I have a Manco 90 that sat for a few years. I put on a new carb, air box, fuel line, fuel filter and battery. Running pretty good but won't idle. I am trying to understand the carb stages, idle circuit, needle jet, and main.So it runs great at full throttle, but it bogs for a few seconds at part throttle (needle jet) and won't idle at all. I moved the needle down (rich) trying to improve idle, so that explains the bog at part throttle because it wasn't doing it before the needle change. It wouldn't idle but would take right off from part throttle. So I had the quad idling before I got a factory air box. But now with air box, no idle at all. With idle mixture all the way out and idle speed all the way in! So it seems too rich in the idle circuit if I am understanding this? In fact there is no change at all in engine speed until I press the throttle fully half way and the slide is 1/3 way up. If I hold the throttle at the mid point (needle jet) it will run smooth as long as I hold that.

 

Read this. Hope it helps. Wether its a motorcycle or an ATV, CV carburetors operate on the same principle. I would check the pilot jet for an obstruction. Just guessing pms screw should be 1.5 to 2 turns out , then adjust the idle screw out , it should idle high, then turn idle screw in until it sounds right.. Sounds like main jet is ok.

 

Thanks so much. So I am on the right track, but maybe the pilot is too small/too big? It is a brand new replacement carb. Though the amazon reviews had multiple people saying it was impossible to get the carb dialed in all ranges. Can the pilot be swapd for other sizes like the main?

 

Same size jets in the old carb?

 

That's what I was wondering, so I swapped the main jet from the original carb and am soaking the pilot now to swap. The original carb looks like it was filled with water for years. Hard white crust inside. LT80 from the symptoms can you tell if it is to big/small? It seems to have no pilot/idle circuit at all. No noticeable effect until 1/3-1/2 throttle. I thought the cable was stretched and not moving the slide but I took the filter off and watched it start moving right away with thumb pressure.

 

You should be able to read what size the jets are.
So far everything points at the pilot jet. Get that cleaned up and we'll go from there.

 

Thanks, I tried hard to find a number to ID it. Doesn't seem to be one. Anyone have an idea what the factory Adly engines came with? Did they change it (doubt it) for different companies ie Artic Cat, Polaris, Kasea, Manco etc.? It is pretty fast, we have an 07 LT80 and they are both pretty quick for my little guys.

 

If cleaning the old pilot jet doesn't work, perhaps you can measure the diameter of the orifice, call Jets R US. They can probably hook you up. Your bike won't care if the jet is a Keihin, Mikuni or a Chinese one. If you have a local company that sells to machinists/ welders, etc. take the jet there and try some small drill bits until you find one that fits, even better, they may sell a gauge set of small diameter measuring gauges. I'll bet that you can make it run perfect!!

 

Just a little update for everyone. So I have pulled the carb several times trying different combos. I can get it to idle with the air box off and the idle mixture three turns out. With the airbox on no go. So it seems that the pilot is too big. I tried both the original and the one that came in the chinese replacement carb. The original is somewhat smaller, but I don't have a gauge that small. There is a little bog on the WOT but the engine catches up and flies. I see why DRR uses this power plant in their racing quad because this rascal is significantly faster than our Yamaha 80's and LT80.

 

Well I recently went through the carb again and no real change. It will idle for a few moments then die unless you hold the throttle at 1/4. The main problem now it the slow acceleration. If you keep it on the pipe she is fast, but if you go back to "idle" and accelerate it slowly builds speed until you are in the right rev range again. This doesn't make since. So is the lack of "snappy" acceleration from being lean or rich? Is is getting too much fuel and needs time to catch up?