Acceleration stops at 50mph - max speed=50mph

[Forkie]

Fuel issues aside - have you had this 'maxed out at 50' SINCE fitting the new ' Champions'.....as i read it, thats where the issue lies....

[Matrix]

i would not know for sure as i had fitted them before the replacement of the fuel pump.
hmmm I did not think that i could have faulty spark plugs.
I will revert back to the previous spark plugs on Sunday and do a test drive.
Who knows...maybe the issue is with the spark plugs as you say. It is definitely worth a try!

[Forkie]

Well its worth a shot, at least that can be ruled out. Try fitting an older set if possible just to try. 'New' parts are nowhere near the same quality as earlier parts. As an example my indie guy was telling me a few weeks ago he fitted a new set of NGKs to a customer's car as part of a service - ran like a bag of nails. Changed the new ones back to the old ones, ran fine... on the phone to his supplier....
I was having a play with mine a few weeks ago, i run a blue rotor arm, and have a spare black one as a back up. Cannot remember if i have even checked the black rotor is ok, so i swapped them over to try. That introduced an uneven idling pattern for some reason!! Swapped back to the blue one, all good again!!!

[Matrix]

I reverted back to the old plugs, and the car maxed at 50mph after a 2 mile test. Then i revert back to the old diaphragm of the EGS, the same behavior after a second 2 mile test.
However this trial proved to be too much for the car, and the engine started stalling from 10 mph and unable to accelerate and maintain its idling.
Every single time I start the engine, it dies after several seconds.
I noticed that the back carb leaks petrol.
I managed to return to my garage with a lot of smoke and serious emission of gas odor and full of agony as fire was very possible to start with all this leak.
The car struggled to run with a speed of 10 mph back to the garage. . .
I had three fire extinguishers in the cabin and moved with the bonnet unlocked in order to stop a possible fire as fast as possible.

My mechanic told me that this may be a problem with carb valves, or the floating unit of the carb, and that junk may have blocked the valve.
I have installed a fuel filter. I also have delivered to him a full set a kit for Stromberg-Zenith service parts which included even new valves.

I opened the rear carb and verified that the needle is in its place.
Is it possible that the new pump i installed, the Powerunit MK2 style pump is malfunctioning and flooding my carbs ?
But if it was the pressure of the pump, then why the issue did not happen the day i used it to return home? (10 mile trip)

Attached is the carb kit that was used for the carbs (were all parts used? - unknown)
and a photo of the new Powerunit fuel pump i installed in place of my old glass AC Delco one.

I am not pleased at all after this outcome. I have spent much money, time and my carbs (assuming that fuel pump is ok) are not working as expected.

UPDATE : increased slightly the idling speed- engine now does not die after several seconds.
Released the screw of the choke cable - although i did not see that the cable was locked in active position.
The engine maintains idling. The car moves normally. i have tested up to 30 mph. i have tested it for 10 blocks without
experiencing the problems i had on Sunday.
Cannot explain how this happened. Maybe i pushed it too much on Sunday at 50mph and the carb flooded ?
So on Monday fuel was vaporized and it could move normally as if nothing happened?
Perhaps i will manage to get her to the mechanic with its own power using very low speeds.

[Matrix]

Update:

It cannot maintain its idling so i increased the rpm via the screw.
Now the symptoms are:
rough idle with much vibration in the engine
when i try to move it hesitates like its trying to climb a steep hill with 2nd gear, but after 2-3 meters it pushes forward with momentum and then
it behaves like it does not have issue.

However i have not - and will not - test it at speeds more than 30mph. Last time i did that i had black smoke and a leaking carb.
I am thinking now what to do with it in this situation:
call a transport service to carry her, or try to go the mechanic with its own power ?
After several meters inside the garage, and the rear carb is not leaking.
I am very eager to see what is causing this mess.

[Forkie]

Sounds like you need to 'start at the start' - strip everything off from the head - manifold wise - check/ renew all gaskets as required and back track right through everything , including carbs, to the fuel lines etc. These engines are fairly basic - although having said that i have had my own issues! - something sounds really amiss somewhere - not a great help i know but i do think that is a starting block - as in start from the start, and ignore everything beforehand.

[johnfrancis898]

Have you checked the valve rocker shaft and rocker/valve clearances? I had a lack of power problem recently and it was a broken rocker. Quite a few of the oilways were blocked. A new rocker and a strip down and cleaning the rocker shaft and rocker oilways sorted the problem. Checking fuel and ignition problems as well but looks like you have had a good go there. Good Luck.

[Charles H]

If you still have a leaky carb, which could explain the black smoke and lack of power but not white plugs, it could be the carb float valves either not set correctly or the new valves are not seating properly, Do you have the original valves still? I have found that the originals tend to be more reliable. If you still have them, try swapping back to see if they are the problem.

[johnnydog]

I have had problems with Strombergs on all my earlier Triumphs - mainly due to periods of inactivity. On each of them, it was the back carb that was leaking. Rather than the actual carb leaking, the cause was the float/ needle valve pin not seating properly and allowing the rear (lowest) float bowl to fill up and then the excess fuel has to find a way out - generally ending up in the air filter box and then dripping onto the offside chassis rail. It has also occurred after a carb strip down where replacement float valves have been fitted - for some reason new valves are much more prone to this than originals. In my case, when this happened, besides the strong smell of fuel, the car wouldn't idle, and if you did get it moving then it used to stall on coming to a stop, be lacking in power and feel like it was only running on less than the 6 cylinders. Replacing the float valves with good used has always sorted the problem as Charles has confirmed.
I've also tried Viton tipped but they were the wrong profile for my carbs, as they fouled the carb body, so I stuck with original known good used valves. Ideally replacements should be marked 150 on one of the flats - there are also 175 versions for CD175 Strombergs, but they do look identical.
It is also important that the aluminium washer below the valve is fitted (there are different thickness) and the tab on the float measured against the height of the body of the float chamber bent to give the correct float height (18mm comes to mind although CW recommends 19mm to slightly lower the fuel level in each float bowl).
I bet this is your issue based on my past experiences of similar symptoms / issues.

[Matrix]

Thank you Charles & Johnnydog for the detailed info.
The difference in quality of the valves explains why my father never had to deal with carb issues. Unfortunately i do not recall keeping the original valves which is a shame.
I suppose it is impossible to find original valves.
I have ordered a set of valves to have them replaced.
I am still not sure if i would make the replacement - never have done such a task - and risk
immobilizing the car. On the other hand i am not sure if it will make it to the mechanic with its own power assuming i will be very conservative and move at low speeds.

The smell of fuel you said, reminded me the fact that during the last year - even more - i was experiencing this smell of fuel, but i had not noticed any leaks, so i gave no attention as the car had no issues regarding power delivery.

All in all i am not happy that i will have to change my valves every 1-2 years because of their bad quality.

@Forkie: after checking the carb issue, if the issue remains i will check inside engine. The reason i gave priority to carbs is the leak i noticed. In your case the broken rocker influenced power delivery at a certain speed or in the whole range of speeds ?