QuestionI have a 7 hp Excuse off an old Atlas, an H70 engine. It sat for years in my shed after I bought a newer electric start blower. I got it running after only cleaning out the bowl and bottom threaded nut and needle but it wouldn't accelerate correctly. Then I started to clean with compressed air and carb cleaner off the engine without disassembly. I accidently blew out the float seat and lost it, put in a new one with it's needle and now it only runs when choked, and kills on throttle advance. I'm about ready to stick it back in the shed. Any clues?
Bob
AnswerBob
This is probably the most common problem you are likely to encounter. The cause is very often the same - lack of maintenance.
Note that the assumption here is that it cranks - the crankshaft and blade rotates in a normal manner but the engine never catches. Some larger (Briggs and Stratton) engines may have a low-oil cutoff switch which will stop the engine if the oil level is inadequate. However, this is not likely on a push mower.
In the case of a recoil starter, you are able to pull on the cord and the crankshaft with the blade rotates and it feels normal but the engine does not start. If it feels like nothing is engaging, then the starter mechanism or clutch may be broken. Of course, if the cord breaks, then the problem is obvious!
In the case of an electric starter, the engine cranks but never catches. If there is no response to the button or key, then the outlet may not be live, the battery may be weak or dead, or there could be a bad connection or bad starter motor. If the motor spins but doesn't engage the engine, the overrunning clutch or gear could be broken.
If you are unable to pull the cord (or the auxiliary starter on one with electric start), there may be a clump of grass stuck between the blade and the deck or there could be serious internal damage, especially if you just encountered an immovable object. However, you didn't forget to engage the dead-man bar, did you? On most inexpensive mowers this safety interlock is needed to both enable the ignition system and release the blade brake.
Most of the time, the possible causes and solutions will be similar to those where the engine doesn't start at all. So, see the following sections for more information. However, here are some specific issues dealing with engines that do start eventually and then run fine:
Cockpit error: If you have a user manual, read it! The starting procedure for all engines is not the same. Make sure you are following the recommended starting procedure. This may not always be best but it is a starting point (no pun....).
Number of priming cycles: The instructions on priming are often optimistic. In colder weather, twice as many presses of the primer may be necessary. However, overpriming and flooding is also possible. Don't overdo it.
Condition of gasoline: Old or contaminated gas will make any engine harder to start. If the problem is with an engine using last year's gas, drain the old gas completely and dry out the residue in the fuel tank if possible. If debris or water is found in the old gas, the carburetor may need to be drained and cleaned as well. Then add fresh gas (not from the batch sitting in the can since last year!). In cold weather, the water can turn to ice inside the carburetor float bowl casusing all sorts of problems including flooding of the engine.
First start of the season: If no maintenance was done at the end of the last mowing (or whatever) season, the first time the engine is started may be tough. However, this may be a one-time problem. Hopefully, maybe. :) Even if all the recommended maintenance was done, the first start may not be perfect. And, for float-type carburetors, after filling the fuel tank, wait a minute or so for the gasoline to fill the float bowl before pulling the cord!
Fuel
Obviously, the engine won't run without gas!
Is there some in the fuel tank? If it is near the bottom, add enough so that there is no doubt about there being enough to reach the outlet pipe regardless of any slant on which the lawn mower is located.
Make sure any shutoff valve is open.
Check for a clogged fuel filter, if there is one. There may be a sediment catching screen at the bottom of the tank as well.
If your engine uses a primer bulb, does it feel like it is doing something? There is a distinctly different feel when it is actually squirting a little gas into the intake pipe. Check that the rubber hasn't deteriorated but if many pushes still doesn't do anything (and you're sure there is gas in the tank and the engine hasn't flooded from TOO MUCH gas), the carburetor and/or fuel line may need cleaning.
If you are using gas from last season, discard it and start fresh. While old gas will usually work in an engine in good condition, this is not always the case, especially with one that has seen better days. The more volatile fractions evaporate leaving behind higher flash point gas. Why add another unknown factor to the puzzle?
There may be water in the gas. If the carburetor has a drain plug, operate it to rid it of the bottom layer which would have the water. If there is no drain, repeated pulling on the starter cord should eventually clear any reasonable amount of water.
Once you have exhausted these obvious problems, determine if gas is reaching the cylinder as follows: Perform the normal starting sequence and then, assuming it shows no signs of wanting to start, immediately remove the spark plug. If fuel is reaching the cylinder, the spark plug should be damp with gas and there should be a very distinct odor of gas from the spark plug hole. If there is none, then there could still be a blockage in the fuel line or the carburetor may need cleaning.
A flooded engine, most likely due to extended unsuccessful attempts at starting or a defective carburetor (float valve stuck open or gas-logged float) will result in inability to start as well and a distinct odor of gas. You might find raw gas coming our of various orifices - air filter as well as exhaust. (Note that in severe cases, enough gas gets mixed in with the oil to significantly increase the level in the crankcase and reduce the effectiveness of the oil. This will require an oil change.
Air
The optimal air:fuel ratio is around 14:1. This must be lower for a cold engine and thus a choke plate or other means to increase the richness of the mixture is usually provided. A choke plate restricts air intake forcing more gas to be sucked into the cylinder. A primer bulb effectively squirts gas into the intake pipe to augment the normal carburetor action. Some carburetors have no choke and no primer but incorporate a small gas reservoir which fills when the engine is off and provides some extra when starting.
To much air results in a mixture that is too lean, burns too quickly, and can result in engine damage over extended periods of operation.
Check that any choke is not stuck in the open position and not doing its job.
The carburetor may need adjustment or cleaning.
Too little air results in a mixture that is too rich - there will be loss of power and possibly black smoke from the exhaust. This could be due to several factors:
Check the air filter. For testing, it can usually be removed to see if the engine will start. However, do not run it for an extended period of time without a properly functioning air filter in place. Some are designed to be washed and reused while others must have their elements replaced.
Check that any choke is not stuck closed. Though needed to start cold, if the choke remains closed, the engine will not restart and will quickly stop (truly choke!) due to an overly rich mixture.
A defective carburetor may also cause the mixture to be too rich or too lean.
