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 Post subject: Carby backfiring
PostPosted: Sat Sep 07, 2013 4:38 am 
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Joined: Thu Apr 21, 2011 4:29 am
Posts: 275
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So I had the first go at firing up the F1 today without success. The bike cranks & sounds like it's trying, but there is a constant backfire through the rear carby, with an occasional exhaust backfire & occasional front carb backfire. I have the mixture screws set at 1.5 turns out (tried playing with these without success) & the idle screws wound out. Would I be right in thinking there's a problem with ignition timing? I set the pickups as per the manual & was quite pedantic about it.


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 Post subject: Re: Carby backfiring
PostPosted: Sat Sep 07, 2013 10:05 am 
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Joined: Thu Oct 14, 2010 7:30 am
Posts: 139
I know it sounds stupid but you didn't switch the plug leads by accident did you? Or the pickup leads? I put a kickstarter pedal through the sole of my shoe OWWWW! when I hooked up my Darmah backwards.
If all seems correct, You might want to open the pickup gaps toward the max. clearance. I had a hard start/backfire issue with my wifes Allazura and it came down to the pickup gap being too close. It was trying to start at full advance.
Just to be sure I'd go back over the basics, cam timing, valve clearance etc.
On the waay outside I have seen two of the Bosch ign. boxes take a dump. They can stay at full advance or not advance and really confuse things. But failure is pretty rare.

Good luck,Bill


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 Post subject: Re: Carby backfiring
PostPosted: Sat Sep 07, 2013 10:23 am 
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Thanks Bill. I've double checked cam timing & valves. I've also checked plug leads & pickup wires (I just replaced the plug to the main harness as a couple of the connections were a bit iffy). All the electrical components are new so I thought I'd give them the benefit of the doubt at this point in time. I was starting to lean toward the carby set too lean, so I was going to pull it off & just go over it all again to make sure it's right. Next will be the pickups themselves if that doesn't bear fruit.


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 Post subject: Re: Carby backfiring
PostPosted: Sat Sep 07, 2013 11:37 pm 
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Joined: Thu Apr 21, 2011 4:29 am
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So I pulled the carbs & double checked everything - couldn't find anything obvious. Floats are set at 18mm & all jets are as they were before I stripped them down. I double checked the pickups & they were spot on, but I opened the gap another .05 mm just to be sure. Re-checked the cam timing & it's spot on too.

She still wont start & keeps backfiring through the rear carb. I also noticed that the rear header gets warm when cranking whilst the front one doesn't seem to have any heat in it. This is pointing me back to a lean mixture on the rear, or could it be that the problem is actually with the front carb? The rear plug came out wet whilst the front one was as dry as a bone. Any other suggestions? Is there a way to check which wire is which for the pickups at the connector end, as it's a new one also, but the wires were identified with the V & O tags (possibly mixed up when it was put together?).

Edit: I also checked for spark & it has possibly the cleanest spark I've ever seen.

Can someone confirm that the left hand coil & box are for the vertical cylinder (this is what I had worked out)?


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 Post subject: Re: Carby backfiring
PostPosted: Sat Sep 14, 2013 9:50 am 
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Joined: Thu Aug 02, 2012 8:29 am
Posts: 34
Try running a thick jumper ground wire from the battery up front somewhere to something solid. That 4 inch long battery ground in the tail is a joke


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 Post subject: Re: Carby backfiring
PostPosted: Sat Sep 14, 2013 8:19 pm 
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Joined: Thu Apr 21, 2011 4:29 am
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It turns out that there were a couple of problems. I stripped down the alternator side of the bike to double check the gear timing (which was OK) then ran a multimeter over the pickup wires. On the lower end of the pickups the one at the 9 o'clock position was marked with a V but at the connector end they were marked with an O, and vice versa for the horizontal cylinder (Ducati quality control?). I swapped the wires over & whilst she wasn't running the backfiring was gone. Next I found that the wires from the starter switch to the harness also had the same problem. Turns out that the starter button was supplying power to the coils whilst cranking, but it cut out as soon as the button was released. I used a new original F3 harness when I put her together and the 3 wires in the harness connector were also swapped around. Unfortunately the next time I hit the starter button the starter sprag let go. I'm now looking for another sprag before I can get her running.


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 Post subject: Re: Carby backfiring
PostPosted: Sun Feb 09, 2014 1:08 am 
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Joined: Thu Apr 21, 2011 4:29 am
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OK guys - latest update. I replaced the starter sprag, put her back together & threw in a quick prayer to Ganesh before having another go. I flipped up the rear choke, gave her 2 full pumps with the throttle & hit the starter. BAM! She fired straight up & settled into a really nice smooth idle. I checked her over before turning her off & trying again. Started first time! After half a dozen starts I shut her down & had a coffee before hooking up the Carbtune to synch the carbs. When I hit the starter this time she turned over but refused to start. Further investigation showed no spark to the horizontal cylinder. I checked the pickups for continuity & found that I was getting readings between the vertical & horizontal wires - it looked like the wiring was shot so I parked her back into the corner until I could get some more time to work on her. A week or so later I suffered a heart attack whilst driving home from work on the Friday, so the bike was off my list of things to worry about for a while.

I managed to get some suitable wire from an auto sparky friend of mine on Friday so spent Saturday re-doing the pickup wires. It was interesting to note that I found the wiring inside the insulation to be badly corroded with the wire covering having all broken up. I say interesting, as these were a set of NOS pickups that I scored that had never been used. This would lead me to believe that he problem everyone see's with the wiring insulation has nothing to do with the fact that thee wires are running in hot engine oil as a lot of people have suggested, but rather that the insulation technology in those days just wasn't as good as it is today.

Anyway, I got the pickups all done & put the bike back together, making sure that the timing was right & double checked for pickup resistance (I got 328 Ohms from both of them with no reading between H & V). I turned on the fuel & the next thing I know the rear carb is pouring fuel everywhere - stuck needle I assume. I pulled the carb & cleaned everything again before putting it back together. I have had another go at getting her started but she still doesn't want to play the game. I think she likes being in the shed left alone! I've given up again for a little while as I have all sorts of medical tests for the ticker to get through this week. It was frustrating given that she started & ran like a Gem for a bit before the pickup wires failed - I was sure that this time she would be a runner.


Last edited by Sumfun4me on Sun Feb 09, 2014 1:17 am, edited 1 time in total.

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 Post subject: Re: Carby backfiring
PostPosted: Sun Feb 09, 2014 1:14 am 
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Joined: Wed Jan 16, 2013 5:28 pm
Posts: 83
Bugger. You'll get it going. More importantly I hope the tests go well, need to look after your own valves first. :)


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 Post subject: Re: Carby backfiring
PostPosted: Sun Feb 09, 2014 6:23 am 
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Joined: Sun Nov 07, 2010 10:54 pm
Posts: 425
Location: Brisbane
Look after yourself, now. PM sent.

Graeme


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 Post subject: Re: Carby backfiring
PostPosted: Mon Feb 10, 2014 10:56 pm 
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Joined: Sat Mar 03, 2012 1:40 pm
Posts: 7
Wow, sorry to hear about you heart attack. Glad to know it didn't end things for you.
Take care of yourself first, there'll be plenty of time for fussy bikes.

Rick


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