Turning into a VFR400 restoration project

Started by 1-600-matt, May 18, 2014, 02:28:11 PM

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Phil_8


komp

KTM 1290 Superduke GT
BMW R nine T

1-600-matt

Not a perfect run today. Was taking it to work this morning so I could go to get it MOTd at lunchtime. Seemed to run lovely on the way into work, but the little stretch at lunchtime across the m4 showed a bit of a fuelling issue... well I think it's fuelling. Between about 4.5k-8k rpm it doesn't pick up cleanly, it will stutter briefly or pop before it starts to rev. Seems to rev out cleanly and pick up fine from 9k up to the red line, but that middle band isn't great. Sounds to be running on all 4 pots ok and I have obviously done a lot of work to it so there could be a few lose ends in there but it's restricted to a small band of revs so I'm thinking it's carb setup.

Any other suggestions?

Farmer Giles

sounds like it might be over fuelling in the mid range as you switch onto the main jets..

If your sure that the carbs are sound, ie no air leaks perished diaphragms etc, then they probably just need balancing and the fuelling set correctly by someone who knows what they are doing and with tiny tiny hands..  lol..

looks good though.. well worth the effort..

1-600-matt

Quote from: Farmer Giles on May 04, 2017, 10:38:28 PM
sounds like it might be over fuelling in the mid range as you switch onto the main jets..

If your sure that the carbs are sound, ie no air leaks perished diaphragms etc, then they probably just need balancing and the fuelling set correctly by someone who knows what they are doing and with tiny tiny hands..  lol..

looks good though.. well worth the effort..

Cheers dude.

I have had the carbs back out to check everything was in the right place, nothing was amiss. All I found was a small fuel leak so resolved that, was worth having the carbs off for that alone really. So have re-balanced them and got them fitted again. I was pretty sure I didn't have any air leaks as it ticks over nicely and picks up cleanly from low down. Just need a couple of hours to get it back together and take it for a spin. If it's still doing it then a run on a dyno will be needed to see what's going on.

1-600-matt

So had a dyno run at JHS to see how fuelling looked... rich, quite rich. It's against speed rather than revs as there was some noisy signals picked up. But the big dip at 40-60mph seems to be the reason why it's not picking up cleanly.



So have got fairings off, carbs out and dropped the needles by removing the 0.5mm shim from under them and dropped down a jet size on the front and two sizes down on the rear. Hope to get out for a spin soon to see if it's helped then another dyno run to verify fuelling is not too lean.

Bit of a tight spot deleloped in the chain so treated it to a new set of sprockets and chain.

It has actually been used this year... twice... and if it's sunny on bank hol weekend gonna go up to silverstone for MotoGP

1-600-matt

Got another dyno run a while back. Carb changes pretty much did the trick. Different dyno so can't really be sure on actual change to power output, but it has got rid of the hesitation and feels like it pulls better, so faily sure there is an actual increase overall.