Carburetor slides off of intake manifold

GoldenMotor.com
B

bailsafe

New Member
Oct 23, 2015
71
0
0
Slippery Rock, PA, USA
2door said:
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
Click to expand...
It slides about 1cm before it hits the angle joint and can't slide any more. I have a new carburetor on the way along with an offset intake manifold (the manifold will be here tomorrow, but the carburetor's coming from China and was shipped yesterday).

Something definitely does seem off here, though I question why it was able to run before; it wasn't a problem before now.

Yes, I am loosening the clamp before installing the carburetor. I don't see why I wouldn't...but I can definitely go and try it again while consciously thinking about that! ^^;

I'm not sure if there's anything missing. I'll take some pictures and post them tonight, since I forgot about the other ones.
 
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,837
252
63
up north now
Also, you can see part of the slot exposed on the carb throat. When ever I ran into that, I ran the carb on my tabletop belt sander until the clamp would cover that. That required grinding off that little nipple that mates with the hole in the clamp as well.
 
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,837
252
63
up north now
It looks wrong, but I can't quite say what it is. All the ones I built, the carbs were a fairly tight fit to begin with, yours looks like the manifold is under size.
 
B

bailsafe

New Member
Oct 23, 2015
71
0
0
Slippery Rock, PA, USA
Bikeguy Joe said:
It looks wrong, but I can't quite say what it is. All the ones I built, the carbs were a fairly tight fit to begin with, yours looks like the manifold is under size.
Click to expand...
Luckily I have a new manifold coming tomorrow (long walk to the post office!) and I can see if that solves the issue. Part of the slot is exposed but it doesn't seem to want to clamp down any further...
 
2door

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
You said, " It slides about 1cm before it hits the angle joint and can't slide any more."

1cm is short. You're about 1/2 cm too shallow. I measured three NT carbs and they all have a throat 19mm deep. If your carb only goes on 1 cm it isn't seating against the ridge in the carb throat. There's something keeping it from going on as it is designed to. Maybe take a close look at the intake manifold and make sure there's not a defect in it that's causing your problem. It is possible that the manifold was cut short on the inlet end.

I had one carburetor, an NT, that the slots were cut too deep and left openings where it is supposed to seat against the ridge. The slots were machined deeper than the ridge. That can be fixed by installing a gasoline compatible 'O' ring in the carb and installing the carb tight against the 'O' ring.

And your air cleaner is installed upside down. It might be interfering with the choke the way it is.


Thanks for the good photos. They tell us a lot and hopefully will answer some questions for you and us.

Tom
 
Last edited:
B

bailsafe

New Member
Oct 23, 2015
71
0
0
Slippery Rock, PA, USA
2door said:
I had one carburetor, an NT, that the slots were cut too deep and left openings where it is supposed to seat against the ridge. The slots were machined deeper than the ridge. That can be fixed by installing a gasoline compatible 'O' ring in the carb and installing the carb tight against the 'O' ring.
Click to expand...
Think an O-ring might help my issue here? Like I mentioned, I do have the new parts coming soon and that will hopefully fix something...

2door said:
And your air cleaner is installed upside down. It might be interfering with the choke the way it is.
Click to expand...
Yep, the air cleaner doesn't fit the correct way, which is why I'm going to install the offset intake manifold tomorrow afternoon.

EDIT: Here's a video showing how much the carb moves around. https://vid.me/eF2S
 
Last edited:
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,837
252
63
up north now
Yeah, that ain't right at all! I am chalking this one up to losechinese 'quality control', or something like that, lol. If the carb is that loose on the new manifold, there is obviously a prob with the carb.

Now fix that cross threaded cap! :)
 
B

bailsafe

New Member
Oct 23, 2015
71
0
0
Slippery Rock, PA, USA
Bikeguy Joe said:
Yeah, that ain't right at all! I am chalking this one up to losechinese 'quality control', or something like that, lol. If the carb is that loose on the new manifold, there is obviously a prob with the carb.

Now fix that cross threaded cap! :)
Click to expand...
Ahhh....just my luck! Kinda wish I could get it jerry-rigged in the meantime. The new manifold was supposed to be delivered today but it's running late (thanks, BikeBerry).

Luckily I preemptively scored a new carb from the eBay seller I got the kit from, he didn't charge me at all but it's shipping from China. Tradeoff is totally worth it though.

Will report back when I have the new manifold.
 
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,837
252
63
up north now
You could always clean it with solvent, then wrap it with electricians tape and clamp it back down if you need to use the bike for short trips.
 
B

bailsafe

New Member
Oct 23, 2015
71
0
0
Slippery Rock, PA, USA
Alright, new manifold is on and it feels quite a bit tighter -- still can't idle though. It'll turn over and start, and get to idle, but it slowly craps out and dies about 20 seconds after idling. It's pretty hard to get it to turn over too. Is this probably a fuel mixture thing? I'm at 1:18 right now.
 
You must log in or register to reply here.
Top Bottom