Benelli Dynamo carb tuning

[Dave Graboski]

Struggling big time. This is our family 1970Benelli Dynamo. Has been back and forth from PA,NJ, NY and now is with me in VA. I did a restore on it the last few months and am beyond proud of it. But.......it starts but doesn't run great. It starts with the choke down and runs ok but has no power. Choke wide open runs with a ton of throttle twist only. Won't idle no matter what. Idle screw is 1-1/4 turns out. Mixture screw is 1 out. Fumbling with these screws hasn't warranted much change. Carb has been off the bike 4 times this past week, every Port and jet cleaned. Float works as it should. 93 octane with 40:1 2 stroke ratio (stp). New head gasket, new cylinder base gasket. No gas leaks. E3 hot spark plug.

 

[Dave Graboski]

Think I figured it out.

 

[Minimichael]

Wow. Excellent deduction, Watson. Did you find the other piece of that ring?

 

[SAS289]

Hopefully just a hone and first over piston.

 

[Dave Graboski]

Rings replaced, still runs like crap no matter what screw settings I use. Carb has been cleaned over and over. Will not idle at all. Needle down it runs but has no power, needle up barely runs but has good power when throttle applied. Where do I go from here?

 

[gotee193]

Sounds very familiar. It was a crankshaft seal that solved my problem. In my case it was the flywheel side but I changed both sides. Any bits of metal must be cleaned up from the broken ring.

 

[Charles S]

https://oldminibikes.com/forum/inde...eron-explains-how-to-tune-carburetors.169530/

 

[Dave Graboski]

Sounds very familiar. It was a crankshaft seal that solved my problem. In my case it was the flywheel side but I changed both sides. Any bits of metal must be cleaned up from the broken ring.

I will order a complete seal set and see what happens I guess

 

[enginecrzy]

Might check carb & manifold for air leaks. Spray wd40 around it while running & see if engine speed is affected. My Honda s90 had a warped carb & manifold flange I found & had to block sand them flat again to stabilize the idle again. I see your carb is not quite the same as that. Small air leaks can really mess with an engine...

 

[manchester1]

I would check for air leak around carb. I rebuilt a carb 3 times and still had a problem. At a mini bike show, a fellow mini biker spotted the air leak. Purrs like a kitten now.

 

[sparkwizard]

On your 2 stroke engine, the crankcase is also part of your intake system. One of those seals leaking might not be visible, but it will leak air in and cause problems.
A small vacuum leak (air leak) will cause problems at idle, when your engine is not using much air and vacuum is highest. That little bit of air leaking in is a much higher percentage of what gets into the cylinder than it would be at higher RPM, when there is much more air coming in through the carb. If you removed the jug to get that piston out, that gasket around the jug is critical to a good idle, also.

 

[Dave Graboski]

Ok, so I started to disassemble. Does anyone know which magneto puller I need? Is it 18mm or 19mm? Being its aluminum I don't want to use a "jaw" puller. Thank u in advance

 

[Dave Graboski]

I can't for the life of me get the gear off to change the right side seals. Anyone have a pic or link to show what gear remover u used?? They actually look fantastic. Kick stand side not so much. Here is my logic....since the right side doesn't have an opening for the chain, I should be able to make this side air tight with gasket maker. My photo is the magneto / kickstand side main seal. (Destroyed) very easy to put the new one in.

 

[Dave Graboski]

Sounds very familiar. It was a crankshaft seal that solved my problem. In my case it was the flywheel side but I changed both sides. Any bits of metal must be cleaned up from the broken ring.

What puller did you use on the gear side?

 

[Dave Graboski]

What puller did you use on the gear side?

Runs perfect now. I replaced as many seals as I could. Thank u all for the advice and input. Now a new issue....won't shift out of first gear. The times that it does, its without using the clutch.

 

[Dave Graboski]

Runs perfect now. I replaced as many seals as I could. Thank u all for the advice and input. Now a new issue....won't shift out of first gear. The times that it does, its without using the clutch.

FIXED: Had to synchronize the transmission starting in 4th gear not neutral like I was doing. All good if anyone is following along.

 

[Dave Graboski]

Here is a video I made of my restoration project. May1st to current date. Runs great now. Thank you all for the input!