Honda Dio - clutch centre spring question (1st post)

[wedgepilot]

Hi all, it's my first post so go easy on me

I've got a 1990 Dio AF27 with the following mods:
- high-speed pulley
- 6.5g roller weights
- Dio ZX belt (longer & wider than standard)

Also, the engine was rebuilt recently (new piston & rings). I do mostly highway riding, so I've set it up for top speed and can get 75kph (about 50mph?). So far so good.

However, around 45kph it hits "top gear" and the revs drop really low and it falls out of the power band. I craaaawwwl through to 50kph, the revs rise a bit, then it picks up again and I'm off.

Is this to do with the clutch centre spring, I mean the one that holds the rear pulley closed? Would a stronger spring keep the revs higher for longer? Or something else entirely?

I've already tried lighter roller weights, they just moved the flat spot a little higher (and took 10kph off my top speed)

I would love to get this sorted, as it's an awesome little scoot apart from that.

Thanks in advance!

[Kenny_McCormic]

i would try a aftermarket pipe. and maybe a bigger carb and airfilter

[chevyguyjay]

u say u want more top end, cause u do mostly highway riding. wouldnt u want heavier roller weights? the heavier weights, the higher the belts going to ride to change that gear ratio all together. did u check and see what exactly your clutch shoes look like? maybe worn out? hm.....just curious, when u get a chance, after taking a little ride, check your spark plug color. id like to know what color it is.

[wedgepilot]

Hi, thanks for the replies. The scoot is plenty powerful, the top end is awesome, and the plug is a nice chocolate brown.

The problem is with the gearing.

I think the driven pulley is opening all the way up too soon, so I'm in "top gear" too early, around 25mph. This means that the revs drop too low and I fall out of the power band.

I need to keep the revs up a bit more until about 30-35mph. I was thinking either the clutch springs or the center spring could be worn?

Heavier weights don't work, I tried that already. The driven pulley just opens up even sooner. The weights I have now work great and I can pull 45-50mph easy with the standard exhaust.

[W/C]

If your running a zx belt,you need to have the front pulley boss-zx or figure out away to space the stock boss out more-shimms.
Also playing with the weights is what you need to be looking at.
Clutch springs are stall
Center spring is to keep the belt from slipping
Run the heaviest weights you can to get your top speed
Run the lowest weakest center possible
As for clutch springs, you want to keep the bike in the power band, if your running a stock clutch, try running either polini blues or green on a stock clutch

[wedgepilot]

Hi W/C, I have a 'high-speed' front pulley, not a stock one, so that should be fine. I tried heavier weights, but it didn't affect the top speed - 6.5g seems to be the sweet spot.

On the clutch I have, the center spring holds the rear pulley closed, which is like first gear. When it's fully open (and the front pulley is closed up), that's like top gear - isn't that right? So wouldn't a weaker center spring mean the rear pulley opens up sooner, so I get taller gearing sooner? I want the opposite, I want to hold it in a 'lower gear' for longer.

[W/C]

The center spring does two things keep the belt from slipping and keep the rear drive closed longer, but that's why you want to run the weakest you can get away with.
You should not go lower on the weights to gain better accel, what you need to do increase your stall, heavier clutch springs will help your bike be in the higher rpm range before you start to move.
Unless you center spring is totally dead-soft- then installing a stonger one will only kill your overall power.
Also if your running a zx belt on a stock rear drive the belt is not able to ride all the way down to the bottom which is affecting your topspeed.
A stock belt setup is the best unless your going to change the rear drive
Try putting the stock drive boss in with your pulley, the stock is shorter then the zx

[wedgepilot]

I'm happy with my top speed, I don't need any more top speed. 50mph on a 'ped is scary enough! Also, the revs are nice and high off the line, so the clutch springs are ok.

The problem is in the mid-range (about 25mph), where the revs drop out of the power band for a while. I actually *want* to keep my rear pulley closed a little longer.

If you can imagine a graph, with engine speed on the vertical axis and road speed on the horizontal axis, it's like a wide-angle 'V'. At the pointy bottom of the V, the engine speed is out of the power band.

I really need that pointy bottom to stay up in the power band - the revs are dropping too low in the mid-range. Does that make sense?

[stillspeeding]

The only restriction on a Japan dio is the cdi, swap it out with a U.S. elite-s-94 and up, this is old school!

[wedgepilot]

Mine is an AF27 Dio, the CDI units didn't come in until the AF28. The only restriction on mine was the front pulley, which is long gone!

Like I say, top speed is NOT a problem. The gearing in the mid range is the issue here.

[W/C]

I set up an S with 8 grams weights, stock drive/belt,stock bore,carb air box , stock pipe,med clutch and some kind of aftermarket pulley ,10% center spring and I think the center is a little to stiff for the stock engine.
If you mid range is lacking, it is more then likely that the belt is riding up to fast, but seeing as your running a wide belt in a narrow rear drive,is your problem.
Since the belt is not dropping all the way down or prob not more then half way means the transition is not a broad as it is supposed to be
low range - belt low in front , high in back
High range Belt high in front low in back
But like I said because the issue of the belt and rear drive combo is making the mid point really short causing your engine to bog because the revs are not able to stay up during the transition, adding a stiffer center spring will be a bandaid fix ,unless your center spring is really worn out, but for a stock bore I would go with a stock center spring

[jeremydde]

Mine is an AF27 Dio, the CDI units didn't come in until the AF28. The only restriction on mine was the front pulley, which is long gone!

Like I say, top speed is NOT a problem. The gearing in the mid range is the issue here.

I have a 2000 DIO SR model and have exactly the same problem. It launches perfectly (pulls wheelies) and top speed is excellent but after 40km/h the engine rpm drops from around 7600 to 5900 right out of the powerband and then takes awhile to climb back up.

I have already ordered a stiffer rear contra spring from vt cycles and will update when I have it installed.

[wedgepilot]

Since the belt is not dropping all the way down or prob not more then half way means the transition is not a broad as it is supposed to be
low range - belt low in front , high in back

W/C, can you explain this one a bit more? I still don't fully get it. If my belt wasn't dropping all the way down, wouldn't that mean I stayed in the low range for longer? Or am I missing something? Thanks for putting up with all my dumb questions, BTW.

[wedgepilot]

I have already ordered a stiffer rear contra spring from vt cycles and will update when I have it installed.

Cool! I look forward to hearing about it. I spoke to a bike mechanic friend and he mentioned the center spring was a right PITA to install - I hope your install goes ok!

At the risk of going O/T on my own thread , how is your digital tacho working out? Was it easy enough to install?

[jeremydde]

I have already ordered a stiffer rear contra spring from vt cycles and will update when I have it installed.

Cool! I look forward to hearing about it. I spoke to a bike mechanic friend and he mentioned the center spring was a right PITA to install - I hope your install goes ok!

At the risk of going O/T on my own thread , how is your digital tacho working out? Was it easy enough to install?

I have already installed an upgraded contra spring once on my bike already (1000rpm) and once on a friends hyosung rally. The large clutch nut is a pain, but that's about it. My friend has no problem holding the clutch down while I put the nut back on. You should have a buddy with you to help you out with the install.




The tach is easy to install. It's inductive so you just wrap the signal wire around the spark plug wire and strap it there. Then just find a power and ground for the gauge.