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T500 Carb body differences

Posted: Thu Jan 01, 2015 10:15 am
by akendall1966
Happy New Year All,

(not sure if this would sit better in restorations?)

I am on the hunt for a RH T500 carb body, but the one off my bike '70 Mk3 seems a little different. Its a 32mm & square float bowl, but the body casting has some differences at the places dotted red. There is a missing boss at the on the slide tube at the start of the logo, and a small upstand which I assume stops you pushing the carb too far into the inlet also missing. While not a big issue other than cosmetic differences. When I look at available substitutes on E...y I can't see the cut out that stops the slide top rotating on those. So I have some concerns about interchangeability of the other bits.

Will my parts swap onto another body OK, even with these differences?

Image

Of course I could get a whole carb, but would this results in a mismatched pair?

Carb with extras, courtesy of Titan Performance.
ImageTitan Performance carb clips by Titan Performance, on Flickr

Re: T500 Carb body differences

Posted: Mon Jan 05, 2015 9:21 am
by argo1974
The VM32SC carbs on T500 are different depending of the production year.
Early carbs have internal float bowl vents while later types from 73" upwards came with external vents. Later type carbs won't flood the crankcase in case of sunken float and/or leaky needle valve.
Easiest way to check carb type, if there is a brass nipple for vent tube on float bowl -> late type.

EDIT: Swapping the internal parts won't work since the carbs are from different worlds.

Re: T500 Carb body differences

Posted: Mon Jan 05, 2015 9:41 am
by akendall1966
Thanks - mine are the earlier type then (as you would expect on the a '70 bike).

Guess I need to hang on for the right body to turn up, or consider a complete later type or a pair.

Re: T500 Carb body differences

Posted: Tue Jan 06, 2015 1:12 pm
by argo1974
Depends, what type cylinders/intake spigots your bikes has. Early carbs are more dependant on intake vacuum since that particular vacuum controls also fuel pressure in carbs jets. So one more variable to consider. Later type carbs just maintain atmospheric pressure in float bowl.
To keep life easier, I won't swap the carbs from late to early or vice versa.

Re: T500 Carb body differences

Posted: Tue Jan 06, 2015 1:24 pm
by akendall1966
AFAIK it's all original 1970 mk3 certainly little evidence it has been apart before I started on it.

So I will take your advice and keep the carbs to correct for this evolution of a T500.

Re: T500 Carb body differences

Posted: Tue Jan 06, 2015 2:46 pm
by jabcb
argo1974 wrote: Early carbs have internal float bowl vents while later types from 73" upwards came with external vents. Later type carbs won't flood the crankcase in case of sunken float and/or leaky needle valve.
That might explain my current saga.

Had a sunken float on my 75 T500 a few years ago. I remember seeing gas dripping from a carb.
Replaced the floats & the bike has run just fine since then.

Had a similar problem on my GT250 a few years ago. Gas dripped from the muffler!
Fixed the carb & the bike ran fine for a few years.
But I now have crank seal problems.

Re: T500 Carb body differences

Posted: Wed Jan 07, 2015 12:02 am
by argo1974
I have had sunken float problem on both of my T500J (now sold) and T500K. J model has had its left cylinder crankcase full of fuel while the K just dripped fuel from carb drain hose. BTW, I could limp home on the K around 150 miles without significant problems (I had to fill up twice as much though) while J refused to run on left cylinder while hot due to over rich mixture. On both floats, just one barrel was leaky.