Question about Mikuni VM18 with stock parts

Will a Mikuni VM18 on a stock 78 Honda express seize my engine? Any idea what main jet size I might need for a stock 50cc? Also would I need to change the stock idle jet of the VM18?

Thanks

Re: Question about Mikuni VM18 with stock parts

It wouldn't seize if you tuned it right.

Your gonna need a new intake, and no carb comes setup for your bike. Every jet it comes with will need to be changed.

Doubt you'll find much info as I can't think of anyone swapping in a VM on a stock cylinder and exhaust.

Without at least an expansion chamber you probably won't see much gains for the trouble, and may actually cause more problems...that's a 6mm Venturi size jump on a stock cylinder.

Looking at your past posts looks like your carb is causing problems. Might be a good idea to find another stock carb, do expresses have the same kehlin as a hobbit? (edited)

Re: Question about Mikuni VM18 with stock parts

Holy shit man your down in Olympia! If you ever need any in person help I'm up in Bremerton.

Re: Question about Mikuni VM18 with stock parts

Not looking for anything over 25-30 mph just something better than this old stock carb.

Only replacing because It cause it has been sitting forever and has huge pits on the inside.

I would attach it to a MLM intake and eventually get a new exhaust.

Would you recommend anything else besides getting this carb?

Thanks

Re: Question about Mikuni VM18 with stock parts

Awesome! Ya, I may take you up on that at some point

Re: Question about Mikuni VM18 with stock parts

Dirty30 Dillon /

Just get a SHA and intake. The 18 is alot of carb for a stock cylinder and pipe and you will have a harder time tuning vs. the SHA

Re: Question about Mikuni VM18 with stock parts

Yeah, an Sha is a single jet carb so it's alot easier to tune. It's also still an upgrade and will work great with a pipe in the future.

Have you removed the exhaust and checked if it's clogged? You should be hitting 28 no problem.

Re: Question about Mikuni VM18 with stock parts

Just keep the sha at a 15/15 if you are keeping the stock cyl. Get a 60's jet range, but also a 58. The 58 will probably be your magic number but the range will make sure you have options.

Re: Question about Mikuni VM18 with stock parts

This intake is meant for a Moby but works just swell as an adapter on an express to run a dellorto Sha, bolts to the stock intake. You'll also need a 1mm Sha shim. Everything's available at treatland. As Jay said you wanna 15:15.

https://www.treatland.tv/motobecane-15mm-SHA-dellorto-intake-p/av7-sha-intake-022066b.htm

This runtong clone Sha 15:15 is the only clone carb I've ever had good luck with, unlike alot of others. But a genuine dellorto is still better.

https://www.treatland.tv/SHA-15mm-runtong-clone-carburetor-lever-choke-p/sha-15mm-runtong-carb-lever.htm

Regardless, don't forget the shim and jets. Ohh, and an Sha air filter. I like the mesh ones

https://www.treatland.tv/dellorto-SHA-stock-air-filter-p/dellorto-sha-air-filter-mesh.htm (edited)

Re: Question about Mikuni VM18 with stock parts

Huge pits on the inside of your stock carb won't hurt a thing , as long as the jet and float mounts aren't affected . You should see the inside of my FA50 carb .

Just clean as much corrosion out as possible and insure that every passage is clear .

Tuned to OEM specs your bike should be hitting close to 30 MPH .

Re: Question about Mikuni VM18 with stock parts

And like aaron said. Get a 1mm shim. The sha comes with a shim but it is like a 1.5mm. Treats is usually good about telling you what shim you need for an intake.

Re: Question about Mikuni VM18 with stock parts

Dirty30 Dillon /

Re: Question about Mikuni VM18 with stock parts

Well wow, don't know how I missed the party pack!

Get what you want, but like Dillon said. I probably shouldn't have suggested a clone. I might be able to overcome problems with a runtong. But being that your totally new to this, just get a real one and skip all the possible issues.

Re: Question about Mikuni VM18 with stock parts

Cool! I was reading around here and someone said the sha was a lot harder to tune. I removed the exhaust and put it in coals on my fire pit for 45 minutes or so.

It’s definitely running rich from the look of the new spark plug I bought a few weeks back. So I dropped the throttle needle for the mid range and I’m getting only about 22-25 mph. But now it does out after idling for a few minutes and gas drips out of the overflow. It’s been dripping since I first bought it though.

That’s why I was thinking about grabbing a new carb

Re: Question about Mikuni VM18 with stock parts

Awesome thank you. I saw a YouTube video and a guy had the same model as me and added a sha and I think he said 58 jet was perfect.

Re: Question about Mikuni VM18 with stock parts

You might be flooding the carb.

Yeah the sha party pack is great. I ran it On my cheap express on the colfax killer race. It was a great swap and was easy to tune. I think I had to modify the stock throttle but you can probably make a new one that would save you the headache of cutting the housing and using a Dremel (edited)

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