Idles fine, but bogs with throttle.

Molotov256

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Nov 6, 2008
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St. Louis, MO
This engine is nothing but trouble, I swear.

A while back I had this same problem - riding the bike just fine, came to a stop light, and when I tried to pull away and give it some gas, it bogged down and barely sputtered along. I pedaled it home, pulled off the carb manifold, exhaust, and head, applied a healthy dose of RTV gasket sealant on each gasket, bolted it back together, and voila, it worked.

Anyhow, I've got maybe 40 miles on it since then, and I'm back to square one with the same problem. It looks like fuel may have been leaking out the front side of the head gasket, so I've got one ordered from SBP, but am I going to keep running in to the same problem? What else can I do? My other motor didn't misbehave like this.
 
Did you also do the base gasket? The bottom of the jug has to seal to the block as well. Also check your fuel flow, and make sure the plug is clean.
 
I got the head gasket from SPB, but it doesn't fit. I asked them about this, and this was their response:

"We only sell head gaskets for the 67-69cc "80cc" and 49cc engines. We also sell both 6mm and 8mm studs sizes in the 67-69cc size. It sounds like you do have a 59-60cc engine and we don't make one for that size engine. You could send the one you got back and we could replace it with the one for the 49cc but you would have to enlarge the main hole to fit your engine."

I don't really have the means to accurately enlarge the hole in the 49cc gasket, so can anybody recommend another retailer who sells a gasket for my 59-60cc engine?

Thanks for the response, Hawaii - the fuel flow seems to be okay, the plug looks fine as well, and I don't see any evidence of leaking sludge at the base of the jug. If there's no visual evidence, is it safe to assume the bottom jug gasket is sealing properly?
 
If the engine idles fine, it pretty much eliminates the possibility of an "air leak". The slightest air leak would upset idle mixture and cause stalling or high idle speed that cannot be adjusted with the throttle stop screw.

I'd look at some simple stuff first, like the spark plug - which might fire OK at idle, but misfires under throttle?

Check the main jet in the carburetor. Maybe it loosened up - which would allow the engine to idle normally, but would severely enrich the mixture as you opened the throttle - leading to a lack of power.

Make sure the exhaust port is clear from carbon deposits (although it takes a lot of running time for them to build up at the exhaust port), and make sure the muffler is clear. (could it be clogged with bits of RTV?) Run it open exhaust for a little bit to confirm.
 
Maybe your float is stuck or needs to be adjusted? Sounds like you run out of fuel...
 
Stuck float?

I just read a thread about somebody with a similar issue - you may be on to something with the stuck float. I will look during tomorrow times.
 
If it idles fine but it bogs down with throttle, your high speed gas jet is probably clogged. Clean your carb and spray carb cleaner in all small passages, make sure air can flow through all ports no matter how small. Put it back together and it should run great.

By the way, since it idles fine I doubt you have a gasket problem, sounds definitly like a carb problem to me.
 
I'm kind of starting to have the same problem last two days but as of now i'm attributing it to humidity?
 
I think I may have found the problem. The float in my carb was filling up with fuel, so it wasn't floating properly. Reference the post below:

https://motoredbikes.com/threads/ca...f-overflow-tube-i-need-help.21877/post-223188

I failed to mention the fact that gas was leaking from my air filter as well, but that's happened so many times on this engine I didn't think it was a noteworthy occurrence. As it turns out, it probably is. My hopeful diagnosis is as follows:

Symptoms:
1) Gas leaking from air filter
2) Engine idles okay, but bogs with throttle

Cure?
1) Float is either stuck or saturated with fuel. Replace.

I'ma order a new float ASAP and see how it pans out.
 
Wait... who sells floats?

Wow - I switched carbs between the working bike and the wrecked one, and it's night and day. It would appear that the semi-sunk float was totally bogging down the carb. All I need now is a new float... or I may just buy an upgraded carb from spooky tooth:


I could have sworn I'd seen a website that sells floats around somewhere. Who sells 2 cycle NT carb floats?
 
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