Help_carb settings_poor pick up after revving to c.4,500 rpm

Maestro, SEI-V

Help_carb settings_poor pick up after revving to c.4,500 rpm

Postby Seagreen » 21 May 2018 17:20

Hi, I have now got my 500 Morini (imported form Denmark) road legal and running but I am experiencing a problem with the engine not really pulling very strongly. If when stationary I rev the engine to c.4,500 rpm, close the throttle and then open it again, the engine bogs down badly but then picks back up again. Engine ticks over well; I have replaced all the jets and needles with new, sizes as per manual. Float heights measured and within the limits specified, chokes seems to be off. Could it be ignition system (I have read some threads on this forum that raided this suggestion) but I suspect that it is the carb settings. Any suggestions as to where I should look first?
Thanks,
Charles
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Re: Help_carb settings_poor pick up after revving to c.4,500

Postby P.I. Staker » 21 May 2018 17:47

If you have the original solenoid tap, have you tried it on reserve?
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Re: Help_carb settings_poor pick up after revving to c.4,500

Postby Seagreen » 21 May 2018 18:57

Hi PI, would I be correct in thinking from your reply that you suspect weak fuel/air mixture? I have tried the reserve on and off but no real difference.
Thanks,
Charles
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Re: Help_carb settings_poor pick up after revving to c.4,500

Postby 3potjohn » 21 May 2018 20:23

So if you don't close the throttle does it pull through that 4500 limit? Can you do a plug chop when it bogs down and check them out e.g.wet with unburned fuel. I think a flat spot at around those revs is something others have experienced. I've played around slightly with pilot jet sizes to lean the mixture to prevent bogging down when pulling away,but no other issues at all.
There's some info previously discussed here maybe helps viewtopic.php?f=4&t=3901

hope you get sorted.
John
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Re: Help_carb settings_poor pick up after revving to c.4,500

Postby Al B » 21 May 2018 20:32

While searching for hints about my bike's stutter on light throttle after a carb rebuild I've come across threads which indicate modern fuels seem to run richer and therefore need smaller idle jets to smooth the progression.
Another symptom of an over rich idle mixture is a tendency for the engine to nearly stall after blipping the throttle. If you have access to leaner idle jets it might be worth trying.
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Re: Help_carb settings_poor pick up after revving to c.4,500

Postby Seagreen » 30 May 2018 22:15

Hi 3potjohn and Al B,
Thanks for your comments and advice. Sorry to be slow to respond but been tied up with one on my son's wedding arrangements. Now all finished so will be able to get back to investigating the fuelling. Thanks again,
Adios,
Charles
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Re: Help_carb settings_poor pick up after revving to c.4,500

Postby penman » 04 Jul 2018 08:55

I spent quite some time on this issue with my 500. Assuming you have balanced the carbs, my money would be on the pilot jets being too big. With the way the Dell Orto carbs work, adjusting the pilot mixture with the screw only affects idle and can leave you with an over-rich mixture in the progression region, and especially affecting off-idle response.

Having said that, I would still say that out of balance carbs is the number one culprit for this effect. It's fiddly on the Morini, but if you remove the rubber inlet elbow and stick a finger in the inlet, make absolutely sure that both slides are rising absolutely together as you just crack the throttle that first few degrees. I see I just used the word "absolutely" twice in one sentence, you really need to be spot on with this. You can of course fine-tune this with vacuum gauges, but the finger test does a pretty good job and gets you well into the right ball-park.

I think I agree with the comment above that modern fuel needs leaner jetting, certainly it's my experience.

Good luck with it, they are great bikes and a lot of fun!

Joe.
1980 Moto Guzzi V50 II
1978 Triumph T140 E Bonneville
1975 Triumph T160 Trident
2014 BMW F800GT
1978 Morini 500
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Re: Help_carb settings_poor pick up after revving to c.4,500

Postby mbmm350s » 04 Jul 2018 11:26

For carb balancing on Morini its better to use the carb tune u tube manometer than vacuum gauges, its much easier to see the throttle synchronisation, which as
penman says is needed to get good progression.

Just an odd thought you do have matching transducers (i.e same type), there are at least 4 genuine Morini types and then many others designed for scooters...and the advance curves are different between types.
Mark
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Re: Help_carb settings_poor pick up after revving to c.4,500

Postby Seagreen » 09 Jul 2018 08:27

Hi Mark and Joe, thanks for your responses. I have balanced the carbs to the best of my ability using initially a simple gauge under the throttle slide to ensure that the take up was even and then using a set of vacuum gauges; when using the gauges it appeared that the initial balancing was pretty good but these vacuum gauges are not the U tube manometer type recommended by you, Mark. I will have another look at the pilot jet setting to see if that improves matters.

Mark, when you refer to matching transducers, how can I tell whether they are matched? Are they stamped with certain coded numbers or what?

3potjohn and Al B - not got round to the plug chop test yet but is on my list of things to do.

As for modern fuels affecting the jetting, I will investigate that in the fullness of time but I suspect that it could be a slow, iterative and tedious exercise? Perhaps start with the idle jet? Anyone got a recommendation for the jet number that might get me a better result?

Thanks again for all your replies, I will persevere adn hopefully be able to report back with what I have found (or not!!).

Adios,
Charles
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Re: Help_carb settings_poor pick up after revving to c.4,500

Postby mbmm350s » 09 Jul 2018 09:40

Hi,
Whilst it is most likely that your problem will be carburetor related it is worth checking this point, but really only for on the road flat spot, poor midrange or poor starting.

Any way some information here may be of interest to other readers.

There used to be two original Ducati-Electrotechnica black transducers fitted on V-twins these are flat sided with no bulge.
The part for 500W was number 323934 with a red dot sticker on it (sticker sometimes looks quite orange) .
The 350/250 had a green sticker and was part 323921.
The only difference was a change in value of one resistor that controls the advance.

There was a grey flat sided transducer with part number number 323974 and red sticker.

There are generally two types of later transducer that have the bulge on the side by the HT lead.
The original ones were number 323984 and were a beige colour should have the red sticker

There were also black ones with bulge I don't know the part number.

There are many different aftermarket types which will work this site has much detail.
http://www.motomoriniclub.nl/tech.html#Indepth

This is in Italian but Google will translate and it is technically correct English ( I am Electrical Engineer)
http://www.marioiovine.it/morini.html

If you mix the types then you may have very different advance curves, even though the full advance @6000 rpm is not so different.
I experimented with this on a 350 and it works fine with two 350 parts, or with two 500 parts after suitable retiming, but with different types is was horrible and gave poor mid-range.
I think there isn't consensus on whether the aftermarket units (ricambi non-originali) are OK on 500W.
To be clear there is no need for matching of transducers within the same type, only not to mix types.

All these transducers will work with the red pickup. This means there are two diodes in series. This has worked fine on both a 250-2c and 350 for many years.

Black pickup needs 2nd or 3rd series transducer according to a sticker on it , but will work if diodes added in series to the red leads,
because the diode originally inside the pickup was moved to the transducer.
I do not know why this was done.

Good luck
Mark
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Re: Help_carb settings_poor pick up after revving to c.4,500

Postby Seagreen » 09 Jul 2018 17:37

Hi Mark, thanks for your comprehensive reply to my question. I will take a look at the transducers and see if I can match them to the descriptions that you have given both in your reply and on the threads that you supplied. Thanks again,
Adios,
Charles
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