Converting Lehr paropane 4 stroke to Gasoline

Discussion in '4-Stroke Engines' started by Mike St, Feb 21, 2012.

  1. Mike St

    Mike St Member

    Any suggestions for a carburetor to convert the Lehr 25cc 4 stroke to gasoline? Would like to find solution not more than $50.

  2. Silvaire

    Silvaire Member

    Awhile back I found a thread on about putting a carb on a Lehr propane engine. There was a mention there stating that the compression of the Lehr was something like 10:1, whereas the Subaru EH025 was something like 8:1.

    I'm just curious, why do you want to put a carb on one?

    If I were in your position and wanted what you'd have after converting the Lehr, I would put my $50 towards a used Subaru EH025 and have the real thing. EH025's were used on a number of weed eaters and blowers and such made by Makita and others, and they regularly show up on eBay.
  3. HeadSmess

    HeadSmess Well-Known Member

    any type of 10mm brushcutter carb.

    search scrap yards. they breed there...

    they do need some modifications.

    hooking up throttle cable is the main concern.

    (but most parts will swap over, such as throttle arms, choke levers, diaphgram assemblies. depends on what carbs you have in front of you exactly.)

    a pulse line on the carb. usually as simple as drilling a hole in the appropriate place on the intake manifold.

    a SUPER LIGHT spring under the diaphgram. the intake can only "suck", the spring provides the "push".

    usually the needle valve spring pinched from another carb ;)

    getting the proper subaru carb works.

    if there is any truth in this compression ratio nonsense (the lehr is actually a HUASHENG copy, so why it would be specifically designed with a higher compression ratio puzzles me.... they copy, they dont design. copy. not design.)

    anyways, if there is any truth, all the better! more power! and they need it! run 95 or 98 octane :)

    the oil goes black real quick on petrol...
    Last edited: Feb 21, 2012
  4. Mike St

    Mike St Member

    I want to convert the Lehr to gasoline because propane is way too inconvenient for extended use on a motorbike. I can understand it for yard use, trimming once every two weeks or so, and I also want to build an MB that meets Illinois law, no more than 1 HP.
  5. Silvaire

    Silvaire Member

    I haven't tried a Lehr engine on an MB, but I have several Lehr weed eaters and a blower. I really like the convenience and useability of propane. They start quickly even after sitting for months. They run very clean in every respect.

    You can get an adapter to refill the 1 lb. disposable propane bottles from a 20 lb. BBQ cylinder or the like - and doing so would be an economic necessity with an MB. Just carry an extra bottle with you if you don't want to risk the possibility of having to peddle home. The money and the time and hassle of converting your engine to auto fuel would go quite a ways in propane expense.

    It is my understanding as well that the Lehr is a Huasheng made engine. As far as the compression ratio thing, I have no personal knowledge. Changing the compression ratio is simply using a different piston. For the quantity of engines involved and everything else that was changed externally to run on propane, a piston change would be a pretty simple matter.
    Last edited: Feb 22, 2012
  6. BigBlue

    BigBlue Active Member

    Attached Files:

  7. Mike St

    Mike St Member

  8. HeadSmess

    HeadSmess Well-Known Member

    when i first got my lehrs i wondered about the rules regarding lpg vessels for a while...cus what if you basically got a (large) fire extuinguisher type bottle...scuba tank?... welded up with a headset and a bottom bracket...would it be certified if the welding is up to standard or break every rule in the book using it as a stressed frame member?

    i didnt think of the alternate piston design...oh my... i cooooould do the old oil in the cylinder trick and if someone with a genuine subaru also did the same then we could have a definite answer on the compression ratios once and for all!:)

    i really prefer the lpg idea for the pushy. if anything really goes wrong you can dump them in the back of a car without petrol going everywhere.

    and as stated, carry a spare bottle.

    does the adaptor to fill the 1 pounders from a big bottle include a spanner for the bleed valve? not quite the same as a tyre valve tool :(
  9. BigBlue

    BigBlue Active Member

    Last edited: Feb 23, 2012
  10. Richard H.

    Richard H. Member

    They're reselling the Stanton kit w/Lehr engine which he seems to have discontinued.
  11. Mike St

    Mike St Member

    Propane tanks are not a problem because they come in all sizes, but it would be difficult to refill larger tanks. These have to be refilled by a propane supplier. So using propane for a motorized bicycle still looks very inconvenient for extended use.
  12. Silvaire

    Silvaire Member

    A bleeder valve is not generally used in the home refilling process of small disposable bottles. You put the empty 1 lb. bottles in the freezer first before filling on order to get the needed pressure differential. You can find loads of info on the refilling process posted online. It is important not to overfill these small bottles - and the consequences of overfilling them is the same as with any other propane bottle. They should be filled by weight. You need to weigh the empty bottles and mark them with their empty weight first. You can then know when you have gotten them full. This is simple to do if you have a small digital scale.

    These small bottle refillers are about a $15 item from Harbor Freight, or one can easily be made by joining a couple of specialized propane fittings that you may likely have laying around.

    Here is a nice writeup about refilling disposable propane bottles:

    Also, I don't know where to buy them, but there is a "legitimate" refillable 1 lb. bottle available:
    Last edited: Feb 23, 2012
  13. Mike St

    Mike St Member

    I'd rather put on a gasoline carb than constantly refilling small propane bottles. Yes, there are demos online of refilling these bottles but very few, maybe two, people who have used the Lehr propane engine on a MB. It just isn't practical.
  14. HeadSmess

    HeadSmess Well-Known Member

    ok, requote your statement. "2 people that have posted anything on a forum board as far as i am are aware are using lehr propane"

    until youve done it you cant say its practical or not.

    it is a matter of personal opinion i guess, but ive found refilling is easy, so thats no problem.

    i need to constantly refill a fuel tank with petrol anyway so whats the difference?

    gas doesnt make a mess when it leaks unless someone sparks up :jester:

    i get two hours run time on however much gas i squeeze in when i do refill (weigh...huh?)

    at the price i get lpg for, theres nothing anywhere near as cheap.

    the only reason im NOT running lpg or propane, whatever, is more because im lazy and got a HT and just didnt bother with mounting the lehr...properly, anyways. found it slightly too gutless for my um...area of intended useage, so shelved it til future times.

    but, back to the original question, almost any walbro type carb will work with modifications, but one thing i didnt mention is that you need to be able to retain the existing airfilter. :eek: it contains the pcv/bypass valve that is part of the lubrication system, not just a breather valve or emissions thingy. its an oiltrap, and crankcase pressure is actually used as the "oil pump". the valve allows excess pressure to escape whilst retaining and returning oil to the sump.

    you CANT bypass or remove it. or use the crankcase as a pulse for the carb.

    makes it slightly trickier. finding the ideal carb is just that lil bit harder again.
    Last edited: Feb 24, 2012
  15. Mike St

    Mike St Member

    Sure you can refill the small bottles by putting them in a frig, but imagine doing this every 2-3 days. Eventually, I would get tired of cooling bottles in the kitchen frig. With gasoline, I can just pour in more gas and I'm done. I think if propane was so attractive more people would use them for an MB. Did you know some large retail chains don't carry the Lehr trimmer anymore? One chain told me there just wasn't enough interest to carry them. I'm not against propane, just don't think this fuel will catch on with builders or with the public for yard use.
  16. Mike St

    Mike St Member

    Here some additional information on the cost per gallon of propane. The cheapest price on propane I can find for refilling a bbq tank is $13.93. The tank holds 4.1 gallons, so the price per gallon is $3.40. At $19.00 refill, the price is $4.60 per gallon. The conclusion is propane is currently not cheaper than gasoline.
  17. HeadSmess

    HeadSmess Well-Known Member

    how many kg is this bbq bottle?

    auto lpg here in OZ is 70c a litre. not sure what that is in kg.

    i can get 1 9kg bbq bottle filled for $15.

    im getting at least 20 fills from 9kg.

    whats with the fridge? run them til theyre empty and they seem to refill again... but id rather use the bleeder and fill them like any other sensible bottle is filled...decanting.

    the biggest killer is the lack of backup/support. its an unfamiliar area, not many people even know about them, ie the lehr on propane. in australia...i must be the only person with one at all! :D

    everyone who sees mine wants them though... novelty factor?

    but anyways, back onto the petrol conversion.

    with my last comment on keeping the stock air filter, yes. true.

    but the carb type has been narrowed down to the type with a BARREL. mainly because the spacer block/ manifold on the lehr has the nifty lil fitting for the cable to suit one. operating the throttle was the biggest challenge i found with my conversion...

    most newer model upper market (husqy, stihl, shindaiwa, etc) are fitted with the barrel types. most POS cheapies (ryobi, mtd etc) are fitted with standard butterfly carbs.

    stating a specific carb other than the subaru one, cant be done...theres way to many numbers!
  18. Mike St

    Mike St Member

    OK, Headsmess, you're paying quite a bit for your propane.A bbq tank is contains 4.1 gallons of propane or 17.425 lbs. At $14-19/ refill, that is 71-109 cents per pound. You are paying 1900/454 is 4.1 lbs or $15/4.1 or $3.65 per lb, way too much. To put it bluntly, you are getting scre. .
  19. HeadSmess

    HeadSmess Well-Known Member

    where does the 1900/454 come from?

    17.425 lb is pretty close to 9.0 kg. 8.5 if you get those lousy swapngo ones.... (its 7.9kg actually). we have 9kg bottles. probably 20#

    i pay $15 for that much. (most people pay 30, ha ha ha)

    thats around 80c a lb to me, give or take... many litre gallons are we talking? 3.75, 4.5 or 5L?

    auto lpg is half the price again, or 70c-80c for 2 lb. we say litres, once again, what gallon are you using?

    petrol, gasoline, benzine, is around 150 a litre here now. despite how better our dollar is currently... or $7.50 a (5L) gallon

    so bottled lpg from my refiller is roughly the same as petrol, and auto lpg is half that price...

    as for screwed...these bernzamatic 1lb bottles are $20 each... and noone has a refill service for them, even though they are refillable.

    now thats getting ripped off! :eek:
    Last edited: Feb 26, 2012
  20. Mike St

    Mike St Member

    I made the calculation on the info you gave, $15 for 1900 grams or, 4.18 lbs. But what you actually meant was $15 for one 9kg bbq tank - much different. Now if you say it's actually 7.9 kg or 7900 grams or 17.4 lbs, than your paying $0.86/lb 0r 86 cents per lb.
    A normal price. It still comes out to $3.65 per gallon, since there are 4.1 gallons of propane in the tank. Not any cheaper than gasoline.