Spitting back through carburettors at 4.5k rpm

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Re: Spitting back through carburettors at 4.5k rpm

Postby pedro » 28 May 2017 21:11

Just to add to the confusion, I am lucky enough to have two 501/350's, in fact my first ride on a Morini was on one of these beasts and it didn't take long for me to think "You and me are getting married" I was well and truly smitten. however, the two bikes that I now have, while both being great fun are quite different. Neither of them were built up by me and so I can't be sure of their origins.

Bike number one, I feel probably has an excalibur cam, it also runs a standard airbox/air filter. The silencers were extremely restrictive until I opened them up a bit.
This one runs very well, no glitches or hesitation, runs straight up to 8,000 rpm no problem. Both bikes have PHBH 28 carbs. It has 112 main jet, 40 slide,265t atomizer, 45 pilot. I run it on NGK BP7ES plugs.

Bike number two, feels livelier, probably has an L5 or similar cam, the previous owner thought that the engine came from an Excalibur, but I managed to track the original builder down and he felt he would have used a sportier cam but couldn't really remember, it certainly feels livelier, will lift the wheel off the throttle, however, it runs no airbox at all, after mucking around with K&M's etc. without much luck (the electrics are where the airbox should be) I finally settled on standard carb to airbox rubbers with nothing on the end of them, they are both in similar air conditions tucked up under the tank. Silencers are quite rorty, no idea of make. After much experimentation I am running 145 main jets, 50 slide, 268T atomizer, X18 needle. I run this one on NGK BP7 EVX plugs. Again no glitches or hesitation, runs straight up to 8,000 but quicker than the first bike.
So, two bikes, both with 501 engines, but very different set-ups. Both work well.
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Re: Spitting back through carburettors at 4.5k rpm

Postby harrymuffin » 30 May 2017 16:01

Out of interest, how many people who have dropped the 507cc engine into the 350 frame kept the original exhaust system? How many changed to the 2-2 500 exhaust system and how many went for the 2-1 system? There will be no point informing of your own carb settings if the t'other end of these engines are all different also applies to whether you have kept the restrictive induction set ups too.
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Re: Spitting back through carburettors at 4.5k rpm

Postby 72degrees » 30 May 2017 16:13

harrymuffin wrote:Out of interest, how many people who have dropped the 507cc engine into the 350 frame kept the original exhaust system? How many changed to the 2-2 500 exhaust system and how many went for the 2-1 system? There will be no point informing of your own carb settings if the t'other end of these engines are all different also applies to whether you have kept the restrictive induction set ups too.


Very good points. I'm still of the opinion that Morinis don't actually like 2:1 systems very much, particularly when it comes to the mid range carburation. Mine are both on S&B pod filters. The 'still air' argument is interesting, but they both go very well once WFO at a fair old speed through the air. Both on 2:1s, but the race replica one you supplied is probably less restrictive (even once re-packed - not needed but required by an unforced error while trying to get the system to fit on a 350 in a 250 frame) than the NLM one on the 375. Currently sounding a bit like a mini Harley after the Loton off. I must get round to removing the silencer and fixing the split in the one input tube joint.
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Re: Spitting back through carburettors at 4.5k rpm

Postby norbert » 30 May 2017 17:06

Rocinante wears nearly the same carb-configuracion as Pedros bike N°2 with original 350 filterbox (with or without filters inside). The tubes of cause have to have the size of the 500. She wears 2in2 and the silencers are the old Lafranconis (doblefolded) from the 350. I opened them a bit to fit on the 500 tubes.

Dulcinea (still running in the motor) has type K+N filters. I´ve cut original 500 rubbertubes (carb-filter) where they are folded an put the K+N on them. They are well hidden under the tank and wind doesn´t seem to influence. The exhaust sistem is a handcraft rised 2in2 that allows fine respiracion without beeing extremly noisy. The carb-configuracion is close to the original 501 (Camel, Excalibur) except the main jet. But still not aproved.

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Re: Spitting back through carburettors at 4.5k rpm

Postby 72degrees » 30 May 2017 17:56

That's a cunning idea. I also love the support brackets. The project PHBH28s are currently just lashed up with big zip ties under the pod filter junction up to the frame. I must dig out the alloy strap and fashion some templates.
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Re: Spitting back through carburettors at 4.5k rpm

Postby harrymuffin » 30 May 2017 19:14

In discussions with another hybrid owner and high ligting a storey to him regarding K&N filters and the raising of whether K&Ns are suitable for Morinis then first think about the V twin Morgans that ofton had two crbs slightly inclined towards to front, not for better volumetric efficiency but because they would not fit otherwise with a straight tract. The problem that these racing Morgans experience was not wearing of the mixture but enrichment and hence eight stroking. Coles put in front of the bell mouths would stop this problem.
When I put together my original 500 genuine Morini, I went up NLM to buy some things more for the ride to see how it went. Parked it outside and I think it may have been Alex came out to look at it and immediately trashed the K&Ns fitted saying that the rear cylinder will burn it’s valve out the reasoning being that it faces the forward and gets a week mixture. I pointed out to him that the gauze has the same effect as the Davy lamp with still air in the chamber - almost except for when it is being drawn in by the engine. He did not understand that if there was going to be any change of mixture it would enriched it as the float bowl would presure rise and force more fuel up into the inlet tract. He walked off throwing half hearted insults and doom and gloom. When I built up my hybrid I wanted long inlet velocity stacks for better breathing and could not wait for the K&N, specially ordered to come. On trying it she would not perform above about 30mph in any gear and eight stroked like bugger on the back pot. When the filters came and were fitted carburation was perfect on both pots . The only problem I have had is when it is very wet and that water gets sucked in and then into the float bowls, cured that with shields fitted to one side of the filter so that moisture is not sucked in and when parked water does not drip off the tank. The problem with the corrugated plastic tube that Morini fit is that it does not induce laminar flow but disturbs the airflow with all those ribs. Think standing on a bridge over a stream, where is the fastest water flow against the cluttered bank or in the middle? Stanley Hooker when he went to work at Rolls Royce during the wa,r was dismayed with the inlet tract into the carburettor of the Merlin engine, No gradual transition between cross sections as the tract bent round through 90deg, no internal vanes and rough and ready joints. His solution to this problem which took up an afternoon increase the volumetric efficient and the same mark of engine increased its power output. Regarding 2-1 exhausts. if they are equal length then, although individual pots of an engine should be treated as though were individual single cylinder engines and completely separate from one another, there is the phenomenon of the exhaust gases creating a depression in the other pipe causing further up the line a greater vacuum in the combustion chamber which will there fore induce a greater differential between atmospheric pressure of the carburettor and that of the combustion chamber increasing volumetric efficient and hence more charge and hence more power. This is a generalisation but competition engines found in cars plus other, will use this extractor effect to utilise all the kinetic energy in the exhaust gases. The Vanwall did this to such affect that compared to the Ferraris and Maseratis they were almost silent just a deep hum as they opened up on full song. I do not see carburettor settings as a problem, I have 2-1 systems on my bikes and there no flat spots only a hiccup occasionally coming off idle which I cannot be bothered to sort. perhaps with the use large overlap valve timings you are mixing up with 'coming on the cam' with flat spots a la Manx Nortons which would not pull cleanly until the revs were up in the 5000 range eight stroking and farting about until then. Certainly the racer I had it would not pull cleanly until about 5500 and a big handful of throttle where she would then start to lift the front without any provocation, I did not regard the eight stroking and spitting back as due to a flat spot.
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Re: Spitting back through carburettors at 4.5k rpm

Postby norbert » 30 May 2017 20:40

Hartmut resolved the problem of the air (especialy of the rear cilinder) this way:

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He uses the rubbers of a Camel/Excalibur 501 (carb-filter) adding some kind of tube inside to fix the K+N. The alloy windshiels can be turned.

The advantage of my solucion ist that I took of the original rubbers from the K+N, who weigh quite a lot, stressing the inletrubber (carb-head). You can fix the filter in the first fold with some silicone. Anyhow one shoud support the carbs. The inlet rubbers for the 501 use to crack easily (at least that´s my experience :evil: )
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Re: Spitting back through carburettors at 4.5k rpm

Postby 72degrees » 30 May 2017 22:20

Very interesting. It's so long since I rode a Morini with a cam less 'bumpy' than an 'L' that it may indeed be more a question of that than anything else. Both are fine up to about 4000rpm and go like the proverbial excrement off a digging implement over 5000. They can be coaxed through the intervening rev range on a small throttle opening, or more usually by adopting the simple strategy of getting it wide open ASAP. When I find some tuits I intend to experiment further in the atomiser/needle range (again) in hopes of making the road 375 more amenable to 'cruising' in that region. The comments on laminar flow are interesting as I wasn't sure conventional gas-flowing techniques were always successful with a Heron head setup that relies on turbulence - though I suppose that's once the mixture reaches the combustion chamber.

I distinctly remember having to dry out the K&Ns I had originally on the 375, in the hand-dryer of the gents of an M6 petrol station halfway on a monsoon rain ride up to Liverpool. The S&Bs seem less prone to the wet, but to be fair it's probably more a case of not riding in the rain if I can help it these days.

I understand that a 2:1 with equal pipe lengths should give better performance. They do seem to at high revs, but given the resonance effects of pipe diameter changes or junctions, I suspect they may not be so helpful at other rpm. It's amazing what 'stepped' headers or 'power bombs' can do on 4T singles. Once you have two (or more) pipes combining I expect its even more complex.

Fascinating stuff.
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Re: Spitting back through carburettors at 4.5k rpm

Postby MickeyMoto » 31 May 2017 06:28

All too complicated. It will be something simple.

Simplicity is great. Look through history and lots of engineering problems have been solved through simple changes. Concorde's air speed reduction for the engines, supersonic tail flutter, Miss Schilling's orifice - she also raced motorcycles! - use of Biros in space (use a pencil).
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Re: Spitting back through carburettors at 4.5k rpm

Postby 72degrees » 31 May 2017 08:55

MickeyMoto wrote:All too complicated. It will be something simple.


Very Zen. "See simplicity in the complicated."

When you find out what it is, let us know.
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Re: Spitting back through carburettors at 4.5k rpm

Postby MickeyMoto » 31 May 2017 10:59

When I were a young technician, two people I worked with had the following ethos to fault finding.

First one insisted it was something simple... unless its not!

The other guy said he used poke and hope.

Manufacturers spend a lot of money getting the bike to run correctly, we then come along and think we can make changes and all will be well. See guy two above, as that is what most of us do - trial and error.

There are too many variables here. Camshaft profile, ignition system, air filter setup, exhaust configuration, carb jetting. So easy to get lost. The Excalibur had a convoluted exhaust system. The camel used a different system. The camshafts are different profile. Change one thing and everything else changes. I have Busso 500 silencers with a standard 500 exhaust with cross over link pipe. A standard 31/2 airfilter box with filters. The only other change is the main jet. It stutters at 2,500 rpm on a nearly closed throttle, pulls to 8,500rpm except in 5th and 6th gears, and is still economical. Others have got their 501s working probably using method 2.

I will not be meddling with mine, so apart from my suggestion to balance the carbs and remove the carb link pipe am unable to offer any assistance. The only cure will probably be to take it to a rolling road and see what happens.
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Re: Spitting back through carburettors at 4.5k rpm

Postby pedro » 31 May 2017 13:13

All very well Micky, but Morini never made a 501/350 hybrid mores the pity, so, yup, poke and hope it is!

One word about the rolling road, I spent some time and money getting mine (with K&N's) set up on a rolling road, got it pretty damn good, then took it on the road and it was so far out as to be useless, I could only conclude that the wind conditions in real life around the filters were so different from the conditions on the rolling road so as to make it a waste of time.
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Re: Spitting back through carburettors at 4.5k rpm

Postby harrymuffin » 02 Jun 2017 14:06

Hopefully we have finally reinvented the wheel, but for information only the oversize 500 6 speed I have with 14-38 sprockets will do the national single carriage way speed (60) at 4200rpm and the 507 top end on a 5 speed bottom end 3800rpm with 14-40 sprockets up from 14-44 which is standard. Both bikes have the same tyres Avons 100/90 fronts 110/90 backs. The 5 speed has accurate Smiths chronometric instruments the 6 speed has Vaglias. Both tick over at or around 1400rpm and pull without any problems from around 2000 -2500rpm with out spitting back, hesitation or hiccups. The bikes do pop on the over run, the 507 and could really do with the needle raising one notch but cannot be bothered, but the 500 is once in a ride occurrence. I know with my overweight fat arse that the bikes will pull 6500 and rising and expect 7000 to be achieved, if Provini was on them going past the Highlander then he would probably be pulling 8000rpm, but then he is or was a 8st 5'3" short arse and was able to mould himself into any bike. I now these figures because I have just MoT'd them after being off the road for some time, the 500 having just had rebuild.
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