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Kraig (WI) 
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 Topic: Carb Adjustment
Posted: 01 May 2010 at 9:37am |
On a Marvel carb, to make leaner, do I turn the screws out? or in? or out on the idle screw and in on the other?
Can someone help me?
Kraig
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7010,D17D,WD45,WD,WC,WC,B,
Gleaner K,60,66,72
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Jeff Z. NY
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Posted: 01 May 2010 at 9:50am |
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Try turning the main jet adjusting needle in a little.
Are you getting black smoke at idle or at operating rpm's ?
Edited by Jeff Z. NY - 01 May 2010 at 9:54am
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Wil M (NEIA)
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Posted: 01 May 2010 at 10:32am |
Kraig,
Are you trying to adjust the idle or the load side of the carb? They need to be adjusted seperatly and tractor will not run the best if they are not both adjusted correctly.
Idle adjustment: engine at operating temp, choke value completely open, adjust idle screw until engine runs smoothly staying on the rich side of the adjustment, which is turning the screw in (right or clockwise) Best way to do this is turn screw in until engine starts to run rough and then back screw out until engine runs smooth and then back in just a touch.
The load adjustment is done with the engine at governed idle speed and perferably under load. Turn power adjusting needle to the right or clockwise until power drops and engine runs rough, then turn needle to the left or counter clockwise until the engine picks up power and runs smooth. To richen this mixture you continue to back the adjustment out (counter clockwise) until good acceleration is used.
HTH
Wil
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"Yet there are soulless men whose hand and brain tear down what time will never give again." Anderson M Scruggs
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Kraig (WI)
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Posted: 01 May 2010 at 12:28pm |
I overhauled this WD this winter and am getting the timing and carb adjusted. It's not firing on all cylinders. I pulled the pulgs and two are wet with gas. I figure it's too rich at idle. I'll play around with it.
Thanks,
Kraig
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7010,D17D,WD45,WD,WC,WC,B,
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Dick L
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Posted: 01 May 2010 at 12:53pm |
Looking at how things work I have adjusted carburetors this way since the 1950's and it has always worked in the field or at a pulling contest.
When the engine is running the governor, if the linkage is adjusted correctly, is putting pressure on the butterfly stop screw on the back side of the carburetor to slow the RPM's to that setting. The stop screw holds the butterfly open to let enough air thru to run the engine at slow idle. The idle adjustment screw is adjusted in conjunction with the stop screw to get the lowest smooth running idle. The stop screw adjust your RPM's. The idle needle adjusts the fuel at the setting of the butterfly to run smoothly at that butterfly setting.
When you are there you are done done done with the idle adjustment screw. It serves no other purpose
For power adjustment.
I then open the throttle to wide open or as stated in some manuals (high idle)
I the open the main power adjusting needle until the engine is running at the highest RPM that I can get. At this point I turn the needle in until I hear the RPM's to start to drop.
This will be the most you will get from a carburetor unless you place your tractor on a dyno.
It is simple, quick and never fails.
Adjustments are much easier when understanding the cause and affect. If you understand the cause and affect/ why you adjust what and what happens when you do,you will find that you have very few questions.
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Gerald J.
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Posted: 01 May 2010 at 1:58pm |
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You'll get more power at high speed if you open the main jet to run rich. Also cooler engine operation, but poorer fuel economy.
Gerald J.
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Dick L
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Posted: 01 May 2010 at 2:26pm |
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Fine line on the statment (run rich) and to rich. If you have it on a dyno and as you open the power jet and you go by the ("run rich") the power starts to drop. If you open it past the proper setting it is the same as pulling out the choke.
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Jacob (WI,ND)
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Posted: 01 May 2010 at 2:35pm |
 Dick L wrote:
Adjustments are much easier when understanding the cause and affect. If you understand the cause and affect/ why you adjust what and what happens when you do,you will find that you have very few questions.
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Well said! This is my way of looking at MANY things in life, not only tractors!
Thanks for this explanation on carbs Dick, this is one of the most clear and easy to understand explanations I have read so far!
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Jacob Swanson
1920 6-12; 1925,1926 20-35 longfenders; 1925,1926 15-25's; 1927,1929 20-35 shortfenders; C; B's; IB; WC's; WD; WD45
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Gerald J.
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Posted: 01 May 2010 at 4:13pm |
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Running rich by opening the main jet is NOT the same as pulling on the choke. Adding fuel does not restrict airflow like closing the choke. Yes it is possible to run too rich and hurt the power, but I've been able to detect on my MF-135 that adjusting for minimum throttle opening (with the governor at work) at maximum speed doesn't get as much torque out when plowing as when running it a tad richer. Just enough to darken the exhaust pipe, not to smoke black, probably no more than a quarter turn richer on that MS carburetor main jet. E.g. when pulling the plow where the governor has the throttle stuck wide open, it goes faster, holds up the engine speed better on the rich side of that lightly loaded mixture adjustment.
A parallel exists in piston aircraft engines. They run full rich for take off and for landings (where they might have to make the transistion to full power quickly) to get the most power from the engine with the least cooling. At altitude the pilot routinely leans the mixture watching for a peak in exhaust gas temperature which gives the best economy. There can be a 500 degree F rise in exhaust temperature from that. The engine has to have good high temperature rated exhaust valves to stand that leaning, and probably hardened seats. The difference in fuel flow on one large 8 cylinder flat engine was 550 gpm at take off and 4 gpm at cruise.
Gerald J.
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Dave(inMA)
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Posted: 01 May 2010 at 5:21pm |
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Gerald - in your 2nd paragraph did you mean to say "...get the most power from the engine with the MOST cooling"? If so, I agree with your comment on those engines!
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Gerald J.
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Posted: 01 May 2010 at 5:39pm |
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Yes, looks like I had a brain fart between works thought least heating typed least cooling...
Gerald J.
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Dick L
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Posted: 01 May 2010 at 6:22pm |
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Gearld, I was not saying you were wrong in how you are adjusting and what you were getting with your adjustments but trying to point out that the word rich does not define the stopping point in opening the power needle.
Understanding the choke. The venturi located in the neck of the carburetor restricts the air flow into the engine to create a vacuum to pull fuel into the air stream thru the feeder tube/discharge jet. A slight closing of the choke will increase that vacuum and draw more fuel into the air stream from this same feeder tube/discharge jet. By adding a slight amount of choke will in fact cause the engine to run rich. Not the way to get more power but you see pulling jockeys using the choke down the track when they start to run out of snot.
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Gerald J.
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Posted: 01 May 2010 at 6:44pm |
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Pulling on the choke enough to richen the fuel also restricts the air flow so they might as well just close the throttle a little. A puller ought to be set for as rich as it will run to produce torque anyway, I'd think.
Gerald J.
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mlpankey
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Posted: 01 May 2010 at 7:12pm |
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Hmmm and this pulling junkie takes the choke out and throws them in a tool box drawer. if it will suck youre hand to the carb inlet at cranking speed it will move enough air at low rpms also. best have the clutch pushed in cause youre done when engine hits 400 rpms cranking speed.letting one roll backwards puts alot of stress on head gaskets and rods.
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Dick L
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Posted: 01 May 2010 at 7:21pm |
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I am not saying it helped all that much but when you have the RPM's pulled down from a load the air flow thru the engine is getting to the point of non existent.
Pulling a transfer sled is not like plowing. Never underestimate what (dumb) pullers will do to win. And never say never unless you have been there and saw it fail. When you see a puller doing something with his right hand your watching the wrong hand. (Right Planky)
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mlpankey
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Posted: 01 May 2010 at 7:43pm |
Dick L wrote:
I am not saying it helped all that much but when you have the RPM's pulled down from a load the air flow thru the engine is getting to the point of non existent.
Pulling a transfer sled is not like plowing. Never underestimate what (dumb) pullers will do to win. And never say never unless you have been there and saw it fail. When you see a puller doing something with his right hand your watching the wrong hand. (Right Planky)
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yep dont ever underestimate what a dumb puller will do to win . my engine build pics proves that statement.
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DaveKamp
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Posted: 01 May 2010 at 9:03pm |
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Okay, so Will SLIGHTLY alluded to the REAL answer to the question, which was:
WHICH WAY makes the engine LEANER?
I believe that MOST of the M-S carb adjustment screws are AIR BLEED, not FUEL METER, which means, if you back the screw out, the mixture gets LEANER, while turning the screw in makes them RICHER.
Someone please confirm this...
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Dave(inMA)
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Posted: 01 May 2010 at 9:07pm |
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Believe that's right, Dave.
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WC, CA, D14, WD45
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RyanTN
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Posted: 01 May 2010 at 9:10pm |
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It is correct. Clockwise or right=rich
Edited by RyanTN - 01 May 2010 at 9:10pm
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mlpankey
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Posted: 01 May 2010 at 9:18pm |
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The idle screw on tsx carbs increases or decreases air flow. So turning it in would richen it by closing the air off. the power needle is richend by turning it out for it adjust fuel. set idle screw 1 1/4 turns off stop pin set idle adjustment needle one turn off seat. set power adjustment needle one full turn off seat. then tweek
Edited by mlpankey - 01 May 2010 at 9:20pm
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Gerald J.
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Posted: 01 May 2010 at 11:24pm |
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Yup, idle mix is air, main get is fuel. So they adjust in opposite directions.
Gerald J.
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DaveKamp
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Posted: 02 May 2010 at 7:57am |
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NOW we've got a proper answer for Kraig- thanks guys!
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Kraig (WI)
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Posted: 02 May 2010 at 8:20am |
Thanks guys, I got it running pretty good now. It still has a sputter, but I might have a manifold leak.
I'll work on that next.
Kraig
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7010,D17D,WD45,WD,WC,WC,B,
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mlpankey
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Posted: 02 May 2010 at 9:10am |
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manifold leaks are confirmed or ditched easily just spray some wd 40 around it if the engine smooths out its loosing vacuum
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Dave(inMA)
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Posted: 02 May 2010 at 11:18am |
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Good point about main jet vs. idle jet. Many of us have experience with M-S carbs that do not have an adjustable main jet, so we think only in terms of the idle jet.
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WC, CA, D14, WD45
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