Briggs and Straton help

[emmy71]

I have a 6.5 hp B & S engine on a push mower. I am not sure of the correct term for this, but the engine has what I call auto-throttle. There is no choke or speed lever, just the priming bulb. Throttle is automatically controlled. The engine has started to fluctuate in speed from a high rpms to low rpms at all times. I see there is a fine spring that is part of the throttle linkage at the carb. Could this spring have become stretched over the years? Can this somehow be converted to have a manual throttle? Carb and air filter are clean. I can manually move the throttle linkage to change speed at the carb so I know the engine funs fine. Any help is appreciated.

Terry

 

[alchemysa]

I have a 6.5 hp B & S engine on a push mower. I am not sure of the correct term for this, but the engine has what I call auto-throttle. There is no choke or speed lever, just the priming bulb. Throttle is automatically controlled. The engine has started to fluctuate in speed from a high rpms to low rpms at all times. I see there is a fine spring that is part of the throttle linkage at the carb. Could this spring have become stretched over the years? Can this somehow be converted to have a manual throttle? Carb and air filter are clean. I can manually move the throttle linkage to change speed at the carb so I know the engine funs fine. Any help is appreciated.

Terry

Its very unusual to have no throttle control on a push mower. Anyway, the motor is designed to maintain itself at a preset speed. An air vane in the base of the engine reacts to air that is flowing over it. When the air flow is slower, (due to a load on the motor) the vane rotates and pulls open the throttle via that spring you mention - and the motor speeds up.

Yes the springs can become stretched or deformed over the years. Shortening it may help. But first check that all the linkages are free to move. Any fuel or carby problems will also effect engine speed so you you need to make sure they are OK too. Its kind of a vicious circle. The vane previously mentioned is is both responding to, and controlling, the engine speed.

Look for the B&S website and download a parts manual for your motor.

 

[Jim Thompson]

I refer to these as fixed throttle and i have in the past converted engines with throttle cables so that they always run at governed rpm. Rpm is easily adjusted by bending the tab that the spring to which you referred is attached, to slightly increase the tension.I don't recall exactly, but, i think that governed rpm should be either 3000 or 3200 if you have access to a tach.

 

[Diamondpilot]

My push mower does not have a hand throttle either. Just a choke and a primer bulb. I bought in new in 1998 at Sears. I think its a B/S or Tecumseh. Never had a issue with it so not much help but just wanted to let you know not having a throttle is not a new thing.

Just though to it but my snow blower does not have a throttle either. Its a Toro and I believe it has a Tecumseh engine also. No throttle, just he primer bulb and a choke.

Chris

 

[Jim Thompson]

Actually, not having an adjustable throttle on these small air-cooled engines is a good thing, because one of the worst things you can do to them is run them at idle. Of course, dirty air filters and dirty oil is worse

 

[emmy71]

I guess I should have looked more closely. It is a 10 year old Sears mower with a Tecumseh engine. Engine isn't clearly marked so I assumed B & S. That spring looks really stretched and deformed. New one is only about $3.00 so I think I will try that. Does the diaphram mentioned ever need replacing? As always, thanks for the quick responses.

Terry

 

[dcyrilc]

I guess I should have looked more closely. It is a 10 year old Sears mower with a Tecumseh engine. Engine isn't clearly marked so I assumed B & S. That spring looks really stretched and deformed. New one is only about $3.00 so I think I will try that. Does the diaphram mentioned ever need replacing? As always, thanks for the quick responses.

Terry

Pix are always helpful. Since the spring is only $3.00, it certainly can't hurt to try. Let us know how things work out from changing the spring.

 

[alchemysa]

Does the diaphram mentioned ever need replacing? As always, thanks for the quick responses.

Terry

Diaphram? Perhaps you mean the vane I mentioned. No I don't think it ever need replacing. Its just a metal flap, not a rubber thingy. (Of course, your engine may be different).

 

[Treemonkey1000]

That is basically a "governor" as the other guys mentioned the vane autothrottles the engine to speed up or slow down as needed. After mowing over the years the linkages get gummed up to the butterfly on the carb. If you have a good compressor with an air nozzle get in there and blow out around the carb and the linkage to the vane. Also make sure you have a good clean air filter. If you are feeling spunky pull off the engine shroud and really clean up under there. After you are done with that a bit of WD 40 on all of the moving linkage pivots should get you back in business.

 

[oldnslo]

Tecumseh engines that are not getting the proper fuel flow will also hunt. I suspect this is a float type carb that is gravity fed. Pull the float bowl off and clean the main and idle jets out. I would replace the float needle & Seat while it is open also. Unless you hit a branch with the throttle linkage spring assembly they rarely wear out. Linkage may get gummy and sticky but the springs rarely fail.

Roy

 

[Ken Cunningham]

Dump some seafoam in there and see if that helps. A clogged carb will cause hunting. The engine wont get enough fuel, so the govenor opens up the throttle to dump more fuel in, then its running to fast so the govenor closes the throttle, then the cycle starts all over again.

 

[mostly_gas]

Sounds like a fuel supply or mixture related issue. Check plug for fouling replace if questionable. Check fuel lines for cracking, flaking and at 10 yr old I would replace. If fuel lines clean, check for intake leaks, if none then pull and disassemble carb, looking for sediment. Typically a stretched spring will change the operating RPM but not cause fluctuating RPM.

 

[bp fick]

I rebuilt a carb off a tecumseh this winter for my neighbor's snowblower. I actually found a lot of rotted out rubber seats and rather plugged up passageways. My guess is this. With the use of so much plastic instead of the metals and brass of by-gone days, it doesn't take much. (ethanol doesn't help!!). I have had two push mowers consecutively that were B&S, fixed throttle and plastic carbs. Again, it doesn't take much for them to start with the "hunting" or oscillating rpms.

Sometimes I kit them, sometimes I just replace the carbs. Start with a cleaning and a kit. If you have to replace the carb, shop til you drop for the best price.

We all want low prices on these small engine devices and we are typically getting more and plastic and less and less durability, imo.

 

[emmy71]

Lots of good advice. I will check out the carb good this weekend and update.

Thanks,
Terry

 

[emmy71]

I managed to have some success today with the lawn mower. I believe I had multiple problems and have most of them fixed. The fuel line was old and cracked so I replaced it. I believe the float was hanging up some in the up position so I imagine that the carb wasn't getting a steady supply of fuel. I cleaned that and the rest of the carb with the spray carb cleaner. I did not have a lot of time to spend on it so I had to give it a quick cleaning but I do plan to disassemble and clean out all the varnish. I also believe there is an intake leak so I will make a new gasket for it. It now runs really well under load. It still hunts a little with no load but not too bad. Thanks for everyones help.

Terry

 

[schmism]

some of the newer carbs are a plastic body and they warp and crack over time. when that happens they run lean and will surge (or hunt). usually a replacement plastic carb is only a few bucks.

i wish you could get an old school metal carb with manual choke and throttle.

Quick story about these new fangled versions with no choke or throttle. had a neighbor with one could NOT get it started in spring. he fought with it for over an hr. (new gas, plug etc)

i walked over, took the air cleaner off, put my hand over the intake pulled the rope twice and it coughed to life while i manually ran the choke with my palm.

after 30 sec or so it was running full bore, put the air cleaner on and he mowed started pushing around the yard....

 

[Bobby R]

Why don't you try putting high octane gasoline in it. My pressure washer did the exact same thing and someone suggested going to a higher octane fuel. This eliminated the problem. The 10% ethanol they put in regular gas is not good for small engines, and I'm told will eventually burn them up.

 

[bp fick]

duplicate

 

[bp fick]

Old thread, but....


If an engine isn't designed for octane higher than X, putting higher Y octane in is usually not worthwhile. Also, most of the ethanol gas around here, anyhow, comes in both regular and premium. Most all of it has ethanol.

 

[Deere Dude]

Why don't you try putting high octane gasoline in it. My pressure washer did the exact same thing and someone suggested going to a higher octane fuel. This eliminated the problem. The 10% ethanol they put in regular gas is not good for small engines, and I'm told will eventually burn them up.

X2. I had problems over the years with chainsaw and mowers and snowblowers, pressure washers etc. and then my brother-in-law who is a stickler for keeping that stuff running good said to put the highest octane gas with no ethanol you can find in it. Throw a little sea-foam in to help it. Everything starts on first pull almost and ruins smooth where everything used to hunt and cycle and start hard. I always used to go to regular unleaded with ethanol that I would use for the car because it was easy and cheaper. Not any more. A few gallons of premium gas lasts a long time using it on those type of engines anyway. :thumbsup: