First moby kit questions

Got an 74cc Airsal with the Pollini head with decomp. on the way--this will be my first effort with a kit. I have read the wiki and been doing some research for a while now--my set-up is 50v 16/16 SHA with 15 intake de-restricted stock pipe and all else stock for now. I have been visiting Mabecane's forum and been reading related articles. Forgot to mention external condensor, point gap at.38mm, plug at .40mm, timing at 1,5mm btdc, plug is ngk b7hs, I have some 70's jets also and extra base gaskets. Jetting with what pipe, variator type with what weights, and what is your method for break-in? Anything else useful you can add to keep me on the right track is greatly appreciated!!!!

Thanks all!!!

Re: First moby kit questions

I recently got that kit with 19phbg, same timing,and pipe, stock vari, stock head. It took 2 thick(.3mm)base gaskets to raise the ports to the piston crown. That left about a 2mm gap between crown and deck. With stock head, compression read 100psi. So I've been considering milling down the deck to raise compression. I'd like to hear if you get the same situation,what you do and how it performs. Mine pulls very hard to 40-45mph with stock gearing(10x54). Also considering a launch lever. and your head. Keep us updated! thanks

Re: First moby kit questions

I have had success breaking in new and reworked parts by running the first tank with the petroil a little wetter then needed (slightly more oil) and keeping her unstressed and un heat soaked for the first half tank. After the first half I top up the tank with correct petroil mix and work on getting the tuning as best defined as I can. The good mix on top of the wet mix will dilute eachother so as long as you dont run her too hard and lean getting the the tuning she will break in nicely.

Make sure that your carb can go wide open throttle as well as full closed, if not modify the cursor slide on the grip so you can have both.

Tuning the carb takes a bit of time, for the carb I index the throttle at the handgrip so I can concentrate on each 1/4 range of throttle. I try to get WOT first as that is about where all of the riding happens.

After the top up tank is empty or close to it then check for any troubles that you might not have felt, heard or thought might be happening, check torque every fastener.

Re: First moby kit questions

So definitely wetter for break-in and some plug chops--Would you say the wiki break-in is the best method though--also Reb when you say unstressed and unheat soaked do you mean do not over heat it by ridding short runs to start with? Mel I'll post when I get the kit together and do some plug chops! Thanks again guys!!

Re: First moby kit questions

Quick question about the Polini head with the decompression--How do you transfer the decomp from head to head--I've never done one and would prefer to do it right so as not to damage either head. Thanks for your feedback(Not the Jimi Hendrix type!)

Re: First moby kit questions

Get an unbelievably small cotter pin or stiff wire to replace the little pin that goes through the metal cover and the top of the decomp valve before you start (easier then losing the little parts even though you put it all in a baggie). Also get some valve lapping compound.

Press down slightly on the sheep hook (where the cable sheath goes to) at the end of the decompressor and use sidecutter pliers to cut the little pin. Keep a little pressure on the sheep hook and remove the little pin. That should allow you to take out the decompressor valve and almost lose the little metal cover.

Use a 6 point socket to get the decompressor out of the stock head because she will put up a bit of a fight. Undo the hex base of the valve assembly, that holds down the spring as well as the hook that holds the bullet end of the cable. There is also a copper washer beneath all of that to act as a seal between the head and the assembly.

All the parts can be thrown into a plastic bowl and given a shot of oven cleaner and allowed to soak to remove the goopy carbon. Give it all a little scrub with some 3M scouring pad EXCEPT do not scratch the seal area of the valve itself.

Transfer the assembly to the new head, before you attach the valve stem back onto the sheep hook you will want to lap it into the valve seat of the new head. Use some lapping compound, you might need to beg some from a gear head who plays with 4 stroke anything because you are not going to need much. Otherwise get a pinch of kiln dried fine sand and make a gritty paste with a blob of general purpose grease. Put the Lapping compound onto the sealing surface of the valve and use a variable speed drill (at the slowest possible speed) grab the installed valve by the stem and rotate the valve and close it with slight pressure so the compound can machine the valve and the seat to a perfect match.

Wipe the lapping compound out of the head after you have lapped in the valve, that grit will mess up everything and could scratch the crap out of your new cylinder.

Attaching the sheep hook and metal cover to the end of the valve stem is a huge pain in the butt. You need to turn the valve so the hole is in the right direction and then push down on the sheep hook and install the cap then with your third hand put the pin in so it holds together.

Re: First moby kit questions

Thanks Reb, I knew you would come through--Merci!!

Re: First moby kit questions

i like waffles /

Im running the same setup, just with the treats cdi, what kind of engine temps are you seeing? I went with the thinner base gasket, and lost out on some of the port timing, but have increased compression. seems to pull very hard when you get the speed up, hit around 48 before i had to brake. I think the low end would be much better but is limited by the stock variator.

Re: First moby kit questions

Waffles I haven't started the project yet--what did you do about the decomp on your head?

Re: First moby kit questions

i like waffles /

I'm running the stock head now, thought about upgrading. But my current decomposition isn't leaky and the bike rips pretty hard as is so I don't think I'm going to bother messing with it. Sure I lose a little performance, but for the little extra gained I don't care enough.

Re: First moby kit questions

According to Reb it is a real pain in the butt to swap decomp valves over--maybe I'll have to try another route--I wonder if I order a new one will it make things any better--I don't have 3 hands with midget fingers either!

Re: First moby kit questions

i like waffles /

Eh it isn't that bad, sure its no fun, but rebel is a genius of Mont things, and explained it. Really well.

Re: First moby kit questions

I'll try it this Sunday or Monday--doing a yard sale at my house early then grill out Sunday--But I'll brave it--wish I had a scrap head for practice!!!

I looked at the treats one for a reference picture and might print it out to look at when I try it out, and yes Reb definitely put the Dots on the I's.

Re: First moby kit questions

I could have put that it is a 1-2-3 minute job and I have never had any trouble swapping them over, but I have had troubles so I would rather you feel I was telling a long tale then the other way around and tools get flung.

LappingValve.JPG

Re: First moby kit questions

I've done it before without a tutorial by Rebel Moby. It took me about 1 hour, and that included 35 minutes of looking for parts when I dropped them and couldn't find them on my gravel garage floor. It's not terribly complicated, but fiddly to get all the tiny parts just right if you aren't patient or experienced. Make sure you have a good beer afterwards for a reward.

Re: First moby kit questions

If Nik W. can walk a wire I can do a decomp switch-over, in the rain with the wind blowing, holding a beer. I appreciate the tutorial on the grind down Reb and the positive feed-back to boost my confidence a little more. I'll work over a magnetic floor--HaHa!!

Re: First moby kit questions

Valve lapping... amazing, no wonder I could not get a good seal when I tried to put in a new valve before. The rubber gasket on the valve stem, wouldn't that get messed up by the drilling action? I told myself I would never attempt this again but now I know the secret, never say never again.

Re: First moby kit questions

Run the drill slow and the mini rubber donut will be fine

Re: First moby kit questions

hey everyone so i have a question.. i'm thinking of kitting my moby also.. 79 50v. and i was thinking if anyone out there has had sucess running a 1616 dellerto with the 74cc airsal.. a cdi le partie.. and STOCK EXHAUST.. i wonder if it would be alright.. and that way i could save money until i buy a really good pipe.. i have heard of a kid running that setup and getting about 48mph and he's over 200 pounds.. so what does anyone think of this.. help and input would be appreciated..

also i should change the ratio of sprokets too right

Re: First moby kit questions

i like waffles /

I run the same thing, just with a vm17-18 and a 48? Tooth rear. Hit 47 with 5 minutes of tuning. Stock pipe is nice and discrete. I weigh well less than 200 so I'm sure 50 is possible, maybe.

Re: First moby kit questions

waffles, what's your timing,and exhaust outlet size(assuming you derestricted)?

Re: First moby kit questions

i like waffles /

Timing is 1.2-1.3 have to double check it later today actually. Exhaust is unmolested.

Re: First moby kit questions

What size jets you using, you have the dellerto 1616?

Re: First moby kit questions

i like waffles /

No I run a mikuni vm17-18 with like a 100 or a 105 or something. Could prolly run a 90 even.

Re: First moby kit questions

So I did the decomp swap over to the Polini head and was surprised at how easy it was--sure made things easier to work with being the new head has plenty of space to swap the decomp valve assembly--probably not as easy swapping over to another av7 head! Started assembling the new cylinder and piston to my av7--quick questions--arrow toward the exhaust right? I'm going to use my 16/16 SHA so what is a good jet to start with? I put in a 76 while the carb was easy to get to. Also use the head gasket or not--2 thick gaskets at base raises up to match exhaust opening but equally creates more space at the head. Pics of head, engine, and spacing issue at TDC--look at the top of piston where it stops! Ideas and suggestions appreciated before I finish the build.

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Re: First moby kit questions

More pics!

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Re: First moby kit questions

Arrow usually points forward but to make sure you can always mark on the piston crown the position of the ring antirotation pegs and test fit the piston without rings into the cylinder and turn it a bit to make sure there is a safe margin between the ring ends and any port window.

If shimming up the base is worrying you about extra deck height then you could measure the volume of the combustion chamber at TDC and calculate the real compression ratio. High compression is really not a big issue if you have a goodly pipe because the reversion will take care of over filling the combustion chamber anyways. You could always shave the head or shave the deck of the cylinder or ramp the piston.

I would suggest you get out the buffing wheel and polish up the combustion chamber relief in the head so it does not become a sticking point for a lot of carbon.

Re: First moby kit questions

Well I was going to start working it today until my 64 moby's crank started locking up--that's the one with no lube holes for the main bearings, so I'm going to see if someone has a decent bottom end that I can swap the magneto and clutch to--tomorrow I plan on working on the kit slowly!!

Still interested on what jet on the 16/16 SHA?

Re: First moby kit questions

SHA 16:16 on a stock AV7 #72 - that is what I throw in by I like to run a bit richer then most people.

First sign of the oldies getting too old is the bearings talk when you turn the crank... then they get tight spots in them... Lot of people dont want to run very wet petroil - 25:1 or 4% - in the oldies and they start to have troubles pretty quickly from that point on.

Re: First moby kit questions

Breaking it in wiki style--I have a 73 jet on the 16 sha but I have to screw in the carb screw almost all the way in to keep it Idling--About a turn and a half--suggestions on how to be able to back it further down--Is the carb just too small or am I missing something?

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