IP2 air bypass pipes

[gripper]

My IP2 is running properly now apart from a tick over that creeps up towards 2000rpm making life difficult. The culprit I believe is the bypass pipes that feed the engine when the throttle is closed. I think there is an air leak in one of these and, whilst not as bad as it was to bleed my vacuum away altogether, I'm looking at some way of improving on the design (without removing the engine). I'm thinking along the line of a nylon flexible pipe with a tapered alloy sleeve end that would fit in the holes in the rotor housing and the carb manifold. Does anybody have a manifold that they can take an accurate measurement of the diameter of the holes for me? Also, should I have to revert to the o rings and existing tubes, what size are the o rings? (Viton I presume)Thanks in anticipationDave

[Interpol2471]

If the idle by pass pipes leak they cause a poor idle more than a high idle. I would check the butterflies in the back of the engine as they can stick open causing a high idle. This is more likely your issue. At idle the butterflies should be shut with very slight clearance on the rod as per the manual.At the same time the idle by pass pipes should be checked for fit as they can often be bent out of shape causing poor fit if not fitted carefully. The O rings are available from Norton and are part number 55-0352 I fit with vaseline but others may suggest alternatives.

[gripper]

Thanks Paul, I suspected the throttle butterflies weren't closing fully and have fitted an extra spring. I don't want to increase the spring strength any more or I won't be able to open the throttle. If I drag the clutch when at standstill to bring the tick over down, it comes down and holds for a while and then creeps up again which is leading me to suspect an air leak of some description.

[JohnOR]

Hi What electronic ignition box and advance retard unit do you have as a faulty original advance retard unit (the Gunsen plastic box under the seat) can give those symptons (it will only retard if the revs are held low enough to retard 1000 rpm ish) These units eventually fail due to water ingress,they weren't sealed properly. I am on my third box!If faulty then either 1) bypass and retune for full advance or 2) buy a new digital replacement or 3) an electronic ignition unit with advance retard built in.John O'R

[gripper]

I've got a digital ignition from Graham Wilshaw. That works well and the retard kicks in as expected once it's warmed up, so I'm concentrating on the induction side of the system but thanks for your ideas John.

[JohnOR]

Hi As Paul suggested check the butterflies, wear between the butterfly and it's shaft will cause them not to shut properly. Even with extra springs! Goodluck hunting.John

[site admin]

In order to minimise the hesitation problems when you twist the throttle to set off, especially on Commanders. I specified a reduction in the maximum retard on 'my' (Julian Kemp did all the hard work) Ignition boxes. It often results in a slightly uneven idle, but in my opinion it's worth sacrificing that lovely Boyer even idle for the real life ability to set off when you want to without waiting a second or two!I suggest disconnecting the retard wires completely then setting the tickover as even as you can at UNDER 1500 rpm. Then reconnect. Above 1500 rpm it's unlikely to retard enough to give you an even idle. On my own bike, I've fitted a micro switch to the left housing, operated by a lever on the left throttle butterfly it gives me full advance as soon as I touch the throttle. I use an ancient Alvis UAV ignition box on my Interpol, it has a bit too much retard at low RPM so the micro switch works really well.Though you may be right, I think it's more adjustment than air leak problems.Graham.

[gripper]

Thanks for that Graham, I must admit I hadn't thought of that. the tick over will come down if I push down on the throttle butterfly levers with a long screwdriver. That was leading me to suspect the closing of the butterflies. Initially the start and fast running is fine, then the retard kicks in and the tick over is sound at about 6-700rpm then as the bike is used and things start to get properly warm then the tick over moves up to 2000 +rpm. There is play in the throttle cables and three springs should close the butterflies down properly. Any wear in the spindles would be effective from the start not just when properly warmed up.

[David Brown]

Hi all,Mine was a similar problem since my gearbox rebuild last month.It was running roughly especially at low rpm, but higher rpm wasn't much better. I double checked carbs and idle pipes, changed o rings, checked wiring connections, could it still be the carbs?Initially it wouldn't start and the battery went flat so I jumped it from the car - could this have caused the problem? Got it running then it went on to one rotor. I thought a blast down the hill (big hill) where I live would clear the problem. It didn't and went from one rotor to no rotor. It then wouldn't start and then the battery went flat at the bottom of the hill. Bugger!! The last time I pushed a GSX1100 up the hill was about 15 years ago. At 49 I am not as fit as I used to be.Give up? Never. Out of breath? I think my heart nearly left my body on several occasions. Finally got it home and went back to basics. Plugs out - what no sparks? After testing electrical circuits and discussing with Graham, it seemed to be pointing towards the ignition unit. Trigger unit was relatively new and ok when the engine came out. Graham sent me an Ignition unit and hey presto It now has sparks. New spark plugs just for good measure. It now fires up and seems relatively smooth all through the rev range. I got there in the end so thanks to Graham and Paul for help and advice.In summary - What started out as a potential carburation issue turned out to be electrical.Good luck, Happy Halloween!David

[gripper]

Latest theory, If the choke/enrichment O rings are shot then they may leak air allowing my tick over to creep up. I've re-tuned the air bleed screws but the tick over is slow to drop back to idle and then not reliable. You don't tend to think about the choke mech. Looking at an old SU from an Austin 1300 I reckon I can replace the O ring by just un-doing the two small screws and pulling the mechanism out. No need to dismantle the choke lever/cam/spring jobbie, or am I missing something?

[Joe]

Hello Gripper, You are correct but you will need to disconnect the choke cable. One choke assembly securing screw is accessible with the choke "off" and the other will require you to open the choke fully to remove it. Easy to replace the "O" ring and be careful with the thin paper gasket. All SU parts are available from Burlen Fuel products. Regards, Joe.

[gripper]

No change, the o rings were in reasonable order but i replaced them anyway. Apart from some gunge in where they live, its looking like the throttle butterflies are not closing completely. I'm going to look again at the springs. Anything to do with the butterfly spindles etc. is an engine out and strip down job. (who designed, or didn't design that?) I suppose I could drill through from the primary chain case and the alternator housing to get at the spindles………………..only joking. With the lack of engine braking on these bikes, approaching a roundabout or traffic lights needs a closed throttle not a slow creep down from 2500rpm.

[johnbirchjar]

I had the same sort of problem some years back with the Classic(throtle butterflies not closing very quickly)so as a "temperary" measure(which lasted for about two years )I fitted an extra return spring,which did the job until the engine re-build last April,J.B.

[Interpol2471]

Did the same on an IP2 recently and cleaned vigorously with some good carb cleaners to make sure the linkages were free and clear of grit. Worked for me thus the suggestion earlier in the thread The linkage rods thru the cases were sticking in this case mainly.