DG Exhaust Jetting and mods for KZ1300 1979

Hi my names Vic and i started restoring a kz1300 last spring and I have it togather running and it runs great. Idles nice around 1,000rpm revs nice and smooth. But once it hits around 4,500 rpms it backfires. Now what I did to the bike was rejet it with the sigma kit. i used what was recomended and which i believe i put a 100 main in and the kit also came with a 105. Then I raised the needles one notch from factory. It runs pretty rich. I didn't do the air modification because i wasn't sure if that was recomended but i wanted to ask around before i mess around with it. Also the dg exhaust collector isn't making an exactly good seal. im sure all these factors don't help. I forgot to mention I did test drive it like this and it runs fantastic except for the back fire in the higher rpm. I would appreciate any advice about jetting and mods for the pipe .Thanks.

Yeh I've got a DG on my '79, didn't do any jetting mods, the seal on the collector isn't the greatest, I ended up elongating the hole on the muffler that bolts to the back foot peg bolt so I could slide the box a bit further forward, still leaks a bit but not as bad, I put the elongated stopper plate on to stop the centre stand hitting the pipes. Maybe put the original jets back in and put the needle back to the centre position, backfire could be unburnt fuel, check your timing, make sure the mechanical advancer is working, maybe a drop of lubrication ?, easy to check if it's working using a timing light when it's running, have fun, cheers pete.

wess.vic wrote: Hi my names Vic and i started restoring a kz1300 last spring and I have it togather running and it runs great. Idles nice around 1,000rpm revs nice and smooth. But once it hits around 4,500 rpms it backfires. Now what I did to the bike was rejet it with the sigma kit. i used what was recomended and which i believe i put a 100 main in and the kit also came with a 105. Then I raised the needles one notch from factory. It runs pretty rich. I didn't do the air modification because i wasn't sure if that was recomended but i wanted to ask around before i mess around with it. Also the dg exhaust collector isn't making an exactly good seal. im sure all these factors don't help. I forgot to mention I did test drive it like this and it runs fantastic except for the back fire in the higher rpm. I would appreciate any advice about jetting and mods for the pipe .Thanks.

Hi Vic,
I have an 81 with the DG pipe. I struggled with the jetting but finally found a combination that works. I started with DynaJet's recommendation for mains when fitting the DG pipe, which was 96's. My first try on the needle was third notch which left the mid range too lean. After several attempts I ended up in the sixth notch and the idle jets at 3.5 turns. This combination works fine through the whole range. I have no real need to but the next time I pull the carbs I'm going to fit 100's for mains and go back to the third notch.

Best of luck
Bill

Hi Vic. I'm tossing in my two cents here about the backfire problem. Before you start messing with the jets and needles, do yourself a favour and seal up that header . I use clear RTV silicone and slather it on the pipe before sliding on the collector and again when mounting the muffler. Don't sweat it if it gets messy. let it dry overnight and a razor blade around the seam line will let you peel off the excess. Easier if you wax up the stuff you don't want the goo on before you start. Backfiring is caused when the hot and not completely burned exhaust gasses have access to oxygen which the gap in the pipe is providing. Good luck. DF