Carburetor slides off of intake manifold

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bailsafe

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Oct 23, 2015
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Hoping for a bit of help here!

My carb doesn't seem to wanna stay put on the intake manifold and, while the engine is running, slides off enough to create a pretty sizable air leak.

Do you think RTV adhesive silicone would help to keep it in place? I tried normal RTV gasket maker which didn't work terribly well.
 
YesImLDS

YesImLDS

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Jun 29, 2013
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Have you tried a different clamp like I mentioned? Might try getting a shorty intake as well. I love my manic mechanic one and haven't had any problems! Comes with a slot for an o ring too so it's sealed always
 
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bailsafe

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Oct 23, 2015
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YesImLDS said:
Have you tried a different clamp like I mentioned? Might try getting a shorty intake as well. I love my manic mechanic one and haven't had any problems! Comes with a slot for an o ring too so it's sealed always
Click to expand...
Haven't been able to get a clamp to fit, not really sure where I can get another to fit...maybe a TrueValue store? I'm gonna spring for a shorty intake one of these days...

Could it work if I just make a gasket keeping it in the position where it keeps sliding off to? I'm not sure that'd be the best solution, though. Maybe adhesive silicone gasket maker?
 
Bikeguy Joe

Bikeguy Joe

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You need to clamp it on properly. Silicone goo may help, but clean everything with acetone, lacquer thinner, carb cleaner, or brake cleaner first.

Good luck.
 
2door

2door

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Most silicone based gasket sealers are not compatible with gasoline. Just read the labels.
We're also assuming you have a Chinese 2 stroke engine. You didn't tell us but it would help. Knowing what carburetor you have would also help.

Something isn't making sense here. The carburetor comes with a clamp that is made to tighten the carb to the intake. If the carburetor and clamp are installed correctly the carb shouldn't loosen and come off unless there's something we aren't aware of.

Bad vibration might be your problem.
How is the engine mounted? Is it solid to the frame? Are you trying to use rubber or some resilient material in your mounts? Are all the mount fasteners in place and tight? Do you have gaps in the mounts where they contact the frame?

Carburetors don't just "slide off". There's something else going on here. Can you post a photo or two of your engine and how it's mounted? Also the carburetor and the intake manifold photos would help us help you.

Tom
 
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bailsafe

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Oct 23, 2015
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Slippery Rock, PA, USA
2door said:
Most silicone based gasket sealers are not compatible with gasoline. Just read the labels.
We're also assuming you have a Chinese 2 stroke engine. You didn't tell us but it would help. Knowing what carburetor you have would also help.

Something isn't making sense here. The carburetor comes with a clamp that is made to tighten the carb to the intake. If the carburetor and clamp are installed correctly the carb shouldn't loosen and come off unless there's something we aren't aware of.

Bad vibration might be your problem.
How is the engine mounted? Is it solid to the frame? Are you trying to use rubber or some resilient material in your mounts? Are all the mount fasteners in place and tight? Do you have gaps in the mounts where they contact the frame?

Carburetors don't just "slide off". There's something else going on here. Can you post a photo or two of your engine and how it's mounted? Also the carburetor and the intake manifold photos would help us help you.

Tom
Click to expand...
I can get some photos tomorrow. It's a 66cc Chinese two stroke with the stock NT carb.

Engine is mounted to the frame pretty tightly, just tightened everything again a few minutes ago. Vibration could be it since one of the mounts was pretty loose and I wasn't aware until tonight, and luckily I had a small socket set on hand...

The clamp is on pretty tight but as I'm aware it's not the best clamp in the world. I put a little bit of sealant around the gasket and will report back tomorrow after I've had a chance to get to school in the morning.
 
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bailsafe

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Oct 23, 2015
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Okay, I've had a bit of luck - a little bit of sealant around the carb, re-tightening the clamp, and re-tightening the engine mounts got me started and got me home today.

However, now I'm having trouble getting it to even start. After I got home, I was going to take a quick ride through town, and the bike ran fine for about 3 minutes and then refused to start back up. The throttle sounded extremely low on power and 90% of the time I couldn't get it to even idle.

It has been raining a lot today - could some water have gotten into my engine somehow and screw something up? I've checked the choke and drained the fill pan in the carb in case it was flooded. Fuel line is on, spark plug is good.
 
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bailsafe

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I can hear the motor cranking when I attempt to start but for some reason it won't turn over and idle. When it does idle (maybe 3 out of 20 tries today) it dies after about 30 seconds. Is this still related to the air leak on the intake manifold?
 
Bikeguy Joe

Bikeguy Joe

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Usually, an air leak will manifest itself as a run away high idle.
Have you tried turning the idle speed screw it a half a turn or so?
 
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bailsafe

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Bikeguy Joe said:
Usually, an air leak will manifest itself as a run away high idle.
Have you tried turning the idle speed screw it a half a turn or so?
Click to expand...
I've tried adjusting the idle speed screw and the choke to no avail, it still refuses to come to an idle. I'm using an 18:1 mix ratio.

EDIT: Just noticed one of the screws holding my air filter/cover on fell out. Might that do it?
 
Last edited:
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
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Maybe. Before you put the screw back in, check your filter, it shouldn't be too saturated with fuel/oil mix.
Then-
Go to 40:1 mixture.
 
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piper

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Jun 20, 2014
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bailsafe said:
Hoping for a bit of help here!

My carb doesn't seem to wanna stay put on the intake manifold and, while the engine is running, slides off enough to create a pretty sizable air leak.

Do you think RTV adhesive silicone would help to keep it in place? I tried normal RTV gasket maker which didn't work terribly well.
Click to expand...
What i do is roughen up the intake pipe with high grit sand paper, then i remove the original garbage clamp from the carb and file down the nub until it is flat then i use a small hose clamp from the hardware store to clamp the carb to the intake pipe, never had it come off again.
 
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bailsafe

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Oct 23, 2015
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Slippery Rock, PA, USA
Bikeguy Joe said:
Just dry it out.
Click to expand...
Thanks! There was a bit of water inside the cover for the magneto coil, and the coil itself was a bit damp. I'm drying it outside right now. I also got a D4x25 machine screw for a replacement for the carburetor cover.

piper said:
What i do is roughen up the intake pipe with high grit sand paper, then i remove the original garbage clamp from the carb and file down the nub until it is flat then i use a small hose clamp from the hardware store to clamp the carb to the intake pipe, never had it come off again.
Click to expand...
Yeah, that clamp is garbage. That might actually be a good idea, I was out of ideas to fabricate a clamp but that should give me a head start!
 
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bailsafe

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Oct 23, 2015
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Update: I'm still letting the coil dry out. The engine starts but sounds incredibly weak on power and eventually stalls itself out after ~30 seconds. The carburetor is really loose and kind of slides around on the intake manifold without much pressure at all.
 
2door

2door

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That engine is never going to run unless the carburetor is sealed and tight on the manifold. A loose carburetor will allow excess air to enter downstream of the carb. Too much air and the engine isn't going to run right, if at all.

There's something very 'hinky' about this. Could your carb be broken? Is there a piece missing where it slides onto the manifold? The throat should be a full circle with slots that allow it to be squeezed against the manifold neck. If one of those tabs is broken off that is your problem. Try measuring how far the carb slides onto the manifold and compare that with the carb throat and the length of the manifold where the carb attaches. Maybe you're aren't sliding the carb on all the way. You are loosening the clamp before you try to install the carburetor aren't you?

The stock clamp works fine when installed correctly and the carb is not damaged some way. There is no need to use a hose clamp.

Tom
 
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