In a previous post on here I’ve asked questions and had a lot of suggestions regarding my GT186 which is running a Varitronic. I’m thinking of changing the crank to a GP taper one for strength which will mean at least changing the flywheel (currently Li taper).
Would I be better to change the whole ignition for something less variable and if so what would be a good way to go? I’ve had no problems with the Varitronic but it concerns me that options are limited on changing or adding parts, for instance if I wanted to adapt or change to a DC system. It also concerns me that at 21 btdc it is possibly still retarding too far to give a lot of performance on full throttle but I only go by what I read, I don’t fully ‘get it’. I’m concerned about advancing it further as I worry about the engine getting too hot unnecessarily.
So, is it better to fit a 58 or 60mm stroke crank (and which crank?) and should I swap the flywheel or just change it all to something more adaptable. To be honest, I only bought the Varitronic as it was a complete solution in a box, I’m not really sure what benefit I get from it. I also know it’s not the preferred ignition for the GT kits.
I know that’s a lot of questions and could be subjective but I’d love to know what those more technically knowledgable than me think is the best way forward.
Appreciate anyone’s thoughts, thanks...
Trying to get an understanding on ignition systems for GT186...
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Adam_Winstone
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Yes, very subjective so please don't take my thoughts as guidance, rather, it reflects what comes to my mind...
Changing to a GP crank - always a good move but essential if running a big cc and or tuned kit with a reasonably heavy flywheel. Not as important if running a fairly light flywheel.
Change of ignition - It is my understanding that Richard doesn't (didn't?) recommend advance/retard ignitions because an over advance at low rpm may contribute to reed damage. This may not be 100% correct or current but I'm sure that he'd respond if you ask him the question directly... he's a nice/decent guy. If advance/retard has not given you reliability issues, why not stick with it?
DC - I've run a number of bikes on 12V DC systems but always, eventually, regret it as battery maintenance lets me down sooner or later. I understand that you can run some of the DC systems without a battery or a no maintenance sealed battery but I still end up returning to the simplicity of AC.
Stroke - Better if the back of the conrod doesn't rub on casing and/or if it doesn't throw your port durations out. Again, I'd ask Richard and/or some of the excellent tuners that give advice freely... but watch out for those that instantly want to sell you what is sitting on their shelf!
Hopefully this brief response may encourage others to give their own opinions too.
Good luck.
Adam
Changing to a GP crank - always a good move but essential if running a big cc and or tuned kit with a reasonably heavy flywheel. Not as important if running a fairly light flywheel.
Change of ignition - It is my understanding that Richard doesn't (didn't?) recommend advance/retard ignitions because an over advance at low rpm may contribute to reed damage. This may not be 100% correct or current but I'm sure that he'd respond if you ask him the question directly... he's a nice/decent guy. If advance/retard has not given you reliability issues, why not stick with it?
DC - I've run a number of bikes on 12V DC systems but always, eventually, regret it as battery maintenance lets me down sooner or later. I understand that you can run some of the DC systems without a battery or a no maintenance sealed battery but I still end up returning to the simplicity of AC.
Stroke - Better if the back of the conrod doesn't rub on casing and/or if it doesn't throw your port durations out. Again, I'd ask Richard and/or some of the excellent tuners that give advice freely... but watch out for those that instantly want to sell you what is sitting on their shelf!
Hopefully this brief response may encourage others to give their own opinions too.
Good luck.
Adam
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Hughieboy
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That's great Adam, thank you.
It's my first complete 'proper' engine build so I was just a little nervous because of the whole 'you must run a GP crank' thing. The scooter runs great and I've pretty much done it all by the book with the exception of changing the fairly recently purchased Varitronic and hardly used Harry Barlow built crank (decent bearings/conrod etc) due to saving on cash outlay, mainly.
The only issue is that it 'tops out' at 6500rpm but some have said that may be down to timing retarding but I've been sceptical over advancing it too much in case of creating other problems with heat and I didn't know about the reed issues.
It starts, runs and performs well in all other aspects.
Regarding DC I just thought it would be nice to have better lights, phone charging and a SIP speedo that didn't keep turning itself off at tickover but I take on board your comments and maybe it's a step I don't really need if it's likely to cause further complications.
By the way, we don't know each other but I live just outside Bicester and am a member of Aylesbury Scooter Club so we know people in common. I've been watching your recent travels on the Roadrunners Facebook page, looks like you guys had a blast!
Hope to catch up sometime and thanks for your insights and advice.
(ps. I have messaged Richard through Scooterotica but I don't think my message got through as I haven't heard back regarding the rev limit issue. I'm not sure my pm's are working on here).
All the best
Hugh
It's my first complete 'proper' engine build so I was just a little nervous because of the whole 'you must run a GP crank' thing. The scooter runs great and I've pretty much done it all by the book with the exception of changing the fairly recently purchased Varitronic and hardly used Harry Barlow built crank (decent bearings/conrod etc) due to saving on cash outlay, mainly.
The only issue is that it 'tops out' at 6500rpm but some have said that may be down to timing retarding but I've been sceptical over advancing it too much in case of creating other problems with heat and I didn't know about the reed issues.
It starts, runs and performs well in all other aspects.
Regarding DC I just thought it would be nice to have better lights, phone charging and a SIP speedo that didn't keep turning itself off at tickover but I take on board your comments and maybe it's a step I don't really need if it's likely to cause further complications.
By the way, we don't know each other but I live just outside Bicester and am a member of Aylesbury Scooter Club so we know people in common. I've been watching your recent travels on the Roadrunners Facebook page, looks like you guys had a blast!
Hope to catch up sometime and thanks for your insights and advice.
(ps. I have messaged Richard through Scooterotica but I don't think my message got through as I haven't heard back regarding the rev limit issue. I'm not sure my pm's are working on here).
All the best
Hugh
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Adam_Winstone
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Hi Hugh
How funny, not far away then! Please say hello if/when our paths cross.
Scotland was a good trip and the range of different bikes/motors showed that there are plenty of viable kits and combinations that can be used well together. We had everything from a home tuned iron 175 to an RB 225 in the group... Casa 185, Mugello 240, iron 230, GT186. All bikes are well set-up and ridden by guys and girls who do most of their own mechanical work and take the time to make sure that the set-up is suitable for reliable use, incl. touring. My regulator failure was the only problem that any of the Lammies had and the one that I managed to borrow worked faultlessly for the return trip.
6500 max. RPM is a little low as it should rev-on higher through the gears. What is the rest of the setup?
Adam
How funny, not far away then! Please say hello if/when our paths cross.
Scotland was a good trip and the range of different bikes/motors showed that there are plenty of viable kits and combinations that can be used well together. We had everything from a home tuned iron 175 to an RB 225 in the group... Casa 185, Mugello 240, iron 230, GT186. All bikes are well set-up and ridden by guys and girls who do most of their own mechanical work and take the time to make sure that the set-up is suitable for reliable use, incl. touring. My regulator failure was the only problem that any of the Lammies had and the one that I managed to borrow worked faultlessly for the return trip.
6500 max. RPM is a little low as it should rev-on higher through the gears. What is the rest of the setup?
Adam
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Hughieboy
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Hi Adam
Sounds like a great tour.... and I suppose it highlights another concern with the Varitronic, if it goes it goes, probably no borrowing regulators etc.... but then it seems to be reliable. And it was expensive!
Set up is....
Dellorto PHBH 30
135 main
X13 needle, 2nd clip (I think)
AV268
40 slide
55 pilot
70 choke
300 float needle
MB mesh/gauze inlet cover (removed remote RAMAIR filter as I thought it might be restricting air)
TSR Evo pipe
17/46 sprockets (no problems with pulling power)
Pacemaker gears
Varitronic set at 21btdc on fast tickover.
Readspeed 5 plate clutch
Starts, runs and rides fine. Just hits a ceiling at 6500 rpm. I don’t want to be riding it at that level all the time but it’s disconcerting when it just won’t rev any higher, especially if your overtaking Sunday drivers in third (as I discovered!).
Appreciate you taking a look,
Thanks,
Hugh.
Sounds like a great tour.... and I suppose it highlights another concern with the Varitronic, if it goes it goes, probably no borrowing regulators etc.... but then it seems to be reliable. And it was expensive!
Set up is....
Dellorto PHBH 30
135 main
X13 needle, 2nd clip (I think)
AV268
40 slide
55 pilot
70 choke
300 float needle
MB mesh/gauze inlet cover (removed remote RAMAIR filter as I thought it might be restricting air)
TSR Evo pipe
17/46 sprockets (no problems with pulling power)
Pacemaker gears
Varitronic set at 21btdc on fast tickover.
Readspeed 5 plate clutch
Starts, runs and rides fine. Just hits a ceiling at 6500 rpm. I don’t want to be riding it at that level all the time but it’s disconcerting when it just won’t rev any higher, especially if your overtaking Sunday drivers in third (as I discovered!).
Appreciate you taking a look,
Thanks,
Hugh.
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Adam_Winstone
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Is it limited to 6500 through the gears or just in 4th?
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Hughieboy
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All gears.. became apparent when overtaking in third gear and wouldn’t rev over 6500... changed up and we were off again. It’s like it has a rev limiter, not a lack of power.
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Adam_Winstone
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Yes, it seems as though a factor, or combination of factors, is acting as a rev limiter.
I have had rev limitations based on pipe, ignition and carburation factors. Compression and gearing would probably not be a factor as they would still allow the motor to rev on through the lower gears.
Ignition - certainly could be a factor if it is over regarding and struggling to burn off the fuel charge. I've experienced this sort rev limitation through over retardation and from faulty pickups on traditional 12v electronic kits.
I have had rev limitations based on pipe, ignition and carburation factors. Compression and gearing would probably not be a factor as they would still allow the motor to rev on through the lower gears.
Ignition - certainly could be a factor if it is over regarding and struggling to burn off the fuel charge. I've experienced this sort rev limitation through over retardation and from faulty pickups on traditional 12v electronic kits.
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Adam_Winstone
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What does the ignition retard to when strobe? You will probably find that ignition copes with burning off the charge at revs until 14 dbtdc or so but then struggles and feels rich or like it has hit that rev ceiling.
I had one of my bikes dynoed and the rev limitation was not identified but I was convinced that it was holding back, in that case a change of CDI allowed it to rev-on as expected.
In your shoes I would strobe it to identify max retard and adjust it to hit 16 at max revs (very briefly on the stand) and let the initial advance be whatever it needs to be. Take note of this starting figure though and watch for heat buildup at lower rpm.
Also note that change to ignition range may impact on jetting, tweaking to suit.
I had one of my bikes dynoed and the rev limitation was not identified but I was convinced that it was holding back, in that case a change of CDI allowed it to rev-on as expected.
In your shoes I would strobe it to identify max retard and adjust it to hit 16 at max revs (very briefly on the stand) and let the initial advance be whatever it needs to be. Take note of this starting figure though and watch for heat buildup at lower rpm.
Also note that change to ignition range may impact on jetting, tweaking to suit.
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Hughieboy
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Thanks Adam,
I appreciate the explanation, heat build up is something I definitely want to avoid..... I will take your advice and give it a try. I have an engine temperature sensor connected to my SIP speedo, any idea what a max safe operating temperature would look like?
At present it reads about 102 - 105c when it's at its hottest, usually when ticking over after a run.
It would be good to eliminate this before forking out for a new pipe, some reckon the TSR is good but some reckon it makes its power lower down than, for instance, a Fran Race. It certainly produces some grunt, not over sure about the top end but will try the timing first.
I appreciate the explanation, heat build up is something I definitely want to avoid..... I will take your advice and give it a try. I have an engine temperature sensor connected to my SIP speedo, any idea what a max safe operating temperature would look like?
At present it reads about 102 - 105c when it's at its hottest, usually when ticking over after a run.
It would be good to eliminate this before forking out for a new pipe, some reckon the TSR is good but some reckon it makes its power lower down than, for instance, a Fran Race. It certainly produces some grunt, not over sure about the top end but will try the timing first.