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General Category => General Discussion => Topic started by: erik_w on April 26, 2015, 02:37:31 PM
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I have recently aqcuired an older two-stroke bike (Izh Jupiter 350cc) and have been trying to get it to run properly, with some success. After setting the carb right and installing a Electronic ignition system I thought it was ready for the road - I just didn't Count on how ready it would be!
After running maybe 5 minutes tops up and down the road outside my house, I noticed that the Engine would not rev down when letting go of the throttle. My first thought was that the slide was stuck, so I drive it up to my garage and as soon as I stop the engine starts revving up to what seems like 4-5k rpms and stays there.
With increasing panic I first throw the kill switch - nothing happens! I then shut of the Electrics, still nothing! In desperation I pull the spark plugs leads - and STILL nothing! The Engine is revving like crazy with no spark! After holding my hand over the intake for a couple of seconds it bogs down and finally dies.
I am to understand that this is called dieseling and what happens is that something in the combustion chamber gets sufficiently hot to keep the combustion process going with no spark.
I would like to hear your experiences with this phenomenon and what might be causing it?
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It sounds like you have an air leak somewhere. Check the carb adapter, cylinder base gasket, head gasket, crank seal, and anything else that could be letting air in. If you get it running when it's cool, you can squirt WD-40 at these parts and observe if the idle speed changes.
Next time, put it in gear and let out the clutch to stall it.
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In the past it was when a lot of coal was in the head. And coal is what you get form not to hot/rich running.
Did you had the head off and cleaned the coal out?
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In addition to checking for air leaks, verify that the carb slide isn't sticking open. The problem could be a combination of a couple of the above items, including a lot of carbon, as Paul said.
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Next time, put it in gear and let out the clutch to stall it.
A 350cc twin with Russian brakes running at 5000 RPM out of control, and you're going to put it in gear and drop the clutch?
Sounds sort of sporty to me. I might do it if I thought about it and did a few calculations, but I'm not sure I'd have the nerve to try to cut one off like that! :o :o :o
Lannis
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There are no airleaks on the instake side, I checked that using starter spray when I first got it running, I checked the throttle Cable and slide and they seem fine, there is a bit of slack in the wire at all times the throttle is not pulled.
What about overly rich carb setting, could that be contributing?
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A 350cc twin with Russian brakes running at 5000 RPM out of control, and you're going to put it in gear and drop the clutch?
Sounds sort of sporty to me. I might do it if I thought about it and did a few calculations, but I'm not sure I'd have the nerve to try to cut one off like that! :o :o :o
Lannis
Haha! Actually I have put in relined brake pads, so they are just fine! But I wouldn't want to try to stall it in gear since the motor is quite powerful, choking off the intake did the trick.
Futher, I haven't had the Engine apart yet - but I guess the next thing is to pull the heads.
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Refusing to idle down is usually caused by an air leak, not by too rich a mixture. Did you check the crank seals and base gaskets for leaks too?
The dieseling part could be from excessive carbon in the combustion chamber, but not always. My H2 did that when I had a throttle cable break and jam open and I was in neutral. Once it starts revving way high, it can happen even without carbon, under some circumstances.
Lannis, I didn't say to drop the clutch. :D I doubt if it was really making much power or it would have revved higher than 5,000, so easing out the clutch like when taking off should stall it.
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A 350cc twin with Russian brakes running at 5000 RPM out of control, and you're going to put it in gear and drop the clutch?
Sounds sort of sporty to me. I might do it if I thought about it and did a few calculations, but I'm not sure I'd have the nerve to try to cut one off like that! :o :o :o
Lannis
A little tread drift here but the story reminds me of a scary situation with a throttle stuck wide open. At the time I worked in the Orthotics department at Warm Springs Ga. where we made braces and all sort so stuff to help disabled people. We also installed hand controls on cars. I had just finished installing a set of hand controls on a 1973 Olds Delta 88 convertible. Now the mechanism was simple push and release on the the lever for the brake. But the accelerator was a bit more complex. It was gear driven. So you pulled down on the lever arm which went through the gear box and then a rod pushed the accelerator peddle down. Alignment was critical for it to work correctly.
Well after static testing in the shop I took it out for a road test. I was on the hwy and pulled the lever arm all the way down to test the accelerator. So I floored as we say, kicking passing gear as well as the 4 barrel carb. Everything is fine until I released the hand control . Shit the mechanism was slightly out of alignment and it did not release the accelerator. I literally had an Olds 88 stuck wide open in passing gear and the 4 barrel sucking fuel. I didn't dare try reaching down to break it loose while taking my eyes off the road. For just a moment I thought what comes next. Next best thing was shut the ignition off and pull over when safe.
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I had a runaway Mecedes diesel startup. Had to shove a fender blanket into the snorkel.
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And then we have the story of the two-stroke that ran backwards. Oh well. :pop :BEER:
Matt
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I had that happen on a moped I had when I was 14. I was riding along, everything seemed fine, and I looked down and noticed that the spark plug wire was dragging on the road! It ran for miles that way, and it was totally controllable, would idle and everything. Finally, it quit, and I put the wire back on and went home. Never did it again. Nobody believed me that it really happened.
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Lannis, I didn't say to drop the clutch. Cheesy I doubt if it was really making much power or it would have revved higher than 5,000, so easing out the clutch like when taking off should stall it.
Yup.
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And then we have the story of the two-stroke that ran backwards. Oh well. :pop :BEER:
Matt
Never had a bike do it, but a Detroit 318 has on me more than once. Rather odd sounding really.
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Sometime it is just evil spirits controling the engine. If prayer and fasting don't help you may have to resort to exorcism.
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Sometime it is just evil spirits controling the engine. If prayer and fasting don't help you may have to resort to exorcism.
I did exorcise one once with a spud wrench that was on the within hands reach bench. SOB bounced of the block and clocked me with the open end right between the running lights. That headache lasted a day or two. When performing an exorcism, get a priest, not a spud wrench. :D
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I saw a Yamaha 200 do this once, turned out the starter was stuck on.
I have only seen single cylinder diesels run backwards, and have only experience of my old Metralla doing that too.
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And then we have the story of the two-stroke that ran backwards. Oh well. :pop :BEER:
Matt
The two-stroke mini cars in Britain with the 197cc Villiers engines got reverse that way. To reverse, you shut the engine off, threw a switch to change the ignition timing and starter direction, and started the motor backwards.
That's where the software developers learned how to change a "bug" into a "feature"!
Lannis
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The two-stroke mini cars in Britain with the 197cc Villiers engines got reverse that way.
As does my 1936 Evinrude Elto Ace. You wrap the rope around the flywheel the other way and move the spark advance lever to the other side of TDC. Also all the old gasoline powered golf carts, I believe.
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The two-stroke mini cars in Britain with the 197cc Villiers engines got reverse that way. To reverse, you shut the engine off, threw a switch to change the ignition timing and starter direction, and started the motor backwards.
That's where the software developers learned how to change a "bug" into a "feature"!
Lannis
Also the way they would reverse some fishing boat(trawler) engines. :pop :BEER:
Matt
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Coast Guard buoy tender White bush was like that. Coming up to the pier they killed the engine then re started it backwards to reverse the screws.
I took an experienced hand to maneuver that 132 foot boat in close quarters.
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Yeah, it is quite cool that you can run a two stroke backwards, haven't done this personally, but had friends who did it with their old mopeds.
Dusty, there is nothing inherently wrong with the Russian motorbikes, as long as you know what you are doing they are Beautiful Machines to work on! The problem is usually just bad maintenance and bad quality replacement parts. And all to often they have suffered at the hand of "Piston Pete" (in Sweden we have this derogatory term for a home mechanic who doesn't know what he is doing - but somehow puts it together anyway).
I have yet to see one that isn't in need of a partial or complete rebuild!
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Yeah, it is quite cool that you can run a two stroke backwards, haven't done this personally, but had friends who did it with their old mopeds.
Dusty, there is nothing inherently wrong with the Russian motorbikes, as long as you know what you are doing they are Beautiful Machines to work on! The problem is usually just bad maintenance and bad quality replacement parts. And all to often they have suffered at the hand of "Piston Pete" (in Sweden we have this derogatory term for a home mechanic who doesn't know what he is doing - but somehow puts it together anyway).
I have yet to see one that isn't in need of a partial or complete rebuild!
'Piston Pete' has an Aussie relative called 'Harry Hometune', I know him well.
There really is nothing wrong with the design of Soviet era crap. It's just the manufacture that made it so tragic.
Pete, (Owner of heaps of Eastern Bloc shit in the past and still having nightmares!)
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I would like to hear your experiences with this phenomenon and what might be causing it?
Here it was a well known phenomenon with older two stroke 125cc and 150cc Vespas, especially if the cylinder had been bored several times (probably due to the little increase in the compression ratio). but in that case they don't tend to rev up much, and it's easy to shut them off by braking while geared, so it was more of a curiosity than other.
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'Piston Pete' has an Aussie relative called 'Harry Hometune', I know him well.
There really is nothing wrong with the design of Soviet era crap. It's just the manufacture that made it so tragic.
Pete, (Owner of heaps of Eastern Bloc shit in the past and still having nightmares!)
I Think I got one of his bikes! Somebody had used an angle grinder to open up the cylinder base ports a bit (very unevenly I might add!) and then put it back together without changing any gaskets... Needless to say the pistons had both siezed and burned!
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And then we have the story of the two-stroke that ran backwards. Oh well. :pop :BEER:
Matt
thats no story, my brother did it by accident on his penton 125. Then he did it all the time trying to perfect it. got pretty good at it BTW.