Carb swap TS 250 Supa 5

[Anonymous]

Hi All

I’m curious to know if anyone here has swapped out the standard carb for an SU ?

If so what effect did it have?

David

[‘AAA Dummy]

I considered swapping out the original carb due to poor starting, lumpy idle and constant stalling at light and junctions. On advice from Phil Speakman at The MZ Shop I dropped the idea and changed the regulator instead. Transformed the running. After about 6 months the bike started to be difficult to start especially when warm. I rebuilt the original carb with new springs, choke plug, float, jets and most importantly the gasket that disintegrated when I dismantled it. Might be worth rebuilding the existing carb. It starts a lot better and warm starting issue has gone away, plus now gained about 10 mph top end with a rebuilt carb. Plus the throttle now closes faster with a new spring where it was a bit slow to close before. Probably cost less than £20 in parts and about an hour to complete. I would have changed the throttle needle as well if I could have found one for sale. Hope this helps.

[Malcolm Thomason]

I remember reading about an SU carb swap in an early MZ Rider a long time ago.
Don’t know how successful it was but from experience with my 350 Jawa I would recommend a Mikuni VM. Brilliant carb and easy to swap if you can use a lathe.
Most MZcarbs must be getting to the worn-out stage by now.

[Michael Brownhill]

Hello Malcolm,
I have considered changing the standard BVF on my TS250 Supa 5.
Do you know if the Mikunu VM improve the very annoying shunting on the over run on the TS250 ?
If so , where can I purchase the Mikuni VM ?
Thanks
Mike Brownhill.

[Malcolm Thomason]

Mike,
Motocarb of Liverpool sell the carbs and include a selection of jets. If he has supplied one for an MZ he will probably know jet sizes. My Jawa was the first so the jet sizes were a bit of a guess but it worked out just fine.
I always suspected that the shunting on over-run was a mixture of a weak ignition system and having the carb stop too high.
I fitted an ETZ alternator into an ES250 and the tick-over/starting and general running were much improved. I also had a supa5 with a power dynamo ignition and that didn’t hunt on over-run. The ETZ alternator was cheaper as I had one and didi my own machining but the power dynamo set-up is very good, probably around £300 now though.
Motocarb number is 0151 924 5383 and the boss is Steve.
Hope that helps.
Malcolm.

[Ger Duhig]

Hi Lads,
Just removed a Mikuni VM off my Jawa 350(Model 634)as the previous owner had it fitted.
I was getting 42mpg.
I fitted the standard Jikov Carb as I have always done and I am now getting 53mpg with no difference in power or top speed.
Just thought I would point this out as this was my experience with the Mikuni.
Regards,
Ger

[Malcolm Thomason]

Ger,
Is your Jikov the square float chamber or the old side float chamber?
mine was the older one on a 632(I think! Jawa model numbers defeat me) and I could not get it to pull. I had a square float carb which I tried but could not get the float to control the fuel level. When running it felt powerful and smooth but I decided in the end to spend my way out of trouble. I certainly got more than 42mpg. The down side was getting the filter housing to match up with the Mikuni!
Cheers,
Malcolm.

[Ger Duhig]

Hi Malcolm, Sorry for the late reply. The Jikov was the older type side float chamber as is correct for my 1976 634 model.My friend used a plastic domestic 1 1/2″ elbow with a piece of 1 1/2″ pipe glued into it and a K&N filter attached to it inside the airbox. He made the outlet of the airbox bigger and pushed the other end of the elbow through and used a carb rubber to go from the elbow to the Mikuni carb. I have the Jikov hooked to the K&N filter now. It runs really well.

[Malcolm Thomason]

Thanks Gerr.
I’m looking for a VM34 to put on my GN400 as the Cv carb is getting a bit long in the tooth now. New ones are a bit pricy!
Ride safe,
Malcolm.

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