G2 Reed/Speed Carb Idling Issues


Ok try this, get some masking tape & piece of paper, cover your air filter up, where only a 1/4-1/2 of the element exposed. See if it goes to idling right.

I started with this one. While taping the air filter didnt seem to do much, on a whim I reinstalled the stock Speed Carb air filter. Dropped in a new plug to check the colour as well. Loss in max RPM/overall power was immediately noticeable, throttle wasnt providing much response past around 5000 on level ground (revs out to 8k normally), but idling did improve slightly. I reduced the jet size to a #85 and was able to maintain a good idle with the needle clip in its second-highest position, however the plug looked very lean after a short ride. Is it possible I need to jet up and change fuel / oil ratio to increase fuel/air ratio? (currently running 1:32 synthetic 2-stroke oil)

Start it up, get it warm and then let it idle until it quits. Pull your plug and see if it's wet or dry. That'll tell you how much fuel at idle.

That carb is a good one, I've used those in the past with good results 5 Five, FIVE connections between the cylinder and the carb.

Tried this as well. The new plug was wet, but I may not have let it warm up enough first unfortunately. Hard to tell at idle though, the engine doesn't seem to get very hot if its not being revved or put under load.

I also forgot to mention, I had the float set to a slightly richer position (about 1mm from the top of the carb), but I suspected the idle mix was too rich and causing it to die at idle for that reason. Ever since resetting it back to 2mm though, I have been getting surging when letting off of the throttle (followed by it dying again), so it might be too lean now. Was using the information located here to tune it.

The only other symptom I picked up on that I didn't notice previously, was that as it idles and starts to die off, opening the throttle causes the RPMs to jump for a split second before immediately bogging/dying, unless I feather the carb open and give it time to pick up more fuel. This, combined with the float position is making me suspect that my idle mix is too lean currently, thoughts?

Didnt get around to swapping the CDI yet, but that's on my do-do list for this weekend.

As a complete side note, has anyone here experienced moisture buildup and condensation on/in your carburetor? It seems as though the top of the slide is getting very damp, to the point where some rust and a fuel/water residue forming on the top of the slide. I don't believe the gas has any water in it, but we are in the wet season and I'm wondering if that high-flow air filter is allowing too much rain/humid air into the carb. I'm also located on the coast, so there is of course quite a bit of salt in the air year round.

Thanks for the tips so far folks!
You're getting too much fuel, that jet is too big and it's flooding the engine. That's why it won't idle.
The proper way to set the float height is with the carb upside down and from the seat it should be 21mm.
Thanks for the tips so far folks!
You're getting too much fuel, that jet is too big and it's flooding the engine. That's why it won't idle.
The proper way to set the float height is with the carb upside down and from the seat it should be 21mm.
That float needs to be measured the way that @Chainlube has just explained it, The stock jet size for that is supposed to be a #70 and initial needle valve setting should be with the C clip in the middle position at or around sea level altitude...That #85 jet is much to large, especially if your at or around sea level...Plug gap also needs to be around .025 thousandths.
Hey folks, been lurking around on these forums for a while and finally decided to ask for some help. Digging through years of old threads has unfortunately not helped me solve my tuning issues.

I have a Grubee Skyhawk GT5B which I put together earlier this summer. It has around 30 hours on it so far, and I've been dailying it for the past couple of weeks. About a month ago I finally took the plunge and installed a G2 Reed valve kit, windowed piston, Speed Carb, drilled out a boost port and started jetting. I immediately went up to a #90 jet because it was obviously running extremely lean, and after applying RTB to the entire intake path and testing it for leaks, the system seems airtight in all the right places. Performance wise, it's right where I want it. Plenty of low end torque, perfect for climbing just about any hill around my city, some of which can be fairly steep. (side note: the 48 tooth sprocket certainly helps with this). Starts fine with only a few seconds of choke, and rarely 4-strokes unless I'm riding with very little load on the engine.

The only issue which I have yet to resolve is the fact that any time I drop to idle, the engine RPMs fluctuate for a short while, then the bike dies almost every time, Anywhere from 5-15 seconds after letting off of the throttle. Turning the Idle screw in to the 3000-4000rpm range helps, but it still bogs down eventually unless I hold open the throttle slightly. Raising the needle helped it hold idle, and I tried raising the float as well, but both make the engine surge when letting off of the throttle, as though it's running lean or has an air leak. I can easily start pedalling and get it going again, but it's annoying nonetheless, and I'm at my wits end trying to track down the cause of this problem.

I currently have an MZ65 expansion chamber clone on order from the jungle site, to replace my current poopoo exhaust which I'm not happy with. I am wondering however if the Speed Carb simply can't supply enough fuel through the reed valves in order to maintain a sufficient air/fuel mix, and if a new carb might be in order.

Any advice is greatly appreciated.

*Edit pics attached
Go back to stock jet and get a reed stuffer maybe even shortin the distant between the Reed valve and the carb some