Backwards Head

kdaddy1980 · Jul 13, 2013

im building this new bike its a shimano 21 speed. its got really large tubes in the frame and there is only so much space in the v portion of the bike. Ive got a 48cc skyhawk and the spark plug normally points to the rear but on this bike the spark plug sticking up and there is no room to fit the engine in. so i figured i could just turn the head around and have more clearance. so i got it stuffed in there and fired up and it runs fairly well, but with a good load or going up a hill the power kinda sucks, it putts and sputters until it gets up to speed but then at high speed and going up hills it backfires maybe once during a load but it just doesnt seems like it going to run right with the head backwards.

any suggestions? has anyone ever tried running the head backwards? what about putting a 66 cc head on it?( of course it would stilll have to be backwards). anyone ever try stuffing an engine in a small spot like this?how did you do it? scratg

wish i could get some pics up so you guys can see how tight this thing is in here, how do you guys post pics on here?

Huffydavidson · Jul 13, 2013

Welcome, first things first. some engines come with the spark plugs facing forward some come with facing to the rear it really doesn't matter it's just a matter of preference it will not affect the performance in any way shape or form . but you're still going through the break in stage you need to check the forum do a search for break in. if you turn the head around you can flip the head gasket one time and successfully reuse it . you'll need a torque wrench to torque the head oppositely my specs are different then most guys way they do it because my torque wrench reads different than the way they recommend here so search your torque specs for the head as well

kdaddy1980 · Jul 13, 2013

Huffydavidson said:
Welcome, first things first. some engines come with the spark plugs facing forward some come with facing to the rear it really doesn't matter it's just a matter of preference it will not affect the performance in any way shape or form . but you're still going through the break in stage you need to check the forum do a search for break in. if you turn the head around you can flip the head gasket one time and successfully reuse it . you'll need a torque wrench to torque the head oppositely my specs are different then most guys way they do it because my torque wrench reads different than the way they recommend here so search your torque specs for the head as well

i have a bunch of extra head gaskets layin around that i can use, do you think im losing compression through the head gasket? because ive taken the head off and retourqued it about 3 times, trying to decide if i was going to flip it or not. it didnt seem to be leaking but ya never know. i thought that might have been the case earlier and i wasnt quite sure if i was getting a good tight seal.i didnt see any oil on the outside of the cylinder but i noticed a little oil on the gasket when i pulled it off.

bigbutterbean · Jul 13, 2013

Did you lap the head to make sure its flat? Also got to remember that these engines develop more power after break-in. They don't come supercharged out of the box. If you're a bigger guy, they will have even less power. There are upgrades you can do, everything from external performance parts to modifying the internals. If you don't have much mechanical experience, especially with small engines, we recommend starting out with external performance parts. But first, you need to see how your engine does once its broken in. When the time comes and you decide you want/need performance mods, there are tuned exhaust pipes, different carburetors, high compression heads, smaller rear sprockets to go faster for single speed, and shift kits for geared bikes if you want to have a multispeed motorbike. If you ride with shorts on in the summertime, and your head isn't torqued properly, you may feel some hot oil on your leg. It happened to me once or twice when I was running the kits.

Huffydavidson · Jul 13, 2013

Hey bean, this oil treatment you mentioned , is it like waxing???LMAO Sorry my bad.

maniac57 · Jul 13, 2013

You can bolt the head on however you like. Just be sure it stays tight. I usually re-torque my new engine heads after the first few good heat/cooling cycles.
They stay tight after they take a set.

kdaddy1980 · Jul 13, 2013

bigbutterbean said:
Did you lap the head to make sure its flat?

lap the head ?you mean like with a file? no i just flipped it around and tightened it down i was using a small wrench and i probably didnt torque it tight enough. my buddy just gave me a torque wrench so i want to get em just right but im having a hard time finding torque specs for the 48cc.

kdaddy1980 · Jul 13, 2013

maniac57 said:
You can bolt the head on however you like. Just be sure it stays tight. I usually re-torque my new engine heads after the first few good heat/cooling cycles.
They stay tight after they take a set.

ill try that once im sure i got a good seal.

crassius · Jul 14, 2013

had a guy come in last week with head on sideways (vertical plug, so he didn't notice) - he wondered why it was running so hot - didn't realize he was getting little air thru sideways fins

kdaddy1980 · Jul 14, 2013

crassius said:
had a guy come in last week with head on sideways (vertical plug, so he didn't notice) - he wondered why it was running so hot - didn't realize he was getting little air thru sideways fins

i thought about doin that too, not really , lol but youre right i could see how that could go overlooked with a straight head though

kdaddy1980 · Jul 14, 2013

ok ive got a new head gasket on this engine torqued to 10-12 ft lbs, seems to be seated good but im having the same problem. its like a backfire and it sprays air out the carb. i took the carb off and i noticed a bunch of little leftover pieces from casting or welding or something in the intake blocking the intake slightly, im going to gring it out and hopefully that is whats causing that misfire/backfire. i dont know what else it could be. timing? something with the magneto i dont know, im also going to torque the head bolts again since i ran it a few times.

CTripps · Jul 15, 2013

kdaddy1980 said:
ok ive got a new head gasket on this engine torqued to 10-12 ft lbs, seems to be seated good but im having the same problem. its like a backfire and it sprays air out the carb. i took the carb off and i noticed a bunch of little leftover pieces from casting or welding or something in the intake blocking the intake slightly, im going to gring it out and hopefully that is whats causing that misfire/backfire. i dont know what else it could be. timing? something with the magneto i dont know, im also going to torque the head bolts again since i ran it a few times.

Good catch, best to clean that crap out before it gets brittle enough to break free and get sucked into the engine. That junk can destroy your piston, rings and cylinder very quickly. Make sure your exhaust port on the jug is clear as well.

mapbike · Jul 15, 2013

kdaddy1980 said:
ok ive got a new head gasket on this engine torqued to 10-12 ft lbs, seems to be seated good but im having the same problem. its like a backfire and it sprays air out the carb. i took the carb off and i noticed a bunch of little leftover pieces from casting or welding or something in the intake blocking the intake slightly, im going to gring it out and hopefully that is whats causing that misfire/backfire. i dont know what else it could be. timing? something with the magneto i dont know, im also going to torque the head bolts again since i ran it a few times.

I'm assuming you will be pulling the jug/cylinder off engine to do this work, if so why not reach down in the transfer ports and clean them up a bit as well, if you have the tools for it, that will increase the flow also.

honestly I dont think the ports having the casting burs removed will have a thing to do with the backfiring issue you speak of, but it will be a good thing to do.
sounds to me like you have a timing or or ignition problem causing the backfire back through the carb.
hope you get it resolved soon, best wishes.

Map dnut

mew905 · Jul 20, 2013

mapbike said:
I'm assuming you will be pulling the jug/cylinder off engine to do this work, if so why not reach down in the transfer ports and clean them up a bit as well, if you have the tools for it, that will increase the flow also.

honestly I dont think the ports having the casting burs removed will have a thing to do with the backfiring issue you speak of, but it will be a good thing to do.
sounds to me like you have a timing or or ignition problem causing the backfire back through the carb.
hope you get it resolved soon, best wishes.

Map

If by backfiring you mean blowing air/fuel back into the carb, its normal for a 2-stroke piston port. It's messy, but its ok. If you really want to stop it, reed valves will stop it 100%, or a boost bottle (much cheaper, but effectively useless) may help.

Unless you mean backfire like the loud bang you hear when a car backfires. That could be caused by either bad ignition timing, or a bad air/fuel mix. Being that the magneto controls your timing, if it is a timing issue, then trying a different CDI may help, but being that these are simple CDI's, I dont think that's the problem. Running too rich or too lean (do you four-stroke alot?) can cause the fuel/air not to burn completely, and send some into the exhaust where the hot exhaust (running lean) will ignite the leftover fuel. Running rich the exhaust doesnt get very hot. Still burning hot if you touched it, but not hot in terms of relative temperature (I run a bit rich that at 60kph I four-stroke at WOT, my exhaust only hits around 230F)

kdaddy1980 · Jul 20, 2013

mew905 said:
If by backfiring you mean blowing air/fuel back into the carb, its normal for a 2-stroke piston port. It's messy, but its ok. If you really want to stop it, reed valves will stop it 100%, or a boost bottle (much cheaper, but effectively useless) may help.

Unless you mean backfire like the loud bang you hear when a car backfires. That could be caused by either bad ignition timing, or a bad air/fuel mix. Being that the magneto controls your timing, if it is a timing issue, then trying a different CDI may help, but being that these are simple CDI's, I dont think that's the problem. Running too rich or too lean (do you four-stroke alot?) can cause the fuel/air not to burn completely, and send some into the exhaust where the hot exhaust (running lean) will ignite the leftover fuel. Running rich the exhaust doesnt get very hot. Still burning hot if you touched it, but not hot in terms of relative temperature (I run a bit rich that at 60kph I four-stroke at WOT, my exhaust only hits around 230F)

well its not so much of a big bang its more like a poof lol like the fire going out or like you said, having it ignite during the intake stroke because of heat or on the exhaust stroke. ive been riding this bike a little more and i notice it usually only does it when its cold.After it warms up even at wot seems to run ok once the engine is hot. but trying to get it to go uphill right on takeoff is when it usually happens or when its got a really big load on it..i thought it might have been too much oil but i ran a tank of ~24:1 through it during break in .then switched straight to 32:1.this is a new carb and i havent adjusted it or anything but i made sure the pin was pulling up with the throttle action and it looked alright. i wonder if it is running lean. im not sure how to check or correct it on this cns carb, only adjustment is the idle screw. what if i turned up the idle a little and just choked it a bit to compensate of it would run a little richer..

for the most part this thing runs good if you dont try to ride it like a dirtbike. it takes a little more pedaling to get these 48cc's going than the 66cc. a little less torque but good top end speed comparible. i bet a boost bottle would probably help but what are reed valves? i have an idea what they are but ive never seen them.

mapbike · Jul 21, 2013

mew905 said:
If by backfiring you mean blowing air/fuel back into the carb, its normal for a 2-stroke piston port. It's messy, but its ok. If you really want to stop it, reed valves will stop it 100%, or a boost bottle (much cheaper, but effectively useless) may help.

Unless you mean backfire like the loud bang you hear when a car backfires. That could be caused by either bad ignition timing, or a bad air/fuel mix. Being that the magneto controls your timing, if it is a timing issue, then trying a different CDI may help, but being that these are simple CDI's, I dont think that's the problem. Running too rich or too lean (do you four-stroke alot?) can cause the fuel/air not to burn completely, and send some into the exhaust where the hot exhaust (running lean) will ignite the leftover fuel. Running rich the exhaust doesnt get very hot. Still burning hot if you touched it, but not hot in terms of relative temperature (I run a bit rich that at 60kph I four-stroke at WOT, my exhaust only hits around 230F)

If you are tuned to 4 stroke at wot you are really loosing lots of power with your engine and consuming a lot of extra fuel also, I'd tune that carb a bit and reduce the main jet size to get a good 2 stroking engine at wot.

Map
reddd

maniac57 · Jul 21, 2013

My opinion the best state of tune for these engines is when it pulls clean under throttle and four strokes a bit at cruise. I like my engines a tad rich for better durability and lubrication.
I run 40:1 after break in at 32:1 or so.

mapbike · Jul 22, 2013

To each their own ways and opinion on the tuning of coarse, if tuned right with a quality oil having it tuned to not 4 stroke but to run like its suppose to run as a 2 stroke should not reduce the life of the engine, Id rather my 2 smoker sound good running down the road than for it to sound like its on it's last leg....LOL! I want mine to buzzzzzzz.......! not brap brap brap......!

Maybe it is possible that the life may be extended a bit by running the richer mix....I cant really make any claims on it one way or the other and considering the way these engines are mostly always a crap shoot as far as how long they last, I think it would be hard to really know if it had helped or not, I know there are people here that have several thousand miles on a well tuned engine and others may get less than 200 miles on an engine that is running rich like they always do out of the box and they fail even though they are getting loads of oil and fuel dumped into them.

I shoot for a good tune that will give me the best overall performance and allow the engine to run as smooth as it can under acceleration and at cruise speed which is 28-32mph on my current bikes.

map
reddd

F_Rod81 · Jul 26, 2013

You can run the head either way; as long as the cooling fins are drawing air and not preventing air. If you index the spark plug right you should get a slight performance increase and it should help your mpg as well.

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Backwards Head

kdaddy1980

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Huffydavidson

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kdaddy1980

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bigbutterbean

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Huffydavidson

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maniac57

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kdaddy1980

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crassius

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CTripps

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mapbike

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maniac57

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