Rough running

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Lewes96
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Rough running

Post by Lewes96 »

3 1/2 Strada running rough at high revs when working hard, such as going up a hill. Worse when air cold. Could this be carburettor icing, fuel flow, or something else? I am running on K n N filters. It has always (since 1981) had these and tbh this has always been a bit of an issue.

Any thoughts?

Ta

PS - carb bodies have a lot of condensation on them
mbmm350s
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Re: Rough running

Post by mbmm350s »

The Club Strada (1976) has an electric fuel tap that plays up - often when you need it most like when in the outside lane of the motorway.
Worth checking the fuel taps for good flow especially if you have the electric fuel tap.
Worth trying some high(er) octane fuel (BP ultimate for example).
Carb icing in the summer? are you at very high altitude :D
Mark
Lewes96
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Re: Rough running

Post by Lewes96 »

So the electronic tap not allowing enough fuel through? I did clean it a year or so ago and the was plenty of dirt under the rubber diaphragm so could be again I guess. Am guessing that’s why some people just fit another manual switch.
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Ming
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Re: Rough running

Post by Ming »

I remember reading some years back that when 'running hard' the fuel flow from a single tap can become marginal, so that people would open the second tap too. I did that once, before realising that the second tap on my tank was the reserve tap. It didn't take long to run dry as I didn't have much fuel on board. No mobile phones then, either...
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72degrees
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Re: Rough running

Post by 72degrees »

Lewes96 wrote:3 1/2 Strada running rough at high revs when working hard, such as going up a hill. Worse when air cold. Could this be carburettor icing, fuel flow, or something else? I am running on K n N filters. It has always (since 1981) had these and tbh this has always been a bit of an issue.

Any thoughts?

Ta

PS - carb bodies have a lot of condensation on them
Define 'rough'. High revs and wide throttle or just high-ish revs on less than that? Misfiring or generally losing power (bogging). Are you on standard main jets?
On K & N type filters I'd expect to have to go a tad bigger on main jets than OEM - particularly in cold weather. I'd start with a thorough clean of the carbs, preferably using an ultrasonic bath for the stripped down bodies and the removed jets and other bits. Rebuild checking all gaskets and O-rings.

I've been struggling to perfect the mid-range on my 2C/375 for years. That runs an L5 cam. PHBH28s and a 2:1 exhaust though. I've got it not too bad, but the worst case scenario on that is trying to hold a steady half throttle at about 5000 rpm up a hill in a high gear.

Check the main tap is flowing freely. I had a similar problem with the Gilera 175 when I first got it. The OEM buzetti taps were silted up and one (the side usually used - keeping the other as reserve) had very poor flow. Fortunately I was able to dismantle it, poke the orifice clear and reassemble without it then leaking. The advantage of the 2C Morini tank is having two manual taps, each providing a reserve position.
Lewes96
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Re: Rough running

Post by Lewes96 »

Revs over 5000, throttle wide and going up a hill/incline. Getting ‘bogged’ describes it well. Easing back on the throttle sorts it out but of course that can mean slowing down a bit, or at least not accelerating. So essentially not a good idea overtaking going up hill. The carbs were cleaned properly/ultrasonically a year or so ago and o rings etc all in good nick. Not sure re the jets it can check those. I am suspecting a blocked/silted tap.
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72degrees
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Re: Rough running

Post by 72degrees »

Lewes96 wrote:Revs over 5000, throttle wide and going up a hill/incline. Getting ‘bogged’ describes it well. Easing back on the throttle sorts it out but of course that can mean slowing down a bit, or at least not accelerating. So essentially not a good idea overtaking going up hill. The carbs were cleaned properly/ultrasonically a year or so ago and o rings etc all in good nick. Not sure re the jets it can check those. I am suspecting a blocked/silted tap.
Temporarily also using the reserve tap (with a full tank!) might be informative.
Lewes96
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Re: Rough running

Post by Lewes96 »

I must admit I always ride it with the manual tap on as well, so this is with both taps open.
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72degrees
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Re: Rough running

Post by 72degrees »

Lewes96 wrote:I must admit I always ride it with the manual tap on as well, so this is with both taps open.
In that case, try a size bigger main jets.
huub
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Re: Rough running

Post by huub »

if you have got it , fit the original air filter.
Never had much luck with K&N filters on morini's
even after setting them up on the dyno , a cross wind was enough to send the mixture all over the place.
probably a problem with intake length , not the K&N filter itself
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72degrees
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Re: Rough running

Post by 72degrees »

Going back to the OEM air intake arrangements would be better if available.

I use conical S&Bs on my PHBH28s. Similar to K&Ns but cheaper. They can be affected by a cross wind, but it has to be pretty strong.
simonnorthroad
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Re: Rough running

Post by simonnorthroad »

One of the UK bike mags put S/Bs and K/Ns on a flowbench. The S n Bs were consistantly worse and hopeless when wet
simonnorthroad
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Re: Rough running

Post by simonnorthroad »

I mount my K&Ns on the end of the carb to airbox rubbers up under the tank -pushed in or on. Theyre not affected by cross/ headwinds. The filters with rubber not chrome ends are better or even the aftermarket foamfilters so they dont interfere with the tank
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72degrees
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Re: Rough running

Post by 72degrees »

simonnorthroad wrote:One of the UK bike mags put S/Bs and K/Ns on a flowbench. The S n Bs were consistantly worse and hopeless when wet
They don't really get much time to get wet on a 70 second hill climb run and I'm far from a TWO so rarely ride the road Morini if it's going to be bucketing down. I did briefly run the hill climber on just intake elbows without any filtration at all, so no resistance to flow and tucked up under the tank in relatively still air. Then I pondered on what might happen if a significant foreign body was sucked in, and put the S&Bs (suitable size for 28mm carbs) on. I don't recall having to change the jetting much to compensate. Having a mystery reground cam rather than the L5 in the road bike makes much more difference to the required main jet sizes (they both run 2:1 systems and identical NLM based ignition systems (though not an NLM pickup).

I looked once at mounting pod filters under the tank but with a 350 in a 250 frame using a 125H tank there isn't a lot of room. Might work on the 2C/375 but I doubt it, without custom tubes between filter and PHBH28s.
Lewes96
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Re: Rough running

Post by Lewes96 »

I have pondered putting an original air box on but they seem quite hard to come by. Step 1 will be to clean the electronic fuel tap, and check the jets. What is standard size by the way? Then get hold of an air box if the previous steps don’t work.
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