May 12, 2021 at 2:49 pm #14076Keith WilsonParticipant
Having rebuilt my ts250/1 engine due to big end failure and re installed it where it belongs I now find it will not start.
As far as I know all wiring is correct , 12v v a p system as used on same engine before rebuild.carb has been cleaned spark at plug. I have repeatedly checked plug, plug cap ,fuel,and timing.still not a cough from the engine! Any help would be appreciated.
May 12, 2021 at 10:04 pm #14077James SuttieParticipant
Hi Keith, I’m not a world expert on MZs but I do know, from experience, that it’s easy to get blindsided by the obvious when you’ve spent a lot of time on a project.
Whereabouts are you, can you ask another member to come and look through the bike? If you’re anywhere near Devon, I volunteer myself!
May 14, 2021 at 9:37 pm #14084AndrewParticipant
Hi Keith, I just wondered if you had checked whether or not the plug gets wetted with fuel as it should do if the fuel is getting through but it’s not firing up?
If the plug is dry, try putting a few mls of petrol down the plug hole, refit the plug and try kicking it again.
If it fires into life just for a few seconds then it proves you have a spark and at more or less the right timing and shows that it’s likely to be a carb problem.
If the plug is really wet, is the carb flooding? If you have had the carb to bits to clean it, have you lost/misplaced the little rubber disk off the end of the choke plunger so fuel runs in all the time?
I would be interested to know the answer as my TS250/1 motor is also in bits at the moment for a new big-end!!
July 10, 2021 at 8:27 pm #14241Chris WilliamsParticipant
I have a similar problem. I’m on a brand new carb, an OM for the MZ251 B30N1 and I have checked everything twice over but no sign of life. Not a splutter! The spark plug is dry and so I think it must be the carb. I’ve also disconnected the inlet stub from carb to combustion chamber and, kicking it over, the piston slides nicely up and down and there is compression, so no problem at that end. I noticed on disassembling the choke from the carb body that the rubber bung had dislodged from the end of the plunger as mentioned by Andrew (is there a way to stop this happening? – it is a new carb btw). I wait with interest to hear others’ views.
July 11, 2021 at 10:16 am #14242AndrewParticipant
The rubber disk is just a push fit in the recess in the end of the plunger so should not easily drop out, especially on a new carb – this makes me wonder about the ‘quality’ of your new carb and whether this is really the problem!
Dry the plunger and disk and use a tiny drop of superglue perhaps to hold it in place.
When the bike is running (if you get that far!) and the choke is in the off position, the plunger with its rubber disk is spring loaded up against the choke fuel feed opening so it can’t just drop out.
You say the spark plug is dry, but if the choke plunger disk is displaced or missing then the carb would flood constantly and there would be fuel everywhere so that is probably not your main problem.
There are reports about the variable quality of aftermarket copies, some report no problems and some report that they just put them in the bin.
I bought a new MZA carb (with the BVF logo cast in the body) which was more expensive than some of the ‘chinese copies’ and have not had any problems (so far) but bear in mind that back in the day, even when new, the original carbs were fairly crude and wear quickly.
Did your bike work ok before you fitted the new carb?
Check fuel is getting from the tank to the carb?
Check fuel actually getting into the float bowl – flip the clip off?
Try a few mls of fuel down the plug hole and see if you get at least a splutter.
Let me know!
July 16, 2021 at 7:22 am #14250Rob LaneParticipant
Foresure – Let us know. Almost in the same boat myself. As mentioned fitted a new Mikuni to my Sup5. It does start – eventually (I was hoping for first kick) and as you say the plug never gets wet. I have even tilted the carb over to favour the level in the enrichment chamber, might have helped a bit. Now a a questo of my own, tinkering with the air/fuel screw yesterday afternoon. It was set about 1-1/2 turns out, I found that it started running smoother and happier with it screwed home, right in !!! What does that mean oh wise ones. Remember its a Mikuni.
July 16, 2021 at 7:59 am #14251Derek ReynoldsParticipant
Depending on whether your Mikuni air/fuel screw adjusts the air, or the fuel at tickover, it will show you either have too much fuel at tickover, or too much air. If the latter, you have an air leak somewhere.
My familarity with Mikunis lapsed after I sold my last CX500 MANY Moons ago! So I will bow out to greater knowledge.
July 16, 2021 at 1:01 pm #14252Rob LaneParticipant
Thanks Derek. Its so easy to get confused over the terminology. In the Mikuni case I think I’m right in saying it is a fuel metering screw. So when it is screwed right in it should shut the fuel off which is now the case but it keeps running so is getting fuel by another route right. The carb came with spare, different sized spare jets. Time to try one. Bigger or smaller. Will be a pure guess on my part. My old brain can’t handle the logic approach.
I vill be back !
July 16, 2021 at 5:50 pm #14253Chris WilliamsParticipant
Hi again everyone,
I think I may have fuel to the plug now but spark is very weak, so no combustion! and my faith in the existing electrical ignition is severely lacking. I am thinking of substituting all the major ignition parts with an electronic system as I don’t trust myself to make the points system work even with completely new parts, which all seem quite costly anyway. Is this the way to go? I would welcome any views on the tezet system. Btw this has gone up in price on eBay recently, although I believe you can buy direct.
September 16, 2021 at 11:11 am #14537Matt JarrettParticipant
Belated reply, but I found this guy (SofCHJanek)in Poland via his YouTube videos. Bought his system via google translate, money transfer (£40!). Dead easy to fit. Bike used more or less daily for last 8 years since fitting. Only grumpy if battery low. Regular use/charging keeps it all ticking over.
Someone was importing them & charging a healthy mark up, but google translate worked for me.
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