V8 Hot Starting Issues

[montyjn]

1988 v8 110 

Have a trusty old 110 with a factory fitted carb rover v8. Starts on the button (cold or mild weather), but has always had issues re-starting once run for a while when stopped (including when stopped for fuel etc!). I've tried to work through issues it could be, but having the ignition side of the system rebuilt (distributor) and new leads, cap, rotor arm and leads (all distributor doctor), but the issue persists. 

Could anyone suggest a list of things I should investigate. I was wondering about cleaning up the carbs (re-built 4ish years ago) and having a general tune up. Perhaps looking at a new battery and starter motor, but given it starts cold, these seem like less of an area for issues. I've had a go at varying my hot starting technique (as it were) with no choke / choke, throttle / no throttle etc.

Any thoughts / advice greatly received!

[Bowie69]

Couple of things -no choke when starting hot, ever, even after a couple of hours the engine is not likely to need choke unless it is very cold weather.

Which carbs are you running? Air filter setup? What state is your fuel pump?

I'd be suspicious of fuel vaporisation -you could try, when stopping for fuel, propping the bonnet before you fill up to stop heat soak -if the engine starts more reliably like that then it is an indication that that is the problem. Then you just need to look at places it might happening -e.g. is the fuel line near an exhaust? Can you insulate it in general from the heat? 

[cackshifter]

If this on SUs, I'd check the float valves were Ok and floats adjusted correctly.   

[montyjn]

Thanks guys. 
 

Running the stock SUs, which I believe are HIF44. Air filter setup is also stock. Fuel pump replaced circa 4 years ago with an in tank version per original. Can’t recall what brand. 
 

So a carb strip down could be in order. 
 

In terms of fuel Vapourisation. Shouldn’t the pump push past any locking?

[Bowie69]

36 minutes ago, montyjn said:

In terms of fuel Vapourisation. Shouldn’t the pump push past any locking?

It can take a while..... 

[deep]

Those V8s can be quite forgiving to badly set carbs, in that they chug along smoothly, though possibly running a bit rich or lean.  Before doing anything else, I'd check the diaphragms in the top of the carb bodies are in good condition.  I know they are only four years old but a tiny crack or pinhole completely upsets the mixture control - in fact, they are quite cheap, so just replace them as a matter of course!  

Then there are some checks you can do without stripping and overhauling the carbs. The first is to check they're balanced.  If you don't have access to vacuum gauges, it's easy enough to use feeler gauges to ensure the slides are at the same height at idle and then to make sure they lift exactly in synch.  It's also easy to check the dashpots are full of the right viscosity oil (it won't be your problem but could have been compensated for with a poor mixture adjustment).  The mixture setting is your next port of call.  Plenty of information about how to do that and you do need a "special tool" as you are setting the height of the needle - I made a tool but cutting a groove in an appropriately sized bolt.  No big deal.  The idea here is to set each carb so that, with the engine warmed up (don't turn it off!), lifting the little pin momentarily causes revs to rise and then fall a bit.  There must be Utube videos out there by now showing the process.  Or get an old Haynes manual.

If the mixture-setting procedure is going strangely, cackshifter's note about float valves and float adjustment becomes very relevant though, of course, you have to do a bit more disassembly to check that.  I have found, over the decades, that the simplest way to tell if the valve is seating properly is to use my tongue and see if it holds a vacuum.  If not, it will bleed fuel (often only noticeable after idling for a while).  They really are simple carbs.  Good luck.

[Bowie69]

SUs, so no diaphragms? 

[cackshifter]

One simple thing to try is to get it warm, ie in a state where it's not keen on starting, and try starting with a wide open throttle (release if it fires). If it starts readily, that points to over-richness, as you are allowing lots of air in to clear excess fuel and counterract too much petrol. If not it points to vapour lock, not enough fuel getting through, in which case it's probably not down to the actual carburettors. 

[montyjn]

Thanks guys. That’s really helpful. I’ll have a play in the coming week or so and report back. 
 

I have an old MG on SUs so have some experience in setting them up and do have an old carb balancer too! Be interesting to see what I find. 

[Eightpot]

Have you got a fuel return line plumbed into the carb feed?  This keeps the fuel circulating and cool, avoids vaporisation. 

[cackshifter]

SUs normally just have a supply and maybe an overflow

[deep]

22 hours ago, Bowie69 said:

SUs, so no diaphragms? 

Whoops, how did I miss that? No matter, I suppose.  I helped a friend set up an SU on his Ariel Square Four motorcycle recently.  Quite a different beast with problems of its very own!

[FridgeFreezer]

My #1 suspect on V8's that play up when hot is the ignition amplifier module either under the coil or on the side of the dizzy.

[montyjn]

Yes. Return line fitted to the carbs / tank. 
 

FridgeFreezer, in my head I’ve discounted this as the distributor doc has refurbed the dizzy and replaced that item?

[FridgeFreezer]

What's the actual issue starting from hot - does it crank & crank and not fire or does it struggle to crank?

[montyjn]

Fridge, yes crank and crank and will not fire.

[FridgeFreezer]

Definitely not your starter motor then

Test #1 is the TSD test - if it fires on easy-start it's not the igntion. If it doesn't, it's probably the ignition.

[Eightpot]

Get a set of spark plug testers, few quid off ebay - pop them on when you have a non-start episode and you can easily rule ignition fault in or out and narrow your focus. Just get four to fit on one bank is ample. 

What spark plugs are you running out of interest?

 

Edited October 18, 2021 by Eightpot

[montyjn]

Thanks guys. Will give both a go. Spark plugs are NGK I think.

[montyjn]

So, finally got some time to look into this issue. 

The carbs were definitely quite out of balance on my flow meter, so have balanced them up and it is definitely starting better when warm. 

I've also leaned the mixture slightly on the carbs, using the lifting the piston approach. Although I must admit this method still feels quite alien to me and the 1mm lift doesn't seem to always give the expected response to understand how lean / rich they are running.

I think the carbs probably need to come off as I can see some black deposits on the pistons, suggesting they might be quite coked up inside. I also noticed some perished piping to the air cleaner, so some things to think about. 

Next step is to change the plugs and take it on some test drives to put some miles through the system.

Thanks again for all the advice!

[deep]

Hmm.  Probably a very good idea to make sure you haven't got vacuum leaks!  Not that a perished pipe on the aircleaner side would cause that but one perished pipe could mean others are the same?  Vacuum hose to distributor and another to the brake booster, probably another one to the diff lock too.

[montyjn]

Yes. Although, the pipe I mean is: ERC3956

[Escape]

On 11/8/2021 at 8:56 PM, deep said:

Vacuum hose to distributor and another to the brake booster, probably another one to the diff lock too.

I didn't know there was a vacuum connection to the diff lock?

[deep]

I really don't know about all the models but my Stage One V8 with the LT95 gearbox had a vacuum operated centre diff lock.  

[missingsid]

Yes but after looking on tintornet an 1988 110 should be 5 speed?