Engine not running right

[Justin67]

I just put a kohler 6.5hp engine on my go kart. I changed the oil in it. When I run it it is fine idleing but once I give it gas it kind of revs up and down, like surging. I replaced the carb and it still does it. Too much oil? I looked up how much oil to put in it and it said 0.6L. So I did so but it seem like a lot. The oil is in the threads where the oil dipstick is. Thanks!

 

[Smerft85]

Are you engaging the governor? If you are maxing rpms and governor is still installed I'd bet on it.

 

[Justin67]

The governer is still on. Im not sure how it works though and what your saying.

 

[Smerft85]

The governor is a rev limiter, if you are holding it at full throttle with no load you are likely engaging that limiter, a car will do the same thing if you floor it in neutral.

In other words, if your engine is "loping" at full throttle it is functioning properly, it keeps you from blowing it up.

 

[Justin67]

So if it is under load it shouldnt do that?

 

[Smerft85]

If you put it under load it will have the ability of raising the rpms gradually, so for example, mine has had the governor removed, so it will float valves at higher rpm instead of limiting rpm, it will gain momentum to the 40 m.p.h. range then float the valves, if I still had the governor installed it would limit my rpms around the 30 m.p.h. range and not float valves thus protecting the engine from an over rev and failure. Putting load on it will give it more time before the governor limits engine speed, so yes, in a way, it wont do that once its installed and has load on it, until you hit the max rpm the governor allows, usually around 3600 rpm.

 

[anickode]

The governor is a rev limiter, if you are holding it at full throttle with no load you are likely engaging that limiter, a car will do the same thing if you floor it in neutral.

In other words, if your engine is "loping" at full throttle it is functioning properly, it keeps you from blowing it up.

A small engine shouldn't do that. It's a mechanical governor meant to maintain a constant rpm, whether the engine is loaded or not. That is its primary function. Secondary to that is to keep the engine from blowing up.

The rev limiter on a car engine is fundamentally different in its function, and is ONLY intended to keep the engine from blowing up.

On a small engine, as set up from the factory, setting the throttle or pushing the gas pedal in the case of a go kart is basically telling the engine how fast you want it to turn. It adjusts the throttle accordingly. When it hits the designated speed, the governor closes off the throttle. If you drive up a hill without moving the pedal, it will give you more throttle to maintain that speed, and so on.

In a car, pedal position dictates throttle position directly.
That's why you can put the pedal halfway down and you'll eventually end up going 70mph. If you go up a hill, you slow down unless YOU apply more throttle.

Small engine governors are more of a mechanical cruise control, that does also limit the top speed. But it SHOULD be able to hold a steady 3600 rpm with or without a load on it. "Looping" is generally referred to as "hunting" or "surging" and is usually indicative of another issue.

Too much oil in the case could conceivably interfere with the function of the flyweights in the governor, but these engines are often filled right to the threads. If there is a crosshatch section on the dipstick, try draining some oil until it's at the top of the marks. Usually these engines are designed so you can't overfill them as long as they're sitting flat though, and the dipstick only indicates a dangerously low condition.

 

[Justin67]

Tommorow I will take a video of it, post it, and send the link here as it is dark now here in Ottawa.
I just ran it with load(moving) and it did the same thing. I have a torque converter on it so it should have good acceleration and speed but it is struggling to get moving because of the "surging". the pulley on the crankshaft can't slide in and out because it doesn't have enough rpm's.
Ive replaced the carb, tested it with load, and checked the oil and still havent being able to find the problem. Any more ideas?

 

[Brianator]

Is there a second (main) spring that's connected between the throttle control and governor arm itself? That arm should have multiple holes for that main spring, try a different hole and see what happens but in all actuality it's not healthy to free rev a engine without a load on it, that load absorbs/equalizes harmonic imbalance that's inherent in internal combustion engines. Sometimes a improper fuel/air mixture can cause that also, more so at idle but it's happened to me with a 8hp Tecumseh in a snowblower at WOT.

Just for the record I have a GX160 that doesn't surge at idle or free revving at WOT, just food for thought.

 

[Justin67]

Here's what my governer is set at. It came off a pressure washer if that changes anything.

 

[Brianator]

Right where I circled looks to be at least one more adjustment hole. Theres also the screw on the throttle control lever (with the spring behind it), sometimes that needs to be adjusted to smooth out surging. What it came off of makes no difference in how its runs, Kohler are great engines too btw they're very durable. Fact of the matter is don't worry about surging unless it's doing it idle (annoying but easily overcome) or while ripping the kart around (we'll figure that out at that time).

 

[anickode]

Tommorow I will take a video of it, post it, and send the link here as it is dark now here in Ottawa.
I just ran it with load(moving) and it did the same thing. I have a torque converter on it so it should have good acceleration and speed but it is struggling to get moving because of the "surging". the pulley on the crankshaft can't slide in and out because it doesn't have enough rpm's.
Ive replaced the carb, tested it with load, and checked the oil and still havent being able to find the problem. Any more ideas?

Just out of curiosity, check your coil to flywheel clearance.

Also check the valve clearance.

$5 set of feeler gauges from the auto parts store will do both, if you don't have a set already.

 

[Brianator]

Shoot I'm sorry I missed the part of it surging under load too! May need to fully reset the governor and get new springs (they do wear out over time) and as I mentioned before sometimes a poor fuel/air mixture can cause it also.

 

[Justin67]

What can I do about the fuel/air mixture?

 

[Brianator]

I'd honestly leave that until last it may not be the issue. Heres what I would do, testing after each thing:

- reset governor. Unbolt tank to lift it out of the way if needed (you shouldn't have to remove fuel line), loosen nut on arm, turn governor rod (in block) clockwise to WOT and while holding it move the governor arm to WOT then snug nut back down.

- try different positions of main spring on governor arm.

- replace springs (they wear out)

Now onto fuel/air mixture:

- while counting, turn mixture screw (not black plastic idle screw) in until lightly seated and take note of how many turns. 1-1/2 out is a good starting point, adjust as necessary and see if surging stops, take notes of how many turns at that point. It may be necessary to raise the idle while adjusting then bringing it back down after.

- remove air filter temporarily to see if problem gets better or worse, that should lead you in the right direction if so.

- play with the choke and see if problem gets better or worse, most engines will still run on half choke.

- next step is replacing main jets but let's hope it doesn't get to that point.

*Please note what Anickode has said also!* Properly set valve lash is important! As is coil and spark plug gap, intermittent spark could cause surging...

You also could be having a fuel delivery issue and what is causing your issue, there should be a fuel strainer that's part of the fuel outlet on the tank and it could be partially clogged but more importantly make sure you have at least a half a tank of known good fuel.

That's all this tired fella can think of atm but that should keep you busy for a bit! Lol

 

[anickode]

Another potential issue is missing or damaged gaskets between the carb and spacer, or between the spacer and block. Air leaking in can cause surging as well.

The old Onan engines are notorious for intake leaks, and it often causes surging, and always a lean condition. Run the engine at WOT for a minute and hit the kill switch. Check the spark plug color. If it's white, that indicates a lean condition which could indicate a leak between the carb and engine.

As Brianator mentioned, pulling the choke partway can also help indicate a lean condition and air leak if it smooths out.

 

[Justin67]

Heres the link for the video.

Let me know if it doesn't work.
When I use about 1/2 choke it seems to work fine I think. What could this mean? I replaced the three gaskets that came with my carburetor kit.

I’m thinking to check the valves last as I may have to replace gasket. I don’t want to do it if I don’t have to. If it works with half choke I’m wandering if there’s something in the fuel or fuel line.

 

[mckutzy]

Maybe... Did you look at the insulator plate carefully for any cracks??

 

[Justin67]

Soooooo.........you guys are all gonna choke up laughing!! I learned something new about small engines today. I was using the choke backwards! When I thought I had the choke off, it was on. And when it was on, I thought it was off! K, everybody laughing now?!? This is why is wouldnt increase rpm's, it had too much gas and not enough air. I appreciate everybody's imput. It taught me a lot about small engines. Glad to give you guys a good laugh, and i'm laughing too because I took the go-kart out for a nice little spin tonight and the results were phenomenal!!

 

[Brianator]

Oh ya I'm laughing, but with you! I've been there and done that! What helped me remember choke on/off was to think of fuel "on" as being in the run position, choke off (or the run position) just happens to be the same direction.

Glad you fingered it out and got out for a rip! Next step : tweak governed rpms for more power!