QT50 Bogs off start

Garrett Jackson /

Bought a non-running '79 QT50. Replaced the charge coil and now it runs. I cannot seem to get it adjusted, even when switching between two Mikuni carbs. It seems to run well for a very short time, but then starts bogging off a dead start. Pilot jet is clean. Fuel/oil mix is clean. Once I get to about 15 mph it will take off and run really strong. It is pretty tough to start. Can someone point me in the right direction?

Re: QT50 Bogs off start

Jack Rutherford /

Are you sure pilot jet is clean? How did you clean it? Adjust air/fuel mixture screw?

Re: QT50 Bogs off start

Garrett Jackson /

Hi Jack,

Took the pilot jet out, soaked in carb cleaner, blew through it, and then shined flashlight from opposite side and saw light. I've adjusted both carbs starting at 1.25 turns out in increments of .25 turn. In my other QT, I used to run ultralight fishing line through the jet, but I'm at the beach this week and don't have any.

Re: QT50 Bogs off start

How is your air filter? Try removing the element to see how it runs without it.

Re: QT50 Bogs off start

Garrett Jackson /

New element in it, but I'll try what you suggest.

Re: QT50 Bogs off start

Jack Rutherford /

out of curiosity, where is your needle set?

Re: QT50 Bogs off start

Garrett Jackson /

Not sure, never adjusted one. Where should it be?

Re: QT50 Bogs off start

Jack Rutherford /

in your case, you may want to try moving the clip down one slot so that the needle sits higher. Don't lose the tiny clip or other parts.

Re: QT50 Bogs off start

Garrett Jackson /

Ok, I'll do that and let you know.

Re: QT50 Bogs off start

Garrett Jackson /

Hi. So I've moved the clip up one notch, run without the air filter, and tuned the carb according to Jack's instructions on his website. It's a tad better, but still bogs about 3-5 seconds after starting from a stop. Runs very, very strong after that. I will mention that the stock exhaust was cut by the PO in the pipe section, and I had a friend weld it back together. It's not perfect and is loud, which indicates to me that the cut isn't sealed completely. Could this have an impact?

Re: QT50 Bogs off start

> Garrett Jackson Wrote:

> -------------------------------------------------------

> Hi. So I've moved the clip up one notch, run without the air filter,

> and tuned the carb according to Jack's instructions on his website. It's

> a tad better, but still bogs about 3-5 seconds after starting from a

> stop. Runs very, very strong after that. I will mention that the stock

> exhaust was cut by the PO in the pipe section, and I had a friend weld

> it back together. It's not perfect and is loud, which indicates to me

> that the cut isn't sealed completely. Could this have an impact?

How does the spark plug look?

A motor needs more fuel when cold. Thats why they make chokes.

If a motor runs worse when warm then there is a high probability that the a/f is too rich.

If you raised the clip it lowers the needle and leans out mid range in a carb. You improved the way it runs and you're on the right track.

Generally speaking a needle should be in the middle position or close to it. If you stray more than a couple of settings then you the main jet is too big. The exception to that rule is if you have the wrong taper needle from installing an aftermarket carb that was not specifically desinged for the application at hand.(edited)

Re: QT50 Bogs off start

Garrett Jackson /

Here's a picture of the plug.

15646748891356305615294524184106.jpg
« Go to Topic — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account