B&S 28Q777 crankcase vacuum line sucking oil up to fuel pump

[warreng5995]

In my experience this is due to coating of the jets.

The EPA has made all engine builders lean out their engines. This started this about 1988. They have gotten progressively leaner in stages, which is why many motorcycles now have fuel injection. If they have their way, look for electronic fuel injection on mowers in the next 10 years, or all-electric mowers mandated by law.

When everything is "perfect" your engine is running on a very minimal amount of fuel. Should anything happen to the float level or the jet size, then there won't be enough fuel to start a hot engine without using the choke.

Enter ethanol loaded fuels. When these are left in the carb for any length of time, the alcohol attracts water. The alcohol and water mixture leaves a very thin layer of (usually dark brown) "varnish" on everything.... including the inside of the jets. This makes the jet smaller on its fuel metering orifice... which in turn further leans out the fuel mixture. It's not much, but it's enough. The engine seems to run correctly, but it's really starved for fuel. Thus, the only way a hot engine will start is by using the choke.

Since the engine seems to run OK, I wouldn't open the carb. In your shoes I'd start using a "fuel stabilizer" AND carb cleaner, such as StarTron. The stabilizer will work to prevent future problems by keeping the alcohol in solution with the gasoline, and the cleaner will work to clean out any varnish that has accumulated. And it will do this while you run the engine on your regular schedule.

I implement this plan in my shop by treating the fuel in the BIG cans as soon as I bring it home from the gettin' place. In this way the StarTron works its way into my chain saw, leaf blower, weed whacker, my Exmark and both my walk-behinds. And the plan works. None of my equipment ever has carb or fuel issues.

Hope this helps.

Fully agree about the ethanol and the EPA garbage. I wish the carbs were adjustable again... what the stupid EPA has forced to be done to them is as stupid as the new "no spill" fuel cans... along with many other things.
As far as ethanol goes, I don't buy ethanol fuel just for some of the reasons you listed. My local gas station is also a truck stop and they sell premium non-ethanol gasoline. Back about 5 years ago when I did buy ethanol, and even though I put some type of stabilizer in it, I kept having issues with my trimmers and chainsaw carbs, even a carb on a very small genset. Clean and rebuilt them, last for a while same issues. Bought new carbs, after a while, same issues. Switched to non-ethanol, haven't had any more problems.

I do use fuel stabilizer in anything engine that doesn't get used often or is going to be sitting more than a couple weeks. Also used it in the storage can if the fuel isn't going to be used directly. Haven't heard of startron before. But I do not like "stabil", its garbage in my opinion. I found a stabilizer called PRI-G for gasoline and PRI-D for diesel. Have used both for several years and it works well. From what I remember reading several years ago, its the same company that makes fuel stabilizer used in most ships.

In any case, like I said in my op, just got done with this full engine rebuild, full carb rebuild including all new jets, float, etc. I haven't ran the engine probably 1 hour in total since rebuild. All fresh fuel, clean tank, all new filters, new fuel pump, new fuel lines, new plug, etc.
Also the first time it wouldn't restart when hot (the first real time running it after rebuild), my Dad had tried it out for about 20 min cutting and shut it down when the UPS guy showed up. When it wouldn't restart I also thought it wasn't getting fuel, so I got some started fluid and shot it in the air intake, got nothing, not even a hit. Just like all the other times since when hot. So at that point I thought maybe the needle valve got stuck or something and might have flooded while he was talking to the UPS guy, towed it back up to the shop pulled plug, little glaze on the plug. cranked over engine, mist shot out of cylinder, but nothing out of the ordinary. So thats when I started trying to figure out what was going on before I ever posted here. Which at that time I thought it was related to the oil in the vacuum line going to the fuel pump, but have since ruled that out as a non-issue.

With that said, I could be wrong, but I really think its a weak coil at this point. When I get some time, I'm going to take the coil out and go buy a new B&S one from my local Stihl dealer. So we'll see what that does. I don't like throwing parts at an engine and see what sticks, but after everything else I've already rebuilt and replaced on this thing, might as well replace the coil too.

 

[Born2Mow]

StarTron was originally developed for boaters. As much trouble as Ethanol caused in mowers and trimmers, it nearly killed the pleasure boat industry due to the proximity of water 24/7. It's a stabilizer AND cleaner, which is far better than a simple stabilizer, like Stabil. As long as you're already buying a fuel additive, it certainly wouldn't hurt to try a different one. It's certainly no more costly.

This is not a comment on your carb rebuilding skills. Please don't take it that way. What I'm saying is that carbs made in the last 15 years are VERY complex instruments, with as many as 4 stages of jetting for a variable-speed engine. It's extremely difficult for anyone to clean all the passageways without an ultrasonic cleaner and a tremendous amount of time.

I really hope the new coil fixes your issue. But if not, then maybe you'll remember this post.

All the best.

 

[warreng5995]

StarTron was originally developed for boaters. As much trouble as Ethanol caused in mowers and trimmers, it nearly killed the pleasure boat industry due to the proximity of water 24/7. It's a stabilizer AND cleaner, which is far better than a simple stabilizer, like Stabil. As long as you're already buying a fuel additive, it certainly wouldn't hurt to try a different one. It's certainly no more costly.

This is not a comment on your carb rebuilding skills. Please don't take it that way. What I'm saying is that carbs made in the last 15 years are VERY complex instruments, with as many as 4 stages of jetting for a variable-speed engine. It's extremely difficult for anyone to clean all the passageways without an ultrasonic cleaner and a tremendous amount of time.

I really hope the new coil fixes your issue. But if not, then maybe you'll remember this post.

All the best.

no offense taken ?, carb bodies are something else to clean sometimes with all the tiny passages and such, and it does take a good amount of time to clean and rebuild them. Smaller the carb the worse they are. But have been using an ultrasonic cleaner in recent years, which does help a lot. Besides the sonic cleaning itself, I also like usings its heater to warm up the distilled water (which I always use when cleaning carbs as I have well water) pretty good, as that seems to help clean a lot better too. Add in some sonic cleaner "soap" and I also add in some Mean Green Industrial Strength (which is difficult to find these days) when ever I'm cleaning carbs, and all together it does a pretty good job. I usually run a carb through several 30 min cycles (as 30 min is the longest cycle my cleaner will set for...?), just depending on what else I'm doing in the shop or how quickly I need the carb done. Then when it comes out of the cleaner, I use my air compressor to blow out all the passages.
I'm no pro by any means, I've just learned over the years what works for me, as I repair all my own stuff, whether it is mowers, 2-cycles, motorcycle, or cars/trucks. Can't afford to pay someone else to do it. And tbh I'd rather do most things myself, at least I know what was actually done... even if I do it wrong the first time and figure it out later, maybe then I'll know how to fix it lol ?

 

[JMK1038]

Hi all thanks for the replies. Didn't get any emails that anyone had replied.
Anyway, try to answer everyone:


I'm not sure how oil is the line is normal, I thought that is what the crank case breather was supposed to stop? Also if there is enough oil to block the line wouldn't that stop, or at least hinder, the vacuum to run the fuel pump? In which case would either cause no fuel to get through, or possibly cause the engine to run lean?
I tried my very best to assembly the flywheel and key very carefully, and torqued it to spec. I don't think that is the issue, as when it is cold, it starts right up fine. But I will look at it if I take the engine covers back off.


Yeah, we ran it for a couple seasons. Did all maintenance when we got it, and changed oil and filters regularly. Never saw the sludge and other until I took it apart though. My Dads nephew (my cousin) bought it from an auction... and yes there were issues from the beginning, but most seemed small and I was able to keep it running. The one that I couldn't fix was a light "knocking" or pinging sound. Part of it ended up being the spot welds holding the baffle inside the muffler had broke, I cut it open rewelded it, and welded the muffler back together (that was about 2 years ago when we first got it). Thought that had taken care of the sound, but could still hear a light pinging coming from the crankcase. It doesn't seem to have this sound now though. The bore being out of spec could be possible. I didn't measure it, as I didn't really have any tool that could do so. A T-Bore hole gauge would have worked, but don't have one and didn't realize at the time that some cheapos could be found.


I did replace the vacuum line, as well as all other fuel lines. But not with SAE hose, I used transparent silicone fuel hose. Thats why I could see the oil in the line. With oil going into that line, I also thought that it blocking the vacuum to the fuel pump could be part of the power issues. I did replace all gaskets, all seals, and etc with all brand new. As you said, 20 years old all those type parts are going to be hard and cracking.


The new rings were the correct part number as per the engine date code according to B&S, and they are B&S brand rings too. I didn't even know they sold oversized rings for these... manual never mentioned it and I hadn't replaced rings on a small engine before. Yeah, I should have found a way to measure the cylinder bore. As I said up above, didn't have the tools, didn't know I could have gotten some cheap, and also there are no machine shops out here so had no where to get it measured either.
I didn't know about the torque spec change, I'll have to go look at the service manual I have and see the spec it gave, as that is the torque I set it too. And if I remember right, I *believe* it was 220. If that it what the manual I have states, I'll step it up to the 250 see what that does. I had thought about going higher recently, but didn't want to strip the threads out of the block. If they raised the torque spec, then compression leakage is most likely why they would have done so.
And yes that web area is the weakest point of these OHV gaskets. Just replaced one on another mower that I got for free as it would put out a literal cloud of smoke that you couldn't see through (due to the blown head gasket), and that is exactly where it blew out too. That mower doesn't have a mower deck, but since fixed it works great to pull my yard trailer I built

Additional Question: Is there a way to know if the muffler is partially blocked??? I read somewhere that this could cause similar issues. But it appears that the exhaust flow is normal. I may just pull the muffler off and see what happens.

Thanks for all the input and information everyone. I will go through some of these tomorrow if I have time to work on it. Once I go through the list, I'll report back if anything changed for better or worse.

I had two mowers that had oil coming back to the carburator and in each the float valve was stuck and the gas was filling the crankcase and forcing the oil out.

 

[donens2018]

Reading the posts, couldn't find any reference to the having done a compression test. When the new rings were put in, did the cylinder show scoring? As someone suggested, I would hook up spark tester and run it. Look for any signs of missing or poor ignition. Also, I would check for oil breather for blockage or sludge.

 

[StarTech]

Reading the posts, couldn't find any reference to the having done a compression test. When the new rings were put in, did the cylinder show scoring? As someone suggested, I would hook up spark tester and run it. Look for any signs of missing or poor ignition. Also, I would check for oil breather for blockage or sludge.

The problem is these engines have an ACR which limits the compression to 60-90 psi. In order to get a valid compression reading ti would require adjust the vavle clearance until the ACR is no longer effective. But there is one problem that as the electric starters are too weak to turn the engine through the compression stroke. Briggs recommends doing leak down tests instead when a compression problem is suspected.

 

[ezcruisn71]

I had two mowers that had oil coming back to the carburator and in each the float valve was stuck and the gas was filling the crankcase and forcing the oil out.

The clear fuel line you are using going to the fuel pump might be some of your problem! This line will collapse and therefore won't work for the fuel pump correctly! That fuel line should be a ridged black double core rubber line. If it collapses it will not operate the fuel pump correctly!

 

[ezcruisn71]

The clear fuel line you are using going to the fuel pump might be some of your problem! This line will collapse and therefore won't work for the fuel pump correctly! That fuel line should be a ridged black double core rubber line. If it collapses it will not operate the fuel pump correctly!

Snowmobiles use the same type of fuel pump and they will not work correctly with the clear fuel line either.

 

[sterobinson]

I'm pretty sure there's a Reed valve under the flywheel that goes bad and that's why you have oil in the vacuum tube.

 

[ezcruisn71]

Snowmobiles use the same type of fuel pump and they will not work correctly with the clear fuel line either.

The fuel line I am talking about comes off the Engine. It is the pulse line to the pump. This must be dual core rubber line. The other lines can be clear line