Running problems using unleaded fuel

[Oldmogman]

Has anyone experience running problems using unleaded fuel - other than valve seat recession?

My 1275cc lightly tuned engine has an unleaded head but will splutter and die when the engine gets hot, especially in traffic and in hot weather. It will usually re-start after 10 minutes or so.

A couple of gallons of proper leaded four star seemed to cure the problem, but the phenomenon returned when I filled up with superunleaded treated with lead replacement additive and octane booster.

Any suggestions?

(The engine runs gas-flowed unleaded head, 8.7 (approx) compression, a HIF4 carb with K&N filter and an LCB manifold.)

[ColinP]

Hi,

Do you have the electric SU fuel pump? A lot of pepole are having problems with vapour locks in the hot weather.

I'm lucky, I don't have it (touching wood as I type), but the modern fuels seem to have a much lower vapour pressure thn the old ones. This means that when it gets hot, the fuel pump "suck" is sufficient to turn a lot of the fuel into vapour = no go! (plus a noisy fuel pump).

I've been thinking about a solution, this involves a damp cloth around the fuel pipe to the pump (evaporation cooling) ....

Colin

[Oldmogman]

Thanks Colin

Yes, it has a (new) SU pump. While it does 'tick' slightly more in hot weather, it's certainly not going crazy.

I've gone down the fuel evaporation route and have lagged the fuel pipe in asbestos cloth and made an aluminium heat shield to sit under the carb.

[ColinP]

Ok,

now we're into speculation, but I'd check the HT side (including coil - though they don't usually recover!).

Is the inlet manifold sitting on the exhaust (hot spot)? - it may be just too much.

Colin

[bigginger]

I've wondered if there's any point in lagging the exhaust with tape which you can buy for the purpose - what do people reckon?

[bmcecosse]

I have done it on my Mini - but that was because the mechanical pump and the pipes are very close to the lcb. I doubt it is fuel related - but is your 'new' SU pump the correct one for the job ? Some folks fit Mini ones - which are designed to PUSH, not SUCK -- and the Minor one is opposite -- it SUCKS and doesn't PUSH (not very well anyway).

[Kevin]

Definatly sounds like good old fashioned fuel evaporation, I assume you have seperate inlet and exhaust manifolds from reading your spec as this improves things, and I also assume that you have the pipe from the pump routed over the carb so it can keep as cool as possible, if you had gone to the National at Donnington last year you would have seen how many Minors sufferred your symptoms in the 1 - 2 hour + queue from the motorway to the site.

[bmcecosse]

Well loads and loads of Minis manage just fine without fuel evaporation locks - and their fuel routing is very compact and very near the exhaust - compared to the 'open' layout on the Minor. Check your fuel cap is letting air into the tank ok.

[Kevin]

loads of Minis manage just fine without fuel evaporation locks

But as you say they use mechanical pumps, the problem seems to always be associated with the electric type as fitted to the Minor, when the engine has the lower plate for the mechanical type of pump fitting, and I know a couple of owners who have gone down this route and fitted a Marina type of mechanical fuel pump it seems to resolve the problem that seems to be worse on the 1098cc engine in slow hot traffic and only seems to affect the Minor non of the other `A` series cars suffer from it as far as I know, A35,A40,Midget,1100-1300 ect.

[Cam]

Probably due to the low pressure (before the pump) side being heated up by the manifold. This is a problem with a high up pump (like the Minor's one). It was not a problem when 'proper' petrol was used, but now it IS a problem! The answer would be to increase the pressure of the hot fuel line (by using a pump lower down or a pusher from the rear). Or simply re-route the fuel line (low pressure side) away from the heat source.

[samheath100]

Could you set the timing to something like 4 degrees before. and see if this cures the problem. also you could make yourself a heat diflector to direct the heat away from the fuel line to reduce vapourisation, then more fuel wil get to the carb more easily.

[Kevin]

I dont think altering the timing well help the problem as the big culprit is heat in slow moving traffic, and mr grumpies made a heat shield kit that did not seem to help much either and as Cam said the modern fuel doesn`t help things either, but rerouting the fuel pipe sounds a possibility has anyone tried it ?

[Cam]

Well, I'm using a rear-mounted pusher pump and don't have the problem, plus I'm using a braided fuel hose and not the original copper item. It follows the original route though.

[jtd.75]

Hi all has anyone tried Broquet I have been using it for over 15 years now first I used it on a 1967 LD Ambulance, it allows you to run on unleaded without any modifications, it gives you more mpg along with other advantages. I have also put it in my 1963 MM 1000. It was first used in the second world war in the planes that were fighting on the Russian front was used because their aviation fuel was no good for our planes. Its a one off installation job either inline or direct into the fuel tank, I put mine in the tank attached to a fishing line so that when i change cars i just swop it over. (its not cheap)The web page is www.Broquet.com

[salty_monk]

Sorry to tell you jtd.75 but those fuel catalysts were tested by the FBHVC & were proved to do absolutely nothing! You may as well just stuck the money in pound coins straight into the tank...
If I was you I'd switch to an additive that's been tested & approved such as Castrol Valvmaster or millers VSP.

As for the fuel evaporation problem - it's not going to do anything for that either! It's interesting how some Minors get this problem & some don't, ours doesn't & is completely standard as was my mum's years ago & that never sufferd either. Both are 1098's.

Lagging exhaust & manifold made a real difference to underbonnet temp on my kit car, not so sure about Minor but can't hurt. The other thing people could try is http://www.rallydesign.co.uk/catalog/in ... th=261_264 encase the fuel pipes in it.

This stuff worked to stop clutch cables frying in our kit cars as they went between two branches of a 4 branch manifold & Rally design are a very good company. Be warned postage isn't cheap though if you can't pick up...

[jtd.75]

If it was good enough for the RAF then its good enough for me, and I think I am right in saying that FBHVC has not commented on it. Also a lot of fleet management lorries use it in the modern vehicles as well. Broquet also give a guarantee that if it damages your engine they will pay for repairs. I know a lot of civil servants that use it, it is recomended by their motoring and leisure mag. Have you read up on it. I do not mean to be rude or insulting but please do not comment on a product you obviously know nothing about.
Fact I have have a mpg improvement, fact I have had co2 reduction, fact I have noticed a slight improvement in power, fact I use unleaded, no valve problems. It can also be used on diesel engines and on marine engines. Various motoring organisations have neither agreed or disagreed on its performance but did say those that they have spoken to are more than pleased with it. I only meant this as a comment on being able to run a engine on unleaded without any problems, iI don't think it would sort out the cutting out problems as I do believe the original question in this forum was.

[ColinP]

With regard to the Broquet system -

It's very difficult to "read up on it". There is absolutely nothing I can find - apart from the Broquet web site (anyone got other references?). The references to external reports are meaningless without the bility to read the original report.

The use of it in "fleet management lorries" doesn't seem to help - most are diesel ...
Nor would I necessarily trust a lot of civil servants to know anything about fuel combustion etc.
The problem with the guarantee is that one has to show the product has caused damage - not that it didn't prevent it. I don't know if anyone has ever had a claim - or a sucessful claim.

I'd love to know how adding lumps of tin into the fuel (or fuel line) works - any suggestions? I know that tin isn't soluble (in hydrocarbons) so it can't act like the old tetra-ethyl lead. The suggestion that it has to be in contact with mild steel (Broquet web site) is interesting - but there does't seem any direct evidence of what happens.

Colin

[bigginger]

Don't mean to be rude, but I am, by nature, a cynic and sceptic. Seems odd that Broquet have refused to put their catylyst up for any independent analysis. Another club has had a small thread on the gadgets - http://www.fiat500club.org.uk/boards/fi ... s/read/446 - apart from that, all I can find is the info on Broquet's page and the company address in Warwickshire. I think I'll stay a follower of Diogenes.
a

[aupickup]

don`t knock it until you try maybe the answer.
a bit like faith healing, sceptical maybe but a lot of folk beleive it

[bigginger]

Far be it from me to "knock it" (that's why I didn't), but I don't think I'll be trying it. Like faith healing, a lot of people don't believe it, but good luck to those who do.
a