the amazing 4 stroke hobbit

Jason Luther /

this piece of crap. i have done EVERYTHING to remedy the 4 stroke issue. and the only thing that works is pulling out the air filter cartrage about 1/2 inch. the carb is clean, the airbox is void of any foreign objects. the filter itself is super clean. i can even take the foam filter out completely, but uless the cartrage is out 1/2'' it four strokes. here are some more possible causes i thought of while taking the pain in the ass apart...again. it says to use 25;1, that seems like a lot. i have been using 32;1. would more oil possibly displace the richness? what is the correct plug? i have an ngk bp6hs. there are no numbers on the main jet. could the previous owner possibly put in a bigger jet 20 years ago when it last ran? can you get different size jets?

Re: the amazing 4 stroke hobbit

correct plug? my '78 seems to run fine with a NGK BP6HS (the '83 manual says use the BPR6HS... R = resistor)

Main jet is marked but might be worn off.. it's a #78 on the PA50II.

If this problem is cured by opening the filter box, all i can think of is insuffient air.. and that's gotta be caused by a closed choke or by some restriction between the choke and 3-holed rubber intake tube. What else /where else could restrict air that would be cured by opening the filter thing?

The otherday i thought my bike was 4-stroking .. you know that sputtering sound.. close the choke and it goes away. But then one time it didnt go away.. It was not misfiring due to a rich mix.

What it turned out to be was misfiring due to a dirty plug.

Re: the amazing 4 stroke hobbit

Jason Luther /

yeah, but if it were an ignition problem, why would pulling the thingy out help? everything is as clean as a whistle, and im at my wits end. i really wouldnt mind just running it with the thing out, but the belt is burning the pull off. italian peds are way easier to get running well.

Re: the amazing 4 stroke hobbit

I meant to say it was not misfiring due to a lean mix.

anyway, afaik alternate main jets are not available from Honda .. i dunno which older-but-not-too-old Hondas used the Keihin and have similar jets in different sizes.

25: is too much oil for my bike.. smokes and the tail drips oil. I'm using near 32:1.

More oil makes the air:fuel mix leaner .. oil takes the place of gasoline.

Plug gap is near 0.6-0.7mm. (0.025 inch)

Whats up with that rubber intake tube.. im looking at a dismantled swingarm / airbox and that tube is all there is between the filter box and the world outside..

Have you dropped the engine and pulled that rubber intake tube out? It plugs into a smaller roundish cavity off to the side that is not accessable through the filter-slide box opening.

Re: the amazing 4 stroke hobbit

Jason Luther /

oh yeah, ive taken the pos apart many times now and i was just looking through the 3 holed tube with a flash light. that was my thoughts exactly. it has to be between the 3 holer and the filter. but the box is completely clean. i wonder if i actually made the jet bigger when i cleaned it for the first time, since it was like a piece of amber. but i dont think so.

Re: the amazing 4 stroke hobbit

main jet matters if you're talking about top-speed operation.. i forget the details of this POS-problem.

I guess some sort of jet damage could make it run rich all the time..

There's another jet.. the tiny idle jet.. under that flat headed cover screw near/under the speed-screw. If that one is (accidentally) bored out too big a bunch of fuel might pour through it at all speeds.

Re: the amazing 4 stroke hobbit

Jason Luther /

its only at full throttle that it 4 strokes. it has to be some thing painfully obvious, im just sick to tearing this thing apart. thanks again.

Re: the amazing 4 stroke hobbit

I had a very simular problem. I pulled the head off and one of the rings was broken and my cylinder wall was very scratched. It felt like I had decent compresion also.

Re: the amazing 4 stroke hobbit

With mine I just put it up on the center stand and held it wide open for a few minutes, black goop started dripping out the exhaust and eventually it straightened out. Good luck with it.

Re: the amazing 4 stroke hobbit

George Smith /

well here's what i do with any two cycle doing that....first...

run with choke full on....then slowly release choke while running for like 2 mins if it continues clean with some carb cleaner then try again....back when i worked on a lot of 2 strokes it was common to get dirt and oil stuck up and have to run them till it blew out also remove yours carb and see if anything is in the intake ya might be surprised at the findings :)

Re: the amazing 4 stroke hobbit

My unit runs exactly the same as yours does. Runs fine right up to 29-30mph and then goes fffppppptttt 4-stroke crazy.

It will then slow down to about 26 and then clean out, running back up to 29-30.

IAs an experiment I pulled the whole filter out of the bike and whoa!, it ran right up to 32+ with no 4-stroking.

This tells me that the intake filter is overly restrictive, not letting enough air thru to the engine. I am now looking for some of that green filter foam to use to see if it makes any difference over the stock sponge.

I will let you know.

Re: the amazing 4 stroke hobbit

one time i cleaned the filter and then oiled it, according to instructiuons in the PA50 manual.. use heavy gear oil, squeeze it out.. and the bike ran like crap.

I pulled the foam element out and rolled it back and forth on a paper towel to absorb and remove all the extra oil.. things got a little better but not quite right. Finally i just washed it all out with soap and water and dried the element.. the bike ran normally after that.

Re: the amazing 4 stroke hobbit

Jason Luther /

this still is perplaxing me. even if i take the foam filter completely out, unless i have the cartrage thingy pulled out of the slot, it 4 strokes. the entire air box is completely clean and so on and on. tonight though, i forgot i never had the cylinder off, so i coaxed it off, and sure enough the piston and rings and ring grooves were well clogged. the second ring was almost stuck solid, but i got them off and are now soaking in carb cleaner, along with the piston. the piston itself has no scoring and the bore is nice and slick. do you think this was my problem? and if so, why would giving it more raw air make it go away? it has a broken speedo cable and the odo reads about 400 miles, im thinking it broke early in its life. judging by the condition of the rings, etc. im digging the 3 transfer ports though. :)

Re: the amazing 4 stroke hobbit

man.. that's filter thing is freakin weird.. what could explain it except some obstruction inside the airbox? I'm stumped. Only 400miles? no way.

i want to tell you that you found the problem and make you happy so you jump up and down and go "YIPPEE" and kiss your old lady and .. well.. whatever :)

but i dunno.. wait and see. This ring carboning thing could just be the result of running rich lately.

I guess the exhaust port and header tube was pretty clear .. and i recall (?) you cleaning that muffler-tube a while back.

As far as why some extra air would "cure" a symptom of stuck rings, i really got no rational idea.

It might have something to do with combustion gas blowing by the rings, polluting the crankcase mixture.. and some extra air improves the mix ratio?

yeah.. all that transfer area makes a big difference .. the engine has potential.

Re: the amazing 4 stroke hobbit

Jason Luther /

it just keeps getting better. i put everything back together, with the piston all fixed up, and it help quite a bit. still four-strokes though, but not nearly as bad. kind of comes in pulses. but it has a lot more power. i think its a compression issue, so tomorrow ill check the compression and see if im getting lots of blow-by. there were blow-by marks at the ring gaps, perhaps time for new rings? is 120 a good litmus test for hobbits?

Re: the amazing 4 stroke hobbit

If you had a partly stuck ring or two and all you see is streaks at the ring gaps, that's not bad. i can't see the connection between compression and the high rpm stutters. anyway, 120 sounds fine.

as an experiment, try increasing plug gap to about 0.040 or 0.050 or more.. i'm thinking if things get better it could confirm the plug is wet-fouling at high rpm. If things get worse ignition might be weak. Either way it's a clue that can be added to the practically empty box of clues.

Re: the amazing 4 stroke hobbit

Jason Luther /

okay i knida forgot that the freewheel doent work anymore, so i cant test the compression. although, after finding out what the points gap _should_ be (quite a bit smaller than italian peds) its been running better, with less 4-stroking, although it still does periodically. so i have exhausted every possible reason and have caved, and have been running with the thingy pulled out a little. so i still think its an engine problem, rather than and air obstruction. i bought this thing with the intention of selling it, but now i like it. it would be a great garage saleing ped.

Re: the amazing 4 stroke hobbit

Jason Luther /

oh, i did have a question. the transfer ports arent smooth at all ('inside ' them) they are as rough as, well rust. are they usually smooth? and if not has anyone polished them up with any success?

Re: the amazing 4 stroke hobbit

i guess you do know that points gap changes result in ignition timing changes .. setting gap is the only way to set timing since the stator plate can't be moved. If adjusting point gap (and timing) made a difference, its a clue.

Most engine castings are rough .. some worse than others. Plans on the engineer's drafting table call for smooth cast surfaces but that aint gonna happen in production.

Cleaning them up and matching port openings is always a good for the engine even if the results are not so dramatic as to be felt in the seat of your pants.

I would not mess with the transfer port roofs (as if you could find some tool that can get up there) since their shape is critical for scavanging..

Re: the amazing 4 stroke hobbit

Jason Luther /

i was more concerned about the roughness of the ports. other things i have been considering is the fact that the engine sat for a loonngg time before i resurected it. and i maybe have driven it ohh 3 miles since i got it going. and it seems that the more i drive it, letting it heat up real good, it runs a little better. perhaps the junk just needs to get burnt out of it. im just grasping at straws now though. i say im content in driving it with the filter out, but im really not, its driving me nuts

Re: the amazing 4 stroke hobbit

you were saying there's no number on the main jet .. It's supposed to have the number stamped on the face (or is it ass??) of the jet ... It's on the same plane suface that the screw driver slot is cut into.. You can read it by turning the carb upside down. Maybe someone dicked with it and the bike can't run with the stock airbox, or its a wrong jet..

my memory of the details of this saga is fading .. if this jet thing has already been determined forget it.

Re: the amazing 4 stroke hobbit

Jason Luther /

i thought of that as well. but i had a hell of a time getting the screws (wtf? screws!) off to remove the carb. before i started they were immaculate and even the thread loc-tight was still on there, so i really think the carb was never removed. how would you go about cleaning out the muffler? i also just remembered that the tail pipe was pinched almost shut (as if someone ran over a log or something) so possibly the muffler is clogged somewhat. i of course tried the cleanout hole and fixed the tail pipe. i remember you dicking around with pa50 exhausts.

Re: the amazing 4 stroke hobbit

loctite? i havent come across any on a carb as of yet.. maybe someonedid mess with it.

i've seen 3 stock mufflers and on all 3 the little tail was slightly crimped, just like yours. First thing i did was open it up but it makes no difference.. I'm thinking it is done at the factory.

Then i cut open an exhaust. There's a much smaller tube that ALL exhaust must pass through inside the muffler. Access that tube through the large bolt under the right side heat shield.

If you can't stick a screwdriver straight in the bolt hole exactly 5 inches or more, you havent completely penetrated the carbon in that tube.. The screwdriver is either hitting the baffle wall or the tube is still clogged. Carbon does not collect to any apprecialble degree anywhere else in the muffler.

Re: the amazing 4 stroke hobbit

btw .. to tell if it's actually clean, the small tube in the muffler is just about 1/2 inch internal diameter.

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