15 mph top speed with an 80cc engine

[SomeGuy]

Alright so I went to grease up the bucking bar, clutch cam recess and the gears under the clutch cover. So when I took off the cover over the drive sprocket, I noticed a small area of the cover was grinded out from the chain. While I was doing that, I noticed a bit of oil coming out behind a screw from the magneto cover, so I unscrewed just that screw and lots of oil spilled out from there. It had to have been flooded inside that thing, not sure if that is normal or not.

When I took off the cover over the clutch gears, a screw/lock washer fell out. It was the large head flat head screw that apparently goes into the pinion on the drive shaft and that screw had been grinding at the cover for quite a while and a good 3/8" of the threads on it were smoothed. So I cut off the smoothed threads and I got it to re thread back in. I made sure to put a lock washer on that and tighten it really well. Then I finally greased those gears and put the thing back together.

The result: no more squeaking and the bike can glide much much more freely. However, I encountered that crunching noise I had described earlier again, but it was actually the chain bouncing around, so I just need to re-tension it. I have yet to test the engine again, kinda rainy around here.

I'll keep your suggestions in mind about four stroking and testing compression once I run it. And I won't bother with new carbs stuff, thanks for info on that

SomeGuy

 

[crassius]

small bevel gear (where that slotted screw was) - first, run the motor a bit with cover off & watch to see that it is turning nice & straight, any wobble means it is not seated well on the taper - if so, loosen it a bit, put the flat part of a large socket against it & smack it good with a mallet - tighten that slotted screw with an impact driver

chain chewing on drive cover - make two cuts with a hacksaw just above & below that area about 1/2 inch deep - grab the piece between cuts with a pair of pliers and snap it off leaving a gap there - done

oil in mag case - dry it well and look to see if it returns after running a bit, if not, it was just leaking in from your previous carb leak, if it returns,you have a seal leaking in there

 

[SomeGuy]

Sorry for late response, there has been crappy weather around here and I've been busy with school

First off, my bike is still running the same in that it is no faster than it was when I began.

So I did as you said crassius, and the small bevel gear spins extremely straight so that is good.

As for the leak, it came back in the same area. I also noticed gas leaking out the bottom of the engine and around the screws in the ends of the block. I am not sure what the leak causes to the performance or what causes the leak itself.

While I was riding it before noticing the leaks, I noticed four-stroking whenever I switch from full throttle to mid throttle. If I pull the throttle as much as it will, it starts going slower so I have to let up on the throttle a little bit. What does that mean?

Lastly, should I check the compression on the engine? If so, what do you guys suggestion I do to check compression?

Yeah, and if visuals help, here's what I'm working with:

Thanks again, your feedback is invaluable

SomeGuy

 

[bailsafe]

Maybe it's just me, but is that steep upward angle that the gas line is taking going to hinder performance?

 

[crassius]

if you're seeing oil seeping along case seams, that may be your problem, use an impact driver to tighten these really well

with 2 strokes one often has to match throttle opening to the power curve and as motor speeds up, then throttle can be opened more

 

[Brassneck]

I bet getting the bike to run more lean will help fix many of the issues you're having. However, might be worth doing a compression check.

My guess is you're running too rich to get the bike to fire well and that causes a trickle down effect: Too rich = fouling plugs/weak spark = minimal burn, etc. etc... if you can lean it out, you'll get a better spark = better burn= better compression= hotter engine= better vacuum/more efficient, etc. etc...

A couple of things that I would do just as an experiment of sorts (And not at the same time)...

1) Get a new spark plug (Start fresh) they're not expensive.

2) Move the needle clip to the leanest setting (furthest notch from the pointy end). Then see how it runs. If better...then you should check the plug again after a few miles on it...and see if it's still running rich. My guess is that it will be (I've found the stock carbs to run rich in general)...so you could consider getting smaller jets for your carb.

2) I'd remove the bottom cap of the exhaust and run it down the street a few times... (This will be LOUD) but if you find that your bike performs much better and goes over the 15mph mark, then your exhaust may be clogged and restricting the flow/back pressure needed to get the bike to perform well.

You may find that getting smaller carb jets and a better exhaust (expansion chamber, etc) will be the direction you end up going in...if compression tests well and the two tests above help at all.

At least that's what I would try... good luck!

 

[2door]

The OP asked about doing a compression test.

You'll need a gauge for that. There are tools made for checking compression. It threads into the spark plug hole, has a PSI gauge and will tell you in pounds per square inch, what the compression pressure is. You'll need to install the guage then pedal the bike, clutch engaged, for a few feet then read the guage pressure. It should be somewhere in the 125 to 150 PSI range.

I usually agree with Crassius on everything but this one I'll need to disagree with. I wouldn't use an "impact driver" to tighten the case fasteners but instead I would invest in a torque wrench and tighten those case screws to no more than 60 inch pounds. If you have leaks at the case gaskets after that it might be time to disassemble the engine and replace the gaskets. If they are leaking it is a very rare occurance.

My guess is your carburetor is flooding the engine because of either a clogged float needle valve or an improperly adjusted float level. This will give you an excessively rich condition due to the float being unable to control fuel level.

I'd be more concerned with cylinder head gasket and torque. 120 to 140 inch pounds, and making sure the gasket is good would be a good idea. Lapping the cylinder head is also recommended. There is a lot of good information via our 'Search' on cylinder head 'lapping'.

Tom

 

[crassius]

I use my own gauge, but many auto parts stores will loan you one for free. I like to hold throttle wide open to do test to get as little fuel as possible into gauge & get results quicker.

 

[SomeGuy]

Well, since it was most important, I looked into obtaining a compression tester. I used your advice crassius about asking to borrow one at an auto parts store, but they didn't have one to loan unfortunately. Instead, I bought a kit from harbor freight. After some tests, I was shocked. First reading I see is only 30 PSI. I noticed it was slightly easier to compress than with a spark plug, but that might be because of the dead space of the 20" tube and gauge. I did not want to believe the reading so I put an extra o-ring on the threads of the adapter that fit and tightened a little more. Still, 30 PSI. I even decided to (despite it not being recommended) blow into the tube to see if I could pressurize it at all. It was easily leaking past something, and it was not coming from the spark plug hole.

So, the compression on my engine has been really low, probably this entire time. With a leak this bad, my guess is that I'll end up having to take the engine off the bike and check it out. What exactly should I look for?

I guess I got a really really cheap engine, yet I paid extra for it as it claimed higher speeds LOL. Honestly, if I could easily maintain 20-25 MPH using this engine, I would be more than happy. As always, your help is highly appreciated

SomeGuy

 

[Brassneck]

30? Hmmm...that seems really low...I am surprised that you be able to even start the bike at that low.

Did you hold the throttle wide open? (You could even remove the carb to get max air in). And just to double check-- you tightened the compression fitting in the spark plug hole good enough?

Also, when doing the compression check...you pedaled until the needle stopped rising, correct...meaning, it takes a few compression's to get the final psi. So you should keep pedaling a few times until the needle ultimately wouldn't go any higher.

If it is that low, pulling the engine is gonna be the next step. Remove the head, check for warn seals, scoring on the cylinder, gaskets blown/cracked, etc... if you don't see any issues there (Post pics when you get it apart) then I'd get new gaskets and retorque the head. Try again.

There are a few youtube vids that may help...this is one that I found (Moped...but same concept) with a quick search: https://www.youtube.com/watch?v=Kt4q23BSaB4

 

[SomeGuy]

Oh, you know what, the threads for that kit were not sealing... In the same kit, it had an angle adapter with a tapered rubber end so I just pushed it up against the hole, I held the throttle open, and I kicked the pedal while holding the bike and I was able to get it to about 110 PSI with it having more pressure than I could hold... I was too hasty to be coming to conclusions, thanks for encouraging me to try again! This easily means compression is not an issue. Should I investigate further?

In the mean time, I'll be getting a 32:1 mix instead of using my 20:1 or whatever it is. Since you asked, I had replaced my stock spark plug before with a matching one from an auto shop not long after I built the bike and I set the gap to factory specification.

Thanks

SomeGuy

 

[Brassneck]

Great...that's a WAY better result and good news. So back to your issue. I'd try my other two suggestions (maybe start with the exhaust end-cap first, since it's SO easy to do... that should lean it out right away) and see how it runs?

If better...then put the cap back on, and work on the needle clip setting... but while you're playing with the carb, might as well clean it out... check the float height/float valves, etc. Couldn't hurt.

That's my vote for next steps. Good luck.

 

[crassius]

I have found several motors in the 110 to 120 range that ran very slowly - usually, at 125 or more, they will come up in speed. Look carefully inside while turning motor to see that transfer ports are coming at least more than 1/2 way open with piston at bottom, and that piston at top has the dome just slightly above level with top of cylinder. If either is not happening, you may be able to play with gaskets a bit to get it closer. Usually, tho, you may find a scored cylinder or broken/stuck ring.

 

[Chaz]

Lots of good suggestions etc. already posted. Now for my two cents worth. If you are using the stock acorn head nuts supplied with the kit, then cut the caps off with pliers or side cutters and re torque the head.

Also, at those oil heavy mixes you have been using at the start, you might have already clogged up the muffler. You can take the muffler off and clean it out with a degreaser or solvent, then rinse it out with water, dry it with compressed air if you have available and re install. Don't let it sit with water in it unless you can put it back on and fire up right away. The stock mufflers are very prone to rust.

And you might as well clean the air filter too. They can get gummed up.

good luck

 

[crassius]

one may test muffler by just loosening it 1/8in or so - if it runs better, then clean it

 

[SomeGuy]

Alright, so I've been a little busy lately but I've finally been finding some free time. So I got a 32:1 fuel mix, got a speedometer, and I took the end of the muffler off. So I've been riding it a lot lately as I can feel it is going considerably faster. With the end cap off, I am able to reach 20-24 mph. With it on, it will max out from 18 to almost 20. (Note that is without pedaling.)

Although I had some good fun riding all around my neighborhood, it bothers me that it runs out of fuel so quickly. With about a quarter tank, it ran me around 5 miles - no different since I started using the thing. While I was going full speed on a long straight road, I looked down and I noticed that out the left side of the bottom of the cylinder, fuel was leaking out continuously - not to mention all the other parts of my engine that all fill up and leak with fuel. I mean all the bolts are as tight as they should be, wasn't able to get them to tighten any more so the factory did them tight.

Suggestions and comments appreciated

Some Guy

 

[crassius]

pics of where fuel shows up may help

 

[Chaz]

Quoting Tom "My guess is your carburetor is flooding the engine because of either a clogged float needle valve or an improperly adjusted float level. This will give you an excessively rich condition due to the float being unable to control fuel level."

I would suggest that you check your float level and any pieces of crud at the float needle valve.

 

[Bikeguy Joe]

Quoting Tom "My guess is your carburetor is flooding the engine because of either a clogged float needle valve or an improperly adjusted float level. This will give you an excessively rich condition due to the float being unable to control fuel level."

I would suggest that you check your float level and any pieces of crud at the float needle valve.

Best answer!

 

[sbest]

Hey Someguy, you've got some work to do!
If fuel is leaking out of the gasket joints, you need to repair the gaskets.
If it leaks at the crankcase split, you will have to open that up and reseal it.
That gets complicated, you can do it but hopefully you don't need to.

Buy a gasket kit ($5), pull the cylinder off and deburr any flashing in the ports. Remove the studs, stuff the case with rags and lightly file the basegasket surface flat. I like to check the rings and pin bearing while I am at it. If the pin or bearing is turning blue, replace it. Clean everything, start putting it back together with the new gaskets. I like to check the head to piston gap with a strip of 0.060" electronic solder taped to the top of the piston. Anything from 0.060" to 0.010" will work OK, but 0.040" to 0.020" is ideal. It is adjusted by filing the head or adding hand cut paper basegaskets.

As recommended, ditch the Acorn head nuts. Replace them with regular nuts if they are standard thread (some are not). File or trim the base, intake and exhaust gaskets to closely fit the ports they cover. You can bake the pipe in an old BBQ or other outside oven to clean it, but for $20 I would buy a new Grubee chrome exhaust pipe. I have had great luck with it. Quiet and free flowing.

Tear the carb apart, clean it, all the little drillings included. Check the float level and especially the inlet valve (float needle). Your motor looks a bit high. I'd cut the rear mount shorter so the motor settles lower. Room for the gas line and hopefully so you can point the sparkplug to the rear. Tighten it all up, you are ready to fly!

Steve