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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / June 200721HP B&S Engine
I have a Sears lawn tractor which is 6 yrs old. It came with a 21HP B&S engine. A few days ago it started to run real rough at idle. If I add about 50% chock, it run ok, but still at times can misfire. At a 100% speed, it seems ok and can cut grass and move around ok. I got this condition a few years ago and was able to clear it by cleaning the air filter. So far I have clean the air filter, replaced and gapped both plugs, replace oil, replaced the fuel filter. With all of that no change. The engine surges up and down at idle real bad. I removed all the gas and tried new one, no change. In the Sears manual it talks about a idle mix adj. I have none of that. No screws to adj other the the RPM. I used carb cleaner and cleaned the carb. No change. What could this be? I called Sears and they want $96 to come over and provide diagnostics. Then parts plus about $100 or so per hr for labor :( Thanks, Fred > I have a Sears lawn tractor which is 6 yrs old. It came with a 21HP > B&S engine. A few days ago it started to run real rough at idle. If I [quoted text clipped - 17 lines] > Thanks, > Fred Has the carb been rebuilt yet? Could be gummed up. Another possibility is the carb might be loose where it attaches to the engine. This would create an air leak that appears at light loads but is less prevalent at high load. Also check the gaskets at the mounting flanges. > fredcar...@hotmail.com wrote: > > I have a Sears lawn tractor which is 6 yrs old. It came with a 21HP [quoted text clipped - 23 lines] > create an air leak that appears at light loads but is less prevalent at > high load. Also check the gaskets at the mounting flanges. Thanks for the reply. The carb is original. I checked for loose connections, and was not able to see any. I also used carb cleaner near the gaskets and the RPM did not pick up. The carb rebuilt kid has a couple of gaskets and two needle screws. I can't see where and how to use the needle screws since this carb has nothing other than the RPM adj. The idle screw and high speed adj screw are not there. I really needed the idle mix screw. Sadly there is a little hole but no screws in to. The strange thing is that the Sears manual shows a screw there! > The carb is original. I checked for loose connections, and was not > able to see any. I also used carb cleaner near the gaskets and the RPM [quoted text clipped - 5 lines] > > The strange thing is that the Sears manual shows a screw there! Am I reading this right, there is a hole there but no screw? Either the screw vibrated out or there is a 'tamper' cap over the mixture screws that you will have to pry off to get at the adjustment and the hole you are seeing doesn't actually go anywhere. Do you have any pictures you can put up somewhere for us to look at? Have you tried spraying carb cleaner into the hole you are describing with the engine running? Any change? If so...chances are something is supposed to be there and it's probably out laying in your yard right now ;-) Chris > > The carb is original. I checked for loose connections, and was not > > able to see any. I also used carb cleaner near the gaskets and the RPM [quoted text clipped - 16 lines] > > Chris Chris, Thanks for the reply. The hole seems to have no treads in it. Factory smooth. It appears to be some sort of a seal or something. I'm not sure if I can remove that. For sure it reminds me of what car makers used to do to make things tamper proof. If it is a tamper proof cap, how do I remove it? In the old days we used to drill a 1/8" hole in to it. The hole size seems just right for the screw, but it seems sealed. I'm concerned if I drill a hole in there and there is an screw, then what :( I did spray carb cleaner in the carb and things did not change. However, when I was maintaining a slow stream of carb cleaner the engine stopped its hunting and ran smooth. This somehow tells me I'm not getting sufficient gas in there. > The hole seems to have no treads in it. Factory smooth. It appears to > be some sort of a seal or something. I'm not sure if I can remove [quoted text clipped - 3 lines] > seems just right for the screw, but it seems sealed. I'm concerned if > I drill a hole in there and there is an screw, then what :( No need to drill anything. Most likely what you are looking at is a port that could have been drilled and used for another purpose on a different model engine than yours. > I did spray carb cleaner in the carb and things did not change. > However, when I was maintaining a slow stream of carb cleaner the > engine stopped its hunting and ran smooth. This somehow tells me I'm > not getting sufficient gas in there. Sure sounds like a plugged up idle circuit. There should be either a removable idle jet or an idle mixture screw somewhere on the carburetor. If not you'll have to take the carburetor off the engine, remove the float bowl(f any) and use carb cleaner/compressed air to try and clear all the passages. What model engine do you have? Model/Type/ser from the fanshroud would help. Chris > > The hole seems to have no treads in it. Factory smooth. It appears to > > be some sort of a seal or something. I'm not sure if I can remove [quoted text clipped - 23 lines] > > Chris The tractor is 917.271832. Engine is B&S 461707 type number 0147-E1. Carb is B&S 693479. If I could find the idle mix screw, I can make the correct adj. The issue is that there are no adj screws other then one for RPM. No mixture adj. All the diagrams, including the Sears one show a key no. 147, part number 693508 Jet-Pilot. However on the carb itself there is no such part. I'm completely amazed. Even a Haynes small engine manual shows where a 4 screw gas pump carb (exactly like mine) would have the mix adj. All the info on the web, the Sears manual and the repair manual show a little screw for idle mix adj. The carb rebuild kit part number 693503 includes this small screw as well!!!! Thank you, Fred >> > The hole seems to have no treads in it. Factory smooth. It appears to >> > be some sort of a seal or something. I'm not sure if I can remove [quoted text clipped - 41 lines] >Thank you, >Fred My 1998 vintage B&S 16HP Vtwin has no idle mix adjustment - only idle speed adjust. It is very sensitive to debris and moisture. I have had some problems with moisture condensation in the fuel tank that eventually gets to the carb. It seems to help to occasionally drain both the tank and the carb bowl. Mine has a drain screw for this. Also, I turn off the fuel and drain the carb if the mower will be idle for a few weeks. You can likely reused the bowl gasket and clean the passages pretty well with a can of Gumout or B12. Remove the screw plugs from the passages to make sure you are getting the solvent thru them. Lugnut > On Mon, 18 Jun 2007 22:14:49 -0700, fredcar...@hotmail.com > wrote: [quoted text clipped - 58 lines] > > Lugnut Folks, I thank all of you who shared you wisdom and knowledge with me. Here is the latest update: I wanted to order a rebuilt kit first before committing to a new carb for $152 from Sears. I first looked at Sears for the carb kit. They wanted around $28 plus $7 for s&h. I looked for the B&S p/n on the web and someone on Ebay had a kit with that exact number for about $22 plus free s&h. I ordered that and got it 3 days later. I replaced the 6 pieces of the pump first since they were easy to do right on the mower. There is a spring, a cap, two gaskets and two diaphragms. The rubber looking diaphragms on mine looked real aged and starched. I put it all together and started the mower. No change. It still surged at idle :( Next in the kit there was top washer which sits between the carb and the air filter housing. I replaced that, No change :( Next there is 1" bolt which has a very small screw with a hole in it. This is called the main jet. Replaced that. No change :( Only parts left were two washers for the idle speed shaft, and a small screw with precision machined holes. This part required me to take the carb off and apart to get too. However having the part in my hand allowed me to locate in on the inside of the carb looking down at it. So, I took a wire tie and clean the one already on the carb. Started the engine. Things seemed a bit better, but not really fixed. Still misfires at idle and sometimes at full load :( Next I took the carb cleaner and placed a small red tube thing that came with it on it and spared right into the little hole. That caused a tiny amount of while looking grass or fiber to blow out of the big nozzle in the carb. After that the cleaner starting to come out of the nozzle right on top of the throttle plate. Started the engine and for about 5 min all ran well :) Very smooth idle. At high speed things look ok as well. Just when there is no load (the blades are not running) there is slight misfire once every min or two. I think this has been there since day one. But idle is back to smooth. I only ran it for about 5 min and left it alone. I think its fixed. Takecare, Fred. > I have a Sears lawn tractor which is 6 yrs old. It came with a 21HP > B&S engine. A few days ago it started to run real rough at idle. If I [quoted text clipped - 17 lines] > Thanks, > Fred Idle circuit in the carb is plugged. Only real way to repair it is to pull the carb off and open it up. That engine has a tamper resistant carb that only has a fixed jet for high RPM and a hidden idle mix needle. You need to drill and remove the plug over the needle when you take the carb apart.  SignatureSteve W. Near Cooperstown, New York |
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