501 main jet

[Russ]

As part of giving the the 501 a check over I stripped the carbs and was happy to find everything clean and almost no wear on slides etc, only one thing seemed out of place, the main jets are 76. I checked the specs with the archived Netherlands Club site and 76 appears to the stock size. This seems on the small size; is 76 really correct?
Russ

[norbert]

Yes it is, as long as you have the original airbox belonging to the 510 Camel or Excalibur/Nueva York.

['It must be a .....']

Yes the 501 main jet size is 76 with the original airbox, exhaust etc

[Russ]

Thanks for the replies, both the air filter and exhaust are stock at the moment but I don't think they will stay that way for long.

[3potjohn]

Best of luck jetting it if you modify the airbox and silencers on a 501, otherwise you may experience poor running at a steady throttle.

[norbert]

These sofisticatet airbox you probably will not beat with other solucions.I only would change them if you are in need of space in that area. (if transplanting a 501 in a sreet frame for example)

[Russ]

I'll have to give this some thought, the air box is heavy, complex and appears to be designed to stop air reaching the carbs in sufficient quantities. If the 501 engine really needs this air-box to make it work in an acceptable way, then what is so different about this particular engine; other versions of what is basically the same design work well with simpler intake systems.

[3potjohn]

My 350 has a standard airbox and runs well- for the 17 years I have owned it.
My 501 had a stripped out airbox and it wasn’t until I acquired all the airbox internals that the stuttering at about 1/2 throttle and cutting out when closing the throttle was almost completely eliminated. Nevertheless I agree the complete airbox appears restrictive and makes accessing front rockers a chore.
Non standard silencers which do not give the designed backpressure probably do not help.
Pre air box rebuild with PHBH carbs
Main jet: 122
Idle 50
Atomisers 264BC
Post airbox rebuild
Main jet 100
Idle 43
No alteration to needle position.
Anyway do not let this experience discourage you!

[norbert]

This motor is not that special. But Morini obviouly spent a lot of time in developing this sofisticated airbox that is working very well. You allways can try to make a motor working better than any producer.
I' m just of the opinion that these airboxes have been developed with much effort, care and very good result. I've made about 140.000 km with two 501 motors in 350 frames during the last 20 years, using 350 airboxes or Polini Filters. If there would be the suficiente space (also for mantainig) I would have mounted an airbox of a Camel 501

These airbox is the reason of the small mainjet!

[3potjohn]

Once I had rebuilt the airbox I dropped the main jet to 80 but I assume due to the non standard silencers had to go up again to 100. Not perfect nonetheless.

[julianharty]

My 350 has a standard airbox and runs well- for the 17 years I have owned it.
My 501 had a stripped out airbox and it wasn’t until I acquired all the airbox internals that the stuttering at about 1/2 throttle and cutting out when closing the throttle was almost completely eliminated. Nevertheless I agree the complete airbox appears restrictive and makes accessing front rockers a chore.
Non standard silencers which do not give the designed backpressure probably do not help.
-- cut --

I've got two Morinis with the 501 style airbox, a Kanguro X and a 501 New York. In both cases the standard airbox, including all the baffles, etc. internally enable their respective motors to perform very well and fuel efficiently. I concur that Morini did a good job when designing this style of air box.

In terms of access to the tappets, the New York's tappet rocker box covers are relatively small and enable the tappets to be checked and adjusted easily, they're held in place with 35mm 6mm cap head bolts. The Kanguro X had the larger 3 1/2 style tappet rocker box covers and use 50mm 6mm cap head bolts. It took me perhaps 10 - 15 minutes to remove the rear cover! I've now fitted the rocker box covers from a Dart to the Kanguro X and it's made accessing the tappets so much easier and I can do so without disturbing the air box. The Dart has black painted versions of the same rocker box covers as the New York/Excalibur which are chromed.

PS: I also have a 501 engined K frame 3 1/2 sport. That has a relatively standard 3 1/2 sport airbox with filters and a significantly larger main jet (probably around 105's but I've lost track of what they actually are, they were fitted 5+ years ago). It also performs well however I suspect it'd actually work better with the larger air box assembly as fitted to the New York/Excalibur/Kanguro/Coguaro. Someone in Germany managed to fit one in a 3 1/2 frame however they don't fit as standard.

I use standard exhaust systems and silencers on all these bikes, for the Kanguro, replacing a worn out silencer with a new reproduction item from Italy improved the fuel economy by at least 15% so I also vouch for using the exhaust systems that Moto Morini designed for these bikes.

[norbert]

The rocker box covers of the 501 engines and obviously Darts as well are some mm lower. The early covers of the first 350 serie also is lower as the normal/current ones, maybe even 1mm lower than the 501 covers. These few mm can make a great diference when dealing with the rockers. I´ve got 501 motors in tremezzoframes from 74 and 81. As for me the funcionality is much more apreciated than the originality, I´ve cut the covers to reach easily at plugs and rocker covers. No problems with overheating at all. I´ve cut some lower 501 covers for the rear cilinder and normal ones for the front.

from the left: 1st serie, 501, normal 350/500

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as you can see there ist a quite good acess to the rocker covers. These K+N replicas were a shit, quitting in the first rain. The aluminium winsdhield worked, but I replaced them later with Polini filters.

The carburation of the two bikes is absolutely diferent acording to needle position and mainjet, both with X18 needle but 268T difusers instead of 264BC (like original 501 setting). The difference of needle posicion (second and fourth notch) and mainjet (130 and 115) is dued to diferent exhaustsytems, cams and airfilters.

[Russ]

I have not had time to do any work on the 501 this work but it I have been wondering why they needed to develop this air box, which obviously took time and expense, at a time when it seems development in other areas had largely come to a halt. That the air box/silencer combination works well is not in question, but why it needed to be done is what I still do not understand. The subject of noise regulations came up in conversation this week and I was told that some motorcycle makers during 80's had difficulty meeting new EEC noise rules that were introduced at that time, apparently one change was in the way the measurement was done and that whole bike was measured driving past a microphone where previously noise was measured with the bike stationary. I have not had time to fact check this but I do remember the were new rules about about approved silencers etc in the 80's, so it may well be true, I was also informed that induction noise was reduced on some models to enable them to pass the new tests. Could this be the reason why the air box so large?

[3potjohn]

Well all I know is the wretched thing is majorly in the way when servicing my engine. I tried cutting down an allen key to access the front rocker cover but to no avail.

[Ming]

I was under the impression that the V model Morinis had their power units designed by an engineer who knew his stuff. One of the reasons why changing any one part (airbox, carb or exhaust) often does not benefit the whole package.
Of course, this was dating back to times with different regulations, fuel and customer expectations.