Starfire GT50 engine fires up but stalls prematurely

[srdavo]

To me, it doesn't sound like you are getting any fuel to the cylinder.

The fact that nothing seems to come out at all when I crank it with no plug in indicate to me that its the carby, however the **** thing is screwed on with the screws upside down for absolutely no reason, making them inaccessible except with a right angle screwdriver thing.

Try this.... loosen the clamp holding the carb to the manifold. this will allow you to rotate or remove the carb & get at those pesky screws, holding the fuel bowl in place. Use caution, because the fuel bowl may have fuel in it. Put a small bowl or a rag underneath the carb, to catch the drippings.

have a look at this thread for some pics of what to expect when you disassemble the carb: http://www.motoredbikes.com/showthread.php?t=24867

Let us know what you find.

good luck

 

[AussieSteve]

im having a lot of trouble testing them however as its **** impossible to crank the wheel and hold a spark plug.. Or ride and hold a spark plug attached to a tiny cable.

Do you have a stand on the bike? What I do is remove the plug, fit it back into the cap and lay the plug on the head with it's metal body touching the head.
Then give the rear wheel a spin. You should see a spark at the plug.
If you don't have a stand, get a helper.

The fact that nothing seems to come out at all when I crank it with no plug in indicate to me that its the carby, however the **** thing is screwed on with the screws upside down for absolutely no reason, making them inaccessible except with a right angle screwdriver thing. So incredibly dumb. Good old chinese engineers.
There might be some vapour comming out though, its hard to tell without literally sticking a nostril to the plug hole.. which seems like a bad idea.

Forget the sniffing. If there's fuel in the float bowl there will be fuel in the mix. Unless your nose is good enough to measure fuel/air mixture, you're wasting your time.
If you slightly undo the drain screw, fuel will flow if there's some in the float bowl.
Those screws - best to remove the carb as Dave says. You can't get at anything properly with the carb still fitted.

Also unsure as to which way the little white thing is supposed to face (up or sideways) so ive had to try everything twice..... Nothing mentioned in the manual about this at all.

What little white thing?

... Steve

 

[Hajuu]

the carb fuel valve.. one way is on, the other is off. Or, that's how the dealer explained it to me, its not mentioned in the manual at all, but the manual seems to also be for the 66cc/80cc that actually uses a different carb.

And the sniffing was purely just to detect if there was *any* fuel. Which there doesn't *seem* to be, as I indicated, but I dont know how rich it's supposed to be.

Anyway i'll try and check the carb and report back in 30 minutes to an hour. It seems to me like it could well be any part of the carb being blocked, so fuel in the bowl doesn't necessarily mean anything? Could be wrong.

 

[AussieSteve]

It seems to me like it could well be any part of the carb being blocked, so fuel in the bowl doesn't necessarily mean anything? Could be wrong.

If the main jet is blocked, there will be no fuel.
I sort of assumed that with a problem like this the carb would already have been cleaned. I'm amazed that you didn't after the sediment problem.
Blow into the tap to see which way is which.

... Steve

 

[srdavo]

It seems to me like it could well be any part of the carb being blocked, so fuel in the bowl doesn't necessarily mean anything? Could be wrong

you mentioned sediment in the fuel line.... so your jet could have some junk in it...... but I bet your needle valve isn't allowing enough fuel in the bowl.

 

[AussieSteve]

In my experience, any junk that gets into the float needle valve tends to make the valve stick open, causing flooding, rather than the opposite. It's rare for it to block and if it was completely blocked, undoing the bowl drain screw would show no fuel.
If it was partially blocked causing a slow flow, the engine would start then starve for fuel after a short time.

Beside the point anyway. What's needed is a good carb clean with compressed air - all orifices.

... Steve

 

[Hajuu]

The fuel drain screw is even more inaccessable heh..

however, What I did was clean the entire system and just let the fuel run through it today in the hot weather.. Figured it would act like soaking dishes in the sink for a few hours. And sure enough today after a few very speedy takeoffs, I managed to get it started, slowly at first, but it was just what it needed.

Now it's back to full power

Thanks so much for your advice and for just letting me brainstorm, its still not complete, but its running, which is a good start

Man when I feel that rumble, I know all the time was worth it.

 

[Hajuu]

(Part 2) Engine running but not that well. (See for details)

Hey guys,

So continuing from my last thread, i've gotten the 'clogged' carb (or whatever it was) fixed, but am still having some quite large performance issues.

For 1, and probably the most concerning at this point, when I let the clutch out to engage the engine at a relatively low speed, I have a kind of.. shudder? Only thing I could think of with this was maybe because of different chain tensions or something? Anyway, with even a tiny bit of accellerator it completely stops.

However, this brings me to point 2. I basically have a complete lack of power in the low range unless I am peddling, which isn't really a problem, but I swear even the first time I had it running it had much more low end pickup. At higher speeds this isn't really noticable (within the midrange) however at the high end I also noticed that there is a stark drop in acceleration.

The engine has currently done less than 7Km in total, could this be nearly entirely due to the enriched fuel and the break in?

Also, as a general question, how hot is too hot? Like, after a short run even, the engine is feeling very **** hot, probably normal though.

Cheers guys.

 

[srdavo]

For 1, and probably the most concerning at this point, when I let the clutch out to engage the engine at a relatively low speed, I have a kind of.. shudder? Only thing I could think of with this was maybe because of different chain tensions or something? Anyway, with even a tiny bit of accellerator it completely stops.

This "shudder" you get..... is it kinda like when you try to take off in a manual transmissioned car, in 2nd gear??
My guess is, you are using a 44 toothed rear sprocket. This will require more pedal assist to take off from a stop. You are basically taking off in 2nd or 3rd gear.
I use 48 or 50 tooth sprockets = smoother take offs & slow "putt-putt" riding, when needed.

However, this brings me to point 2. I basically have a complete lack of power in the low range unless I am peddling, which isn't really a problem, but I swear even the first time I had it running it had much more low end pickup. At higher speeds this isn't really noticable (within the midrange) however at the high end I also noticed that there is a stark drop in acceleration.

The engine has currently done less than 7Km in total, could this be nearly entirely due to the enriched fuel and the break in?

Your engine will start running smoother & better after you run a few tanks of fuel through it.
While breaking in, (IMO) be gentle,,,, throttle it hard some....just not too hard.
The engine will tell you what it likes.

Oh... keep your fuel rich, while breaking in.

Also, as a general question, how hot is too hot? Like, after a short run even, the engine is feeling very **** hot, probably normal though.

Here's an old thread (fun) about engine temps:
http://www.motoredbikes.com/showthread.php?t=4775

 

[AussieSteve]

The fuel drain screw is even more inaccessable heh..
however, What I did was clean the entire system and just let the fuel run through it today in the hot weather.. Figured it would act like soaking dishes in the sink for a few hours. And sure enough today after a few very speedy takeoffs, I managed to get it started, slowly at first, but it was just what it needed.
Now it's back to full power
Thanks so much for your advice and for just letting me brainstorm, its still not complete, but its running, which is a good start
Man when I feel that rumble, I know all the time was worth it.

Good to hear it.
My drain screw is readily accessible. Do you have a pic?
Still, best thing is to only disassemble the carb when it's removed from the engine, then everything's accessible. That's why you're having problems.
Just unscrew the top cap, remove the slide/cable/spring assembly complete, remove the fuel line, then remove the carb, check float level, ensure that there's no fuel in the float, clean the jets etc. and blow out the carb body.The dish washing/soaking analogy is OK for dishes. Best thing for a carb and it's jets is a blast of compressed air.
One quick pointer - close the fuel tap when you stop the engine and only turn it on again just before starting.
The fuel tap can leak a bit, potentially flooding the engine with fuel.
Then, give it a couple of rides, then check the spark plug colour.
More often than not, some adjustment of the air/fuel mixture is needed to get the most out of these engines. Mine did 33kph when I got it, but a bit of carb tuning and it now pulls to 51kph. (Smaller main jet, slide needle set low.)
All engines tune slightly differently. In fact, I bought a new stock NT carb last week and it performs very differently to the previous, (supposedly identical), carb.
Go by plug colour - see NT Carb Tuning Basics

Also, often the stock carb and inlet tube leak, causing a lean mixture. See NT carby/inlet leaks - a reliable solution for a fix.

... Steve