4a. Won’t start after full rebuild. Any ideas what to check next pse?

[Michel Higuet]

Because it don't start with easy-start. possibilities are :

1. The ether is not intaked because no vacuum in the inlet manifold, massive air leak ( to vacuum gauge test)

2. No spark to ignite the ether  ( spark plug against the motor and look at the sparks )

3. they are sparks but come at the wrong moment or the ether is not compressed due problem with valves ( but with all? it is impossible or the timing of the camshaft is seriously wrong ).

to precise here your " I tried to start it and no difference, but it did try a little. "

Courage what I am sure that at the end it will run!  

 

 

 

 

[Bfg]

10 hours ago, Steven Whitaker said:

I haven’t checked this.  I don’t have a vac gauge.  Is it possible without?

Simply put your fingers flat across the carb mouth as the engine is turned over. You'll feel the suction of the air. 

Pete

[Steven Whitaker]

Thanks again for all your ideas.  If the crank/cam valve timing was wrong, would it still 'try' to start.  It just seems so close.  Thanks.

[rcreweread]

You say it fired a few times but when you pulled the plugs, they weren't wet - there should have been evidence of fuel on them if you squirted some fuel in through the carb mouths -I would try a bit more fuel squirted into the carbs, or put a little squirt direct into each cylinder but don't overdo it or you will flood the plugs.

One other longshot - if you have the original cast exhaust manifold fitted, make sure you haven't fitted the gasket to the down pipe 90 degrees out because it will fit in any orientation but get it wrong, and it blocks the gas flow by approx 50% which will cause back pressure

Cheers Rich

Edited November 22, 2023 by rcreweread

[Bfg]

Another thought, which will make starting difficult is if the main jet is adjusted too high.  I say this because the Brookland's book I have on SU carburettors says "Screw the jet adjusting nut until the jet is flush with the bridge of the carburettor, or fully up if this cannot be obtained."   ..well that is not how mine is . . .

^ This is one of my carbs, and as you can see the top of the main jet is a good 1mm or more below the level of the venturi's bridge.

Admittedly I'm just in the process of re-tuning my carburettors, having previously lost a bottom manifold clamp and so an air leak passed the gasket.  Although on Sunday (70 mile round trip) she was running just a little rich, this jet position is not very far out for the needles fitted and the air filters I'm using.  This is of course with the shoulder of the needle being flush with the bottom face of the piston.

Hope that helps

Pete

[andyhall]

10 hours ago, Andy Moltu said:

Have you mis-timed the cam?

These engines are non-interference so the valves & pistons won't meet if you get the timing wrong.

So you can really do one of two simple errors - time using no1 exhaust valve or set it so that no1 inlet is fully open say 105 degrees btdc rather than after. (105 is an example as many non-standard cams will have different numbers to 105)

 

+1 check the compression, especially if it appears to be spinning over slightly quicker than normal

[Bfg]

2 hours ago, Steven Whitaker said:

Thanks again for all your ideas.  If the crank/cam valve timing was wrong, would it still 'try' to start.  It just seems so close.  Thanks.

On the TSSC forum last month there was a topic regarding a "GT6 Mk3 only runs well with VERY advanced timing" (10 deg's or more than the standard 13 deg BTDC). It would start and run easily though.  It was found to be because the valve timing was out by one tooth (equating to 6 degrees on that engine).  < here >

If you suspect that.. simply turn your distributor around. Of course it's easiest to temporarily mark the distributor's position you have it presently set to (hopefully correct) so it's easy to put back if to that position if this is not the problem.

Pete 

Edited November 22, 2023 by Bfg

[Bfg]

If all else fails - go back to basics.  Easier done on a motorcycle with a kickstart but the same applies to a car engine.. 

Valve and Ignition timing ....

On a motorcycle I've removed the spark plugs and leaving one in its lead resting against the cylinder head with ignition on, so as to check when it sparks, I've turned the engine over (kickstart lever) with my finger over the spark plug hole to feel when that cylinder was on its compression stroke. As it neared TDC the spark plug should fire.

Doing this on a car engine is more awkward but the same principles apply. Remove spark plugs from their holes, leaving just #1 plug in its lead resting against the block. Remove the rocker cover and turn the engine over until #1 cylinder is on its compression stroke. ie., both inlet and exhaust valve rocker arms are not  resting upon / pushing against the valves. Check, with a piece of plastic tube, that the piston is near the top of the bore.  Turn the engine back 1/4 of a rotation and turn the ignition on. Turn the engine forward again until the spark plug fires (it earthing against the engine's block) and check that the piston is just before TDC.    It all sounds very inaccurate but an engine with fuel will start if the valve and ignition timing are each 'close enough'.

Turning the engine over can of course be done via a spanner on the end of crank, or else by rocking the car along in gear.

My sincere apologies if I'm teaching grandpa to suck eggs, but when we get to the point of pulling our hair out and our mind is filled with frustration, then a 3rd party's simple instruction can sometimes help.  I'm just trying to be supportive and helpful,

Pete

p.s. if compression is much below 6:1 it won't run. This might be because the valves are not seating properly.  A finger over the plug hole while the engine is turned over will barely be pushed away with such low compression.

 

Edited November 22, 2023 by Bfg

[Andy Moltu]

An apparent low compression can be valve timing too.

[Steven Whitaker]

4 hours ago, Michel Higuet said:

Because it don't start with easy-start. possibilities are :

1. The ether is not intaked because no vacuum in the inlet manifold, massive air leak ( to vacuum gauge test)

2. No spark to ignite the ether  ( spark plug against the motor and look at the sparks )

3. they are sparks but come at the wrong moment or the ether is not compressed due problem with valves ( but with all? it is impossible or the timing of the camshaft is seriously wrong ).

to precise here your " I tried to start it and no difference, but it did try a little. "

Courage what I am sure that at the end it will run!  

 

 

 

 

Thanks Michael.  I will have another evening in the garage tonight and first of all, I will check for vacuum.  I think because plugs are dry, this could be an issue.  All new gaskets and everything is tight so far as I can see..  Thanks for your ideas.

[Steven Whitaker]

3 hours ago, rcreweread said:

You say it fired a few times but when you pulled the plugs, they weren't wet - there should have been evidence of fuel on them if you squirted some fuel in through the carb mouths -I would try a bit more fuel squirted into the carbs, or put a little squirt direct into each cylinder but don't overdo it or you will flood the plugs.

One other longshot - if you have the original cast exhaust manifold fitted, make sure you haven't fitted the gasket to the down pipe 90 degrees out because it will in any orientation but get it wrong, and it blocks the gas flow by approx 50% which will cause back pressure

Cheers Rich

Yes rich, when I'm spinning it over, sometimes I can hear the starter motor noise change tone, like the load on it is reduced, which I'm guessing is partial ignition.  But that could be me willing this...  I'll try some Easy-Start again.  I have a tubular manifold as per the photos so can rule that out.  Thanks.

[Steven Whitaker]

2 hours ago, Bfg said:

Another thought, which will make starting difficult is if the main jet is adjusted too high.  I say this because the Brookland's book I have on SU carburettors says "Screw the jet adjusting nut until the jet is flush with the bridge of the carburettor, or fully up if this cannot be obtained."   ..well that is not how mine is . . .

^ This is one of my carbs, and as you can see the top of the main jet is a good 1mm or more below the level of the venturi's bridge.

Admittedly I'm just in the process of re-tuning my carburettors, having previously lost a bottom manifold clamp and so an air leak passed the gasket.  Although on Sunday (70 mile round trip) she was running just a little rich, this jet position is not very far out for the needles fitted and the air filters I'm using.  This is of course with the shoulder of the needle being flush with the bottom face of the piston.

Hope that helps

Pete

Hi Pete,  I had the carbs apart last night and reset this very same thing so the the main jet is flush/level with the 'bridge'.  In fact I noticed that the spring on the adjuster was fully compressed and wouldn't allow the jet to go any higher, which I thought was odd.  Shoulders of the needles are flush with underside of pistons so that's OK.

I might try dropping the jets and see if it helps.  Thanks for your ideas.  Steven 

[Steven Whitaker]

2 hours ago, andyhall said:

+1 check the compression, especially if it appears to be spinning over slightly quicker than normal

Good question, but I did check as per the photos above and all seems ok.  But I could be a tooth out, or a half tooth I suppose.  I think this is where I'm heading next.  I'll have to drain and remove the radiator to get access if I go back to basics.  It's the first time I've done this, so I don't know if it spins easily or not.  Did you see my video above as I'd appreciate your view on this.  Thanks, Steven.

[Steven Whitaker]

2 hours ago, Bfg said:

On the TSSC forum last month there was a topic regarding a "GT6 Mk3 only runs well with VERY advanced timing" (10 deg's or more than the standard 13 deg BTDC). It would start and run easily though.  It was found to be because the valve timing was out by one tooth (equating to 6 degrees on that engine).  < here >

If you suspect that.. simply turn your distributor around. Of course it's easiest to temporarily mark the distributor's position you have it presently set to (hopefully correct) so it's easy to put back if to that position if this is not the problem.

Pete 

Thanks Pete.  I have tried adjusting the dizzy a little at a time, and there is a sweet spot, but it still wont run.  I may go back to basics and check the cam gears again.  Thanks for the link and ideas.  Steven.

[Steven Whitaker]

1 hour ago, Bfg said:

If all else fails - go back to basics.  Easier done on a motorcycle with a kickstart but the same applies to a car engine.. 

Valve and Ignition timing ....

On a motorcycle I've removed the spark plugs and leaving one in its lead resting against the cylinder head with ignition on, so as to check when it sparks, I've turned the engine over (kickstart lever) with my finger over the spark plug hole to feel when that cylinder was on its compression stroke. As it neared TDC the spark plug should fire.

Doing this on a car engine is more awkward but the same principles apply. Remove spark plugs from their holes, leaving just #1 plug in its lead resting against the block. Remove the rocker cover and turn the engine over until #1 cylinder is on its compression stroke. ie., both inlet and exhaust valve rocker arms are not  resting upon / pushing against the valves. Check, with a piece of plastic tube, that the piston is near the top of the bore.  Turn the engine back 1/4 of a rotation and turn the ignition on. Turn the engine forward again until the spark plug fires (it earthing against the engine's block) and check that the piston is just before TDC.    It all sounds very inaccurate but an engine with fuel will start if the valve and ignition timing are each 'close enough'.

Turning the engine over can of course be done via a spanner on the end of crank, or else by rocking the car along in gear.

My sincere apologies if I'm teaching grandpa to suck eggs, but when we get to the point of pulling our hair out and our mind is filled with frustration, then a 3rd party's simple instruction can sometimes help.  I'm just trying to be supportive and helpful,

Pete

p.s. if compression is much below 6:1 it won't run. This might be because the valves are not seating properly.  A finger over the plug hole while the engine is turned over will barely be pushed away with such low compression.

 

Thanks Pete.  Wise words.  I've done the same on old bikes so I can relate.  Bit harder on the TR but still the same principals eh.    As above, I think I will have to go back to basics.  I'm grateful for your ideas, and have followed the above and think the cam timing is OK.  If only I could rule out my carb rebuild.  I think they went back together correctly.  I was very careful.  I had the head re-machined with new valves/guides and lapped and skimmed with new head gasket.  When I put my finger over the plug holes I can feel the 'pull and push' as the pistons cycle up and down.  I think it's not far off, but my hair is starting to fall out now in frustration ha ha.

How do I measure compression?  Thanks, Steven.

 

[mike ellis]

3 hours ago, Bfg said:

Another thought, which will make starting difficult is if the main jet is adjusted too high.  I say this because the Brookland's book I have on SU carburettors says "Screw the jet adjusting nut until the jet is flush with the bridge of the carburettor, or fully up if this cannot be obtained."   ..well that is not how mine is . . .

The SU book does say this but goes on to say to then lower the jet by two complete turns (which makes it about 1mm down) and adjust from there.  If the jet is level with the bridge it is likely to be very weak.

Mike

[iain]

Going back to your original photos, the rotor arm is pointing correctly at number 1 cylinder spark plug, however, the cap when on would have Number one lead just coming off the rotor arm………. Try Johns idea slacken the dizzy and rotate clockwise by 25-30 degrees .  It might just be the issue , fingers crossed for you.

Edited November 22, 2023 by iain

[Bfg]

20 hours ago, mike ellis said:

The SU book does say this but goes on to say to then lower the jet by two complete turns (which makes it about 1mm down) and adjust from there.  If the jet is level with the bridge it is likely to be very weak.

Mike

You are absolutely correct Mike, but that 'turn down the jet adjusting nut' is noted under item 3. 'Replace the piston/ suction chamber .. Check that the piston falls freely onto the bridge  ..If it does not do this, then...' 

When the piston did drop freely, I moved onto the next item ..without taking much notice of the last sentence of item 3.   oops ! My Bad, so it's why I posted about this and included a photo.

As I say, imo, it's a poorly written, proof-read and edited book. Where even the illustrations, Fig.6  included, are somewhat difficult to unravel. 

It may be different for those who know the subject, and are just checking up a detail here and there, but for a novice like myself it's warther confuuzing. 

Pete

p.s. perhaps you can advise me.. why is the orientation of the dashpot (aka 'the piston/ suction chamber') important and different between carburettors.?

 

Edited November 23, 2023 by Bfg

[Michel Higuet]

4 hours ago, Steven Whitaker said:

Thanks Pete.  I have tried adjusting the dizzy a little at a time, and there is a sweet spot, but it still wont run.  I may go back to basics and check the cam gears again.  Thanks for the link and ideas.  Steven.

Adjusting dizzy is a detail see first the important one, how much are the compressions in the 4 cylinder? how much is the reading of the vacuum gauge in the manifold?

Those cost now peanuts and delivered with amazon... 

[Michel Higuet]

7 hours ago, rcreweread said:

You say it fired a few times but when you pulled the plugs, they weren't wet - there should have been evidence of fuel on them if you squirted some fuel in through the carb mouths -I would try a bit more fuel squirted into the carbs, or put a little squirt direct into each cylinder but don't overdo it or you will flood the plugs.

One other longshot - if you have the original cast exhaust manifold fitted, make sure you haven't fitted the gasket to the down pipe 90 degrees out because it will in any orientation but get it wrong, and it blocks the gas flow by approx 50% which will cause back pressure

Cheers Rich

He never says it fired a few times... 

[Motorsport Mickey]

It sounds like a mammoth air leak on the inlet manifold, normally caused by the manifold not being fitted correctly over the dowels on the cylinder head, hence no vacuum being able to pull fuel up from the jets on the carbs. Take out all the plugs and put 5cc (teaspoon)of petrol through the spark plug holes directly into the chambers, plugs back in and turn it over looking for life. Even if it doesn't kick somehow I'd reseat that inlet maniflod to remove it from the list of "could be's".

Mick Richards  

[keith1948]

On 11/20/2023 at 11:02 AM, gloide69 said:

Check there is no air leak at the carbs, I think the spacer orientation could be important.

+1

the photo shows the spacers are oriented differently for each carb.  They should be the same. Only way to check is detach carbs and make sure no leaks.

Keith

[Steven Whitaker]

I just spun the engine over without ignition on holding a piece of paper loosely over the carb mouths and there’s virtually no pull.  See video.  Maybe a bit on the front carb.  Does that point to valve timing?  Thanks

[Steven Whitaker]

20 minutes ago, Motorsport Mickey said:

It sounds like a mammoth air leak on the inlet manifold, normally caused by the manifold not being fitted correctly over the dowels on the cylinder head, hence no vacuum being able to pull fuel up from the jets on the carbs. Take out all the plugs and put 5cc (teaspoon)of petrol through the spark plug holes directly into the chambers, plugs back in and turn it over looking for life. Even if it doesn't kick somehow I'd reseat that inlet maniflod to remove it from the list of "could be's".

Mick Richards  

Ok, thanks.  So far as I can see, the inlet mani is sat down, but will look further.  Cheers.

[Steven Whitaker]

11 minutes ago, keith1948 said:

+1

the photo shows the spacers are oriented differently for each carb.  They should be the same. Only way to check is detach carbs and make sure no leaks.

Keith

I corrected this last night.  Thanks.