T500 Knocking its head off

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PhilatHooton
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T500 Knocking its head off

Post by PhilatHooton »

I am running in my rebuilt T500 L. New crank seals,rods,pistons +.5mm. New points ,condensers, plug caps. Carbs (153 13 2Y) ultrasonically cleaned,new mikunii pilot jets 30 , new mikuni jet needles -5FP17. Floats set to 27.3mm. Mixture 1 1/2 turns out

She starts first kick and after a minute or two will idle at 1500. Sounds sweet and revs cleanly. On the road she drives beautifully (only taking her to 3.5k) but after several miles when really warmed up she starts knocking loudly and pinging on light throttle and when pulling away from a stop. If i just start her and let her idle for 10 mins or so till really hot and blip the throttle i get the same loud knock.

The timing , plug and points gap are spot on . Battery is good and fully charged. Have tried mixture screws in every position, tried the jet needle in position 2,3 and 4 and even changed the pilots to 32.5. Tried Denso W24FS and Bosch W3AC plugs - they are a nice colour after a good run.. I'm using Shell Super unleaded.

Have read as many previous posts on this subject but not found the answer yet. All help,tips,ideas greatly appreciated. :)

Thanks.
Zunspec4
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Re: T500 Knocking its head off

Post by Zunspec4 »

Try retarding the ignition. The original Suzuki timing was established when we had good'ol leaded petrol. Modern unleaded burns faster so does not need such advanced timing. Retard about 5 degrees as a start.

Cheers Geoff
PhilatHooton
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Re: T500 Knocking its head off

Post by PhilatHooton »

Thanks for your suggestion Geoff. I set the timing using a strobe and i must confess am not familiar using a timing disc. Is it a case of moving the stator timing line to the left of the fixed mark for later ignition or is the only accurate way to do this with a disc/gauge ?
Cheers Phil
Zunspec4
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Re: T500 Knocking its head off

Post by Zunspec4 »

Hi Phil,

You could make a quick adjustment by turning the points plate in the same direction as the rotor rotates. Move 1mm at a time and see if it makes a difference. The only accurate way is to use a degree disc or a dti if the heads are off. The Suzuki timing marks are often found to be slightly out when properly set up with a d-disc/dti.

Cheers Geoff
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Re: T500 Knocking its head off

Post by Vintageman »

I have a T500M. Stock exhaust now Jemcos (can cause it to ping even more if not tuned well).

The T500 will ping if too lean/too hot. Now since you said light throttle, I don't think we are talking main jet.

Should use a dial gauge for timing. If you do that at least once you can see how good your timing marks are on rotor vs case.

Try timing as suggested (or 93 octane... which you did), but, I have no problems running stock timing and 87 unleaded. And, when I set points I usually usual go a degree or two more degrees advance since the points arm wear down in time , I am lazy and i prefer mid-range grunt such timing provides.

I agree, the T500 will ping easy when you are say between 1/8 to 3/8 throttle and lightly loading or heavy if things not spot on. It is fussy I have been there myself. The head combustion design sucks. Here is something I have found that may be a problem->


Did you check the inside of you Needle Jets? I mean did you look inside the first view mm where it's precise machined surface meters with the jet needle? You need a good light and youthful eyes to verify OK. It should be perfectly smooth and shinny. If its is pitted at all you can run lean... ping ping ping. No ultrasonic cleaner will fix that. How was the jet needle? I rarely find engines that old whose needle jet are not corroded inside to some extent. It must be perfect, expect no less.

So that 182(?) series Needle Jet is obsolete... You will have to run a 195(?) series... I forget number someone can correct me or can look at my old posts. The 195 will work directly. done it many times, many bikes with many thousands of miles

I have found a little extra fuel cools thing down well and can alleviate ping

If all is well, stock and set to creators spec your bike should run OK. A ping now and then when pushed at extremes can happen, but not as I think you have described here.

Good luck
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argo1974
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Re: T500 Knocking its head off

Post by argo1974 »

Late models are prone to pinging since they have less exhaust height and very lean mixture at 1/8 to 1/4 throttle openings. Also, oversize pistons add extra compression.
Check the compression and check head gaskets not protruding into the cylinder. Lowering the compression with thicker head gaskets is the way to go, until there is no detonation with stock jetting/needle pos.
Igntition retard and/or richer carb setting may help but turn the bike into gas guzzler.
Been there myself with my T500K and T500 Cobra until I found proper squish heads. If I remember correctly, Ivan from Ivan performance lowered the compression to 135 psi on his Cobra.
1x T500 Cobra (1968)
4x T500K (1973)
PhilatHooton
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Re: T500 Knocking its head off

Post by PhilatHooton »

Guys,thanks for your analysis,comments and suggestions which i am taking on board. Have ordered new 188-P4 Needle jets which are readily available here. Hopefully this will eliminate any carb issues. Timing disc on the way and then some testing. Regarding cylinder head gasket thickness anyone know where i can source alternatives and what are these centre plug heads i keep reading about. Cheers, Phil
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Re: T500 Knocking its head off

Post by sportston »

All previous advice is good and worth following, but it also is a good idea to make sure your oil pump is correctly adjusted to avoid excess heat from excess friction, if you haven't done so already.
PhilatHooton
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Re: T500 Knocking its head off

Post by PhilatHooton »

Update: I took on board the suggestions made and firstly having tried some new needle jets which turned out to be not the 188 -P4 as promised by the Mikuni dealer but something similar he said with the numbers ground off and as he refused to tell me what they were i moved on to compression. With a standard 020" gasket i was getting 161 psi in each cylinder. I ordered some 032" from Lani Visconti at coppergasketsusa .Top bloke and great service. They came within a week . These reduced the psi to 150 so following on and having read Ivans post i ordered another set at 062". With these on the psi is 125 and the bike is running sweet. No pinking or knocking and pulls cleanly on light throttle low down.I measured the step in the head and at 3mm i presume they have not been skimmed so i'm puzzled why i ended up with such high compression but very happy to have found the solution. Thanks to all for their advice and the forum for invaluable knowledge and tips. :)
sportston
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Re: T500 Knocking its head off

Post by sportston »

PhilatHooton wrote:.I measured the step in the head and at 3mm i presume they have not been skimmed so i'm puzzled why i ended up with such high compression but very happy to have found the solution. Thanks to all for their advice and the forum for invaluable knowledge and tips. :)
New pistons higher compression ratio than expected?
Wrong heat rating on the plugs?
Vintageman
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Re: T500 Knocking its head off

Post by Vintageman »

A little extra fuel cools things so no/reduced ping... good trick. Backing off compression loose mid range power. Backing off timing same thing. I am not sure why with all stock parts compression would be too high compression. And, It is already low from Suz as is. But if that was the case, runs well albeit.

Did you look into the barrel of your needle jets? If I had only one point to offer it needle jets must be pristine. You can cross the 188 to 19(?) series. If surface is just starting to be rough inside where it meters you run lean... a lot of corrosion on surface may run be rich but won't atomize well either so runs rough.

Just another point, I know argo1974 said late model cyls have less ex height. The few sets I have checked not the case . Only difference is the intake port (lower by ~2.5mm if I recall and more timing, which is huge how it runs... no Aluminum divider either... ).

I think +/- 1mm is probably production tolerance (didn't see that either) But, I have only sampled few sets of each ... not enough to say definitively. Back when I was real curious what the difference that was my conclusion of my investigation. Could find nothing published from suz on later specs I run early cycls on a late setup. Just recently widened Ex about 4mm overall left height alone... gain +500 RPM top and goes there easy... no loss of mid range.

The T500 pings easy is my finding, if not spot on fuel/air ratios especially lean side. I had suffered for a while too. As tuned, I am getting low 40s mpg (USA Gallon) not trying so me thinks not too rich now ( I was in the mid 30s at one point). I hate poor mpg, with small fuel tanks and gas station too far apart where I am.

Glad you are enjoying it!
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argo1974
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Re: T500 Knocking its head off

Post by argo1974 »

I have around 20 sets of T/GT500 cylinders on the shelf.
Exhaust height on the early ones is around 40mm, while late ones come with 40.9-41.5mm.
1x T500 Cobra (1968)
4x T500K (1973)
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Re: T500 Knocking its head off

Post by Vintageman »

argo1974.

I think you and I had this difference back when. You inspired me to go buy some extra sets. Are you in Europe and me in USA? I agree I didn't have enough samples to say, but what I had I did not see any diff . The big diff was intake. If you measured several sets I am sure you saw what you did.

What I would tell anyone with late setup, thinks their bike is a short on top end/breadth, just get the early cylinder and that alone you will feel difference: compare port dimensions

When I ran the late sets on my 1975 T500 tune to factory specs/exhaust I never pinged once all jets were new and proper. Even when running jemoco chambers (did have to change jetting a little richer). The T500 will ping and when it does it is very obvious and ugly.

My point for this post maybe is to ensure proper AFR and that should fix pinging vs reducing compression/timing vs nominal specs. A lot of 1973 -1977 T/GT500 sold. As street rider I just resist anything that takes away midrange power. If reducing ratio i what fixes it and runs well that is awesome.

I just looks at T500 (or at least what is called out today) parts and same piston and head called out for both years. maybe .9 - 1.5 mm was not enough to male them change anything

I recently put 1979 RD400 Daytona head on my 77 rd400 . If I recall the exhaust height is published at 3mm higher on Daytona. I did check them and indeed the difference was as stated.

The Daytona piston from Yamaha is different and has noticeably less dome height. The heads have little more CCs on Daytona...s owas stated... the Daytona gasket is thicker . I bought the Daytona pistons only when doing swap, left the 77 slightly higher compression Heads/head gasket. I think both the rd400 and T500 were a few points short of 7:0 Compression (6.5 and 6.6 ?) so low to start.

Have many miles on RD now, still run 87 Octane (have no choice, gas station have one hose and topping off your tank you will never get much of the higher octane full if person ahead bought the lower), factory timing... this is another mod I highly recommend... Oh, the Daytona Ex was 3 mm wider too or something like that. If you look Yam did widen cast liner and first part of aluminum casting but not very far way down exhaust port passage. Remove a little more of Aluminum casting 20%-40% of the way down the passage looks to be the correct things to do to enjoy the extra width fully. To me the peak RPM is the same, I just have much more mid range power and fronts ends gets light when accelerating more so now. The 77 RD stock lacked the mid-range IMO and I understand why the Daytona was down to improve it as a street bike. Much more enjoyable to ride now.
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77 Yamaha RD400 (Daytona Cyls),
Vintageman
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Re: T500 Knocking its head off

Post by Vintageman »

argo1974.

I think you and I had this difference back when. You inspired me to go buy some extra sets. Are you in Europe? I am in USA? I agree I didn't have enough samples to say, but what I had I did not see any diff on Ex. The big diff was intake. If you measured several sets I am sure you saw what you did.

What I would tell anyone with late setup that thinks their bike is a short on top end/breadth, just get the early cylinders and that alone you will feel difference: compare port dimensions if you do.

When I ran the late sets on my 1975 T500, tuned to factory specs/exhaust, I never pinged, once all jets were new and proper. Even when running Jemoco chambers (did have to change jetting a little richer due to pinging). The T500 will ping and when it does it is very obvious and ugly.

My point for this post maybe is to ensure proper Air to Fuel Ratio may fix pinging vs reducing compression/ retarding timing vs nominal specs. A lot of 1973 -1977 T/GT500 sold. As street rider I just resist anything that takes away mid-range power. If reducing compression ratio is what fixed it and runs well then awesome.

I just looked at T500 (or at least what is called out today via partzilla) parts and same piston and head called out for both early and late. maybe up to 1.5 mm was not enough to make them change anything.

I recently put 1979 RD400 Daytona head on my 77 rd400 . If I recall the exhaust height is published at 3 mm higher on Daytona. I did check them and indeed the difference was as stated.

he Daytona piston from Yamaha is different part # and has noticeably less dome height. The heads have little more CCs on Daytona (so others have said)... the Daytona gasket is thicker . I bought the Daytona pistons and gasket when doing swap, left the 77 Heads. I think both the rd400 and T500 were low compression to start (~6.6:1 ?).

Have many miles on RD now, still run 87 Octane (have no choice, gas station's have one hose and topping off your tank you will never get much of the higher octane fuel, if person ahead bought the lower octane), factory timing and usually a degree or so more advanced for me and cover wear tolerance. This Daytona mod is another I highly recommend... Oh, the Daytona Ex was 3 mm wider too or something like that. If you look, Yam did widen cast liner but only the very first part of aluminum casting and, not very far down exhaust port passage a there is a bottle neck. Remove a little more of Aluminum casting between 20%-40% of the way down and the passage looks correct for flow to enjoy the extra width. To me the peak RPM is the same, I just have much more mid range power and fronts ends gets light when accelerating more so now. The 77 RD stock lacked ta strong mid-range IMO and I understand why the Daytona porting was down to improve it as a street bike.
Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
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74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400 (Daytona Cyls),
Skaal-tel
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Re: T500 Knocking its head off

Post by Skaal-tel »

My machine is suffering from the same symptoms, but is 1.5mm overbored AND using pod filters. I've gone up a few jet sizes and just about have it right but just as you say -- good when cold and then when warm or fairly high rpm, part throttle, pinging.

I'll have to see if I can find some thicker gaskets myself, I suppose
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