[dirtdigger13]

Hello,

I have an LT1000 with 17.5 B&S model 31C707-0230E1. I've been having problems with the engine. To keep it brief as of now, it starts up fine with choke and runs good with choke. At idle speed it continues to run fine. As I increase throttle speed it gets rough, surges, misses and is inconsistent.

To date I've confirmed; fresh fuel, gas cap vent is good, new fuel filter, air filter, spark plug, fresh oil. I took carb apart cleaned thoroughly (more than once), replaced float needle and new gaskets. Ran Sea Foam thru carb. Added Sea Foam to fuel. Adjusted valves to specs. Adjusted throttle linkage per the manual. Took float bowl solenoid out and confirmed it operates when the key is turned. Any other suggestions?

It seems like its not getting enough fuel every 2 seconds but don't see how the carb isn't clean. Only has idle adjust screw and mixture needle with limiter cap. Manual says the mixture needle can't be removed without breaking it. I suspect it could be a problem sense it doesn't seem to effect engine when adjusting it within the range allowed by the limiter cap. I sprayed carb cleaner in the hole while turning the needle hoping to clean it. Also, I replaced the fuel filter with the same kind that was on it. The package says for engines with fuel pumps (which mine doesnt have) although it originally ran fine with the old one.

The throttle/air vane moves sporadically as the engine does. Possibly governor issue? Any suggestions would be greatly appreciated, I'm out of ideas. Thanks in advance.

 

[Five Points]

Hello and welcome, Just to verify, did you completely take the carb apart and soak it in a carb cleaner like gunk or berrymans and throughly blast every hole and orifice clear with compressed air?
Also some of those non-adjustable mixture needles do come out. You have to pop the cap out and there is a regular screw head on the needle. You can remove it, there not adjusted just torqued in there to some inch pound rating. There could be junk in there.
Also there is an aluminum welch plug you need to pull out on the side of the carb to expose the mixing chamber. There could be junk in there as well. The replacement welch plugs come in a rebuild kit however the plastic cap for the mixture screw may not. Also did you check the play in the throttle shaft? They are brass (usually) and could wear and suck air creating another vacuum leak.
Maybe this might get you going.

 

[dirtdigger13]

I didn't remove the welch plug because I was told you really didn't NEED to if you remove everything else and soak the carb. Would you disagree?

So the mixture needle really isn't adjustable, it just needs to be seated?

Now that you mention it the throttle shaft did seem fairly loose. I didn't notice any physical wear but should there be some resistance when you move it? From memory I would say there is Very little to no resistance. Would that cause those symptoms? Should there be equal resistance in the throttle shaft and choke (with the spring removed)?

 

[Five Points]

Dirt and debris cause wear on the throttle shaft. There is usually a seal, felt or foam to keep it out but they disappear after time from oil, gas or someone blasting the carb off with water or air. The wear would look very subtle but would be enough to allow a vacuum leak and yes it would wobble back and forth.
I will do the welch plug when rebuilding to eliminate any problems later. All you need is a little varnish or gunk inside of the chamber to plug a hole and you'll be chasing problems later
The mixture needle has a manufactures torque (carb specific)when you tighten it so it does not loosen up with vibrations. You can over torque it too smashing the seat. Some needles have small hole or ports in the sides near the end that can plug up too.
Reference the throttle/choke shaft, there may not be resistance but it should be nice and smooth with a good fit without back and forth play.

 

[dirtdigger13]

I looked at the service manual for the engine, can't find any torque specs for the needle. Are we talking about the same part? It seems like it has to be adjustable or what purpose would it serve? Doesn't the spring essentially apply the torque to keep it from moving?

 

[Five Points]

Just so I'm not thinking about a different carb could you give me the model, type, name of the carb.

 

[Five Points]

If its a walbro than yes it does have spring, I was thinking of a different series, but they do come out and I would inspect the tip for any grooves or nicks. The throttle shaft also has a replacable bushing, so I would inspect both the bushing and shaft for wear.

Reinstalling the idle mixture needle, you would turn it in untill it just seats and back off 1 1/4 to 1 1/2 turns.

 

[dirtdigger13]

Its a Nikki... 796109? The limiter cap can just be pulled off without damaging anything?

 

[Five Points]

Here is a blow up of your NIKKI

Yours is on the right, if you look at part1091 you can see the two seperated. It may or may not come in a rebuild kit.
You can also replace the throttle shaft seal. I would inspect the shaft for wear though just in case.

 

[Five Points]

BTW You may or may not break the cap while removing it. You can order it seperatly if it does not come in the kit.

 

[dirtdigger13]

Thanks for the input, I'll give it another shot.

 

[Five Points]

Your welcome, let me know how it goes and if we can help with any other issue, feel free to ask.

 

[dirtdigger13]

Hopefully I can push it off and work on it during the winter, but I'll let you know what I find. Thanks Again Five Points!

 

[themidniteryder]

See if you can wiggle the throttle shaft sided to side. This it the play Five Points is referring to. Being a Nikki, there is no replaceable shaft bushing. If there is play like I suspect then it's toss the carb and get a new one. And the limiter cap does not come with the kit. What king of shape is the weird shaped o-ring (137A in the drawing) in? The plastic piece below it has a brass jet that tends to fall out when you disassemble. Did it fall out and you not catch it, or did you get it in backwards? Hate those Nikki's, I would say 1 in 4 that come through her get replaced. Not so with the walbros.

 

[Five Points]

This is what I'm finding,

Item 131A
699501 BRIGGS AND STRATTON ENGINE PART 699501

This is the throttle shaft kit that you can get for 24.90

Item 141B
792777 BRIGGS AND STRATTON ENGINE PART 792777

This is the choke shaft kit that you can get for 11.30

These are for the Nikki Carb that you can get from M&D mower.

Yes, I like the Walbro carbs better. I dislike disposable.

The price for a new carb is between 80-95 bucks

 

[themidniteryder]

The 699501 throttle shaft kit will probably be no help. Usually the wear is in the aluminum carb body, not the shaft. There are 2 different Nikki carbs, depending on your engine date code.

 

[Five Points]

Are the throttle shafts on the Nikkis steel or brass? I usually end up with the Walbros and they are a piece of cake.

 

[dirtdigger13]

So I finally got a chance to look at this mower again. Upon starting up the other day everything remains the same and it struggled thru another mowing. Tonight I took the carb apart and cleaned everything and adjusted the valves. Five Points and themidniteryder I didn't see any sign of wear on the the throttle shaft and no side to side movement either. themidniteryder the o-ring is in decent shape and the brass jet never came out and appears clean.
This time I also removed the welch plug and the mixture needle when I cleaned the carb.

Here is a youtube link of the engine running after the carb cleaning. The video starts at idle, slowly increase to WOT. The engine seems to run 'ok' when I hold the governor/air vane. Hopefully the video does a better job at describing the issue.
LT 1000 B&S 17.5 hp - YouTube

I adjusted the governor according to the manual with no change. One thing to note is that the mixture needle still seems to have no effect on the engine. I seated it backed out 1 1/4 turns, then with engine running tried to tune it in. I completely seated the needle and back out 3 turns and I couldn't detect any change in the engine.

Any ideas/suggestions would be greatly appreciated.

 

[Five Points]

Have you checked for vacuum leaks at the manifold? Your plastic manifold has an o-ring at the part that bolts to the head. Have you changed or checked that one? Does it chase like that when under load like when you are mowing or does it settle out?

 

[dirtdigger13]

Yes the red o ring is in good shape and the gasket between the carb an manifold is new. Is there any way to check for vacuum leaks without special tools? It may get slightly better under load but it still chases.