trips to the hardware store and the auto parts store, way too much time spent with no improvements.
An experience of diminshing returns.