5HP Briggs IC plus hunting

[lee]

My small pressure washer "hunts" when unloaded and in bypass mode causing the pump pressure to go up and down. I decided to take a look at it today. So I pulled the pump off the engine. The little 5 HP Briggs L head stills hunts at high speed. I figured the idle circuit was blocked causing it to run lean under no load. So I backed it down to idle and it idles just fine. This engine was made in the 90's with the plastic gas tank on top and has a carb with a float bowl and idle adjustment screw. I turned the idle screw in and it started to surge then I backed it out until it started to run rich, then set it in the sweet spot in between lean and rich. So it idles fine and runs fine under load with the pump on and the wand trigger pulled. I installed a new J19LM plug just for the hell of it and of course it made no difference. While watching the governor linkage move back and forth while the engine hunted I put my finger on it to stop its movement and the engine stopped hunting and ran fine. The spring that takes up the slack in the linkage to the carb is installed so it's not that. So the engine starts on the first pull, idles fine and runs fine under full load but hunts at high speed unless you stop the gov linkage from moving. What's the problem? Worn out governor? I've never seen this before.

[38racing]

sometimes a static adjustment of the governor will fix that.

[lee]

That was a good idea. Unfortunately the original adjustment was good so readjusting it didn't move the adjustment if that makes sense. I did notice there are 8 holes for the spring to go in on the gov arm 1 being the lowest and 8 the highest position on the arm. It's in hole 5 now. Would moving the spring to a higher hole help with the hunting problem? What's the purpose of having 8 holes on the gov arm?

[bgsengine]

That was a good idea. Unfortunately the original adjustment was good so readjusting it didn't move the adjustment if that makes sense. I did notice there are 8 holes for the spring to go in on the gov arm 1 being the lowest and 8 the highest position on the arm. It's in hole 5 now. Would moving the spring to a higher hole help with the hunting problem? What's the purpose of having 8 holes on the gov arm?

It could maybe help - On some, the holes are for a slight change in governed RPM, on others it is a sensitivity adjustment, if the length of the spring is changed, the RPM range changes, so if the holes are in a straight line you'll probably boost (or drop) your RPM a little bit - if they are on more of a curvature, then its for sensitivity (because the holes are all same distance from the other end of the spring) so moving the spring closer to the governor shaft would tend to decrease sensitivity (if I remember right) - Also, you could go ahead and move the spring to a different hole , but you will want to have a tachometer handy to re-set the top no load RPM for correct operation of the equipment.

[KE4AVB]

With being a unit form the 90's the governor spring could just have lost some of its spring rate (weaken) and just needs replacing.

Also I am thinking you probably have a carburetor with the main jet in the fuel bowl bolt. If so then it need a little extra cleaning and maybe even going one size larger. I have seen where the brass would tarnish and reduce the jet size slightly. Some engine after some wear needs a tad richer mix in the off full load mixture. I had a Powermate generator earlier would hunt but ran fine holding the throttle. Resized main jet it ran fine but I went ahead order a new governor spring and new jet. Even after new governor spring and new jet still hunted. Finally resized the new jet and resolved the problem. I ended right back where I resized the old jet to.

[lee]

It does have the main jet in the bowl nut. I cleaned the carb, readjusted the idle mix screw, but it still hunts only unloaded at 3/4 to full throttle. I tried gradually giving it some choke to see if it would stop hunting, nope, it hunted until it choked down. Then I pulled the air filter off and put my little propane torch up to the carb inlet to give it a little propane to richen up the mix and see if that might stop it from hunting, nope. I backed it down to idle and waved the propane torch in front of the carb and it killed it. So I'm not sure if drilling the main will help this poor old Briggs or not. Today I pressure washed with it for almost an hour. Full throttle, 3600 rpm on the tach, fully loaded it never misses a beat. Let off on the wand trigger, goes into bypass, starts hunting. The fact that it runs great at idle and at full load eliminates a lot of things that could be wrong. Is it possible that it's hunting due to being too rich when it's unloaded at full throttle? I've never seen that before on a fixed jet carb like this. I have seen it on engines with an adjustable main jet if you back the jet out too far you can make it hunt due to being too rich. The carb isn't flooding and it idles fine. I've seen a leaking needle valve cause the carb to flood and it would run full throttle but would smoke and choke down and die at idle.

[KE4AVB]

Well Lee I look things this way. Anything is possible even when someone says can't be. I was told recently that a fail memory chip could not possibly mess up my operating system on the hard drive but it did just for spite. If you have a size smaller try it, the worst that could happen would be it make it worse.