CD150 carb questions

[byakk0]

I've posted my troubles on triumphexp, mainly as duplicating threads among various boards is a pain, but if any of you have been following over there, you know what I've got going on... feel free to read it otherwise
http://www.triumphexp.com/phorum/read.php?8,1296074

Anyway, on to the questions.
but first, the lead up.
It would appear I have CD150SE carbs in which the temperature compensators have been removed.
http://www.triumphexp.com/phile/8/46835/20150611_120539.jpg
Additionally, the bypass-valves have been sealed off. (I've seen pics of other cars with them sealed off, so I haven't been concerned)

Right now the engine idles around 1500-2000. Lifting the piston on the rear carb even 3/32 the engine starts to die. Lifting the piston any amount does nothing to the front carb. As far as I know the two carbs are setup identical, aside from the vacuum advance on the front. Removing and even plugging the vacuum advance has no affect.
butterfly's and shafts have minimal play, nothing alarming.
I rebuilt them years ago (deep cleaned, new gaskets & o-rings, and diaphragms only), but afterward was unable to test them beyond starting my engine for a few seconds here and there. I never did the piston lift test before, so I have no point of comparison.
That said, it seems to run the same way now as it did then, though I don't recall idle speed.

see and hear it running here. (both carbs are disconnected from each other during this run)
https://youtu.be/iCqkgEmWclM

car info, in case it helps:
67 Mk1 GT6, KC1293, Engine code KD92721
From my research it looks to me like these were carbs used on comm# KC50000+, so perhaps that is the reason the temperature compensators have been removed and bypass valves over-ridden.

I drove it for 2 years in this state and it ran fine.

1)what is the purpose of the temp compensators and how will having them affect the carb when the engine is running vs not having them
2)what is the purpose of the bypass valve, and how will having them affect the carb when the engine is running vs not having them.
3)with the vacuum tube to the bypass sealed, it looks to me like the bypass valve is rended non-functional. do I need the bypass valve at all?
4)will running and driving as is, with idle around 1500, affect it at all?

[Pete Lewis]

Hi read thr other posts , pleanty of good advice
temp compensators open a small plunger to let air bypass the throttle plates and speed idle and weaken mixture when very HOT, having them fully closed at normall temp is the only way to set the idle mixture, if they are open you cannot set it right.
if fitted they must be closed at normal temp.
if the temp comps have been removed ( the device with a plastic cover and bi metal operated plunger the ports where it fitted MUST be blocked off or you have a air flow to the back of the throttle and fast idle.

the other 3 screw device was pretty much only fitted to usa spec emmission cars , not used much in the UK  if removed blank off the ports with a fuel proof gasket

lifting the pistons with cleaner off is a waste of time as the cleaner really affects the mixture , best have filters on and use lifting pins if fitted, only raise the pin to just touch the piston and then lift it 2mm max ,
do centralise the jets first

have a look at buckeye triumphs web site brilliant clues and pictures , not the same carb but the basics are the same   http://www.buckeyetriumphs.org/technical/Carbs/CarbsII/CarbsII.htm


use engine oil not cats pee in the dampers,

if the throttle plates have been removed are they replaced the right way round ?? that gives false idle speeds

[byakk0]

Thanks Pete.
The large dished head hex bolt in the side next to the bipass valve is there to plug the to block off the temp compensator then, I presume.
I can try blanking off the bypass valve and see what happens, but I suspect nothing.

I have never removed the throttle plates myself (I presume those are the round brass disk's in the opening), but there is no telling what any of my PO's did.

Been through those buckeye pages recently and they did indeed help.

My next roundof work I plan on pulling the plugs and have a look, and hopefully do a compression test at the same time. If I recall, I did one when I was driving it, 18 or 19 years ago, I think they were all 120 +/- a few.

[Steve AKA vitessesteve]

Quoted from byakk0

1)what is the purpose of the temp compensators and how will having them affect the carb when the engine is running vs not having them
2)what is the purpose of the bypass valve, and how will having them affect the carb when the engine is running vs not having them.
3)with the vacuum tube to the bypass sealed, it looks to me like the bypass valve is rended non-functional. do I need the bypass valve at all?
4)will running and driving as is, with idle around 1500, affect it at all?

I have a Dealer Training Note about carburetors that explains about some of the various bits of Zenith Stromberg carbs such as the temp compensators.  http://vitessesteve.co.uk/Dealer_Training_Notes

[byakk0]

sweet. Thanks Steve!
That said, it looks as if I have the wrong carbs altogether. I have a set of CD150's that need rebuilt. the CDSE are emission carbs for later US spec models.