5HP Briggs pulsating

Cliff_Johns · May 27, 2004

I have a Dr. Trimmer that's about 8 years old or so. It has a 5HP electric start verticle shaft Briggs & Stratton engine.

The problem I'm having is that when it's idling, it pulsates, like it's getting more gas then less then more then less. When it's under load it runs great. When I disenguage the cutter, it starts pulsating again.

I pulled off the top plastic and cleaned the various springs and levers that are near the air intake, hoping that something was just sticking, but it didn't seem to make much difference.

Before I take it apart further, is this a common problem with small engines? What should I look for? I hope for some sage advice from someone so I know what I'm looking for when I start dismantleing it. My knowledge of small engines is limited, so don't worry about insulting my intellegance by stating obvious possibilities. It's quite possible that I missed the most obvious thing.

Thanks for any help you can offer,
Cliff

nobull1 · May 27, 2004

Remove air filter and start for a couple of seconds.If it runs smooth dirty/contaminated filter.This happens quite often if the motor gets flipped over.You don't want to run it long like that or have any dirt handy that could be sucked in.Easy place to start, after that it gets a little more complicated but not rocket science /forums/images/graemlins/grin.gif

Cliff_Johns · May 27, 2004

I did remove the air filter. It was still very clean (i'd replaced it last year). I tried running with the filter off, but with the same results.

Good idea though. Any others?

Cliff

nobull1 · May 27, 2004

How about some more info such as first time used this year, worked fine when put away last year,didn't run dry and remove remaining old gas etc etc etc

livincountry · May 27, 2004

I have an 18 HP B&S that has done the same thing from time to time over the years. I take mine to the dealer for spring prep and it comes back fine. He said the carb needs to be cleaned. He said today's fuel plugs them up.

Cliff_Johns · May 27, 2004

OK,
It did this last year, though not as bad. Last year it was a bit annoying, but this year the whole machine turns left and right with the force of the on-then-off pulsing unless I enguage the cutter, then it's OK. I have not used it this year yet except to start it up and try to make it stop pulsating. I use Stabil in the fuel regularly -- and left fuel in it over the winter. I figured the stabil would keep the gas from turning bad on me.

It starts OK, though the electric start won't start it. It needs a pull -- always has.

Cliff

Cliff_Johns · May 27, 2004

( He said the carb needs to be cleaned. He said today's fuel plugs them up. )

I wonder how today's fuel is different. No lead?

Can you clean a carborator by spraying gumout down it's throat while it's running, or will that blow up the engine?

Cliff

nobull1 · May 27, 2004

I think livincountry has your answer.What I find is it is best to do is run dry than remove all remaining gas from tank.It is a good idea to take the carb off and clean in the spring anyways.After you do it once it's no big deal.

Molerj · May 28, 2004

Take the bowl off & clean out the carb & all the openings with spray carb. cleaner. Spray up into the center of the carb; main jet. If their is a hole in the bolt that holds the bowl on, make sure it is clean. Sounds to me the idle circuit is plugged up a tad. Not an uncommon problem in small engines. Today's fuel is different & problems do occur when the fuel gets stale.

KENSFM · May 28, 2004

Sounds like the governor and linkage may need adjusting. Have you checked this out?
Ken /forums/images/graemlins/smile.gif

Cliff_Johns · May 28, 2004

( Sounds like the governor and linkage may need adjusting. Have you checked this out?
Ken /forums/images/graemlins/smile.gif )

Can you give me a clue as to what the governor and linkage look like and what adjustments that would be? Is it related to the long piece or stiff wire with the loop in it that appears to be controled by a oval loop on the end of a spring?
Cliff

slowzuki · May 28, 2004

I've got 2 briggs that surge like that, it is something to do with the governor. I unhooked the one on the tiller so I could do the garden. The tractor I just don't let it idle any more because the surge ends up stalling it.

For a guy who likes tinkering I sure hate little IC motors! It is probably a dry linkage, missing spring or something like that.

Ken

jlbota · May 28, 2004

Is this a fuel tank mounted carb or one that mounts on the side of the engine? It sounds like the side mount type if it vertical. On the Carb mount type it is usually one of two things. Those type of carbs use a rubber pump diaphram that sometimes get a pin hole in them and causes surging and they also have a small siphon type tube in them that clogs and can cause this.
On the side mount type it is usually a clog in the low speed siphon that feeds off the bowl. If you take this carb off and clean every little hole with carb cleaner it usually takes care of the problem.
Just make sure in either application you have fresh fuel. If it is varnish smelling...get it out of there as it will gum up everything and even ruin the rubber fuel line making it gummy feeling. An out of spec governer will cause this also but if you haven't messed with this setting I would guess its a fuel delivery problem.

Oh and wear safety glasses when spraying that carb cleaner /forums/images/graemlins/smile.gif

Cliff_Johns · May 28, 2004

( Is this a fuel tank mounted carb or one that mounts on the side of the engine? It sounds like the side mount type if it vertical. )

You are right. It is mounted against the side of the engine.

( On the side mount type it is usually a clog in the low speed siphon that feeds off the bowl. If you take this carb off and clean every little hole with carb cleaner it usually takes care of the problem.
)

I was hoping to avoid taking off the Carb. It's unlikely I'll ever get it to run again. I'm rather bad with fidly bits. You know, tiny springs and levers all of which can be installed in a variety of ways.

Oh well.

Cliff

RobertN · May 28, 2004

I have a 6hp mower that pulsates sometimes. It is mostly due to my son filling the gas tank and oil fill with water, trying "to help out Dad". Something in the carb float valve seat is messed up. The gas leaks down, through the float jet/valve,, into the cylinder, past the rings, and into the oil.

It runs aweful when the gas is not disconected. It spits icky gassy-oil up through the vent into the carb,, as well as just being icky for the bearings. The oil is thinned out, so it does not seal up the rings, causing blowby which puts pressure in the crankcase. It then blow up into the carb courtesy of the crankcase venting.

fwc · Jun 1, 2004

As previously mentioned, it sounds to me like the carb idle area is plugged or out of adjustment. I have had the similar problems after leaving gas in the engine for long time - it kind of turns to varnish and will plug up passages - Your carb may have a high speed and low (idle) speed needle valve adjustments - if so you may be able to limp by, with an slight adjustment of the idle needle valve. Or clean them out might be better - lightly screw them in (one at a time..) until they bottom out - counting the # of turns - then back them all the way out until the hole is empty. take the little plastic tube of some good carb cleaner that says will remove varnish buildup) and spray good into the hole. Put the needle valve back in - screw in all the way and back it out the number of turns you counted when you first bottomed it. Be careful (light tough) on the bottom out procedure because you could drive the needle hard into the seats and malform some parts.

Also see the following - scroll down to the troubleshooting section - it lists several possible causes. You may need to tweak the settings slightly after getting the passages clean.

Small Engine Repair faq - carb adj

Good Luck
fwc

Cliff_Johns · Jun 1, 2004

Thanks for the link fwc.
Cliff

Nasty135 · Jun 4, 2004

Cliff, When idling do you see the linkage moving at the carb? Pulsating with the engine. If so My vote is for the govenor. The govenor is located off of a rod with a long tension spring and more than likely it has gotten loose over time and slipped on the shaft (going into the block) which is attached to the rod going to a pivot point in the block... Adjust the lever on the shaft (if everything else looks correct ) one way or the other about 3/16" too see if it helps or hurts if so go the other way that should do it.. My father has a snow blower that was doing same thing that fixed it so maybe thats your trouble too, Good luck ,Mark S.