Hi guys…really needing some help from the collective and vastly more experienced than I, on an engine such as this…not something I’m too familiar with at all really, but having to learn fast, after a quick fault finding session this evening.
Long story short…she’s a friends ‘89 Yamaha 225 v6 2.6L 2 stroke. A rare engine over here for sure and perhaps elsewhere too. Not much info available about them, that I can see.
Despite being quite an old machine, she’s made further an oddity perhaps, in that she has a cdi (or whatever the proper term is) ignition system and a TPS too. Something I didn’t know existed or featured on such an engine with carbs back then. Especially given that I know of and perhaps fairly familiar with same age 200, 150 v6 carb versions that don’t have it. V4 smaller versions too.
Anyway. The engine has had a fair bit of attention just recently, after suffering an overheating. Won’t bore you with all that, but we are now to a point where it’s mechanically sound and healthy…rebuild and exhaust chamber wall crack repair (amongst other niggles) later…she now seems not to be firing properly or almost at all, on her port bank of 3 cylinders. Coils tested since, one replaced…but still not behaving.
Symptoms are…idles ok or well enough…but a serious bog or reluctance to rev when throttle opened from around idle up through the rpms perhaps 1000ish higher, then seems to rev freely after. But under load and in gear…she really struggles to pick up rpm through that dead spot. If she does manage to get past the first couple of thousand rpms…and get on plane and lessen the load, she will perform decently, but not as she did. Be aware that only once has she been allowed to get to this state. Any of the handful of other attempts, the test has been cancelled after displaying the same bogging behaviour. Then back to the workshop.
So…finally…just before we got fed up with it this evening…we realised she had a TPS (I just wasn’t expecting she had one at all, given the era and my unfamiliarity perhaps). All three hard wired wires going into the tps were blatantly and obviously perished, in terms of the insulation, just a mm or two before they’re adjoining at the tps itself. The black wire in particular was only just hanging on, and actually came completely off with the slightest touch of finger. No doubt she now needs a replacement for sure. But as she was, certainly, at best, these wires must have been a detriment to the signal given to the cdi in terms of any advance or retardant control signal (if I’m right…please correct if not). At worst, it wasn’t even functioning at all and/or arcing amongst the wiring. Red, black and a white (cream or light brown perhaps) were the 3 wires referring to.
Is it possible that if this wasn’t functional, it could be just signalling at what it thinks is an idle rpm state and something like (the usual from other tps I am familiar with) 0.7/0.8v meaning it’s not resulting in the required timing adjustment, when the throttle is opened ? Resulting in the earlier described running behaviour?
Sorry for the long post and even the ignorance and unfamiliarity with such an engine.
Would love the opinions, corrections, advice and similar, from the more experienced than I.
Thanks,
Allan.
Long story short…she’s a friends ‘89 Yamaha 225 v6 2.6L 2 stroke. A rare engine over here for sure and perhaps elsewhere too. Not much info available about them, that I can see.
Despite being quite an old machine, she’s made further an oddity perhaps, in that she has a cdi (or whatever the proper term is) ignition system and a TPS too. Something I didn’t know existed or featured on such an engine with carbs back then. Especially given that I know of and perhaps fairly familiar with same age 200, 150 v6 carb versions that don’t have it. V4 smaller versions too.
Anyway. The engine has had a fair bit of attention just recently, after suffering an overheating. Won’t bore you with all that, but we are now to a point where it’s mechanically sound and healthy…rebuild and exhaust chamber wall crack repair (amongst other niggles) later…she now seems not to be firing properly or almost at all, on her port bank of 3 cylinders. Coils tested since, one replaced…but still not behaving.
Symptoms are…idles ok or well enough…but a serious bog or reluctance to rev when throttle opened from around idle up through the rpms perhaps 1000ish higher, then seems to rev freely after. But under load and in gear…she really struggles to pick up rpm through that dead spot. If she does manage to get past the first couple of thousand rpms…and get on plane and lessen the load, she will perform decently, but not as she did. Be aware that only once has she been allowed to get to this state. Any of the handful of other attempts, the test has been cancelled after displaying the same bogging behaviour. Then back to the workshop.
So…finally…just before we got fed up with it this evening…we realised she had a TPS (I just wasn’t expecting she had one at all, given the era and my unfamiliarity perhaps). All three hard wired wires going into the tps were blatantly and obviously perished, in terms of the insulation, just a mm or two before they’re adjoining at the tps itself. The black wire in particular was only just hanging on, and actually came completely off with the slightest touch of finger. No doubt she now needs a replacement for sure. But as she was, certainly, at best, these wires must have been a detriment to the signal given to the cdi in terms of any advance or retardant control signal (if I’m right…please correct if not). At worst, it wasn’t even functioning at all and/or arcing amongst the wiring. Red, black and a white (cream or light brown perhaps) were the 3 wires referring to.
Is it possible that if this wasn’t functional, it could be just signalling at what it thinks is an idle rpm state and something like (the usual from other tps I am familiar with) 0.7/0.8v meaning it’s not resulting in the required timing adjustment, when the throttle is opened ? Resulting in the earlier described running behaviour?
Sorry for the long post and even the ignorance and unfamiliarity with such an engine.
Would love the opinions, corrections, advice and similar, from the more experienced than I.
Thanks,
Allan.