fbpx
Login

 

Jump to Forum..

Carb Rubbers/Sockets

in 912 / 914 Technical Questions 13 years ago
I wondered if anyone else had experience of using the JBM Carb sockets over the Rotax ones.
I purchased a pair over a year ago and show no signs of cracking on last inspection. I googled the rotax carb sockets, and, as you can imagine, there were lots of hits about them cracking. I couldnt find any hits in relation to the JBM sockets cracking.
Apart from being half the price, I purchased them with the view that the Rotax ones are going to crack anyway, so they must be worth a go. There are a few on the net that think they are brilliant, and I did read about a school in America somewhere that installed a JBM one on one side, and a Rotax one on the other, and were keeping an eye on them to see which one would crack or split first.
Unfortunately I have not been able to find out the result, anyone know.
JBM also make carb sockets for the 2 stroke rotax engines as well.
They are called JBM Industries if anyone wants to look.
Dai

  • Re: Carb Rubbers/Sockets

    by » 13 years ago

    HI David,

    Some of the Rotax carb sockets have cracked, but many were overtightened and some left on past their service time limit. Rotax many years ago had an SB out on them because people over tightened the clamp that secures the carb. There is supposed to be a 8mm gap between the clamp ends. Rotax later and now supplies with each carb socket a 8mm spacer to prevent over tightening. If you over tighten these sockets they can crack or cut through. The older engines didn't have spacers and people damaged them by not reading the manuals. Then they complained that Rotax had faulty sockets. The other issue is this is not following the Rotax 5 year rubber replacement program, it is supposed to be tossed and replaced. A very large number of people don't do this and later when it cracks they complain. ( It had to be Rotax's bad part because I didn't do anything) No truer words were ever spoken. I have not had a single carb socket within the 5 year service limit crack that was applied properly. It is in the Installation Manual on page 91 sect 15 and figure 58. I know you know that after market parts shouldn't be used because they may have some subtle differences that will cause you expensive issues. Experimenting can be very risky and expensive. Think of it this way. If you saved $30 on each carb socket by buying an after market, but then because of a slight difference one carb fell off and went through the prop. Then you would pay $1100 for a new carb and maybe another $1000 for a new prop. Was the $60 worth it? There was a gentleman here on this site that bought an after market starter. It has a subtle difference that allowed oil to leak and cause damage. Now it is costing him 2-3 times more than if he would have just purchased the Rotax one.

    We are all tempted to do this and I was one many many years ago. Now I'm cured. It can be hard lesson and hard to resist.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

    Thank you said by: Ralph iRMT Sneer
      
    Report

  • Re: Carb Rubbers/Sockets

    by » 13 years ago

    Roger,
    I hear what you are saying, and some extent agree with you entirely, but I think it unlikely that every failure was due to incorrect installation.
    Rotax rubbers, I feel anyway, were not up to the job, hence the SB. They may have put things right now by the 8mm spacer etc, but there were a hell of a lot of failures prior to that.

    I am not saying that the rubbers rotax now sell are rubbish, all I am asking is has anyone else had experience with the JBM ones. I purchased them and am happy with them, they have a locking ring inside and the carb locates nicely inside. No doubt they are a direct copy of the rotax ones, but made from a different material. They do feel a better quality part, but whether they actually are remains to be seen.
    I will be the first one to put on here if my carb fell off, but 2yrs down the road they seem fine.
    I have seen a 912s throw a carb at Spamfield with genuine rotax rubbers with the 8mm spacer in.
    Why that happened I dont know.
      
    Report

  • Re: Carb Rubbers/Sockets

    by » 13 years ago

    Your points are well taken David, as are Rogers, in the end the product will speak for itself and as long as it doesn't cost anyone personal damage or injury might be worth the risk, but personally I wouldn't want to be the one doing the testing!:)

    Too often I've seen were something looks straight forward and simple, but in the end turns out to be a big mistake. As Rodger mentioned Rotax has gone to a lot of trouble and testing to address the carb socket cracking issue, and certainly since the 8mm spacer has been introduced I haven't seen any carb socket cracking issues. That said, I have seen on an un-related product(snowmobile engine), were a after market carb socket was used and created a completely different problem then anyone expected. In this case the after market rubber sockets used too thick a density rubber which failed to adequatly isolate harmonic vibration from the engine and chassis, causing fuel foaming in the float bowels at certain operating RPM's leading to lean running condition. The fix was going back to the stock carb sockets!

    I only mention this experience to raise awareness that things are not always as they seem, and in the case of these after market sockets would challange the company who builds them as to exactly what testing they have done for vibration, durability, fixation etc.. I can tell you Rotax does non-stop testing, in fact there is probably 912 series engines running in various test cells as we speak at the factory right this minute. If any part were to fail I can assure you they have more engineers anylizing and working to correct the problem then any after market parts supplier I know of.

    This certainly does not circumvent the fact that many product improvements do in fact come from the aftermarket, and often these improvements or their concept get adopted by the factory, but only after adequate engineering, anylisis and testing are done. A case in point is the BullyHawk Soft Start. It does work and improve starting and was a product that went through extensive design engineering and testing. Rotax adopted the concept and made it available on new model engines in their own rendition. In the end everyone benefited, but only by taking very careful baby steps through reputable companies with proper engineering, testing and analysis, not by letting the end use customer act as a guinea pig!

    As with the BullyHawk Soft Start which helps compensate for other less then desirable installation and maintenance issues, so might be the case with your experience on the carb sockets. As Roger has mentioned, there were a multitude of reasons carb sockets may have failed, fixing those reasons might be more viable then experimenting with the unknown?

    Hope this helps with you evaluation process, good luck and happy flying! :side:
      
    Report

  • Re: Carb Rubbers/Sockets

    by » 13 years ago

    Yes this does help me as I would never have thought of the fuel foaming etc.
    I do think though that there is a fundamental problem with some of the rotax parts including especially the aftermarket ones that are used by Rotax. I now fully appreciate more what goes in to the testing etc, and to be honest you have opened my eyes to some degree, but what really gets people going over here in the uk are some of the prices that are charged for the parts, including the after market ones used in other applications as well.
    For example, a plug cap for a 912, its part number off the top of my head is something like NKG05FMH.
    I was quoted £34 plus postage for 1, diaphragm for the carb I think is near the £60 mark.
    These items can be purchased elsewhere, not copies but originals far far cheaper.
    Plug cap £7.50 and a diaphragm for £10
    I know the prices have nothing to do with you, but it does have a bearing on why some people would think that Rotax deliberately inflate their prices, hence going elsewhere.
    I spoke to a friend who knew someone working in Bing, they told him there was only one part number listed for the Bing 64 Diaphragm, but once they knew it was going on a rotax 912 refused to give any more info.
    Sorry if you think I am having a go at you lads, which I am not and I think its excellent to have this forum with such knowledgeable people on to help us out, which I am really grateful for, but I bet you would get less failures if they made their parts a little more accessible as many of us are only just affording to fly.
      
    Report

  • Re: Carb Rubbers/Sockets

    by » 13 years ago

    Hi David,

    Didn't know you were from the UK. I think Rotax parts are more expensive here in the states. I actually buy Rotax parts at times from the UK because they are cheaper even with the shipping.


    Just a side note:
    Many, but not all the engine issues I see are from the owners either doing things they shouldn't or for not doing things at all. Most of the time I can track a problem right back to an owner or mechanic. The manuals are your Bible when it comes to your engine and they are just as easy to follow as not.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report
You do not have permissions to reply to this topic.
Related Topics
Title Category Replies
Carb sync varies over throttle range 912 / 914 Technical Questions 5
No 912uls carbs in US?! Rotax-Owner Community 1
New carb socket fits loose 912 / 914 Technical Questions 67
Engine will not make power after carb install, post-overhaul General Tech Discussion 42
Carburetor Piston Wear 912 / 914 Technical Questions 8
Follow Us

Recent Videos

Safety First!

 

To receive critical-to-safety information on your ROTAX Engine, please subscribe to
ROTAX-OWNER.COM

Prize Giveaway!


SUBSCRIBE NOW
to automatically enter this years draw!

Login