G not getting enough gas under load

grniron58

Member
Have a puller G that coughs and sputters when under 3/4 or more load. Using big nut carb that all passages are clean. Carb has been honed out. I can have load jet backed out completely with some improvement. Have gas line directly to carb for max flow. Running a good hi octane gas. Did drill very small hole at bottom of neck below load needle seat so more gas gets to main jet. Has anyone else done this? Do I need to drill hole larger but careful to not go too big? Looking for some ideas or to hear from someone else on what you did to get more gas under load.


PS I am using electronic ignition.
 
Measure the main jet port and go up one machinist size drill bit & enlarge the jet, try it & go from there. Too big & it will be new carb time.
 
1. 4 rounds out on the load needle is wide open.
2. #51 carbs came with a .040" hole in the lower stem near the load needle opening.
3. Verify your float level is correct.
 
How many cubic in. are you running? Are you aware that you can run a carb off an unstyled B or even an H on a 321 inch A and it will start/run/transition and load on a dyno and never spit/sputter? A carb will flow less and make less hp but will always mix the correct fuel/air ratio (if all is right in carb) to make the engine run correctly. If the engine size is such that it is trying to suck way more air in than throttle plate size will let it, then any other air leaks between carb and head will show their weakness. Spit/sputter is either lack of fuel or too much air for the fuel it's getting. A 426 hemi will run just fine on a two bbl carb even under wot and acceleration...it just won't have a lot of hp but the fuel/air that it does get is of the correct ratio to run perfect. Any size throat bore on that carb could not be large enough that a corresponding richening of the load needle should correct the ratio. Has it got the correct load nozzle in it and more importantly, is it pushed all the way up into the bore so it seals at the top? Easy mistake to make. ANY air leak from carb to engine will cause a lean mixture ratio and spitt/pop. Even more on a larger modified engine trying to suck more air than carb will allow.You are probably not running a choke but if you are , try closing it just slightly when this happens and see if it improves. My '66 GTO has 3-2 bbl carbs on it at 400 cid. I can unhook the front and rear linkage and run just a two bbl and it runs just as good as all three...just less power. Put a 321 "A' #71 on it if you have access to one. see what , if anything, changes. If it's same then you have air leak or EI ignition problems. Put it on a dyno with a stock 71 and bet you don't see much diff. and maybe even better at lugging rpm. We would all love to know what you find. Please post back when you cure it.
 
Just a side note. That style load nozzle with the angle cut at the bottom, sometimes gets put in upside down and/or not pushed all the way up because it's very fragile and if it was just slid in until it stopped, there's a good chance it is not all the way in. They normally "stub" themselves at the top and need some TlC to get them up that last 1/2". How far does it protrude up into carb bore ? If not all the way up and sealed at top, then air will be sucked through the front air bleed/vent hole and if it can suck air,it won't suck fuel...(lean ratio).
 
Fuel pump? They suck a lot of gas under load. Run it about 400 rpms and set the idle till it starts to smoke. Back it off 2 clicks then set the load at about 600 rpms till it smokes. Then back it off 2 clicks and see how it runs.
 
Any time you hog out the Venturi for more airflow - you remove vacuum signal which is what lifts the fuel from the bowl. It's a ratio between the throat size & Venturi size that matters. That being said, all the big Deeres I see pulling have fuel pumps to keep the carb full. You can't flow enough through the needle/seat area without it. 3-4 psi is what I'm told.
 
Most that I've seen with fuel pumps were because they took out the original heavy fuel tank and put on a small alum. one below carb level and need it to get fuel uphill to carb. I could be wrong as to their intent. I guess no one has mentioned whether this sputtering is when pulling with front end up or at any time he puts load on it? If he has his fuel supply opened up for a full 5/16 line that runs full constantly, I can't imagine needing added fuel pressure to keep that bowl full. Here again, I could be wrong but I believe that carb with 1 11/16 throttle disc will supply all the fuel that size air hole needs to get optimum air/fuel ratio at full load. Again, it's lack of correct fuel/air ratio , not volume, that makes one spit/sputter. Also, he never did say where his fuel tank is located. We can't just assume it's in original location on a puller?? Some more info might just explain the problem.
 
Many times these large cubic inch pulling engines will suck MORE fuel due to higher port velocity through ports that are still relatively small. The fact that this tractor starves out makes me think the problem is on the delivery side as well. An electric pump with regulator should take care of the problem. Mike
 
I don't know how big your "G" is, but I feed a mid-600 CI A with a ported DLTX71, 3/8ths fuel line, no filter, gravity flow (no fuel pump)and stock sized needle/seat. I did enlage the fuel nozzle, but don't know to what size unless I pulled it out and measured it (been too long ago). As was mentioned by another, check float setting. Do a wet check by putting a fitting in the drain cock hole on the bottom of the bowl and a clear line up the side of the carb. Another thing to check is the bowl vent. I put another vent to the bowl on mine and that fixed the same type of problem. Drilled a small hole in carb body above the bowl, put a very small fitting and a length of plastic hose. If the bowl has a restricted vent fuel can't flow in fast enough to keep up with demand. My $0.02 worth, your mileage may vary, plus many other disclaimers. Mike
 
I did drill another hole to help vent carb and improve fuel flow as mentioned in one or more posts. That helped a lot but also drilled a larger hole on bottom of neck below load needle seat. Now load jet is out 2 1/2 turns and runs great. My G is 6 3/8 x 8 3/8. I know there are bigger ones out there but where I pull here in south central MN you can't hardly make use of all those ponies with the type of tracks and speed limit rules.

Thank you to all who responded.
 

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