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Kohler cv15s with Nikki carb runs lean.


masterstroke's Avatar
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07-12-10, 10:06 AM   #1  
Kohler cv15s with Nikki carb runs lean.

Simplicity Tractor:
Package #1693081 MFG #1693080 Serial #01678

Kohler Engine:
Model cv15s Spec #41508 Serial #2513218574

The problem: Engine starts fine but runs rough. It surges, seems under powered and will only stay running with choke almost fully closed. If I open the choke, the engine runs ok for 15-30 seconds, then starts to sputter and will stall unless I apply the choke again. After reapplying the choke, the engine still labors for awhile, sends some black smoke out the exhaust and takes a while to recover. If I it shut off, it restarts fine, but still needs choke almost fully engaged.

History: The engine was running rough, so I put in a new spark plug and cleaned the air intake pre-cleaner. But, I stupidly didn't let it dry out and probably put too much oil on it and the engine was worse. When I realized my mistake, I bought a new air filter and pre-filter, cleaned the bits of oil out of the air cleaner and carb throats, drained the gas and started with fresh gas. No luck. I installed new fuel line from the tank, a new fuel filter and new fuel line going into the carburetor. Still no luck.

Time to check the carburetor. There was a little crap in the bottom of the bowl, which I cleaned out, but everything else inside was really clean. No varnish, no gunk. The float was good, and properly adjusted, the needle and seat are clean and the rubber needle tip is straight and clean. I cleaned the outside and all the little holes with the little balls inside. The shut off solenoid is clean and works fine. I've poked skinny wire through every opening in the carb and solenoid where gas should go through and they're all open. I've sprayed carb cleaner into the air intake with the engine running. The fuel pump works and there's always plenty of gas in the carb bowl. I've adjusted the throttle cable and choke, all according to the service manual. Still no better.

What I haven't done is take the little balls out of the carburetor because I don't know how to get them out and I'm afraid I might loose them and/or mix them up. I haven't adjusted the low idle fuel needle because there is no adjustment on the Nikki carb. According to the manual "Certified engines have the idle mixture preset and sealed at the factory, no adjustment is possible". I haven't adjusted the low idle speed because this model has a single throttle control/choke lever and the engine dies long before I can get the lever to low idle. I haven't adjusted the high idle or the governor because, correct me if I'm wrong, they should have nothing to do with the problem and it seems useless to deal with them until I can get the engine running properly.

One last note. While I was putzing with the carb, I noticed that the hose going out of the carb to the engine is cracking and has a little split in it. Could it be sucking air? I taped it up with electrical tape, although the tape has long since come loose. I suppose I should tape it again. Meanwhile, I have a new hose on order.

At this point, I'm so tired of taking the carb apart that I'd be willing to buy a new one, but I don't want to drop the bucks if I can possibly fix this one, or if the carb isn't the problem.

Anyone have any ideas?

 
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5dollaralien's Avatar
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07-12-10, 03:38 PM   #2  
I know what it is like to tear these apart several times.
And these questions will sound redundant to you
sounds to me like there is still a restriction in the carb somewhere, not too many places on that carb to be blocked. The main jet that screws into the bottom of the fuel shutoff solenoid is that clear?
also when you spray carb clean up thru the main nozzle does it come out of the nozzle into the venturi?
Is the intake gasket leaking air?
The idle circuit is it clear? hard to get to without taking out the welch plug but you can spray cleaner up through it and such.
Also does your carb have a little rubber plug inside? Not related to your problem from what I can tell but just curious.

 
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07-12-10, 06:54 PM   #3  
Posted By: 5dollaralien I know what it is like to tear these apart several times.
And these questions will sound redundant to you
sounds to me like there is still a restriction in the carb somewhere, not too many places on that carb to be blocked. The main jet that screws into the bottom of the fuel shutoff solenoid is that clear?
also when you spray carb clean up thru the main nozzle does it come out of the nozzle into the venturi?
Is the intake gasket leaking air?
The idle circuit is it clear? hard to get to without taking out the welch plug but you can spray cleaner up through it and such.
Also does your carb have a little rubber plug inside? Not related to your problem from what I can tell but just curious.

Well, yes and no. As I said, I'm a beginner at carbs, so here's what I can tell you. When I checked the fuel solenoid, I grounded it to the the engine with the key in start position. The pin on the solenoid pulled down to open the holes at the base. While the solenoid was open, I poked thin wire down the center of the solenoid (is that the main jet?) and it went straight through to where I could see it through the holes at the base, which I assume means that the path for the fuel is clear. I tried to take it off the tip using a screw driver in the top slot, but it just started to chip the brass (I cleared away the chips before reinstalling). Should I try to remove it with pliers?

When I sprayed the carb cleaner, I assume it went into the venturi because the engine sputtered a bit. Is there another way to check?

I don't think that the gasket is leaking air. When I first went in, the old gaskets were stuck to the carb, so I scraped them off and replaced them with the gaskets that came with the Walbro carb rebuild kit that Jack's Small Engines assured me was the right kit, when I asked them if I might have a Nikki carb (I hadn't taken the carb off when I ordered). They're a slightly different shape than the Nikki gaskets, but they are the same shape as the ones I peeled off and I think they make a good seal when I crank down on the bolts that hold the air cleaner base on. I bought gasket sealer at the auto parts shop, but I don't want to use it until I have the carburetor fixed because I don't want to have to destroy the new gaskets if I have to pull the carb off again. I could order the Nikki gasket set and see if that helps.

I have no idea if the idle circuit is clear because I have no idea where it is or even what it's supposed to look like. If you can tell me how to find it, I'd be happy to spray some carb cleaner on it, as suggested. The repair manual only mentions welch plugs in reference to the Walbro carb. Annoyingly enough, it doesn't say much about the Nikki at all, other than how to adjust it. If I do need to remove the welch plug, where is it and do I need the special tool they spec in the manual, and do I need to pierce it? If I do, I imagine that I'll need the buy the Nikki rebuild kit for $40.

And yes, it does have the little rubber plug. I pulled it out and reinstalled it just to check if there was any gunk behind it, but there wasn't and it seems to stay in place well.

Do you think this thing could benefit from a full soak in carb cleaner? I've been a little reluctant to try it because the stuff is expensive and I saw somewhere (can't remember where) that it's not a good idea. If I do soak it, do I need to take the float off and the pin out? I'd hate to ruin sensitive parts with such nasty caustic stuff.

Ahhh, so many questions. Your help is greatly appreciated.

 
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07-13-10, 03:02 AM   #4  
Posted By: masterstroke Well, yes and no. As I said, I'm a beginner at carbs, so here's what I can tell you. When I checked the fuel solenoid, I grounded it to the the engine with the key in start position. The pin on the solenoid pulled down to open the holes at the base. While the solenoid was open, I poked thin wire down the center of the solenoid (is that the main jet?) and it went straight through to where I could see it through the holes at the base, which I assume means that the path for the fuel is clear. I tried to take it off the tip using a screw driver in the top slot, but it just started to chip the brass (I cleared away the chips before reinstalling). Should I try to remove it with pliers?

When I sprayed the carb cleaner, I assume it went into the venturi because the engine sputtered a bit. Is there another way to check?

I don't think that the gasket is leaking air. When I first went in, the old gaskets were stuck to the carb, so I scraped them off and replaced them with the gaskets that came with the Walbro carb rebuild kit that Jack's Small Engines assured me was the right kit, when I asked them if I might have a Nikki carb (I hadn't taken the carb off when I ordered). They're a slightly different shape than the Nikki gaskets, but they are the same shape as the ones I peeled off and I think they make a good seal when I crank down on the bolts that hold the air cleaner base on. I bought gasket sealer at the auto parts shop, but I don't want to use it until I have the carburetor fixed because I don't want to have to destroy the new gaskets if I have to pull the carb off again. I could order the Nikki gasket set and see if that helps.

I have no idea if the idle circuit is clear because I have no idea where it is or even what it's supposed to look like. If you can tell me how to find it, I'd be happy to spray some carb cleaner on it, as suggested. The repair manual only mentions welch plugs in reference to the Walbro carb. Annoyingly enough, it doesn't say much about the Nikki at all, other than how to adjust it. If I do need to remove the welch plug, where is it and do I need the special tool they spec in the manual, and do I need to pierce it? If I do, I imagine that I'll need the buy the Nikki rebuild kit for $40.

And yes, it does have the little rubber plug. I pulled it out and reinstalled it just to check if there was any gunk behind it, but there wasn't and it seems to stay in place well.

Do you think this thing could benefit from a full soak in carb cleaner? I've been a little reluctant to try it because the stuff is expensive and I saw somewhere (can't remember where) that it's not a good idea. If I do soak it, do I need to take the float off and the pin out? I'd hate to ruin sensitive parts with such nasty caustic stuff.

Ahhh, so many questions. Your help is greatly appreciated.
Do Not Remove the welch plug!! because the replacement that came with my kit was too small... and the kit does cost 35-40$$$. anyhow where the rubber plug is that is the idle circuit, above that you will see some passages that connect to some holes in the venturi, make sure everything is clean and connected, blow carb clean thru. You need to make sure everything is clean when it is off on the bench. There is also a hole that connects from the idle pickup to the main pickup above that rubber plug make sure it is clear. Up to you if you want to soak it or not, I usually do not, if you do take the float and gaskets and anything rubber off. Do not mess up the main jet by trying to get it off, just make sure it is clear, and do not put too big a wire up thru it as this will change the fuel mixture. Also the main jet does not come in that kit.
My best advice is to make sure it is very clean and all your gaskets are good. ie: especially the intake gasket that is between carb and engine. the one between the air cleaner and carb is not as crucial but still should be in good shape.
good luck

 
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07-13-10, 08:20 PM   #5  
Thanks so much for the tips and descriptions. It'll be easy to leave the welch plug alone, since I still don't know what it is or what it looks like. I know what the carburetor does, but I've finally found a good diagram of a basic float carburetor and I'm getting a much better grasp on how it actually works. Unfortunately, the construction of the Nikki carb seems to be a bit of an anomaly, but I'll figure it out. I can't afford not to.

I was looking at the rebuild kit and noticed that it has two small rubber rings. Where do these go? I didn't see any little rubber rings when I was in there. There were also two needles. I know that one goes onto the float, but does the other go into the solenoid?

Next stupid question, where, exactly is the main jet? Is it that little hole in the middle when I'm looking down through the center hole of the float?

I'm going to order the kit and a new header tube, which I probably won't get for a few days. Meanwhile, will I ruin or cause excessive wear to the engine if I run it the way it is, with the choke on? My grass is getting awfully long and I don't mind going slowly, but I won't do it if it's at the expense of the engine. Please say yes. I really don't want to mow 2 bumpy acres with the walk behind mower. Ugh!

 
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07-14-10, 02:34 AM   #6  
If you can get it started and the carb doesn't have a mechanical problem you can get it cleaned up with Sea Foam - runs about 8 bucks a can at auto parts stores.

 
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07-14-10, 06:48 AM   #7  
Thanks for the idea. I've never heard of Sea Foam, but I just googled it and it looks way cool. I'll swing by Autozone today and give it a try before I drop $38 bucks on an overpriced rebuild kit. Even if it doesn't completely solve my carb problem, this is an old and well used engine, so anything that might clean it up a bit has got to be good. And, if it does fix the carb problem without me having to open the thing up again, I'll be forever grateful.

 
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07-14-10, 02:15 PM   #8  
Posted By: marbobj If you can get it started and the carb doesn't have a mechanical problem you can get it cleaned up with Sea Foam - runs about 8 bucks a can at auto parts stores.
or you can do this as marbobj suggests, hopefully it works for you

 
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07-14-10, 05:07 PM   #9  
Picked up the Sea Foam, going to try it out tomorrow. I'm probably a dreamer thinking it might magically take care of everything, but here's hoping.

 
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07-15-10, 01:58 AM   #10  
It might help, good luck....

 
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07-16-10, 08:28 AM   #11  
Well, I'm still 0 for 0. I tried the Sea Foam in the carb, got lots of smoke, but no change. I'm sure there must be some crud lodged in some hole or jet somewhere, so off it comes for yet another disassembly today or tomorrow. I'm nothing if not determined.

Meanwhile, being oh-so-clever and needing something to do until I have time to deal with the carb, I decided to adjust the high idle speed, as it seems a bit slow since I adjusted the throttle cable last week. Too bad the bolts sheered off when I went to loosen them. And, correct me if I'm wrong, but I'm guessing I shouldn't be attempting to start the engine with the throttle/choke plate hanging loose. So, it's off to the hardware store to buy an easy-out set or something like it.

 
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08-02-10, 08:11 AM   #12  
Success, maybe?

Ok, so it only took me two weeks and many drill bits to get the sheared bolts out, but I did it. Helpful tips for drilling hardened steel: Go to www.bogstool.com and drop $11 on a solid carbide bit and use lots of cutting oil. I can't say it'll make drilling hardened steel easy, but it does make it a whole lot less miserable.

Took the carb off, yet again, blew it out really well. When I went to replace the air filter base, I noticed that the breather tube was cracked. Took it off, and a wad of crap fell out of it. Taped it up from stem to stern, put everything back together and the engine ran beautifully. Until I'd been mowing for 30 minutes. Then, I needed some choke, another 15, more choke, another 15 and the engine is overheating.

After a bit of web research to figure out just what a breather tube is for, I'm figuring that there's still some crap and/or a leak in the breather tube and dirt is getting sucked into the carb and causing trouble. So, it's off to order a new breather tube and blow out the carb one more time. I *will* get this engine to run properly. Unless the engine is trashed from having dirt sucked into it...

 
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08-02-10, 02:47 PM   #13  
I understand the carbide cutters as I work in the tooling industry.
another thing we try is using a dremel with a carbide burr mill to cut a screwdriver slot in the sheared bolt, then just back the bolt out if possible, unless it is locked up or something. well hopefully you get your machine going correctly, wish we could be of more help but it is hard to do by writing.

the main jet is screwed into the solenoid, it is brass. the nozzle is the hole going into the venturi (Main body) of the carb in the same circuit as the main jet.
this is a pic of the kit you would need, there are no fuel mixture needles here cause that carb does not have one.
I did not need the big brass plug and spring either, or the welch plug (the shiny disc in the pic) as it was too small for my carb.



 
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