kssue, there is "nothing exotic" about those bolts.
You do not need to try for an OEM replacement bolt.
You can take your one remaining bolt to an auto parts house or a good sized home improvement store or hardware store and have the bolt length and threads matched up. Don't try to "guess" the size or threads, the staff of the store can help you get the exact bolt you need.
You can get the bolts with a standard hex head on them if you prefer that configuration.
To keep the bolts from shaking loose, buy a small bottle (or tube) of medium grade thread locking liquid (compound) and coat the threads evenly with it before inserting and tightening the bolts.
If the threaded holes have indeed become stripped a machine shop or a local outdoor power equipment shop will be able to repair the holes by installing (not a task for a novice) thread repair insert bushings (one brand is Heli-coil).
Installing these types of inserts allows you to continue using the OEM specification bolts.
Generally, you CAN reuse carb gaskets unless the gasket is broken or torn anywhere. My opinion of your gasket is that it should be replaced because it has already been "run loose" and probably is not sealing adequately enough to ensure against dirt entering the intake stream somewhere on the gasket perimeter.

Thanks Mownie, that is what I needed to know. We had the thought to go with a thread-locking compound but I wanted to be sure it was ok to use in an application like this. Did wonder if those bolts were standard hardware; when I tried to take the original remaining bolt out of the bottom hole to double check it against the replacements I got, I could unscrew it but I couldn't get it out of the hole because the cover on the top of the muffler is blocking it and the two rusty old bolts holding THAT on are gonna take some elbow grease and copious WD40 to remove.

But will take your advice for sure on the gasket;certainly can't HURT to replace that. Hopefully the bolt holes will be fine with just the goop and a new gasket and we won't have to get any machining done on it. Pretty please... I will let you know how it works out; might be a few days to go get some thread locking liquid. THANKS.

The way to tackle clearance problems such as that muffler in the area can best be handled like this.
Approach the job as if you intended to remove the carburetor itself and not just the screw.
With this thought in mind.........get everything loose from the carburetor that would prevent you from lifting the carb (and its mounting screws still resting in the carb) out of its place on the engine.
Then you can pull the screw out of its hole without clearance issues. Remember to take pictures of the carb in place before you start removing linkage and other stuff. Trust me, you will be glad you took pictures.
I hope that will work for you as I try to avoid messing with exhaust system covers and bolts unless I have no other choice.
I would rather remove an exhaust system where it bolts to the cylinder head or even lift an entire engine than to attempt muffler cover screw removal. And I am not exaggerating, well.........not too much :^)

OR alternately, take your bolt to a hardware store, get an allen head cap screw next size longer. Take the darned muffler off to get it out of the way, not that big a deal, and put the thing together. MOST likely, the threads are deep enough so that there will be no problem with the longer bolt, IF there is, shorten it a little since OR put a washer under the head.

Walt Conner

Being old jet engine mechanic I would just drill holes in the heads of the new bolts and Safety wire them. Now they will never loosen unless you don't know how to safety wire the heads in the tighten direction.

Well it is a flat head, holes are in block, the holes must be where they are. I should have said get TWO Allen head cap screws, replace both.

Walt Conner

The original bolts have a hex head outside with a torx head hole. Not enough clearance on the outside of the screw next to the carb throat thing to even get a socket around them. Replacement bolts have an exaggerated phillips slot but flat head top otherwise. I did have the thought to try a longer bolt, and will probably try that since I need to make a trip to Lowes to get thread-locking compound anyway. Allen head cap screws would be my choice. Guess it doesn't matter one way or another...

Walt, and Mownie, the muffler itself isn't in the way, it's the shield attached to the top of it that shields the carb from the muffler (presumably). THAT is just a curved piece of sheet metal bolted to face of the muffler with a gap between muffler and shield, and I have tried in the past to take it off but afraid the rusted bolts are going to shear off. Incidentally it bends down enough at the edge next to the carb bolt on the engine to give the needed clearance but it's stiff enough gauge that you need another set of hands and some leverage to push it down out of the way while pulling the other bolt...just don't feel like bothering my hubby with it unless I have to, lol. And probably will. So actually kind of a stupid girl thing, haha.

rc, I don't have a clue what you mean by Safety wiring them. haha. Sounds like Walt refuted that for me anyway. But there is no shortage of jet mechanics around here since I live near Wichita... :)

What he is talking about are special bolts that have holes drilled crosswise thru the head and you run thin wire thru the holes and twist after tightening the bolt to keep bolt from backing out.

Walt Conner

Oh, ok...I was picturing holes drilled into the top of the head, INTO the head, not crosswise. Haha, that didn't make much sense. I think that given what it feels like trying to tighten these bolts, if the thread in the hole extends past the end of the bolt it would probably hold better to use a slightly longer bolt, and that is certainly worth a try.

No special bolts needed though you can get aircraft grade bolts with hole already drilled in the heads either all the through or through half the hex points on the bolt heads, most of them are in Fine threads which you mower engine probably has standard threads (course threads).

You can do this will standard bolts Hex head or allen head bolts (allen head bolts are easier do to the hole for the allen head wrench) by hand drilling the holes yourself using # 59 drill bit or any bit that will fit in your drill that .035 thick or so Aircraft safety wire usually comes in three sizes .020, .032, and .041. diameter) also you don't have to have special safety wire pliers to wire them. The army still hand twists they safety wire jobs on Helicopters using duck bill and dyke pliers to cut the wire off and bend the pigtail (pigtail; bending the end of the safety wire job so you don't get poked (cut) by the straight piece of wire sticking out)(USAF uses special pliers)

In your case the bolts probably worked loose and caused wear in the threads in the block or the bolts. If the holes are not captive you could remove the washers and safety wire (lock wire same thing just different term) or get new longer bolts using lockwashers. This may alow the bolt to go little deeper to get better grip as suggested. If the bolts wiggle when loose you have thread wear on the bolts (old ones) or thread wear in the block. Good lock tite may also aid in keeping them tight also. Safety wire will prevent them from loosing on what ever bolt you use you just got to hand drill the holes and get some wire to wire them. If you know Jet engine machanic's they will have access to wire and pliers. drilling the holes in SAE bolts are not that hard providing you don't drill too fast (high speed drill bits don't mean run them as fast as the drill will run, if so the tip of the bit will get hot and dull it and won't cut right. Drill just fast enough to see metal slivers or chips being thrown from the bit) and start the hole in the center and drill straight.

this may help and it may not if the new bolts loosen right back up like the old ones. I usually on none flying equipment just wire them or drill to size instal heli-coil insert the bolt hole threads in the block bringing it back to spec.s. But installing heli-coils you only have one shot of doing it right unless you are master welder able to fill the hole up with weld and redrill and cut new threads. So that would be my last resort.

Thanks for the details on safety-wiring, RC!! Good info and will tuck that away for future reference. The successful solution to the problem, at least for now, was the first thing I tried and easiest: a slightly longer bolt. The original bolt was 1/4" x 20 x 3/4"; got some 1" bolts in the same gauge and thread and that did the trick. Bottom one still shook loose a bit but will work that out of there later and replace it too. Just happy to be able to mow the vast wasteland of yard and culverts tonight before the impending rain in the forecast for the next couple days... THANKS ALL for the suggestions and advice. And now have some fresh unopened lock-tite handy too should it become necessary. :)

Postscript to this story: Wouldn't you know that this thread pops up at the top when I googled how to fix a stripped mower carburetor bolt hole. SAME bolt has worked itself loose again, same old TSC riding mower, still running strong. I believe I put locktite on it after all, and it has held fast for the last three years. I guess I may as well try the locktite again??

Some OHV engines had a support bracket that came off the block and went to the airbox to provide additional support.

Thanks, I don't think this is an OHV engine? There is a bracket near the bottom of the carb on this engine but it doesn't hold the carb against the engine.

Yes, I know. This is not a real common issue. Does this engine shake due to a PTO problem or is the engine itself loose from the frame? My thought was that after you apply your JB weld or locktite to the retaining bolts, that a simple bracket at the rear may help stabilize the assembly.

That might be true, on the vibration. This engine is 24 years old lol; it's still running strong when I can keep everything firmly connected. I HAVE had issues with the engine mount bolts coming loose and have to tighten them up regularly. Discovered when we inherited the tractor from hubby's grandma that the engine was being held to the frame with only three of four bolts, and those just regular bolts, not the OEM engine bolts, if it makes any difference. Got four OEM B&S engine bolts on eBay, and the lock washer that was supposed to go on one of them, but that one somehow came loose and fell out someplace. So back to a regular bolt in that hole. But I periodically tighten those bolts because they do seem to work loose; there is definitely some vibration going on but don't know if it's related to the PTO or not. No problems engaging or disengaging; no unusual vibration. So probably a good case for the carb bolts working loose; once they loosened (before I discovered the problem with them and the engine mount bolts) maybe they started wearing on the bolt hole threads???

Anyway, back to current problem. The bottom screw on the carb mount still can be tightened I think, but the muffler shield on top of the muffler directly below the carb is in the way making it REALLY difficult to access or pull the bolt; you can barely work a screwdriver in there to turn it and you have to bend the back edge of the shield down to do that. I think I need to use Locktite on both bolts though.

I tried re-doing the Locktite on the top bolt and tightening the bottom one, and it held for all of about 5-10 minutes of running. After that I ended up bungee-cording the air cleaner to the engine to hold it against the engine block just to finish mowing, but by the time I was done both bolts were loose again. The carb mounts to the left side of the engine, btw. I can link you to a diagram if you like. (see below)

I used the same tube of locktite I had from three years ago (still pretty liquid) but maybe it was no good? It was the removable type of Locktite and I am wondering if I should try something with a little more hold? Would JB Weld be better? I noticed it did grip the bolt in the hole better once it began to set but was afraid to tighten it down too much; just turned it till it felt like it was catching a bit and then let it set. Otherwise the bolt would just spin in the hole. I have gotten some more OEM bolts to try new ones but they are shorter than the bolt I used last; last time I just used an ordinary bolt that was a little longer than the original, and it did the trick, but this time I used the same longer bolt and it let go, after applying Locktite, tightening as best I could, and letting it cure 24 hrs before running. Should I replace the carb mount gasket again too? Seems to be ok but I haven't pulled it; I replaced it last go-around. The mower starts and runs just fine if I can just keep the darn carb on the engine!

Here is the link showing the carb and air cleaner assembly for my B&S engine, no. 280707-0411-02. If you look at the carb bottom left, you can see the attachment point (intake??) you can also see the bracket I was referring to (no. 662 in the chart). Just a strip of metal that attaches to the little box with the choke linkage on it. Doesn't really support the carb-to-engine connection; the whole unit including aircleaner and bracket moves, I think. It's screwed down pretty tightly regardless.

Carb and aircleaner assembly B & S 280707-0411-02

Thanks for any suggestions or advice!

here's the manual with a picture of the engine that shows the configuration; page six, diagram on the right, is the one I have. B & S 280707-0411-02 operation manual

One would think that it is vibrating too much? These can have issue w/ the syncro balance weight/ pins really inside the block if the pto end is as it should. I would support that carb best you can from the rear and set those mount screws. Clean the threads w/ carb spray and let them dry. JB may do the trick. Makes you want to use a sticky sealant as well on the gasket or maybe sleeve the intake (round?) and seal it w/ an elastomeric sealant like Right STuff. Wits end I am sure.

Haha yes, you got it. Definitely at wit's end on this one. It's something with this machine every season but I always manage to fix er up and get er moving again. LOL. Starting to get attached to it. NOT.

Yes, I do think that there is a vibration issue with this engine/machine; it's not obvious but everything shakes a little loose so you have to keep tightening it down again. Wear and tear probably. Like I said, it's 24 years old.

I didn't think of carb cleaner in the bolt holes; that's a good suggestion. I did think they might need cleaning before trying the Locktite this time, and would hope that's why it didn't hold. Should I try to take the whole muffler off so I can get to the bottom carb hole better? I can't see how it's attached and wondering if it might just be threaded on. Those same links under the muffler diagram show the current muffler but not its attachment end. It's the one in the box labelled 300A; the shield that's in front of the carb hole is part no. 725 on top of it; it's the top back corner directly in front of the hole and bolt. The shield bolts are rusted on pretty good (tried WD40 to no avail. Did not want to shear them off...) so not really an option to remove them with the shield. Just stupid little obstacles like this, you know?

What do you mean by sleeving the intake? I know what the intake is but not sure what kind of material you're referring to using. Like wrapping something around it and sealing to the block?

I'll take a look at it again in the next couple days and maybe get some fresh JB Weld and see if I can figure out a better support system. I'll take another look at that rear bracket too and see if there's anything amiss.

Thanks so much for your patient help haha.

Sleeving is probably a reach here. If you envision a round hole in the block and the round hole in the intake, a sleeve or thin bushing between the two sealed up good and solid. It may help support the assembly- though won't address the cause.

Oh, ok, yes, that makes sense now. I was picturing something around the outside of the intake lol. Yeah, probably more involved than I want to mess with but certainly an option. I think it makes sense to try what worked before, with clean bolt holes and new bolts...and stiffer stuff, ie JB Weld. Ha. And maybe devise some sort of support system.

I don't know what if anything can be done to alleviate the cause (assuming vibration) but hey, maybe it's time for me to tackle this other starts-then-dies John Deere RX90 (I think it is) I bought for $50 last spring! Next project...