OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Briggs 35 Classic over revving

Hi. I have had a look at a couple of other threads on this problem and have noticed what seems to be a subtle difference in the govenor link. Some of them seem to have a different length from the looped spring attacment back to the governor vane. In my mind I would think this would have an effect on engine speed? By fiddling without distoring the spring in any way because they are new, I could only get the idle to 2900rpm.

Any suggestions?

This mower was a see if you can sort it by a mate but if no go no loss type of arrangement. It had a snapped intake manifold, no govenor or idle spring, govenor link or muffler. The fuel tank was zip tied into position and any carby linkages were operated by a piece of tie wire. It actually deserved a picture but I missed out.

Anyway it does run but very high rpm. I cleaned the carb and tank, cleaned the air filter, cleaned under the top cover and govenor vane.



Would this hole lower the idle?


This end of the link seems shorter than some of the links in other pictures


The idle spring which I removed for the pictures


I had the idle spring between the link loop and this tab


I have realised from the pictures I need to turn the fitted spring around. At this point I doubt that it would rectify the engine speed issue though.

Here is a pic of the linkages from a running (albeit scrap) motor I have

Can you post the model, type and code please aldot?

It is a governed idle engine, so it has no idle speed screw. The small governor spring essentially controls the idle speed, and the larger spring controls the speed from there on up to maximum speed. Maximum speed is normally 3000 rpm for vertical crankshaft engines, but may be 3500 for horizontal crankshaft engines. The reason for this difference mainly relates to US blade-tip speed restrictions in the US. Idle speed is usually 1750 rpm for Briggs small vertical crankshaft engines.

The engine speed in air vane governed engines such as that is determined by a tug of war between the air vane and the governor spring. The faster the engine runs, the harder the air vane tries to close the throttle. The more you stretch the governor spring (by moving the speed control toward high speed) the harder the spring tries to open the throttle. The vane and spring find an equilibrium speed that is almost unaffected by the load on the engine. Note that the speed depends only on the governor spring's characteristics, its amount of stretch set by the speed control lever, and the governor vane's characteristics. The speed is not affected by the length of the governor wire link. Essentially, the design engineer puts the vane, the carburetor's throttle butterfly, and the speed control lever where he must, then designs the governor spring, and the location of the loop in the governor wire link, to give the required speed range.

The idle speed is determined by the air vane and the idle speed spring, and is set by bending the stationary tab to the right of your thumb in the last picture. The main governor spring should be more or less relaxed at idle, so it should not have much influence on the idle speed.

To find out why your idle speed is way too high, you might try removing the idle spring and checking the idle speed. It should be approximately zero. If the engine still idles briskly without the idle spring, you have either the wrong main governor spring, or a mechanical foul up in the governor linkage. It might be some jamming in the vane, the link, or the link's pivots at the vane and the throttle butterfly. However my first guess would be that you have the main governor spring installed backwards, so the coiled part is hitting the throttle butterfly bell crank, instead of the straight end of the spring sliding easily over it. I'd like to pretend that I got this idea just because I'm intensely familiar with that governor, but in reality I took a look at the diagram in the Briggs manual:




Post-edit: Looks as if we both figured out the same solution at the same time, Aldo. Just check if the coiled part of the spring is hitting the butterfly bell crank.

Aldot,

If you put the idle spring back as shown in Grumpy's post it will correct the issue that you have and all you will have to do is bend the metal lug to adjust the idle speed which is the one closest to the engine. To adjust the high rmp you do the same where the spring is on.

Hi Aldot, Apart from the backward spring,it looks to me like the metal tab where the main governor spring is hooked on is bent too far out, thus causing a little more tension on the spring than you'd like in the idle position. Bend the tab back towards the carby and this should reduce your idle rpm, although it will also bring down your top end rpm. It then becomes a balancing act; pull it out for higher rpm's, push it back to reduce rpm til you find the happy medium.