4000 revs : is that a maximum for GT6 mk 3 ?

[Royston W]

Hi all, First post for me !

I'm proud new owner of a lovely Powder blue GT6, it has not been on the road for at least 6 years and I have set about returning it to good health.

I have spent the last month rewiring as previous owner had begun to dismantle the loom and add extra equipment ( including power steering) and the original 3 fuses were just not enough !

I've also stripped and rebuilt the twin Stromberg carbs , fitted electronic ignition, dismantled and adjusted brakes, etc etc and at the end of my first month of ownership have at last driven the car.... what great fun too. Played around a lot with timing and carb adjustments and had a bad spell of backfiring and very little power and although I'm getting closer I still cannot get the engine to run past the 4000 rev mark, even when stationary, despite the rev counter going up to red line at 7000.

I'm not intending to race the car, but even in overdrive my max speed is in the low 50's . 

Am I expecting too much ? or can the wealth of experts here offer some advice ?

I have also spent MANY happy hours reading the Forum content, and gaining tips from past posts but can't find anything relevant so would be pleased to hear of your thoughts. ( and should I get some age related Black and silver aluminium pressed plates do you recon ?)

Cheers

Royston 

[Badwolf]

Hi Royston. Welcome to the madhouse of help, experience and utter mad stuff, but if you have been reading this stuff for some time, you know that. I have silver on black plates on my '72 Spitfire. I prefer them to the modern colours and feel that they fit in better to a classic car. Others will disagree but they suit me. Not sure of the current cut off year for using them. Someone will be on soon to tell you. Lovely looking car. I have no experience about best revs etc but a lot here have. Just sit back, share your problems and enjoy it here, I do.

[johny]

Hi, lovely car. I think you need to start from scratch with the engine set up by checking compression, valve timing and tappet clearances. While your at it you could confirm that TDC of piston 1 is really where the timing marks indicate as these have been known to move...

[Iain T]

Could be a mass of things including the rev counter being incorrect! Are you sure it's reading correctly? 

What happens at 4000rpm does it cough and splutter? It could be something simple as the cable not fully opening the butterflies. With the engine off fully depress the accelerator pedal and look to see if both butterflies are horizontal. 

Must be (hopefully) something simple. 

Oh yes and welcome to the land of thread drift. We're masters of meandering off course.........why take a motorway when you can take a B road? 

Iain 

[JohnD]

"Electronic ignition".  Some makes include programmable rev limiters.  Check your manual!

John

[Royston W]

Thanks Guys, barely time to peel the potatoes before responses !

At 4000revs it runs fine just won't go past it, the electronic ignition may well be the limiter, it is an old Lumenition one , taken off a Dellow ( ford sidevalve) so no manual but could well be stopping further increase. I've checked butterflies and they are both horizontal on fulldepression of pedal.

Royston

[Wagger]

That could be it. Sidevalve engines were not normally great revvers. Can you do a quick convert back to points and condenser just to check it?

[Wagger]

1 minute ago, Wagger said:

That could be it. Sidevalve engines were not normally great revvers. Can you do a quick convert back to points and condenser just to check it?

The Dellow used a 4 cylinder 1172 sidevalve. That produces 2/3rds of the number of sparks required compared with your straight six per revolution. If it was set to limit at 6000 rpm for the 4 cylinder, then the six cylinder would only be doing 4000 rpm.

[Pete Lewis]

the idea of timing maks moving is very valid  the crank damper with the tdc degs marked on is supposed to be rubber bonded to the crank pully 

this bond breaks down and the out ring will move /rotate so tdc is not as it shows 

we  expect JohnD to bring his demo rig to duxford  to show how this damper works and can move 

i first found this on my Vit1600   can cause chaos with timing 

to confirm you need to make a piston stop to replace a spark plug and turn engine carefully  to the stop in both directions and mark the damper ring  

tdc will be halfway between the marks 

if it all ties up your fine 

other ideas about power outage  is fuel pump output 

carb diaphragms fitted incorrectly  there are two location lugs  

can you refit the orig  dizzy  ???   

Pete

[johny]

4 hours ago, Royston W said:

At 4000revs it runs fine just won't go past it, the electronic ignition may well be the limiter, it is an old Lumenition one , taken off a Dellow ( ford sidevalve) so no manual but could well be stopping further increase. I've checked butterflies and they are both horizontal on fulldepression of pedal.

Ive never come across any Lumenition system that has a rev limiter facility so think that can be discounted as the problem....

[Royston W]

I've also checked on the Lumenition website and agree that I can't blame it on the optronics !

Back to timing and carb adjustments 😕

I'll try the " advance till pinking" method , I'm also wondering if dizzy is not doing its stuff with centrifugal or vacuum advance so will check that out this morning too.

 

 

[Stratton Jimmer]

Lovely looking car. I will add my vote to the electronic ignition being the problem. I have two sixes and both rev freely to 6000. On the number plate side, my 77 Sxfire has modern plates while my 1973 Mk3 GT6 has black on silver. 

[Pete Lewis]

the dizzy vac unit has no effect on performance its an economy device and only advances at part throttle for better cruising  MPG  

at full throotle it does nothing as no vac is generated 

its more electrics than fueling if it peaks at 4000 flight speed and on road speeds   

running it up from idle there little in the base design that would rev limit it 

pete

[Clive]

I doubt it is fuel starvatio if it won't rev beyond 4000rpm when stationary. 

What happens if you pull the choke out? does that help (indicating weak mixture)

But indeed the distributer is the most likely issue. A simple strobe light will tell you if the distributer is advancing. 

My other thought is an issue with the electronic ignition, maybe gap too big?

[NonMember]

Just as another thought... my GT6 developed a "perfectly smooth but completely gutless" problem some years back - not quite as bad as yours, perhaps - which turned out to be the throttle linkage between the two carbs. Only the rear one was opening.

And don't completely rule out the Lumenition. They may not have explicitly designed in rev limiters but I encountered a Vitesse (at the start of the 2004 RBRR) which would run perfectly up to 3000RPM but flatly refuse to go any higher, and it was due to a faulty Lumenition unit. Putting it back to points fixed it.

[JohnD]

Ah, Lumention, a very basic electronic ignition!   With no rev limiter.    But ignition failure at speed remains on the card.

A plug lead spark checker might help.    They are sold in sets of four, which is annoying for a six, but you can by one for less than a fiver, and swap it across the block.     It will flash when the plug fires, so failure of ignition becomes easier to see.

John

[johny]

But surely youre going to know if the ignition fails above certain revs (cutting in and out etc) while the problem here sounds more like it just runs out of steam?

With the number plates I think a car like that merits the classic reverse engraved black plastic type which although difficult to source I think are still available👍 

[Clive]

Re number plates. 

Any new car sold from teh late 60's on would have had yellow and white plates, nobody would have used the old fashioned silver on black. 

I like this ype, just looks right

However, if you want pressed ali ones, avoid the cheaper type that look just that. Tipper plates are very good, but not budget friendly. (My dolly has tipper plates from 1980 when the car was made, lovely patina)

[chrishawley]

15 hours ago, Royston W said:

stripped and rebuilt the twin Stromberg carbs , fitted electronic ignition

Could you help with a little more info? Which carbs in particular do you have: CD150, CDS, CDSE? Could you give a bit of info about the rebuild. For example if CDSE, were the jets replaced. Spindles? Needle valves? Springs? etc.

Did you have the vehicle in running condition prior to carbs/ingition work? Any info there to give a clue as to 'new' v. 'pre-existing' problem.

And what were your particular procedures for timing and carb setting (strobe, static, coloutune, piston lift etc)?

There's a lot of possibilities and perhaps these can be narrowed down a bit. But eliminating the electronic ignition from the equation does seem a practicable place to start in that it provides a firm answer one way or another.

 

[Colin Lindsay]

6 minutes ago, clive said:

Re number plates. 

Any new car sold from teh late 60's on would have had yellow and white plates, nobody would have used the old fashioned silver on black. 

I like this type, just looks right

Me too. My 1967 Estate, despite being older than my GT6, had those when it was found, and I'll get a new set. Some cars suit the black and silver, some don't especially cars of a later era. 

Who makes those raised plastic letter plates these days? Those are as close to the ones I need as I'll probably get.

[Clive]

18 minutes ago, Colin Lindsay said:

Me too. My 1967 Estate, despite being older than my GT6, had those when it was found, and I'll get a new set. Some cars suit the black and silver, some don't especially cars of a later era. 

Who makes those raised plastic letter plates these days? Those are as close to the ones I need as I'll probably get.

https://www.tippersvintageplates.co.uk/

[johny]

Yes thats them and a step up from pressed plates if you do change....

Mirrorline "Hand Engraved Plates"

Reverse Engraved Acrylic Plates were developed in the early 1970’s and feature the registration engraved into the black backing of the plate thus allowing the backing material of either polished or brushed aluminium to be seen through the clear acrylic.

These plates use the 3.1/8" size character for most vehicles.

We are able to use smaller digits for these plates, meaning they can be used on smaller cars, motorcycles and scooters.

[Top Banana]

16 hours ago, Royston W said:

Royston you said...

I've also stripped and rebuilt the twin Stromberg carbs , fitted electronic ignition, dismantled and adjusted brakes, etc etc and at the end of my first month of ownership have at last driven the car.... what great fun too. Played around a lot with timing and carb adjustments and had a bad spell of backfiring and very little power and although I'm getting closer I still cannot get the engine to run past the 4000 rev mark, even when stationary, despite the rev counter going up to red line at 7000.

I'm not intending to race the car, but even in overdrive my max speed is in the low 50's . 

Am I expecting too much ? or can the wealth of experts here offer some advice ?

Royston 

 

 

When I got my GT6 it wouldnt do more than 35mph completely gutless and I felt heartbroken, how can a 2 litre 95Bhp on a car only weighing 840 odd Kg be so slow. There is a solution and you will find it. I doubted the carbs and the electronic ignition as you are. I worked on the carbs when there was probably no issues with them in reality (but boy you learn a lot). Finally with mine it was the timing it was badly off, but stupidly it started well and idled okay which gave me a false sense of security thinking it cant be the timing.

I cant believe it your electronic ignition - its not intelligent enough and as others have said check the timing with a strobe or before doing that  keep advancing the timing if you have a micrometer advance/retard adjuster on the dizzy. That was the solution to mine in the end, not enough advance even after I timmed it with a strobe - the car would flat spot  and not rev or go any faster. Now it bloody a responsive and different beast and it going to sound stupid but the engine tone has changed and I have an understanding of what "Good Sounds Like". The slightest movement of the throttle and the car is responsive.

All the things I did in desperation and panic were: 

1. Changed fuel pump

2. Checked the Tappets

3. Checked the compression (burnt valve scenario or worn engine)

4. Rebalanced the carbs and checked the throtlle range and adjusted the choke

5. Made the carbs richer

6. Doubted the my Electronic Ingnition - even when and purchased a set of points.

7. Thought it was fuel quality and not having octane boost 

8. Prayed to the god of cars and watched YouTube on how to use a Strobe (Bought an expensive one with as many options as the Wife washing machine) 

The thing i learnt is dont change too many things at once, go for a test run after a change then reflect. 

John

 

[Pete Lewis]

yes one at   time   is the rules  for any changes 

good strong tea works whisky induces a nap 

timing by ear is worthwhile , set the idle a bit faster than normal    turn the dizzy body ,   clockwise advances and  speeds up ...  anticlockwise  retards and  slows it down

rotate the dizzy body to get the fastest  rpm and back it off to be less than best    take for a run  if she pinks back a bit more till the pinking... doesnt.

too much advance will give a kick back , you have gone too far 

this eliminates any problems with the damper ring being on the move 

no strobes .lamps or gauges  just you ears 

Pete

 

[Wagger]

Get an old plastic shirt button and connect a piece of HT lead from coil to the distributor centre breaking the lead with the shirt button hole so you introduce a visible spark gap. Rev it up in subdued light and check if the sparks cease at 4000 rpm.

Don't do it for too long as you could wipe out all TV and radio around you. (AND wifi).