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1974 TR6 hesitates above 55 mph (only under load)

Moss Motors
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Dudley1675 Avatar
Dudley1675 Dan Dudley
Douglas, MA, USA   USA
I read the two other threads on this subject, they were helpful, thanks to all those who contributed to them. Someone suggested that I post a new thread on my issue, so I have. My take away from reading the other threads was that I should check the timing 1st, so I will. The other potential causes ranged from the carbs to electrical and clutch problems. Sounds like a potential world of sh*×? to me. My timing skills have not been employed since I sold my '55 Chevy in 1969 prior to joining the Navy, but I am game! What I have done so far, new fuel pump and filter, new plugs set to .25, new Pertronix "flame thrower" coil & Ignitor electronic ignition. New cap & rotor. All of these mods helped but it is still there at highway speeds under a load when passing or going up hills at half throttle, full throttle makes it worse. I am concerned about the many mods by previous owners to the emission system, most of it has been bypassed or modified. All that remains seems to be a mod to the idle vacuum line. I have taken some photos to illustrate these mods as best as I can.
Anyone know of a good TR6 mechanic in central Massachusetts?
Thanks!



Edited 5 time(s). Last edit at 2019-02-10 11:02 AM by Dudley1675.

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Marksg1 Avatar
Marksg1 Mark Greenbaum
Evanston, IL, USA   USA
1976 Triumph TR6 "Nigel"
Dan, check the timing, its hard to tell much until then. Get a timing light, you can also check using the static method, lot's written on that. How is the idle?



I love the smell of hydrocarbons in the morning.

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
I know you have a new fuel pump and filter, but can you test to ensure that you have good fuel flow?

You symtems sound just like those of a blocked fuel filter.

I had a car once where a PO had fitted an extra hidden fuel filter in the line.angry smiley

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Dudley1675 Avatar
Dudley1675 Dan Dudley
Douglas, MA, USA   USA
The idle is a little high after it warms up but left it there as it idles down quite a bit at traffic lights when running at normal temperatures. My guess is that the idle vacuum line is not operating properly as it is not connected to the tubes at the radiator end of the engine. I will be getting a timing light today.

Dudley1675 Avatar
Dudley1675 Dan Dudley
Douglas, MA, USA   USA
I agree, will do and let you know.
Thanks.

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
In reply to # 1595565 by Dudley1675 The idle is a little high after it warms up but left it there as it idles down quite a bit at traffic lights when running at normal temperatures. My guess is that the idle vacuum line is not operating properly as it is not connected to the tubes at the radiator end of the engine. I will be getting a timing light today.

You could well have vacuum leaks and such, which might effect idle, but at the speed/rpm you mention a little leak would have little effect on running.

Have there been any changes made to the exhaust system or a performance cam fitted? This could also leave the engine running lean under load at higher rpms.

After a good run when the problem has been occuring, shut the engine off and check the colour of a couple of spark plugs.

LFMTR4 Avatar
LFMTR4 Lou Mijares
Scottsboro, AL, USA   USA
That can do it. Plug off the vacuum port at the carb or pinch off the hose near the carb to close it off and see if it still does it. Another culprit might be a torn diafragm in a carb.

Dudley1675 Avatar
Dudley1675 Dan Dudley
Douglas, MA, USA   USA
There are a ton of timing lights online, found this one on Amazon, it has quite a few good reviews. Does it make any difference what one you get?
INNOVA 3551 Inductive Timing Light https://www.amazon.com/dp/B000EVYH72/ref=cm_sw_r_cp_apa_i_S3hyCbVF1Y6N2

poolboy Avatar
poolboy Ken D
Sandy Hook, MS, USA   USA
Where is the small hose that's connected to the top of the rear carb going ?
I can tell you this...not where it was supposed to.



ZS carb repairs
kencorsaw@aol.com

LFMTR4 Avatar
LFMTR4 Lou Mijares
Scottsboro, AL, USA   USA
Looks like to the retard Cher. Lotta hoses in there.

Dudley1675 Avatar
Dudley1675 Dan Dudley
Douglas, MA, USA   USA
The vacume hose comes out of the carb, bypasses the thermostat area all together and enters the disk on the rear distributor. Photos attached


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Dudley1675 Avatar
Dudley1675 Dan Dudley
Douglas, MA, USA   USA
Missed a photo.


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Dudley1675 Avatar
Dudley1675 Dan Dudley
Douglas, MA, USA   USA
I viewed a replacement disk like this at Moss Motors, it supposedly restores the ability to advance the timing? As apposed to only being able to retard it?

poolboy Avatar
poolboy Ken D
Sandy Hook, MS, USA   USA
That hose to your distributor's vacuum RETARD is activating the retard just when the centrifugal ADVANCE weights are trying to advance the timing,,,that's counterproductive.
The vacuum Advance module you asked about is manufactured by British Vacuum Units (BVU) and sold by various retailers including Moss...I have one.
With or without that 'modification' your timing will still advance adequately with the increasing rpms by the centrifugal advance weights within the body of the distributor housing.
BUT... the hose from YOUR rear carb to the retard module needs to be disconnected and either cap the nipple on the carb or hook the hose up to where it was meant to be,,,the EGR valve on the cylinder head.
IF you want to RETARD the ignition timing at idle as it originally was, that vacuum comes from a little larger nipple on the bottom of the front carb,,,,but if you are not using the Retard (and why would you ?) then at least see if you have a TIGHT fitting cap on the nipple in this picture.. There's a red straw as an indicator of it's location.



ZS carb repairs
kencorsaw@aol.com


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VACUUM RETARD NIPPLE 001.JPG

LFMTR4 Avatar
LFMTR4 Lou Mijares
Scottsboro, AL, USA   USA
Yeah, see post #7.

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