Muffler cap fell off, lost all power and won't idle, 50cc bgf flat head

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rudyauction509

New Member
May 8, 2012
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Spokane, WA
Hi I have about 80 miles on my bgf 50cc flat head kit, and the muffler cap fell off. I didn't notice the nut holding it on, so I didn't tighten it and locktite it. I instantly lost all power (even before I stopped to pick it up), and it won't idle. I found the cap, it was crushed by a car. I straitened it out a bit and taped it on enough to seal it, and it idled and ran ok up to about half throttle, with about 50% of its power. I tested it for about 10 minutes. The 6 inch long pipe in the cap was bent and kinked a little. At the end of the 10 minutes, the tape blew a hole so I stopped. Would the cap coming off have damaged the breaking in motor? I am using about 22:1 gas to oil, and the power loss happened the same time the strait pipe sound started. I was going about 20, down hill and shut the motor off as soon as I noticed the difference. So would this have damaged anything? Would a standard bgf 49/50cc muffler work as a replacement? (he says it fits) and fix the problem? I can take pics of the broken muffler and the top of the piston if it helps, but I don't want to go deeper into the motor if I don't have to. Also, are the cylinder head gaskets glued so I would have to replace them after getting to the piston?
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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Shouldn't have hurt anything....probably lost power due to the tube being crushed. Just replace it,and you should be fine.

No need to pull the head, and if you did, the gasket isn't glued.

BTW- I'd go to something more like 40:1 at this point as well.
 

rudyauction509

New Member
May 8, 2012
160
1
0
Spokane, WA
Thanks, here's some pictures. The picture of the bike was taken before the muffler broke. I am planning to go a few more miles on the 1/4 gallon I have left and then switch to 32:1. I will order a bgf muffler as soon as I can. Also, are all mufflers universal for these motors, not including expansion chambers?
 

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Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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252
63
up north now
I know there are several different types, and shapes. Some with "catalytic converters".
I would replace it with one as close to the original as possible.
 

rudyauction509

New Member
May 8, 2012
160
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Spokane, WA
Another thing, I have seen alot of home made caps, will they ruin the motor, or do they give the right back pressure or what ever is needed? Because the rest of the muffler is fine.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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Can you straighten out the tube a bit, and just rivet or use some sheet metal screws and put the one you have back on?

Maybe use some can or other thin metal, and make a "band" around the muffler and cap and run the fasteners through both sides?
 

rudyauction509

New Member
May 8, 2012
160
1
0
Spokane, WA
good point about the bad exhaust, I will switch asap. The BGF muffler is very similar but has an extra 1/4 inch on the little pipe and the cap appears to be welded on. Does this sound OK? (same seller)
 

rudyauction509

New Member
May 8, 2012
160
1
0
Spokane, WA
For now, would something like a soda can work? I've seen it in other threads, but they never say anything about proper back pressure... Is it the size of the hole or where it is?
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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If you can get a can to fit snugly over the end, and put a hole the same size as the outlet, you should be fine. When you reduce back pressure to the point it can cause problems, you have other problems like the engine not transitioning from idle to higher RPM's.

Having said that, when I was a kid, we had a MCcullogh go kart engine that ran straight off the open exhaust port....for a year, and then we sold it. It never had any problems at all. I have also run many sevral model airplane engines with an open port, and other than the not-wanting-to-throttle-up thing, they never blew up either.

So, as long as you run some back pressure, you will be fine, other than annoying the neighborhood.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,837
252
63
up north now
Might have run it lean, and the cap blowing off was just coincidence.

Make sure you check your plug for the color, and make any corrections before you run it after you replace the parts.