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Carburetor airleak

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agjell

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I have a Hyper .21 8-port engine I've had some trouble tuning. It seems to constantly overheat in high rpm's. I'm familiar with the tuning process so please don't tell me I'm running too lean, cuz I'm not :)
Anyway I started searching the net about articles that could help, and found that airleaks are quite common even on new engines. So I removed the carburetor from the engine and did a blow test, it seemed there was a leak between the carburetor body and the throttle barrel. Now I know there is supposed to be a rubber boot covering the barrel and the carb, but I have a huge hole in mine. Is this boot the only sealing there is between the carb and the barrel? It's been a while since it broke, but I think I remember having trouble tuning the poop even before it broke. So my second question is; Are there other possible solutions for my problem? Please answer the first question, too :)
 
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The boot is ripped on my Hyper 21 and I have no airleak problems. What I did to make my engine easier to tune was change the carb. I use an O.S. 20E carb ($60-$65 on ebay) now and it is very easy to tune and it keeps a tune great. There has been a 20-30 degree change in air temp in the last month where I live and I haven't had to move the HSN or LSN more than a 1/8 turn either way.
 
I'm thinking about doing the same as it has been recommended to me many times before. Still, I think it's pretty poopy if the default carburetor doesn't work, seems like lots of people has trouble with it.

BTW my first question remain unanswered :)
 
I'm pretty sure it's an airleak, especially since I've already tested and verified it :)

I'm still wondering if the rubber boot is the only sealing between the carb and the barrel. Is it?
 
agjell said:
I'm pretty sure it's an airleak, especially since I've already tested and verified it :)

I'm still wondering if the rubber boot is the only sealing between the carb and the barrel. Is it?
Click to expand...
Probably. I pack the rubber bellows on my carbs with Castrol medium grease. If you are going to do this then obviously you will need a new bellows with no extra holes. Also, the seal around the middle needle screw (the one you are not supposed to touch) can be poor. Wind the middle screw out exactly 5 turns, apply some RTV sealer around the head of the screw and wind it back in exactly 5 turns. Leave the sealer to set overnight.
 
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agjell said:
I'm still wondering if the rubber boot is the only sealing between the carb and the barrel. Is it?
Click to expand...
There are orings in each needle. Also Oring on the neck of the carb and inside the throat of the block. Another place for airleaks is right behind the collet (AKA the front bearing) and on the rear plate. There's lots of places to seal and check. Also under the head.
 
I just "air leak proffed" both my engines, get some Permetex Ultra Copper (oxygen safe) and put it between the bottom of the nipple and the carb body and it forms a seal, not on the threads!
you can get it at an auto parts store, I got mine at NAPA, also put some between the backplate and the engine and between the carb and the crankcase.
make sure you get the high temp one....
ultra-copper.webp
 
You may notice I live in Norway, so I might not be able to get Permatex at NAPA, but I bet we have a good alternative as well ;) Anyway; thank you very much for the tip! I'm doing this today in addition to buying a new airtight boot. After troubleshooting the whole weekend I've come to understand these engines are pretty draughty :)
 

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