Transmision snatch.

[johnbirchjar]

Hi Guys,can anyone help me cure "transmission snatch" on the Classic?it occurs when ever I shut off the throttle with the clutch still engaged,e.g.going down hill,or in traffic,the only way to stop this is to have the throttle open just a whisker,but this puts a stop to what little engine braking there is,I have checked the rear drive chain for slackness,checked the adjuster for the primary chain about two thousand miles ago,it was fine,had a good look at the cush drive rubbers when I had a new tyre fitted recently,they all seemed in good nick,the engine idles at 600rpm,I regularly clean all the "sliding bits" on the carbs,so I am at a bit of a loss as to what to do next,or is this a case of "they all do that sir" (this is not a new development, the old girl seems to have had this problem for years!!)regards,J.B.

[MrB]

I'll watch this with interest too as my water cooled IP2 was horrible. Balancing the carbs helped a lot.The clutch hub rubbers were shot. I could tell this because they fell out when I removed the hub cover! Replacing them also improved things but the problem still occasionally appears.I think the primary chain tensioner isn't up to scratch as it can be compressed by hand, albeit slowly, with oil leaking past the slipper pistons. Once I get hold of the replacement from Graham I'll see whether that is the end of it.Mr B (that's actually the bike, not me!) did develop a leak from the exhaust manifold which made things worse, I guess because it affects the carburation. I'm waiting on a new manifold as welding the old one up wasn't entirely satisfactory. I have a new cush drive rubber for the rear but haven't fitted it yet, it don't think it's a contributory factor though.If you decide to check your clutch rubbers I made the tools necessary to change them which you are welcome to borrow. They'll need picking up though, I'm in North Herts.Johnny

[johnbirchjar]

Hi Johnny, I think my clutch rubbers are fine because I changed all the transmission oils today(g/box,primary chain & rear drive chain) and all the oils were more or less the same colour as they went in about five thousand miles ago,(and I seem to remember some time ago, some one being advised to re-new their clutch rubbers because the oil that came out of the g/box was all black and gungy)but thanks for the offer anyway,hopefully someone will come up with a cure,regards,J.B.

[andy588tt]

Hi JohnnyI have had this problem too on the Interpol, Commander and F1, I'm not an expert nor do I profess an instant cure but this is my train of thought. If correct it might be causing the snatching in the first place - it might help us all to ride around the problem. With the rotary engine so efficient with minimal throttle openings the slight whiff of petrol the engine ignites whatever it has in the combustion chamber. If there is not enough petrol on the next rotor to fire it holds back only to fire again when enough petrol is available. To obtain a combustion causing a bucking effect or snatching, I find the SU carbs "constant vacuum" more user friendly especially on minimal throttle openings compared to the carbs. On the F1 this snatching or bucking is more evident below 2000 rpm, the balance of slipping the clutch and keeping the throttle constantly adjusting to obtain a good balance in traffic.1.Check that the carbs are clean and working properly, no air leaks, also having balanced, air/fuel and synchronised throttle openings, also on SU carbs the damping piston that even amounts of oil in the dash pots ( black knob on top of each carb )2.Has the primary chain tensioner worn beyond its working limits ( black rubber boots worn ) or has the small venting hole been blocked with grit or has sealing mastic stopped pistons moving freely in chain tensioner. This has been a pain on my F1.3. Cush drive rubbers in the clutch and rear wheel can be overlooked for signs of wear.I tend to ride my F1 bike in a higher gear or rev higher at low speeds to counter this bucking or snatching at low speeds.Ride SafeAndy

[commando-rotary]

Hi John, this may or maynot help in your case. But when I put my interpol away last winter it was running great but when I got it out this spring it was awful, I initially thought of crap petrol as all the symptoms suggested carbs/fueling. I was then told that if the wires from the ignition trigger are run alongside the generator wires the power in the generator wires will upset the ignition signal. I have now routed these two cables as far apart as practical, and he presto what was a real crap running bike is now brilliant once again. hopes this helps.Dave Green.

[johnbirchjar]

Hi Guys, thanks for your comments,I have been giving the problem much thought of late,and have come up with a couple of theories(1)When I first fitted the Sprint fairing to the Classic way back in '05 I had quite a problem with the horns,they would only work with the lights on if the engine was revving over 2000,and also the indicators were "slow",I tried various ways to cure this,(me thinking that the alternator was not punching out enough power to cope with the TWO headlights)even to the extent of fitting another ignition system 'cos the factory fitted one used a tad more power!! all to no avail.(I discovered many thousands of miles later that this was the "thin end of the wedge"for the horns being knackered)so, could the "non standard" ign:system be causing the problem?I ca'nt see how,but who knows.(2)the other theory being,after riding the Classic for about three years (and was no longer scared to death to touch anything) I had become fed up with the way factory had set up the choke(cold start) system,no rise in engine revs when the choke was pulled out, which made the bike a real pain to ride slowly when the engine was cold,so I adjusted the idling rod (by trial and error)until I achieved a satisfactory result,could this be the problem? I await a response from those more knowledgeable than I,regards J.B.

[johnbirchjar]

Hi guys,I have been playing with the "cold start" again, fine tuning it,so to speak,also tweaked up the engine idle to 900rpm, and guess what?!! the trans:snatch has all but gone!admitted this was on but a short run,(about 30 miles) but a vast improvment,J.B.

[johnbirchjar]

Hi Guys,I'm afraid that the bike has returned to the "status quo", the "snatching" has returned because the engine seemed to take forever to come down to "idle" at 900rpm(dropped down in steps,a first for me) so I reduced the idle back to 600 and the idle now doesn't "step",but the snatch is back.I checked the carbs interiors,in-case they were "catching" but both were nice and shiny,and the oil was as it should be, so once again I am at a loss,regards ,J.B.

[gripper]

You might try a very thin oil in the dashpot of the carb for better throttle response both up and down the rev range, I tried three in one in my IP2, seems ok. My Commander hangs up on the way down the revs and I bring the revs down by dragging the clutch, it comes down and then stays down till the next time I open the throttle, pain in the arse in traffic.

[commando-rotary]

as previously stated rerouting the trigger cable away from the generater cable on my interpol did make a big difference but when i took it away for a week with the vmcc I found travelling at low speeds with just a sniff of throttle the bike became very snatchy and unresponsive making low speed driving very difficult and uncomfortable. As I found ABZ needles suited my commander (with it's Geoff Madden exhaust) very well I thought I would give them a try in the interpol. Voila low speed riding and responsiveness is now brilliant. Judging by the colour of the exhaust it is now running a slightly richer but this appears to be the only down side, it is also running cooler. I'm sure RN will be along with a constructive comment soon but for the moment plod is a joy to ride in any situation. I am sure there is an even better needle but I have neither the knowledge or experience to know where to go with it, maybe Richard can enlighten us based on trials by norton?Dave Green

[johnbirchjar]

Hi Dave,ABZ needles? what are they? where do I get them,? they seem to be the cure that I need. Regards J.B.

[commando-rotary]

Hi John, ABZ's replace the original AEF's you can get them from Burlen they advertise in the old bike mart and also have a website. They are the manufacturers of su carbs and carry all the spares for them, the needles are about £14 a pair + p&p. I hope they give you as much benefit as they have me. D G.

[Interpol2471]

I will have to give those a try as I have a pair here in my spare carbs, thanks for that Dave