Author Topic: '73 TX500A woes.  (Read 3640 times)

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Offline Rob Patterson

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'73 TX500A woes.
« on: January 05, 2017, 04:16:52 AM »
I recently bought a low mileage (8,412m), one owner, ?non runner, '73 TX500A that had been sitting in a shed since 1975.
The previous owner said he'd started it 4 or 5 times during the past 41 years... most recently 2 weeks before I bought it from him. I'm not one for calling a bloke a liar but the carbs were both gummed pretty much solid so I do have some reservations about his truthfulness.
I have had it running in a fashion a number of times but it always does the same thing... runs sort of ok (won't rev out much and misses and farts a fair bit) for a while then 'bogs down' and eventually dies. Once it cools down it'll start again with the same result.
Since owning it I've done the following:
# Read every post on this forum at least twice.
# Repalced damaged starter wheel assembly.
# Replaced omni phase balancer chain.
# Changed the oil (put Nulon 15w40 in).
# Cleaned the oil filter (waiting on a new one to arrive).
# Disassembled the carbs and cleaned a huge amount of gunk out of every possible place.
# Checked for blockages using Carb & Throttle body cleaner and compressed air.
# Rebuilt the carbs using ebay rebuild kits.
# Rebuilt the carbs again using the original jets (after cleaning them thoroughly in lemon juice) after reading a comment here about ebay kits.
# Reset float levels to 22mm as per the workshop manual.
# Bench synchronised the carbs as best I could with no vac gauges.
# Replaced the missing factory set timing plate with a home made one.
# Established TDC as best I could using my digital calipers (pretty happy with the result).
# Cleaned the points and reset them at 0.4mm.
# Reset the timing.
# Reset the points again.
# Replaced spark plugs with NGK D8EA and checked spark (nice bright spark present) and set them to 0.7mm.
# Cleaned fuel tank.
# Disassembled and cleaned both stopcocks.
# Tried every possible setting on the air maixture screws.
One issue I had was with the workshop manual and the timing cam.
The manual states that the mark on the cam be aligned with the locator pin on the shaft... I found it impossible to set the timing until I reversed the cam. (I had taken it off to clean advance weight etc without looking at the mark so don't know how it was set previously).
The timing marks for the right cylinder simply wouldn't come anywhere near close to lining up and were approximately 1/2 turn away when the piston was at tdc.
Each time I get it to run I find the plugs are black after it dies.
Sorry about the book length post but I've tried to give as much info as I possibly can.

Offline guylr

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Re: '73 TX500A woes.
« Reply #1 on: January 05, 2017, 03:30:50 PM »
I believe those sensitive Keihin (aka "Honda Carbs") are the source of your problems. Click on the thumbnails below to see if you have the pilot jet plugs and retaining clips are installed. Your symptoms sound a lot like what happens if that plug is missing.







Yes, that's a real Yamaha training cutaway carb that I was trained on back in 1973!

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline Rob Patterson

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Re: '73 TX500A woes.
« Reply #2 on: January 05, 2017, 08:35:13 PM »
Thanks for your response Guy.
The plugs and clips are in place although the plugs are showing signs of age.
Do they need to make a perfect seal below the pilot jets?
Can you recommend a setting for the mixture screws?... The bike always seems to be running rich when it dies and the plugs are consistently black.
Another question if I may... How hot should the crankcase be after only a few minutes of running?
I ask because the left side does seem to get hot and it happens quickly.
Keep in mind that I have replaced the starter wheel assembly and the omni phase balancer chain.

Offline guylr

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Re: '73 TX500A woes.
« Reply #3 on: January 05, 2017, 09:53:06 PM »
A tight no leaks seal on the plugs is prefered. Try the 1975 specs for the mixture screws of 1.0 turn on the left side carb and 1-3/8 turn on the right side. I have no idea how to answer your temperature about heat. Sorry.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline Rob Patterson

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Re: '73 TX500A woes.
« Reply #4 on: January 06, 2017, 05:17:01 AM »
I set the mixture screw as per your suggestion and started the bike again today.
It wasn't quite as bad as it had been but the end result was the same... a couple of hiccups, a backfire and death.
Leaving the petrol lid slightly open (I thought that perhaps the tank wasn't breathing) didn't do a lot.
I have the floats set (as per the workshop manual) with the bottom of each one at 22mm above the body of the carb with the tang(?) just resting on the needle valve.
Do you think lowering them and allowing a higher fuel level in the bowls would help? If so, what level would you suggest.
I did manage to rule out a problem with the coils... heaps of spark present after running and stalling.
Thanks for all your help with this... I'm confident that we'll get the thing running properly in time  8)

Offline guylr

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Re: '73 TX500A woes.
« Reply #5 on: January 06, 2017, 02:49:52 PM »
You set the float height to the correct spec so I would leave it there. Plus or minus 1 mm or so would not cause the engine to cut off. What would be good to confirm is the actual fuel level in the bowls. To do it right would require and adapter to screw in at the bowl drain that you could attach a length of clear tubing to then open the petcocks and start the engine. By holding the tube up vertically next to the carb body you can see the level of fuel in the bowl as the engine is running. There is no spec for the TX500 but I would guess it to be somewhere around 2-6 mm below the bowl gasket line. The hose adapter threads are fine pitch 6 x .75mm.

If you can't come up with an adapter to do the running level check then you might try switching the fuel supply hoses to clear ones so that you can watch the flow into the carbs. Also you could fill the bowls by opening the petcocks for a minute or so, close the petcocks then drain the bowls and measure the volume from each bowl. Then fill the bowls again, run the engine until it pops and quits, shut the petcocks, drain and measure the fuel amounts again. 

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline Rob Patterson

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Re: '73 TX500A woes.
« Reply #6 on: January 07, 2017, 06:45:53 AM »
Ok... 40 degrees celsius here today so haven't done a lot.
I drained and measured both bowls cold...right =50ml, left 75ml. I had inadvertantly left the stopcocks open overnight so measured again and got 52ml left, 50ml right.
I took the carbs off again and fitted the original rubber tipped needle valves.
I checked the rubber plugs and thought they might be perished to the extent of letting fuel past so fitted O rings to them and adjusted the retaining clips to put more pressure on them when the bowls were refitted.
Mixture screws set as suggested.
The bike started and ran a lot better but still won't idle... we certainly made progress though and I'm trying to source new rubber plugs for it with the hope that they are the issue.
I've put a video of it running on my facebok profile...I hope you can access it.
https://www.facebook.com/rob.patterson.167/videos/vb.100001509275783/1284250724968558/?type=2&theater&notif_t=video_processed&notif_id=1483771223742603
Thanks again for your help Guy.
Rob.

Offline Rob Patterson

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Re: '73 TX500A woes.
« Reply #7 on: January 08, 2017, 01:07:48 AM »
This morning I advanced the timing (assumed that my DIY timing plate mark was out), reset the points, fiddled with the mixture and got it to idle without my hand on the throttle  :D
Got real cocky and took it for a ride.
It ran the best it has since I've had it.
I had no problems, cruising happily at 60mph, until I slowed down to turn around at about the 5 km mark (sorry about the mixed km and mph's but the speedo is in mph).
It stalled, started again straight away but would only chug along for about 1/2 a km then, when I was about to give up and phone for the trailer, it allowed me to give it a rev and came home much the same as it went on the trip out. Sat on 60mph at 5,000rpm and was pretty much a delight to ride.
When I put it back in the shed I noticed that the right pipe had discoloured but the left hadn't. The attached pics give a bit of an idea.

Offline guylr

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Re: '73 TX500A woes.
« Reply #8 on: January 10, 2017, 02:09:02 PM »
You need to use a dial indicator to accurately locate TDC for #1 cylinder to set the timing pointer. Then use a strobe timing light to verify the total advance on both cylinders.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline dave835

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Re: '73 TX500A woes.
« Reply #9 on: January 10, 2017, 11:46:05 PM »
   Rob ,   
 The absolute best way to find top dead center on your engine won't be easy , but would be very accurate . Get a degree wheel (speed shops or catalog hi-performance sellers carry these ) and secure it to your alternator rotor so that the 0 degree mark is near straight up when you have your "close " current TDC marks set up . Using a piece of stiff wire or welding rod , shaped to point at 0 on the wheel and secured to a convenient engine nut or bolt at the other end . Using a dial indicator , find the high point of piston travel as the engine rotates . from this point , rotate the crankshaft till 5MM of piston travel is indicated . Note the reading on the degree wheel . Now rotate the crank the other direction till the same 5MM reading is obtained on the indicator . You can now see a certain number of  degrees on the other side of TDC . If the degree readings do not agree (such as 17 degrees before TDC and 25 degrees after ) , add your readings , divide by 2 , ( in this case , 21 ) and adjust the degree wheel to that reading at your 5MM point . Repeat the readings to confirm the distance/degrees at equal readings , and TDC on the degree wheel is true TDC!
 Now set and secure your timing pointer and move ahead with tour tuning .
                                                                                                            Dave

Offline guylr

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Re: '73 TX500A woes.
« Reply #10 on: January 11, 2017, 11:31:06 AM »
Dave, I have to say that your suggestion is one way to find TDC but is a whole lot more work than using a dial indicator.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline dave835

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Re: '73 TX500A woes.
« Reply #11 on: January 12, 2017, 12:35:11 AM »
     Guy ,
 More work , but more exact . Dwell time of a piston at TDC might leave one at +/- 2 degrees  off . I guess I am just one of those fussy types ...

Offline guylr

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Re: '73 TX500A woes.
« Reply #12 on: January 12, 2017, 04:17:45 AM »
Which method do you think the factory used to set the pointer? Beats me but I'll bet a degree wheel was not involved as there just isn't that much time on the assembly line. Probably just a stop set on top of the left cylinder bore before the head went down on it and then the line guy eyeballed the pointer to the TDC mark on the governor, tightened the screw and gave it the dab of white paint. Done in 15 seconds with maybe that +/- 2 degrees from true 0. So the factory fudged a bit setting the pointer as we do when using it to set the points. Your method will get it closer than that for sure. Oh darn, forgot to take the point shaft gear lash into account  :P
Old bikes are fun to work on.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline Rob Patterson

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Re: '73 TX500A woes.
« Reply #13 on: January 14, 2017, 07:19:10 AM »
Thanks Guy and Dave;
I bought a dial gauge and made an 'extender' that reaches the top of the piston.
It consists of two aluminium tubes, one fits inside the other.
One end of the thinner tube attaches to the end of the probe on the dial gauge, into the other end I threaded a metal stopper which has enough weight to ensure it keeps in contact with the top of the piston.
The thicker tube slides onto the gauge and the other end sits on the head at the plug hole when I'm using it.
I set tdc by turning the motor clockwise, noting where the piston stopped rising the continuing turning until the piston started going down again. I set tdc halfway between those 2 points.
Once I had tdc I adjusted the timing and points but I seem to have only sporadic spark on the right cylinder.
It did run but after a few minutes the left cylinder seemed to be doing all the work and was blowing a fair bit of black smoke from the left muffler. It eventually bogged right down and stalled.
I'll check the rhs plug lead and coil connections tomorrow (beer O'clock now).
I have new points on the way and may well have to murder the piggy bank and buy new coils and/or condensor.
New pilot jet plugs for the carby (#19 on the TX500 carby parts breakdown) are also on the way along with new O rings for the mixture screws. The plugs are the part #22V-14968-00-00 (honda?) ones from boats.net so I'll need to trim them a bit.
Cheers.
Rob.


Offline guylr

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Re: '73 TX500A woes.
« Reply #14 on: January 14, 2017, 06:00:48 PM »
The part number is from Yamaha. Have you checked spark Strength? If not it's easy to do the quick method of laying a new fresh plug against the head while cranking the engine. If you can increase the gap on the plug to 7mm or more and still get a spark then the strength is adequate. Note: Do not remove the plugs from the engine while doing the test as you may have a sudden unintended fire in your garage. If one or both sides seem weak check the voltage to the coils on the red/white wires. Under 10.5-11V while cranking and you need to troubleshoot all the connections back to the battery.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"