Modern Vespa

The carb I need help for is on my 1965 Honda 50, hence the NSR…

When I bought this bike, the carb was filled with calcium crust due to years of condensation during storage. I was able to fully clean it out. I took the opportunity to rebuild the carb. Could not get same jets but bought a kit. I could make it idle and run, but the engine has no guts - acceleration was truly poor.

I know the bike did not run this way from the factory so I took the carb off and re-installed the original jets. It now runs better but not right. Still no acceleration.

I see only three adjustments, air/fuel, idle screws and the needle valve.

Any guidance or help? This is such a simple device, one would think I could make it work…

Thanks,

Chris from CLE

Anything online about the proper air/fuel adjustment specific to that bike? Usually it's warm it up, set the idle to xRPM, adjust the air/fuel screw until it sounds right, readjust the idle. Having an old tach/dwell meter helps to know what RPM you're running.

These little carbs can be finicky.

Not totally related (but not UN-related), but his was a great video. Destin's channel is pretty sweet.

Check the valve adjustment, timing and point gap. Then move onto the carb. But it's good you cleaned it already.

I'm not helping till you show a picture of the whole bike! /jk

Will do.

Moved (shortened) the needle and it seemed to help,

Will check above prior to further adjustments.

Thanks,

Chris from CLE

Does the needle on the slide have more than one groove for the circlip?

Ok, you’re up.

Chris from CLE

Yes, that is the exact procedure, but manual states that adjusts idle and low speed up to 1/8 throttle. Intermediate speed is needle adjustment and needle jet sizing. With more than one thing to change, I am hoping someone has dealt with this before and can help me pinpoint the issue.

Thanks for the info/video.

Chris from CLE

How does the spark plug look? I've been running way too rich and had the symptoms you describe.

BTW Awesome pics and sweet machine!

What's the fun in that? It's always better to change SIX things at once and the try to figure out which of them worked after the fact.

I gotcha, man. Keep at it; you'll get it.

Nice bike, BTW. That's super clean.

How's the air flow side?

Filter OK?

I once had almost similar engine from 80's, the carb was Keihin too, but a newer looking model. The carb itself worked usually fine, but was a bit sensitive to both clogged air filter and my hacks with less filtering

I also did found the contact breakers, points, to be quite sensitive to the correct gap...but to me this was typically shown as reluctancy to run well at higher revs.

Filter is brand new, so I assume OK. Points were somewhat open so I closed to .014 (manual calls for .012-.016).

Set the needle to 4th slot (second most rich). Adjusted idle and air/fuel mixture.

The bike still bogs under-load during hard acceleration. For example, going up slight incline I cannot get up to speed in third gear even with WOT. Going down hill, runs and accelerates fine. On flat, it is a long time to come up to speed. I think top speed is also down (35-37) instead of 42-45 formerly.

Next step is to set valve lash and check spark plug - one would think that would be first but changing one thing at a time…

Any other suggestions?

Chris from CLE

If after adjusting the valves and timing does not get you want you want out of it, I would suggest a compression test.

I am no help here because as far as carburetors are concerned I am a zero to the left. Just wanted to say I just love your ride.

Thanks for the compliment Max. It is truly a time capsule. It has only 1500 miles and is all unrestored original (the seat in the photo is a replacement to save wear on the original). However, that also is part of the downside - the brakes and the tires are 56 years old. I have said on this forum before, 40mph seems really fast on 56 year old tires…

Clearly, I am on par with your carb skills as well.

Chris from CLE

Ok, valves adjusted. Exhaust was just a little tight. Intake took two tries - I was thinking “this is it” when the intake was super tight. Turns out that is how it feels if you stupidly adjust it at TDC of the intake stroke… Funny how loose it gets when it closes. Still ran though. Should have lived by Measure twice, cut once, right?

So I am down to timing. There is not much adjust on the timing, just a degree or two by turning the breaker point plate on set of slotted screw holes. I am starting to wonder though about the spark advance. The timing marks are a good 10 - 12 degrees off of TDC. Could the spark advance be stuck? Would this show as low power under load and heavy throttle?

Thanks,

Chris from CLE

It sounds like its not getting fuel. Check the flow from the petcock. My own Honda 150 Benly had sat unused for years and crap from the tank had restricted the flow through the petcock so the engine simply outran the supply once it was off idle.

Also, if the carb was filled with mineral build up from condensation the fine drillings through which the fuel flows could still be restricted, these are damn near impossible to clear without removing the brass drilling plugs and reboring them which is a really nerve wracking job (yup, done it, don’t recommend it) you might want to see if you can find another carb, I see NOS stock ones on ebay for under 100 bucks and Taiwanese knock offs for about the same money.

The winner is seamus26 with the advice above ^^^^ Yesterday I tweaked and tweaked the carb and got it running pretty darn good, not perfect but darn good. Today I checked the timing, it was perfect. I checked the spark advance, it was working and perfect. I took the carb off and was going to replace with a Chinese knock off I bought on eBay a year ago or so. When I went to install the new carb, the bolt holes did not line up - wider than the existing studs. I have no way to machine the holes so I put the old carb back on.

Voila! It runs like a champ. Ok, not perfect but I have decided to not let perfection be the enemy of good enough. Starts on one kick. Has pretty good power, took it up to 45 mph and had some throttle left.

So I have changed many things at once, and kind of backed into it. Which one did it? I don’t know.

Thanks to all who replied with advice, ideas, and encouragement.

Chris from CLE

Way to go, man. Glad to hear it.

Check your plug colour periodically over the next while to be sure its still not running a bit lean. If the insulator is bright or glazed white it might still be lean enough to be an issue... wouldn’t want to hole a plug.