Boxxer 421 engine problem

**wandwizard** · 11-11-2009, 04:42 AM

The Briggs & Stratton engine on my Boxxer 421 starts fine and works fine when cold until I have to stop to dump water and then restart the engine. When the engine is hot it will spurt and sputter and almost refuse to run when I restart it. It will idle fine, but when I throttle up is when the problem occurs. If I throttle extra slow it will usually struggle a little and then begin to work fine. Also, if I allow the engine to cool for 10 to 15 minutes it will restart and throttle up fine. This problem only occurs when the engine is hot and is restarted. Any suggestions about what I can do to fix this would be appreciated.

**Rug Spa** · 11-11-2009, 08:21 AM

sounds like some type of vapor lock to me. CHeck to see if the jets in the carb are worn or full of crap. Do the valves need to be adjusted? check you oil sending unit it could be trying to shut the engine off. Maybe Chris S has some ideas ? On this one I am at a complete loss.

**Chris Sheldon** · 11-11-2009, 09:48 AM

Yeah, Nick, this is a strange problem.

Randy do you have to choke it to start it? Next time this happens, pull the choke out while trying to run the throttle up, this will tell us if we are dealing with a "too much fuel problem" or a "not enough fuel problem".

Do you dump your tank voluntarily or are you dumping it after the engine shuts down? I am not sure, but I think on this machine the waste tank overfill switch kills the engine spark. This would leave alot of gas in the carb and combustion chamber, so when you went to restart it, it is actually flooded. Just a thought.

Have you done the preventive maintenance? Plugs, air fulter, fuel filter, etc?

**Ara Klujian** · 11-11-2009, 10:56 AM

Spark plugs could be the wrong heat range. Or the butterfly inside the carb could be getting stuck. Other than that Nick and Chris have good ideas.

**wandwizard** · 11-11-2009, 03:50 PM

Originally Posted by Chris Sheldon

Yeah, Nick, this is a strange problem.

Randy do you have to choke it to start it? Next time this happens, pull the choke out while trying to run the throttle up, this will tell us if we are dealing with a "too much fuel problem" or a "not enough fuel problem".

Do you dump your tank voluntarily or are you dumping it after the engine shuts down? I am not sure, but I think on this machine the waste tank overfill switch kills the engine spark. This would leave alot of gas in the carb and combustion chamber, so when you went to restart it, it is actually flooded. Just a thought.

Have you done the preventive maintenance? Plugs, air fulter, fuel filter, etc?

I almost always dump my tank voluntarily and the kill switch in the tank is rarely ever activated. I only choke the engine when initially starting cold. I will try to choke it next time, but my best guess right now is that it is struggling to get fuel because I could smell it if it were flooded. I try to keep clean filters on it and new plugs at regular intervals. However, Jondon did not install a fuel filter on it to my knowledge. I looked all over for one and cant' find it. The machine has over 7 years running w/o a fuel filter. I traced the fuel line from the floor all the way up to the top of the engine and there is no fuel filter.

**Ara Klujian** · 11-11-2009, 07:51 PM

Did you look underneith the van? I was thinking about this today and the symtoms you are explaining can happen if there is a leak at the neck of the carburator. But that would be more likely to happen if the engine was cold.

**Rug Spa** · 11-11-2009, 08:34 PM

maybe the fuel pump is going bad? when it gets hot could be doing funny things.

**wandwizard** · 11-11-2009, 08:47 PM

Originally Posted by Ara Klujian

Spark plugs could be the wrong heat range. Or the butterfly inside the carb could be getting stuck. Other than that Nick and Chris have good ideas.

What you said about the butterfly inside the carb getting stuck does sound like a real possibility. It seems to me that something is getting stuck when I throttle up, but eventually opens. When it does open the engine runs fine after that. Would spraying some carb cleaner in there do any good or should I think about replacement. Also, if there is not a fuel filter underneath the van should I put one on? I can't really imagine them putting the fuel filter under the van, but who knows.

**Ara Klujian** · 11-12-2009, 12:06 AM

Randy what you can do is remove the airfilter and take a look to see if there is any binding going on. The butterfly you want to focus on is below the choke fly. So it may be difficult to see if its binding. Spraying carb cleaner isn't such a bad idea. I think it would be worth a shot. I would take a look at the neck of the carb to see if there is any sweating going on. if you see some serious residue, the gasket between the carb and runners my need replacing. In the event you see residue or sweating do not try and crank on those bolts because you can warp intake. It may be a little difficult to have a look but try your best to accomplish a visual on the neck of the carb.
As for the fuel filter being underneith the truck is very possible. One of my trucks has the filter underneith. Take a look. I just cant see the engine running seven years without one.

**wandwizard** · 11-12-2009, 04:14 AM

Thanks for the help guys, I will try some of your suggestions tomorrow. I have been under the van before and don't recall seeing a fuel filter, but I'll look again. The only really good reason I can think of to put the fuel filter under the van is to keep from spilling gas inside the van when you change them. Because the fuel filter has been out of sight it has also been out of mind. As long as the machine was working ok I never really thought about it. If there isn't one I'll put one on and if there is one I'll put a new one on. I'll also inspect the carb carefully and clean it too.

**wandwizard** · 11-14-2009, 03:39 AM

I found the fuel filter under the van between the gas tank and the fuel pump. Now it makes perfect sense why they put it under there, because it would keep the fuel pump clean as well as prevent gas spillage in the van! I went ahead and pulled it off and replaced it. I also used carburetor cleaner on it, but I couldn't even see the butterfly at all. I put a used, but very clean air filter on it just for good measure. The air filter that was on it was burned from back fire that occurred when I tried to pull the throttle out to quickly while it was hot. I also tried choking the engine when restarting while hot and it killed instantly. I'm certain it is not flooding. I will probably wait and see if the things I've done so far have done any good next week since I have no work scheduled for this weekend.

**Rug Spa** · 11-14-2009, 09:16 AM

I was thinking . I had aproblem with a honda once. It was about 4 years old and it had a bucnh of hours on it.

The honda would do something simmilar and then it started doing up and down reving for no reason. Turned out the carb wore out with the needle seat. I replaced the carb and it worked fine. for about a year till the cam shaft broke.

**C Spot Stop** · 11-14-2009, 03:53 PM

same machine

Mine will do the same thing IF the doors are closed or IF there is no wind.

Just sayin

**wandwizard** · 11-14-2009, 04:53 PM

Originally Posted by C Spot Stop

same machine

Mine will do the same thing IF the doors are closed or IF there is no wind.

Just sayin

Mine does it even with doors and windows open, good breeze, and a cool day. I'm thinking I may need at least a carb rebuild which isn't too expensive. I'll know soon enough.

**Rug Spa** · 11-14-2009, 05:57 PM

Randy here is my advice. Take it for what is worth . You said the machine is 7 years old ,I am assuming the engine is 7 years old.

Just buy a new engine and be done with it. You could very easily drop 1000.00 and not fix the engine. Buy a new one and keep the old one for a spare or build a gokart.

**wandwizard** · 11-14-2009, 07:57 PM

Buying a new engine is certainly one of my considerations, but I'm still hoping this is a fixable problem. I wouldn't consider sinking a whole lot of cash into the engine to get it fixed, but I'm not willing to put up with too much grief if this problem continues or gets worse either. Right now the problem is pretty manageable. I just need to be careful when I throttle up after a shut down or give it about 15 minutes or more to cool down before a restart. I'm hoping the things I've already done and a couple more things I'll do next week will help it. I'll be talking to a small engine guy here in town Monday about it too. He's got a lot of experience and maybe has seen this before. I'll keep you guys posted on what I find.

**Ara Klujian** · 11-14-2009, 08:12 PM

Did you get a visual of the neck of the carb yet?

**wandwizard** · 11-14-2009, 08:31 PM

I took the air filter housing completely off to try and look inside the carburetor. I could see some residue, but not a lot as far as I could tell. By the time I started looking at it then it was already getting dark. I couldn't even see the butterfly at all looking directly down into the carburetor with a flashlight. I'm guessing it's mounted vertically on this carburetor. I saw a couple things that need replacing and I am going to either get them or order them Monday. I broke the gasket that goes between the carburetor and the air filter housing and there is a rubber tube that goes from one of the ohvs to the air filter that is very worn and has lots of cracks in it that needs replaced. I'll get a better look at it Monday. As you probably know it's hard to work on these things after dark w/o good lighting. There is only one small engine place in town now and they are not open on the weekend and for some reason they closed early Friday. Just my luck.

**wandwizard** · 11-19-2009, 09:54 PM

I went to the local small engine place and told him my problem and that I thought it was something with the carburetor. I ask how much for rebuild kit and labor. The rebuild kit for my engine is a little on the high side at 85.00, but he said if I had the work done there he would only charge about an hour and half labor or about 75.00 so I agreed and ordered the rebuild kit a a few other parts. I checked at Briggs & Strattons' web site and they had basically the exact same prices he quoted me. I hope this solves the problem. I'm a little nervous about it and think I might should have just bought a whole new carburetor for 223. and put it on myself. Too late now though so we'll see how this goes. The engine did seem to run a little smoother after changing the fuel filter so it may have been starved a little for gas. I will post again after I've had it rebuilt which will probably be next week or week after. Btw, his rebuild includes removing the carburetor and boiling it out.

**wandwizard** · 11-26-2009, 09:18 PM

It appears the carburetor rebuild solved the problem. Yesterday, after running the machine about 2 hours strait, I dumped the water and immediately turned the machine on w/o any hesitation at all. It did diesel some though at idle so I may need that adjusted.However, after I got home I noticed there was oil all around the engine and some splattered on my van wall, probably by the belt. I don't know yet if they got the oil on it while working on it or if they caused some kind of leak somewhere. They were supposed to seal one valve cover gasket for me and used silicone rather than the gasket that is made for that engine, but it did not appear to be where the oil came from. I cleaned the machine up real good and will be watching for leaks next time I run it.