Question about sealing carburetor to the intake

Discussion in 'General Questions' started by Nevada, Jan 8, 2014.

  1. Nevada

    Nevada New Member

    Got some good weather coming this weekend and I thought I'd get out in the garage and get my current and 1st build running. It's a standard China girl 66/80 motor with the stock carb. I don't see anything in the kit that looks like it's designed to seal the carb to the intake. What's the preferred method to prevent vacuum leak at the point where the carb neck mates to the intake manifold?

    Thanks in advance for any replies!
     

  2. HeadSmess

    HeadSmess Well-Known Member

    pushing it all the way on...
     
  3. Fabian

    Fabian Well-Known Member

    Placing 3 o-rings inside the carburettor till they hit the internal step. Press carburettor onto intake pipe and you will have a perfect seal.
     
  4. Nevada

    Nevada New Member

    Cool! Thanks fabian! I'll take the carb to Ace to make sure I'm getting the right size.
     
  5. Fabian

    Fabian Well-Known Member

    You just need to get o-rings that are the sectional width of the internal step inside the carburettor bore. From memory it's around 2mm.

    With o-rings installed, make sure you press the carburettor against the intake tube as you are tightening the carburettor clamp. Unfortuntely it's a process that requires three hands, but with a heck of a lot of cussing, it can be done with two hands.
     
  6. butterbean

    butterbean Well-Known Member

    Honestly, it may seal on its own. O-rings are a good idea, but never waste time or money on an unnecessary repair. Install the carb, push it all the way on, make sure it's tight, and start her up. Spray some wd40 or starting fluid around where the carb mates to the manifold. If the engine begins to rev higher, you've got a leak and you'll need an o-ring (one will do the trick, three might actually not seal at all). If the engine sounds the same, no leak.
     
  7. SANDSA

    SANDSA Member

    I used 1 o-ring,appears to seal just fine,for now.I had to smooth down the end of the manifold.Actually both ends.
    How long have you had your o-rings installed,Fabian?
    I'm concerned that regular everyday plumbing o-ring will start to decompose over time..hmm. *still going through break-in period.
     
  8. Fabian

    Fabian Well-Known Member

    I have used ordinary automotive o-ring's. They've been inside my NT carburettor since first installing my engine kit; nearly 4 years ago now, though i have been using a Walbro style diaphragm carburettor, since the start of last year, and never looked back.
     
  9. butterbean

    butterbean Well-Known Member

    Yeah, you definitely want automotive o-rings. Sick bike parts sells a 3 pack for like $4, or go to an auto parts store and get assorted sizes and one will likely be the size you need. Some hardware stores may also possibly carry automotive grade o-rings.
     
  10. HeadSmess

    HeadSmess Well-Known Member

    never needed an oring, and as the joint isnt designed for an o-ring...im with butter balls on this one. you dont need the oring. except for the spray test. when lean and sucking air...it will rev higher. it will slow down if it sucks in extra fuel, even stall.

    hence why, if anything... use grease. smear it over the joins. but by that point you have already filed, used a gasket, used silicone...etc etc etc. personally? only done two leak tests....EVER. and not on these engines! doing the work in the first place is easier than covering everything in grease, washing it off, then doing the work anyway!


    page 37 onwards may look daunting to some...but are just simple line drawings. orings should be supported on two sides, with restriction on movement on other two sides. tis what makes them work.

    http://www.parker.com/literature/Praedifa Division/PDF files/Catalog_O-Ring-Guide_ODE5712-GB.pdf

    just another item for the engine to digest if it fouls up which o-rings are notorious for doing. theres nothing to stop it springing into the bore, especially if you get the wrong type and it swells up. bean is the man. use real auto grade ones, if you must pursue this path.

    NT(why doesnt anyone ever say nttc?) carb has slots, so it can be clamped, with then 3mm of straight section that "should" be a press fit on the manifold. always have been in my experience, and the only really suitable oring i would think of using would be 3mm thick, which then brings the end of the manifold flush with those slots... hmmm?

    on that note...make sure that... the weld at the bend is not preventing the carb from being pushed COMPLETELY on! there may be some filing needed. of carb and or manifold.

    worth your time popping the manifold off, cleaning out all the dags from inside it, and matching it as best it can be matched to the intake... then you can really make sure the carbs pushing on too.

    and, maybe just a SMEAR of gasket goo...
    replace that freaking clamp or at least the bolt and nut with something that works.
     
  11. Fabian

    Fabian Well-Known Member

    A couple of o-ring's solves all of the potential air leak issues between the NT carburettor and intake tube.
    A cursory check of the clamping system revealed an o-ring to be the solution - cheap, simple and effective.

    How many threads have been rehashed and remade over idle problems and transition problems with the NT carburettor - hmmm, maybe air leaks might be playing a good part - i wonder why; could those 4 slots have something to do with it...
     
  12. SANDSA

    SANDSA Member

    HeadSmess,Thanks for your input.The common sense approach to things is the key.I'll try to run without o-ring first ,before I get auto grade.
    Sometimes these forums & the "World Wide Web"surfing tends to flood our R&D ideas with too much info.
    I installed o-ring,hardware store grade,in my carb from the start to prevent any leak issues,the typical "if it's not broken dont fix it syndrome,now it seems like it was all just a waste of time and money,I dont have much of either.In the long run,you really cant put a price tag on learning.I'm sure I'll find a use for those o-rings in the future.Hey, I'll be back in a sec...

    *pedals down to the freaking clamp store>>>>>>>>>>>>>>zoom
     
    Last edited: Jan 11, 2014
  13. butterbean

    butterbean Well-Known Member

    There is a very simple lesson to be learned here, and I've already said it but I will say it again. To save yourself time and money, never make a repair until you know it's necessary. Most repairs are free to test if you know how, and there is lots of good info here on how to test for just about any repair. Use the search function.
     
    SANDSA likes this.
  14. HeadSmess

    HeadSmess Well-Known Member

    yeah, my casual inspection of the setup showed that one has to really push those carbs on, PAST the slots. then they seem to, or at least, all of mine have, seal effectively without...anything.


    and i will admit that the very first time i put one on... i thought it was on good and proper, until i had a really good look because the next morning i also noticed how the clamp was hitting that weld, and the morning sun just happened to glimmer through the base of the slots at the same time.

    assumptions versus cold logic. which ones correct more often than not?

    they ARE deceptive, to people that either arent familiar with working on engines or "sliding" interference fits.
    the amount of force required can sometimes have the layman concerned that something is going to break...read....99% of people on forum boards. everyone came here looking for answers in the first place, about something or other... me myself included. never really got an answer either!
    the internet abounds with plenty of DIS-information unfortunately.

    .
     
  15. Rockspider99

    Rockspider99 Member

    I shortened my intake Manifold and just used some Loctite high heat exhaust silicon to seal up any of the imperfections that I may have caused. left it to cure for 24 hours and no issues.
    Just make sure you don't put it on the inside of the carb, rather put the layer around the manifold.
    Also being silicon if a little get sucked into the motor it should not cause too much harm, I hope.
     
  16. Fabian

    Fabian Well-Known Member

    A high tech variant of the o-ring theme.
     
  17. Fabian

    Fabian Well-Known Member

    So did mine, just not effectively enough.
     
  18. butterbean

    butterbean Well-Known Member

    High heat silicone isn't fuel proof. Seal-all is. Do you actually know if your carb is leaking, or did you just assume it was going to?
     
  19. Rockspider99

    Rockspider99 Member

    I machined my cut down nicely, but yeah I just assumed. though I didn't go out and buy, was left over from when I rebuilt my cars engine, loctite exhaust gasket maker.
     
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