SFCR at Pembrey

Gareth99

Gareth99

Full member
The SFC replica had had it's fair share of problems at Cadwell a few weeks earlier but I'd eliminated them by getting a new set of plugs (the 4th set), trimming the HT lead and removing the resistors from the plug caps. She then ran beautifully for a couple of parades and I was happy - here's the youtube link

I noticed on the last run however, that the engine didn't slow down fully when I shut the throttle, and although I managed to ride round it, after the meeting I stripped the carbs to find some black tarry gunk on the outside of the slides that was causing the slides to stick. I cleaned this all off, put it all back together and took her for a run round a few villages in Staffordshire - lovely.

At Pembrey we put in fresh fuel and set off for practice but I wasn't allowed out. I'd taken two bikes, and because I'd been out on the Honda in the earlier session (to scrub in some new tyres), I'd used up my practice allowance. Oh well, no worries. We were up first race and after sitting in the holding area for ages, we set off to form up on the grid. Sat there with engine running for a while then we were waved off. First, second, splutter, die. Aaarrgh !!! I pushed her off to the side and watched the race from the bank. At the end of the race I tried to start her again before the recovery van arrived, and she started up beautifully and allowed me to drive all the way round back to the paddock.

I thought it was fuel starvation because she ran well until a certain point and then wouldn't go, but if you waited a while everything was good again. Logic said the engine was using more fuel that could get into the carbs. We replaced all the hoses and the vents (and removed the NRV !), and for good measure stripped the carbs and blew out all the jets - they were spotless. We checked fuel flow into the bowls from either side and it poured in. I started her up again and drove 10 laps of the paddock to see if the fuel starvation issue had been resolved. No problems.

My next race was called, and off I went to the holding area - grid position 18. I pulled up to the spot in assembly and she spluttered and stopped again, refusing to start. Pushed her back to the paddock and tried to start up - no joy, even after waiting for an hour over lunch when no engines are to be run.

I'd big fat sparks, and a strong battery so electrical gremlins were eliminated and so we went into full fuel mode. The tank was drained, swished out with fuel, and the fuel taps removed, cleaned and replaced - the filters were in pretty good condition which disappointed me a little as I was desperate to find a clear and obvious fault. We filled up with 99 octane zero ethanol fuel and for good measure took the bowls off and flowed the new fuel into both carbs and through the balance pipe.

We attached a van battery to make sure we had plenty of power but she wouldn't start and spluttered like a real bugger. It was a this point that I felt the race Gods didn't want the SFCR out on track at Pembrey that weekend so I decided to acknowledge this fact and put the Laverda in the van.

At least I had the Honda to use so I could go out and play in the glorious sunshine that blessed the Welsh coast that weekend. In a pique of divine intervention the Honda, which ran faultlessly on the Saturday and every race previously, decided to pour petrol out of all four carb overflow ports just as I approached the holding area! I took her back to the paddock and missed that race. We removed all float bowls, blew out the carbs and flushed fuel through the float valves and buttoned her up again. Perfect, seal tight.

For the last race of the day I thought I'd just check the Honda would start in plenty of time and she did, no leaks. Fifteen minutes later I heard "First call" for the race so I went and got changed and when I came back, fuel was pissing out of the carbs again. I was not happy, as I just needed to finish the last two races to lead the championship going into the last round at Cadwell and now I have an uphill struggle to get a decent season.

But back to the SFCR.

I'm going to send the carbs off to Ducati Paddy and will completely replace the ignition system so that I know it's right and may even get the engine looked over as I don't know SFs. We've got some time before the Cadwell round and hopefully the race Gods will be appeased by then, although I'm not sure if I need to make some animal sacrifice or pilgrimage in the meantime. Any guidance welcome !
 
Shite, Gareth, that is one crap weekend of racing!! Whatever is eating the SF it will end up being something very simple I reckon. Normally I'd put my money on electrical ... coil, a bad connection, whatever. But the 'not dropping back to idle' could be connected to the issue. Have you had the bike running on a dyno at full song? Not knowing what state of tune and degree of modification you're running it's hard to make suggestions. What type of ignition system? What type of coils?

The black tarry gunk sounds very strange - firstly, where did it come from? if any of that got into your pilot fuel system (via one of the holes on the inlet side of the carb) it will wreak havoc and maybe it needs more thorough cleaning. SFs are notoriously reliable and Tippie has raced his for about 12 seasons with virtually no problems. So once you trace this fault I'm sure there's fun ahead!

As for the Honda weeing itself, my ZZR250 Kwaka had a sticking/leaking float needle - very annoying prob but easily fixed.
 
Hi Gareth. What a frustrating tale but thanks for sharing. I wondered what had happened on Sunday.

I remember Bob Dixon having problems with a sticking throttle on his Barcelona at Spa a year or six ago. The slides were covered in a sticky residue which turned out to be the GRP fuel tank epoxy being dissolved by the petrol. Apparently it’s held in solution until the fuel is atomised. Gijs van Dijk immediately identified the problem at the time. I think you said your tank was lined, so that may be irrelevant. I used Tank Cure to line my spaceframe replica GRP tank and that worked well. Bought an ethanol resistant GRP tank from Boba for the SFC which has been ok although I try and only use leaded fuel with no ethanol, after wrecking two Italian made tanks previously.

Tank Cure
 
Thanks for the help guys. It will be something simple and there's no doubt there are multiple issues playing out here which is why a "back to basics" approach is required to remove the gremlins, because, as you say, the SF is a simple reliable design that should work well. It's using a boyer ignition system and what looks like the original coils so there's potential for faulty earths and coil breakdown, but then I wouldn't have expected it to run so well at Cadwell if they were the faults.

The fuel tank is a weird design (all in one piece with the tail unit) and is fully lined, but does look a bit scabby inside. The black tarry stuff is definitely some fuel reaction residue, so I'll clean and wash all the parts before assembly and put in fresh fuel again. It could be that I got a bad batch of fuel of course......

I never got it on the dyno because the two guys I booked in with, one fell off his tack bike at Cadwell and is still in Lincoln hospital, and the other got pinged for Covid, but I definitely want a proper dyno run before the next track session - I'll let you know how it goes !
 
Gareth99 said:
Thanks for the help guys. It will be something simple and there's no doubt there are multiple issues playing out here which is why a "back to basics" approach is required to remove the gremlins, because, as you say, the SF is a simple reliable design that should work well. It's using a boyer ignition system and what looks like the original coils so there's potential for faulty earths and coil breakdown, but then I wouldn't have expected it to run so well at Cadwell if they were the faults.

The fuel tank is a weird design (all in one piece with the tail unit) and is fully lined, but does look a bit scabby inside. The black tarry stuff is definitely some fuel reaction residue, so I'll clean and wash all the parts before assembly and put in fresh fuel again. It could be that I got a bad batch of fuel of course......

I never got it on the dyno because the two guys I booked in with, one fell off his tack bike at Cadwell and is still in Lincoln hospital, and the other got pinged for Covid, but I definitely want a proper dyno run before the next track session - I'll let you know how it goes !
Click to expand...
All one piece with the tail unit, that is pretty unusual with an SFC tank and seat. I would have suggested for fault-finding the fuel issue to just fit a steel tank and give it a go, but that is a bit hard with a one piece unit.
Revs not dropping has been from my experience either air leak to the manifolds letting it get too lean, or ignition timing all wrong.
 
Cheers Tippie. I'm going to try to slave tank idea when I get it on the bench, just to eliminate on other factor in this saga.

The revs not dropping was definitely from the black tarry gunk as I could see that the slides weren't going back down when the throttle was closed. At one time I could see the end of the throttle cable poking out of the bottom of the slide ! However, I will pressure test the air manifolds while I've got them off, just as a precaution - thanks for the advice.
 
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