Morini doesn't cruise smoothly

[Goat Herder]

The sure fire way to absolutely check for a vacuum leak is pressurize the block in my humble opinion. Plug the intake and exhaust make a schrader valve attachment or something of the sort. Then bust out the soapy water. Here is the just of what I am thinking will rule out all doubt for you . Might be that you can simply watch the gauge if it don't drop?? http://youtu.be/ySu2NC1X7s4

Dunno what you got without being there my self? Subtle things like the restrictiveness of a new air filter, climate changes, and a carb getting finicky? Sometimes it helps just to simply try another carb? Reason I say is been working on Chinese ATV's lately as of this year I have come across some carbs that just would not give up the Ghost. Who knows what the customer tried to do to them before I got them too lol. Darn thing shows up because they could not fix it and nether could I. Methodical trial and error.

I definitely don't know everything and learn something new for practicing often.

Chinese brand carbs this year have been very entertaining this summer.

My over sized Itailan PHBG carb changes it's personality from winter,fall ,summer a bit yet has always been manageable. Been loving my Dell 21mm. Gotta say tho took me a while to get it tits on. I give this brand carb still great credit for a simplified reliable design in my humble opinion. I have good faith in this carby... Carbs can be a riddle as sometimes it is not even the carb at all?

Sounds like you need to make darn sure you don't have a vacuum leak?!!

At altitude here and being the big ol circus bear I am. I have never tried for 70 mph.. That is pretty darn good!! I tend to run my carb jetting rich enough to 4 stroke a bit with out a load in all phases of my throttle position. Just where I found the most brute thrust for my riding habits in the hills I have to battle.


Had a Chinese Baja 150cc 4 stroke go cart last week that I chased a vacuum leak for a few. Every 18 seconds it would rev up high then idle back down. I covered the air adjustment screw on the side of the carb and general area with silicone as a temporary aid in diagnosis and it still did it. Despite having perfect gaskets etc.

My carb spray routine kept taking me to that corner of the carb tho. Never did pin point it exactly and was not getting payed to find it lol. Finally changed the carb out for a good used one charged to the customer and it ran perfect!! All I did was swap the jets over. Had the carb apart 5 times

 

[Goat Herder]

I have to chime in here. If you have a ACE Hardware store around you, that is the place to get your exhaust O rings and kickstart shaft O ring. That's where I got my replacements from. They have a huge selection. Standard and Metric.

I changed out my kick start shaft O ring and found that the trust washers for it were the same as for the bell. Took the play out of it and been loving it. It did not have bad play to it and had used it forever the way it was. Just saying made a pleasant improvement. Needed to finally change out that O ring.

 

[Goat Herder]

Goat herder, I respect your knowledge of small two stroke engines. You always have good advice. Ive done two rebuilds on my s6c. The engine runs great until I hit max rpm, and it tends to be sluggish at the top end. Ive already replaced the crank hakves gasket, so I doubt I have a leak there. The bike used to scream at 70, now struggles at 60 and strikes fear at seizing the piston. . Do you have any advice on what could be a solution to this problem?

Also wanted to say move your crank around a little while pressure testing. Not so much that you are cycling the piston ports. That's a given...but move it a little in light of this approach? http://youtu.be/ySu2NC1X7s4

Had a chain saw that was running lean once. Customer would burn up a piston and we were asking about his hired help and such as to what gas they were using etc. Was moving things around when we found it. The leak never showed up with carb spray at the work bench as the vacuum leak came with the personality of the seal. Heat cycling load and such. In the case of the chain saw it was worn crank races and the seal.

Sounds to me with new bearings in the equation and new seals you should have it whipped?

 

[Old Reliable]

Well I have to say that is quite a unique and effective approach. Is that something I will have to fabricate? Or do they sell that sort of diagnostic tool? I was thinking I can fire it up and elevate the rear tire, and spray specif areas down around the intake and exhaust, as well as the gasket areas between the crank cases with soapy water, and see what happens. If I dont see any leaks, I think ill have to end up purchasing that dell 21mm you are talking about. I also saw a racing red phva 21mm carb made by dellorto. Looks very cool. I wonder if it will adapt to the rubber intake boot...

 

[Goat Herder]

The 21mm PHBG Del will swap right over to the same rubber boot. All the inside guts jets, slide etc swaps right over too. There is a Chinese PHBG imposter out there as well.

The improvement with that carb is that the back end of it is more opened up than the 19mm PHBG. The effect would be more like when a fellow first port matched his H.T. motor. Just a little more ump every where.

O.R. Gosh you would prolly have to fabricate everything to do that pressure test. Should not be too hard. Only looking for things to hold a small amount of psi. I don't sell anything. I am not even a vender. I am not even sure where to look for a kit ATM? http://youtu.be/radOV6rAJJU

http://www.aa1car.com/library/vacleak.htm

 

[Old Reliable]

That 21mm phbg sounds very enticing. Ive seen ut, but havent had the urge to get it. What youre telling me strikes that urge, haha. If I hit 80, ill be sure to let you know. I know it does 70 after passing an undercover la county detective in Irvine. He pulled up next to me at a red light and told me over his pa that he got me at 70. Oh dear me I thought my bike was going to be impounded, but he was cool. More impressed than anything. Going that fast scares the crap out of me! But its such an adrenaline rush! The fastest speed of a 50cc motorized bicycle is 80mph. The guy built this super aerodynamic and elongated bike, using a cobra 50cc. Im hoping to break his land speed record haha! Gotta work out those bugs though...

 

[Old Reliable]

This is the s6c I have mounted on the giant frame. Nothing too crazy, but still very fast. I mounted the engine by machining mounts out of aircraft grade aluminum. That is also an old gas tank. I had to upgrade to a plastic tank because metal cracks under hard riding...