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Hi Gang
Brand new here - just joined. always nice to have a place to do fixes yourself
Anyway here is my issue
I have a TroyBuilt Bronco riding mower
It has the 18.5 hp engine

I was cutting grass yesterday and noticed it started losing power.
So today here is what I had gone threw to try and fix it.
I put in new oil; cleaned plug; took off and cleaned out carb (it was already clean I noticed when I removed it) Disassembled everything from the gas tank to the place where carb mounts onto motor.
Put in new gas, checked lines for leaks.

Engine will start but not rev up. It does not smoke, skip, or anything like that - just seems to get revved up to about 1/2 speed, and won't rev no higher. When I put the throttle on high it seems just about 1/2 speed, and as I decrease the speed on the throttle the motor revs stays the same until I get to about 1/2 speed, then it decreases and as I lower it some more; then it will just dies. Never smokes, coughs, or sputters.

I have NO clue what is causing this, and like I said it ran fine while cutting the grass yesterday until I was just almost done. So this came up all of a sudden. Had never gave any indications of problems before, and I have used the mower off and on all winter.

SO what kind of ideas can you folks throw out that I might fix it easily.
I am guessing it won't be anything 'major' it's just trying to figure out where to start.

Sounds starved. Pull the plugs and "read" them. Tell us color and deposits- none , white, tan , brown? Fuel filter plugged? Fuel line plugged? Fuel tank cap breather hole open? Does throttle cable open and close the butterfly?

Checked fuel line; it is open, filter is good, cap hole is open and throttle opens and closes butterfly...
Spark plug had no deposits, but was the normal 'brown' color. No signs or white or tan.
Cleaned the plug back it 'new' shiney state on a wire brush wheel. Looks almost like new.
Re-installed and got the same results as before.

Well, In my limited work on my Intek and reading these AC engines that run at 3000 rpm have no ignition advance, but are sensitive to timing problems such as sheared fly wheel key which could retard the timing, or a loose ignition module?? Did you hit something? You did not touch the float setting like too early cutoff of incoming gas for main jets? Others will respond I am sure.

Ckoke working properly? Does it rev up if you move the governor arm when running?

SO far looks like you are the only one to respond LOL
In reply to your questions,.. negative to all them.
I was out in the wide open front yard just mowing along... happy as a clam
Yard is even smooth without any big bumps or anything.
I 'first' thought it was my drive belt as it is getting old and i figured I didn't have the 'speed' I was used to because of that. Then I noticed the engine was actually running slower and didn't rev up like it should of been.
I can't figure why it'd just all of a sudden only rev up to about 1/2 way without any prior problems.??

When it appears to be running half throttle what position is the throttle butterfly in. I want to know if it is the full wide open position just like it would be if the throttle was at the fast position, but the engine not running.

ILENGINE said:

When it appears to be running half throttle what position is the throttle butterfly in. I want to know if it is the full wide open position just like it would be if the throttle was at the fast position, but the engine not running.

Click to expand...

I'll have to take it off and look at that - didn't think to look at that.
When I had the throttle linkage and could just move the govenor arm by hand it did rev up... I could pull it as far as possible, and it seemed it 'over-rev' - (run faster that it does normally when throttle is wide open)

I believe that eliminates what I was thinking. Maybe something to do with the governor spring or governor arm possibly.

Just checking but is the choke plate all the way open.

yeah - it appears to be working properly...
closes all the way when I choke it; and opens fully when I don't
hhuummm :confused2: :mur:

well I did everything we talked about - everything 'looks' perfect.
Now it'll won't 'kick in' to start. Motor turns fine, but it just never 'hits'...
Have no clue about that either.

I know it'll flood when you try and start it with the choke on,... tried it that way,... turned it until it cleared up;
then let it sat and tried again later when it wasn't flooded.
Motors turns free; just won't ever hit or try to fire. Checked plug again, etc

Is there any way to get a compression check on it. I am starting to think there is more going on them just the run at half throttle. More like something leading to more of a serious issue.

wouldn't know how to do a compression check - or who to get to do one - any suggestions?
We've been tinkering on it today some more. Double checking what I did the other days for the most part.
Dad helped me look at it and he was left scratching his head too. :smiley_aafz:

Remove the muffler and try again.
There is a lot of wildlife that mistake a ride on muffler as a wildlife hilton ( not paris type hilton, bed & breakfast type Hilton ).
Bad thing is they did not read the manual and so die in there and partially block the exhaust thus choke your motor.
I have had this problem many times, Bugs die but stay put for a while then eventually fall off, get caught up some where and partially block off the exhaust.
Most common on blue smokes but have found some big lizards cooked a bit better than medium rare blocking off the outlet.

OK I'll check...
but the mower is kept in a garage and had worked for over an hour before this started...
But at this point I'm open to all suggestions... :wink:

Also take a picture of the throttle set up far enough back to show all of the controls & springs.
I am starting to think a spring may have dropped off allowing the govenor to work too well and keep the throttle closed down further than it should be.
Look up your mower on partstree.com and check that all the springs & linkages shown are still on your mower

The compression check I do on my Intek is like one done on an auto engine. Get a cheap compression gauge, even one with the rubber (universal) cone. I open the throttle while cranking. No magic.

bertsmobile1 said:

Also take a picture of the throttle set up far enough back to show all of the controls & springs.
I am starting to think a spring may have dropped off allowing the govenor to work too well and keep the throttle closed down further than it should be.
Look up your mower on partstree.com and check that all the springs & linkages shown are still on your mower

Click to expand...

I'm not sure what the spring for the govenor is good for.
(I think it's the govenor)
The spring is hooked into the arm attached to the block,.. and also attached to the toggle on the rod that attaches to the carb.
SO I can't see where it has any effect because it seems to be pulling against itself. Of course this is the way it's always been

Maybe pics will show what I mean..??
The image #0837 shows the whole length of the rod and spring
Image 0838 is a top down view where the rod attaches to the carb. and also you can see the spring right next to the rod.
Image #0839 shows the other end where the rod goes, and the arm it attaches to. You can also see the spring attached to the rod.
The rod and spring move as one unit... so I can't see where the spring does anything

Street_Rod_Guy said:

wouldn't know how to do a compression check - or who to get to do one - any suggestions?
We've been tinkering on it today some more. Double checking what I did the other days for the most part.
Dad helped me look at it and he was left scratching his head too. :smiley_aafz:

Click to expand...

So I take it that it's not starting up now?
You should be able to get a compression tester at most auto part stores. Just make sure you tell them your using it for a small engine. I like the screw in type myself.

Ok it goes like this.
When you pull the throttle fully open, the throttle wire pulls on that big spring on the bottom which pulls the governor arm ( the bit that come out of the engine ).
The top of the govenor arm is connected to the throttle linkage which goes to the throttle butterfly at the carb.
When the engine is not running , pulling the throttle on fully should move the throttle link far enough to make the butterfly open and rest against the stop which in your photo is not happening.
So the metal ( not the plastic ) arm on the carb should be as far counter clockwise as it can go. This is wide open.
The tiny spring over the throttle linkage that looks like it is pulling against itself is there to smooth out the movements of this arm.
If you push & pull the arm you will see a tiny amount of stretch in this spring it is just a damper

When the engine is running the governor pulls on the throttle rod which will close down the throttle butterfly and make the engine go slow.
So I will guess that the Govenor arm is in the wrong position, or the govenor spring is in the wrong place.

Now I did notice that you have buffed the magnets on the fly wheel.
This is a no no as you can affect the strength of the magnets by doing this carelessly.
If you want to remove the rust then use a rubbing block with some wet , wet & dry paper.
Now when you did this that will have changed the air gap and the air gap controls the spark timing so it will have to be reset.

To take things any further we need to know the engine details which should be stamped ino the engine cowel near the spark plug.

Thanks for the informative reply.
Couple clarifications....
Sorry if I implied somewhere the engine wasn't running or wouldn't start. It is.
In the photo I took the throttle wasn't up fully (in the choke position) so as it would make the butterfly open on the choke.

The govenor arm nor spring has every been off the back mounting point. It was just disconnected from the butterfly on the carb. The photo shows the throttle at the slow position here (maybe this is where you meant for me to take the photo from with the throttle in the full fast position - I wasn't sure where you wanted me to take the picture 'from' or what you wanted to see; so I just took a few pictures and started from there). There was only one place to put the spring and link when I put it back on (one small hole and one bigger one). Also as a 'fail safe' I took picks of everything before I disassembled anything to avoid putting anything in the wrong spot upon replacement; and this is where they were originally.

As far as buffing we did use a piece of sandpaper on a air grinder. Dad is very familiar with how magnets and timing; so we doubled checked it after we cleaned it to make sure the gap was correct. Since It's only running 1/2 speed right now; I can't say for sure the timing is off; but running at the speed it is now; it sin't skipping or sputtering or anything. Appreciate you notcing and mentioning about that because when we get it running wide open if it seems out of time, we can adjust it.

I want to thank you for the wealth of info and the time it took to write it and carefully look over the pics. You seem very knowledgeable and I'm sure many folks here could count on you to help them out with issues. I'll tinker a bit more (really not sure what else to do I hadn't done. But I'll tinker a bit more - raining here now so I can't use it anyway. LOL.

Well I finally gave up on it and took it to a small engine mechanic.
I looked it over and he said everything externally was as it should be.
They just called and said the cam was bad. It'd cost $200 to fix it.
The mower is 10 years old. I know Troybuilt makes a great product; so now I am wondering if I should fix it; or buy a new mower...??
Just curious what else may be coming down the road....

Street_Rod_Guy said:

Well I finally gave up on it and took it to a small engine mechanic.
I looked it over and he said everything externally was as it should be.
They just called and said the cam was bad. It'd cost $200 to fix it.
The mower is 10 years old. I know Troybuilt makes a great product; so now I am wondering if I should fix it; or buy a new mower...??
Just curious what else may be coming down the road....

Click to expand...

And that is what I was suspecting was wrong, but didn't have enough info to determine.

The guy had a brand new 21 HP motor on hand and offered it to me for $600 + tax.
It's going to cost close to $250 to fix mine; or I can buy the new motor and install it myself for just an extra $400. To me that sounds like the smart route to take. The motor also comes with a two year warranty.

Street_Rod_Guy said:

Hi Gang
Brand new here - just joined. always nice to have a place to do fixes yourself
Anyway here is my issue
I have a TroyBuilt Bronco riding mower
It has the 18.5 hp engine

I was cutting grass yesterday and noticed it started losing power.
So today here is what I had gone threw to try and fix it.
I put in new oil; cleaned plug; took off and cleaned out carb (it was already clean I noticed when I removed it) Disassembled everything from the gas tank to the place where carb mounts onto motor.
Put in new gas, checked lines for leaks.

Engine will start but not rev up. It does not smoke, skip, or anything like that - just seems to get revved up to about 1/2 speed, and won't rev no higher. When I put the throttle on high it seems just about 1/2 speed, and as I decrease the speed on the throttle the motor revs stays the same until I get to about 1/2 speed, then it decreases and as I lower it some more; then it will just dies. Never smokes, coughs, or sputters.

I have NO clue what is causing this, and like I said it ran fine while cutting the grass yesterday until I was just almost done. So this came up all of a sudden. Had never gave any indications of problems before, and I have used the mower off and on all winter.

SO what kind of ideas can you folks throw out that I might fix it easily.
I am guessing it won't be anything 'major' it's just trying to figure out where to start.

Click to expand...

This is hard to explain...when your foot brake is released is it coming all the way back because this is what determines the tension on the drive belt to make it go faster or slow it down. What can happen is dirt and grass can build up on the of the base of the pedal arm where it contacts with the cross member of the chasis. This is what happened on my Craftsman and it took me a while to figure it out.