Wildguzzi.com
General Category => General Discussion => Topic started by: erik_w on July 31, 2015, 08:50:53 AM
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Having recently made a major overhaul of my Izh Jupiter two stroke (350cc, 180 degree twin) it now simply refuses to start. Startgas, bump start, flooding it, not flooding it, simply NOTHING works.
New is seals, bearings, pistons and rings.
It doesn't sputter, doesn't cough, just nothing - I might as well be trying to start it with the ignítion off. Ignition system works thou, nice fat blue sparks, have tried two different systems (from working bikes) with no results.
I suspect the problems are compression related.
- Dry compression is 80 psi
- Wet compression is 160 psi
- This would suggest badly worn rings, but they are brand new and haven't had a chance to wear in since the Engine doesn't start.
I did manage to get it to run once, after pouring oil into the spark plug holes, the kicker felt much stiffer and the Engine started on the first kick, ran for 0,5 seconds and then died.
What am I doing wrong here, is there something I am missing? Are my cylinder walls to far gone and need a overbore? They were honed prior to putting in the new rings.
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80 psi is indeed too low.
Did it run before the new rings?
Correct end gap gaps not in line?
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The fact that adding oil in the cylinder made it run briefly does point to the compression being too low for the engine to run. A good engine with new rings and a hone job should have decent compression before the first time it runs, although maybe a little below its final numbers.
If you put 1/2 a teaspoon of gasoline (normal gas-oil mix) in the cylinders through the plug holes, does it run for a couple seconds?
What's the skirt-bore clearance?
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Yes, the cylinders were from a running Engine (a bit worn thou), piston are new, due to the design of the pistons the ring ends can't line up.
Negative on adding gasoline or start gas directly into the plug holes, it has no effect. Not sure on the clearence, but I suppose it is a bit bigger than spec, between 0,05 and 0,1 mm.
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For the curious minded....
JB
http://www.southbayriders.com/forums/threads/98763/
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Not sure on the clearence, but I suppose it is a bit bigger than spec, between 0,05 and 0,1 mm.
That means about 0.002" to 0.004", which is fine. But measuring it would help find out what's going on. You can use feeler gauges between the piston skirts and bore to get an approximate idea of the clearance.
Anyplace else that could be causing the low compression? Like something odd at the head gaskets. Did you hold the throttle wide open and kick until the gauge quit rising when you did the test?
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Compression test is done like this:
Both plugs out, throttle wide open, 5-6 decisive kicks and then taking the measurement. It might go a little bit higher if I kick it more, but after 5 kicks the gauge virually stops rising with each additional kick.
Since adding oil makes such a difference, I would not suspect the head gaskets, both of which are new.
I'll try to get a measurement tomorrow of the piston / bore clearance.
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Yeah, something is certainly odd. Sometimes spark can be weak, so it fires a plug lying on a head, but not under compression, but you tried two different systems. Finding out why the compression is so low would seem to be the next step, even if it's not the only problem.
Assuming it's not a wasted spark system, could the plug wires, or something upstream, be reversed?
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Sounds like fun, not! (kick starting and pushing). Are the pistons in the right direction? Just thought I'd ask, you never know. If not, then if there is an intake port/window on what would be the intake side, it would then be facing the exhaust side and that would mess up the entire order of things.
Sounds like you know what you are doing, so I'm just throwing it out there because you've tried everything else to no luck. I think even low compression (more than none that is), it should still fire up especially when you pour gasoline in the spark plug hole.
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If your crankshaft seals were worn it might do this..scavenging would be compromised.
Best,
Peter
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Might be a good idea to pressure test the engine. Plug the intake and exhaust ports and pressurize the engine through the spark plug holes. I made a handy pressure tool using the fitting from a compression gauge and a small regulator. Start with the regulator set to 0 psi and slowly open it up - no more than 8 -10 psi. Soapy water sprayed around the crank seal(s) and sealing surfaces will show any leakage.
That low dry compression number is the culprit. Remember, suck, squeeze, pop, fooey all need to be in order.
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the ignition system is a wasted spark so it doesn't matter how you put the plug wires... it is all set up correctly and sparking really strong.
pistons are the right direction...
the bores did look a bit scruffy even after the hone, but since they were from a running bike to start out with I thought it wouldn't be a problem.
could it be that after the hone the bores are too damaged to seal to the new rings?
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Even low compression engine will fire and pop if the timing is correct. Check that the spark is coming at TDC or slightly before. Did you mention that it DID pop with fuel into the plug holes? 80 psi sounds ok at slow speed cranking and should generate a few revs running. Double check bottom end seals. Jurgen
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Jurgen,
the timing is set at 2.5 mm before tdc. it does not even pop when putting gasoline or startgas right into the plug hole.
even if the bottom end is leaky it should still fire and run when p
I put start gas into the cylinder?
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a stab in the dark here. Base gasket covering passage to port or missing so it sucks air, center seal bad or missing??
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all gasket and seals are there at least, if they are leaking I don't know. but even with a bottom end leak, it should start and run?
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Two strokes with low compression wiil not even try to start. Had a Honda CR with lightly scored walls, it was enough so it wouldn`t start. New cylinder, pistons and rings installed and it did.
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have a four stroke bike that will start and run with 60 psi ...
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There are two rings on a two stroke. When you put the new rings in did you happen to line up the gaps? If so, that might be your problem. Make sure the gaps are not aligned.
Experience with Kawasaki's 250 triple.
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have a four stroke bike that will start and run with 60 psi ...
There's a good place to start. Here's what I think. The four stroke will work with very low compression because it still has enough VE to fill the cylinder to the point the engine will "run". With a 180 degree two stroke twin however, if the crankshaft seal between the cylinders is poor, the bike probably will not run more then a couple seconds on plug hole fuel because it is incapable of generating enough pressure in the crankcase half to get good mixture back into the cylinder. This could be because it's leaking into the other crankcase half instead of being sent to the cylinder. So you have one piston descending and pressurizing it's crankcase half and the other piston rising creating vacuum in it's crankcase half and there's nothing to impede the flow of gasses between the two. Based on what you've told us I can't think of any other reason for this motor to fail to run. I am therefore, probably wrong :grin:
Best,
Peter
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Peter, I deras you being right, if the crank seals are bad I have to split the cases again ...
but since it won't even fire on startgas I'll start by sorting out the cylinder walls , if it still won't run - then apart it comes again.
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Could be camshaft failure? It's going around ya know. :tongue:
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Or, it could be tinnitus. :cheesy:
Best,
Peter
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"It ain't got no gas in it!" Karl Childers :grin:
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Bore it to first over with new pistons and rings. Wipe the cylinders and pistons with two stroke oil. Make sure baffles are not clogged up in mufflers too. Check compression, should be close to a little over 90 psi. Next be sure both carbs are full of gas, set choke and kick!! I have worked/ ridden two strokes for forty years.
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I don't know anything about these bikes, but there aren't any safety (sidestand/kill) switches are there?
Rich A
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There's a good place to start. Here's what I think. The four stroke will work with very low compression because it still has enough VE to fill the cylinder to the point the engine will "run". With a 180 degree two stroke twin however, if the crankshaft seal between the cylinders is poor, the bike probably will not run more then a couple seconds on plug hole fuel because it is incapable of generating enough pressure in the crankcase half to get good mixture back into the cylinder. This could be because it's leaking into the other crankcase half instead of being sent to the cylinder. So you have one piston descending and pressurizing it's crankcase half and the other piston rising creating vacuum in it's crankcase half and there's nothing to impede the flow of gasses between the two. Based on what you've told us I can't think of any other reason for this motor to fail to run. I am therefore, probably wrong :grin:
Best,
Peter
Agreed, inability to pressurize in the case.
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no, there ís nothing to stop it from working, no sidestand kill function or anything like that.
No, i didn't curse the bike at all in fact - bad manners! :grin:
I guess the question is really this:
If compression is only 80 psi - will this make the bike impossible to start during anything condition or only given that the crankcase preassure is ALSO too low?
It didn't start even with a drop of gas down the spark plug hole.
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Once I fouled the plug on a new, right out of the shipping crate Honda 250 Elsinore, with only 2 kicks.
Plug looked New, Perfect. But NO firing at all.
Boss said try a new plug. That did it.
?????
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I agree on changing the plugs as well. In regards to the compression... I don't think that is the problem. For example, there are many piaggio mopeds, 50cc 2-stroke that have a compression relief lever which you pull when you pedal to start the engine. The lever when pulled opens a valve on the cylinder head that basically lets most of the compression out so you don't have to pedal so hard to start the engine. That's why I don't think conpression is the culprit in this chase, as in the case of the mopeds you basically drop all compression as part of the factory designed startup process.
I suspect something else, possibly electrical. Did the bike rum before the rebuild? was the engine completely disassembled, or did you just do top end? (Not touching other areas). Knowing that will help us trouble-shoot with you.
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Except on a two stroke you need compression on the crank (bottom) side of the piston so as to force the air/fuel mixture out of the crankcase through the transfer ports and into the combustion chamber.
https://www.youtube.com/watch?v=xNLE8G3pC0k
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Everything was apart on this Engine, crankcases, gearbox ... So if it is put together wrong somehow, that is entierly my fault! :D
The crankcases are seperate for each cylinder, sealed up with two seals and one o-ring. It is possible that there is such a huge leak it won't even start at all, but it would then have to be on both sides, otherwise the Engine should at least fire on one side.
I have tried changing the plugs around, but not after every starting attempt. Can anyone suggest a good drill for this?
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Try delaying the timing maybe as a test. Maybe when you put the oil in the head it delays ignition enough to make it start.
Could be a number of things. As some as suggested, could be bad coils as well, bad condensors, etc. if you have bad condemsor(s)?, you'll see a spark at the points when they open. (They spark a little, but excessive spark means bad condemsor). Do the test in the dark. Coils...: Those are tricky. I had s similar issue with my p125x and finally resolved the issue by changing points, condemsor, and coil, even though everything seemds to be ok.(what appeared to be normal spark, etc).
Good luck.
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Erik-there is a great article in last months issue of "Motorcycle Classics" magazine on conducting a "leak down test". They used a Yamaha RD350 for the article. You can also find the article in their on-line site. I cant recall what the compression was on their test bike but the leak down indicated a bad crank seal s well as bad carb/reed valve surface issues. Having raced and ridden 2 smokes back in the day I found the article very informative.
You say you installed "previously used" cylinders. Were they from the same year and model as your? If a different model year the port specs may have been changed which would throw off your piston port timing. Just a wild as$ guess. If it were my bike, do the leak down test first, (this is the least expensive), remove the cylinders and check the port measurements between the originals and new to you. Have the newer cylinders bored or honed to proper specs. This may involve another set of pistons and rings but you are eliminating a possible problem and at least will have a fresh top end for the engine.
Good luck.
Jerry
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I agree with that as well. It's possible that the Pistons are wrong for those cylinders. Definitelty take a close look and understand the flows and make sure everything is correct. Just the up and down motion is not enough to say it should work (if/when mixing and matching in 2-stroke engines)
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That just occurred to me also, I should have mentioned to check/compare the newer and old pistons while you have it apart. Check for overall height, ring placement, wrist pin to piston top measurement as well as pin to skirt bottom. Some bikes had transfer ports in the intake side of the skits, if so compare sizes and locations.
You stated you already checked ignition timing but did you install new points and condensers? And I would throw another set of new plugs at it when the other work is completed. The oil you poured into the cylinder my have fouled one or both of your plugs when it initially started. Just trying to help you go thru a process of elimination.
Jerry
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Also be sure that the ring ends fall on the continuously solid part of the cylinder sleeve (No ports) otherwise they'll catch on the port and break messing up a lot of stuff along the way.. This ilocation is driven by the piston having the pins in the ring grooves, which is another reason to have compatable pistons.
Anyway, that's just a side note to all side notes.
Good luck!
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yes, that there might be something with the pistons occurred to me too, but they are suposed to be the same for all model years (on russian bikes the spec changes every 20 years instead of minutes as on a jap :wink:)
i have now ordered a complete set of new pistons and cylinders, which is actually cheaper than doing the bore job on my old ones. I should have it all set up in a couple of weeks
no, the condensers are fine to my knowledge, both ignition systems I have tried have come from working bikes
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Does that thing have two crankshafts connected mid-engine? And a rotary valve setup. If so, very "impressive" ???? engineering and is indeed a puzzler.
You may be on the right track going for better compression. Interesting project.
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the Engine has two seperate crankchambers, one in each Engine half. the cranks are connected by the flywheel but there is no valves or anything else to connect them. The carburettor plugs straight into the crankchambers without reeds.
it is a very simple design that easy and fun to work on - but it is hard to find quality spare parts...
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The carburettor plugs straight into the crankchambers without reeds.
Do the intake ports get covered by the piston skirts when the pistons are down? The intake has to be valved somehow. In this case, I'd expect a piston-valve setup, where the piston skirts cover and uncover the intake ports when they travel up and down, or reed valves between the carburetor and the intake ports.
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Eric, feel free to post more pics of the engine; You've got us all intrigued! From the photos it looked like the intake manifolds were going into the cylinders, which would indicate a piston controlled intake interval as Triple-Jim descibes, but you mention crankchambers (crankcase?) which to me indicates a rotary valve which would be one of the crankshaft shoulders controlling the timing. (the 2-stroke Vespa design is this way). If rotary, then you may need to inspect that as a shot rotary pad will make it impossible to tune (though terrible low end performance and idle, it should still fire at least, so that may still be a different issue).
Edit: I looked at your photos again, and it certainly looks like a piston/cylinder driven intake system (not rotary pad),
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if that is a piston port 2 stroke, which I suspect it is, 80 psi is plenty to get it running. Are the plugs getting wet? if not then you know you're not getting fuel. If they are wet, and it's not water, then maybe your timing is out of whack. Not sure of that engine, and on most 2 strokes it's pretty hard to get timing way out of whack, but it could be enough after TDC to keep from kicking off. If it were before I'd think you'd be getting some serious kick back.
2 sets of points I assume? is there an advancer? or just points on mag?
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Fixed timing in the neighborhood of 23- 25 degrees before TDC is normal for a 2-stroke.
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While a compression release may make it easier to pedal that moped, it's akin to dumping the clutch. The compression gets thrown back on for start up. It takes, I think, about 75-80 lbs compression for a 2 stroke to run at all. I could be wrong, but as I recall, 60 psi is a dead duck, 70 is weak, 80 should run, over 90 is best. Ideally you should get 110 or a bit more. Also, you need more rpms to build the reading than just the couple of turns needed on a 4 stroke. Crank pull engines take as much as 5-6 pulls to accomplish this. You can gain 40 psi from pull 1 to pull 5.
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Right, and that's why I asked "Did you hold the throttle wide open and kick until the gauge quit rising when you did the test?" above. Eric pretty much said he kicked until it quit rising.
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Fixed timing in the neighborhood of 23- 25 degrees before TDC is normal for a 2-stroke.
what????? I've had several 2 strokes, including 2 right now, and neither one of them are even close to 23 degrees BTDC. Try 3 degrees or so. If you were running that much it would not start or would kick you back badly.
As a matter of fact, some smokers are timed so close to TDC they can actually run backwards.
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The Engine is quite cool, it is basically two 175 cc Engines put together - that is to say the cylinders don't interact in any other way then getting fuel from the same carb, but were I to set it up with two carbs, the two halves of the Engines would be completely independent.
Yes, it is a piston port design - as the pistons rises it allows air fuel mixture to enter the crank chamber, on the downstroke this is then compressed and pushed into the compression chamber via ports on both sides of the cylinder. The pistons work at 180 degree opposities of each other and there is one ignition cam driving two breaker Points.
Last night I charged the battery up to full (it was already good), just to see if this would help. Still nothing!
After doing the priming procedure (kicking it with full choke and ignition off for 2 kicks), both of the plugs are wet with fuel but still it is not firing.
I Think the manual calls for a compression of around 130 psi, and currently it is between 70 and 80...
Yes, I had both spark plugs out and throttle wide open, then kicked it five times, at which Point the needle wasn't Rising by any siqnificant amount... Wet the compression came to well over 150 psi and dry to under 80...
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what????? I've had several 2 strokes, including 2 right now, and neither one of them are even close to 23 degrees BTDC. Try 3 degrees or so. If you were running that much it would not start or would kick you back badly.
As a matter of fact, some smokers are timed so close to TDC they can actually run backwards.
The manual calls for setting the Point of ignition to between 3 and 2.5 mm Before TDC depending on that gas you are using.
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In regards to the timing, maybe it depends on the engine design and CC. For example, the Vespa p125x is 21 degrees BTDC, and it's 23 degrees BTDC for the P200.
http://www.scooterhelp.com/scooters/VNX1T.p125x.html
http://www.scooterhelp.com/scooters/VSX1T.p200.html
Hope that helps some.
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The manual calls for setting the Point of ignition to between 3 and 2.5 mm Before TDC depending on that gas you are using.
That would seem right, at least from my Suzi and Yam 2 strokers. Once i set mine with a dial indicator, I then verified the mark on the flywheel to ensure it was spot on for future timing and it was. That way I didn't have to muck about with dial indicators any more.
Hard to say what your problem is then. I still have to ask, and didn't read it anywhere. Is your plug wet when you take it out? If you are kicking that much and it's not firing, that plug has to be wet. If not, you got a different problem.
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After doing the priming procedure (kicking it with full choke and ignition off for 2 kicks), both of the plugs are wet with fuel but still it is not firing.
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Eric, have you tried putting it in second gear and pushing the crappola out of it? I know that's not what you want to do normally, but sometimes that's what it takes for a problematic 2-stroke to get it going then if it starts you'll know what and where to tweak.
Having a second person help with pushing will be very helpful....
Good luck.
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Eric, have you tried putting it in second gear and pushing the crappola out of it? I know that's not what you want to do normally, but sometimes that's what it takes for a problematic 2-stroke to get it going then if it starts you'll know what and where to tweak.
Having a second person help with pushing will be very helpful....
Good luck.
tried it and it didn't work ..
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....... . The pistons work at 180 degree opposities of each other and there is one ignition cam driving two breaker Points.....
It can't be timed 180 degrees out can it?
Did that (360 degrees) with a Ford Escort lump once :embarrassed:
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It can't be timed 180 degrees out can it?
Did that (360 degrees) with a Ford Escort lump once :embarrassed:
It is possible, fires every time up and cylinders alternate. with 2 sets of points they could be off but don't know what the thing looks like behind the flywheel. My Suz twin would be very hard to get it wrong though, that's my only point of reference on a twin smoker.
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Jurgen,
the timing is set at 2.5 mm before tdc. it does not even pop when putting gasoline or startgas right into the plug hole.
even if the bottom end is leaky it should still fire and run when p
I put start gas into the cylinder?
Eric, If the spark is ok with plugs out of the engine (fat blue spark) and the plugs are NEW, then they should fire in the engine. I'd try one other thing: instead of gas in the plug hole, try starting fluid (ether) in the carb inlet (let your buddy spray it in) while kicking the engine over. This way fuel actually gets into the inlet, thru the bottom end and up the transfer ports. If it does not run for a few strokes that way, there is something wrong with the ignition, because some fuel will get to the plugs. Jurgen
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Going out on a limb here but I thought it ought to have been mentioned. Could the plugs be getting too wet to fire?
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Eric, be sure to let us know what the problem was when you finally get it running. Lots of conjectures here, we'll all learn something. Jürgen
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Eric, be sure to let us know what the problem was when you finally get it running. Lots of conjectures here, we'll all learn something. Jürgen
yes! absolutely I will let you know.
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The manual calls for setting the Point of ignition to between 3 and 2.5 mm Before TDC depending on that gas you are using.
I don't know what the stroke is on your engine, but with a Kawasaki 350 triple, 2.6mm before TDC corresponds to 23 degrees before TDC.
Irutt, are you possibly confusing mm before TDC with degrees before TDC?
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I don't know what the stroke is on your engine, but with a Kawasaki 350 triple, 2.6mm before TDC corresponds to 23 degrees before TDC.
Irutt, are you possibly confusing mm before TDC with degrees before TDC?
Thanks Triple Jim.!!!
I am going to pick-up a '74 Suzuki GT750 tomorrow and I've never had a two stroke before ,so, I've been looking at how they work and trying to figure out what you guys were talking about.
The TDC confusion in now cleared up in my pea brain Thanks to you. :thumb:....Alan
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Slow combustion requires allot of advance.
23 degrees doesn't seem like a lot, compared to 4-strokes that typically have 30-40 degrees at running speed.
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Thanks Triple Jim.!!!
I am going to pick-up a '74 Suzuki GT750 tomorrow and I've never had a two stroke before ,so, I've been looking at how they work and trying to figure out what you guys were talking about.
The TDC confusion in now cleared up in my pea brain Thanks to you. :thumb:....Alan
Hey, congratulations! That's a cool old 2-stroke that has a lot of potential if you want to play with it, and is a great touring bike in stock form.
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I don't think that it's been covered yet but it might be worth checking the exhausts. I've had a couple of small capacity 2 strokes that have had fully or partially blocked exhausts that will not run. A wasp built a nest in the muffler outlet of one and that engine would not fire. Broke up the mud blockage and fired straight up. On another the spark arrester screen was blocked with carbon and that engine would only just idle and die when asked to rev. It's a long shot on a twin but maybe worth looking at if you haven't already. Good luck.
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Mystery has been resolved!
Just as we suspected - it was low compression that was the culprit! After taking the cylinders apart again and having them rebored properly together with oversize pistons the compression is finally up to spec.
130 psi read cold and now the bike starts up on the first kick!
With 80 psi it simply refused to start at all and with 130 it starts every time.
I hope this can serve as a cautionary tale - have your cylinders done properly and not sloppily and save time!
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Great! Thanks for the follow-up. I have been wondering about this. Glad you worked it out, and this is good to know. I've started 2-stoke engines with hardly any compression, so this is a learning experience for me too.
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no, there �s nothing to stop it from working, no sidestand kill function or anything like that.
No, i didn't curse the bike at all in fact - bad manners! :grin:
I guess the question is really this:
If compression is only 80 psi - will this make the bike impossible to start during anything condition or only given that the crankcase preassure is ALSO too low?
It didn't start even with a drop of gas down the spark plug hole.
I told you that on July 31st post #16. Happy you got it fixed though.
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Just an odd thought but, could the cylinders be out of round? If that were so, oil in the cylinders would give compression but as soon as it burned away the engine would die.