Source of my massive vacuum leak on my 50cc is:

[sgtp]

....the throttle cable guide going into the top of the carb. Apparently the tube that comes out of the top cap has gotten loose and is causing the engine to go so lean, it dies when opening the throttle. This has been a on again off again issue with this scoot, as it will seal from time to time. So, the question is:

Can this be fixed or do I need to buy a new carb?

I might be able to do a ghetto poor man fix, using RTV or epoxy. Another idea would be to very carefully try to flair out the tube from the underside of the cap, so that it is more rigid and not have any gaps for the air to pass thru.

Any ideas or suggestions?

[Juzz976]

A new carb is cheaper than the labour to fit the new carb, let alone pissing around with what is obviously a defective carb to start with.

[sgtp]

yeah, true...I am a DIY'er that fixed many a defective part in my day. I'd rather spend hours diagnosing and fixing an issue before I open my wallet. Some might argue that my chinese scooter is defective by default, lol

[bogan]

I'd probly give the RTV a hoon, might not last long, but it will tell you for sure if that is the problem

yeah, true...I am a DIY'er that fixed many a defective part in my day. I'd rather spend hours diagnosing and fixing an issue before I open my wallet.

Cheap mechanics school that is!

Some might argue that my chinese scooter is defective by default, lol

Some might argue that a defective part on a defectively designed bike, is in fact, perfectly normal, and not defective at all

[sgtp]

Hey everyone...My scooter will now run (after warming it up) but its not fixed by a long shot.

Right now I have to restrict the air going into the airbox (putting fingers in front of the intake) to get the thing to start. Once started it will die if you give gas, but the improvement over before is that it will run fine after warming up. I have removed any vac leaks at the airbox, cable guide cap on carb, and around the reeds on the intake manifold. I even raised the needle to try to get the air/fuel ratio right (this change I believe finally got it to run when warmed up). So, do you think I still have a vac leak? I am wondering if the auto choke is dead. If so, a new carb sounds like the answer as I wouldnt know how to convert to a manual choke.

Any ideas?

[paturoa]

Right now I have to restrict the air going into the airbox (putting fingers in front of the intake) to get the thing to start. .......I even raised the needle

So it sounds like it is still running lean.

As a generatlisation raising the needle is a mid range thing so prob wouldn't make any difference and I'd NOT be considerring changing carb settings to solve the problem (unless someone changed them to create the problem!).

Idle and Pilot jets do low throttle opening, needle size and height mid range and main jet open throttle. They obviously overlap as the throttle oepns and the load varies.

Did this start suddenly (ie who fiddled or changed something) or did it come on over time?

Have you drained the float bowl and seen what came out?

Suggest that you start from the fuel tank and work your way forwards for fuel flow right through to the carb to ensure that enough gas is getting there.

The other option is an air leak. I use an enclosed area and get some smolderring string / cigarette smoke to test AFTER checking the intake manifold / boot for fit, splits etc.

[sgtp]

Well, Ive owned this scooter since it was new, so I know all thats been don to it.

The fuel is a week old. Ive tested the fuel petcock and it flows freely with a vacuum to the second line, so I am leaning toward airleaks still present. I used a half a can of CRC on it yesterday and am convinced my leaks are on the hose between the airbox and the carb inlet. The hose seems to be made of the same material that GN250 tires are made of....hard and plastic, very little resemblence of rubber. I am re-epoxying the airbox to hose conenction, and think all I can do to insure a leak-free connection from the hose to the carb is to ditch the stock clamp and get a screw-drive hose clamp. Is there anything else to try for this connection? I dont think RTV would work well....wondering if something else can inprove that seal. As for further down the line, I think I was torquing down the hose clamp too much on the carb outlet connection and not getting good seal. Again, i wonder if anything can be done to help it seal there completely, like polishing the carb surface that the hose inner surface contacts. We'll see how this goes..............

edited to add: this scoot had on and off issues where you get it full throttle and it would hesitate and then finally speed up...a tell tale sign that it is lean. i suspect that my removing of the airbox to clean the filter and degraded that seal to the carb.....

[sgtp]

ok, heres an update:

I got a new hose clamp for the airbox to card connection, I found some methods of using RTV to seal that connection as well (applied rtv, let it dry, then connection everything) but what I think sorted that source of vac leak was connecting the airbox elbow to the carb while both were in my hands. For the longest time the carb was installed and I was trying to force the airbox elbow onto the carb, but the hard plasticy rubber never allowed me to get it to seat completely.

So, currently the scooter idles and rides fine (restored the needle to the stock height, too) no longer dies when given throttle, no longer heisitates before the engine speeds up, but I still need to restrict the airflow into the airbox to get it started when cold, IE: make the ratio richer. So that leads me to believe that the last issue to sort is the auto choke. Is there an way to test what is currently happening with the stock one? like checking resistance with a multimeter, or similar?

[paturoa]

Is there an online workshop manual you can download? If you are testing 'lecky stuff then that would the way forward.