New Lifan 420 with lean stumble, stock exhaust and intake.

carbidecutter

I just bought a Lifan 420 for my Manco Carbide go kart. After getting everything connected, I fired it up (had to choke it naturally... but that will be fixed). I didn't give it a lot of time to warm up but it seemed to have a pretty good lean stumble from idle to WOT. Has anyone else had to jet the carb right out of the gates with no intake or exhaust modifications? I have micro bits and have no problem drilling the jet. I'm just wondering if anyone else has experienced this and if it's normal? Or maybe I need to give it more warm up time?
I know they tune these new engines pretty lean but DANG! It shouldn't hesitate the way it does from idle to WOT.

As a side not, any suggestions for getting the idle mixture screw that they kindly break off out? I'd like to add some fuel to the idle side to help with tip in.

Thanks for any input.

BGW

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justwondering

I did my first LIFAN swap earlier this summer.... really all summer long..lol

I tried the drilling out of the mixture screw and it was a total failure for me.
Too hot, too much humidity, and my glasses fogged over before I let the trigger off the drill... very, very sad.

I wound up buying a new carb from Vegas Carts which has a much easier system to make that screw available.

I have not solved my air box solution long term. I tried the vegas carts, low profile airbox but was not happy with the end result. Too tight and close to the passenger side rear shock.

Mind did stumble and still needs choke which means I still don't have it dialed in well. But then I'm on my second airbox solution and this is not going to be the last.

My hope is to get to a pick-n-pull and get a small car box solution to try next.

So I can't say that I drilled any jets but I did get rid of some of the problem with a different carb that let me change the mixture.

Cavemandrew

I have no experience with that engine. But my 670 does the same when cold. Gets better after it warms up and after I messed with the mixture screws.. After I got the tamper proof caps out. Still not perfect. Planing on opening up my main jets soon.

You could try a left hand drill bit and see if it would pull your mixture screw out. If not use an ez-out. Just be sure not to drill too deep.

Shepard

Try to find an adjustable main jet kit on ebay. There listed for a 212 predator but will work in any clone engine. Much better then trying to drill your main jet. Pull the cap off of the air/fuel screw so you can open it up. Between the 2 upgrades maybe a air filter/velocity stack adapter and a clamp on air filter. After this you'll need to work on the exhaust and open it up some to achieve full benefit of your carb improvements.

Shepard

How much adjustment do you have on your engine plate. Like if you used Vegas Carts engine plate -- if you could go to a longer belt and slide the engine more to the front of the carts engine compartment. A couple of inches in there could make a big difference on what kind of air filter you can use.

carbidecutter

Thanks for the input from all! I did some looking on the Vegas Carts site last night. MAN I wish I would have went the Lifan/Predator route a long time ago. I spent north of 100 on a carb for my old EX27 Subaru where the modded carb from VC is only $29. I'm not going to be as gentle with this car trying to remove the mixture screw when a new one will only run $30 plus shipping.

carbidecutter

Remember when you're adjusting the carb that you want to work with the idle side and main. The idle circuit has input on the mains and you can actually lean the main while making the idle circuit richer which will help make it so you don't have to choke it to start. I had my EX27 dialed in to where I didn't need to choke it at all but it was fall when I was playing around and temps do make a difference. If you can get to your idle mixture screw try a lean best once the engine is warm. Turn the mixture screw in until you get a lean stumble at idle. Next back it out until you get a stumble from being rich while counting your turns out and then shoot the middle. It should improve your idle circuit and mains. When adjusting my main I always made a slight idle mixture adjustment while also drilling my main. I use a micro drill set and pin vise for drilling jets so I can go slowly and by very small increments.

sho305

You have a couple issues, the EPA wants it lean as possible so they only run good completely warmed up and still likely would make more power a little richer. Next they are made to run on the governor so they run 1200rpm idle and faster where a little lean is not as big a deal. You load it in the cart and throttle it all the time and you see the mixture is not good. Now if you make any changes to airflow it will be worse yet.

You need to richen the idle to make it start without the choke, at least in summer weather. You need to richen the main some depending on what you change to get the best power. Richen more if you mod the airbox and/or exhaust. Easiest way is get torch tip cleaner and file the main larger, or get a jet drill set with the pin vice you just drill by hand its brass and easy. You have to get the plug maybe the screw out of the idle to adjust that, or buy a vegas carb that has the screw open to start with. Or, Vegas also now has the larger carb you can get if you want an upgrade.

carbidecutter

I haven't had time to play much since posting this. Work got in the way of having fun again! I'm going to try to work on it today and get that idle mixture screw out. If I can get that out and replace it, I can start playing with the main sizing and do a few WOT runs to test for some color on the plug.
I'm probably not going to remove the governor until I have run a few tanks of fuel through this thing to get the engine broke in. Later on I'd like to bring the idle up to about 1600 to get it closer to my cut in for the series 40 driver.

I have been reading a lot about this engine and it appears they have a rev limited coil. Can anyone confirm that? I saw one thread where a guy said he was floating valves at around 4200 and I'm wondering if he wasn't just hitting the limiter. My EX27 could go well above the 4200 range without floating the valves. Maybe the springs on the Lifan aren't quite as stout?

carbidecutter

I went ahead and ordered the VC adjustable carb today. With the fear of messing this carb up now gone, I FINALLY got the idle mixture screw out and was able to put the one from my EX27 in. I went up about 2 sizes on the main. I also went up 2 sizes on the pilot since I wasn't getting the desired effect at startup, still had to choke. Even with the mixture screw and 2 sizes larger on the pilot I'm still having to choke it to get it to fire but the lean stumble is now completely gone which is a plus. While I'm waiting for the new carb to arrive I'm going to get my drive and driven pulley aligned and hopefully take this thing on its maiden voyage tomorrow. Then I'll have to see if I have to change back to a different sprocket on the driven since I dropped a couple teeth trying to get more out of my old EX27.