First ride and "rich" experience

[emdude]

Finally got my motorized huffy cruiser on the road yesterday for the first time. It fired right up and once I adjusted the idle speed screw would idle fine. But WOW did my engine ever run FAT right out of the box. This thing would never stop four-stroking at all!!!. It's set up to run real rich from what I can tell. This stands to reason since I would imagine the makers don't want a seized piston within the first few miles of use. I decided to ride a bit even under these conditions and then go back home and have a look at what could be done about this.

I need to add that I live at altitude, 1600 feet to be specific and that of course doesn't help.

I also had some leaks from the carb, one was due to a loose float needle seat and the other from a not all to good seal of the float bowl. Got those items taken care of.

Another thing that indicated really rich mixture was the old "shut off the fuel and see what happens" trick. So I shut off the fuel supply on a long straight away and sure enough power picked up for a brief moment just before the engine shut off. This increased my confidence in assuming the engine was running way too rich.

So in examining the supper richness of the engines running I tried the following:

First I ran it with out the air cleaner just to see if this made any difference. Nothing of note here, seems this flows enough.

After that I lowered the jet needle to its lowest position and lowered the float level. The float level seems to be suspiciously high. This made a major improvement. Most of the four stroking was now gone. I could get up most hills in my area with out having to help it along by pedaling.

Of course it still four stroked at higher RPMs which I would sort of expect. Most small engines like this do because it reaches a point at which the exhaust is the limiting factor. It just won't let enough out anymore. Actually this can be caused by pretty much anything, not enough getting out, not enough getting in, or even any not ideal timing event including transfer ports. I did think it was the exhaust though in my case.

Then I removed the end of the exhaust. And that made all the difference!!!. Plenty of noise of course and no more four stroking at all. It really picked up and went at all RPMs. There's a lot being lost in the EPA exhaust that came with my engine.

I'm going to work on getting the mixture as right as I can get it and if I find anything noteworthy will report.

In my first post I had described how I had a close look at my engine before ever installing it. I had found that on my engine the cylinder base gasket was not cut all that well and was quite substantially covering the transfer ports. I had decided too leave it alone, which I now regret. This could be quite a limitation after all. I may have to take the engine out get this cleaned up just to be sure I'm not taking a hit here.

Udate:

I went home for lunch today, after writing the above earlier this morning and tried to start the bike. It's fairly cold here so I set the choke. No deal, would not run. Started right away with the choke turned fully off. Another indication of a rich mixture.

Regards

emdude

 

[Mountainman]

hey emdude

sounds like fun you are having on that motor bike THING
you seem to have read up and done your homework
you are breaking it in a little -- right ?

enjoy the ride on that THING

 

[emdude]

>sounds like fun you are having on that motor bike THING
>you seem to have read up and done your homework

Actually it's not so much that I read up on anything but more memories of when I was growing up in Germany where 50 cc mopeds was all we had. I remember going through all these things trying to squeeze every bit of performance out of those government strangled little engines.

>you are breaking it in a little -- right ?

Well yes. But my theory on this follows the idea of lots of thermal stress in the sense of heating it up and letting it cool down often in addition to lots of varying RPMs.

>enjoy the ride on that THING

Yeah, sorry about that THING bit. But I'll tell ya, this is a lot more fun than any moped I ever had!!!

Regards

emdude

 

[oldsalt]

emdude

I'm getting the idea that the needle is never completely withdrawn from the main jet, even at WOT, regardles of which groove the c-clip is on. If so this is the first slide carb I have ever heard of that used a a needle to change anything but the 'midrange'. I suppose I'll find out when the carb is torn down. I too have a new motor [my first] that is incapable, in its present state of tune, of doing anything but 4-stroke. Very rich at all throttle openings. The newly offered "EPA" muffler came with my motor. I'm thinking the first move, before float heigth and needle height adjustments are undertaken, would be to open up the exhaust track a bit, then mess around with the carb. Does that make sence?

 

[emdude]

Well, just last night after work I took my MB out for a spin around the block. Ran ok but still some of four stroking. Basically the engine is still running too rich even after what changes I made in my first post.

Again
I thought of the muffler and again went home and took the end off. And that really did it. It's such a huge improvement. I can now make it up any hill in my area pretty comfortably, and there are MANY of those where I live. and the only four stroking I do get is at top speed rpms. And that's ok because that can be out later.

On my EPA exhaust, on which the fine paint burned off in the first minute of running the engine BTW, the pipe that exits to the outside goes INTO the exhaust by quite a few inches. I have not examined this all to closely but in any case the internal pipe is going to be cut today on a band saw a my work. I'll let you all know if this made any difference.

regards

emdude

 

[oldsalt]

emdude

Believe that'll be my first move; get rid of some of the restriction in that limp-wrested EPA muffler. There's no hope of ever getting the carb to work with an exhaust system incapable of resonable scavaging. THEN work on the needle and float level.

 

[emdude]

restrictive exhaust

Well, yesterday I cut off most of the internal pipe in my EPA muffler. A good 5 or 6 inches worth. It did make a difference. The exhaust is definitely louder but not enough to cause much concern that I'll be annoying the neighbors. The engine does run stronger with less four stroking but is still too rich.

Bu I'm basing that on my distant past experience with the little moped engines I messed with mentioned in earlier posts. I recall that the best performance was obtained, with any given set of otherwise given conditions such a exhaust being what it was when the carb was leaned out to the point in which the engine NEVER four stroked und full throttle. The engine would produce good power and simply spin up to maximum RPM at which they could just do no more. Top end four stroking was completely gone is this case.

Short of removing or modifying internal baffles in the exhaust this is about what can be done and from what I can tell if the carb could be leaned out just a bit more the engine would be running quite good. Although I do think there is quite a bit of power to be had if one were to try and max it out.

So the next step will be an attack on the main jet. I've seen that some on this forum have soldered it shut, so to speak, and then re-drilled it for a smaller diameter. This is I'm sure ideal, short of getting a smaller diameter main jet.

But in my case I think I'll start with the old "small wire in the main jet" trick just to see if this can get me any closer. If it does I can make a more educated guess on just what size to drill if I do solder the jet closed.

One thing that does NOT help in my case is that I do have some some small amount of air leakage between the carb and the intake manifold, engine stalls when carb cleaner is sprayed near the area. So tonight or tomorrow I'm going to fill in the slots on the carb with silicon. That should take care of that problem and give a better platform for getting the carb set up right.

 

[srdavo]

One thing that does NOT help in my case is that I do have some some small amount of air leakage between the carb and the intake manifold, engine stalls when carb cleaner is sprayed near the area. So tonight or tomorrow I'm going to fill in the slots on the carb with silicon. That should take care of that problem and give a better platform for getting the carb set up right.

you can put an o-ring in the carb, where it meets the manifold.
also....it's a good idea to replace the manifold gasket.
once you stop all the air leaks.... you should see a great improvement.

 

[emdude]

Yeah, I was thinking of the O-ring thing also. And I just so happen to have an O-ring kit with plenty of selection in my garage. My concern with that is just that I would want to see a real good tight fit because I'd hate to see the O-ring wander down the intake. Maybe I could glue it in place with some silicon?

But I'll examine that option and If I come up with something that works I'll post.

Thanks

 

[wildemere]

Don't wire the main jet, file 2.5mm of the bottom of the slide duplicating the 1mm cutaway. Measure it with a vernier first.

Incidentally the cutaway's size tunes off idle response, a 1.5mm cut will be leaner up to around half throttle.

Each notch in the needle is 1mm so you will gain 2.5 notches of leanness with this method I developed.

A side benefit is you can now have a carb with perfect tune at 2.5 mm before the slide stops so your full throttle is position now earlier in the slide travel and so there is 2.5mm of extra richness for high load conditions.

Or you can set it perfect at "full throttle" and it will be a tad leaner everywhere else.

I use 0.5mm washers on the needle then plug readings to get close then a thermometer aimed at the head near the plug to set full throttle tune.

180 degrees celcius seems right when its 20 ambient more is lean and cooler is rich.

A pyro in the exhaust would be better though.