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Peculiar Carburetor Issue(s)
- Thread starter heimannm
- Start date
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How about the lever rod is bent just a little
Some people stretch the little spring before installing the lever, might have something to do with it?
It was MacAttack who had the flooding issue. His carb was a Walbro MDC, and after readjusting the metering lever, he was set. I haven't heard from him in a while though.
As for Heimannm's problem, it's real strange. I've never seen, or heard of a lever bending itself out of adjustment that quickly before.
I do however remember being completely stumped with a carb that would flood itself similar to what Heimannm's carb is doing. It was a Zama as well, an RB. I took it apart (again) and saw that the lever was stuck open. Like it was forced really hard. It would sit fine, then make a giant puddle where it would suddenly flood like mad. When it would run, it would flood out the engine and keep hemorrhaging fuel. I don't recall the lever ever coming out of adjustment though.
It would hold pressure, had no reason to, and wouldn't bind, and the needle would reseal and hold pressure.
I never bothered to do a deep dive into it to confirm what the problem was. I was so pressed for time, that I just swapped it. Like the others here, I did settle on the probability that it was/is a main check valve issue. As ignorant as it sounds, I believe that somehow pressure builds up and it overpowers the lever and it floods, or bypasses it completely and it floods.
I think my solution to the Walbro HDC is to replace the check valve under the metering plate, problem is, the little check valve costs more than the saw is worth!
Like other saws, that inlet lever runs off of the intake pulses, I think. I know that doesn't answer the initial question, just might give you a place to start. On anything fuel related I usually check the crankcase to make sure it's not filled with fuel. Possibly even an ignition not timed perfectly might alter the input pulse. Just guessing at this point..
Actually, the metering diaphragm is only affected by atmospheric pressure on one side, and fuel pump pressure on the other side. As fuel is consumed from the wet chamber atmospheric presses on the diaphragm to open the needle. The crankcase impulse only works on the fuel pump diaphragm.
Mark
Mark
I didn't mean it directly ran the big diaphragm but eventually, without the impulse, none of it would work. Of course that doesn't solve our problem of the bent lever unless you came up with something..
Long time no see fellas, life has kept me busy.
My Mini Mac flooding / rich issues were due to the metering lever being set too high. One thing I would caution as a possible cause of the metering lever changing, if you adjust them too many times they WILL start to weaken. Think of the bending spoon magic trick where they bend a normal spoon back and forth just to point of nearly breaking.
I've lost at least one metering lever due to this effect. I wonder if there is a point at which the fuel pump pulse can actually bend a weakened lever??
Hi Mark,
The situation that I experienced was caused by an aftermarket metering diaphragm where the nub intersecting the lever was incorrectly finished (too high). I cant see how this would bend your lever up, but it did bend the levers on the HDC carbs down far enough that they would not draw fuel. If you still have the parts, compare an original Walbro HDC diaphragm with one of the aftermarket ones and see what you think. There are alot of these aftermarket HDC diaphragms floating around, so keep an eye out.
The situation that I experienced was caused by an aftermarket metering diaphragm where the nub intersecting the lever was incorrectly finished (too high). I cant see how this would bend your lever up, but it did bend the levers on the HDC carbs down far enough that they would not draw fuel. If you still have the parts, compare an original Walbro HDC diaphragm with one of the aftermarket ones and see what you think. There are alot of these aftermarket HDC diaphragms floating around, so keep an eye out.
