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post #1 of (permalink) Old 11-05-2005, 10:53 PM
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rickman zundapp has screaming high idle

I am working on a Rickman zundapp 125 and have run into a problem I can't seem to figure out. I was hoping someone could point me in the right direction.
When I start the bike the engine screams at a real high idle. If you move the throttle the rpm's just increase. I have gone over the carb and it's settings but any changes seem to have no effect. Today I went over the engine for external air leaks, and found what looked like a very slight headgasket leak. In trying to fix it, the cylinder came off easily, so i also replaced the base gasket and piston ring (i had the parts), the crank and bearings were good. This did nothing to fix the problem but now the bike starts first kick instead of 3-4. I have now been restoring the bike for a year and a half and befor I began the bike idled normally. All I did to the engine and carb during this time was to remove it from the frame and re install it with a good cleaning. All fluids and fuel are new.
For those not familiar with this type of bike it is a brittish built enduro with a german made 125cc 2-stroke engine, it has a bosh cdi ignition fron the factory. I am told they were good bikes in their day, and would like to get this one running right. Thanks in advance to anyone that can help.
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post #2 of (permalink) Old 11-07-2005, 06:00 PM
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Re: rickman zundapp has screaming high idle

Can't say I'm very familiar with these bikes. But, just in general, here are some things to check. First, make sure the throttle cable has some slack. It could be adjusted too tight, or sometimes the cable may just be routed incorrectly and this can cause it to be too tight. Next, make sure the slide is in the carb throat properly (all I have seen have a keyway so that the slide is supposed to fit only one way, but you can obviously turn a round slide the wrong way and the key holds it up) or the slide isn't stuck for some other reason. Then, you mention that the crank bearings are good (I question this unless you have taken them out, but that's another issue altogether), so what about the crank seals as a source of a vacuum leak? Just some thoughts, hope this helps. If not, let us know. [img]/ubbthreads/images/graemlins/cool.gif[/img]
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post #3 of (permalink) Old 11-08-2005, 08:04 PM
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Re: rickman zundapp has screaming high idle

I think I figured it out, it's not something most people would have thought of. Thanks for the ideas. First I went over the throttle and cable, that is, after taking it off the carb. The cable and throttle worked smoothly. I then took the carb off the bike to check it's mounting. I looked it over, made sure the jets were clear and so forth. Everything looked good untill I got to the throttle return spring. It looked a little bent and when I compressed it it didn't seem fluid (uneven). I put the carb together off the bike without the cable, and sure enough, the spring was shot. It allowed the slide to move up a half inch befor it even made contact, then as you moved it further it felt like it was binding up. I found another spring and put it in, it was a little soft, and probably not for a carb, but it worked better than the one that I took out. I put the bike together and started it and sure enough it started up at lower rpm's. The adjustments on the carb even have an effect when you changed them.
Seems that the air flow on the slide was moving it up to the point where the spring slack was taken up, this let the engine run like the throttle was open all the time. The bike definatly needs a little more work,it's not getting a good idle and i won't rule out crank seals yet, as I did have it rev up high and stayed there once (it can also be the weak spring I put in there, tomorrow I am going to try it with a spring from an old flat side carb I had laying around).
Just wondering on the crank bearing issue - why is it that you would need to remove them to check them? I have worked on many engines, including rebuilding two motorcycle lower ends, and have had little problems telling bad crank and crank bearings by checking the play on them. Of coarse I'm no expert, and having the origional shop manual and thousands of dollars of automotive tools at my disposal to use does help me, but I don't see why a person who knows what to look for couldn't spot them.
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post #4 of (permalink) Old 11-08-2005, 08:52 PM
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Re: rickman zundapp has screaming high idle

There are three types of loads on a ball bearing. They are axial, lateral, and radial. The lateral load on the crank bearings in a two stroke motorcycle engine should be rather negligible. The main load should be radial, that is, from the center of the bearing outward toward the outer race. However, hypothetically, it is possible that you could have an axial load as well. If the crank were slightly bent, or the rod pin which holds both sides of the crank together was assembled out of tolerance or has otherwise somehow moved. There is no way you could find an axial load fatigue with the crank in place until you had an almost full failure. You would need to be able to try to rotate the inner race by appling force 90 degrees to the direction of travel, like if you were trying to pick up a single end of the crank with only one end installed. Diagnosis of a radial load fatigue faces the same problems. By trying to move the end of the crank up and down, any play in that bearing is masked by the interference of the other components, such as the other bearing, piston (if still in the bore), etc. You could be on the verge of complete failure before you would ever feel any play, and that's not good. Bearings really need to be "naked" when you check them. Ever "feel" a bad wheel bearing by moving the wheel? It's always at complete failure at that point, huh? [img]/ubbthreads/images/graemlins/cool.gif[/img]
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post #5 of (permalink) Old 11-10-2005, 10:23 PM
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Re: rickman zundapp has screaming high idle

Beekilla, you seem like a well educated man, I like that, you also seem like a good guy, and I could see myself having a beer with you.
Back to the bearings, Shorly you don't disassemble every engine that you work on just to inspect a crank bearing - if you are asked to check them that is. Maybe it's just my mentality, but if I were to rip down every engine to pull out a bearing to check it and then have to reinstall it, thats just wrong to me. And the time to do that, wow.
My mentality is IF you would do that, IF you would be right there, IF you have the engine apart, you would already have the needed parts to get there and re assemble, why wouldn't you put new bearings in, It's only a matter of a few dollars in parts, the labor is the same if you have taken them out, and it would be a good idea since you usually dont know when they were replaced last or know when they will be open to replacement again. If I did end up in the position that I would have to pull a bearing to do such advanced test on it it would get new, why do $50 in tests to prove a $3 bearing is bad.
However, befor we both get to far off track, lets remember the basics. I dont know about you but I would never be able to sell that inspection job to the average person, sure maybe people who race, people who need the best, or those who need the strictest of military specs, but those people are in a catagory of their own.
Also remember that there are other conciderations, sure two bearings are on one plane or shaft, maybe one goes bad, and maybe the other one masks it for a short while, however when you get a stackup of tolerences like that, the first bearing being bad would cause increased wear on the second, causing early failure on what was the good bearing, now both are bad, and this is where most people would catch it. If not caught this engine could still have many hours on it befor one would have a total failure, but engines on a whole are amazing things, and sometimes run when they shouldnt, and dont when they should. I have pulled a running engine apart that, well, it needed everything, and badly.
Rarely you would find that one totally bad and one like new, and your right you probably would need a teardown to check that one bearing being bad, i'm just saying here that the time one would be able to spot that perticular condition is small, especially in a high rpm condition such as a two cylce.
There are also the incidentals such as the metal bits in the oil, unless the person who owned the engine was oblivious or is trying to decieve you, those sighns should be the first indicator of a problem. And getting back to the wheel bearing, sure when you feel a bad wheel bearing it is in complete failure, maybe you see it on your befor ride inspection - but how long has the bearings been making noise? when did the ride quality start to suffer? Were the seals leaking or blown out? what caused you to check those bearings if you didn't do it on rutine? Some one who knows what to look for should have known of a potential problem there way befor that failure point. Most would hear it being bad long befor they feel it.
Sorry to all if I got off track and subject, This probably be in some teck forum. I Think it's time for that beer now.
post #6 of (permalink) Old 11-11-2005, 12:32 AM
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Re: rickman zundapp has screaming high idle

Yeah, brew sounds good. And yes, educated. You sound like you've learned a thing or two as well. Practical to (thoroughly) check the bearings? Well, depends on how far down you are. Sounded like you may have been close, so my point was not to go to all lengths to check what probably is OK, but rather not to make huge assumptions which could become huge problems later. It would be one thing to call it impractical on, say, a 1998 CR250, where parts are readily available and cheap. Personally, however, when you have the machine of the caliber that I think you may have, I would want everything to be in top-notch order. Just my .02. Anyway, it's really not about a lecture, just trying to help. Hope the bike works very well for you. Would be interested in pix if you get the opportunity. Either way, let us know how it goes for you. And it's good to "meet" new friends in different places. [img]/ubbthreads/images/graemlins/cool.gif[/img]
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post #7 of (permalink) Old 11-13-2005, 09:45 PM
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Re: rickman zundapp has screaming high idle

Bee killa, it's all good.
The bike came out nice, and with the exeptions of hooking up the aftermarket rectifier, and setting the idle, the bike is done. If I can figure out how to post a pict to this I will. I am loosing my shop space for now, so I wont get to finish it for a while. I was shooting for a 9/10 bike but it probably ended up as an 8.5/10 since I had to rush some things.
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post #8 of (permalink) Old 11-13-2005, 09:59 PM
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Re: rickman zundapp has screaming high idle

And here is a pict to show how it started off. Now this is my parts bike, so keep in mind that it is not the exact bike I finished, but it does show the condition of how my bike started out. Unfortionatly, the picts of my bike were lost in one of many past computer crashes.
While viewing this pict please note the highly advanced fuel efficient engine installed in it. It gets great milage, but has limited range.

Ha,Ha,
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post #9 of (permalink) Old 11-13-2005, 11:04 PM
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Re: rickman zundapp has screaming high idle

SWEET! Nice work, considering start to finish. Certainly there is no shame in riding that, other than perhaps getting it dirty [img]/ubbthreads/images/graemlins/cool.gif[/img] Let us know how she ends up. Enjoy!
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