My B&S 13HP engine, model # 28M707, is always on high revs, have checked throttle cable and levers and linkages next to engine but can't see problem. can you advise please

if you look at the engines code it will be model , type, code. The code is the yy/mm/dd of its production. so 990314 is 14th day of march 1999.
tho it may be yyddmm.

find the bottom carb , see where the linkage from the remote cable moves the lever on the side of the engine then disconnect the cable from the remotes ! on the bottom carb there should be a screw to adjust the tickover where the linkage meets the carb linkage , turn it in 2 turns then with water attatched to water intake on gearbox turned on start the engine , it mite be slightly high or low pending ! set at 900rpm , rev engine several times back to tickover and if ok then refit throttle cable , cable should be pushing lever against its stop and then when you select forward gear it shouldnt move till you throttle up ! when in water start engine and select forward gear and tickover should be 7 to 800rpm and idle ok if not adjust till ok !

Yes, it will be corroded. Just have to find where.
Look to remove the cable from the link arm in the motor.
Can you now set the throttle lever in fwd and rev? Does the cable moves? If Yes, it's in your engine that you have trouble. If no, disconnect cable at the throttle lever and re-check...
If it's the engine: Remove the gearhousing. If now you have movement, the gear housing is stuck ( water inside that has corroded everything, good luck)
If still no movement, check the linkage, you'll have to remove the engine block from the exhaust plate.
The best is to find a service manual to get the right way to disassemble and reassemble...

on the side of the carbs you will find the throttle linkage and on one of them there should be a screw that touches the linkage and this is where you screw in or out to adjust the tickover ! get engine running and see the linkage move and then hold the revs at 1000 rpm with your remote control box then adjust the screw so it just touches the linkage , pull back the remote lever to neuteral position and the revs should stay at 1000 rpm , then turn screw back so the rpm is at 800 rpm and the engine should then rev up and down and return to 800 rpm ! always run engine with water turned on at the hose flush attachment or in a tub of water or lake etc ! P...

I need more details to answer this with one statement, but I will give you some solutions based on my experience.

Newer lawnmowers have a dead man lever which will either shut the engine off immediately or stop the blade by the use of a clutch system. If it the dead man lever, it just needs to be released. If the engine has the blade stop, then the throttle cable would control killing the engine. If the mower is really old (>20 years) then the only way is the throttle cable.

To adjust the throttle cable:

Follow the throttle cable down to the engine, it will terminate by the carburetor. There should be a single screw where the cable attaches with a clamp that goes over the cable. Loosen this screw and you can adjust the cable forward or backward to adjust the position (ever model is different based on throttle cable and engine configuration). You can figure the direction out by pulling the lever to the slow speed/off setting and watch the motion of the cable at the carb. If the cable pulls inward then you have to move the cable assemble away from the carb. linkage. This will allow the throttle linkage to pull closed further.

If you pull the air cleaner off, you should be able to see how the throttle linkage and cable interact. There is a ground wire that connects under the linkage, which when shorted out kills the ignition system and the engine turns off. If this wire is not in place or something else is preventing the wiring from shorting out, you will not be able to kill the engine no matter how much you adjust the linkage. If the wire and switch seem to be in the correct place and the throttle linkage is working, but it still doesn't kill the engine, just short the wire out directly to a clean metal surface to verify the condition of the wire.

check throttle cable and linkages for sticking and holding the butterfly throttle plates open and try starting without giving any throttle

One possible cause for this problem is debris,sticking,or frozen linkage between the governor and the throttle butterfly. Depending on the make and model of your engine it will either be a mechanical governor that has a arm that goes down into the case or a air vane governor that is behind the recoil shroud of the engine. Move all the linkage that connects between the governor and throttle and speed lever to make sure it doesn't bind or sticks. If it does pray a little silicone or wd 40 spray on it to help reduce friction. Also on air vane governors they can become stuck from debris that inhibits it from moving make sure there is nothing in the way of the governor. If all of the linkage is working properly and you still have the issue try adjusting the the fuel mix screws and the high rev. settings on the throttle lever (if equip.).

sounds like throttle sticking check cable to throttle linkage & linkage

i think the problem is the idle\air control module if you have one take it out and clean it. the idle module works when your vehicle is idleing. A clogged throttle body or intake would cause the module to compensate for the problem by allowing air in and around the throttle body bypassing it. so i think some thing in the intake system is clogged.

You definitly have to check the cable installation/adjustment. Remove the air cleaner and with the engine off, advance the throttle to full open and then let it snap closed. The throttle plate should come completely closed. Also check your linkage to make sure that the progressive linkage is not hanging on the high steps oft the choke linkage. This could also have been affected by the cable installation.

Question, did the problem occur after the cable installation? If so, this is the area of your problem.
Bill