[ffparts]

Yep, tell me about it, I go through this almost every day. I don't mean you can't adjust them at all, there is a small adjustment you can stilll do. Theoretically the dealer removes the caps, adjusts the carb so that the engine runs within specs, and reinstalls new ones, in the position that the carb cannot be adjusted any richer.

[lexmarks567]

well I think its time for a update as Im about ready to toss the thing in front of a moving car. I had the carb rebuilt so now it idles but will not go to full throttle. Try to give it gas it dies. tryed reversing the fuel lines no go. The carb can't be adjusted as it as those stops that prevent you from adjusting the carb yourself instead its there to force you to take it in so they can make money off of you. any ideas what to try next

[Stoner]

I just saw it's Robi product.
I have a Robi weed wacker that acted like you first described.
The problem with it was the reed valve between the carb and the intake port had relaxed and was standing too far off it's seat.It was acting like a lot of fuel standoff at the carb as a lot of the fuel air charge came back out of the crankcase at idle and low speeds .
On mine, I think the reed gap was at about .020"
Replacing the reed fixed it.

Hope that helped.....good luck.

[JohnWill]

FWIW, I had a similar issue with my snow blower, and I just bought the whole carb, it was around $30. A total replacement made it like new. I got 12-13 years out of the first carb, if I do that well with the second...

[lexmarks567]

hmm maby a new carb would work but I just had it rebult why is it not working

[ffparts]

Sometimes the small passages get gummed up inside the carb where you can't get to them, even if you could adjust it, it may not help. BTW that is a homelite product, any homelite dealer should be able to get that carb for around $50, IMO the unit might not be worth putting that kind of money into. Also check for a plugged exhaust screen, it will do exactly what you have described, idle but not run wide open.

[JohnWill]

It's hard to say why it's not working. I went a couple of rounds with a carb on a lawnmower years back, and never could resolve what the issue was. A new carb fixed that one too. Everything looked OK, but it just didn't run right.

[lexmarks567]

maby I should toss it then. The carb been rebult has good spark good compression. Before it would go full thottle but not idle. Now it idles but no thottle. No leaks anywhere (take a can of WD-40 and spay around gaskets on the engine block see if it speeds up or slows down) nothing no change. the carb has stops like I said to prevent it from being adjusted. I could break those platic tabs off but might break the carb

[Stoner]

That is a 2 cycle engine, correct?
Does it have a reed block between the carb and intake port?
If so, again, I recommend you check out the tension of that reed.


Another thought, have you checked the seals on both ends of the crankshaft ?

[JohnWill]

Well, if tinkering with the carb changed the symptoms that much, I think he's working in the right area.

[Stoner]

Or made it worse

[lexmarks567]

no reed the carb sites on this plastic 1 inch seat that leads to the intake. There air fliter sites on top of that carb and is bolted down.go to www3.sears.com enter model number 517.797941 click diagram

[ffparts]

Also, I just thought of something, if the carb was not rebuilt professionally, a lot of times people will just put everything in like it came out, and not adjust the metering lever for the inlet needle. That could also cause your problem. Just a thought

[SurferJoe46]

Quite frankly, these are not a "carb" but really a simple diaphragm-driven form of fuel injection.

They rely on case pressure pulsations or changes in the engine to actually pump the fuel by squirts into the throttle body where it is ingested by the inward flow into the engine.

Most problems with these units are from gum or varnish build-up to the point of not allowing fuel to flow during one or more of the circuits or adjustments to supply sufficient gas to keep the mixture correct and the engine running.

There is a Walbro and a Tillotson, and these are the most typical types that occur in US 2-cycle devices. These also show up on Trail engines which are a Canadian manufacturer, so you can see they are quite universal.

Anyway, usually the act of disassembling the unit and reassembly takes care of the problem "mysteriously" as the diaphragm was usually stuck from the gum and is now freed up by the act of "looking" for a problem...which isn't really apparent to the tinkerer.

The plastic limiter caps should be pried off the stems of the high and low speed mixture control needle valves, as you don't have to worry about any guarantees or warranties at this late date anyway.

The reason for taking them off is so you can GENTLY! bottom the needles into their seats to remove any debris that might be caught there. Try to count the number of turns you made to get them to the bottom, and return them to their original positions as well as you can.

Both needles will affect the others' territory for mixture control unfortunately.

Turning the high speed will also cause a small loss of adjustment at low speed and vice versa. It is a "seek & destroy (and learn)" experience and once you do it correctly, you'll know the procedure for a while.

Start with the low speed jet, this is assuming you have taken the unit apart and don't see anything amiss...like I said, it may not have been anything but a stuck diaphragm anyway.

Try to get a good idle mixture at low speed...if you need to use the choke to keep it running, the mixture is too lean so back out the screw a little more.

After you get a decent (but not perfect) idle, then go for the high speed adjustment. Here you need to be a little carefull...too lean can overheat the engine and it will run badly.

There are a few things to consider here.

Lean creates a lot of speed for a few moments..but it will usually "sag" and lose speed and stall.

Rich creates a "fat" running condition that will break into a four-cycle-type of sound...firing on every other beat or skipping a few and then firing randomly. This can be adjusted by turning the screw IN a little until you get a clean "on the pipe" type sound. We aren't done yet.

Repeat the idle adjustment..trying to get it better than the first time.

Now go to the high speed again, and when you get it running very well, just back out the high speed screw a tiny but until you hear a slight change of exhaust note. It should lose a little speed, but not too much.

We want the engine to be slightly fat at high speed to keep it cool and keep the power up when it is really working harder.

Another thing that most people get wrong is this:

Adding more oil than necessary or specified in the premix will make the engine run hotter, as the gasoline content is what counts here. More oil = less gasoline in the mix and that means overheating and engine damage. Do the little guy a favor and keep the mix in the proper ratios.

Don't buy outboard engine mix/oil, as this is designed for water cooled engines, and yours is NOT water cooled! They are very different oils for very different purposes.

DO NOT USE engine oil in the premix either! It is not designed to go thru combustion...

[lexmarks567]

well I was messing with it a few days ago. it will run in choke but when it dies your supposed to go to 1/2 choke does not start or not for very long. before I sent the carb out for repair it would only run full power no idle. then after awhile it would not start at all. He replaced the diaphragm as the old one was stiff there was a long blade of grass in one of the ports. and alot of dirt and a spring was streached out.theres 2 screws missing on the aircleaner cover there should be 4 could that cause anything.