New Mikuni Conversion Problems

gman · Post by **gman** » Sun Jul 22, 2007 12:49 pm

Hi All,

I'm new to this forum so I would like to say Hi from Oz!

About month ago I purchased a 1988 750 Paso and have since upgraded the electrics with the JS mod.

The original Webbers were giving me some starting/running issues so I picked up a couple of 38mm Mikunis from a wrecked 750 Monster.

After installing these carbs I still have a starting issue. It only seems to start after I clean the plugs. Pour some fuel directly into the carbs and spray some Aerostart into the carb intakes.

It takes a while to start but when it does it seems to idle well. When I twist the throttle fast or "blip" the throttle it splutters and the engine dies. If I very slowly twist the trottle it seems to splutter past 1000-1200rpm them revs nicely. Also once it has warmed up it starts at a touch of the red button.

Any Ideas ?

I have not fitted an aircleaner to the bike yet. I have ordered the Uniflow/Unifilter PK79 which hopefully will be a good fit.

Can anyone tell me if once I fit an airfilter with these issues be fixed ?

Thanks in advance!

Glenn

ducapaso · Post by **ducapaso** » Mon Jul 23, 2007 4:47 pm

I'm not sure it's a carb trouble.
Are you sure that the electrical upgrade works well?
You just need to measure the voltage on the orange wire of the coils DURING engine starting (while pushing red button).
You might happen something's going wrong, or the battery itself is a bit exaust and it doesn't work well.
In any case, DO NOT USE A JUMPER TO START THE ENGINE!!!
Ignition boxes are very sensible to overvoltage!!! :ugh:

Finnpaso · Post by **Finnpaso** » Mon Jul 23, 2007 7:09 pm

I dont know anything about Mikunis yet, but i have HEARD, that those are VERY sensitive about airbox(!!!!), so it CAN be, that Your problems are connected to air filter systems. It can also be, that Mikunis NEED very suitable airBOX, not anykind of "pod filters"... Anyway i am intrested now, cause i have option now to buy very good Mikunis with manifolds to me(to my 750 Paso)

Fraser · Post by **Fraser** » Tue Jul 24, 2007 8:54 am

Antti,
I have the Unifilter foam pods on my Mikunis and they work really well. The size was a PK79, which are 57mm. The Mikunis were off a 1994 900SS and I have fitted a Dynojet stage 2 jet kit for a 750SS (they both have the same physical size 38mm Mikuni carb, but different jetting). The Dynojet kit is suitable for pod type filters and an open exhaust.
Also a Yamaha TDM850D 1992 (possibly other models) has the same size mikuni carbs, I bought float bowl gaskets from the Yamaha shop after my local Ducati dealer couldn't get them for several weeks. The Yamaha dealer had them the next day.
The Mikunis absolutely transform the Paso's performance, with a steady slow idle, no stalling at traffic lights and instant throttle response. Best of all is the fantastic induction roar when you fully open the throttle, it's addictive, you just want more.
Fraser.

ducapiero · Post by **ducapiero** » Tue Jul 24, 2007 10:24 am

On my experience mikuni are fantastic only with airbox,with pod filters there was large erogation hole at 4500 gg , now wth the modified airbox and two in 1 she goes great

I think the airbox solution is the best solution between power and fuel consumption.....
lamps
Piero

gman · Post by **gman** » Tue Jul 24, 2007 10:37 am

Thanks for the input guys,

I just recieved a set of unifilters. I originally ordered the PK79 but the air intakes on my Mikunis are 60mm not 57mm as the PK79s are. The guys at Unifilter really helped out and shipped me some units with a 60mm opening.

After oiling the filters and installing them the bike was still hard to start but once I got it going and warmed up it was a lot better. The idle is smooth and when I gave it some gas it did not splutter around the 1000-1200rpm mark AS much.

I will look into rejetting the Mikuni's but will first check my voltage at the coils as Nicola has suggested.

I have also noticed that the choke does not help (makes things worse) at all on these Mikunis. Does anyone have an idea why ?

Glenn

Desmo_Demon · Post by **Desmo_Demon** » Tue Jul 24, 2007 11:31 am

gman wrote:The idle is smooth and when I gave it some gas it did not splutter around the 1000-1200rpm mark AS much.

Just how low of an rpm are you idling your bike? The Ducati engines should be idled higher than a Harley. :laugh: I think both my ST2 and 748 are around 1400-1500 rpm for idle. Heck, my Harley used to idle at 800, but I bumped that up to 1100-1200, now. I still haven't started my Paso, yet, but I imagine I'll set its idle around 1200-1400 rpm.

Part of your problem may be that you are expecting too much from the engine at too low of an rpm. My ST2 is just about worthless under 3000 rpm for rideability. I'm sure someone else can give better insight to the Pantah engine's characteristics, as I have no experience with a running one....yet. :laugh:

Finnpaso · Post by **Finnpaso** » Tue Jul 24, 2007 7:06 pm

Normally (not tuned!) Ducati engines should have idle close 1200 rpm, but if any modifications, like lightened parts, then need more, at least 1400-1500 rpm! More tuned, more idle rpm...

redpaso · Post by **redpaso** » Wed Jul 25, 2007 4:30 am

Hey Glen, a little off the topic but where abouts in OZ are you?

gman · Post by **gman** » Sun Jul 29, 2007 9:32 am

Good news. I took my Paso for a run yesterday and everything has improved

and I did'nt do anything to it. The run must have cleaned out the carbs as for the first few kilometres it was spluttering and backfired a few times.

I took her out again today for another run and she runs great. Changing over to the Mikunis has really transformed this bike. Accelleration is now smooth and so is the idle.The bikes now starts easier than with the Webbers and the idle has picked up and stays around the 1100rpm mark from 800rpm when I first did the conversion.

btw Redpaso - i'm in Perth, WA.