GT186 - any expert advice?

[Hughieboy]

Just wondered if anyone has any sage wisdom on GT186 kits and how to get the best from them. I’ve been running one on my S2 for a few years now. It doesn’t do a high mileage, runs like clockwork and doesn’t heat seize. It’s a definite improvement over standard, probably quicker than a standard 200 but it’s not in the realms of what other users report. My set up and known stats are below, would be interesting to know if I’m missing something.

GT186 kit with Porcupine head
GT 60mm crank
Dellorto 30 with elbow and ram air foam filter
Varitronic ignition with Readspeed switchable CDI set to 17 btdc static timing
Avanti Ex Box
Li 150 Special engine with 16/46 sprockets and Pacemaker gears

It was dyno’d and the carb jets tweaked at Shiny Red and makes 14.5bhp. Speed generally tops out at just over 60mph GPS at about 6-6500 rpm according to the rev counter on my SIP Speedo. It does seem quite thrashy at that level but it’s obviously short of others achievements when they talk about power figures in the late teens/early 20’s bhp, revving beyond 7500rpm and doing 75mph!

Don’t get me wrong, I wasn’t looking for a fire breathing 80mph monster but I had kind of expected to cruise at 65-70mph and not be thrashing the knackers off it compared to other reports. And I had expected a bit more power. For reference, it came out 0.5 bhp higher than my brothers RT195 with BGM box pipe.

I’d be grateful if anyone can advise on whether there are areas I need to address or whether my expectations are too high.

[Storkfoot]

I wouldn’t profess to be an expert in anything but I did do many thousands of miles in UK and Europe on a GT186 fitted in several S3s and a Spanish S2.

Looking at my notes from 2013, mine had a v1 bgm/ MB Clubman and 30mm PHBH at the time (main 122, AV264, x13 second clip, slide 40, pilot 55, needle valve 300). I had a filter but can’t remember what type. It would rev to just over 7000 which, with a 4.9 final drive ratio, would make 70 ish with no rally gear on). On the dyno at PSL in Knowsley it made 15.75 hp and 12.02 torque.

I used to use ear defenders back then. That made my cruising speed over 60, I think, but without the earplugs my ears would bleed

Ignition was nothing fancy, a bgm stator and a lightened Indian flywheel. It’ll have been static at either 17 or 18.

Did the dyno operator make any comment, especially about your ignition?

What jetting have you got now?

Do any 185s cruise at 65 in the real world?

[dickie]

These figures are about what you should expect from that kit and set up. A few years ago I had a GT186 that went through a bit of an evolution.

1. Ancillotti pipe and 25phbl through drilled airbox and varitronic ignition. Made 9.5bhp on dan clare's dyno

2. Swapped to BGM v3 box pipe and phbh30 open mouth. Made around 13bhp on mick abbey's dyno.

3. Sent the barrel to Chris Sturgess for tuning and changed to 60mm crank. Made around 17bhp on Mick Abbey's dyno.

4. Changed to JL3 curly and static ignition at 17degrees. Made 23bhp on Darrel Taylor's dyno.

[Hughieboy]

Yes, it is loud - the Ron Moss pipe is many things but quiet isn’t one of them, even with the tail pipe. Or maybe I’m just getting old…. My jetting is the same as yours I think Storkfoot with the exception of a 120 main. To be fair, it’s a while since I had the carb apart and I can’t find my notes on the last set up. Gary at Shiny Red didn’t seem surprised at the results and thought it was about as expected as I recall.

Interesting to see how much difference the expansion made Dickie, although I thought the Ron Moss pipe was supposed to behave in a similar way.

I haven’t used it much in the last couple of years and have just got it out and realised I’d really like something that will cruise more quietly at lower revs so therefore needs to have more power. Hence wondering whether there are improvements I can make to this kit or whether to move on and start again. For current use I could really do with something that will cruise comfortably at a real 65mph plus two up and without terrifying the wildlife…. It’s not about tearing about, more about touring with the Missus.

Any recommendations on a motor that would achieve that?

[Warkton Tornado No.1]

I’m certainly no expert concerning the GT kits, but brief encounters lead me to believe them to be a capable, torque biased, low revving kit.

However - as with any engine - without the full picture, it is difficult to assess any factors that may influence the performance. Squish, compression ratio & port timings are data that should be noted during any engine build & whilst the porting may be difficult to change, or to know what to change it to, there are, in general, optimal squish & compression ratios for a given size of engine, albeit with some tolerance.

Judging by engines that I have worked on, a lot of people have no clue how to build an engine with the intention of the outcome being a reliable unit with enhanced capabilities.

To my mind, the starting point in trying to figure out why an engine is not giving it’s best is to look at those fundamentals & work through the whole process.

Admittedly, there are grey areas with the Lambretta engine, primary compression being just one. Do we subscribe to the ‘Old School’ HPC or adopt the ethos of manufacturers that build the most powerful two stroke engines? I confess to looking toward lowering the primary compression at every opportunity for reasons I won’t go into here.

To summarise & to answer your question, I don’t think your expectations too high. How to achieve the desired performance will be a matter of methodically working through what you have with some understanding of how various factors influence performance. I doubt very much that the exhaust is a problem in achieving that aim, other than the noise…..

[Storkfoot]

Have you seen this?

https://lambretta-images.com/wp-content ... nual_3.pdf

I have just remembered that mine had a 115mm RD400 conrod with an 8mm packer. That was a successful trial to make a smooth engine although fettling was needed to keep the exhaust away from the stand.

I may also have messed around with raising the exhaust port and, at the end of its life with me, I had the barrel tuned for a bit more mid range when it needed a rebore. But, my overriding recollection is that the barrel is best in its standard form.

I remember chatting to someone who had the GT186 mated to a Franspeed Race exhaust (not the Supertourer). They loved that set up.

If you do opt to go with another kit, I’d be interested in buying your GT186 if it is standard