Carburetor size
-
Hi all
Some help please.
I have researched the threads ,but still a bit stumped.
Can someone tell me what size the factory carburetor is.
I'm trying to get a project bike running,I suspect the carb is way too big.
It's a mikuni TM slide valve carb.
The intake bore measures 34 mm
The air cleaner side 60 mm.
The bike did actually run , although poorly,it was ok at wide open throttle.
I did some work to the wiring,(stripped out everything except the power to the cdi and coil ,it's on a kill switch)
It won't start now ,there is spark.
I did bend the needle by accident when I re-assembled the carb ,so suspect that's not helping ( I straightened it as best I could).
I'm looking at the cheap aftermarket carbs on the internet,any suggestions.
Many thanks to all. -
@theo5042 The stock carb for the DTR is a round slide Mikuni VM26SS for the first 1988 bikes, then in 1989 it was changed to a Mikuni TM28SS flat slide. This was part of a pretty extensive redesign of the DTR after only one year of being on sale (including different bore and stroke, electrics, fork oil level etc.), I'm not sure why this was done as '88 and '89> bikes look identical. I suspect it may have had something to do with Suzuki releasing the TS125R in 1989 which looked to do everything a little bit better than the DTR (at least on paper).
Either way it sounds like a previous owner has shoehorned a carb off a 125cc MX bike into your DTR. Lots of people try and turn thier DTR into a YZ125 by doing this kind of thing but in reality the two bikes are too different to achieve this and you're better off just enjoying the DTR for what it is, after all YZ125 engine life is measured in hours rather than thousands of miles. It will potentially still run well at high revs after some setting up, but you'll lose low-end performance as bolting on a massive carb tends to reduce the "signal" when the ascending piston creates a depression in the crankcase and opens the reed valve (this is what causes the fuel to rise through the jets and into the carb venturi during the induction phase).
It might cost you more but I'd try and get hold of an OEM DTR carb if you can, if you get a good one without a seized low speed mixture screw and pretty standard jetting the bike will probably run better just by bolting it on. Put your VIN number into Yamaha France parts lookup and find out what carb your bike should have, it translates quite well if you do this on a PC:
https://www.yamaha-motor.eu/fr/fr/service-maintenance/parts-catalogue/
-
@HOTSHOT-III Well said, covered everything I would have said and a lot more!
I just want to reiterate the importance of obtaining a quality OEM carb, especially if you want it to run correctly. These cheap pattern carbs are not worth the hassle and you can pick up many alternative genuine carburettors.
I run the Yamaha TZR R 4DL carburettor, which ran the 3MB cylinder, this is a flat slide 32mm. Albeit jetting is vastly different and my bike is heavily modified. That said it runs a treat for me.
If sourcing a Mikuni proves challenging, then obtaining a Dellorto 28mm shouldn't be a problem. The VHST is probably a good alternative, these are commonly found on many other bikes, such as the very latest Aprilia RS 125s(2007-2011). The nice thing about this carburettor is that they can be had cheaply and it's well supported in terms of jets etc.
Sounds to me like you have done quite a bit of work to the bike. If you're stripping the loom etc then you need to make sure that this hasn't affected the running of the motorcycle. This often trips people up, where they have modified the loom, incorrectly bypassing things which thr CDI needs. This can be a bit of a headache to resolve on a forum since often the devil is in the detail and the user omits key information.
-
Ps
The YVPS has been removed by previous owner .
Thanks for all the helpful replies .
I will look for a decent carb.
I will also do a compression test.
I have a feeling that something I did too the wiring is also causing an issue, although there seems to be good spark.
