I've run the '79 with the 90mm piston a couple of times now. I know I need to double-check the valve clearances. I adjusted the chain tensioner properly. This piston makes a pretty hellacious banging right now. Can I expect that to settle down? It does calm slightly after warming up a bit. I haven't actually let it warm all the way up yet. BTW, it's running on 100 octane unleaded (just happened to be in the tank when it fired).
Post by wotavidone on Feb 13, 2007 21:45:07 GMT -5
Weeellll, lessee. I seem to recall seeing a photograph of this motor which suggested you had just received it back from your engine builder? So let's assume for now that there is nothing mechanically amiss with the rebuild. Though I would take the plug out and see if anything seems to be hitting the piston when its around TDC.
There seems to be something a little amiss with the electrics - i.e. headlights and indicators not working. Now you have a bit of a knock. Allright, a hellacious banging. And it was a right royal pain in the butt to get running in the first place. Ones gotta wonder whether the ignition timing is a long way out.. I have read up on the CDI a bit. Seems like, these things get an advanced signal from the sensors, then they retard that according to the revs being done at the time. So, I am wondering whether the beast is a bit too far advanced. I suggest first job after making sure the valves don't hit the piston is to very quickly run it and check the timing with a light. Mick
Thanks Mick. Yeah, I did have it built, but it was almost a year ago. It's been quite a journey to this point. A bit farther to go I guess... I'm a doof when ti comes to the electrical stuff... this could get interesting again!
Hallo hopwheels, as for the mechanical part take the manual and check everything again. did the engine ran before you touched it? ar you sure you have the right rotor/statorpair with a good cdi try swapping it with a known good one. if your not colorblind and in possesion of a multimeter you must be able to check the cdi yourself. it is not that difficult. but you will need a diagram.
Hi sjef: The bike was starting and running without any of the lights working. What part of the electrical system would fail, yet still allow the bike to start and run?
I have to check to be sure the piston isn't hitting the valves.
Also, if the ignition was far out, would it start without kickback and run and rev without hesitation? When it did run, it idled and revved with the metallic banging sound, but again, it did idle and rev up. (BTW, the starting I've managed with this is all with no choke. It doesn't seem to want it at all?). When I put my '78 top end together with the timing out, I couldn't even budge the kick starter.
The other thing is, last night I tried starting it again, and this time it was hard to start. Still no indication of lights working on the kicks (remember it has a bat eliminator).
I started swapping out main jets (this carb came with a #260). I moved down to 240 and up to 330. Each time I swapped the main, I pulled the plug and let the engine air out a bit. It wanted to fire, and was turning over with the #330, but still curiously wants no choke.
So, I know it's a long story, but it seems it will be a little "cat and mouse game" to get it running consistently, not just firing up.
Thanks again gents!!
Last Edit: Feb 14, 2007 14:48:41 GMT -5 by hopwheels
according to your story i do not think the ignition/timing is very wrong.You can check this with a timing light. basicly there are 2 coils in the generator one for the ignition and one for the rest of the electrics. this is a ac generator with 3 windings you must have about0,73 ohm between the wires(white/yellow)(0,80ohm between the white ones). after this comes a rectifier/regulator, you can check this also with an ohmmeter.do you have voltage on the fuse? regards sjef
Well sjef, like the big dummy that I am... I took the fuse out of the mix when I hooked up the bat-pac and forgot to add it in line, before the capacitor. If it's the voltage regulator, at least I have a spare. If it's the lighting coil(s) in the stator, I'm going to be bummed. I have a spare, but I'll fry it also if I don't figure out the problem before swapping them out and that's an exensive blow-it. If I'm reading you right, it's probably not the CDI? Correct?
MORE Also: Just went out at lunch time and swapped back to my baseline main jet (#260), cleaned the plug, and it started. No lights still, and the bulbs are fine.
It required priming the carb A LOT (20 seconds or so of full throttle) and the bike seemed to only want to run for a few moments. Then it became hard to start again.
On and beyond the knocking (which I'm going to try and capture on audio and post), it seems there's still a fuel issue. I'm wondering if it's sucking air somewhere. And perhaps, despite reading the manual on the compression lever setup, maybe I got it wrong?
More to check... more to check...
Last Edit: Feb 14, 2007 16:55:19 GMT -5 by hopwheels
Post by wotavidone on Feb 14, 2007 16:48:53 GMT -5
Can offer two more bits of advice which may or may not help. One - I had this problem with my V8 Monaro when I put the new motor in - it started, it ran at idle and revved easy under no load, but had a really very metallic knock that went away as soon as I retarded the seriously advanced timing back to where it belonged. Two - My SR, which allegedly has a big piston in it, when I got it did this until I put really high octane fuel in it. All the best - I'm sure it will work out eventually. Mick
all i can say: check your timing. do not think your cdi is broken. it will be if you have ignition without a sparkplug grounded you won`t fry your generatorcoil that easy if something is fried it is your regulator/rectifier
Thanks again Mick and sjef! There's more of an update above (I just added to my last post, see "MORE"). I'm running 100 unleaded. Maybe I'll go to the VP110 leaded race gas I have and see. As far as timing, I need to get it to run for a while. And I still have the issue of having two brand new inductive timing lights that I cannot seem to make work (I'm telling you, my brother got every last bit of electrical engineering genes in our family. I am left many cards shy of a full deck when it comes to electrical issues)
Let's see if this works...
Hmmm.. I did it in iMovie (It's a .mov Quicktime file) and the sound is more tinny and distorted than the original. You can hear the metallic knocking.
So, let's recap. I can get it to run (obviously). It takes a bunch of priming before it will fire. If it quits, it's nearly impossible to restart until it's sat for awhile. It has that knocking sound, and no lights or horn.
Last Edit: Feb 14, 2007 21:48:52 GMT -5 by hopwheels
When I first got mine fired up (similar specs) I also had lots of noise so I started to trace back what I had done. it turned out that I had forgotten to tighten the stator bolt (thats what happens when you move interstate during a build up) and the stator was rocking back and forward on the shaft of course getting progressively worse as the key wore out.
I have no idea if you have checked this or not but mine sounded very much like your engine and I thought I had screwed something up badly during build up but it just turned out to be a $4 key.
Hmm it will always sound bad with a stereo turned up...
Have you looked through the plug hole to ensure that nothing is hitting the piston, both inlet and exhaust and on the overlap?
Was the head to piston clearance checked during the build?
You always need to check the squish clearance on a piston like the 90mm, and piston to valve clearance when fitting a high comp piston, especially if a performance cam is fitted as well.
Wiseco's used to run large clearances on their piston to bore fit...possibly to do with the metal they were made from and the expansion rate, however, now they run much closer tolerances. Metal again I feel. The larger clearances made the older pistons slap a bit in the bore and my black cafe racer is like this...
What piston do you run I can't recall?
Look at the valves and piston carefully as you turn it through...get someone to hold the de-compressor in and gently turn it over...see if you can feel any resistance as you do so...and look at the piston and valves at the same time. If all seems OK there look at your valve clearances and see if they're OK...are they meant to be different to standard now? Check them again!
Try higher octane fuel and see if this helps...
The carby:
Have you checked the float height? This makes a difference to the engine operation...17 to 19mm is the range on a 38mm carb. Measure to the bottom of the float from the body's metal surface not the gasket and with only a very light load on the needle.
While it is idling adjust the mixture and see what difference it makes. Turn the screw in until it lightly touches, then turn it out again...it should ideally be highest RPM at about 1.5 turns out. If it is highest somewhere else then the pilot jet may need changing to a different size. As I recall it if's high in close then you need a smaller jet...opposite out further of course. It's a matter of playing around.
To get the MJ set you need to really do a run at high power...hold the bike flat then pull the clutch in and kill the ignition...look for a nice light tan colour on the plug electrode...if its black one size lower...too white one size larger and so on...can be a pain on unleaded sometimes. Plus the bike needs to be run in a bit too.
For fine adjustment on this raise or lower the needle a notch at a time.
The slide cutaway has a large bearing on the lower end as well...another place to go...this can totally change the jetting as well. Less cutaway richer down low and through the midrange (eighth to half throttle) and the opposite with more.
Thanks for your response! And for everyone's help. On the piston... it's a JE Piston. I have no idea if the squish clearance was checked. I can't reach the guy that built this a year or so ago. I'm not sure how to check all the things you mentioned. Just take the tappet adjuster covers off and the plug out and take a look? Or the engine back out of the frame, and the rocker cover off and taking a look? Hope the former not the latter! So, can this thing be OK with piston slap if that's what it is? Or is it a timebomb?
Thanks for the info on the carby. I'll try all those adjustments.
you can check all the clearances by taking of the head and put some placticine or playdoh or solderwire on top of the piston put everything back together ,turn the crank around remove the head and you see were the material is squeezed.at that point you can measure the clearance .about 0.050 inch is oke.
on other thing: get your carb ultrasonic cleaned, you cannot get it cleaner yourself . solved a few problems with idle and revving on my XV a while ago.
Thanks sjef. The carb is brand spanking new. Would it still need to be cleaned like that? If I were to take the engine back out, and do the squish test as you described, what happens then? Do I have the piston machined down to the proper tolerances by someone, or is it chuck it and get a new piston? Since I have no idea how or where to get that done... I think I've effectively screwed the pooch on this engine. I think I would be better off rebuilding the head on this thing to a less finicky (closer to stock) set up. I really want to ride this thing, not fiddle with it endlessly. I enjoy a lot of the process, but there needs to be some sense of completion and satisfaction... like throwing your leg over it, kicking it into life and roaring out the driveway onto the open road ;D. Seems like I'm still a ways away from that .
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