Honda 50 4-stroke help!!!

i have a very old 50cc over-head valve 4-stroke honda moped, with a 3 speed transmission on it. I dont know much more about it then that. I had it running today, and it ran like crap, but it did run. My problem is that i was riding it, and i put it into first gear and stalled it. When i went to start it back up, it only ran at a slow idle at full throttle. It runs really low, and theres a loud pop, and a flash that comes out the carburator every so often. Adjusting the screws on the carb dosent seem to help, and the carb looks to be very clean, and there is ZERO rust in the tank. I had an old honda 90 which is basically identical to this moped, only bigger, and it did the EXACT same thing. I never fixed the old 90 for my friend, but the 50 is mine, and id like to getting running. I REALLY need some help here, because i have no clue as to what is wrong with it.

RE: Honda 50 4-stroke help!!!

It's the camshafttiming or the valves. If there's a loud pop and flash coming out of the carburettor the mixture inside the cilynder also ignites the mix in the carb. The only way this is possible is when the inletvalve is NOT closed during ignition. You have to check the camshaft timing first. Loosen the centre bolt on the right side of the cilinderhead and tap it back in, the left-side cilynderheadcover will fall off, try to catch this, it's would be a pity if it got scratched. Now you can look into the cilinderhead on the left side. You can see the sprocket on the camshaft there. On the sprocket is an O-mark stamped into it, this is the timing mark. Now screw off the left-side engine cover, underneath this is the flywheel. The flywheel has a mark with the letter T, this T stands for Top Dead Centre. Turn the flywheel until the T-mark alings exactly with a mark in the engine above the flywheel. The O-mark on the sprocket should now be exactly in line with a mark in the cilynderhead on the left side of the sprocket. The O-mark could also be on the exact opposite side of where it should be, if so turn the flywheel a full 360 degrees around. The flywheel is supposed to turn twice as fast as the camshaft so this is normal. If the O-mark still doesn't line up with the mark in the cilynderhead you have to unbolt the sproket from the camshaft and shift the chain over the sprocket untill it's aligned propperly, then bolt the sprocket back onto the camshaft and check if it's set right. If this is all well and the carburettor still pops the valve's are leaking. Usually they leak because some cheap idiot drove the bike with unleaded feul for years, ALWAYS use LEADED feul for Honda 4-stroke mopeds. The valve-leaking could have 3 causes. 1. The valves have overheated and are litterally burnt. You'll have to replace the valves for new ones and you'll have the grind them in before you drive with them. 2. The valves are leaking because they need to be grinded in, see the above. 3. The valve seats are completely worn out because someone used unleaded feul for a long time. In this case you'll have to have the cilynderhead revised or you may even have to buy a whole new cilynderhead ($150).

P.S. Calibrating the carburettor is NOT done by fiddling with the screws on the right side of the carb, that's only part of what you have to do to set the carb. You'll have to use a main jet of the right size and you'll have to set the needle-height propperly. After that the screws on the carb have to be set.

You may also have to set the tension of the chain on the camshaftsprocket, how that's done depends on the type of engine you have. I suppose you've got a Honda C50 (or Cub). In that case the tensioning of this chain is fairly simple. Next to the gear-lever on the left side of the engine is a 12mm bolt. Loosen this bolt a bit and unscrew the adjuster that was held by the bolt. If you've got the type of engine I think you have, the chain should tension itself automaticly. Watch the chain through the left side of the cilynderhead. If the chain did not tension itself, turn the flywheel around a bit. If it still didn't tension itself you've got a different type of engine. If it did tension itself than screw the adjuster back in and rebolt it. Otherwise you'll have to unbolt the 14mm bolt on the bottemside of the engine (NOT THE 17mm!! That's to change the oil!). A bit of oil will comeout now, whipe this off because you're going to have to get underneath the engine and look into the hole the 14mm bolt covered. There you can see an adjuster, screw this in fully and then turn it back out 2 full turns. Now the chain should be set propperly, rebolt the 14mm bolt, screw the adjuster next to the gearlever back in and rebolt it. If the camshaftchain is still way to slackened the chain is completely worn out and should be replaced.

Another thing to check are the contactbreakers, set the flywheel so that the F mark (left of the T mark) is about 1/3 of an inch on the right of the alignment mark above the flywheel. Now loosen and retighten the contactbreakers with a philipshead through the opening in the flywheel. If the spring on the contactbreakers will have set the timing correctly. If the contactbreakers are worn they should be replaced.

That's about it.

I suggest you get the Honda C50 owners workshop manual. This book tells you everything you'll ever need to know. It's published by Haynes. I don't have the ISBN-number for the manual of the C50, but I do have the manual for the Honda SS50, the engine is exactly the same except for the gearbox and the clutch. The ISBN number of this book is ISBN 085696 167 1

RE: Honda 50 4-stroke help!!!

i appreciate your help very much. Ill try fixing it this weekend. I pretty sure nothing is worn out or anything, because we rode it all last spring, and it was fine, and theres only 5000 miles on it. i hope you will check this often in case i have any more questions. my email isnt working

RE: Honda 50 4-stroke help!!!

Ron Brown /


Most of Ivo's advice is probably relevant, however, backfiring through the carb is also a symptom of a lean mixture, I have an old 650 Yamaha which is very prone to this if I take the choke off too soon. Even if your carbs look clean on the outside, make sure you have good gas flow into the carb and that the jets are perfectly clean.

Most of the time, a bike which has been sitting a long time will have fuel system problems caused by rust and or varnish and often corrosion on the points.

Don't get too complicated until you try the simple things.


RE: Honda 50 4-stroke help!!!

Ron Brown /


Tell me more about the unleaded gas problem. I have Honda motorcycles, one of them a 1967 and I never heard of a Honda requiring leaded gas.



RE: Honda 50 4-stroke help!!!

All oldfashioned 4-stroke cycles need leaded gas. They'll appear to run fine on unleaded gas, but if you do the valveseats will wear much faster than they should. The lead is needed for lubricating the valveseats. More modern engines have a newer type of valveseats, these newer ones do not need the lead for lubrication.

RE: Honda 50 4-stroke help!!!

Regarding lead in gasoline, the tetra-ethyl lead gasoline additive was developed at the General Motors Research labs back in the late 1930's-40's to improve the burning characteristics of gasoline, particularly under conditions of high pressure and temperature. This allowed 4-stroke cycle engines to operate at significently higher compression ratios than in the past (9,10, even 12:1 rather than 5-6:1 without TEL) without destructive dedonation occuring and therefore produce more power and increased fuel efficiency from the same displacement. This was a big deal for piston engine powered aircraft during WW-II. This technology naturally spilled over into the auto industry and led to the development and introduction of engines like the Oldsmobile and Cadillac V-8's in the late 1940's and the famous Chrystler "Hemi" and Ford "Y-Block" and Chevy "Small Block" V-8's, as well as similar engines from Studabaker, Packard, and Hudson, to name a few, during the mid '50's It was not until twenty years later that another advantage of the TEL additive was discovered, it acted as a higp pressure - high temperature lubericant. At this time, almost all engines had cast iron cylinder heads and the valve seats were machined from the parent metal and induction hardened and ground to finished form. Unknown to the industry, the TEL was preventing the steel valves from welding to the cast iron valve seat under the high temperature and pressure conditions in the running engine. Wjen vehicle exhause emissions regulations became so stringent that the only economical way to meet them was with "after-treatment devices, specifically exhaust catalyic comverters, the TEL had to be discontinued as a gasoline additive because even the minute ammount that was expelled from the engine in the exhaust would quickly destroy the effectiveness of the catalyst in the converter. It was then that "NO-LEAD" gasoline cam on the scene and not long after that serious valve problens began to occour in engines everywhere. New engine production was quickly addapted to include special valve seat inserts to prevent the problem, but the all the earlier engines were, and continue to be vulnerable to damage caused by the lack of the luberication that the TEL additive once provided. Many suppliers of modern un-leaded gasolines claim that they have included additives to replace the luberication of TEL, I am skeptical. Therefore, for my vintage 4-stroke cycle (and them only, NOT 2-strokers) machines like my 1948 Cushman and 1962 Honda Super Cub, I add an aftermarket "lead substitute" to the gas, there are several available at your local auto parts store, pick one from a reputable oil company like Valvolene, Texaco, Quaker State, etc. . I might not need it, but I don't want to find out that I did!

RE: Honda 50 4-stroke help!!!

Ron Brown /

Tony and Ivo,

You got me going on this lead vs. no lead question. I have been riding old bikes for ever and currently own nothing newer than 1975, my oldest being a 1967 Dream 305.

I know that when leaded gas was going the way of the Dodo, I read many articles in magazines about this question. My best recollection was that most motorcycles, having alloy heads and being air cooled, use hardened steel inserts for the valve seats. I especially remember that there was no such thing as a 4 cycle Honda which required leaded gas as I owned a couple at the time.

Just in case, I got on a few motorcycle web sites and although it was tough to find anything on this subject as it has been beaten to death in the past, everything I did find confirmed my recollection.

I guess I will continue to run no lead, my 1971 Honda 500/4 has been running on it for 4 or 5 years for 20+ K miles, it now has 42K, with no apparent ill effects. i.e. no sudden valve clearance changes.


leaded gas and dirty carb dirty carb dirty carb

I KNOW any Honda produced after 1968 does NOT need unleaded gas.

I don't know about ones before that.

But I bet they don't.

It was true for the old cast iron heads... like Tony said.

But is not true for any Jap 4 strokes with hard alloy valve seat inserts.

I know a guy who restores old Hondas for a living.. I am going to ask him and put this topic to rest.

Tim's problem with not running right is almost certainly clogged orifices in the carburetor... particularly the pilot jet.

It needs to be dissassembled and carefully cleaned with aerosol carburetor cleaner and compressed air blown thru orifices.

RE: leaded gas and dirty carb dirty carb dirty car

Ron Brown /


Thanks for the confirmation on unleaded. My panic is subsiding.

On carburetor gunk, on old bikes which have been sitting a long time, I have come across gunk which laughs at todays enviromentally friendly spray cleaners. Some Auto parts have a can of liquid carb cleaner you can soak the carb in and Yamaha has a carb cleaner I have heard realy good reports on.

The bottom line is that you should examine the jets under a bright light and a nagnifier and make sure they are clean.


Fogey's 'R' Us

This is not about Mopeds ...sorry....(old motorcycle info)

One fun thing here Ron is that we both have extensive experience on the same old bike.... My all time biggest mileage is on a '71'CB500 (with a '74' 550 motor)... I put about 55,000 miles on that thing...still have it... One day I pulled up to a gas pump and when it dropped momentarily to a sub-idle speed... it stopped... instantanaeously, mechanically...not just stalled... I thought ...well that was different... I figured it either dropped a valve or broke the cam chain or something... the engine wouldn't turn at I pushed it 2 miles home..... I parked it and have never taken it apart (10 years or so)

I bought it as a basket case with a whole bunch of new parts... the guy had taken it apart and was going to make a "cafe racer" out of it.. then never did it... I bought it for $800 in prob 1981 and rode it for 10 years... It had brand new Lester Mags, JR exhaust, Martek ign advancer, Magura clip-ons, small cafe fairing, S&W air shocks, chromed swing-arm (all new!)... and then I lucked out and a friend at a used parts place found a brand new Yoshimura camshaft in its original I rode the heck out of that bike, for a long time...and it was pretty fast too..ran dead even with an '85' Kaw GPZ550..up to 105mph...then the GPZ got into a wobble.

It was very warn out when it died... blew a lot of smoke...clutch slipping a lot...chain and sprockets gone... cables gone...fork tubes had been extended and rechromed and the chrome was gone where the most wear spot is.(extension above the triple clamps for the clip-ons)

Anyway..... that was kind of fun, telling you all that stuff... maybe it will run again someday.

I imagine you've seen the Yam XS650 Society site?

I mostly ride a "80" Suz GS1100E... but have other stuff too.

For peds I currently have a Honda 79 PA50, and a Suzuki 82 FA50.

RE: Fogey's 'R' Us

Ron Brown /


About 4 years ago, in early September, my trusty (25 years of service) Moto Guzzi V7 spun a rod bearing. Panicking at the thought of not having a ride, I perused the local "Bargain Hunter" free ad rag and found a 71 Honda 500/4 for sale for about $400.00. Having lusted after a 4 cylinder ever since visiting the west coast (7,000 miles in 5 weeks) on a 72 Honda 450 twin (read maximum vibration).

When I saw the bike, it belonged to a woman who had it painted pink with white surround and black pin striping between the colors. Picturing a can of spray paint and the ease with which I could paint the tank and side covers, I bought it for $325.00.

It took me a couple of weeks to free up the front caliper and decontaminate the fuel system from tank to carbs. By this time, several of my friends had added "personal touches" including pink Oury moto cross grips and a large "Mary Kay" decal for the windshield. I found a genuine enamelled salad bin from a '60s salmon pink refridgerator to use as a trunk and bungied this to the rear rack. Some very interesting bumper stickers have been added since. If you have ever perused the stickers sold at swap meets, you know what I mean.

I have had more fun riding this bike than any other bike I ever owned. It is comfortable for long trips and convenient for short trips. It does not handle as well as modern bikes and is definitely not overpowered, but as I like to explain, I can experience butt clenching exitement at much lower cornering speeds. Of course, stopping at freeway rest areas is out of the question but generally speaking, most people, including Harley riders, find it hilarious.

Other than normal maintenance items, tires, chains, sprockets etc., it has been 100% reliable. I do however, have a low mileage 74 550 engine standing by, just in case.


RE: Fogey's 'R' Us

Simon King /

Any chance of getting a photos of this?

RE: Fogey's 'R' Us

Ron Brown /


You've got to be kidding! On this site they call Mopeds Gay!

Seriously, I'll see what I can do. Given the current weather, I have been cleaning off the road grime instead of riding so maybe I can borrow my friend's digital camara and snap a few.


RE: Honda 50 4-stroke help!!!

Hey Tim. If you want to see foto's of this you should visit my website. This site is in Dutch, so I don't think the advice on my site is going to help you much but the pics will.

Go to

Then click on the word SLEUTELEN at the left bar on your screen, this is the part of my site that deals with maintenence on 4-strokes. I think you'd best check all the subpages you can choose from, there are many heplfull foto's there. These foto's are made from my Honda SS50. It's a different type of moped but the engine is nearly the same. The only difference in the engine is that yours is a 3-gear with an automatic clutch and mine is a 4-gear with manual clutch.

Ritje : De 1e Oude Leidse Sluiproute Rit

Mike Zwetsloot /

Beste vier takter,

Hierbij willen wij onze 4 takt rit aankondigen, bij deze ben je van harte welkem, en als je een 4 takt of honda site hebt zou je deze rit toe kunnen voegen aan je rittenbestand

We hebben een leuke route uitgezet die begint bij het centraal station van leiden, we rijden dan even door de steegjes/stad van leiden, we zullen daarna richting hazerswoude rijden en vandaaruit naar alphen waar door het dorp heengaan, in alphen houden we een benzine stop en later een eet/drink pauze op een gezellig dorpsplein. We rijden vervolgens over koudekerk a/d rijn en leiderdorp terug naar leiden waar we eindigen op de beestenmarkt bij de Mac waar we even wat eten.

Groeten en tot ziens :

Naam : De 1e Oude Leidse Sluiproute Rit.

Datum : Zondag 11 Maart 2001 en Zondag 26 Augustus 2001

Plaats : Leiden

Locatie : Het centraal station leiden (Adres volgt)

Verzamelen : 12:00 Rijden 13:00

Organisatoren :

Mike Zwetsloot : 16 jaar en rijd op een singa,


Tel : 06-28736217


Bo Willems : 26 jaar en rijd ook op een singa

E-Mail :

Tel : 06-24575238

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