Reedless 2 cycle engine

[Pafrig]

Ok, so im taking a small engines class at a vocational school, and were making theese lame kit go carts as a final project. the teacher handed out engines, the most powerfull being a 4.5hp briggs. For some reason, he gave me the project from hell, (a gocart which a previous student had tried to extend, fail misirably, then lost half the peices.). in the last few days ive repaired the frame, found peices, and got it back together. then the teach gave me a 3 hp flathead briggs with an almost dead clutch. 1/4 mile in about 5 miniutes, know what i mean? after reciving quite the load of from the other people in my class about my snailcart, i went outside looking for a replacement engine. what i found (and the teacher said i could use) was a REAAALLLY OLD snowmachine engine.. Its a Hirth 191R4e 300cc with a snowmobile clutch. the thing is air tight, has a cable for a pullcord, awsome compression, good spark, carb is clean. Brought it home tonight to get it running. ran into a few problems with fuel not pumping...

the first thing i did was wetted the old gaskets inside the carb, (specifically the one way flappers) and that kind of helped. The engine would now suck fuel up the intake hose, but only when choked. This was the first confusing thing.

after pulling it over i got a few pops, then a few more, followed by a few more. but nothing consistent. the plug was wet every time i took it out. i tried leaning down the mixture, tried a bunch of adjustments, ran best when gas was poured into plug hole. i figured that it was a problem with the carb. so i took the airfilter off and pulled it over for the hell of it, and air came back out the carb.........

obiously somethign was wrong, right? I just figured that the reeds werent functioning properly. guess what? NO REEDS.Not even a place where any reeds could possibly fit. wtf? I asked my dad who spun wrench for 35 years, and he said he had only seen one 2 stroke (an old detroit diesel) that had no reeds, but he didnt understand how it worked. Basicly, im really confused. How is this supposed to work?

[newrider3]

Piston port. That is all there was back in the days before reeds, still common on smaller (ie weedwhacker etc) engines.

[greenhuman]

The piston acts like the reeds by cutting off the inlet tract like reeds do to seal the engine for the transfer ports to work. To improve performance on these engines you could trim the bottom of the piston to let in more fuel before the piston cut off the flow for the transfer action to take over. The early LT250R Quadracers were a combination of piston port and reeds into the sump.

[KASEY]

Don't forget rotary valve engines too,,, no reeds

[3wheelmecca]

And also sleeve valve and piston valves from the 20's. most 2 strokes from '74 ish back did not have them. My TS does not.
in soviet russia, Crank is the way to get fuel in, through side.
The RM80 and 125s had crank port intakes as well as Rotax engines.

[Vealmonkey]

The 1972 yamaha r5 was a 2 cylinder, 2 stroke, 350cc reedless engine. It was replaced by the rd350 in 73 later to be replaced by the rz350 engine which was a water cooled 2 cylinder, 2 stroke 350 which later went on to power yamaha 4 wheelers. Most all the early 2 stroke engines were reedless. They were either piston port or rotary valve. My Tiger 250 which is watercooled is rotary valve.

[jeswinehart]

On my 1986 Polaris 250 2 stroke there are no reeds either.
One thing that will make it not run is if the carb leaks thru (even just a little) and gets fluid in the bottom engine case.
There is a convenient drain on the bottom front to drain any gas/oil mix.
Believe me when I say if there is a any fluid in the bottom case, it will not run/start.
Just something else for you to check.

Good luck ! john

[toocheaptosmoke]

Piston port engines are common to sleds, still used today, that hirth is a decent engine for what it is. "Spit-back" out the intake is common at low rpm, you always smelled like gas riding those old sleds with the carb sitting in your lap. Trimming too much off the piston skirt amplifies this effect, can't take too much off. It probably has a tillotson carb, right? They sometimes need the gaskets and diaphragms replaced if they sat dry for a while. If it only pops when gas is poured in, it sounds like something is still plugged or not working in the carb.

[Grizzlypeg]

I had a 1974 Suzuki T500 and it sure didn't look like it had reeds. Next bike was a '77 Yamaha RD400 and the reeds were there for sure.

[fabiodriven]

I asked my dad who spun wrench for 35 years, and he said he had only seen one 2 stroke (an old detroit diesel) that had no reeds, but he didnt understand how it worked.?

I know this isn't going to help you any, but two-stroke diesels use a supercharger to positively charge the intake. They do not rely on atmospheric pressure like a gasoline powered two-stroke. That's a whole other animal though.

I too have seen many old two-strokes with no reeds. I must say Pafrig, for a younger guy doing some learning you sure do have the right mindset. You've got all the troubleshooting skills down and you seem to have all the basic principles as well. Are you still in high school?

[84honda200s]

ive delt with a few of these older sled engines .. well allot of them lol .. the hirth engines were known to be cold blooded but hauled butt .. sounds to me like maybe your fuel pump is either gummed up or the inerds are dryd out to the point of no return . but here are all the specs i have on this engine .

the 191r is a single cyl 300cc fan cooled engine it uses a hr style carb . the fuel ratio is 25:1 plug gap is 0.020 the points should be set at 0.016 and allows for timing advancements ..

if i were you id find a single cyl mikuni fuel pump and a mikuni carb and run them .. but it will only work if you have a vacuum line coming out f the crank case that attaches to your carb . it should have one seeing that most if not all of the older sleds ran a vacuum style fuel pump .

the difference between the hr carbs and mikuni carbs is the hr has a built in fuel pump and the mikuni carbs ran off a external pump . not to mention allot better throttle response then the older hr carbs . now if your engine doesnt have the vacume style fuel pump then you could probably get away with running a mikuni with a gravity fed fuel tank .

if you need any help or questions let me know . i have a few friends that deal with these older style sled engines . and i have a few books with specs .

ive never seen a older sled with reeds ..

[RIDE-RED 250r]

i second the recommendation to rebuild that carb. as mentioned before, it could be a Tillitson or also a Walbro. if you take the numbers off the carb and stop by your local parts slinger who deals in sleds, you should be able to get a carb rebuild kit for about $25 give or take depending on the model. if the carb is a walbro, its also possible to get a kit through a chainsaw dealer as many chansaws use walbro carbs. you could also check with large mail order catologs like Dennis Kirk. im pretty certain they still sell carb rebuild kits for the vintage diaphragm carbs. i grew up playing around with those old diaphragm carbs, and i found that alot of times after they sat for a while like that, the only real sure-fire fix to carb problems was to rebuild them....good luck with your build, when you get that ol Hirth going and get the cart geared to the engine, you "friends" will be laughing out the other side of their faces cuz you will blow that 4.5 briggs outta the water!!

[84honda200s]

it should be a tilly carb .. if it is the rebuild kits are real hard to find . ive tryd finding rebuild kits for all my tilly carbs and had very little to no luck thats why i converted to mikuni . they are allot easier to work on and find parts for .

i agree that hirth will kill the 4.5 hp throw away motors . sled engines on go karts is like putting a rocket engine in a dirt bike lol. but its all in the gearing.

[RIDE-RED 250r]

looks like dennis kirk has them..... offered for HR and HD carbs.... http://www.denniskirk.com/jsp/produc...fCatId=&mmyId=

84honda200s: might come in handy for ya in the future if you dont want to bother with the Mik swap...

[84honda200s]

looks like dennis kirk has them..... offered for HR and HD carbs.... http://www.denniskirk.com/jsp/produc...fCatId=&mmyId=

84honda200s: might come in handy for ya in the future if you dont want to bother with the Mik swap...

lol thanks man = ) but im a mikuni type of guy . i know them pretty good and as i said they have way better throttle response than the tilly carbs . but thank you for the link man i book marked it just encase ..