Engine heat

[marsh]

Hello everyone

I've recently purchased a late 1965 408, which I am delighted with, except for one small thing; it doesn't start at all well, especially when warm.

Is this a common thing and is there an easy fix? I am aware the Carter AFB carb can suffer from heat soak and fuel vapourisation.

I was considering fitting a phenolic spacer between the head and the carb. If anyone has any suggestions, I'd be very interested to hear.

Best regards

Marsh

[Kevin H]

I would first suggest checking that you are getting adequate fuel pressure at the carburettor when this problem occurs. You need around 5 psi. You can buy an inline fuel pressure gauge quite cheaply. For better accuracy use a gauge with a range up to say 15 psi rather than one that goes up 100 psi.

[Geoff Kingston]

The choke on the early V8's is controlled by a spring in the manifold below the carb on the rh side of the engine, you will see a rod going down to it, it is adjustable but I cant remember how but it is in the workshop manual and Bristol cars can sort this out for you or tell you what to do to adjust the spring.
An easy check when the engine is cold is to take the air filter off , if the flap in the front of the carb is not totally closed push it shut having pumped the throttle a couple of times before and it should start straight away, if it does the spring is the problem and is fairly easily obtainable from American parts suppliers and ebay.com if it should be broken and the usual sources don't have it.

[Geoff Kingston]

On the hot start side the 408 and 410 I had had a metal fuel pipe coming into the engine compartment and a rubber pipe connecting this to the carb, all a bit close to the manifold so careful use of cable ties will help to keep these off the manifold.
However all the V8's I have had 408, 410, 411 and 603 benefit from a bit of throttle to catch the engine when it fires when hot, rev it until it settles down and you should have no problems.
If this does not work a new or overhauled carb might be a good idea and you will save yourself a packet and have more choice by ordering direct from the USA.
You should also be able to get a rebuild kit direct from the states as well.

[Kevin H]

Originally Posted by Geoff Kingston

An easy check when the engine is cold ...

I thought this was a hot start problem?

Unfortunately there are numerous things that can cause starting problem, but there are a couple of fundamental requirements - fuel and a spark

Marsh, what's the cranking speed like?
And when it won't start when hot, is there any combustion happening - is it almost starting or is there no sign of combustion?

[Geoff Kingston]

Kevin,
I realised it was both hence the two replies, I think you are right about the fuel pressure as well, on my 411 it was poor with the manual pump so we converted to electric and eventually a new Carb with a manual choke, now starts no problem hot or cold. On my 603E the carb was damaged so was replaced and an overhaul kit obtained to rebuild the old one at a later date.
The engine still had the block mounted pump but the previous owner had fitted an extra small electric pump to aid starting. We replaced the lot with an electric Facet pump with an in line fuel pressure regulator and have had no problems since.
Hot starting was a issue I suffered on an R Type Bentley we found that the spark was too weak to ignite the fuel when the engine had stood for a few minutes, having gone through everything with little improvement on the standard set up, the general forum advice was to fit electronic ignition.
The system I chose was Fred Winterburn's capacitor discharge unit which cured the problem completely and made the engine run a lot better on modern fuel.
Edlebrock do heat insulating spacers for various manifold and carb set ups and according to some postings on a Chevrolet forum have cured the hot start issue for some owners.
Geoff.

[marsh]

Thank you gentlemen - that gives me some food for thought!

When the car is hot, I'm getting pretty much nothing; certainly little signs of combustion - the starter is churning away merrily with no discernible firing and only after very aggressive pumping of the accelerator will it finally catch. In terms of cranking speed, my gut instinct is that the battery may not be long for this world - it's kept on a conditioner and appears to be ok, but from past experience of V8's, It would be better to be sure and invest in a new one.

I've only had the car for a month or so and am now getting used to it; it is due to go over to my mechanic in the coming weeks for a full check over and he's going to take a proper look - I'll obviously keep you posted on progress.

I've yet to join the BOC, but just for reference, my car is a 408 Mk 2, chassis number 408/7214 which I'm given to understand is the penultimate one made. It now carries the registration number VEW408, but was originally KPG675C. It was fully restored between 1997 and the early noughties by previous owner David Rowlinson and remains in lovely condition.

Best regards

Lee Marshall, aka Marsh

[Kevin H]

I also have an electric fuel pump and inline pressure regulator on my 411, and a reduction gear starter motor which spins the engine quite quickly. The engine starts easily even when it has been standing unused for months. When it's warm it starts the instant I turn the key.

I have also seen a 412 that used an electric pump to prime the fuel supply to the carb initially then it ran on the original mechanical fuel pump once started.

Good advice Geoff about applying a small amount of throttle when starting the V8 engines when they are warm. That was recommended to me and was required with the original set up, although I find I don't need to do it now with my modern accouterments!

For what it's worth Lee, it's not just us V8 Bristol owners who encounter starting problems, plenty of Mopar owners in the US have the same problems and many opt for the electric fuel pump and/or modern starter motor.

It's probably worth mentioning the carburettor also. If it's the original on the 408, it probably needs a full overhaul. But it's likely it has been changed at some point. After I bought my 411 I discovered the carb was incorrect for the engine (too small) which added to my starting woes.

Another thing to bear in mind is that ignition coils don't like heat, and a coil that works fine when cold can become unreliable when hot. It goes without saying that clean, correctly gapped spark plugs and sound ignition leads also help.

However, from your description Lee it sounds like a fuel supply problem to me. We look forward to hearing how you get on.

Best regards,
Kevin

[marsh]

Thank you Kevin, I'll add the coil to the list of potential suspects and plugs too, though I think they were changed prior to the car being delivered, though it's anybody's guess if they'r correctly gapped.

Typically, I took the car out last night and it started on the button and ran like a dream - being new to Bristol ownership, I'm still unused to the reaction it gets when out and about - a guy nearly fell off his bike, craning his neck to see what it was!

My gut feel is that the core issue is fuel supply, though I'll also give some attention to battery, starter motor and heat sink too, just to be sure, a it needs to be utterly on the button in time for the Revival in September, as I have a 350 mile round trip.

Over the summer I may also look get the manifolds off and send them to Zircotech to be treated in a heat resistant coating too, as every little helps.

Here's hoping for a reliable season of motoring - update to follow.

Marsh