Air leak..?

AzZ

AzZ

New Member
Hi everyone, I'm new here and to motorised bikes and have a slight problem.

Basicly I think I have an air leak (a small one) but first a quick intro and history around the problem. (I did search the forum before posting btw :))

Me and my friend built up the bike fine but when the engine was mounted and the carb in place the air filter box wouldn't fit as the seat tube was blocking it. At first I just ran it with the plastic spacer and sponge but eventually decided that in wet conditions the air filter box was needed. I wanted to re mount the engine to try and accomdate it but my friend suggested another idea which we followed out. What we did is trimmed the intake manifold by a few mm and cut down the airbox. The air box is now able to be mounted to the carb and one screw was cut down to allow the choke to be moved up/down. Since the airbox was cut there is a gap between it and the outer area of the carb so I taped it up with duct tape to stop any water getting onto the sponge and into the carb.

With all that done I rode home happily but then came the irratic idle and high revs and by the time I got home (not a very long ride) a hotter than normal engine. We knew it must be an air leak so the next day we put two 'O' rings between where the carb and manifold join. Before I can continue the method I used to check if there was a leak was to run the engine until warm and lift the choke to full, if it cuts out all is good but if it still runs then theres a leak right? How reliable is this method btw? Anyway it didn't cut out but it wanted to, and the rpm was quite low.

Finally today I went to buy some Instant gasket paste to use to eliminate the air leak between the carb and manifold. I don't know what the equivalent in the US is but it's a blue gasket silicone like paste (link). We placed it on the end of the manfifold and all around and let it set, then attached the carb back on. We then started the engine and ran it till it was warm, and hoping our efforts payed off that when we lifted the choke up the engine would cut out, but no luck....it was nearly there however. This is where I am now. The rpm is very low and the engine will cut out with a very slight twist of the throttle (after it is warm and the choke is fully up) Another thing I forgot to mention is we replaced the intake gasket as the old one was ripped and used gasket paper for it ;)

Well I have ran out of ideas and hope that someone may be able to help me. Any other ways of checking or knowing if it's an air leak? Does the engine always cut off when the choke is lifted after a warm up? My friends engine cuts off instantly. Any other areas I should check or maybe use more gasket paste around the carb and manfiold? I really want to get this sorted so any help will be appreciated.

Very long post but more detail is better right....? :D

Thanks in advance :ride2:
 
Do to it being winter and that I haven't been able to ride at all anymore (brain freeze), but if I remember correctly, the choke is on in the "UP" position for starting, and then you push it down to close it.
 
Sounds like you know what you are doing and the only thing I can suggest is to take the filter off and have a look at the choke to see if it is covering the intake completely when on. It may be why it won't stall out.
Other than that, I guess you should re-trace your steps to make sure you and your pal did not screw up along the way. I did not know the "o-ring" modification used "two"
o-rings, I thought it was one.
An air filter can be one of the most important parts on a long lasting motor and maybe you should consider using a cars rad hose with a K&N filter at the end. The rad hoses come in all sorts of sizes and shapes and will help with getting around your frame.
 
I think you got it O.K.

The reason it may not completely die out when you use the choke could be from a slightly lean setting of the carb, or other lean condition, not due to an air leak.

How does the bike run overall since the repairs?
Have you tried moving the clip on the slide needle?
 
Toytime,

I will have a look to see if the choke is covering the intake and report back..lol. As for the O-ring, only one was originally used but another was put to try and solve any leaks between the carb and intake.

Joe,

I sure hope so. What other factors would cause a lean condition? I haven't tried moving the clip but maybe I should try it? Up or down? The bike is running O.K I guess but the engine gets hot quick. Today when I was riding it was drizzling so when I got home and turned the engine off the little water drops were sizzling as they fell on the engine. Is that normal or is it running too hot?

What are, if any, the other methods for checking for a leak? I read about using propane to check for leaks. I have got a torch but the gas is mixed gas 60% Butane and 40% Propane will it work and what shall I check for. No idea about this method :)

Any other ideas or suggestions just lemme know :D

Thanks again guys!
 
AzZ said:
Toytime,

I will have a look to see if the choke is covering the intake and report back..lol. As for the O-ring, only one was originally used but another was put to try and solve any leaks between the carb and intake.

Joe,

I sure hope so. What other factors would cause a lean condition? I haven't tried moving the clip but maybe I should try it? Up or down? The bike is running O.K I guess but the engine gets hot quick. Today when I was riding it was drizzling so when I got home and turned the engine off the little water drops were sizzling as they fell on the engine. Is that normal or is it running too hot?

What are, if any, the other methods for checking for a leak? I read about using propane to check for leaks. I have got a torch but the gas is mixed gas 60% Butane and 40% Propane will it work and what shall I check for. No idea about this method :)

Any other ideas or suggestions just lemme know :D

Thanks again guys!
Click to expand...

moving the clip up, dropping the needle will make it leaner, lowering the clip, raising the needle will make it richer. These engines do run hot, because they are air cooled, and being new will make it run hot til broken in. What is your oil/fuel mixture ratio? What kind of oil are you useing?

DO NOT use propane to find the air leak, you can use a carb cleaner or water will also do it and the water is the safest bet.
 
water in a spray bottle. spray it around any gaskets while the engine is running, any change in engine speed and you found an air leak. dont stop because you found one there may be more. i had an air leak around the base of my cylinder.
 
Im not sure I clearly read all you did already but those gaskits that it came with fall apart quickly and that is between the manifold and the engine, so you could have fixed the leak at the carb and manifold but still leak between the manafold and engine. I would use carb cleaner and spray the connection and see if the rpm changes to be sure it is an air leak like misteright1 suggested.
 
I would have a look at your plug as well, white or light grey is too lean- move the clip DOWN one.

Should be a chocolate brown or black semi-gloss.

24/1 fuel/oil mixture to start.
16/1 or 20/1 will give you a lean carb mixture, and that's bad. The more oil in the mixture, the less petrol in the mix....lean mix.

Too much oil is as bad as too little.
 
I will have a look at the plug and move the clip and see if it makes a difference. I will also try using water to find any leaks.

TexasDav, I changed the gasket between engine and the manifold ;)

Regarding the fuel mixture I wasn't aware of the best mixture and followed the chinese instructions so i'm running at 16:1 which is too much oil! Can't do anything about it as I pre mixed a 5 litre can. I've still got 2.5 left for another tank :O I'm using Castrol fully synthetic 2 Stroke oil.

What are other signs of an air leak...also how will I know if the engine is running hotter than it actually should?

Thanks again and I'll let you know how it goes.
 
Thanks alot Joe.

What I have done today is spray around the engine to check for leaks. I sprayed around the carb and intake manifold but didn't notice any change in the engine speed. It may have been very small or none at all? I did however move the clip down.

What happens now is after I have warmed the engine and then raise the choke to full the engine does cut out. This is sometimes after 3 seconds or as long as 6. Could it be because of my rich mixture? I forgot to check the plug so i'll do that tomorrow :)

Any other things to check for? Maybe there is no longer a leak but I need to be sure so I can ride in confidence :D Let me know your thoughts ;)

Thanks again guys!
 
AzZ said:
Thanks alot Joe.

What I have done today is spray around the engine to check for leaks. I sprayed around the carb and intake manifold but didn't notice any change in the engine speed. It may have been very small or none at all? I did however move the clip down.

What happens now is after I have warmed the engine and then raise the choke to full the engine does cut out. This is sometimes after 3 seconds or as long as 6. Could it be because of my rich mixture? I forgot to check the plug so i'll do that tomorrow :)

Any other things to check for? Maybe there is no longer a leak but I need to be sure so I can ride in confidence :D Let me know your thoughts ;)

Thanks again guys!
Click to expand...

Another update. I checked the plug today thinking it would be white but it was the complete opposite. It was black and looked powdery. Any ideas or suggestions.

As for the choke, after a good ride today I lifted it up fully and it only cut out after about 7 seconds. Sometimes I have to give it a tiny amount of rev before it does.

Had a good few rides today which is cool :D
 
I would think the plug looks that way from killing with the choke. Sounds pretty normal to me.

Does it break into a four cycle (staccatto sound) when you have little or no load on the engine at cruise speed? It should, or at least break back and forth between a rich two cycle sound, (slight miss) and the four cycle sound.

If it's too rich, it will never "clear out" and if it's too lean, it will sag or surge at steady throttle.
 
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