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Thread: Bloody carb for RS70 big bore

  1. #31
    apriliaforum Member
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    remember the main jet size with not affect starting

  2. #32
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    well fitted the black one again but with the pipes off and it would not even start got a little chug for a split second but worst try yet . Ran better with the RD50LC carb on .

  3. #33
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    assuming this is just a fuel problem
    its starts with a good spark with a known good spark plug
    then add the correct fuel and bang......

    you have spent a long time on this, perhaps go to the local shop?

  4. #34
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    Quote Originally Posted by vailon View Post
    well fitted the black one again but with the pipes off and it would not even start got a little chug for a split second but worst try yet . Ran better with the RD50LC carb on .

    yes starts first rotation of the piston instant as soon as you hit the button with the 50lc carb . revs clean and strong ticks over fine of the choke runs and rides fine unless you try to go over 4500 rpm . so i think i need the rubber inlet but no one seems to have a spair one for me and as far as i can see you cant get one out side of a kit .

  5. #35
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    your running an AM6 i think, not a derbi is that correct?
    what is wrong with your rubber inlet as long as no air leaks it will work?
    if stiff drop into boiling water to soften
    if to small for your carb many many options to buy from cheap to bloody expensive this will not stop it running but it will limit performance
    regarding not running over 4500 rpm this is probably a main jet or needle issue to little or to much fuel could be either.

  6. #36
    apriliaforum expert Spudgun60's Avatar
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    I know this is going stupid, but I'll mention it for what it's worth.

    I've seen two different types of rubber manifolds (I'm ignoring the ones with spigots on them). One has a very small hole on the engine side. The other has a large hole. The one with a small hole would match the size of the reed block that has the air director fitted. The one with the large hole would match the reed block without the air director.

    Obviously, the inlet manifold with the small hole would be for the bike with its original carburetor. THe one with the large hole would be an aftermarket part for bikes fitted with large carbs. However. The bike should still run either way.

    Just a thought.
    Gone, but not forgotten. 1999 RS50.


  7. #37
    apriliaforum expert ToraTora's Avatar
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    You don't have to Attend the School of Hard Knocks

    At the risk of being redundant:

    Make an air leak check kit, and check for air leaks. This could easily be your issue, and will point you in the proper direction. Also, spend some quality time reading the posts in this carb thread.

    If you don't have an air box installed work towards getting one. The pod filters can make tuning much more difficult.

    I would also stop messing around with those carbs as they all look like they have issues. Get a new carb they are very affordable, and don't buy another fake. I would suggest getting a Polini CP carb as they are very easy to tune, but they also work very well. For a 70cc kit the 19mm would probably be the better way to go, although the 21mm will produce more power, and a quicker bike. Top speed will very likely be the same.

    The CP has a number of accessories, like the main jet quick access float bowl that make tuning even easier. I've linked the cable pull choke version of the carb. You can get the non-cable version, but on an RS that is hard to reach. Depending on the year of your bike you may need to get a choke cable kit. There are a number of different ones available.

    There are lots of intakes available. I would't waste any money on a cheep one.

    Malossi intake with reeds

    Polini intake (no reeds)
    Last edited by ToraTora; 09-13-2019 at 04:58 PM.

  8. #38
    apriliaforum expert Spudgun60's Avatar
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    I agree with Tora as regards carb size. I used a 19 and 21mm carbs on my old RS. With the 21mm carb. The bike accelerated harder, but the bike was no faster. It also drank a lot more petrol! The 19mm carb (I'd say) would be the optimum size.
    Gone, but not forgotten. 1999 RS50.


  9. #39
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    I've had a look at the inlets and they have a large opening. the reason im thinking it may be the problem is the one that came with the bike had a very small holl and i ground it open i was thinking i may have over done it and made it to big but the opening in these are bigger then the one i moded.

  10. #40
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    Your right im going to get the 21mm carb in the link and the choke kit . im just sick of all this crap now and if thats not it them im giving up .

  11. #41
    apriliaforum expert ToraTora's Avatar
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    Quote Originally Posted by vailon View Post
    im just sick of all this crap now and if thats not it them im giving up .
    The “I'm going to this, and then give up attitude” wont get you very far with these bikes. Take a more zen outlook on it. Think of it as a puzzle that you solve one piece at a time. Sometimes moving forward, sometimes back. If you get overwhelmed, then take a break from it for a while, and come back at it when you have recharged.

    Learning doesn't come very fast for most people, and there is a lot to learn with regards to getting an engine to run well. It takes time. Those of us with a clue have been doing this for over a decade in most cases, and even we get stuck at times. If we have knowledge on these subjects it is very likely that we have slogged through much worse. GPR Camp is my attempt at trying to short circuit some of this learning for people by providing better resources than I had when I was learning this stuff.

    The thing is you do have victories. You do get past these things, and before long you wonder why some of this stuff was ever difficult. You just have to hang in there.

  12. #42
    apriliaforum expert Spudgun60's Avatar
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    Quote Originally Posted by ToraTora View Post
    The “I'm going to this, and then give up attitude” wont get you very far with these bikes.
    Oh, I don't know. I do like to buy cheap bikes. Sort them out and sell them for a profit.

    Mind you. The cock-ups and gaffs I've made over the years are without number. The internet didn't exist then as well. The learning curve was steep. However. It all pays off when the bike hits the road!
    Gone, but not forgotten. 1999 RS50.


  13. #43
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    I have built a few bikes over the years but ive always had lots of parts to try on them and in the end i always get them sorted . But ive never had an RS befor and this problem. could be i spend £90 on carb and kit and its still not right thats why i wanted to borrow one first to try on and see if its fixed . When you have to keep buying stuff to try it can rack up a hell of a bill .

  14. #44
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    A new properly jetted carb will give you a very good starting point
    it should start and run
    it may require further changes to optimise things
    patience you will enjoy it in the end

  15. #45
    apriliaforum expert ToraTora's Avatar
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    If you keep buying junk parts I can see how it would get frustrating. That's why I say not to buy the junk parts. If you have developed some acumen with regards to these bikes then it isn't all that hard to sort nearly any issue with them. But it's going to take a lot of time, and money to develop that level of understanding.

    I also suggest taking a bunch of time, and reading through the project threads. There is invaluable information in those threads.

    Here's a post of a friend's bike where I fitted the Malossi intake with the CP carb on an RS50. I also fitted the Gila kit to the bike. Very nice top end for the AM6 engine.

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