High Quality Chainsaw Bars Husqvarna Toys

what would cause a carburetor to suddenly become stupid rich?

LogicallyCompromised

Well-Known OPE Member
Local time
1:48 AM
User ID
3457
Joined
Jun 28, 2017
Messages
6
Reaction score
7
Location
connecticut
Country flag
back story...
dolmar 7900, ran minto for 3 years with minimum carburetor adjustments throughout the seasons. about 4 months ago i cut a 9" hickory hanging over a friends house. saw popped on 2nd and idled minto on 3rd like it has countless times before. i let the saw warm up as i put some ropes in the tree and made my face cuts. after the face cuts there was a teaching moment so i shut the saw off...the saw has never ran correctly since.

i know, i need to find the source of this unregulated fuel, during starting, it pisses fuel out intake, compression release and exhaust. the couple times i have got it to run is with the low side all the way in. one puzzling question is, when i pulled apart the carburetor for first time in 3years it did not appear to have a welch plug. i have seen images on here of other 64xx/79xx zama carbs without welch plus either. were these people rebuilding carburetor and took an image in between progress or do some carbs not need them? this does not make much sense to me as i would think it would cause the saw suck more fuel in?

i did put the welch plug that came with the rebuild kit in but maybe it is not sealing well?

what is the point source of all the extra fuel?

thank you for your time!
 

huskyboy

Sorta a husqvarna guy...
Local time
1:48 AM
User ID
1352
Joined
May 30, 2016
Messages
10,025
Reaction score
43,448
Location
Ct
Country flag
Sounds like the needle is sticking open or something. A new carb is cheap enough where I’d just throw one on if it doesn’t get resolved after a rebuild kit. You can get a HD12 walbro (it’s a upgrade over the zama). Don’t loose the plastic spacers when you take the carb off.
 

Fruecrue

certified hand catcher
Local time
1:48 AM
User ID
2417
Joined
Jan 4, 2017
Messages
4,391
Reaction score
21,689
Location
Alden NY
Country flag
I’d guess the Welch plug is poorly sealed, I believe it’s the long skinny one in that carb right?
Had to be one in there originally.
If you take the L screw out and apply a slight positive pressure, you can bubble test the plug.
 

cus_deluxe

terms of service violator
Local time
1:48 AM
User ID
393
Joined
Jan 3, 2016
Messages
5,195
Reaction score
24,216
Location
Michigan
Country flag
Carb on my 262 started doing the same thing. Overnight went from running perfectly, next time i used it flooded to beat hell. Metering diaphram had reached its limit and was sticking “down” so that needle was wide open. Carb kit fixed it, but sounds like you may have a different issue with the welch plug...
 

Larry B

Pinnacle OPE Member
Local time
1:48 AM
User ID
3952
Joined
Sep 2, 2017
Messages
619
Reaction score
1,806
Location
SW ohio
Country flag
If you have a suitable tool pressure test the carb. Lots of vids on YouTube how. Some carb had Welch plugs sealed with some sealer. Ethanol can over time start to dissolve it and it comes loose and can jam up the diaphragm or metering lever.
 

Junk Meister

Pinnacle OPE Member
Local time
12:48 AM
User ID
1674
Joined
Aug 10, 2016
Messages
710
Reaction score
2,000
Location
Nebraska
Country flag
Metering diaphram had reached its limit and was sticking “down” so that needle was wide open. Carb kit fixed it, but sounds like you may have a different issue with the welch plug...
The welch plug may have not been the original issue but may now be the issue (Just thinking)
 

LogicallyCompromised

Well-Known OPE Member
Local time
1:48 AM
User ID
3457
Joined
Jun 28, 2017
Messages
6
Reaction score
7
Location
connecticut
Country flag
wow, this forum is active.

thank you all for the advice! happy to know the welch plug should have been there. there is small chance that it went somewhere when i pulled the carburetor off for the first time. i tend to have great accountability and i work in a clean shop but maybe it escaped me?

i will pull carburetor back off and seal it with something, maybe solder or jb weld epoxy. i will do some research on this.
i bought a cheap carb kit and did not like that the needle that came with it as it did not have the soft polymer tip(silicone?). maybe the original is part of the problem? i will use the solid machined one.

the kit had a much longer compression spring. so assumed the oem one was worn out. there have been several times i thought she would start choutching like before only to become disappointed.

i will head down to the basement and pull the carb one last time and seal the welch plug. i will watch some pressure testing procedures so i cn preform the tests. i am one of the most frugal people alive so i will waste more time in problem solving before i just concede it is beyond my ability. i just know someone can do it so why can't i?

i had read about the hd12 so it is nice to know i do not need to swallow a 50$ purchase for an oem zama and can get a hd12 much cheaper. i had a friend give me an 025 stihl (fixed it for under 2$ replaced a hose) and that saw laid out some tall red pines today. would have been nice cutting from one side and watching the dolmar throw corn in the air but it will have to be another job.
 

LogicallyCompromised

Well-Known OPE Member
Local time
1:48 AM
User ID
3457
Joined
Jun 28, 2017
Messages
6
Reaction score
7
Location
connecticut
Country flag
wow.....i wish i had a tree to noodle for the community.

late last night i tried to solder to no avail so i looked up the physical properties of some uv epoxy resin i use for fly tying. it claimed excellent chemical resistance so that was all i needed to read. i gave her the old college try with the contingency plan of just buying an hd12 for < 23$.

just got home from work and installed the carb, choked her...took 3 pulls to pop, choke in and minto pinto running...so happy! wish i knew where that original welch plug may have gone as my attention to detail is better than average. o well here is a couple images of the saw. i will try to get a noodling video up or just a video of this thing sending some corn into the heavens.

video link here
9cEjxIu.jpg
 

qurotro

Cookie Cutter
Local time
12:48 AM
User ID
6198
Joined
May 19, 2018
Messages
1,272
Reaction score
5,159
Location
Ar
Country flag
Carb on my 262 started doing the same thing. Overnight went from running perfectly, next time i used it flooded to beat hell. Metering diaphram had reached its limit and was sticking “down” so that needle was wide open. Carb kit fixed it, but sounds like you may have a different issue with the welch plug...
I think when you took it apart the diaphragm looks like cardbox paper.
There is another situation the diaphragm is swelled and wont push the needle far enough to let enough fuel in at WOT, causing engine to run lean.
 

cus_deluxe

terms of service violator
Local time
1:48 AM
User ID
393
Joined
Jan 3, 2016
Messages
5,195
Reaction score
24,216
Location
Michigan
Country flag
Yeah that diaphram was pretty crinkly haha
 

qurotro

Cookie Cutter
Local time
12:48 AM
User ID
6198
Joined
May 19, 2018
Messages
1,272
Reaction score
5,159
Location
Ar
Country flag
I have a Zama c3m carb off a husky 365 that did the opposite. I guess it's the same as dolly 7900's. It wont rev even the L needle is 3 turns out. Diaphragms are new.
Any ideas?
 

psuiewalsh

Basement Bodging
Local time
1:48 AM
User ID
124
Joined
Dec 23, 2015
Messages
1,864
Reaction score
5,520
Location
Nottingham,pa
Country flag
Is the fuel line correct between tank and saw body? I had one kinked and hole out of tank opening.
 

qurotro

Cookie Cutter
Local time
12:48 AM
User ID
6198
Joined
May 19, 2018
Messages
1,272
Reaction score
5,159
Location
Ar
Country flag
Is the fuel line correct between tank and saw body? I had one kinked and hole out of tank opening.
The saw runs fine with just a carb swap. So...
I wanna know how to fully service a zama c3m. Its the same as op's dolly carb
 
Top