Minarelli/Polini/Dellorto

I am running a Polini 75cc kit on my Minarelli. The carb I am using is a SHA14-12 that I bored out to 9/16" (14.29mm) and a manifold that I also bored out to 9/16"

Here is the problem: The bike seems to run lean in the mid-range. What happens is when I am going along at say a constant 35mph the engine will heat up and then tighten up, not really sieze, but getting there. If I blast up a hill at WOT I do not get this condition. The plug is a rich chocolate brown.

I am running Redline oil at 40:1

I think that I have about 150-200 miles on the engine.

So the questions are these:

Do I have to break it in some more? The Polini instructions say 300 mi.

Is there anything about the Dellorto carb that makes it run lean in the mid-range? Is there anything I can do to it other than changing jets?

Thanks in advance for any info given

Re: Minarelli/Polini/Dellorto

Perfekt Timing Angel /

You know what I'm going to say...lol! Bigger carb, bigger intake. That Polini intake port is way too big for that puny 14/12. That kit needs the volume to keep it running cool. Even if you put a bigger intake on it and upjet, it might help it out a good bit.

I know exactly what you're talkin about (lean mid, ok when WOT uphills). I reaaaaaallllllyyy believe it is just too small of a carb. You are full of good Minarelli advice that you have given to myself and others on this forum, and I hope I'm not being a dick by being a broken record on this subject. I hope you can get it to work, and if you manage to get it right, I would humbly like to inquire about your technique.

Re: Minarelli/Polini/Dellorto

Hmmm... bigger carb, huh?

I can't wrap my mind around the concept. What makes the engine internal temperature run hot or cool? I would have thought that the fuel/air ratio would be the determining factor and that a larger carb would only determine the ultimate top end.

If I do go to a bigger carb, are there any suggestions for a manifold and carb size? How about carb model?

Thanks

Re: Minarelli/Polini/Dellorto

phgm 19mm dellorto! just do it! your kit will thank you!

Re: Minarelli/Polini/Dellorto

Ben Van Zoest /

Like you said 300 miles break-in running 40:1 and you blasting uphil!!! Tried Marvel Mystery oi?l

Usually 75cc calls for a bigger carburator but from what I read on a Dutch tuner site not always nessessary.

BTW 75cc is a hell of a load on the punny crankshaft and rod.

Re: Minarelli/Polini/Dellorto

Perfekt Timing Angel /

No, it's not cooler as in temperature. Sorry, I guess that was the wrong context. More volume = more lubrication = happier, longer lasting kit.

I was running a 14/12, 64 jet (68 was WAY too rich), Mamba pipe on my last Polini set-up. It ran BEAUTIFULLY! I even opened it up WOT for a spell or two on a gently hilly backroad. It performed well, for the first 200-something miles. One day I was headed up a fairly steep hill, keeping it around 1/3 throttle when all of a sudden...VVVVVRR-ZZZZZIIIIIIPPPPDEATH.

Soft seize. It started right up, but since then, it hasn't run the same. That's the second kit I mangled from that 'suggested' 14/12 set-up in the directions. It is way more practical to go with a 19mm or higher. That intake port on the kit alone is about 20mm in diameter.

And that's my story :oD

Re: Minarelli/Polini/Dellorto

With a larger carb a larger amount of fuel/lubrication is getting in. And the PHBGs are way more tunable.

I've heard of so many people seizing that kit because of a 14.12.

Re: Minarelli/Polini/Dellorto

WE are doing well with this equipment

1205744332_avanti.jpg

Re: Minarelli/Polini/Dellorto

Sorry something is missing...

DELLORTA SHA 16-16 and a Minarelli 47 mm cyl.

Could not enter the pics.

Re: Minarelli/Polini/Dellorto

What manifold is necessary to mount the PHGM19?

Re: Minarelli/Polini/Dellorto

Re: Minarelli/Polini/Dellorto

what else is new?

Re: Minarelli/Polini/Dellorto

dude, i thought i told you like last year that all you need to do is reuse the stock exhaust as an intake manifold.

Re: Minarelli/Polini/Dellorto

You're lean at mid throttle because you can't adjust the SHA carb to compensate. It really has nothing to do with its size. Its just the design of the carb. You can make it work by opening up the holes a little in the tube. But its hit or miss.

Re: Minarelli/Polini/Dellorto

I've been running a 14/12 with a 54 jet (as suggested in the polini manual) on that kit for 2 years. Port matched with Puch Bullet pipe.

Had a couple of issues with soft seizing at first, but it worked itself out as the kit broke in. Bike does 45.

You are running a synthetic oil, which is a big no-no when breaking in a kit. Switch to a crappy 2 stroke oil to continue breaking in, and things will be better. Switch back to synthetic once the kit is actually broken in.

Re: Minarelli/Polini/Dellorto

I just noticed this thread is 2 months old, so my advice probably comes too late.

Now might be a good time to look at the piston and cylinder, however, and sand down the high points on the piston, and maybe polish out any smears in the cylinder.

Re: Minarelli/Polini/Dellorto

synthetic is fine to break the cylinder in on. i dont see why everyone has that myth that its not. ours was broken in on it. hell its first 15 minutes of life im pretty sure it had more oil that gasoline.

Re: Minarelli/Polini/Dellorto

Because if you lubricate it too much, the wear that needs to occur for the rings to seat won't happen. People say that synthetic is "slicker" and doesn't allow the parts to wear into that seal. You need to be lubricated enough not to seize, but not so lubricated that the parts don't take the wear that needs to occur to seat the rings.

Re: Minarelli/Polini/Dellorto

not true at all, you cant lubricate it too much, only too little. our rings seat perfectly. its not the lube that cuts the hone, its the sharp edges of the rings. let me guess, you think the earth is flat too huh?

Re: Minarelli/Polini/Dellorto

I didn't read all of the posts so someone may hav already said this but inorder to make my minerelli polini run proper mid range/throttle I had to make the bottom ventury hole a bit bigger(the brass tube in the middle of the carb bore) just a bit though, it was barely noticeable with the naked eye but I could tell I did something by the brass shavings.

Re: Minarelli/Polini/Dellorto

wait . . . if the mid range is lean, don't you just bump the needle up a notch, or else swap out the diffuser for one with bigger holes?

Re: Minarelli/Polini/Dellorto

There are no needles in a Dellorto model SHA carb.

Re: Minarelli/Polini/Dellorto

get one with needle settings then! problem solved :)( i was thinking the same thing)

what does teh sha have for midrange then? or is that what is stumping everyone?

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