low to mid range flat spot

[70sbikes]

What model are they please

VM28's (probably a bit bigger than necessary, but re-jetting isn't that difficult). You also need the "top hat" type plastic/metal insert that goes into the carburetor mouth to allow them to be mounted to the standard Morini rubbers (I bought aluminium ones from NLM, and had to cut off about 10mm so an air passage wasn't blocked). K&N filters aren't cheap either...

[barney 66]

Great Thanks for the reply and pictures, I will decide end of the Summer if it’s a keeper or not, actually fancy a 500 Strada, as well
Thanks barney

[mad muller]

I know you said you have checked the timing, if you have a stobe light ,see if the advance is working when you rev the engine , just a thought as all the carb issues have been covered , you should see the timing marks move away from each other upto 6k then full advance , you prob may have tried this .

[barney 66]

I am going to try it again Tomorrow, was busy yesterday and Today, I did also find that my fuel tap wasn’t opening properly when I came to drain the tank

Thanks barney

[barney 66]

I know you said you have checked the timing, if you have a stobe light ,see if the advance is working when you rev the engine , just a thought as all the carb issues have been covered , you should see the timing marks move away from each other upto 6k then full advance , you prob may have tried this .

Sorry never actually answered your question, yes timing spot on and advances fine, also put new plug wire on yesterday and ordered new plug caps
Thanks barney

[3potjohn]

And make sure to have both taps open. Is one the electric variety? A good flow is very important as us old chaps know.

[barney 66]

Yes one is the electric,I will hold my hand up and say I have only had the electric tap on while riding, but will do what you have suggested Tomorrow
Thanks barney

[barney 66]

Ok update on this, out again this morning following my mate 25 mile round trip (ran out of time for an appointment)
maybe very slightly better but still very much there same revs and it almost stutters if you hold it between 3-5000rpm like it’s missing, wack throttle open fast it’s fine up to red line, got back put timing light on it again and at the rpm the problem is the timing light also goes erratic, have only done this on front cylinder, seems worse when warm have put new leads on
any more ideas please ?

Thanks barney

[MickeyMoto]

Buy a Honda?

[barney 66]

I did 8 weeks ago, sold it to my mate 6 weeks ago,

If that’s how they are and it’s something I have to live with then fine, if there’s something wrong I need to put it right
Thanks barney

[George 350]

A very large contributor to this mid range flat spot is the Sport cam. It has a very large amount of overlap and a significantly late inlet valve closure point. This causes significant intake pulsation, which is why it goes so rich.
As has been said before, Strada's don't do it to any great degree as their cams are so much milder.
It is also one of the reasons why many consider the 'M' cam the best compromise on the 350's. It is sportier than the Strada but not as extreme as the Sport.
If you do decide to keep the Sport, before you decide to spend a good amount of money on Mikunis, have a look at getting an M cam instead.
Regards,
George

[barney 66]

Thanks George, I will give this some thought and see where I could get a cam and price up, I was starting to think it could have been ignition problem as well.

I was hoping I could get used to this but not convinced I will, I find it awkward in the lower speed limit areas.

Thanks barney

[barney 66]

Another update on this, I tried some 1.5mm washers under the atomisers ( I had seen this suggestion somewhere ) was a lot worse didn’t even bother taking it out for a ride, so took them out in the morning and lowered the needles so there in the top notch, balanced carbs again just in case and on the bike ramp appeared to be much better reving it on the ramp and didn’t appear to be any stuttering or flat spot.
Took it out this morning definitely better the rev range is smaller that the flat spot is in but still there and definitely worse when it’s warm.
Would like to maybe try new atomisers and needles as these are obviously worn, as you can see where the atomisers have had some corrosion on and the needles, guess where it sat sometime unused, if any body know where to get some that are in stock or some I can modify to make 260BD that’s what’s in now ?
I except what people say about the cam but I am trying to make it as best as I can with some simple changes to worn out corroded things before I decide if it’s a keeper or not,

Thanks barney

[barney 66]

Ok final update on this hopefully, float heights were set with sight tube after I made a float bowl adapter and found fuel level was to high ( I guess the reason rpm altered when on side stand or turning round )then early this morning took atomisers out and drilled an extra hole near the top, back in carbs balanced again then out for 20 mile run, way better now, I am now happy with it

Thanks for all the help, tips and knowledge off everybody on here,
hopefully I can return some help one day,
Thanks barney

[3potjohn]

Really good work and a great result. You might consider a quick write up for ATG.