Performance issue

[TimBell1962]

Morning everyone. First post, be gentle. Picked up my first 3 1/2 Sport, and 81 model, earlier this year. Restored by the previous owner, its not standard, but engine performance wise, that just a Valentini 2 into 1 pipe and NLM ignition.

The issue is the performance in the top gears. I appreciate they're not the most powerful bike made and from reading numerous road tests, they like to rev, but it struggles to get past 70mph and has never got to 85. It pulls to the redline in lower gears, revs well enough on the bench, although it always feels better when cold.

The bike hasn't done many miles in the previous two years since the rebuild. It had a NOS tank, carbs were balanced and rebuilt.

Not sure where to start.

[morini_tom]

If it were me, the fist thing I’d do is strip the carbs to find out what jets, needles and atomizers it’s got (unless you already know)

The 350 can suffer from being overly rich in the midrange and sometimes top gear puts you right in the band where it’s rich and doesn’t want to pull out of it. If you find this is the case (say 4-5000rpm where it won’t pull further) try dropping it down a gear- you might find that’s enough to get you out of the rich and then back into the powerband. A Morini should love to rev so don’t be afraid of taking it all the way into the redline (if it feels willing to do so)

If the above is the case then chances are a bit of rejetting could help to enlean the area it doesn’t want to pull through, but let’s see what carb setup you have first.

Next thing to consider is if your bike has an original electric fuel tap, these can cause fuel starvation at higher fuel flow. Try putting the second manual tap in reserve and if the issue is improved then I suggest you buy a new fuel tap diaphragm from the Morini riders club for your electric tap.

I’ve not had to jet a Morini for a Valentini system but my 350 sport has an RMS 2:1 which is not dissimilar. I did have issues after I bought it with it being overly rich and not pulling brilliantly in top but not as bad as you describe. I’d have to check to see what jetting I’m on now but I know it’s not far from standard. Slightly leaner pilot jets definitely and perhaps 1 size richer (or maybe still standard thinking about it) main jet I think are the only differences, I did for brand new atomosers and needles of the correct spec which made a difference- wear here can be hard to see but will cause you to be too rich where the wear is.

[TimBell1962]

Thanks, I'll start with the jets. The tank has two manual fuel taps, which I'd not seen before.

[Galligaskins]

It might be worth checking the ignition timing with a strobe. The Strada I bought a few months ago had been a bit lacking in recent maintenance and was a reluctant starter. It had plenty of low and mid range punch but was unwilling to rev past 7k in the higher gears. As part of the routine of new ownership (oil change, new cam belt, check valve clearances etc.) I checked the ignition timing. The alignment marks on the engine are rather open to error in my view, so I like to use a DTI to find TDC and fabricate a jig that bolts to the engine cases and carries a mark that is right next to the mark on the rotor. Doing this I found that the ignition timing was set about 5 degrees retarded. Having corrected it, the bike now starts first or second kick and flies round to 8500. Really picks up its heels at 5/6000. Although the bike is fundamentally a Strada, I noticed after I'd bought it that it has the 'S' stamped on the cases below the front cylinder which prompted me to check the valve timing and confirm that it has Sport cam. I have yet to check to see if it has Sport pistons. One never knows on bikes this old, especially mine with its chequered history. It's a Dutch import.

[3potjohn]

Has it got standard air filter?

[BumbleBee]

Another thing given the age of the instruments is to remember the speedo /tacho may no longer be accurate. A second point of reference like a satnav or a mate on another bike would validate the speed you are doing.

As Tom alluded to; If you are aiming at getting up to high speed its no good sitting there in 5th or 6th and expecting to get there by just twisting the throttle. The claimed 42bhp lives somewhere but its not in the lower 2/3rds of the rev range

Nice looking bike

[BumbleBee]

Thanks, I'll start with the jets. The tank has two manual fuel taps, which I'd not seen before.

Twin manual taps is not uncommon, the electrotap sometimes doesn't flow fuel well as it ages. However nowadays the MRC has brand new diaphragms available for fixing electrotaps (pause for applause for the MRC). I have had (or added) twin manual taps on every 3½ that has passed through my ownership. A good electrotap is fine and also the original setup.

[Bison]

If you have tried all of the above and it's still not quite right, get a strobe on each of the plugs and check to see if it's advancing on both cylinders when revved. My sport was advancing on the rear cylinder, but not the front one.
Lovely bike, mine was the same colour when new, and will be again.
Alan.

[norbert]

If the bike was not used for a long time you also might have a look if anyone was living in the airbox.
How many dents has the rear sprocket?

[Andy_C]

I'll second checking the air box - when I bought my 3 1/2 Strada a few Months back I think it must have had the original 40 odd year old filter elements in it.

The bolts holding the air box together all sheared off when I tried to undo them as they were all rusted in place, once open it revealed a pair of very "crusty" air filter elements, covered in cobwebs / dead spiders and some horrible bluish corrosion on the mesh on both elements.

Susprisingly with what looked like 40+ year old air filter elements, the bike still ran reasonably well, but ran a whole lot better once I fitted some new elements.

Got to be worth a look.

[huub]

as mentioned before . probable culprits are carbs and ignition.
set the ignition with the strobe on full advance.

If that fails , i have seen quite a few leaking exhaust valves , so a compression check should rule that out

[norbert]

First you have to adjust valve clearence, second ignicion Timing and third carburators. If you start with carburators is like buildung a house beginning with the roof

[TimBell1962]

Thank you all. Didn't think about the sprockets and gearing, I'll have a look. Not sure about the airfilter, I'd be surprised if it was old but might be non stock. Other than sorting a few minor niggles away from how she runs, I've not laid a spanner on it yet.

[mad muller]

Firstly, great looking bike!

I have got a two into one system on mine and K and N filters - and the bike performs pretty good. The only difference is that my bike has the original ignition system on. If all else fails, it may be worth considering trying the old set up - if you still have the parts to do it. It sounds like the ignition isn’t advancing enough and maybe whilst you’re at it check the timing belt and the timing marks are all in line.
Hope you sort it soon - I do like the paint job you’ve gone for, I’ll have to do mine in blue now

Cheers
Muller

[BumbleBee]

I have got a two into one system on mine and K and N filters - and the bike performs pretty good. The only difference is that my bike has the original ignition system on. If all else fails, it may be worth considering trying the old set up - if you still have the parts to do it. It sounds like the ignition isn’t advancing enough and maybe whilst you’re at it check the timing belt and the timing marks are all in line.
Hope you sort it soon - I do like the paint job you’ve gone for, I’ll have to do mine in blue now

I would second that. The stock ignition system is indeed perfectly good and has advantages which people sometimes overlook. People fit other systems for a variety of reasons and the results are sometimes good and other times not so much.