# fc420v carb problems



## 1989gta (Sep 13, 2009)

I have a fc420v 14 hp on a 36inch hydro scag mower. The mower will only start when the throttle position is dead center. On the carb the throttle blades are barely open. It idles great until it warms up then dies. It will also die if you give it more throttle seems to be dumping too much fuel. 

-has new fuel
-new plug 
-spark seems good
-I confirmed valve lash is .06

I have removed the carb several times cleaned all the parts and passage ways. On the last cleaning i used an air compressor blowing everything out. But is still will not allow me to throttle up.


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## bgbass (Jan 11, 2008)

The butterfly needs to open up or you are choking the motor check the linkage to make sure its hooked right sounds like you have it in the the wrong hole


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## 1989gta (Sep 13, 2009)

maybe my original post wasn't too clear sorry i'll try again, if i open the throttle all the way engaging the choke the motor will not fire(throttle blade completely open). If i move the throttle to the middle so the choke blade is open and the throttle blade is open slightly it will idle for a few mins


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## 1989gta (Sep 13, 2009)

I ran a leak down test on the cylinder was 20% leakage so it's pretty good. 
I checked lash on the valves again one of them was off by .01 didn't make much difference. 
I adjusted the governor that seemed to help a little but i'm still not able to throttle up or start with the choke on.
I checked and cleaned the plug again set to .30


tomorrow i'll get a spark tester and try and put up video that may help you guys see what it's doing 

Thanks for you help


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## 30yearTech (Sep 14, 2006)

It really sounds like a carburetor problem to me. From your description of the problem, it sounds like it's only metering fuel through the low speed circuit of the carburetor and that you are getting nothing through the main or high speed circuit. If the carburetor was dumping an excessive amount of fuel, you should be able to get at least some throttle and speed out of the engine, before is chokes down and dies. From your description, it's running way to lean and as soon as you open the throttle, the engine dies, from lack of fuel.


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## 1989gta (Sep 13, 2009)

i tried spraying carb cleaner into the carb when i throttle fast but it kills the motor


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## 30yearTech (Sep 14, 2006)

1989gta said:


> i tried spraying carb cleaner into the carb when i throttle fast but it kills the motor


While carburetor cleaner may work to prime the engine, it rarely works good to run an engine off of. Try your trick with brake cleaner and you may have different results.


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## 1989gta (Sep 13, 2009)

i'll pick up some brake clean all i have right now is carb cleaner and starting fluid.


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## 1989gta (Sep 13, 2009)

i had some time so i threw it back together here is a video of the spark 





and another of the machine at idle throttle closed, choke open. You can see as i throttle up it blows black smoke and dies. 






Still needing to pick up some brake clean.


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## 30yearTech (Sep 14, 2006)

I don't think you need to try running with brake cleaner. Looking at the video of it running, it really acts like either a valve issue, or ignition timing. Have you checked the flywheel key to make sure it's not somehow sheared? I know you set the valve clearance, did you look at the valve operation and notice if both valves looked like they are opening all the way? It's possible that one of the valve lobes on the camshaft may have wear and your valves are not getting proper lift. Something you might want to look at anyways. Good Luck...


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## 1989gta (Sep 13, 2009)

i'll check the key on the flywheel, and see if there is a way to measure if the valves are opening all the way.


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## 1989gta (Sep 13, 2009)

what is the likely hood that the key sheared and the timing is off? I'm not able to get the flywheel nut off. I don't have a compressor that will run my impact gun.

Is there another way to check the timing?


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## 30yearTech (Sep 14, 2006)

The possibility of the key being sheared is not very high. It's just something I would want to check to be sure of before looking at the valves or camshaft.


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## 1989gta (Sep 13, 2009)

My brother came over tonight we got the machine to idle then he shut the fuel line almost closed limiting the amount of flow and we were able to get it to throttle up higher (3/4) with out bogging down and blowing black smoke.He is thinking something is going on with the carb it almost seems like the jetting is off.


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## bgbass (Jan 11, 2008)

sounds like your float level to high and flooding


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## 1989gta (Sep 13, 2009)

tonight i'm going to try playing with that


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## 30yearTech (Sep 14, 2006)

I don't think the float is adjustable on that carburetor, should be a molded plastic float.


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## 1989gta (Sep 13, 2009)

you are correct and bending the tab on the float does nothing for me. it's set right.


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## 30yearTech (Sep 14, 2006)

Is the main jet in the carburetor? It's possible it came loose and fell out and this would allow way too much fuel into the engine, however I don't think it would even idle without the jet in place.


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## 1989gta (Sep 13, 2009)

yeah main jet is in place i'm thinking bgbass is correct the fuel level is too high in the carb bowl. but i'm not sure how to check that or what would cause it. Aside from a bad float or needle vavle not seating, i'm Just going by the flow chart in the service manual


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## 30yearTech (Sep 14, 2006)

Unless the fuel is flowing through the carburetor all the time, the float level being high is not going to affect the running of the engine that much if any at all. 

Fuel would have to be running through constantly, does fuel fill up and puddle in the throat of the carburetor? Otherwise I don't think this is your issue.


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## 1989gta (Sep 13, 2009)

i'm not able to see in the carb when it's running but with the air box off as i throttle up fuel does not puddle but splash the wrong way up towards the air cleaner.


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## 30yearTech (Sep 14, 2006)

1989gta said:


> i'm not able to see in the carb when it's running but with the air box off as i throttle up fuel does not puddle but splash the wrong way up towards the air cleaner.


That would indicate a valve issue, particularly the intake valve not seating good.


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## 1989gta (Sep 13, 2009)

i ran a leak down test it was like 25% leakage that should be more than adequate i would assume when hot leakage would be less but could not get the machine to run long enough to get it hot.


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## 30yearTech (Sep 14, 2006)

1989gta said:


> i ran a leak down test it was like 25% leakage that should be more than adequate i would assume when hot leakage would be less but could not get the machine to run long enough to get it hot.


Hot leakage will not necessarily be less. 

Where is it leaking at??

Have you done a compression test? and if so what was your reading?


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## 1989gta (Sep 13, 2009)

I did not run a compression test.
i borrowed the leak down from my brother. The leak down test on a single cylinder engine is slightly more challenging than on my sbc. mainly because the rotating assembly is smaller and there is not anymore cylinders building compression to prevent the engine from turning. 
As for diagnosing where the 20% leakage was it could be a number of things could be me not holding the assembly at the correct spot where both valves are closed. Could be blow by in the rings. It was difficult to hold and diagnose where it was coming from. The important thing is i'm getting good compression. 



> Hot leakage will not necessarily be less.


I have not taken the piston out or reviewed the specs but i would assume there is gapping in the compression ring that is taken up when the engine gets hot.


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## 30yearTech (Sep 14, 2006)

1989gta said:


> The important thing is i'm getting good compression.


While a leak down test will tell you if your engine is capable of generating good compression, and invaluable to tell you why it's not. A leak down test won't tell you if it is developing good compression. Valve timing, or camshaft issues will not be apparent from a leak down test. To find out if your engine is in fact producing sufficient compression, you will need to perform a compression test as well.


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## 1989gta (Sep 13, 2009)

point taken i'll kick out some emails and see if can locate one or add it to my arsenal.


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## 1989gta (Sep 13, 2009)

located a compression tester i'll pick it up tomorrow and post my results.


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## 1989gta (Sep 13, 2009)

good and bad news it's not the key in the crank and i'm really surprised my bostich pancake compressor ran my 1/2 impact


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## 1989gta (Sep 13, 2009)

ran a compression check 40 psi and leakage was pretty fast. I need to check to see if i created the problem when i adjusted the valves or if it was like that.


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## 30yearTech (Sep 14, 2006)

40 psi is way low, even with the compression release kicking in. I would look for a minimum of around 70 psi.


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## 1989gta (Sep 13, 2009)

i agree checked the manual it states 71 psi minimum also had an issue with my compression tester leaking at one of the seals corrected the issue and confirmed 40 psi

now i need to find out if that is valve or ring issue


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## 1989gta (Sep 13, 2009)

i'm hooked air up to the engine and roll the machine to tdc but the pressure wants to roll the motor so i'm finding it hard to tell where the leak is how do you guys test for a leak?


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## 30yearTech (Sep 14, 2006)

1989gta said:


> i'm hooked air up to the engine and roll the machine to tdc but the pressure wants to roll the motor so i'm finding it hard to tell where the leak is how do you guys test for a leak?


You can do a leak down test at BTC on the power stroke to determine where the leak is. You can also Hold the crankshaft with a wrench on the bolt that screws up in the bottom or lock down the flywheel retaining bolt to hold the engine at TDC.


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## 1989gta (Sep 13, 2009)

okay good to know doing this at btc will that prevent the compression realese in the exhaust valve?


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## 1989gta (Sep 13, 2009)

i had another thought this morning when i should have been working. what if i loosen the valves and rerun the compression test.

I did this and was able to achieve 90 psi and found out why the acr was included with this engine good news right. So that would suggest i messed up when i set lash on the valves right? Well i rotated the engine back to tdc and set the lash again confident i found one issue. I reran the compression test 40 psi again? I pulled out the tester rotated to tdc and checked lash my .006 feeler goes in snug what am i doing wrong????


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## 30yearTech (Sep 14, 2006)

You need to make sure that the engine is at TDC on the compression or power stroke, otherwise there is some valve overlap in other positions.


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## 1989gta (Sep 13, 2009)

agreed i will have someone double check my work but in the mean time i changed the lash from .006 to .012 and the compression went from 40 psi to 58 psi?


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## 30yearTech (Sep 14, 2006)

1989gta said:


> agreed i will have someone double check my work but in the mean time i changed the lash from .006 to .012 and the compression went from 40 psi to 58 psi?


Did you ever observe the valve operation on BOTH valves? 

With the valve lash properly set, slowly rotate the engine. Take a look at the intake and exhaust valve operation, note how far the rocker depress each valve when opening them. 

Do both valve appear to open pretty much an equal amount?

I had an engine run pretty much like yours, and it had a worn lobe on the exhaust valve, it was just barely opening. The engine would run at an idle but would not accelerate, just kind of flood out and die.


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## 1989gta (Sep 13, 2009)

both valves open the same amount .375 of an inch i used a ruler not a dial indicator so there is a small margin for error but both seem to measure and travel the same distance.


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## 30yearTech (Sep 14, 2006)

After looking at your video several times again, I still believe it's either carburetor or valve issue. I can't really see in the video when the engine is running and you are showing the top of the air cleaner base. 

Is there blow back out of the carburetor while the engine is running? 

Just before the engine chokes down and dies is there perhaps a lot of blow back out through the carburetor?


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## 1989gta (Sep 13, 2009)

when i throttle up it blows black smoke and yes there is blow back through the carb. I'm starting to wonder if the intake valve seat is loose.


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## 30yearTech (Sep 14, 2006)

1989gta said:


> when i throttle up it blows black smoke and yes there is blow back through the carb. I'm starting to wonder if the intake valve seat is loose.


That is my suspicion, I was going to suggest pulling the head off for a look, but then opted to study your video again and ask about the blow back. I don't often see issues with the valve seats on OHV engines, but this is characteristic of a problem with the intake valve and or seat.


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## 1989gta (Sep 13, 2009)

did some cleaning and some wire inspection today and noticed one of the wires were shrink wrapped the rest had that nice braided stuff around it. After cutting the shrink wrap off i found that there was about 1/2 inch of exposed wire on both wires leading to the charging coil they were touching. I wrapped up the wire eager to put the engine back together however it seems this may have been causing some issues but doesn't appear to be the complete issue. I am now able to get it to pop a few times with the choke on but still won't start normal. Tried the closed throttle trick like before but she popped through the carb. I'm going to do some reading about magneto's but i'm leaning towards pulling off the head tomorrow.


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## 1989gta (Sep 13, 2009)

Pulled the head off tonight. Piston, cylinder and valves all look pretty good. Can't see the cross hatch in the cylinder anymore but what do you expect for an 8 year old engine. I was able to remove the intake valve, seat does not move and valve has a nice even line around it where it mates with the seat. I'll get a hold of a spring compressor tomorrow and pull the exhaust valve.


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## 1989gta (Sep 13, 2009)

as you can see there is significant deposits in the exhaust port and on the exhaust valve. Both valves appear to have a nice seal mark on them. Neither of the seats are loose.


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## 30yearTech (Sep 14, 2006)

How are the valve guide bushings? Are they both in place and tight?


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## 1989gta (Sep 13, 2009)

they are in place and seem to have the necessary friction


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## 1989gta (Sep 13, 2009)

after cleaning the carbon deposits from exhaust valve i resembled the head and took it to an engine shop where they vacuum tested the the seals. Intake was good the exhaust needed some grinding had some minor pitting after they both sealed great. Just need to get a head gasket then she'll go back together.
Edit/Delete Message


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## 30yearTech (Sep 14, 2006)

What is the variation number of your engine? (i.e HS01, GS01 etc...)


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## 1989gta (Sep 13, 2009)

fc420v gs14

I just replaced the regulator no change


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## 30yearTech (Sep 14, 2006)

Have you pulled the flywheel and inspected the key?


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## 1989gta (Sep 13, 2009)

i pulled the motor down to see if the key was intact but i did not pull the fly wheel off.


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## 30yearTech (Sep 14, 2006)

Since this engine uses a woodruff key, you can't really tell if the key is broken just by looking down the channel in the flywheel. You have to pull the flywheel off to make sure. If the ignition timing is off, this could be the problem.


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## 1989gta (Sep 13, 2009)

good to know i'll pull the flywheel tomorrow.


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## 1989gta (Sep 13, 2009)

ok so i pulled the flywheel the key is intact but do you think this mess will cause a timing issue?


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## 30yearTech (Sep 14, 2006)

No, that won't affect the ignition timing. That's the alternator coil under the flywheel. While it would be a good idea to clean it off, aside from trapping some extra heat in the alternator, it should not have anything to do with your running issue.


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## 1989gta (Sep 13, 2009)

i'm back to square one then maybe a carb issue?


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## 30yearTech (Sep 14, 2006)

I notice some tape on the wire from your coil to the (I am guessing) ignitor, you may want to inspect this wire to make sure there are no areas where it could be grounding out. You may want to test it for continuity and make sure there are no breaks in it either. Since you have your coil off, you may want to get it tested as well.


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## 1989gta (Sep 13, 2009)

i ran continuity test through all the ignition related wires the coil tested with in spec. Looking at the condenser its not shorted but is there a way to test that? I don't have a spec in the manual i have?


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## 30yearTech (Sep 14, 2006)

Your engine should have an electronic ignition ignitor on it, there should not be a condenser.


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## rick-l (Sep 16, 2009)

1989gta said:


> i ran continuity test through all the ignition related wires the coil tested with in spec. Looking at the condenser its not shorted but is there a way to test that? I don't have a spec in the manual i have?


Depending on the meter and the size of the capacitor it should briefly conduct and then read open. 

Is there the possability of an RPM related glitch in the ignition?


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## 1989gta (Sep 13, 2009)

not sure what you mean by rpm related glitch? 

here is a link to the ignition parts 
http://kmcb2c.econnect.partsandwarr...tType=2&historyDepth=2&CHANGENUMBEROFITEMS=63

also i measured the condenser and get 8.5 Mega Ohms


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## 30yearTech (Sep 14, 2006)

That's the start up capacitor for the electric PTO clutch that operates the blades on the mower. It has nothing to do with the ignition system.


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## 1989gta (Sep 13, 2009)

that is good to know i guess it threw me off that it is mounted right above the ignition module and on the same screen on the kawi site.


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## 30yearTech (Sep 14, 2006)

That's not the ignition module it's mounted above, that's the voltage rectifier. At least I think that is what your looking at. The part just below the capacitor with the cooling fins mounted on the mower frame. The ignition ignitor or module is mounted on the side of the engine block and is small less then 1" square.

Looks something like this:

http://www.mfgsupply.com/m/c/31-9334.html


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## 1989gta (Sep 13, 2009)

i'm unable to find that part on kawai's site or on the engine


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## 30yearTech (Sep 14, 2006)

1989gta said:


> i'm unable to find that part on kawai's site or on the engine


If the spec number on the diagram you posted is the correct one for your engine, then your engine has a solid state ignition coil and it's a complete unit.


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## 1989gta (Sep 13, 2009)

30yearTech i appreciate all your help. I'm confident the ignition system is functioning properly. I'm going to revisit the combustion chamber. I have a leak down tester so hopefully that will yield some results.


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