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EOS100 mystery carburetor

Mike Christiansen

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Hi All,

I have an EOS 100 engine on a parajet parameter I purchased used. 

Im having trouble with low power output and want to start by rebuilding the carb however the one on the engine has no markings and does not seem to match any of the carbs on the EOS manuals, either the early one or the Walbro WG8-1.

It looks very much like a walbro, possibly a WB32. It has a high speed needle adjustment. 

Pics on dropbox because I cant work out how to share them otherwise. 






I would love to work out which carb this is and to know some needle adjustments to start with.

Thanks for any help,




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Hello Mike

Apologies for the long post but if you get to the end it may help you in some way.

I have an EOS 100 from the pre Sept 2017 production which came with a WG8 carb (stamped on carb). https://www.eos-engine.com/userfiles/files/appendix_manual_EOS_100_EOS_100_Booster.pdf this bulletin explains the change even though they still list the WG8 on the technical details page. EOS ended up sending me a WB37 (there is a long story why they did this which some on here may know about the issue EOS had) to change out my WG8. Note that if you do this you need a new plate that goes between the crank case and carb and new SST throttle cable bracket as the two carbs have completely different mounting orientations. Also note that the WB37 is modified so you can't just bolt one on from a random source or you may end up overheating your engine. Your photos are definitely not of a WG8 but it does look a lot like a WB37, especially the shape of the pump side plate. My WB37 has a high speed and low speed needle, as well as the idle adjustment. You mention a high speed needle but the photos don't show if there is a low speed one. A serial number will be stamped on the crankcase of the EOS 100, this will determine if yours is post the Sept 2017 production change and will possibly confirm the carb model. Email Herbert at EOS if you want clarification. 

You mention lack of power and I have a bit of experience in trouble shooting this. The changes I made achieved a consistent RPM at WOT, and a higher WOT rpm, however they may not be endorsed by EOS or others. In saying that a lot of what I did is just general good maintenance. My engine was well out of warranty and it was worth a shot for me instead of buying a new more powerful engine. There is a wealth of information at https://www.southwestairsports.com/ppgtechinfo/ppgtechinfo.htm and I recommend reading everything you can on this site. Start with the basics - clean carb and install a new carb kit (once you've identified the carb), new correctly gapped spark plug, fresh fuel, correctly adjusted metering lever height (1mm for the WB37 according to EOS) and correct pop off pressure (11-13 psi according to EOS). The bulletin in the link above indicates the starting points for the high and low speed needles. Those needle adjustments were almost spot on once I'd confirmed or did everything just mentioned, and the additional changes below. If you can fit a rpm meter and CHT gauge then do it - well worth the investment and helps in the testing phase.

My engine suffered from WOT rpm fade, it would get to about 8500rpm then drop off into the low 7000s. I thought it was from overheating but eventually diagnosed as vapour lock or fuel starvation (which would also probably lead to overheating). I had a bunch of air in the fuel hose just before the inlet into the carb and it stayed there throughout the throttle range. I did these additional things to eliminate vapour lock. I'm not sure what one achieved the most so I assume it was a cumulative effect. 

  • pulled out in-tank filter. This was a Walbro one with a felt sleeve and small round gauze secondary filter. Both the felt and gauze was removed leaving just the weighted clunk. I drilled out the nipple orifice as much as I could (3or 3.5mm I think). Reinstalled into tank
  • Added a 10micron inline filter just before the primer bulb
  • Installed a new 4mm ID engine pulse nipple into the crankcase. This required drilling a new hole and tapping it, then blocking off the existing nipple hole. You could re-tap the existing hole but I couldn't drill out the existing nipple to the 4mm ID as it was too small so elected to go for a new hole so could return to the original pulse hose if I need to
  • Pulled the pulse nipple out of the pump side of the carb (it is interference fit not threaded) and drilled this out as much as I could. I think I got to 3.5mm which was close enough to the 4mm on the crankcase nipple and much bigger than the 2 or 2.5mm ID on the stock nipple. According to Southwest this allows a much stronger pump pulse to power the carb
  • Pulled the fuel inlet nipple from the carb and drilled that out. Again it was only about 2mm and I think I got that to 3 or 3.5mm as well.

All of the above allows for a much more consistent flow of fuel into the carb without any unnecessary bottlenecks. During the first test I immediately got well over 9000rpm with more throttle trigger to pull, a steady 9000rpm for a takeoff throttle setting and most importantly no fade at WOT. Temps were as you would expect on a lengthy WOT run but I wasn't concerned about overheating. Any air bubbles in the fuel line at starting moved towards the carb, into it and then didn't reappear. I'm happy with the results and don't think I need to consider any more "fixes" or something like Southwests FSM.

Hope this helps, happy to take questions or send photos.



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Thanks so much for that reply David, this is gold! 

The document that you link gives me the exact info I need to rebuild my carb and go back to base settings. I have also wondered if belt slip has played into it at all, and the doc you link details how to tighten this. 

I have read quite a bit of southwestairsports stuff. Very helpful. To my eye it looks to be a WB37 fitted to mine, has a high speed and low speed needle. The high speed never seems to have been locked off per the EOS document however. 

My engine is SN#375, the parameter was built in 2017,. Can you tell from the SN if the unit was pre or post Sep 2017? 

Do you by chance know of the modifications EOS do to the WB37? I would like to check these have been done to my carb and might look to purchase a spare carb (original Walbro) and may need to modify it to work. Im not convinced my carb is a genuine walbro, it lacks branding or any model stamps in it. 

Regarding the lever height, do you know if the original carb from EOS with 1mm lever height had a tang on the diaphragm? This page details different lever heights for either the tang or button membranes. https://www.southwestairsports.com/ppgtechinfo/top80/hrservicenotes/walbrowg8/ml_height-variations.htm

Any suggestions on CHT and RPM devices? Im a bit of a data geek, would love to find an Arduino data recorder project or something that can log these values. 


I think my plan from here is to 

- Rebuild carb with a fresh kit now I know the model, set pop off and lever height. 

- Make the fuel system modifications you list above.

- Get some form of RPM / EGT gauge / logging so I can quantify improvements. 


Ive not yet had any help from EOS, ive emailed them twice in the last 2 months but just their generic addresses, I might give Herbert as you say.


I want to thank you again so much for your reply, I think you have saved me hours / days of frustrating googling!

Fly safe! 



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Hello Mike
Glad the info was of assistance.
Both the WG8 and WB37 that I have have Walbro cast into the pump cover plate so maybe yours is aftermarket, although if supplied by EOS I wouldn’t be concerned. If it was some random brand unmodified carb then I would recommend replacing with one you know has come directly from EOS. The issue I referred to with mine was that a handful of 100’s were sent out with an unmodified (too small main jet orifice) WG8 where at factory needle settings it was likely it would overheat, and in my case blew a hole in the piston. EOS acknowledged the issue and sent out replacement parts and the correct jet. I rebuilt and had it working fine and out of the blue EOS sent me a WB37 which I subsequently fitted. Herbert advised that engines from serial number #370 to #402 delivered between June 1st to August 5th 2017 could have been affected, they weren’t sure how many left the factory wrong so they just offered parts for all 30 odd units. Mine is #377 and I confirmed by measuring that mine did have the wrong jet installed. Given your serial # of 375 it is in the batch as well but appears to have had the change already implemented. EOS did send out a official announcement to their customers about the issue but it never reached me via Parajet and my NZ retailer – I found out the hard way!
As mentioned, the off the shelf carbs are modified by increasing the main jet size to allow more fuel flow. The WG8 jet has a threaded brass insert with a hole through it and was easy to find and replace on the WG8. I can’t recall it being as easy to find on the WB37 when I was looking for it during a carb overhaul. The metering lever height may also be specific to the engine as well as with the metering spring, EOS could confirm this. Note that the metering spring does not come in the carb repair kit. The metering diaphragm on my WB37 has the tang type fitting which has to be slotted into the metering lever. I would only get a new carb from EOS otherwise you may create more problems than you solve. Herbert does sometimes take a while to respond but try him directly on hofbauer@sunflightcraft.com . He may even be able to confirm that a replacement WB37 has been sent out for your serial number, and if so it is likely to be the one fitted. He may even be able to comment on why yours has no branding and mine does.
One of the more common RPM and CHT gauge suppliers is Trail Tech. https://www.trailtech.net/en-us/shop/accessories/motorcycle-parts/kickstands/?gclid=EAIaIQobChMIpJPinf3r9QIVHphmAh0_OgvBEAAYASAAEgJMY_D_BwE these are stand alone gauges so I doubt they can be integrated with anything although there may be some other products of theirs that will. Some flight instruments also have add on sensors for fuel gauges, temp and rpm. I had quite a bit of trouble getting a consistent reading off the TT rpm gauge. It was dependent on the number of wraps and how far spaced the wraps were but I have got it going pretty good now.
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Thanks David,

Im also in NZ, I wonder if our units were imported at a batch given our very close SN's. Small world! Did you buy your unit new? If so can I ask who the dealer was, they might have info on my unit.

Ive contacted Herbert about the issue and asked if he has any suggestions of getting an EOS supplied and modified WB37 carburettor. It would make me feel a lot more confident in the unit. Looking forward to a reply so I can get into the air with a bit more power! 

In the interim ive ordered a K10-WB rebuild kit to see if this will fit and improve things. I would love to hear from Herbert prior to running the engine tho, I dont want things to get lean! 

Im looking into the PPG Meter https://www.flyhenry.cz/index.php/en/products/ppg-meter-eng Looks like theres a dealer in NZ so I have contacted them. Integration into my Vario would be awesome but that may be stretching the budget! 


Thanks again,

Regards, Mike. (Wellington Club) 

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Hello Mike

I wished I had read a bit more of my email correspondence with Herbert and I would have put 2 and 2 together quicker. At about the same time I bought my Maverick from Wings and Waves they got in another for someone. It suffered the same issue as mine with a blown piston from what I understand - the serial number was 375 according to the info I was given to forward to Herbert. I arranged for another set of parts to come in for 375 at the same time as mine but I can't recall if that was engine repair part plus a new jet for the WG8, or a new carb.

I did correspond with the guy who owned 375 about his repair but can't find his contact details now. If I remember correctly he was a mechanic or had the technical know how to do the repairs. You could contact Eva or Reuben at W&W in Auckland to see if they have the contact details so he can confirm what was done. 


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