QuestionQUESTION: Hi Barrie,
I hope you don't mind me giving you the entire history :-)
About 2 -3 years ago I started getting hot restart problems with my 1978 MGB. It will start immediately when hot but leave it much more than 5 minutes and it wont start for maybe an hour in very hot weather.
The engine is bored out to 2000cc, unleaded head with higher compression, B700 camshaft, stainless tubular exhaust manifolds and "sports" exhaust, but with standard HIF4 (rebuilt)carburation (AAA needles) and the standard distributor. All the work was carried out by Oselli Engineering about 20 years ago and up until 2-3 years ago I had no problems at all. I have now disconnected the Newtronic electronic ignition and reinstalled CB points with new condenser, installed a Sports Coil (the original was leaking oil, replaced the leads etc and retuned the carbs with a colortune and rebalanced them. The hot start problem seemed to go away, until that is, I took to the MOT station when it failed on emissions. The boss of the garage adjusted the mixture to get it through the MOT and when he came to drive it out of the workshop, it wouldn't start. Eventually it did start. He says it was due to fuel vapourisation with modern petrol which contains ethanol 5%. He advised a fan to blow cold air over the carbs.
Because the vehicle was so unreliable I didn't use it at all last summer unless I was going out for a drive and getting home without stopping, or going somewhere where I would be staying for an hour or more!
This year I have tried to attack the problem again. I put my 3rd new coil in, because people were telling me the cheap Chinese ones break down when they are hot. So I put a more expensive one in. i have lagged the exhaust manifold and fitted a replacement larger stainless steel heat shield. I have lagged the steel fuel pipes and wrapped the rubber ones with aluminium foil tape. I put the colortune back on and the rear carb was running very lean while the front one was spot on. I have adjusted the mixture, rebalanced the carbs and refitted the original filter boxes rather than the K&N ones which were fitted when the engine was rebored etc. I have also fitted some new vacuum hoses as they were looking tired.
The hot starting has improved somewhat. I couldn't say its totally fixed as the weather has been cool of late, but it seems OK for waits of 15 minutes, so I can at least fill the tank without worrying! However cold starting is now not very good. In the garage in the morning it often takes 5 or 6 attempts to get it started. Previously It always started first turn of the key when cold. Once started it is OK for the rest of the day.
In an attempt to remedy this, I have tried to adjust the cold start valves. One was opening before the other and the carbs were way out of balance at fast idle. I have now fixed these issues, but am unsure at what point on the cams the fast idle should be adjusted to 1300RPM. I tried to work it out from the diagram you published, but have found there is a line scribed on each cam. I am assuming that is the fast idle point? Anyway this is what I have used. I pulled out the choke to line up the heads of the fast idle adjusting screws to the lines on the cams and set it to 1300RPM with the engine up to temp, but it is now hard to get a satisfactory idle with the choke out and my instinct tells me to turn the fast idle up so it will idle at 1000 RPM when cold. Questions:
1. Do you have a procedure for adjusting the fast idle/cold start valves?
2. Are you familiar with this hot starting issue is there something else I should be doing to help that? It has been suggested a modern electronic fuel pump would be better at pushing the vapour through the system.
3. Also I have been advised to use Texaco Super Unleaded fuel as that is supposed not to have any ethanol. It certainly stops the engine running on when it is switched off. Is this a good idea in your experience?
Thanks for listening
Mike
ANSWER: Hi Mike. The problem of hot restart is a big issue and it is not going to go away. Most 95 octane fuel now has 5% ethanol in it, which seems to be the culprit. Your efforts at lagging the exhaust, new heat shield, etc are all correct and exactly what I would have recommended.
The specification of your engine does require a high octane fuel. 95 octane is too low and super unleaded is the way to go. I have heard good reports of BP and Shell, but I have not had reports of Esso or Texaco. In Dorset it would all be Esso (Fawley) anyway, no matter what label appears on the pump.
One little trick - whenever you stop for fuel, it would be a good idea to open the bonnet immediately to let the heat out.
It has recently been announced that most Super Unleaded does NOT contain any ethanol at present, so that would be another bonus.
Your car is a 78 so it only has to comply with a VISUAL SMOKE TEST and does not need to be tested for emission levels, so I would lower the jets to richen the mixture as well. Tell your MoT tester to read his rule book, emissions levels only apply from 79 onwards.
The mark on the cam is the point at which the fast idle adjusting screw should START to make contact with the cam.
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QUESTION: OK Barrie,
Thanks for your reply.
I had this argument with the MOT tester about the car not needing an emissions test because the previous garage had never checked (in fact they never measured my 1981 car either!). However he showed me the official manual and it says pre 1975 is visual only. I have just checked on the official VOSA site and he is right, so it must have changed. No matter I will let him adjust it and retune it as soon as I get home.
So the fast idle screws shouldn't start to move at all until the line on the cams? At what point should the 1300RPM fast idle speed be set then? Or is that not relevant? It is what is in the ROM.
Thanks,
Mike
AnswerGlad to help, Mike.
I am surprised about the 1975 cutoff. I won the argument with a 1978 Land Rover last month.
As regards fast idle, set it so BOTH carbs hit their marks at the same time, and when you fully pull the choke out you might get 1,300 rpm with a WARM engine. It is all a bit academic really, because why would you want to do that?
Balance is more important than emissions.
Set the mixture so the engine runs right and worry about emissions at the next MoT.
