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Here's the problem:
After about 1-2 minutes of idling, the exhaust starts to glow red - starting at the point where the exhaust pipes enter the muffler and then proceeding to make the entire muffler and pipes red (if I let it get that far)

Here's the engine info:
2005 Kohler CV730s (CV 730-0040)

Here's what I've tried so far:
Brand new carb.
New spark plugs
Changed muffler
switched out plastic diverter inbetween the carb and the main engine (not sure what it's called)
Checked the shear pin under the flywheel. - perfect condition.
Reset the magnet parts outside the flywheel (sorry, not a technician so I can't remember what they're called)
Checked for fuel/ oil in exhaust ( a friend smelled it and didn't detect odor of either)

Other info:
I bought the tractor off an older gentleman who had used it for years. The only thing he changed recently was the carb. After he changed it, he only ran it briefly, so never noticed the muffler issue. I can't image that he ran it for years with the muffler getting that hot.

The mower starts great, idles great, runs smooth, but occasionally will have a backfire out the exhaust when shutting down.

I've exhausted my friend help, online video help, and am turning to you

I really think it still has something to do with the carb... but the only screw that we can adjust (beside the idle screw) is on top of the carb... but didn't seem to help when we adjusted it. Maybe we're adjusting incorrectly? - I've never worked with this kind of carb before (without L and H screws).

The only other thing I've seen mention online was the exhaust valve clearance, but I see no way to adjust them on this engine.

Any ideas?

this video might help

It is running extremely LEAN.. too much air, or not enough fuel.
i would remove the carburetor and thoroughly clean it (even though you replaced it, sometimes i have had to clean the CCP carbs) and replace the intake gaskets
4,3&,2 are gaskets i would replace.

If the previous owner replaced the carb with a "Will Fit CCP carb" it is not uncommon for the jets to be too small for the engine size.
There is also no adjustment for the valves on this engine since it uses Hydraulic Lifters.

Mowerlove29 said:

this video might help

Click to expand...

Watched that one. Thanks though!

Scrubcadet10 said:

It is running extremely LEAN.. too much air, or not enough fuel.
i would remove the carburetor and thoroughly clean it (even though you replaced it, sometimes i have had to clean the CCP carbs) and replace the intake gaskets
4,3&,2 are gaskets i would replace.

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If the previous owner replaced the carb with a "Will Fit CCP carb" it is not uncommon for the jets to be too small for the engine size.
There is also no adjustment for the valves on this engine since it uses Hydraulic Lifters.

Click to expand...

I was thinking there was too much air ( lean) but with all new gaskets and such couldn't figure out where it was getting in ( or how to adjust the carb). Does the horizontal screw in the picture adjust the fuel/air mixture? Didn't seem to have much affect when we turned it while running at low RPM.

Just talked to my brother and he mentioned that I should adjust the screw at high RPM. Does that sound right?

Quick & dirty test for lean running is to turn the choke on just slightly
If the muffler stops glowing red then it is a too lean problem.
Other trick is to restrict the air passing through the filter .
Things line covering 2/3 with glad wrap or a brown paper bag with a small hole in it .
Start the engine and it will probably blow some black smoke so you then cut more holes till it just stops smoking.
If the engine runs fine & muffler does not become red then you have confirmed too lean running .
There is this little grey band between just too lean but makes the muffler glow red and lean enough to cause the engine to surge .
Your engine could be in that band

bertsmobile1 said:

Quick & dirty test for lean running is to turn the choke on just slightly
If the muffler stops glowing red then it is a too lean problem.
Other trick is to restrict the air passing through the filter .
Things line covering 2/3 with glad wrap or a brown paper bag with a small hole in it .
Start the engine and it will probably blow some black smoke so you then cut more holes till it just stops smoking.
If the engine runs fine & muffler does not become red then you have confirmed too lean running .
There is this little grey band between just too lean but makes the muffler glow red and lean enough to cause the engine to surge .
Your engine could be in that band

Click to expand...

Pulling the choke more than just a little causes it to die out. Haven't tried just a small amount. I'll try that tomorrow and see. Thanks!

jpdodd said:

Pulling the choke more than just a little causes it to die out. Haven't tried just a small amount. I'll try that tomorrow and see. Thanks!

Click to expand...

Ok. So I started it up this morning. Pulling choke a little had no effect on heat. Pulling a little more causes engine to run rough.

I also noticed that when I put the air filter on, it causes the muffler to get red hot faster...I was thinking the air filter would help restrict air flow some...

jpdodd said:

I was thinking there was too much air ( lean) but with all new gaskets and such couldn't figure out where it was getting in ( or how to adjust the carb). Does the horizontal screw in the picture adjust the fuel/air mixture? Didn't seem to have much affect when we turned it while running at low RPM.

Just talked to my brother and he mentioned that I should adjust the screw at high RPM. Does that sound right?

Click to expand...

I also tried adjusting the horizontal screw on the top of the carb while at high RPM. Turned it all the way in and out with no change in engine performance...something strikes me as weird there...if that is a fuel mix adjustment...then it should cause it to run lean or rich affecting performance right?

I got a good idea that OP didn't buy the OEM carburetor since it is nearly $500 retail; PN 24 853 102-S. So it is very likely just a will fit after market that has a problem internally or is simply the wrong carburetor for that 23 hp engine.

StarTech said:

I got a good idea that OP didn't buy the OEM carburetor since it is nearly $500 retail; PN 24 853 102-S. So it is very likely just a will fit after market that has a problem internally or is simply the wrong carburetor for that 23 hp engine.

Click to expand...

Thanks. I thought the same thing which is why I bought a new carb. But it acts the same with the new one as it did with the one he put on. They are actually the same carb. Could be both are faulty..but I've bought other carbs for small engines and never had an issue.

Then your is much then mine nearly every one that I tried didn't work right.

Also I even spindles for the same CC deck from three different places and all were bad right out of the box.

StarTech said:

Then your is much then mine nearly every one that I tried didn't work right.

Also I even spindles for the same CC deck from three different places and all were bad right out of the box.

Click to expand...

So do I have to buy the OEM? Not worth it to me to buy $500 carb...

I don't have the knowledge to tell what might be wrong inside the carb....

Time to take a different direction we have now ruled out running lean
That leaves retarded timing or leaking exhaust valve
Do a leak down test on both cylinders.

bertsmobile1 said:

Time to take a different direction we have now ruled out running lean
That leaves retarded timing or leaking exhaust valve
Do a leak down test on both cylinders.

Click to expand...

From what I understand, the timing is achieved with the shear key under the flywheel. That is in perfect shape. Not sure what a leak down test is...is it similar to a compression test?

Leakdown test | Lawn Mower Forum​

or:

how to do a LEAK DOWN test on a lawnmower - YouTube​

Also I would use a spray bottle of soapy water, run engine & spray around the carb to intake gasket. If it has an air leak, it will can cause very lean condition. You will know if there is a leak when the soapy water makes the idling engine stumble or quit running. Plus the plugs could show very white burn on them.

I am going to through out something else since we don't know the history of this engine. Could it be possible that somebody has installed the wrong ignition modules on this engine. Using the spark advance timing system on a system that was designed for fixed timing CDI, which is throwing off the spark timing causing the hot exhaust symptom.

Let it run with the glowing exhaust for a little while the pull the spark plugs and take a pic of the business end and post the picture. And the spark plug number.

Sorry. Had to take a mental break from it yesterday, as I was ready to push it off a cliff. I'll get pictures of the plugs uploaded, and thoroughly clean the carb tonight.

I don't have the equipment to do a leak test. $70 was the cheapest kit I could find...hoping not to have to put a lot of money into this tractor...

The older gentleman I bought it off of, ran the mower for 12+ years. The only thing he changed was the carb, and hasn't used it to mow since he did. He wouldn't have been able to use it for that many years glowing like it is.

I just don't understand carbs well enough- especially this one that has a solenoid and accelerator...but my gut tells me this is where the problem lies. It's just weird to me that it can run so smooth and not be functioning well...

Ok, so I attached two video links above for the mower running and the glowing muffler. Which is actually better than it was before! I got to thinking about the fuel and air, and noticed bubbles in the fuel filter. I put some new clamps on the hoses, and it helped!

But, it's still getting hot ( not sure if the amount is normal or not, but way better than before when the whole muffler glowed. ) and it does backfire when turning off.

Here are the pics for the spark plugs.. one is new, one is old (that I replaced). The other ones look the same, so I didn't take pics of them...

Plugs are not overheated. Have you checked for a dead cylinder? Possible afterburning in the muffler.

So its not the fuel that I used in the race car?? So I can still run the moonshine..

Too Easy...Most Air Cooled small engines are not designed to run at Idle or with Shrouds Removed. It's not getting cooling air and is oil starved. Run it at Normal Working RPM or Blow it Up! Also, look for the hidden Rats Nest, Dirt Dauber Nest between Shroud and Head.

Go to YouTube and type in "exhaust glowing red". Many answers there. To lean, sheared flywheel key [timing], needs valve job, etc.

This might be a silly question but is there a chance there is diesel in the tank instead of gasoline?

I have a 3 cylinder Kubota gas engine that caused the inside of the muffler to glow red, It was caused by one of the coil packs being defective and not firing. This is a new grasshopper mower that was shipped from the Grasshopper factory in this condition. After it was fixed no more glow and the exhaust sounded smoother, running on all cylinders.

66vette said:

I have a 3 cylinder Kubota gas engine that caused the inside of the muffler to glow red, It was caused by one of the coil packs being defective and not firing. This is a new grasshopper mower that was shipped from the Grasshopper factory in this condition. After it was fixed no more glow and the exhaust sounded smoother, running on all cylinders.

Click to expand...

So the engine still ran without a cylinder sparking? Wouldn't it have a noticeable performance issue? This is a two cylinder..I would imagine that performance would be even worse if they weren't sparking... but could they not be sparking optimal? "Mostly working "? So that there isn't a performance issue, but not burning enough?

Mowerlove29 said:

this video might help

Click to expand...

It is running lean but put that plastic Insulator back between Carb and Cylinder. It is there for a purpose.
You may have to drill out main jet a bit. Are you keeping engine shrouds in place/

Gord Baker said:

It is running lean but put that plastic Insulator back between Carb and Cylinder. It is there for a purpose.
You may have to drill out main jet a bit. Are you keeping engine shrouds in place/

Click to expand...

I'm not sure what you mean by the plastic insulator...

jpdodd said:

So the engine still ran without a cylinder sparking? Wouldn't it have a noticeable performance issue? This is a two cylinder..I would imagine that performance would be even worse if they weren't sparking... but could they not be sparking optimal? "Mostly working "? So that there isn't a performance issue, but not burning enough?

Click to expand...

Twins like that can have a dead cylinder and not be noticeable unless under a load. The dead cylinder can dump raw gas into the muffler and ignite there causing what is called afterburning. Looking at the plugs it is not running lean and the engine is not overheated. Try running it on one cylinder then the other by pulling a plug wire. See if it won't run on one of the cylinders.

I would check the ignition timing. If it's retarded, unspent fuel might be burning late and inside the muffler.

2005 engine - valve lash adjustment. One way to test this is to observe muffler in evening. If fire coming out of end, I'd suggest checking and setting valve adjustment. (Exhaust valve opening too soon).

@enigma-2 Kohler Command engine so in this cause has hydraulic lifters and no adjustments.

check the exhaust valve clearance, on one of my engines the exhaust valve would stay slightly open allowing some of the fuel/air mixture to escape and ignite in the muffler , blew a hole in muffler and you could see flames coming out

Ok. Couldn't start with only one plug in, but once I got it running, I pulled each plug one at a time. Decrease in performance, but each plug kept it running.

Hammermechanicman said:

Twins like that can have a dead cylinder and not be noticeable unless under a load. The dead cylinder can dump raw gas into the muffler and ignite there causing what is called afterburning. Looking at the plugs it is not running lean and the engine is not overheated. Try running it on one cylinder then the other by pulling a plug wire. See if it won't run on one of the cylinders.

Click to expand...

zagato said:

check the exhaust valve clearance, on one of my engines the exhaust valve would stay slightly open allowing some of the fuel/air mixture to escape and ignite in the muffler , blew a hole in muffler and you could see flames coming out

Click to expand...

Kohler command engine with hydraulic valve lifters. No clearance to check and non adjustable.

Ok, so I was able to mow for a good 15 minutes and the glow didn't get any worse than in the video. (Mild glow where muffler meets muffler tube)Which is a huge improvement from before, where the whole muffler would glow within 2 minutes.

So, I'm hopeful at this point that fixing the air leak in the gas line has helped!

What are your opinions on running it with a mild glow? Everything seemed to work fine, but it was a colder windy day. Mid summer may be different...

Have you taken the muffler off and checked it they have a spark arrester in them and if that has malfunctioned the muffler may be partially plugged.

Caregiver5354 said:

Have you taken the muffler off and checked it they have a spark arrester in them and if that has malfunctioned the muffler may be partially plugged.

Click to expand...

He said he replaced the muffkin.

Put a new set of Champion Rc12YC plugs in it and use it for a couple hours or so running at full throttle ( no idling) then pull the plugs and check color of center insulator.
White = bad
Tan = good
Black= not so good
Will tell you how the engine is operating. Lean/rich. Too hot/too cold.

If you get in there again, look at the flywheel, there should be a part number on it. See if it is the correct one. The times that I have had a mower like this, the timing was off, usually the key. But since you bought it off someone, he may have had someone work on it that put the wrong flywheel on it.

As others have touched on, I have had the red glowing exhaust (and visible flames at night) when the shrouds were stuffed with a mouse nest, and the exhaust valve needed to be adjusted to avoid opening too early. I'm not sure which one was the most critical - I found both during my maintenance.

Thinking outside the box. I had the same issue with a briggs years ago and it was a stopped up oil screen. I took it in for warranty work and they resealed the sump gasket with permatex. The bead eventually came off and stopped it up.

Throw that E3 spark plug away & put in a matched pair of what it calls for.

jpdodd said:

So the engine still ran without a cylinder sparking? Wouldn't it have a noticeable performance issue? This is a two cylinder..I would imagine that performance would be even worse if they weren't sparking... but could they not be sparking optimal? "Mostly working "? So that there isn't a performance issue, but not burning enough?

Click to expand...

I purchased it new and it was delivered in this condition. Even though it was running on two cylinders it was still faster and more powerful than my previous grasshopper with a similar 3 cylinder engine that had 23 hp instead of the 29 hp of the new unit. The only reason I knew something was wrong was the exhaust noise it was like an echo chamber which I conveyed to grasshopper factory and my local dealer along with the red hot interior muffler. They immediately knew what was wrong and fixed it.

If none of this stuff has worked, I would get ahold of the seller and see if they perhaps still have the original carb. That can possibly be cleaned and reinstalled. Still glowing? Valve job.

I didn't see anyone else mention this, but it could be a broken valve spring, or a valve seat that has come loose (not sure if that engine uses replaceable valve seats). Good luck.

bertsmobile1 said:

Quick & dirty test for lean running is to turn the choke on just slightly
If the muffler stops glowing red then it is a too lean problem.
Other trick is to restrict the air passing through the filter .
Things line covering 2/3 with glad wrap or a brown paper bag with a small hole in it .
Start the engine and it will probably blow some black smoke so you then cut more holes till it just stops smoking.
If the engine runs fine & muffler does not become red then you have confirmed too lean running .
There is this little grey band between just too lean but makes the muffler glow red and lean enough to cause the engine to surge .
Your engine could be in that band

Click to expand...

these are good tests to tell if it is lean. If issues seems unresolved or you are getting black smoke when no glowing, then it may be a hyd vaalve issue. There have been a few service bullitins on these lifters.

IN addition, do not discount a prior report that an aftermarket fixed jet carb is not a good solution and may be the cause. The only solution to such a carb is reaming the jets by someone who can and knows how and has the knowledge of specs and has the proper two sizes and the jets are accessible.

enigma-2 said:

2005 engine - valve lash adjustment. One way to test this is to observe muffler in evening. If fire coming out of end, I'd suggest checking and setting valve adjustment. (Exhaust valve opening too soon).

Click to expand...

Off topic but I found an arcing motor run cap on my 5 ton air con compressor unit at night. Wouldn't have seen it in the daytime. Freaking Crinese capacitors. Got some American made caps now.

slomo

Fish said:

If you get in there again, look at the flywheel, there should be a part number on it. See if it is the correct one. The times that I have had a mower like this, the timing was off, usually the key. But since you bought it off someone, he may have had someone work on it that put the wrong flywheel on it.

Click to expand...

Exactly, used mowers can be interesting. I would check EVERYTHING over like on CSI. Bought a gently used Snapper Commercial pusher that the lady installed the blade upside down. She said it didn't cut properly. Best 80 bucks I ever spent LOL.

slomo

To me red mufflers are retarded/improper cam timing and or improper ignition timing mostly. Vacuum leaks and lean carb conditions need to be ruled out.

Put the choke on 3/4 the way closed. See if the red glow goes away.

slomo

Thanks for all the replies..but I found someone willing to buy it for more than I paid.

Send them the link to this thread...LOL
??

I hope you are informing the new owner of this issue.

slomo

slomo said:

I hope you are informing the new owner of this issue.

slomo

Click to expand...

Buyer: why is the muffler glowing?
Seller: that is just the catalytic converter and the glowing is normal. It meets california emissions.
Buyer: OK, thanks.
Seller: no problem bud.