Typical newbie question with a twist..

[Kluttsy]

Hey all! I've got an old mgt 4.6 and am having some problems with it. I've tried searching for it but cannot for the life of me figure out the problem. The issue is when I start it it runs balls out, mind you I've taken the carb apart and cleaned everything thoroughly and ensured that theres is no leaks in it. I then reset the settings back to factory, when it starts it does not stay running, I've tried adjusting the hpn and lpn to no avail.. I am at a loss any help or words of wisdom would be great..

 

[cbaker65]

Hey all! I've got an old mgt 4.6 and am having some problems with it. I've tried searching for it but cannot for the life of me figure out the problem. The issue is when I start it it runs balls out, mind you I've taken the carb apart and cleaned everything thoroughly and ensured that theres is no leaks in it. I then reset the settings back to factory, when it starts it does not stay running, I've tried adjusting the hpn and lpn to no avail.. I am at a loss any help or words of wisdom would be great..

If its the original AE 4.6 engine ,those engines run good with the needles set at ,HSN 2 3/4 to 3 turns out from closed.
LSN at 5 1/2 to 6 turns out from closed ,also depends on your elevation .

Those engines came with 2 different types of carbs. in which one has a mix meter needle an the other don't ,the one
with out in my opinion is better an easier to tune!

That truck also came out with a muffler that has the fuel tube that is shoved in a hole ,make sure that the tube is NOT
bottomed out inside the muffler causing to plug itself off ,My remedy to that ,is to cut the tip that goes inside the
muffler in an angle so it does not plug itself off!

If it does plug off ,you will get a lean out an high rev.
Also a dirty tank filter an a leaky tank lid seal will cause lean high rev problems!

 

[Kluttsy]

If its the original AE 4.6 engine ,those engines run good with the needles set at ,HSN 2 3/4 to 3 turns out from closed.
LSN at 5 1/2 to 6 turns out from closed ,also depends on your elevation .

Those engines came with 2 different types of carbs. in which one has a mix meter needle an the other don't ,the one
with out in my opinion is better an easier to tune!

That truck also came out with a muffler that has the fuel tube that is shoved in a hole ,make sure that the tube is NOT
bottomed out inside the muffler causing to plug itself off ,My remedy to that ,is to cut the tip that goes inside the
muffler in an angle so it does not plug itself off!

If it does plug off ,you will get a lean out an high rev.
Also a dirty tank filter an a leaky tank lid seal will cause lean high rev problems!

Thanks for the reply, ill take a look at that tomorrow morning when i get off work.. By the looks of this pic

my carb does not have the mix needle, correct? Just the hpn, lpn, and throttle adj?

 

[cbaker65]

That's the 21 ,not sure about the carb needles on it ,so look on the side were the throttle rod hooks
onto an see if there is a screw in the inside of it!

An get a pic of it!..

 

[Kluttsy]

That's the 21 ,not sure about the carb needles on it ,so look on the side were the throttle rod hooks
onto an see if there is a screw in the inside of it!

An get a pic of it!..

are these the needles you're talking about? If so, what do I adjust the mix needle to? I can't find the specs on it and I've gotten the engine and complete mgt manual printed off.

 

[cbaker65]

Ok ,yes that does have the mix meter screw!
The mix meter screw will be the big brass one on the side in you first pic ,an the LSN needle
is inside the throttle barrel!
A lot of people get confused from them because the LSN is hidden inside ,in which a 2 needle
carb. ,the LSN is on the side were the mix meter screw goes ,so yes ,that is a mix meter needle
an should be set flush with the its housing ,once set flush ,it should never be moved again!

So ,a base line set for that engine is 3 on the HSN an about 5 1/2 to 6 turns out on the LSN!
When tuning the LSN ,you want to open up the throttle an run it all the way in ,but don't close
it off hard ,then back it out 6 full turns to start with ,then yoo want to start an warm the engine up to
fine tune that needle setting!...Remember ,its in the throttle housing!....

 

[Tzicul]

And check the LSN, it seem the oring is broken. Or what is that black spot on the upper left side? If it is indeed a part of the oring, there is why you can't set the idle, you'll get a lot of air around the LSN

 

[Kluttsy]

I believe I am confused, I thought the brass one was hsn, the screw right under it was the lsn, and in the last pic that screw is covered up by the throttle linkage.

 

[Tzicul]

The brass one is hsn and on the opposite side is lsn

 

[cbaker65]

The tall brass one pointing upward is the HSN ..........
The big silver screw is the mix meter....in which other carbs it is the COLOR of brass.........

However ,your LSN IS in the throttle barrel!

 

[Kluttsy]

The tall brass one pointing upward is the HSN ..........
The big silver screw is the mix meter....in which other carbs it is the COLOR of brass.........

However ,your LSN IS in the throttle barrel!

Got it, I apologize for my ignorance I'm still trying to learn. And to answer the other question that black spot on the lsn is the holding screw for the throttle.

 

[Tzicul]

And to be more clear
I'm talking about this black spot on the LSN

 

[Kluttsy]

And to be more clear View attachment 91484
I'm talking about this black spot on the LSN

Yes sir (or ma'am) that's the set screw for the throttle linkage that goes to the servo

 

[Tzicul]

Oh, ok, now I see! And no ma'am here Nevertheless, check all the orings as they can be old/brittle/worn out

 

[Kluttsy]

So, based off those settings my engine is still going balls out wide open. I can turn my LSN and or the HSN in or out a 1/8 or 1/4 turn and still get the same result. I've looked at my fuel (pressure?) line which is still good not bloated or anything, the fuel lid is not weak. I've sealed my back plate, my carb, my glow plug is good. I'm at a complete loss.

 

[Tzicul]

All I can think now is the front bearing and/or the piston/cylinder are completely worn out.

 

[Kluttsy]

All I can think now is the front bearing and/or the piston/cylinder are completely worn out.

Ding ding ding. We have a winner.. I've looked at this engine a hundred times and finally I've found it. I have no idea how I didn't see it sooner. Now I've gotta find out how to get it out.

 

[Tzicul]

View attachment 91488
Now I've gotta find out how to get it out.

You can find a lot of videos on yotube. Basically by heat. A LOT! And, because of this, you will probably loose the rear bearing also.