quick question for small engine guys

[DanMcG]

I just replaced both ignition modules on my 23 hp kohler sv820 which fixed the skipping/ dyeing but now it starts hard and backfires out the exhaust when I put a load on it. (mower)
Kohler says the air gap should be 0.011-0.013 so I used a 0.012 business card. I'll be checking the gaps again tomorrow, but would I want a smaller gap or larger to fix the issue?
Oh and I'll get real gauges next time.
Thanks

 

[Blue Ox]

My first guess would be a lean condition. But I'm a diesel mechanic, so maybe get a second opinion.

 

[AuroraGirl]

I just replaced both ignition modules on my 23 hp kohler sv820 which fixed the skipping/ dyeing but now it starts hard and backfires out the exhaust when I put a load on it. (mower)
Kohler says the air gap should be 0.011-0.013 so I used a 0.012 business card. I'll be checking the gaps again tomorrow, but would I want a smaller gap or larger to fix the issue?
Oh and I'll get real gauges next time.
Thanks

id start with real feeler gauges. i dont have a machine that i worked on yet with air gap because it goes off the camshaft on mine, but i know if its older, you may want to use a slight abrasive like stock paper or fine fine sand paper, clean the contact and the magnets, so no rust, clean off with alcohol, then set your gap. could make it have incomplete spark, which should be more like rich than lean. your plugs look hot?
otherwise, exhaust backfiring sounds like your valves out of adjustment. your exhaust and intake should have a pre-determined overlap and if no one touched it, it should be OK but wear over time can necessitate adjustment OR if someone played with it. have you owned this engine its whole life? valve guides on old kohlers can get gummmmmmmmed up real bad and valves have a hard time moving properly if that is the case. they sell files which ream the valve guide but idk how hard it is to access that. on a ohv it should be on the head.. right? idk how engines work
i think on a flattie like mine its on the block, which means pulling engine

 

[AuroraGirl]

Most of my small engines are wisconsin, briggs, or stihl, kawasaki, etc. My one kohler is the 20hp cast iron PIG the thing is ancestor of your engine, the courages i think came in a opposed twin which would be the OHV variant like mine. yours is a v twin, yes?

Check your debris screen, check your air filter, if your engine ran badly check the plugs!

I also know kohler is very sensitive to plug wires. do you have new ones or can you check resistance? Old kohlers need solid wire wires, not sure when they started to like modern wires

 

[Rusty Nail]

Bad/ incorrect spark plug (heat range)?

 

[wanderinthru]

Generally when lean they want to pop back through the carb, through the exhaust cold be rich. Which could be caused by lack of or weak fire. Your gaping spark plugs? Also are you replacing plugs and wires? If not, do there is a reason the modules went bad.

 

[DanMcG]

The wires come attached to the new modules and the plugs are also new. It never backfired in the 7 years I've owned it , that is until I replaced the coils so I don't think it the carb.

 

[AuroraGirl]

did you verify plugs to heat range and gap? .040 is a common spark plug gap i believe but some do call for different gaps, and are they knew koils or coils from CHINA?

Krohler knows how to make ignition modules for hteir engines, for some reason others dont. maybe its a patent thing? Idk

 

[AuroraGirl]

did you verify plugs to heat range and gap? .040 is a common spark plug gap i believe but some do call for different gaps, and are they knew koils or coils from CHINA?

Krohler knows how to make ignition modules for hteir engines, for some reason others dont. maybe its a patent thing? Idk

beings you put new coils on, too, if you messed with air gap or had fly wheel off, and its now has new parts elsewhere assuming you gapped and got the right plugs you should definitely get another feeler gauge. often time a new coil or points will come with a card that is the air gap thickness if you dont have a feeler gauge set. get one, btw. they are helpful

if you had points id say use .020 but you dont i dont think

 

[wanderinthru]

This thing has points?

 

[DanMcG]

no, no points

 

[wanderinthru]

no, no points

Didn't think so. I'd say check clearance on the rocker arms, be sure the valves aren't sticky. Check spark with new plugs and wire, modules. Might even try another set of plugs, they can be weird and not fire under pressure?? Is there any chance you got some bad gas?

 

[DanMcG]

Thanks everyone, I think I'll just start over tomorrow and see what happens, reset gaps, check carb etc. I really can't find anything on the air gap effecting the spark.

 

[austinado16]

Your air gap is fine. It has hydraulic lifters, so valve adjustment isn't your issue unless the studs that hold the rocker arms have come loose in the head, which is not uncommon. The Kohler V-twins are also known for blowing head gaskets. The gaskets fail between the combustion chamber and the galleys to the crankcase around the hydraulic lifters. This pressurizes the crankcase and causes a number of running issues as the breather system dumps (at random intervals) the excess pressure and oil vapor, directly into the carb throat.

If you didn't replace the spark plugs, replace them with an OE plug, don't use cheap aftermarket plugs. If that doesn't cure the issue; some of these twins use a module to control both of the ignition coils. You can see if yours uses one, by looking up the parts break down on a website like www.partstree.com or www.ereplacements.com. For example; SV820-0016 build spec engines use such a module; 24-584-31S

Lastly, old fuel damages the carburetors, especially if you live in an area where ethanol blended fuel is sold. You can rule out the carburetor by pulling partial choke and if the issue goes away, and the engine makes full power, you know the carburetor is wrecked. Sometimes they can be cleaned successfully, especially if you buy a little ultrasonic cleaner. Otherwise, you'll be dropping $150-$350 for a new carburetor and base gaskets.

 

[AuroraGirl]

Your air gap is fine. It has hydraulic lifters, so valve adjustment isn't your issue unless the studs that hold the rocker arms have come loose in the head, which is not uncommon. The Kohler V-twins are also known for blowing head gaskets.

If you didn't replace the spark plugs, replace them with an OE plug, don't use cheap aftermarket plugs. If that doesn't cure the issue; some of these twins use a module to control both of the ignition coils. You can see if yours uses one, by looking up the parts break down on a website like www.partstree.com or www.ereplacements.com.

Lastly, old fuel damages the carburetors, especially if you live in an area where ethanol blended fuel is sold. You can rule out the carburetor by pulling partial choke and if the issue goes away, and the engine makes full power, you know the carburetor is wrecked. Sometimes they can be cleaned successfully, especially if you buy a little ultrasonic cleaner. Otherwise, you'll be dropping $150-$350 for a new carburetor and base gaskets.

thats a lot for a carb. mine was 20$. rip.

didnt think about head gasket, you might not have enough compression for load