same issues, but more irritating

James Foster /

The reason I put this in this forum is because my 78' Puch maxi free spirit barely runs, and all I want to do is just get it to go somewhere.

Issue; it idles, but any throttle above that and the RPM's go down, usually until it dies.

Things I've checked/tried already:

1)throughly inspected and cleaned the whole electrical system.

2)checked compression, and it's right on the money.

3)cleaned entire fuel system multiple times, but no matter what jet I try (I've tried 72-82 already), nothing seems to make it run right.

New/existing parts installed on the bike; 70cc Airsal kit, 14mm stock carb and intake manifold, bi-turbo exhaust, new ignition coil/cable/resistor cap, new points, and a performance air cleaner(not currently installed for testing).

Ok, so there's the facts, now it's quiz time. Does anybody know ideas on how to fix this problem correctly? Thank you for your time on this matter. You're reply's will be graded accordingly. lol JK :)

JF

Re: same issues, but more irritating

did you double check to make sure you didn't install the piston wrong??

just a guess

Re: same issues, but more irritating

John Joedicke /

sounds like a good guess Paul. Those saddlebags look great on my motorcycle. Thanks again.

Re: same issues, but more irritating

James Foster /
jf OP

well, the thing is, I did check that, but a good point nonetheless...

JF

Re: same issues, but more irritating

Jason Luther /

i _know_ you tried a new plug. on top of that sounds like you are not getting enough gas. id check your carb again and see if there is any crap in your main jet. and are you _sure_ the piston is on correctly?-jason

Re: same issues, but more irritating

James Foster /
jf OP

Hmm, I'll go check, hold on.

JF

Re: same issues, but more irritating

glad your happy with them double.

Re: same issues, but more irritating

James Foster /
jf OP

Checked the piston and the spark plug. Not fault there. All I can figure is that my jetting is too far off, but which way I'm not sure...

JF

Re: same issues, but more irritating

If you have a Bing Carb I would try adjusting the needle jet. To get to it, take the top of the carb off. remove the throttle slide and you will see a tapered pin coming out the bottom. This is the needle jet.

It has four adjustments at the top. You will see a clip on it in one of the four grooves. If the clip is near the top groove it is set where the tapered needle will allow a lean mixture during low speeds. If you drop the clip to the bottom groove it will raise the needlejet and make a richer mixture.

The symptom you describe is a bog and is caused when the air does not get enough fuel mixed with it. When you are idling, the throttle slide is closed and very little air passes through the Ventura area of the carb.. When you open the throttle your engine sucks a greater amount of air. This requires a rush of fuel to atomize with it. Raising the needle will allow that extra fuel at the initial opening of the slide.

Re: same issues, but more irritating

i dont wanna be picky, but the "needle jet" is the hole (or tube) the needle (tapered pin) slips down into at the bottom of the venturi.

On many carbs, that needle jet (tube) can be replaced with another one with a different size hole. Usually, after the main-jet in the float bowl is removed, the needle jet can be pushed down and out.

Re: same issues, but more irritating

James Foster /
jf OP

But why replace the needle jet when the main jet is what adjusts fuel flow to the carb at WOT? I could possibly fiddle around with the needle setting, but I doubt it would do any good. Why do I get the feeling that messing with my carb day and night won't fix the overall problem, whatever _it_ is...

JF

Re: same issues, but more irritating

First off, I guess you have a BING carburator? This carburator has only one place that will supply fuel to the engine. This is the main jet. Whether it is idling or WOT the fuel is supplied through the main jet. The idle screw should probably be called a slide adjustment screw because all it does is raise and lower the throttle slide, in the Ventura, controlling the incoming air at idle. Ventura is the name of the bore through the carb.

Now the fuel fills up in the float bowl to a specific level and then the fuel inlet needle stops the flow of fuel. As the air passes through the ventura it pulls the fuel, up through the main jet, into the needle valve and the fuel mixes with the air going into the engine. If the fuel level is low, not much fuel gets pulled up. If it is high, a greater amount of fuel gets pulled in. Why? The difference in the distance that the air has to pull the fuel up.

The needle rod is tapered and hangs in the needle jet above the main jet. This tapered rod controls how much fuel passes to the engine at various throttle positions. If you look at the needle jet you will see that there is a orifice at the top that the needle drops into, it is similar to the jet but bigger.

Now the four grooves at the top of the needle rod, they are for setting the distance that the tapered part of the needle hangs in the orifice. IF the top groove is used, the tapered rod hangs deeper into this orifice, smaller opening, less fuel supply. If the bottom groove is used, it raises the rod and a narrower part of the taper is in the orifice creating a bigger opening allowing more fuel throughout the throttle positions. At wide open throttle, it is completely out of this orifice to supply the maximum amount of fuel. Hope this helps,

Re: same issues, but more irritating

I stand corrected, thanks joew. it is a needle rod.

Re: same issues, but more irritating

Whatever it is.. well, i'm thinking the problem is so simple or obvious it will bite you in the ass when you finally see it. What is the last modification you made to the engine just before this condition started? The kit and/or the exhaust?

My first guess was a basic mechanical error but you seem to have done all the proper checks.. so now i'm thinking the doctor left a sponge in the patient's chest or something..

Re: same issues, but more irritating

James Foster /
jf OP

Yea, I see what you mean Joe. It's probably something so simple that I didn't even bother to look at it. The last modification I did was to swap both the 15mm intake and carb for 14mm ones. Reason being that they were cheaply made by some weird company other than "bing", and both have something broken on them. Intake; had a crack next to one of the bolt holes and in the process of removing it, it broke off. Upper throttle body on the carb; had a small crack on one of the little metal pieces that holds the float's needle in place, then it broke off. So, I had to switch back to my original carb for now.

The problem is, I've tried a 72, 76, 78, and a 82 size bing jet in the 14mm bing carb already. But even with adjusting the air intake, it won't run right. If I restrict the air too much, it has horrible top end, and if I don't restrict it enough, then it usually dies. This was tried with every jet I own, but nothing seems to work right, like there's something else at fault. Whats irritating is that I'd taken apart the crankcase awhile back, but everything looked fine. I've tried every major trick that I can find/think of, but nothing seems to work. Even if there were like a dozen of the best moped people I know looking at my bike right now, even they might be stumped. I just don't know what to do. :(

Still pondering,

JF

Re: same issues, but more irritating

Hey James look at what you did. reduced the carb air volume 15 to 14mm. This will increase the speed at which the air is entering the carb because the engine still needs the same amount of air. This will cause faster pulling of fuel through the needle. You said if you restrict the air, it idles, you have slowed the air down and it is pulling less fuel. If you lower the needle rod, higher clip setting, it should do the same thing. When it is running wide open, the rod will be out of the picture, does is it four stroke? Maybe the horrible running is that it is four stroking. Just something to think about.

Re: same issues, but more irritating

James Foster /
jf OP

Good point, I knew that changing carburators would have a significant effect on the engine somehow. But still, when I try different jets at WOT, it either dies or the RPM's go down below idle. I'm wondering if its something electrical, because when I WOT with no brake on/nothing stopping the wheel, it rev's right up. It's like the engine has to get past a certain point, no matter what the throttle. So nonetheless, my low end is still having issues. I have already cleaned everything on the strator plate very well, but THE only thing I haven't replaced yet is the condenser. Although it's a part of the ignition system and could be at fault, I don't know if that would cause this much of a problem. Whats unusual is that under any carb modification it seems, it always has that similar problem. I might try and take out that condenser and see if it's having issues or not.

JF

Re: same issues, but more irritating

Jason Luther /

my riverside was having the same problem. it had the wrong type of trans fluid, so the clutch wasnt working as it should. is everything in order in that respect? -jason

Re: same issues, but more irritating

James Foster /
jf OP

Well, I did put Royal Purple max ATF tranny fluid in there, it's the best there is. I asked the head guy at a near-by Royal Purple plant and he said that they're max ATF tranny fluid would be fine in there. As for the clutch itself, I don't have a clutch puller so I haven't been able to inspect it thoroughly yet. As soon as I get a puller, I'll check that out as well...

JF

Re: same issues, but more irritating

Jason Luther /

did it work before with the royal purple? if not, i think you found your problem. the viscosity of the different oils is very important.-jason

Re: same issues, but more irritating

James Foster /
jf OP

I put that oil in there awhile back, haven't had a problem with it since then. But I'll look at it anyway though...

JF

Re: same issues, but more irritating

I suppose an exhaust restriction could cause the symptoms.. If i still had the stock exhaust or any other substitute i'd bolt that up and see if things change. Otherwise i'd just make sure the pipe was as good internally as it appears to be externally.

If something rusted out or broke loose or got into the pipe it could mess up the way things run.

Re: same issues, but more irritating

James Foster /
jf OP

True, you've got a point Joe. I'll check that as well...

Anyway, I got the condenser off, but how do I test it with a multi-meter?

JF

Re: same issues, but more irritating

Visual inspection says a lot.. If the condenser's can bulges out of there is any leakage, toss it. Meters that accurately diagnose capacitors are expensive. So the short easy answer is to substitute a known good condenser.

I've got a DMM (digital multimeter) that has a capacitor checker.. What it does is fully charge the condenser and then measure how much capacity it actually has.. Although this says the cap is not dead-shorted or has some major malfunction, this doesn't determine if the cap is leaking more than it should. (Charge in a condenser always leaks cross the plates but only at some acceptable rate in a good one..) Another thing is the meter can only charge the cap to a low voltage.. not the voltage is sees normally. Breakdown voltage is important. An oscilloscope to test a cap while it's in the circuit might be needed.

If you are suspect misfires, how about hooking up a inductive timing light .. the flashes of light would not be steady BUT the plug would not show a wet, fouled condition.

Re: same issues, but more irritating

James Foster /
jf OP

Interesting observation... Do you think that just the condenser would cause bogging? Because it doesn't misfire, and the points arn't pitted/burnt either. I'm thinkin' it might be something as simple as changing the type of tranny fluid in there. Whether or not that would fix the problem for good, I dunno, but it's worth a try anyway.

JF

Re: same issues, but more irritating

Reading you fist post again, you said that you installed a new coil, wire , resistor cap. This resistor cap, is this the boot?. Are you running a resistor plug too. I have read other post and they say that they have allot of problems with this. Weakens the spark I believe.

Re: same issues, but more irritating

When the points open, the condenser quickly absorbs electricity stored in the coil's high resistance winding. This speeds up the collapse of the magnetic field... and that produces a higher voltage, powerful spark than a coil can produce on it's own.

If you don't have misfires then the bogging has some other cause.. it's pretty safe to say the condenser and other ignition parts are doing their job.

Tranny fluid is easy to change .. and if you notice any difference afterwards that would be a major clue even if it's not the complete cure..

Re: same issues, but more irritating

Well I have a question, did it started when you changed the carb or did it start prior to you changing the 15mm carb?

Re: same issues, but more irritating

Try removing the air filter. If that makes a difference, then your air filter is restricting the air flow causing it to bog.

Re: same issues, but more irritating

James Foster /
jf OP

It started before I changed carbs, so I know that it probably isn't the issue. And I did check the spark, it's a nice constant blue/orange color, so I don't believe ignition is the issue either. Also I've tested running the carb with and without an air filter, but with no real difference. I've eliminated almost all possibilities already, so that leaves me with only a few places to look now; transmission fluid and the clutch. If anyone has any other things I might've overlooked, let me know. :)

Thanks,

JF

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