av7 rebuild - clutch or air leak? so many threads like this one

this seems like a classic moby issue. and not just for mobys.

engine can rev great and idle great on the stand. revs not so well with the rear brake engaged. clutch appears to be engaging and disengaging properly. throttle position and revs sound proportional and nothing seems to be sticking there. reassembled decomp and it seems to be working great. starts up on 1-2 kicks almost everytime. and the exhaust is cleaned up and doin great as well.

carb is clean and has another filter after the petcock.

when I start to ride on the ground it seems almost normal but definitely lacking low end torque. I can get it to mayyyybe 15mph before it bogs out and not even enough power to get me up mild inclines. With throttle open on inclines im getting way bogged out and the bike wants to shut down. this makes me think that it is not the clutch.

ive replaced all the gaskets twice now and trimmed out the base gaskets to open up lightly ported transfers on the case.

thinking it might be the seals. uggggggh.

If i do a leak down test and none of the the gasket areas or showing leaks what else could it be besides the seals?

is it time to fully disassemble the case too? replace the bearings and seals, and maybe do a the race crank good pack

av7

airsal 74cc

high comp head w/decomp

stock pipe (working on derestricting for more power once this is figured out)

sha 15 (running well with 68 jet- no bogging - up jet later)

Treats CDI

Dimboy Clutch

thanks in advance for your help!

Re: av7 rebuild - clutch or air leak? so many threads like this one

i should also not that my timing may be off since i forgot to buy the cdi puller tool - so waiting for that. i checked with my micrometer and it appears that my timing maybhave slipped since the install from what it looks like my timing could be quite a bit advanced - beyond 1.5-2 mm btdc.

could that be causing this huge lack of power? but still seems fine on the stand??

Re: av7 rebuild - clutch or air leak? so many threads like this one

Dirty30 Dillon /

Timing can 100% brick a bikes power, but still let it idle and run.

That said, you should just rebuild the bottom end to rid yourself of the worries of old shitty seals.

Re: av7 rebuild - clutch or air leak? so many threads like this one

thanks for the info. puller should arrive today. will update again.

Re: av7 rebuild - clutch or air leak? so many threads like this one

From experimentation, I found best timing on AV7 or AV10 with static timing CDI box is 1,2mm BTDC.

Stock peashooter exhause is a HUGE restriction on a 50cc, so 74cc kit it is going to be like riding with a bunch of cinder blocks dragging behind you. Open up the exit pipe to 11mm and get fatter jets for that SHA15. Also check if the intake needs derestricting, some neck down to 13 or 14mm at the transition from round to rectangle.

> evil cloud Wrote:

> -------------------------------------------------------

> i should also not that my timing may be off since i forgot to buy the

> cdi puller tool - so waiting for that. i checked with my micrometer and

> it appears that my timing maybhave slipped since the install from what

> it looks like my timing could be quite a bit advanced - beyond 1.5-2 mm

> btdc.

>

> could that be causing this huge lack of power? but still seems fine on

> the stand??

Re: av7 rebuild - clutch or air leak? so many threads like this one

thanks reb! ive looked through your tutorials on derestricting. im wondering if jb weld will hold up on that exit pipe refitting. i saw someone else did it a while back but wondering if it held up.

going to try to time at 1.2 today or tomorrow hopefully.

i have the curvy intake. chopped to a bit shorter. its pretty bored out looking on the inside and where it necks down but im sure it could be cleaned up a bit.

Re: av7 rebuild - clutch or air leak? so many threads like this one

JB Weld will stand up until you start up the bike, it can not take the heat of exhause and the expanding metal. Need to braze, weld or mechanical methods to keep a pipe in. You can just get rid of the whole backing plate and long exit pipe and replace it with a fabricated plate with two 1/4IPS lamp nipples as exit pipes. Loud and dirty way to get the exhause out and maintain some containment. You will also need fatter jetting.

Curvy intake will not easily give up 15mm all the way through, where ever it necks down will restrict the volume of air-fuel getting through and mess up the vacuum signal over the main jet. I would suggest a correct shorty 15mm and derestrict it to save headaches.

> evil cloud Wrote:

> -------------------------------------------------------

> thanks reb! ive looked through your tutorials on derestricting. im

> wondering if jb weld will hold up on that exit pipe refitting. i saw

> someone else did it a while back but wondering if it held up.

>

> going to try to time at 1.2 today or tomorrow hopefully.

>

> i have the curvy intake. chopped to a bit shorter. its pretty bored out

> looking on the inside and where it necks down but im sure it could be

> cleaned up a bit.

Re: av7 rebuild - clutch or air leak? so many threads like this one

yea i have a shorty intake but cant seem to make it fit under the moby 7 frame along with the dellorto. il see if i cant file out more of the neck in the curvy.

Re: av7 rebuild - clutch or air leak? so many threads like this one

First mention of it being a Ranger 7 serie Moby... you need to fabricate a intake from steel and get some welding happening, a old handlebars is a good source of tight radius mandrel bent tubing, then just duplicate the mount end and match the port at the intake to cylinder union.

> evil cloud Wrote:

> -------------------------------------------------------

> yea i have a shorty intake but cant seem to make it fit under the moby 7

> frame along with the dellorto. il see if i cant file out more of the

> neck in the curvy.

Re: av7 rebuild - clutch or air leak? so many threads like this one

ah yes. my mistake not mentioning the model. i have some spare handle bars and a friend that welds. maybe its time i learn how to as well. thanks for all your insight rebel!

Re: av7 rebuild - clutch or air leak? so many threads like this one

If you make yourself a set of drop bars you will have two pieces of leftover pipe for intakes :)

...just saying...

DoIt.jpg

Re: av7 rebuild - clutch or air leak? so many threads like this one

yessss! retimed timed it to 1.1 btdc. pinched the plug gap down just barely. derestricted the outlet tube exhaust tube. basically gone. pretty loud. and blasted off... hit 30 mph easy. seriously rips.

untilllll i noticed the mains on my petcock are clogged up. tank is not lookin good. thatll be the next steps.

jetted at 71 for the moment. plug loooked just barely wet/brownish black at the base of the thread zone. didn't ride long enough to do a proper plug chop. gonna need to get some even numbered 70s jets.

it feels so taboo having this much power and torque under a model 7. im gonna have to be careful!! but honestly feel safer being able to keep up with traffic and drivers not riding my ass. especially here in portland. some very piss poor motorists and downright bad attitudes toward non cars.

thank you so much your insights yall!

especially you, Rebel! you are legendary!

1D99809D-9DE8-4363-B82D-68F7C5BEF48A.jpeg

Re: av7 rebuild - clutch or air leak? so many threads like this one

Thanks for the kind words.

The Ranger 7 frame is a bit more robust than the serie 40 or 50 at the seat base, so for a bone rattler (hardtail) it is a goodly one to get some speed from... Hardtail one-speeds are better for sprinty bikes, so good one to mod for excellent pickup rather than top end, it will keep you from ending up under some ahole's bumper in traffic.

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