Playing with carbs

by Alex

After two hillclimb events in the car with the new engine set-up, we have some work to do to fine tune things.

At a very wet Wiscombe at the end of April, the front engine carb jet dropped out after running really well. It happened quite quickly with little or no poor running beforehand, suggesting that the jet had been adjusted out too far when on the rolling road, and that the needle may be too lean thus requiring artificial enrichment by screwing out the jet.

We rebalanced the carbs and lock-wired everything in place as a temporary measure.

The following weekend at a sunny Werrington the car ran reasonably well but without the sizzle it had before. We then experienced misfire at the start line usually coinciding at the first gear change then clearing. The car revs out to 9k and the misfiring only happened on Jenny’s run after mine as the ‘A’ driver. This suggested that the plugs were fouling up with all the tickover waiting time, so perhaps the needle could be too rich low down. The plugs certainly looked fouled up but it was difficult to tell after a run up and then back down the hill. Changing them certainly helped, as did getting Jenny to rev it like a boy-racer before the start! On further inspection of the old set some of the porcelain had broken down.

Our conclusions are that the needles are too lean at the top and too rich at the bottom, as the plugs seem to be getting too hot and fouling up at the same time. Also, starting requires the choke but the engine will not run at all with it left on and a very light foot is required on the throttle.

We also wondered about dirty fuel, the facet silvertop pump has a poor filter which is easily blocked.

We are using SU needles in Strombergs, so using www.mintylamb.co.uk found a couple of alternatives using their comparison graph. BG which is much leaner low down and richer top looked perfect, but the curve proved too steep at the crucial 3 to 5k rev range, so we have tried CS2 which has the same curve as the CS1’s previously fitted, but richer at the top with a smoother curve.

After road testing and installing a glass filter before the fuel pump we await Wiscombe on the 17th/18th May with baited breath!

The Howells Championship 2014

Our first event this year was on March 30th at Clay Pigeon Kart track for a sprint, our first one. The track is very twisty as would be expected, and we are still not sure whether or not we like it!  Still it was good weather and a warm up for us and the new engine/gearbox and we had some fun sliding round the corners.. it would be interesting in the wet!

April 26/27 saw a very wet weekend at Wiscombe Park hill climb and the first proper test of the engine. All was going really well and the track wasn't too bad, Alex got very close to last year's personal best on Saturday afternoon.  On his last run the jet fell out of one of the Stromberg carbs, luckily falling on to the custom belly pan and not onto the track until he got to the top finish paddock.  Having found the jet he refitted it and Jenny got her final run.

Having made steps to prevent it coming out again, we started on Sunday but soon realised that the carbs were out of balance and we couldn't better 63 seconds.    The final run was cancelled because of the muddy/slippery state of the paddock, it was only a matter of time before a car slid into another, or worse into a pedestrian. Getting out and loaded up and away from the site was organised in batches so we were pretty much first away being in the first batch.  The quickest we've ever loaded the Imp on to the trailer and packed away the stuff in the van!

The carbs are being checked out, and hopefully the car will be running better for Werrington hill climb this weekend.

You can find a couple of videos from Wiscombe on YouTube:
Jenny final run Sunday:  http://youtu.be/GomQBB05lxc
Alex fastest run Saturday: http://youtu.be/B1dNTTFTHTM

The score in the Howells Championship to date is Alex 2 - Jenny 1.

If you haven't already found it, we now have a Facebook page at www.facebook.com/imphillclimb - come and find us!

Upgrades all round

Crikey, I didn't realise it was October when I last wrote on here, a lot has happened since then!

We now have the 998cc engine fitted in the Imp, with twin Strombergs, an R17 cam, Maniflow exhaust and a closer ratio box. These changes necessitated an upgrade to more hefty half shafts as well! We have taken it on a few test runs and are sorting out the inevitable tweaks needed to the mixture and a mystery minor oil leak, other than that it goes like a dream. We are going to check the decibel level though, as it seems quite loud....
 

Alex enjoying a wet Wiscombe. Photo by www.teltphotography.com

 

Our first planned event is the sprint at Clay Pigeon in Dorset on 30th March, and then a gap until the first Wiscombe hill climb at the end of April which marks the start of the season proper.

Both Alex and I have upgraded to Nat A licences this year, partly because we took all the trouble to get the upgrade card signed! Partly because it makes us feel as though we've arrived, and partly because it gives us more choice of which events to do. Often when an event has both A and B events on, the Nat B classes are very generalised into eg. all road going cars, so we'd be better off in the Nat A classes. We'll see how it goes this year.

Last year people who saw us may remember we usually had our elderly Pointer dog with us, who was happy to sleep in the back of the van, but sometimes came out for social visits around the paddock where allowed! Sadly we lost him in mid-December so will not have his company this year, it won't be the same...  We have decided not to get a new puppy until the end of this season; it had been a concern of mine that we are planning to do some further afield events this year and some sprints, and I'm sure it would have been an issue at some stage, and definitely would be with a pup!