Can a HT have a plastic intake manafold?

autobo7

Member
Joined
Apr 11, 2008
Messages
65
I have a new build progressing and I wont be about to attach the carb directly to the stock intake manafold. The frame of the bike is a little smaller but I want to stick with it.

So i am going to extend the intake manafold about 6" so the I can move the carb to a different spot on the bike(I have read that a longer intake manafold can help tune the bike a bit?). I am thinking of using a plastic tubeing for ease of construction, but a 2 stroke expelles some of its exhaust through the intake and that could heat things up.

So my question is will a plastic coupler between the carb and manafold work or do i have to make some thing out of copper?

here is the bike;
http://motoredbikes.com/album.php?albumid=207
you can see in the engines picture that the carb is mounted behind the clutch cover
 

Simon_A

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Joined
May 2, 2008
Messages
224
It depends what plastic you use, dont forget this is an air cooled combustion engine. The top of your engine gets extremely hot.

Most plastics cant withstand the temperatures the cylinder gets to.
 
A

andyinchville1

Guest
HI,

FWIW - I was one of the people tinkering with intake runners...You can do a search to see some of the results...I have been fairly busy and haven't had a chance to tinker with this further but it can really make a difference....(I used an intake that was was too long and had too small a diameter tho).

As far as plastic....I am not too sure that would work because the engine can and does get pretty hot...

For my intake build I went to a shop nearby that uses/bends hydraulic tubing (standard size pieces so a shop near you could probably duplicate it) it was nearly a perfect fit for the stock HT carb...Plus they had the bending machine and could weld too if needed....All I had to provide was the metal flange (cut out to match the intake port of the cylinder and pre-drilled for the mounting studs....This may be the easiest non plastic way to go ....

Hope this helps you

Andrew


PS - Soldered copper may work but I can't say for sure...I think somebody here tried it for an exhaust but I think it didn't work....But then again the intake side is probably somewhat cooler than the exhaust side....
 
L

Large Filipino

Guest
Add a 90 degree bend from even a PVC pipe that fits over your existing manifold then get a short PVC to the carb so it faces to the side. The PVC bend shouldn't melt because the original intake is taking most of the heat from the engine.
If you get the carb to exit to your left then handling the choke could be done with your left hand while your throttle is on your right.
Epic Win.

Here's an example of a PVC elbow. Bring that manifold with you when you go to the store.

I guess it could be glued into place?
 

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BigDaddyT

Member
Joined
Jul 19, 2008
Messages
151
Id get it up to temp and laser it to see how hot it is. If you dont own one I bet you could con a quicky lube or someone like that into lasering it for you.
My brothers hemi dodge has a plastic intake manifold. Doh!
 

Mountainman

Active Member
Joined
Jun 15, 2008
Messages
3,569
Yes, over the years I have seen plastic used for intake manafolds several times. I must say though - they all seemed to be rather special looking - very strong and I am sure - made to withstand heat. Would our so called common PVC work ? At my job sites - repairing broken water lines and replacing valves - I have seen direct heat - torch - applied to PVC so as to make bends - never did like to use this method - but it is done occasionally.

Note: Andrew's idea above -- MUCH BETTER.

Happy Riding from - Mountainman
 

autobo7

Member
Joined
Apr 11, 2008
Messages
65
Thanks for the input all,
Andy's idea is definitely tops, but i don't know of any one in the area that will do that for me(at a reasonable rate). I think I'm going to J-B weld some bent copper tubeing to the manifold as the extension, and then just clamp the carb to that. I am waiting on a few links of chain to complete the drive line, and if they are in tomorrow then I'll tackle this too.
 

silverscreen

New Member
Joined
Jul 2, 2008
Messages
11
The problem I had with PVC is that it does not melt or bend when the engine is running, however it starts to melt and sag after the engine is off. This happens because there is not any air going through the intake to keep the PVC cool, and the heat from the engine migrates back through the intake to the carb. I ended up using a 90 degree copper elbow an sealed it with black high temp RTV gasket maker. There are a few pictures in the picture gallery under the heading "First build... almost needed a shoehorn!"
 

autobo7

Member
Joined
Apr 11, 2008
Messages
65
oh ****...

I got it running today, and although it looks great and is super confy to ride, I have idle and fuel ratio problems. I used 2 street elbows to attach the carb, but the elbow next to the manifold would quite fit in inside so i notched it much the like the carb is, and i crushed it down a bit to make it fit.

Now it wont idle if i open the choke, and if i keep the choke shut the engine loses power between 1/3 throttle and WOT. I am guessing that this means that i made the extension to narrow?
 

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