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nab301 said :-
Hopefully the premix may have prevented corrosion in the petrol tank?
Nigel
28/10/2024 14:10:54 UTC
Glyn said :-
Exactly Nigel, the tank is better inside than on the outside. I’ve had all the carb bits in the ultrasonic cleaner and they’re looking much improved. I’m trying to understand the throttle linkage. The cable from the twist grip goes into a 3 way splitter. 1/ left carb slide 2/ right carb slide 3/ to another splitter. This 2nd splitter has 1 cable to the autolube pump (it’s missing) and another to the power valve solenoid. So what does the powervalve cable do? As the revs increase does it allow the valves to open or perhaps it may be part of a power restriction device as the Japanese did not allow full power out of these bikes on their roads. The input cable is connected to one side of a floating arm and the PV solenoid is connected to the other with the oil pump connected to the centre point. There is no fixed fulcrum and so the 3 cables work together in some way. A bit more though is needed here.
28/10/2024 16:41:04 UTC
ROD¹ said :-
Glyn, It has been a long time since I run two strokes, and I am always worried that I am teaching my grandmother how to suck eggs when posting on here.
The three cables are as you described one for each carb and the third for the oil pump.
When tuning two strokes for performance back in my teens and early twenties the exhaust port would be raised to give better power at high revs. Achieving peak power would make the bike almost unrideable on the roads with very narrow power bands and gearing that was too wide with standard ratios. At this state of tune the clutch would have to be slipped when changing gear to keep the bike in the power band.
The bikes improved with the introduction of reed valves which helped with power at lower revs.
The power valves of the later two strokes utilise a metal guillotine device in the exhaust port. This valve is closed at low rpm and opens ( raising the exhaust port timing ) at higher rpm. This gave the bikes the best of both world performance keeping the higher power of a tuned bike with raised exhaust ports when the power valve is open and low down power when the power valve is closed.
I believe from memory that the power valve on the Yamaha was opened via a cable which is attached to an electronic sensor which detects the engine revs, and opens the valve via the cable at higher revs. I think the unit was located under the fuel tank, but I may be wrong ( its not unusual).
I owned the similar Kawasaki KR1.
I apologise in advance for any distress caused too the Ed on reading the contents of this post.
28/10/2024 21:11:26 UTC
Glyn said :-
Thanks Rod, I agree that’s how the theory has been explained to me. I’m not sure why the throttle cable goes to the rotor on the power valve motor. If it pulls up the right hand side of that lever in the white box then it would pull the cable to the oil pump further when throttle is applied. Similarly. If it slackens the right side of the lever then the oil pump would provide less oil to the inlet manifold with the same application of throttle. As there is no current cable from the junction to the pump, and they’re no longer available, I will need to make one up but have nothing to go on with respect to inner and outer lengths etc.
29/10/2024 08:04:10 UTC
Ian Soady¹ said :-
Sounds like another fascinating project. I love the problem-solving aspects of rebuilds - apart sometimes from the angst caused by previous owners' bodges!
29/10/2024 10:56:37 UTC
Glyn said :-
I have a possible theory that perhaps the oil pump needs to up its game when the power valves open. The extra power might well need an advance in the upper cylinder lubricant supply. Someone will know and I will get to learn eventually. If this is the case then the previous owner ( who removed the oil pump supply in favour of premix) may have been running the engine slightly starved at the upper end of the rev range.
29/10/2024 12:00:22 UTC
Ren - The Ed¹ said :-
The case against 2 strokes has been clear made by the various learn-ed council's statements above. The defence rests M'lud.
30/10/2024 07:11:02 UTC
Glyn said :-
Point of order your honour! Surely, the Jury is still out until the end of the renovation. As temporary council for the prosecution, I request an 8 month recess prior to final deliberation.
Another few hours in the garage today saw the carbs reassembled with various new parts and refitted onto the manifolds. Whilst gazing into the reed valve holes I turned the motor over and saw that the sides of the crancase weigts were covered in oil, the same oil as I found in the carbs. Oooh err missus, thats not nice and I cant see any drain plug either. I thought I'd take a look at the electrics whilst I was pondering the engine and so fitted the new battery. I was somewhat amazed that most lights and indicators worked. In fact the only thing that did not work was the horn and the rear brake light switch. The switch is hanging in mid air as a previous bodger has fitted aftermarket hangers and there is nowhere to fit the switch pull wire or return spring. Feeling generally pleased with much electrickery working I turned to find the fuse box smoking heavily. A poor connection on the headlamp fuse has caused a lot of heat and melted the fuse holder. It wont do any harm to replace the entire unit but the list is growing.
30/10/2024 18:23:51 UTC
Ian Soady¹ said :-
"the list is growing" - don't they always? You start off with a simple oil change only for it to turn into a full rebuild.
Soeone wrote in one of the classic bike mags that any old British bike will be a 6 month restoration however good it looks. Very true* and also seems to apply to japanese machines...
*Not of course in the case of bikes I sell.
31/10/2024 10:07:23 UTC
Glyn said :-
That is certainly true Ian. I’ve now run through the operating system for the autolube pump. What actually happens is that the power valve servo motor, when open, reduces the oil flow from the pump to the upper cylinders. I can’t think why but it has cost Yamaha in design, parts and production to do this and so they must have a good reason to implement it. The engine is the same unit as that fitted to the TDR 250 but they don’t alter the output of the oil pump on that model. Perhaps they assumed the TZR would be more likely to be thrashed.
01/11/2024 11:58:52 UTC
nab301 said :-
@ Glyn , Oil in the crankcase is surely better than rust? Is it oil from the gear box I wonder or did a previous owner add oil to protect it in storage?
Nigel
01/11/2024 12:00:17 UTC
Glyn said :-
The oil is very much a yellow shade of brown so I’m thinking it’s premix with the fuel element evaporated Just like I found in the carbs. If so, it would indicate a faulty shut off valve in one of the carbs plus a leaking fuel tap. The latter is a vacuum operated device of which I’m not happy with because I’ve had this failure before on the Diversion. In that case, I modified the tap to give me on,Res and off loosing the prime position. You had to remember to turn it off when you finished riding but you never had the crankcase full of fuel.
01/11/2024 13:38:52 UTC
Ian Soady¹ said :-
Don't mention vacuum taps Glyn or I'll give you the sorry sga of my little Yamaha V twin. I think I've finally sorted it out....
No idea why Yamaha used such a ridiculous system whose only merit is that people didn't have to remember to turn the tap off when they parked the bike up. Instead they had to use the prime function if they left it more than a couple of weeks.
01/11/2024 14:57:51 UTC
Upt'North ¹ said :-
Ian, what do think about Vacuum Fuel Delivery Devices?
I know, I'm sorry. God made me say it.
The ST11 have a Vacuum Cotrol but no actual fuel tap. These can be problematic when age gets at the diaphragms. They're often bypassed and plugged without issue.
Upt.
02/11/2024 09:55:45 UTC
Glyn said :-
By Jove it goes! Yes indeed it’s alive. I rigged up a fuel bottle, sprayed brake cleaner into the intakes and she fired first kick. She ran second kick and really well. The smoke was overwhelming but I’m putting that down to the oil in the crankcase. I couldn’t take a ride as the clutch refused to release but that should be easy to rectify. So, supercharged with success I proceeded to take the thing apart.
02/11/2024 16:44:07 UTC
Glyn said :-
Picture for the Ed. He loves these bikes don’t ya know.
02/11/2024 18:57:21 UTC
Ian Soady¹ said :-
I can almost smell it!
03/11/2024 12:16:41 UTC
Ren - The Ed¹ said :-
Ewwww! I've got that sting from a little vomit in the back of my throat just from seeing that image.
Maybe I've got PTTSSD - Post Traumatic Two Stroke Stress Disorder. Where there's blame there's a claim - Glyn my lawyers will be in touch.
04/11/2024 16:05:00 UTC
Glyn said :-
Harsh Ed, harsh. Perhaps we could settle this with a race off, my 250 against your 500 (or your Honda 125 if you prefer). I will probably win providing I can prevent the thing from breaking down for the duration of the event.
I've solved the Autolube cable problem. I was given an LC cable to try. The pump 90 degree end, adjuster and nipple were perfect but the joint end had an inline nipple instead of the required T nipple. I found an old steel nail and drilled a 1.5mm hole in it. I then cut the nail 4mm each side of the hole and soldered it on to the end of the cable. Incidently, the autolube pump works in exactly the opposite way to which I described above. It actually provides more oil at high revs. The reason for this is that when on a long straight, if you shut off at the end of it and use engine braking, the the lack of oil can cause the engine to seize. Similary this can happen when travelling downhill. Barry Sheene would get over this by taking a large blip of throttle but it was a risky thing to when entering a corner.
04/11/2024 20:44:06 UTC
Glyn said :-
So there’s been progress on the TZR. New lower rear shock bearing (£76 may the lord forgive them), new sprocket cush drive, new wheel bearings and grease seals. I’ve fitted a new ( not crappy Yamaha) fuse box and blade fuses.The frame , swingarm and various other bits have been painted. Sadly, there was a nice gold heavy duty chain fitted but it’s covered in rust, especially on the rollers and will have to find its way into the recycling bin.
10/11/2024 18:05:56 UTC
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