Carburetion problem

tech2353 · #1 07-14-2008, 11:07 PM

Hello, I'm wondering if anyone could suggest a good allaround carb for these engines. I have tried 5 different style carbs "stock included" on this thing and keep coming up with the same problem which is= at wot or accelerating engine cuts out as if starving for fuel. Or will 4-stroke or both. These engines seem to have very poor manifold vaccum to pull fuel. Right now I have a 50cc hp walbro style carb on it which seems to be about the best running of the bunch. By the way I have soldered and drilled jets till I am blue in the face, just can't find that happy medium, its too rich or too lean. I have the catylitic muffler because I want it to be as quiet as possible. Im wondering if it is posing a back-pressure problem. I have also been through the ignition throughly. Well guys and gals any ideas would help as I am about out of answers. Out of time for tonight but will be back tomorrow. Thanks all..

misteright1_99 · #2 07-15-2008, 12:03 AM

I have the same problem and am under the opinion that the CDI MIGHT have some kind of rev limiter or maximum voltage built into it. Maybe others might have a thought on this........

**Bikeguy Joe** · #3 07-15-2008, 07:59 AM

I have revved a 70cc engine until it should have blown, so I don't think they have a rev limiter in them. Usually that will require a "black box" or computer.

I do know that the stock petcock is or can be VERY RESTICTIVE.

Try a new 1/4" ball valve as a replacement.

**Bikeguy Joe** · #4 07-15-2008, 08:00 AM

http://motorbicycling.com/f3/my-petcock-broke-1734.html

tech2353 · #5 07-15-2008, 09:18 PM

Hi all, I took the bike for a short ride last night after tinkering a little but when I got back the engine was so hot you could have fried a bacon samich on it, though I burnt it up for sure because this morning it wouldn't start, wouldn't pull fuel. This afternoon I took the walbro style carb off and put on the carb I had on it and all is well, still missing a little but much better now. Which is the carb shown in pic. Whewwww. If you notice the hose and air filter attached to carb, now, if I run it on the carb the motor starves out at wot but runs fine without it. Absolutely no restriction in the air filter or hose what so ever. Still haven't figured that one out. Also have taken out the manifold extenders too. Well as they say back to drawing board and keep plucking away at, will be back tomorrow, god bless..

**Bikeguy Joe** · #6 07-15-2008, 09:27 PM

Sounds like you only need to richen the H or high speed screw for WOT performance.

What model/size is it?

Clotho · #7 07-16-2008, 01:50 AM

I was experiencing something similar with the same carb as Tech2353. Turns out that I had to set the pin to the leanest setting (top notch) and set the mixture adjustment to the leanest as well (The screw to the left of the idle adjustment. Fully turned in).

Remarkably the plug shows that it is still running a bit rich but at least now it runs well.