B&S 3.5 Max Walbro Carburetor refurbishment

[wag123]

You mean the curved piece top center? Does it get bent at the end with the hole, where the spring attaches, or more twisted at its base?

Yes. Twisted at it's base. This is the tool that comes from B&S...

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The slotted part at the end of the tool fits in the short vertical part of the throttle arm/tang and lets you bend/twist the throttle arm at it's base to adjust the governed speed. You can do the same thing with a long needle nose pliers. Bending the throttle arm to the left tightens the spring and raises the RPM. I still recommend that you replace the wire throttle link #201and governor spring because the proper function of the governor and throttle control depends on the correct relationship of the governor air vane to the carburetor's throttle valve.

 

[JHZR2]

Yes. Twisted at it's base. This is the tool that comes from B&S...

Loading…

www.amazon.com

The slotted part at the end of the tool fits in the short vertical part of the throttle arm/tang and lets you bend/twist the throttle arm at it's base to adjust the governed speed. You can do the same thing with a long needle nose pliers. Bending the throttle arm to the left tightens the spring and raises the RPM. I still recommend that you replace the wire throttle link #201and governor spring because the proper function of the governor and throttle control depends on the correct relationship of the governor air vane to the carburetor's throttle valve.

Thanks!

I have the link on order from a NOS supplier, and the spring I have, I just forgot to bring it with me to the mower when I went to install the carb.

I think it will be much easier if I remove the shroud and fuel tank.

When you say left and right, you mean looking at the engine from the front of the mower, right?

 

[wag123]

When you say left and right, you mean looking at the engine from the front of the mower, right?

Looking at the spark plug.
Working on carburetor side of the engine will be much easier if you remove the fuel tank. The shroud doesn't need to come off unless you want to clean the cooling system.

 

[JHZR2]

Looking at the spark plug.
Working on carburetor side of the engine will be much easier if you remove the fuel tank. The shroud doesn't need to come off unless you want to clean the cooling system.

The 3.5Max has an integral cover over the whole thing.

Which I guess is the fuel tank and cover in one.

If I’m going this far I might as well take as much as I can off and clean it all. That said, everything I’ve encountered has been pretty clean…

 

[wag123]

The 3.5Max has an integral cover over the whole thing. Which I guess is the fuel tank and cover in one.

Yes, the fuel tank covers the entire engine, but no, the fuel tank and cooling shroud (which is steel and contains the starter) are separate.

 

[JHZR2]

Yes, the fuel tank covers the entire engine, but no, the fuel tank and cooling shroud (which is steel and contains the starter) are separate.

Understood. I was using the wrong terms.

I also need to figure out why the tank to block bolt isn’t in. Everything is solid, but obviously this isn’t ideal.

 

[wag123]

Understood. I was using the wrong terms.

I also need to figure out why the tank to block bolt isn’t in. Everything is solid, but obviously this isn’t ideal.

View attachment 221867

Somebody that doesn't know what they are doing has been messing with this engine.
You are missing the black plastic spacer that goes between the engine block and fuel tank mounting tab. Furthermore, the bolt holding it is incorrect, it is supposed to use a shoulder bolt that only has about 3/8" of thread on the bottom. Additionally it is missing the rubber washer that goes on the head end of the shoulder bolt to help dampen vibrations. If you tighten the bolt that is in there it will break through the engine block or pull the threads out of the block.

 

[JHZR2]

Somebody that doesn't know what they are doing has been messing with this engine.
You are missing the black plastic spacer that goes between the engine block and fuel tank mounting tab. Furthermore, the bolt holding it is incorrect, it is supposed to use a shoulder bolt that only has about 3/8" of thread on the bottom. Additionally it is missing the rubber washer that goes on the head end of the shoulder bolt to help dampen vibrations. If you tighten the bolt that is in there it will break through the engine block or pull the threads out of the block.

Yes, I ordered the right one nos a few days ago.

I like this mower and even if it has issues it is perfect for the use case at my property where I keep it.

Thanks!

 

[JHZR2]

Somebody that doesn't know what they are doing has been messing with this engine.
You are missing the black plastic spacer that goes between the engine block and fuel tank mounting tab. Furthermore, the bolt holding it is incorrect, it is supposed to use a shoulder bolt that only has about 3/8" of thread on the bottom. Additionally it is missing the rubber washer that goes on the head end of the shoulder bolt to help dampen vibrations. If you tighten the bolt that is in there it will break through the engine block or pull the threads out of the block.

Ok, here’s one more.

So on the weekend I got it running finally after the carb install/no fuel flow issue, and then ran it a bit to warm it up, drained the oil, filled it back with Rotella SAE 30.

When I was trying to get it started, at one point I thought maybe I had flooded it (I hadn’t), so I pulled the plug, and noted later a little puddle of oil on the mower deck under where the spark plug hole is. I had never seen that before…

Since I got it, the oily dirt stain at the head hasn’t changed. I have not cleaned it. It looks like this:

Makes me wonder if the engine has a weepy head gasket.

And maybe some oil in the cylinder, that doesn’t hydrolock, but also doesn’t burn off? The engine starts first pull after sitting for over a week, it doesn’t smoke, and doesn’t smell particularly bad like a real oil burner might. FWIW

Reason why I show this is because of what else I saw - clean oil residue on the carb bowl. You can see the line on the right side of the bowl. I had it fully clean, so when I looked at that smudge, I realized it was oily.

When I changed the oil, I drained it from the bottom. When I filled it, it went perfectly in the top, no sign of any loss, leaks, certainly didn’t miss, etc.

So why would I have oily residue on the carb bowl? It had to migrate from somewhere. It was clean and slick, so it was fresh new oil like is on the dipstick, not dark dirty brown.

Is this indicative of anything in your experience? Should I do something preemptively? I mean, it’s only a 34 year old air cooled engine… it’s certainly perceivable that a HG or something else is seeping or needs replacement. What typically goes on these?

FSM seems to imply so:

I don’t think it’s enough oil loss to matter. Like a significant burning or anything. I’ll be watching it. I only used this mower last fall, and the patch it mows isn’t huge. But it would be nice to have it running tip top if there is something that is worthwhile to do…

Thanks!!

 

[wag123]

Ok, here’s one more.

So on the weekend I got it running finally after the carb install/no fuel flow issue, and then ran it a bit to warm it up, drained the oil, filled it back with Rotella SAE 30.

When I was trying to get it started, at one point I thought maybe I had flooded it (I hadn’t), so I pulled the plug, and noted later a little puddle of oil on the mower deck under where the spark plug hole is. I had never seen that before…

Since I got it, the oily dirt stain at the head hasn’t changed. I have not cleaned it. It looks like this:

View attachment 222065View attachment 222066View attachment 222067

Makes me wonder if the engine has a weepy head gasket.

And maybe some oil in the cylinder, that doesn’t hydrolock, but also doesn’t burn off? The engine starts first pull after sitting for over a week, it doesn’t smoke, and doesn’t smell particularly bad like a real oil burner might. FWIW

Reason why I show this is because of what else I saw - clean oil residue on the carb bowl. You can see the line on the right side of the bowl. I had it fully clean, so when I looked at that smudge, I realized it was oily.

View attachment 222068

When I changed the oil, I drained it from the bottom. When I filled it, it went perfectly in the top, no sign of any loss, leaks, certainly didn’t miss, etc.

So why would I have oily residue on the carb bowl? It had to migrate from somewhere. It was clean and slick, so it was fresh new oil like is on the dipstick, not dark dirty brown.

Is this indicative of anything in your experience? Should I do something preemptively? I mean, it’s only a 34 year old air cooled engine… it’s certainly perceivable that a HG or something else is seeping or needs replacement. What typically goes on these?

FSM seems to imply so:

View attachment 222072

I don’t think it’s enough oil loss to matter. Like a significant burning or anything. I’ll be watching it. I only used this mower last fall, and the patch it mows isn’t huge. But it would be nice to have it running tip top if there is something that is worthwhile to do…

Thanks!!

It doesn't look like a head gasket leak. The oil appears to be leaking from the sump gasket under the cylinder, a common problem on old B&S engines. It won't leak oil when the engine is not running but it sprays out as a fine oil mist under pressure when it is running. Oil spraying out from there will go everywhere (makes a mess) and makes it hard to determine exactly where it is coming from.

 

[JHZR2]

It doesn't look like a head gasket leak. The oil appears to be leaking from the sump gasket under the cylinder, a common problem on old B&S engines. It won't leak oil when the engine is not running but it sprays out as a fine oil mist under pressure when it is running. Oil spraying out from there will go everywhere (makes a mess) and makes it hard to determine exactly where it is coming from.

That’s very helpful. It doesn’t leak out enough to really matter. The carb wasn’t particularly dirty when I pulled it, for example. If I hadn’t touched it I wouldn’t realize that my new Rotella oil was on it.

The oil that leaked out when I pulled the start cord with the spark plug off is slightly more concerning. It was maybe a silver dollar in diameter.

Do you think it’s worth it to pull the head and clean the carbon, per the 300hr recommendation? Doesn’t seem hard to do… I’ve just never done it before. Seems to imply that even the HG is reusable.

Thanks again for all the insights!!

 

[wag123]

That’s very helpful. It doesn’t leak out enough to really matter. The carb wasn’t particularly dirty when I pulled it, for example. If I hadn’t touched it I wouldn’t realize that my new Rotella oil was on it.

The oil that leaked out when I pulled the start cord with the spark plug off is slightly more concerning. It was maybe a silver dollar in diameter.

Do you think it’s worth it to pull the head and clean the carbon, per the 300hr recommendation? Doesn’t seem hard to do… I’ve just never done it before. Seems to imply that even the HG is reusable.

Thanks again for all the insights!!

"If it ain't broke, don't fix it". Considering that the engine starts and runs good, I would not recommend pulling the head to remove the carbon. What I would do is clean the caked-on mess from the cooling fins (to help prevent further overheating) and check the head bolt torque (140 in/lb) as you will likely find some loose ones. BTW, ALWAYS replace the head gasket when you remove the head.
Replacing the sump gasket is not a difficult or expensive repair, and it doesn't take a rocket scientist to do it.

 

[JHZR2]

"If it ain't broke, don't fix it". Considering that the engine starts and runs good, I would not recommend pulling the head to remove the carbon. What I would do is clean the caked-on mess from the cooling fins (to help prevent further overheating) and check the head bolt torque (140 in/lb) as you will likely find some loose ones. BTW, ALWAYS replace the head gasket when you remove the head.
Replacing the sump gasket is not a difficult or expensive repair, and it doesn't take a rocket scientist to do it.

Haven’t had time to address everything. But I did have a few minutes to put a torque wrench on the head.

I set my torque wrench to 120 in lb, thinking I wouldn’t get much. Every bolt turned a decent amount. I turned them all a little bit at a time in a diagonal fashion until it clicked. Then I put it to 140 and repeated the process and it went a bit further. I was surprised at how much tightening it took.

It didn’t run different, I guess I didn’t expect it to.

Next time I’ll replace the spring and governor connection, clean everything out, etc.

I took out the 79112/J19LM plug, and put in an NGK B4, marginally cooler, I guess time will tell if it makes a difference.

I do need to figure this out: