# Rebuilt carb with multiple problems - Help!! (please)



## Phonic (Mar 26, 2008)

Hello all, quick introduction as I woke up with the headache from hell.
Moved from UK to Gloucester VA 8 years ago and bought our first home one year ago which included a small MTD ride-on which I sold last week.
I'm almost beginning to wish I hadn't sold it because it was so reliable.

On to my issue.
I was given an older Murray GT with a 460777 20HP Briggs opposed twin, full pressure lubrication, and a carb that housed half the native wildlife of VA.

After tearing down the whole fuel system, replacing the carb and inspecting the cylinders for more wildlife and wear, I replaced the head gaskets along with a carb/pump rebuild kit.

She ran well for a few months until winter storage.
I started it up every week, mainly because riding my tractor is my therapy but partly to stop things from getting stale.

Anyhow, Yesterday morning I changed the oil/filter and fuel filter ready to start aerating my lawn.
I'm getting the usual hunting problems after 15 minutes and when that happens it'll only run with 1/3 choke. If I pull the choke all the way then push back in it'll also run for 5 secs until I repeat it.

I took some cleaner to the carb and gave it a healthy spray which didn't do anything so I pulled the bottom plug in the bowl that hides the main (?) jet and cleaned it.

That also made no difference but one thing I have noticed is that I seem to have a leak at both sides of the intake manifold, I can see exhaust gunk round the outer edges.

Can I use RTV for resealing these? I replaced the gaskets when I took the intake manifold off and tightened the bolts properly.

Gotta grab some more coffee.
Thanks for any replies.


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## 30yearTech (Sep 14, 2006)

The low speed circuit of the carburetor may have some restriction in it, but if you have an air leak anywhere in the intake manifold you will have similar symptoms.

If you think it's the carburetor causing the problem, you will at the very least have to separate the top and bottom half of the carburetor to gain access to the low speed jets for cleaning.

Best of Luck.... :thumbsup:


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## Phonic (Mar 26, 2008)

30yearTech said:


> The low speed circuit of the carburetor may have some restriction in it, but if you have an air leak anywhere in the intake manifold you will have similar symptoms.
> 
> If you think it's the carburetor causing the problem, you will at the very least have to separate the top and bottom half of the carburetor to gain access to the low speed jets for cleaning.
> 
> Best of Luck.... :thumbsup:


I decided to rebuild the whole thing, I took the lower cover bolt out to peek inside and it was pretty nasty.

I really wanna keep this engine running as sweetly as possible for as long as I can, the guy who gave it to me was meticulous in servicing and it shows - there's no nicer sound than a twin stroker idling.

I haven't had the chance to refit the intake/carb but hopefully this'll clear the problem, it looks brand new.

One last question, the front idle mixture screw, is it 4 turns out or 2 turns out? I've read conflicting information.

Thanks for the advice - it's appreciated


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## pyro_maniac69 (Aug 12, 2007)

1 1/2 turns out to start out with, than turn it in as you go along


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## 30yearTech (Sep 14, 2006)

I start at 2 with these carburetors, and adjust after engine is warmed up.


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## Phonic (Mar 26, 2008)

1 3/4 turns it is 

Couple more questions if you don't mind?

What am I listening for when I'm turning the screw CCW? I think it's a rise in RPM but if anybody can clarify i'd feel better.

On the left cylinder, looking from the front of the tractor I noticed the intake was fairly gummed up. There wasn't any leaking from either intake gasket so all I can think of is unburnt fuel.
Before I get the calipers out, does this sound like a sticking intake valve?
I should change the plugs and run it before I go any further .

As usual, any advice is greatly appreciated


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## pyro_maniac69 (Aug 12, 2007)

no, if the carb. is as dirty as you make it sound, that will make it run rich. and you want to turn in clockwise after you have unscrewed it out the 1 1/2 turn out. about the best thing you can do is listen at the rpms until they sound as if they have smoothed out, and then bring the motor down to an idle, let it sit for a moment, and then bring the RPMs of the motor back up fast, if it dies, than it is to lean, if it tries and you see black smoke coming out've of the exhaust, than you have it to rich


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## 30yearTech (Sep 14, 2006)

Start at 4 or 2 turns from seat it does not really matter, this is just a starting point, if it's open too far, it's just that much more you will have to turn the adjustment screw to get it right. I use 2, it's just my personal preference.

This is the low speed adjustment, adjust after the engine is warm and at the idle setting. You won't be able to tell much if you have the throttle set at a medium or fast speed when you turn the low speed adjusting screw. Turn the screw clockwise first to achieve a smooth idle if it falters then back up some, then test acceleration as pyro described, if it hesitates open the adjustment screw about 1/8 turn and try again until the hesitation is gone.

Your carburetor is not running "Rich" because it's dirty. Based on your description of your problem it is running "Lean" and most likely because it's dirty and restricting fuel flow through the metering circuits of the carburetor.

A good cleaning should take care of your problem.

*You may also want to check your fuel cap and make sure it's venting properly. If it does not start acting up for 15 minutes this could be the problem and not the carburetor.*


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## Phonic (Mar 26, 2008)

I'll bolt her all up in the morning and see how it runs.

Thanks again.


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