A little something about primers and check valves.

[PTmowerMech]

I'm not sure if this is an actual fix or not. I'm just now trying it. The carb I'm working on now, C1QS186B, wasn't priming before. Also bogging down at WOT. The metering diaphragm was about 1/2 hard & soft. Long story short, I US cleaned it, then rebuilt it. And it still won't prime.

Thinking about something star tech said the other day, I thought I'd post this from a guy who claims to work for Zama.

Been having a lot problem with Zama carbs on Stihl units not priming this year and the parts cost as much as a new carburetor.

And not able to find the 591597 on the Power Portal site. Are sure of the PN?

I'm working on one today C1Q S186B, that's not priming. Have you ever heard of soaking the disassembled carb in gas for an hour? I just watched a video about this. Common soft spoken guy (no drama), who works from Zama (according to him) seemed to know what he was doing. He explained that 99% of the time, no priming is because of a check valve. And that soaking it in gas (or gas/2cycle mix) usually does the trick.

IIRC, you don't watch video's. But someone else might find this helpful.

 

[PTmowerMech]

After soaking the disassembled carb for a couple of hours, there was no change. It still won't prime. Maybe it's completely flubbed up.

 

[PTmowerMech]

@bertsmobile1

I remembered a trick you told me about a few years ago. You said to blow compressed air through the venturi of the carb to help start something I was working on. I remembered you saying it creates a vacuum and sucks the fuel out of the carb, like when it's running. I once seem my old boss connect fuel line to the inlet and outlet of a carb like this, with fuel like in it. This is how he checked to see if it was priming before he installed it.
Well, I took your idea and connected one end of a piece of fuel line to the inlet of the carb. The other end into a bottle of fuel mix. Then I blew through the venture with the air gun. At first, it was only small amounts of spray coming out. The air bubbles in the fuel line I could see was barely moving. When I'd pump the primer, the bubbles might move a little. But not much. Then stop all together.
So I blew more air through it and repeated the process a few times until the primer started priming as it was supposed to.

I don't have a clue as to what this means. But the trimmer (KM55) is running like a top. And the carb is now priming as it should. I've killed it a couple of times. Let it sit for a few minutes and prime it. So far it's primed every time.

 

[StarTech]

The ones I have been running that failed are beyond this and actually needs new check valves and welch plug. None of which Zama will provide. I have tried changing the check valves but haven't found a suitable welch plug to refit.

I sounds like the one you had was just either sticky or had trash in it.

 

[PTmowerMech]

The ones I have been running that failed are beyond this and actually needs new check valves and welch plug. None of which Zama will provide. I have tried changing the check valves but haven't found a suitable welch plug to refit.

I sounds like the one you had was just either sticky or had trash in it.

It's possible that it was as you said, sticky or had trash in it. But it was cleaned with the USC and rinsed out thoroughly. This new chemical I'm using , "Awesome" is the best I've seen so far. The carbs come out super clean & shiny. You seriously can't tell they're not brand new.

In fact, the heater core in my dodge was getting clogged up to the point that even after letting the engine warm up for about 10 minutes, it would still take about 10 miles of driving before heat would start coming out the vents. I removed the heater hoses from the engine, sucked as much of the water/anti freeze out as I could, then filled it with "Awesome" and let it sit for about 30 minutes. Used a water hose to flush it out and put everything back together. Cranked the truck, got the water level back up in the radiator and bam, within just a few minutes, I had heat again.
The only problem was that it was dark when I was doing this, so i didn't get to see what came out of the heater hoses.

Anywho, about check valves. I'm guessing you need a magnifying glass to get them in and out then inspect them? I've never even attempted to mess with one.