Supa5 electric start

[george123]

If ever a bike needed an electric start my supa 5 does.
Owned the bike now for about 9months..bought as a non-runner.
Bike will rarely start on kickstart,usually have to bumpstart in 2nd
Even then will only start 50% of the time.
Have checked everything,timing 2.5mm BTDC checked with dial gauge and degree wheel,
new points ,different carb,checked throttle and choke cables,different coil,different plugs
wired coil direct to battery and points with new wiring,not thru ignition switch
When bike fails to start when check plug..appears very slightly wet
Have checked Petroil flow from tank ok,using 50 to 1 mix..mixed in separate container ,changed petroil.
Compression check on bike returns 75psi..head is torqued to 26Nm,when try to torque above this
threads start to strip on studs,squish value ok
Have checked different Mz forums..can’t find any info for compression figures.
I suspect low compression is causing problem..but what is a good compression figure on a 1975 Mz ts250/5
Any help much appreciated
Thanks
Willie2sheds

[Blurredman]

I'm not entirely sure what the compression reading should be on your bike, sorry.

But how does it run when it is running and warm?

[Puffs]

Sounds like you made many right moves, but your compression of 75psi = 5.2bar is very low. On my ETZ251, which is pretty much the same engine, I measured a cold/dry value of 8.75bar, and a warm value of 9.80bar, with a 0.96mm squish (CR=11:1). Check piston-to-bore clearance & rings I guess. And rather than over-tightening those studs, consider using a bit of silicone sealant on the head (though that's normally not required). Check head & barrel for straightness if you suspect it leaks there.

An engine like that needs a good adiabatic compression to start igniting the mixture. When it runs with low compression, it might run fair, and even good at higher revs, because then it all goes quickly and there is no time for it to leak.

[george123]

Greetings from Belfast
Thanks for replies,bike runs ok when eventually starts,I will try using silicon on head and see
If this improves compression.If no joy will check piston rings and barrel.After reading up a bit on the net
see people use leak down tests to check for leaks
I don’t want to have to get parts made up to block inlet and exhaust to do this,.was wondering if
I used a compression test and kept piston at TDC and then with a water pistol full of washing up liquid solution
Went searching for leaks at all usual suspect joints…suspect compression will not stay in cylinder for
Long..but with repeated tests might find leak.

Cheers
Willie2sheds

[Puffs]

Oh right, you mean measure how the crankcase seals. That's not likely the cause for your low compression pressure of just 75psi. Put a big cork in the exhaust & a flange on the intake, with a connection on that flange, for sucking & a pressure gauge. Suck, close & see what the pressure does. Lots of hassle, never done it & not my first thing to check for in your case.

The part below the piston can leak on the CS seals, the separation between the case halves, the cylinder base gasket, and the intake manifold gasket, but none of that reduces the amount of air entering the combustion chamber. You measure the compression with the throttle fully open: that gives a rather big hole (ID30=mm?), which makes any other leak insignificant. Low compression pressure --> either head gasket not sealing (or the connection in the plug hole), or blow-by past the piston. For leaks between the head & barrel you should see traces (looking like exhaust gasses escaping), and you would hear that too, but if I had bought a non-runner 2T the first thing to do was pull the barrel off, certainly after an observed low compression.

I don't quite understand the bit on the washing-up liquid, but it doesn't sound attractive. I'd just pull the barrel off, it's easy.

[george123]

Recheck.

I previously measured my squish at 0.8mm
On rechecking Haynes manual see squish should be between 1.4 to .1.6 mm
Took barrel off,two head gaskets fitted,each 0.2mm.
Piston,barrel and rings appear ok,
Measured piston crown at 67.5
Barrel measuring at top of bore 68.7mm
No lip on barrel
Barrel has +1 marking
Piston has 6,7 marking on top
Unfortunately stripped thread on one of head studs when
Dismantling,time to order up some parts
Headstuds,head gaskets and base gasket.
Wondering if low squish value is affecting bike starting
I Don’t think it would affect compression if anything
Would low squish increase compression.
Two head gaskets are worrying..is this what is causing my low compression,see can get head gasket in 4mm size,will try this and some
Silicon gasket to get squish within limits.
Unfortunately can upload photos.

Willie2sheds

[george123]

Correction meant to say in previous post two head gaskets fitted,each 2mm thickness,
Gaskets sitting on top of each other…no other gasket or glue on head,barrel base gasket was in good order.
Ts250/1 still on 6v electrics standard points with vellerman k2543 kit to assist ignition
Original Bvf carb fitted,standard exhaust.

[Puffs]

Hi, some comments.

Mine is an ETZ251, yours is a TS251, I do not have the Haynes manual for yours, but you mentioning those squish numbers (1.4 to .1.6 mm) made me look it up in the original MZ manual, where I find:

That's the same 0.9 - 1.2mm as is mentioned for the 250cc ETZ's, maybe Haynes is in error here? The pic above pertains to the TS250/1, which is different from the 4-gear TS250. (Btw, you upload pics via the 'Upload attachment' tab at the bottom.)

I'm not sure head gaskets in 2.0mm thickness are sold, but you could make them yourself. A thickness of 0.2mm is common, and yes, if you need 0.4mm for the right squish, you can fit 2 on top of each other. There may also be 0.40mm thick gaskets, I don't know. I think 0.50mm is the thickest available.

A piston should always be measured at the skirt. Because of thermal expansion, the crest always expands more in use, and is therefore a bit smaller (pistons are made to be tapered). Again the manual shows how to measure:

See the maximum clearance they specify for the TS250/1. For the ETZ this is increased to 0.10mm, and honestly, you could go a little higher IMO. But it is important to mention these clearances pertain to original pistons, Megu, HAL, KAL, in K20 alloy. Aftermarket pistons may need more clearance, but if it gets in excess of 0.15mm surely work is required.

I guess crown = crest, and I just measured an old Megu of mine, where the crest is about 0.13mm smaller than the skirt.

It seems you made a typo, or your piston has in excess of 1mm clearance??? The standard bore is 69mm, and 'no lip' is good.
Note there is also a recommended way to measure a cylinder (and the MZ way is very much the common standard way).

Well, of course the squish size does influence the compression. While the idea behind squish (and the shape of the combustion chamber inside the head) is to enhance turbulence in the mixture just before it ignites (to enhance combustion), obviously if you increase the squish by a height of s mm, in a D mm bore, you increase the size of the combustion chamber by s*¼πD². So for a 69mm bore that's 3.74cc per mm, while under normal conditions the volume of the combustion chamber is quoted at 27cc. So if you have 0.5mm too much squish, you have increased the CV to about 29cc, hence reduce compression, and loose a bit of the swirl effects; but it should still run I guess. Nevertheless, I'd go by the book on this.

I have no experience with a 'vellerman k2543 kit to assist ignition', but I don't think it is required, and it might contribute to your problems? My ignition is bog standard/original points, and that works fine. In bikes like this, I think millions of people have used a standard ignition for decades, maybe try it without that vellerman gizmo? What is it supposed to do?

[dave47]

My Haynes manual makes no mention of measuring squish but merely says "fit a new gasket. Do not use jointing compound".
The Mz manual says squish of 1.2 - 1.6 mm for the TS250 4-speed, and doesn't specify anything different for the Supa5.
Yes Puffs, the ETZ has a higher compression ratio, hence 0.9 - 1.2 mm.

[dave47]

I agree with Puffs that it might be a good idea to temporarily remove the Vellerman unit and revert to the original ignition to see if it is the problem. Apparently the Vellerman retains the original points and coil so it would only involve replacing the small capacitor and its bracket which are usually removed when fitting units of this type.

[george123]

Thanks for replies,rechecked Haynes manual page 109 in section for later ts250/1 and other models
says 1.2 to 1.6mm for squish and to use shims of 0.2mm or 0.4mm to achieve this.
Apologies for my previous typos.Have ordered 0.4 shims /head gaskets,I was hoping
To fit these and also use a copper gasket spray with gaskets to get a better seal
Between cylinder and head..will this cause further problems.?
I have used the velleman k2543 transistor ignition before on an etz250 20yrs ago,I found bike ran better on tickover
And different throttle openings,the diy k2543 kit can be used on 6v or 12v bikes.it uses points as a switch
Less current flowing less wear on points,points condensor left disconnected.
I have tried my ts250/1 on points and with the k2543,bike still hard to start on either,
if anything bike appears to run better on the k2543..better tickover.
..when it eventually starts..have noticed I get a stronger spark when using
The k2543..the kit I have fitted was bought on eBay for around £ 12,it is do it yourself
electronic components and printed circuit board,takes about 30mins to assemble
With soldering iron,good instructions supplied.

[dave47]

You were ahead of me on the Vellerman unit. I assumed you had just inherited it with the bike.
My Haynes manual is obviously a different edition to yours - 1979. The Supa5 appendix only covers the gearbox, forks and lights. A revised edition was badly needed, but I didn't know Haynes had actually done it.
I can't make any other suggestions about the starting problem, apart from what you are doing. Good luck.

[Blurredman]

I wouldn't worry about multiple head gaskets. I have 4 or 5 on my etz250>298cc piston. No leakages there. All are standard aluminium gaskets that I had just cut the inside bore larger to accomodate larger piston.

[george123]

Supa5 sorted I think?
Fitted new stud and 0.4mm head gasket,smeared both sides of head gasket
With Halfords copper silicon gasket,also put more silicon gasket on base
torqued heat nuts to 26Nm in diagonal sequence
When I did compression test ..first measured 75psi after about 4 kicks
I kept on kicking (8kicks) and compression went up to 100 psi.
Tried starting bike in usual Mz manner..two kicks choke on ignition off
Nothing..not even a kickback.
For some reason I kept on kicking over..6kicks with choke off..still nothing
Then choke on full and 6 kicks later ..engine sprang into life
Couldn’t believe it..ran engine for about 15mins.had to keep tickover
Over 2k to stop cutting out.
Stopped engine,restarted ok after 2 kicks with no choke.
Waited until engine got cold then started after 2 kicks usual Mz start routine
Ran engine again 15mins..tried adjustment of air screw..didn’t seem to make any difference.
Today I have started bike on kickstart 6 times with no more than two kicks..each time,
I think using new 0.4mm head gasket with sealant has sorted starting problem.
With engine running and hot suspect gasket glue has hardened and given better seal.
Thanks again for advice given.
Willie2sheds