Gas bike reed set up

[Stoneman]

I may have trouble tuning my VM18 as well but haven't tried to run that engine yet too many problems with the spacer and bent studs. I'm going to run a stock motor on my predator frame for a while.

The VM18 is a nice carb and you shouldn't have any issues with it, unfortunately this one isn't my build so i will just have to go back over it all.

Just needed a bit of an idea where to start and if there is any known issues to look out for.
The young fella at least has a go at it so i figured id try and help.

 

[Frankenstein]

I think maybe an air leak, I remember having a very similar problem that behaved exactly the same way that I could idle and adjust idle just fine, but opening the throttle just killed it, I could make it run on the largest and smallest jet I had (main jets, without touching the idle jet) for an idle and just a hair of throttle but nothing else. Weird that it did it when I had a reed, while any leak before that was just a racing engine. Get it to idle and grab a can of starter fluid and spray around lightly. Just give it a shot, it's so obscure and anti-intuitive but I'm pretty sure that's the behavior I had, it I think was my magneto crank seal.

 

[Stoneman]

I think maybe an air leak, I remember having a very similar problem that behaved exactly the same way that I could idle and adjust idle just fine, but opening the throttle just killed it, I could make it run on the largest and smallest jet I had (main jets, without touching the idle jet) for an idle and just a hair of throttle but nothing else. Weird that it did it when I had a reed, while any leak before that was just a racing engine. Get it to idle and grab a can of starter fluid and spray around lightly. Just give it a shot, it's so obscure and anti-intuitive but I'm pretty sure that's the behavior I had, it I think was my magneto crank seal.

That's exactly how its behaving. The main jet was making no difference.

 

[Frankenstein]

That's exactly how its behaving. The main jet was making no difference.

If it does it with the muffler removed but not as badly like mine did it's probably a leak, I think the weird thing I noticed was that the seal was basically ok, but the little spring inside clamping it to the shaft had come apart, I remember it being odd because the seal was basically new as I had just installed it during a top end replacement. It was all going fine and then suddenly went dumb.

Maybe having a reed to block off the path and pressurizing the crankcase more than a port timed intake would has something to do with how they react. Maybe more fuel is lost and more air than normal is sucked in (reed increases resistance of air sucked into case through the intake) from the leak and this bad combination makes for a weak pulse into the com chamber to push out old stuff, along with a weak venturi if too much air is sucked in from elsewhere and the throttle opening is too big to really pull fuel with the lower air velocity because of those factors, just snowballs into a stall.

Sometimes I hate engines, they act so weird.

 

[Street Ryderz]

That's exactly how its behaving. The main jet was making no difference.

They are known to have issues between the base plate and cylinder but most have used rtv or some type of gasket sealer to slove that issue hoping that wouldn't be the case here? As I mentioned above an # 80 jet is just way too small for a reed and 18mm carb,I say this because with a properly windowed piston the intake duration can now be upto 172 degrees and that means alot more air needing to be mixed with the right volume of fuel.When I ran my CNS carb bored out to 18mm I think the main jet was in the high 80's low 90's and that was p/p far less intake duration,it was after modifing that carb that I had fuel delivery problems and could suck the bowl dry faster than it could replenish itself LOL ended up boring out petcock and carb body entry even now for the bigger carb trust me they want fuel to make power!

 

[Stingray Chopper Man]

Vacuum leak from black radiator hose some where take them off apply crazy glue cram back on tight the f*** out of them.
Also check for lose reed bolts vibrations cause them to loosen a crack giving one lot of mysterious problems.
Also did you remember to put the gasket seals on during assembly?
If your problem still exist take the reed off.
I took both the reed and air filter off and mine runs fine.

You took the whole block reed off of yours??

 

[Megaphone]

my son has the zeda 80 with OKO 21mm and DIO reed … make sure your nipples are all connected, the one on the reed port needs to be sealed.. we have a 41 jet and a 105 jet installed, mixture screw 1 1/2 turns out … bike rides great except sometimes the idle is erratic .. we already checked for all leaks .. we had huge issues until we messed with the fuel bowl