G2 Reed/Speed Carb Idling Issues

sockeye101

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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
 

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sockeye101

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Have you checked the crank shaft seals for an air leak?
I had both the clutch cover and magneto cover off and held up a propane torch to them, and it didn't effect how the engine ran. I checked all the bolts around the crank case, everywhere except underneath the clutch for tightness, but it was all solid.
 

DieselTech

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Does removing the air filter have any effect on idling if the air filter is removed?
 

DieselTech

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As far as I can tell no, it's one of those high-flow air filters though, so I doubt it's causing much restriction.


Stage 1 CDI from BikeBerry
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.
 

DieselTech

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Only reason I'm having you try this is: I have a dellorto 15:15 carburetor & it will not maintain a steady idle with a high flow air filter. If I put the stock air/box filter on it it idles just fine. It's something about them getting too much air flow & messing with fuel in the intake stream/tract.
 

Chainlube

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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.
 
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