what would cause a carburetor to suddenly become stupid rich?

[Larry B]

https://www.google.com/url?sa=t&sou...FjABegQIBhAB&usg=AOvVaw3gvoAMl6jAGdg-ecYrkOPS

Here is a link to zama manual

 

[LogicallyCompromised]

Need to make up a shroud to keep the cylinder cooled.

i made one out of carbon fiber, it is installed on the saw; the air spinning off the flywheel is captured and encouraged through the cylinder head. i think there is a good chance the current setup actually cools better than oem configuration. there are less areas of high pressure (reduced flow) and the cool air is able to be exchanged quicker. this localized environment which the cover encouraged resulted in the radiant heat being captured and adding a higher work load to the air cooling system. areas which the heated air would stagnate now it is open to ambient. i did something similar with a computer 5-6 years ago and the results suggest this narrative is correct; open layout desktop computer.

 

[Rob Stafari]

i made one out of carbon fiber, it is installed on the saw; the air spinning off the flywheel is captured and encouraged through the cylinder head. i think there is a good chance the current setup actually cools better than oem configuration. there are less areas of high pressure (reduced flow) and the cool air is able to be exchanged quicker. this localized environment which the cover encouraged resulted in the radiant heat being captured and adding a higher work load to the air cooling system. areas which the heated air would stagnate now it is open to ambient. i did something similar with a computer 5-6 years ago and the results suggest this narrative is correct; open layout desktop computer.

Have any pics of your carbon fiber fab?

 

[Stihlms]

I had a Zama pop the Welch plug. Long skinny one didn't even realise one went there.

What is a Welch plug never heard of it

 

[grizz55chev]

What is a Welch plug never heard of it

Soft plugs used to block drilled passages, most times they don’t need to be farked with.

 

[Poleman]

If the Welch plug was miss it could cause the flooding/over rich issue especially if it’s loose or fell out. That’s one issue to address and get it replaced and sealed again.
Second issue is the solid tipped needle and the spring change. Being the tip is solid it won’t seal correctly on a used carb, so I would put one on with a soft tip. Secondly changing springs changes the carictoristics of the carb. If it’s weaker then stock it will have a tendency to flood, If it’s to strong enough fuel won’t be supplied and cause a lean condition. Both will cause the saw not to run properly but in different directions. The spring is something that can be changed, swapped, stretched, trimmed to produce and change different running conditions.
When describing the sudden change from running fine to flooding I first think of a bad nozzle. If the small fragile diaphram some how was weak/worn and there was a sudden but unnoticed surge or backfire through the carb upon restarting rupturing it it would flood and cause a rich condition upon running. When this happens it’s impossibe to correct the issue without replacing it or changing carbs.
Seems there’s a lot going on here with the loss or missing Welch plug. That would have had to fall out upon breakdown of the carb because it wouldn’t run properly or normal without it. If it had become loose it would have caused the sudden change.
You might hook the carb to the fuel line with fuel in the tank and view down the Ventura to see if you can see fuel leaking from inside it. Pressure testing would also help in a diagnosis.

 

[LogicallyCompromised]

Have any pics of your carbon fiber fab?

here are two from fabrication

and here is one i just took on the saw.

thank you poleman for your detailed response!
i never installed the solid tip needle. i did however change the spring and the aftermarket one was longer but did not compare the spring constants. i had to change the low side after i got it running so i believe i have accounted correctly for the possible lean condition you cautioned me.

thank you also for the advice about looking for the leak, i knew the seal was trash with the aftermarket welch so i decided to address that before i wasted any further time with tests, the odds were in my favor i had the correct point source for the problem.

thank you all for brainstorming and problem solving. you gave me the necessary motivation and information to solve this problem i put on the back burner for several months.

live long and prosper all!

 

[LogicallyCompromised]

after the fix i last posted the saw sate for a couple months and the same flooding cylinder scenario happened. i pulled carburetor and the issue was the uv epoxy did not last. with additional research, it appeared jb weld would would in that environment. that fix did not last long either and i have since found a thread stating the use of jb weld in such environments is temporary.

the most recent fix which i suspect is failing as we speak was permatex ultrablack around a poorly fitted welch plug. i am going to pull the old zama c3m tomorrow and suspect the silicone is no longer holding well but did not fail as catastrophically as the other temporary fixes.

becoming a suckfest and i like the saw so much when she eats but after running several tanks through those g660 saws i almost want to move on. it does not make much sense to have a larger saw but to stop short of the 92cc saw. the dolmar is much lighter, better on fuel and will get just about all jobs done around here but the g660 made me feel so bad in that 34" red oak buck. i brought the dolmar to work to show off and as it was eating and sounding great i looked up and could not match the feed rate on that g660. i believe i have the edge in sharping most the time as well but i just could not pull as close as i wanted with that g660.

i will investigate the carburetor again tomorrow and may try to get a new welch plug from the local shop if they stock them before buying a knockoff hd12.