Try drilling out the lo speed jet under the idle screw , readjust lo speed screw . Measure and drill out the air inlet you described earlier . If there is no change or is worse put a drop of radio solder on it and re drill back to original size .
Not sure if you solved this yet, but I have a slightly different theory (probably not a fix, but a working guess). I haven't got in to mine yet, but I suspect the 440cc doesn't have a dedicated fuel pump (?). You may be leaning out at idle with your double fuel filter causing a flow restriction. I ended up going with a k&n fuel filter that looks suspiciously like an in-line air filter for air compressors, but it has replaceable filter elements which should be dandy down the line and the micron filtering medium should work great for fuel. The unit its going into was pump driven but is being converted to gravity fed on the notion that the duromax is also. If that's all bubkis on the duromax having a fuel pump, then this all goes out the window, but worth a check if not.
I really wonder if it's a fuel delivery problem. I've heard that the paper style fuel filters do not work well with pulse style fuel pumps. Many people recommend going to screen style filters with a pulse pump.
I would double check your tach, sounds to be running slower than indicated. .....has you put a billet flywheel and bumped thr compresion and increased the cam duration ? ......al things that even v8' struggle with getting a smooth low idle .....singles dont lope they die when you miss a beat.
there is a old last resort trick that may work in your situation with the carb you have. Drill a small hole thru the throttle plate in the carb. This will in turn allow a higher amount of air thru the carb while plate is closed. After hole is in should still be able to adjust the idle.
So I'm about to put a new air intake on my 420cc duromax but not sure what to do with the hoses coming off the back of the old air filer mind helping me out?
Im not sure about the big block (440cc) but on my small blocks (196cc and 212cc) they like to idle around 1600rpms. And my 212cc struggles at 1300rpm. But I do have performance parts on mine and I don't know about the 440cc. RedBeardsGarage here on CZcams has so much info on the 440cc and 420cc engines
That is about what I decided. But after several people made it a point to claim it would fix it. I figured it was worth the experiment. I think on the GX390 it might have worked out. But this carb is giant in comparison and needs a 3 jet carb.
IT'S ALWAYS WORTH A TRY. GOOD VIDEO 😊👍
Try drilling out the lo speed jet under the idle screw , readjust lo speed screw . Measure and drill out the air inlet you described earlier . If there is no change or is worse put a drop of radio solder on it and re drill back to original size .
Not sure if you solved this yet, but I have a slightly different theory (probably not a fix, but a working guess). I haven't got in to mine yet, but I suspect the 440cc doesn't have a dedicated fuel pump (?). You may be leaning out at idle with your double fuel filter causing a flow restriction. I ended up going with a k&n fuel filter that looks suspiciously like an in-line air filter for air compressors, but it has replaceable filter elements which should be dandy down the line and the micron filtering medium should work great for fuel. The unit its going into was pump driven but is being converted to gravity fed on the notion that the duromax is also.
If that's all bubkis on the duromax having a fuel pump, then this all goes out the window, but worth a check if not.
Good video but could tell me where you got the carb an air filter.
great!
Ever thought about upgrades to a round or flat slide carb, they are way more tunable then factory carbs, just a thought.
I really wonder if it's a fuel delivery problem. I've heard that the paper style fuel filters do not work well with pulse style fuel pumps. Many people recommend going to screen style filters with a pulse pump.
I would double check your tach, sounds to be running slower than indicated. .....has you put a billet flywheel and bumped thr compresion and increased the cam duration ? ......al things that even v8' struggle with getting a smooth low idle .....singles dont lope they die when you miss a beat.
there is a old last resort trick that may work in your situation with the carb you have. Drill a small hole thru the throttle plate in the carb. This will in turn allow a higher amount of air thru the carb while plate is closed. After hole is in should still be able to adjust the idle.
Alot of automotive carbs have holes in the butterfly valve
So I'm about to put a new air intake on my 420cc duromax but not sure what to do with the hoses coming off the back of the old air filer mind helping me out?
Mine idles just fine just really hard to start and ain’t enough information out there to diagnose it
I run a 32 mm Nibbi carburetor on mine
How do you get a electric start on yours
What did you do to relocate your fuel supply?
Im not sure about the big block (440cc) but on my small blocks (196cc and 212cc) they like to idle around 1600rpms. And my 212cc struggles at 1300rpm. But I do have performance parts on mine and I don't know about the 440cc. RedBeardsGarage here on CZcams has so much info on the 440cc and 420cc engines
Can you please post the actual size of the drill bits used? Thank you
I'm guessing it's 1.1 mm
Research and Further Development...
Sometimes it can be a real bear!
Just keep your idle turned up a little high and go on with life lol.
That is about what I decided. But after several people made it a point to claim it would fix it. I figured it was worth the experiment. I think on the GX390 it might have worked out. But this carb is giant in comparison and needs a 3 jet carb.
@@RCGRacing I fully agree man. You tried non the less. Bigger carb throat does make for a weaker vacuum draw compared to a smaller carb.
Just get a dirt bike carb. 34mm mikuni and tweek it
Needs more air