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I've got a Briggs 5HP outboard that I can't get the idle mix adjustment screw to the right position. Looking for some tips to help get it set right. I pulled the whole thing apart and cleaned it well. Put the idle mix screw back in and turned it the same six turns it took to bottom it out when I took it apart.

Now it will only run on full choke and even then I had to turn up the idle screw. If I turn it off choke one notch, it dies.

New fuel lines, new carb bowl and jet gaskets. Fuel pump is new. Carb is clean. Model: 12y602 0110 E5 030530 FA

12Y602-0110-E5

Did you clean the fuel nut (bolt) as it is the main jet?

StarTech said:

12Y602-0110-E5

Did you clean the fuel nut (bolt) as it is the main jet.

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Yep. Clean as can be.

Did you set the high speed mixture first? My experience tells me to always set high first, then idle.

Rivets said:

Did you set the high speed mixture first? My experience tells me to always set high first, then idle.

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There's only the idle mixture screw and throttle valve screw.

Then there is still a clog the carburetor most likely and a good ultrasonic cleaning might be in order. I have seen carbs to take 2-4 30 cycles in 160W USC unit to get them clean.

I thought so too, but I'm able to spray carb cleaner through every hole and get fluid out of the other end. Do you think that there could be some buildup behind some of the plugs that are one way only?

check to make sure that the gasket between the carb and body isn't screwed up, like it popped off one stud while you were putting the carb back on. Sounds like a huge vacuum leak.

Checked that also and it's good. All gaskets are in the same order and orientation that they have always been.

Now it will only run on full choke

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go thru the carb again if you can't find a vacuum leak. Also check the manifold for breaks if it is a plastic manifold. Check all the jets and float level. Check the fuel pump if it has one. The description screams of too much air or too little fuel, or both.

The problem with just checking to passages are clear with spraying fluid into passages is there are some cross passages that can't be visual checked like those around the non removal nozzle.

That's a good point. For as much as I do this, I should probably invest in an ultrasonic cleaner.

Never noticed a welch plug in the bottom. Either it's never been there (unlikely) or it was removed by a previous owner. It's ran fine for me many seasons without it, but I guess I'll be putting one of those in this week. Might as well pull the other one and replace it too.

It's sitting in a vat of carb cleaner now.

And avoid using carb cleaner sprays
Whatever they make the check valves out of , most seem to be adversely affected by the sprays
For once I will endorse a factory branded product
The very expensive Walbro carb cleaner spray is worth the pot of gold it costs.
What I have noticed is if a cleaned carb ( using std spray) is reassembled and run strait away it seems to work
But if you run carb spray through the carb then leave it for a couple of hours then the check valves stick closed
I rarely use any carb cleaner at all now days
I use spray degreaser to test the passageways because it is cheap & seems to have no ill effects
Then a "flush" with WD40 followed by low pressure air
The original ultrasound has worked to death & I replaced it with 2 new units
A small one sold for jewlery for cube carbs and a really big one for mower parts .
The small unit is almost dead again but it runs near full time in my shop

Check to see if the tip of the idle screw is broken off and stuck in the hole. Had this happen on an Evinrude and it drove me nuts until I found it. It was impossible to get the tip out so I got another carb on FeeBay.

I never thought to check this. I'll have a look tonight.

Rivets said:

Did you set the high speed mixture first? My experience tells me to always set high first, then idle.

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When you say idle screw, are you talking idle mixture or idle speed? If it needs a choke, you most likely have plugage in the carb if no mixture setting makes a correction. There is also a service buletin on that carb system. Model info - means I do not research it.

Carb is completely clean and idle mixture screw is unbroken. Removed the welch plug in the side and made sure all passages were clear. Reinstalled the two new welch plugs and put it all back together. Zero fuel getting through the carb now. I've done something wrong. Maybe I didn't seal the welch plugs good enough. I was in a slight hurry.

I'll pull it apart once more tomorrow after work and try again.

is there fuel in the bowl?

Yep. Fuel getting to it, just not through it.

It's sitting in another bowl of carb cleaner. I put everything back correctly. Still not getting fuel through the carb.

The only thing it could be is my welch plug install and I have no idea how to tell if I did that right. I put it in and smashed the center out toward the edges until it was nearly flat and couldn't be removed easily. Any other ideas before I light it on fire?

I don’t know what others will say, but many times I don’t reinstall welch plugs. Most times they’re not needed.

I can get on board with the one in the bowl because that one hasn't been on since I've owned it and it ran fine. The one on the side is the one I'm worried about.

Is this a 2 or 4 cycle engine ?

4

I would do a compression test, could be that you don't have enough vacuum . Possible stuck/bad valve or rings,etc.

90psi after 4 pulls. not great.

I can spray fuel in the carb and it runs.

The key word is spray.

Why would it start 4 days ago and not now though?

Fowled plug?

Not fouled enough to not start when I spray fuel down the carb.

rebelyell said:

Why would it start 4 days ago and not now though?

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I was replying to what you said earlier.

rebelyell said:

Never noticed a welch plug in the bottom. Either it's never been there (unlikely) or it was removed by a previous owner. It's ran fine for me many seasons without it, but I guess I'll be putting one of those in this week. Might as well pull the other one and replace it too.

It's sitting in a vat of carb cleaner now.

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I'd just replace it. There is so much corrosion in that carb it may never run right again,

Normally, yes. I would have at this point. Part is discontinued and the one on ebay "didn't idle right."

My next step is to dump it in an ultrasonic cleaner. If that doesn't work I'm going to look around for a carb body that's pretty close enough to the same and swap all the linkages over. Like this one.

$149 canadian dollars used. He has a for all price, and then each individual part. Sounds outrageous but maybe make him an offer what you think it is worth https://www.ebay.ca/itm/292496024443?hash=item441a1f237b:g:gHAAAOSwrjhatXGR


ALSO - lots of small boat engine shops and lawn mower shops have shelves full of older parts that they don't advertise or put on online lists. Call around. That carb was used on other products. The shop near me the other day sold me some obsolete parts they had which no one else showed available. There are many busy small shops that have 20 year old inventories sitting on a shelf. But you have to call around. I'd start with the shops nearest you then expand into other towns further away. I found a part for a Mercury motor once that way, got a list of Mercury shops on the West Coast that had been around 20 years and started calling. About the 10th don't have it the guy had it and shipped it to me. Solved my problem too. Infact years later a shop in San Diego sold me a new case, crank, plates, reeds, pistons, and full carb set for it $200 that someone had ordered and never picked up. Even lent me the special tools to stuff the pistons in. Engine was like new after that.

I've done that a few times with other major mower parts, but carbs have usually been either superseded or in good supply. Never thought they'd have an old briggs outboard carb. I'll call around tomorrow. Thanks for that.

Found a carb. It doesnt have an idle mix adjustment and doesnt have an idle speed screw. Seems to be from a later model.

Installed it anyway and now it runs on choke only. As soon as you turn it off choke, it dies. Classic clogged carb. Except this one is spotless. No welch plugs to pull and all holes spray clean.

Could it be something with weak spark? Im at a loss here.

Think I might put a hose clamp on the choke where it runs fine and let it go.

classic case of either a vacuum leak, or a bad fuel supply / fuel pump. Try spraying some berrymans around some of the fittings on the manifold and see it that changes the idle. You can use an unlit propane torch too. Or a smoke tester.

Having the choke on makes the engine pull lots of fuel. If there is a vacuum leak that makes the mixture burnable. If the fuel supply is bad, the choke may create a vacuum that pulls fuel from the tank.

Using propane to find an air leak is one thing that appears to be unique to the USA.
And when you think of it unbelieveably stupid
The combustable air fuel ratio for propane is huge
SO combustable fuel. hot engine, face close to the engine all you need is a stray spark, bit of red hot carbon or rust coming out of the muffler and you can join the very fashionable no eyebrows club
The blinded by your own stupidity club also take members this way.
It is a bad practice with car engines where the exhaust is sealed better & the mechanic is a long way from the engine.
In the government motor garage doing that is instant dismissal
Apparently it is a practice locals learned during WWII from US military workshops

bertsmobile1 said:

Using propane to find an air leak is one thing that appears to be unique to the USA.
And when you think of it unbelieveably stupid
The combustable air fuel ratio for propane is huge
SO combustable fuel. hot engine, face close to the engine all you need is a stray spark, bit of red hot carbon or rust coming out of the muffler and you can join the very fashionable no eyebrows club
The blinded by your own stupidity club also take members this way.
It is a bad practice with car engines where the exhaust is sealed better & the mechanic is a long way from the engine.
In the government motor garage doing that is instant dismissal
Apparently it is a practice locals learned during WWII from US military workshops

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ya know, you don't have to open the propane tank full blast for10 minutes straight. Personally I used to use windex, or a tiny amount of Berrymans. Now I use a smoke generator. But if propane is all I had I would not hesitate to use it in the open air for a few seconds on low.

It even might just need re-jetting.

I'm assuming that this exhausts through the lower unit like most outboards. If so, make sure that it is not plugged by a rodent, mud dauber, sea weed, etc. Nothing goes in if nothing gets out.

northcreeek262 said:

I'm assuming that this exhausts through the lower unit like most outboards. If so, make sure that it is not plugged by a rodent, mud dauber, sea weed, etc. Nothing goes in if nothing gets out.

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more likely a carp

northcreeek262 said:

I'm assuming that this exhausts through the lower unit like most outboards. If so, make sure that it is not plugged by a rodent, mud dauber, sea weed, etc. Nothing goes in if nothing gets out.

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Nope. Exhaust is on the side. Briggs managed to bolt a foot to the bottom of a vertical shaft 5hp motor. I can get in real shallow water.

I don't even know where to begin to check for leaks. Surely can't do it while the motor is running.

Took the boat out today and it ran, but I had to play throttle with the choke. I don't have an intake manifold. Carb bolts directly to the cylinder head. Could I have a bad head gasket? Fuel pump is newer, so I doubt that's the issue. I could have gotten a bad one, but it runs wide open with the choke in the wrong place, haha.

Sprayed carb cleaner everywhere I could think to with zero change. Around the carb mount, around the breather, and around the breather tube. The only place I didn't spray was the head gasket.

I'm going to replace the exhaust gasket (needs it) and the breather assembly/gasket. Maybe it's sucking in air around that somewhere. I can't find anything else unless the head gasket has totally failed.

I swapped the breather and the gasket and it runs fine. Who knows.

rebelyell said:

I swapped the breather and the gasket and it runs fine. Who knows.

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some carbs the breather powers the fuel pump diaphragm.

sgkent said:

some carbs the breather powers the fuel pump diaphragm.

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Yes the crankcase vacuum powers the vacuum operated fuel pump. The breather operates the same as the PCV unit on cars which allows the engine to exhale but not inhale. This way the engine blow by gases are vented from the engine and vacuum impulse is created after the exhale of these gases. Without this full vacuum impulse the fuel pump will not operate properly so a defective breather assy can cause problems like the one the OP had.

It is just not a common problem for these to fail.