porting/tuning newbie / guide to homebrew tune

[Special X]

I've had great results by scooping the transfers about 10mm into the cylinder walls, smoothing, slightly opening and flowing the transfer passages (make sure you don't go too far as you'll have to match the casings to the cylinder transfers) and setting the transfer timing 124d. Also if you widen the exhaust port 2mm each side (maintain the same aprox radius on the sides and top as although squarish ports give better power they have a tendency to break rings) Exhaust timing 170d. Open the inlet on the right hand side to straighten the path of the inlet charge but don't go wild here. Smooth out the inlet port and match the manifold to the port. Inlet timing aprox 148 (people go higher here but you'd get loads of spit back and mixture stand off). Take time to get the squish just so, about 9:1 mechanical compression and Timing at 18d BTDC

This will leave some bottom end and should rev out to just under 8000rpn before tailing off too much with the fresco.

There are loads of combinations that will work but this has worked well for me. Using these timings when my Mugello street engine was measured at a fraction under 80mph through the traps at Elvington (with Corrado riding)

[olliewtf]

I completely understand where people are coming from with regard to the time/ money people have put into learning these things. I just wanted to amass enough knowledge to have a go myself.
I also have an awful habit of not being concise with my questions!
Specisl x, thats really helpful stuff i will take that into account! my understanding is that your essentially offering slightly reduced inlet timings to what i quoted in my last post. This sounds sensible.
Well until i can get round to this i think im quite satisfied with the info ive got so watch this space!
Cheers all

[coaster]

I have had some very generous advice to tuning questions on here to be fair, Olliewtf it might help if you were a bit more specific about what you want to get out of the tune. Do you want a back lane screamer or is more of a touring tune to your liking? Which carb and exhaust will you be using?

i agree coaster read it and too much info needed before good advise can be given and theres a books worth of info to provide to answer all ,its not as easy as it looks either ,i read fastfrogs post on tuning a cast barrell(great article) and be good for him to add some info of timeframes required to get to where he is now with it and share his experience level compared to a job for a newbie to tackle ,the cost of pistons heads etc and what tooling is needed to do the job in hand at that point most realise it would be cheaper to let a tuner do it or buy a pre tuned kit,commercially available performance kit.

Bang on the mark Darrell, I spent a lot of time messing about with Ally 225 barrels, fitting reed valves, grinding finger ports and other general fettling. I managed to burn holes in several pistons and eventually decided to tot up how much I'd spent. I was somewhat surprised to find I'd spent around £750 It was that point that I decided to cut my losses and buy an Avanti kit

Having said that, having a go myself has made understanding stuff I've read much clearer

[eden]

I agree to an extent, however I fully understand why olliewtf wants to have a go at doing his own tune. its more fun than other hobbies like ermmm............. fishing for example

[olliewtf]

I agree to an extent, however I fully understand why olliewtf wants to have a go at doing his own tune. its more fun than other hobbies like ermmm............. fishing for example

this is bang on. ever since i got into scooters i had an attitude of 'lets see if i can have a go' and yes that mainly stemmed from not being able to afford to take it to a shop!
infact eden it was reading your blog that made me thing wow i wanna know more about tuning. its a fascinating topic and is helping me understand my bike better. atm im not looking to try and whack on a reed valve and drill big boost ports as i know my skills and the tools i own arent up to it but i do hope that when im a little older and actually have a garage that all these things will be more do-able. im just aiming to open ports a little and hope it works, and if it does, then great, i have a knew skillset for the future!
as said, to anyone reading this who is thinking of doing the same, graham bells book in conjunction with MB's tech site is a fantastic starting place.
anyway, cheers all, will hopefully revive this thread in a month or two and moan that im in way over my head!

[olliewtf]

UPDATE: so i finall got round to it. Things i found difficult were marking the inside of the bore with my desired timings. Either way i got it together and it runs! And its feckin fast too! Just getting the jetting sortedand then ill go thrape it and see what it can really do. I also found it difficult to set the squish; most readings were well over. I ended up running with no base or head gasket and that still didnt give me a perfect squish. I need to double check this, but i think the head wants machining. Its an sr kit so although dissapointing im not surprised. Maybe it would work out better to get someone to make me up a head with proper compression ratio but that will have to wait til i jave some money! Either way i have a grin from ear to ear whenever i ride it!

[jaco]

I have read your topic with interest. Your search for knowledge is very inspiring. I admire your courage to do it yourself instead of leaving it to the experts, who probably also learned it the hard way.
Can you share your experience of how you actually did the job. What was the port timing you finally used, did you change your plan based on the response you got. What tools did you use. How much time did it take. What would you do different next time.
Are you still pleased with it after using it for a couple of months. Can you tell something about the change in performance and fuel consumption after tuning.

[olliewtf]

hi jaco, I took the barrel off to do a port map of what the timings were. I shouldve really measured accurately how far the piston was sat below the top of barrel, and if it was level at bdc with the ex port. I then did some research, MBs tech pages, graham bells book and here, and pretty much used the timings Special x gave above as they matched the timings on MBs page. I used a Lidl dremel with carbide bits to open up the inlet to match the new manifold as best as i could. I also matched the ex port to a big bore gasket. I then worked out using an online calculator (Eden's, very useful tool!) how many mm id need to get rid of to get the timings how i wanted them.
I found it rather difficult to mark the barrel clearly on the inside, even with a metal scribe, to the desired timing as it has to be to the mm. Mine werent really to the mm, and i tried to stay on the safe side with these. Eventually i got to a point where i thought i cant make this any better with the tools i have and experience, so itll have to do!
I also made sure to chamfer all edges and widen all ports a little as suggested above.
It took about two, three days to go from a full scooter, strip it, tune it, add new outer throttle and clutch cables, new exhaust new carb etc...
What I did check was my squish, and this really needs sorting properly, but i need to find a machine shop i fell comfortable enough with to let them sort the head out.
Once this is sorted ill feel better! Jetting is still not right, but as i use it everyday its good enough, all on the rich side. With the right jetting i feel itll run a lot cleaner than it does now. It doesnt spitback loads, dont have trouble starting it, and it can sit at genuine 60mph with out screaming itself to pieces. I have yet to GPS a top speed, but I think im starting to get the best out of it!
There's still alot left to sort, the fresco has fallen apart again so wants re welding, Im adding an electronic ignition with plastic fan flywheel which should help it rev out more, in the long run Ill fit an mtech or similar to regain some torque and sort the head out. I should also stop it rattling as badly as it does, i think the engine mounts are way passed it. Front forks want rebuilding too. Rear tyre wants changing (after only 400 miles if that??!!) and plenty more little niggling things!
And im also constantly paranoid that my iron liner is made of cheese and all was for nothing, as i swear the compression aint as good as it was!!

[eden]

if I was you I would raise the exhaust port some more, if you have the timings special x stated above you will only have 23 degrees blowdown.

[olliewtf]

if you raise the ex does that increase or decrease blowdown? and is it the same relationship with the transfers?
I take it blowdown affects where the power comes in, old standard cylinders had small blowdown periods so were torquey but wouldnt rev, and big block kits harve large ones and produce power further up the range. I imagine there isnt a single magic number for all tunes, but what do different blowdown periods mean in the real world for different states of tune?
cheers mate