carburetor issues


My 841 is idling perfectly at all RPM ranges. The problem is rapid throttle increase causes hesitation to engine dying depending on the rapidity of increase. The carburetor is completely clean, all passages clear, no manifold leak, float set at 1/4 inch. I have adjusted main jet in 1/4 increments from one turn all the way to unscrewed repeatedly and I cannot get a satisfactory response. The Marvel has main screw at bottom of bowl.
A short history. Tractor was derelict when purchased. Bought Tisco carb kit that had faulty main nozzle. Nozzle was not drilled through. I drilled nozzle so as to have same diameter throughout shaft. Nozzle clean with correct passages. I am almost to the point of trying an aftermarket carb.
Any thought are much appreciated.
 
(quoted from post at 10:11:10 10/12/15)
My 841 is idling perfectly at all RPM ranges. The problem is rapid throttle increase causes hesitation to engine dying depending on the rapidity of increase. The carburetor is completely clean, all passages clear, no manifold leak, float set at 1/4 inch. I have adjusted main jet in 1/4 increments from one turn all the way to unscrewed repeatedly and I cannot get a satisfactory response. The Marvel has main screw at bottom of bowl.
A short history. Tractor was derelict when purchased. Bought Tisco carb kit that had faulty main nozzle. Nozzle was not drilled through. I drilled nozzle so as to have same diameter throughout shaft. Nozzle clean with correct passages. I am almost to the point of trying an aftermarket carb.
Any thought are much appreciated.
41 is not a Ferrari or a Corvette or even a Ford F-150. It has no accelerator pump or FI acceleration enrichment features. A tractor generally runs at a near constant governed speed during most all working life, so does not need "acceleration" features.
It is a tractor.
 
Thanks JMOR but when the tractor needs to respond to increased engine demands which require the governor to open the throttle, the carburetor needs to respond. I'm not
trying to create or simulate a racecar. I know the difference between gravity fed fuel supply and mechanical.
 
(quoted from post at 10:30:49 10/12/15) Thanks JMOR but when the tractor needs to respond to increased engine demands which require the governor to open the throttle, the carburetor needs to respond. I'm not
trying to create or simulate a racecar. I know the difference between gravity fed fuel supply and mechanical.
ell, ...you did say, "The problem is rapid throttle increase....".
 
(quoted from post at 10:41:08 10/12/15)
(quoted from post at 10:30:49 10/12/15) Thanks JMOR but when the tractor needs to respond to increased engine demands which require the governor to open the throttle, the carburetor needs to respond. I'm not
trying to create or simulate a racecar. I know the difference between gravity fed fuel supply and mechanical.
ell, ...you did say, "The problem is rapid throttle increase....".
I remember your nozzle problems & drilling operation, so I ask, are you sure that the tiny nozzle air bleed holes (~0.028") are clear after drilling operation? If obstructed, they could potentially result in your problem, as they supply an extra measure of fuel into the nozzle from the 'acceleration well' upon throttle position change.
 
Yes passages are clear. This is what is so frustrating. If I nurse up RPM,s everything is fine. But if governor decides to increase RPM's quickly, say going from level ground to suddenly climbing a slope, then engine boggs down. Or another example is letting out clutch too fast. If I don't ease my foot off clutch pedal, then tractor stalls or struggles to regain RPMs. It feels like a fuel delivery issue but fuel flow is strong and I've has the carb off again yesterday to make durn sure that all passages are clear. I'm also pretty sure the governor is adjusted properly and regardless, I can disconnect governor and just use throttle plate to test.
thanks again
 
Does choking it hurt or help?? Could still have something clogged up and not letting enough fuel threw the main jet areas
 
(quoted from post at 07:11:10 10/12/15)
My 841 is idling perfectly at all RPM ranges. The problem is rapid throttle increase causes hesitation to engine dying depending on the rapidity of increase. The carburetor is completely clean, all passages clear, no manifold leak, float set at 1/4 inch. I have adjusted main jet in 1/4 increments from one turn all the way to unscrewed repeatedly and I cannot get a satisfactory response. The Marvel has main screw at bottom of bowl.
A short history. Tractor was derelict when purchased. Bought Tisco carb kit that had faulty main nozzle. Nozzle was not drilled through. I drilled nozzle so as to have same diameter throughout shaft. Nozzle clean with correct passages. I am almost to the point of trying an aftermarket carb.
Any thought are much appreciated.

SWAG - check timing and mechanical ignition advance?
 
This is a very facinating system. Looking at the diagram and the text it seems as though the carburetor has no dedicated idle
system. I'm thinking that if the float level is too high the needle adjustment would have to be screwed in (lean) to smooth
the idle possibly making it too lean to accelerate (opposite what one may think is normal). And a low level might require the
screw to be backed out (for idle) possibly enriching the main system. I also wonder what holds the venturi in place and if it
is possible to slip so ruining the suction where it needs to be. Seems I'm able to learn something new on this site every day.
 
(quoted from post at 12:35:30 10/12/15) This is a very facinating system. Looking at the diagram and the text it seems as though the carburetor has no dedicated idle
system. I'm thinking that if the float level is too high the needle adjustment would have to be screwed in (lean) to smooth
the idle possibly making it too lean to accelerate (opposite what one may think is normal). And a low level might require the
screw to be backed out (for idle) possibly enriching the main system. I also wonder what holds the venturi in place and if it
is possible to slip so ruining the suction where it needs to be. Seems I'm able to learn something new on this site every day.
F, it does have a dedicated idle circuit. That diagram posted was for explaining a specific aspect of the carb & is not complete carb. Venturi is compressed between upper & lower halves of carb body. However, if installed upside down, it will not be compressed & will be loose. This is very close, but not exactly what he has:
 
It helps to choke Rich so that's why i'm leaning to fuel delivery. Surely the kit I bought from "hardly ever right" is not the culprit. I get a good flow of fuel from bottom plug of carb and all passages are clear, that i'm sure of.
 
All passages clear as in have you run a piece of wire threw them and then air an spray carb cleaner?? If course that part you drilled out may not be as big as it should be. As for fuel flow if you pull the carb drain plug and it fills a pint jar in 3 minutes or less your flow from the tank to the carb is good
 
Ran wire through passages and cleaned multiple times with carb cleaner and air. Drilled blocked nozzle to same diameter as top and bottom of nozzle and fuel flow is as you describe.
 
Is that area you drilled out nice and smooth and not rough from the drilling?? Rough is not good and can cause funny problems. Is this with the air cleaner hooked up or tube off??
 
smooth and air cleaner hooked up. I ran it unhooked at 1st then hooked because I knew it would cause it to richen with the extra air resistance.
 
Maybe the side holes in that tube are to small or not as they should be since you know it was a bad new parts from the get go they could be wrong size or not placed right etc
 

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