Pinking

[PSC GP200]

Hi,

First time post on here.

I have just fitted a run-in 225 rapido race with an NK road pipe, Agusto 7000 and a CHT gauge.

There are two problems really: at about 60mph and 6000rpm the engine will gradually start to pink and will slowly get worse if you allowed it to. The CHT shows that it is only 105-110 O/C when this starts, which I don't believe is not that hot? Opening the throttle right up or putting the choke on seems to stop it, which leads you to suspect that it is running lean at this point. It also seems to run out of steam on the last 1/4 of the throttle, but that may be the pipe? The other problem is that it will not respond to the tick-over screw at idle. I can screw it in all the way and it will not idle above 1400 rpm. I've not had chance to do much testing/plug chops etc, so any help much appreciated.

Engine set up:

Rapido 225 race, NK road pipe, Agusto 7000 retarding to 17 deg @ 6000 and 16 deg @ 70000, N3C Plug, AF cyl head, 1.5mm Squish

New 30mm delly, round slide with MB ram air. Main 138, idle 55, 40 slide, AV268 and X7 2nd clip, 5:1 gearing (Indian GP200 box).

Many thanks, Nick

[Norrie Bodge]

Try a AV266 m8

[Andy W]

Try lifting the needle one clip or try a X13 needle to richen it up. I take it you mean it won't idle below 1400 rpm?

[Special X]

I've never been able to use an X7 needle without pinking, even with a grossly overlarge atomiser and main such as you're using. try going to AV266/X13 2nd or end clip. Also reducing that Mahoosive main jet to at least 128 (may find you need to go down to 125) will help the WOT response.

AS ALWAYS CHECK MIXTURE BY USING PLUG CHOPS/DYNO! If your mixture is anywhere near correct as is you must have a huge air leak.

[mick1]

Main jet in my Rapido was 125 (ran fine/lovely colour) but with a 48mm Clubman. I ran an AV266, 55 pilot, 40 slide and an M-tech.....not sure on the needle ?

[PSC GP200]

Thanks for the replies so far.

It will idle a bit lower if req'd. I discovered it wouldn't speed-up when I wanted to adjust the idle mixture at fast tick-over. The pinking is my main concern at present. I did try 3rd clip but was the same but have an AV 266 and an X13, so I'll try that. I took good care with the gaskets etc when building the motor so I hope it hasn't got an air, but I have ordered some rubber bungs and a blood pressure gauge to make a pressure/leak tester just to make sure.
Interestingly, my other GP Rapido 225 Classic with same spec but with a 48 Fresco runs (from memory) 50 pilot, 128 main, 40 slide, X7 2nd clip and does not pink. I was advised to go up on the sizes by a reputable dealer/tuner close to where I live to counter the problems with Ethanol in modern fuels. They tend to favour static timing and open mouth carbs though. Can anyone tell me what temps to expect when the motor is sorted while cruising at around 60mph and is an N3 plug the best choice for this spec engine?

I will update when leak test done and running again.

[PSC GP200]

Update:

I ordered the parts off eBay and made a pressure tester and sure enough it has an air leak. Because one of the inlet manifold stud holes is exposed due to the bore size the air is escaping past the threads on the stud. I have refitted the stud with Loctite and now it's not leaking. Apparently it's not unusual for the inlet stud hole to be exposed with larger bore cylinders, you just have to remember that it is subject to engine vacuum and so must always be sealed.

I will post another update when I have it running again.

[GP240]

Have you strobed the timing ?
I dont know what the low/high revs timing should be but just wondered if it has been checked.

[PSC GP200]

Hi,

I have strobed the timing and it's 17 @ 6000 and 16 @ 7000 rpm. Been busy so not run it yet