September 8th 2016
This was very handy for me as I only live about 3 miles away, so I had a late start and didn't set off until 9am.
I hadn't arranged to take a passenger. The last practice day I went to I didn't have a passenger and it worked out really well with various people jumping in and giving me advice.
This was to be a more disciplined affair with more structured teaching etc.
I wasn't sure about that, but it was only nearby, so nothing lost.
When I got there plenty of people were arriving and I had a wander around and a chat to people. It looked like I may have to borrow other people's passengers a bit, but there were only 4 Hills to have a run at and no particular order. You can spend all day on one Hill if you want.
Luck would have it that a guy there, Mike Storrar, was about to start the sport, having bought a member's car, but didn't have it yet so had come to get a feel for it.
He has been a long time rally driver using, until it was outlawed for International rallies, an Anglia and now is pedalling a Marina with a Honda S2000 motor and mainly Ford suspension.
So we started on the baby Hill and moved on after we cleared that. Actually the car was behaving really well. I may have picked up a few tips during the year, but the car seemed to climb without much problem and the torque from such a little engine was amazing. We kept cresting steep climbs when I had been certain the engine was going to cough and give up.
I think my new approach of getting as much momentum going before the tough bits is working. It is a technique obviously in need of polishing when you have to make a sharp turn and then climb, but it's getting there.
Yes that is a "1" post we are about to reach!
A problem was that I was still getting misfiring after starting the engine , and in some cases rough running and lack of revability on a hill. There was no smoking now and the water temperature seemed fine.
This was where having Mike, an accomplished fettler, with me was invaluable. He spotted something I haven't encountered for many years .......
Fuel Vapourisation.
The exhaust manifold on the Imp motor is curled up under the inlet manifold and carb. The rising heat and low speed of travel prevents the heat getting away and my nice, shiny, bonnet is trapping the heat around the top hose and carb. Even worse, the air inlet for the carb is in the same area under the bonnet and it's drawing in very hot air which has the effect of weakening the mixture even further. I say even further because until the float chamber is purged it's mainly fumes going into the engine anyway.
The arrows point to the exhaust header which runs under the top hose, the fuel line and the skimpy little heat shield. You can see the inlet for the carb which is closed-in when the bonnet is fitted. This area in the picture is also covered over by the bonnet and traps the very hot air.
We ran without the bonnet for a while and the car started running better. The bulkhead was so hot you couldn't touch it and even the fuel float chamber was too hot to touch.
Getting home I decided the first thing to deal with was ventilation in the bonnet so the heat was not trapped. A simple hole saw cut holes for heat escape and also one for the carb to draw fresh air in from outside the bodywork.
Then I needed to make the heat shield better. It needed to be removable. If I have a larger one in place I can't get to the manifold nuts.
So I cobbled one up from some alloy sheet offcuts and bolted it under and alongside the small shield already in place.
It had to have a profiled bottom to protect the jet-feed pipe from the exhaust manifold.
This shot shows how it diverts heat past the carb. In this shot I have stuck heat-reflective tape onto the fuel feed pipe as well. I may also put that on the cooling water hose to prevent that absorbing heat from the manifold.
(That red button looks just like the one you use to prime your lawnmower. That because that's what it is.
I had noticed a high pitched hum on light acceleration and thought it must be an air leak in the inlet side. I used heatproof silicone sealer on the manifold and carb gaskets to try to stop it but that didn't work. Then, when I had the carb off to do the heat shield I noticed the throttle spindle was a bit loose. I wondered if that's where the air was being sucked in. A quick fix was to find something to slip over the bush housing for the spindle and that primer bulb was what I had to hand. Still to try it yet.)
So, we have moved from the original skimpy heat shield shown here ....
.... on to this more tailored version plus some heat-reflective tape.
The area to the right of the heat shield is the space where the heat rises and the holes in the bonnet are directly above that.
Plus the carb now has a small bellmouth (flattering myself there, it's a bit of plastic pipe) to allow it to breathe in cool, fresh air.
I'm full of confidence that this will solve the fuel vapourisation and make the car more tractable.
There is a further solution. Wrapping the manifold in heat bandage. It works well enough, passing the heat further along the exhaust.
However even on shiny new manifolds the heat soak is enormous and enough to cause premature failure of the pipes. (We are talking competition engines here, with very high temps). My manifold is not in the first flush of youth and would probably just disintegrate if it got really hot, so I'll pass on that idea for the moment.
Another little problem was a mist of oil on the back of the engine and bellhousing. I've traced this to the stud bosses in the alloy rocker cover, which have some fine cracks around them. I have a mate who is a wizz at alloy welding so I'll get him to seal them with a bit of luck.
The next trip out should be trial at Firbank, near Sedbergh at the beginning of October. Small engines and overheating are the last thing you want there.
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