IP II Engine won't idle

[dave perry]

:lol: Hello Folk, can you provide a little advice please, on SU carbs. I've bought the bike a couple of months ago, and it has always started instantly, but never idled properly.The engine only runs cleanly above 2000 rpm. I have just fitted the NML Digikit system, which is wonderful, so this must be a carb problemI've taken the tops off, and cleaned everything (again)and checked the jet tubes, they are now a gnats over 3mm "sunk" The engine will tick-over, just, at 600rpm, but it will not pick up. As I say, if I manage to get it up to 2000, it spins up perfectly. I've had the bike down the lane up to 75 mph, so it has been well warmed up, and has fresh petrol.One of the blanking plugs on the carb to engine pipe is very perished, and sucks in loads of air, but that cannot be the whole story - can it ?I am now working away from home, but next time I'm back I will remove the carbs, will check the main and idle pipe seals etc, and replace the plug. Do the symptoms ring any bells with you chaps ?Did I read somewhere that the engine breathes through the idle pipes up to 2000 rpm, then the main pipes take over ??Any advice or comment most welcome, regards dp

[graham]

Hello Dave,The throttle butterfly shuts completely on a closed throttle so air then only passes through the small pipe. Even a small hole in the big inlet pipe will greatly upset carburation. To test, remove one plug lead (Allow it to jump to earth for safety or fit an old plug in the plug cap)and run the engine on one rotor, it should be possible to keep the engine running as a 300cc down to 1500 rpm or lower without it stalling.Repeat for both sides, this should tell you which side has a problem. If both sides are good, it may be the throttle butterflies opening one before the other.(would have to be a long way out or the arm loose maybe) Air cooled engines take a while to come back to life when left standing so you might have to do a few hundred miles before compression returns to it's best.See ya,Graham.

[dave perry]

IP II Wont Idle - Part III have now fitted a new petrol tap from NML, which has a ‘prime’ position. This meant I could dispense with the vacuum connection, and blank off the tapping point – one less possible problem.I then did as Graham suggested; this showed that the left hand side was at fault. I fitted the LH carb from the Commander, no change. I reasoned that it could not be the ignition system, as the original Sparkrite, then NML’s Digikit, and then Sparkrite with retard box were tried in succession- with no improvements.Next I borrowed a compression tester from a local bike shop – 90 psi on the Good Side; and only 60psi on the left side ! getting somewhere at last. The engine was fully overhauled by NML in 2002, moly’d, with new apex seals and springs. It has not done many miles since, so I am assuming I have a stuck apex seal. I have sprayed in various compounds through the plug hole, left them soak awhile, then blown them out on the starter motor. I put a rag over the plughole, to keep flammable mists away from grounded sparkplugs! A quick squirt of oil, plugs back in, then a few fast passes down the back lanes, room enough to get up to 80 odd. This has not given any improvement, as yet. It does pull very strongly from 2500 to 7500 or so, and sounds fine at full chat. I do not hear the classic choka choka sound at low revs.My plan, (when I am back home next) is to inch the engine round until I can see an apex seal through the plug hole, then soak it in Redex and prod it gently with something like a chopstick to try to get it to unstick. I will make sure that the chopstick does not dissolve in said potion first!Any comments on compression readings, and recommendations as to best freeing-off juice most gratefully received, Best Regards dp(Thanks to Graham for continued support and advice; and Adi’s Motorcycles for the comp tester)

[dave perry]

:lol: An Update - After soaking the apex seals in expensive injector cleaner, which by the way came in a nicely shaped triangular bottle; broggelling them with a steel rod, and then wapping up and down the lane at full chat, there is an improvement !The engine now ticks over at 1,000 revs, not perfectly, but much better. It does still pop and f*rt a bit, but we are nearly there. What I need is more of that precious commodity - time, and then an MOT, and, as the Wise Sage has counselled, a few hundred miles to free her off fully.Regards to all, dp

[dave perry]

Nearly there, I had the engine out and up to Startrights. Graham found a cracked left hand end plate and supplied a replacement. He also found that the side seals were below bottom limit; these were the only items not replaced during the Shenstone rebuild. This I thought to be a bit odd, as no expense had been spared on the rest of the rebuild; the apex seals, all bearings and both rotor housings had been replaced, so why not replace the side seals; are they less critical than the apex seals ??\r\rThis did mean however that we had located the source of the problem, blowing seals, super duper.\r\rSo with the engine back in, we pressed the starter button with high hopes. She fired up after only a few seconds; but just the bl**dy same as before, would not idle. \r\rI re-read emailed and forum advice from both Graham and Richard, and the line 'air leaks into the induction' came back into focus. The idle was improved slightly when I screwed in the screw to drop the jet and enrich the mixture, so maybe this is it ? I rechecked the idle pipe o-rings, and found one that was too thin, this was replaced, but no change\r\rI refitted carbs, and as normal, I pushed the idle pipe into the engine, and guided the carb end in with fingers. The engine end collar disappeared into it’s recess, and with the aid of a mirror on a stick and curled fingers, I noted that the carb end of the pipe felt loose. My poor little brain slowly realised that the idle pipes had become shortened after a good few years of ham-fisted replacement of the carbs to the extent that the carb end was not entering into it’s o-ring ! Richard confirmed that they had had this problem before. With carefull positioning of the pipes to ensure that both ends entered their respective o-rings, she now idles at 600 rpm. A new pair of idle pipes from NML are a good 10mm longer than the old ones !! I will rebuild it all this weekend, and will have wap around the lanes, then MOT, and Cadwell on May 7 -inshala\r\rIf you need an sparkrite ignition system inc coils, or any of the fairing, frames or panniers for an IPII, please give me a bell on 01757 618182.