malossi 112 low power

[andrax]

Hey guys,

So I mounted my engine together with a fancy malossi 112, mazzucchelli crankshaft disc valve, 3.0 transmission and a dellorto 24 fitting a pinasco banana style exhaust
I matched all transfers together checked timing and the engine starts really good with lots of compression.

The problem is that I got really high torque meaning low end power, but the engine sooner stops to increase rpms and the power deliver is really weak.
I tried simonini exhaust, it went a little better but the symptoms are still there. No power and no high revs. I made a test with a friend running 102cc kit with 21mm carb and at some point he passes me and I can notice his engine revving much more through gears.

Some say that to much compression can cause this. I think the problem is on disc valve intake that has not enough flow to my cylinder.

Can you guys give me some advice?  I can think what is causing this, already tried different exhaust and added a thicker gasket on the cylinder to reduce compression and raise the ports....

Thinking about going to 136cc direct intake. What crankshaft would be needed to suit this application?



Thanks,
Regards

[spiderwebb]

pull choke out while riding WOT
does the engine like the extra fuel and air...??
if yes its jetting

remove air filter and go for a very short ride
does the engine rev higher...??
that would mean carb it too rich, choke is stuck ON or air flow is restricting intake mixture

if the timing is too retarded = you loose power in the higher rpm

squish should be 1.5mm

[andrax]

I'll have a look on squish!
And i'll try to pull choke at high revs. maybe its too rich, but that wouldn't cause this symptoms...
I gave a try with no air filter thinking about restricted intake but its the same.

Now I have the engine on the bench, so its good time to try everything!

thanks

[andrax]

Im going to improve porting on his cylinder by raising exhaust port.

Any advice for jetting the phbh24 carb with 112 malossi? Currently running main jet 100

[andrax]

New developments on this. I changed my primary gear from 3.0 to 2.54 in order to use my low end torque (turned out too long!). At same time I opened my intake port on the case and the cylinder ports. Gave also a touch on the exhaust port, raised 2mm for more rpm and slightly changed its shape. Putted all together, timing in 16° and give it a run. Sadly is the engine now detonating. I can hear simply by reving in low end, and it starts griling, and come again on high end revs... I am using original cylinder gasket so original CR... Ah and the recommended sparkplug for this kit. What could be causing the detonation???

Also got a new simonini down and forward exhaust hoping better results...

[henri]

pinking , too tight squish , too retarded timing ,too high comp ratio , wrong jetting . new to this thread ,but ya original symptoms sounded like jetting/timing related .now youve torn engine down an rebuilt to find new symptoms you'll have to start from basics again . check squish first , as too small raises comp ratio an resulting high pressure band gives detonation . an also down jet the main ,as too big a main would give ya 1st symptoms ,bogging , an also too high a fuel load which in high comp tunes makes pinking more likely .H

[tzsteve]

pinking can be advance timing, thats why the new fasion is to have electronic ignition that retards at high rpm
(but i`m sure you know that H and just slipped on the keys while tipritting on the ompuuttterrr)

[andrax]

Hey guys! Thank you all for the inputs! They are all good points to start with... I had thinking about the compression too. But since I am using original gaskets... Will give a try into this first. Checked timing with strobe light and seems on the point. Of course an electronic ignition would help, but will try to sort out this first as I think jetting or CR need fine tuning!

[henri]

yep your right steve ,mine was the short answer an should of read too advanced .mind was on the original symptoms an thinking too rich n retarded giving too high a fuel load an late spark =enuff time for detonation from compression heat .
andrax what octane fuel you using ,higher octane=more anti-knock additives , higher comp needs higher octane ,you can buy octane boosters for fuels its used in classic sports/luxury cars made to run on 5 star fuel. regular gas=2 star ,premium=3-4 star , tho premium is more likely to have 5-10% ethanol with some brands ,most regulars 5% . had a friend doing rally miles on a mallosi kit an he ended up retarding to 15 btdc after 3 pistons in 1 summer . H

[andrax]

I will try to reduce timing, currently 16 btdc. Im using 95 oct fuel, but I can get here 98 as well. Time for testing! Thanks all

[andrax]

Hello all. A few years later I just striped the engine to mount a 3.00 gear ratio. The low power/no high rebing problem was still there so I decided to do some modifications. Crankshaft was cited about 10mm on the opening side (earlier opening) and the exhaust port was modified. The engine is reving a lot better. Tomorrow will do more testing but I'm quite happy. I may give an extra touch on the port since I think the gases outlet it's not yet optimal.

Thanks