Thought I would post these pictures in the right section as well...anyone know which carb this is besides a Mikuri ?.....cannot seem to find a diagram in the Haynes manual which has the same parts; specially the main nozzle ?....bikes confirmed as being a march 1980 build and 1981 model by Yamaha, but she is wearing an older year model fuel tap ?....any help would be appreicated

is it a 3U500 carb? check the id on the side

Hi there doesn't seem to be any numbers on the carb ? Looking more into it today it does seem to be like the 1980/1981 diagrams found online.... Is it normal to have an older style fuel tap ? Or do you think its been fitted later on ?

my fuel tap is like that on a 1979 mk1 id marking on the carb is quite feint, on a flat square section

Airhead, on 18 Nov 2014 - 8:34 PM, said:

is it a 3U500 carb? check the id on the side

Good call....old age I missed the small numbers lol it does indeed say 3U500....does the main nozzle come out easily ?....I can remove the "O" ring easily but didn't want to damage the nozzle if it was difficult to remove ?...

yes it taps out with a suitable tlat faced punch, only needs a gentle tap downwards if I remember correctly, youll see a locating peg in the bottom flange

heres what they look like

Thanks ever so much, I will have a play today and report back I don't think anything is wrong but whilst I am waiting for the fibre washer to arrive from Yamaha I might as well check this nozzle....tank was full of rust when I got her and bad fuel; PO had ultrasonically v;eaned the carb but I think they only dropped the whole carb in as there was a deposit of gunk in the float bowl....saying that the rest of it was pretty clear....Used a battery charger and some mild steel strip to clear the rust out worked pretty good...and some baking soda lol

Reporting back, so glad it came out as the small holes were well blocked up.....thanks for advice.....will let you know when she is back up and running....

Yuk!

Could you recommend / advise on which grade of oil would suit the DT ?....the book calls for SAE 20W/40 which my local Yamahe dealer doesn't stock, I have plenty of Silkolene Super 4 Semi Synthetic 4 Stroke 10W40 knocking about which goes in my other bikes would this be OK or should I try something else ?.

yeah that'll be fine mate, had it in mine once, all oils are better than they were 30 years ago anyway

Well all my new parts arrived today, typical me fitted them all within 30 minutes....anyway she started 2nd kick but is drinking fuel for some strange reason; even more than my ZX12-R uses lol....cannot really work out why, she isn't running great produces loads of smoke cough couch and has stunk the house out....I am running her as I found her apart from cleaning her carb out I have not altered the needle position or even looked at it....I have set up a syringe as a fuel tank and you can watch the fuel disappear into her and she will empty a large syringe in a matter of seconds .....any advice on what to check would as always be appreciated she will rev in a fashion but I cannot think why she would start so easily if she was being flooded with fuel ?...I tried to do a video but she stops before I can start recording lol...

is the choke off (pushed in) ?

The fuel has to be going somewhere if you dont think its being ignited

Any on floor?

Does it drain out the syringe even if the bikes not running and fuel tap on?

Combustion chamber full of fuel?

Air filter soaked?

No leaks between carb intake and outlet?

that fuel is filling up your engine cases, i'd take out the plug overnight let it evaporate off is the float bowl overflow intact ?

Choke was out to start, she started 2nd kick as mentioned but as I could only put a small amount of fuel in she died, started her again and she rev's sort of half way and dies back when releasing the throttle, my garage is carpeted and there was no fuel anywhere out of the carb, I checked all the jets / overflows when I stripped the carb all looked clear apart from the main nozzle as pointed out above.....just cannot work out why she would draw in so much fuel and still run ?.....how can it fill the cases ? reed valves ?...to be honest I never removed them but will do if you think they might be causing the sudden dropping of fuel ?.

Now back in 81 I had a new MT5 and I could knock the fuel tap off and ride home on what was in the float bowl/pipe am I right in thinking the bike should run for a period of time with fuel in the bowl ?, as she stands as soon as my syringe empties the bike dies within a few seconds; the syringe is connected straight to the carb via 3 inch length of fuel pipe ....

I mentioned the overflow because it is also the vent for the bowl, if this vent is blocked or the pipe attached to it is, then a vacuum is developed in the bowl which literally sucks the fuel from the tank (or syringe) and fills up the engine!

Will pull the carb again and check the overflow and the choke...also whilst at it I will take the reed block out and check them....to be honest didn't think about looking at these when the bike was waiting new parts.........no fuel leaking outside the bike anywhere Neversaydie....will check the fuel dosn't drop when the engine is not running, there is no fuel tap just the syringe and 3' of hose to the carb .....starting to bug me now....saying that bike is a winter project and only had it 6 days, most bolts have been removed/replaced new airfilter, stator gasket, sump plug & gasket, cover screws, rear inner mudguard rubber thingy...horse shoe shape, petcock seal and a few other odds and sods....

Took carb off again and checked everything including float height..21.5mm so spot on, I removed the reed valves which again looked perfect, stuck her back together but she still seems to drink fuel....see video...the syringe was well over half full after filling the bowl, by the time I had started recording it had dropped....

https://www.youtube.com/watch?v=WU2Jp44paHE&feature=youtu.be

I had a thought about the seal at the end of the choke rod....it seems dented slightly so I removed it and added a small thin piece of plastic where it sits then flipped the rubber over and popped it back in...bit like swapping over a tap washer...not tried it yet but would appreciate your thoughts on the video.

it looks like the choke is pulled...(lots of shaft showing?), it sounds like the choke is on too ?