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 Carb Comparator 
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Joined: Tue Mar 09, 2010 9:46 pm
Posts: 235
Areomyst wrote:
Thank you for taking the time to reply to my questions Larry. I myself find a hard time finding the time to get on forums (even one that I own) - I really appreciate the help! Surely you can tell by my questions that I am a novice, and your attempts to better educate me mean a lot.

larrycavan wrote:
I see. What make are the engines?

The engines that I want to test vary from 50cc to 250cc. Most will be 50cc though. The short list below should encompass the majority of the engines I plan to work with though:
Honda NPS50S (Ruckus) is a 2-valve 50cc
Yamaha YW50F (4-stroke Zuma) 3-valve, 50cc
Chinese QMB 139, also called a GY650 sometimes (crappy, but common)
Vespa LX50 (old ones are 2-valve, new ones are 4)

Most of these engines make around 3HP at the rear wheel according to my dyno. Some of them have aftermarket cams available, but none of the manufacturers really tell you much about the cam. I hope that with the flow bench, dyno, and by plotting the cams I can get a better idea of the relationships of the porting, cams and other engine mods to the power output. I have not done much with 4-stroke porting yet. I have been waiting on getting the flow bench done before doing a lot of 4-stroke port work. I have had a lot of fun with 2-strokes over the years though! :)

Quote:
How do they figure 1 inch of water column is useful?

I don't know. I figured this little bench was better than no bench, but now I tend to second guess that. I was hoping for a set of instructions from Simons but as of the mail delivery today none have arrived.

Quote:
You could test the pilot fuel circuit with perhaps 1 inch of water column but certainly not the throttle bore.

Seems to me that by the time you get the slide fully open on a CV carburetor your inclined gauge is going to be pegged....


Perhaps a more realistic inclined manometer will make this at least a little more useful? I got excited about this Simons machine because it was already assembled, and I thought I was going to be able to more or less "plug and play" with this thing after making a cylinder adapter. Indeed, as you suspect, when testing any parts that I've tinkered with so far the inclined gauge was pegged...



Glad to help. I'm a bike guy too so I find this interesting. I got into modifying PW50 Yam 2 strokes about 20 years ago so I also understand the interest in small motors. They're actually a lot of fun. You can make those little things fly...

For not a lot of money you can build a perfect bench for the motors you're focused on. A sheet of MDS, a few motors a weekend in time and you could be cruising. The little valves in the motors you mentioned won't require a lot of vacuum power. What are your running for carbs on the 50cc units? You might look at the SF60 for some ideas. I had a lead on a SF110 for $1000 a while back that a guy wanted to sell. I can contact him if you're interested and see if he's still got it. If he does he might be willing to negotiate the price. He's in Rochester or Buffalo NY. If you were nearby you could use my bench pretty much anytime.

You could get by with a flow element and big shop vac but the price is stupid. Better off building a bench.

Just a thought but for cams, you might want to talk to Megacycle. They do the best hard welds you'll find.

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Larry C

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Thu Jun 26, 2014 9:06 pm
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Joined: Fri Apr 08, 2011 9:07 am
Posts: 68
larrycavan wrote:
What are your running for carbs on the 50cc units?

Mostly little Keihin clones like this one: http://www.partsforscooters.com/151-233_Carburetor

One one engine that I upgraded to 88cc from 50cc, I ended up using the 24mm variety off of a 150cc scooter. It went okay I suppose. I was surprised that I didn't have to change the jetting from stock.

Quote:
You might look at the SF60 for some ideas.

That's a neat little flow bench! Would be perfect for my needs it looks like.

Quote:
I had a lead on a SF110 for $1000 a while back that a guy wanted to sell. I can contact him if you're interested and see if he's still got it. If he does he might be willing to negotiate the price. He's in Rochester or Buffalo NY. If you were nearby you could use my bench pretty much anytime.
I saw one on eBay a while back for $750 and was so irritated that I didn't click the "buy it now" button. That said, I'm already committed to building my PTS bench, as I have the plans and several of the parts. I'm just going to go ahead as I originally planned.

I appreciate the offer to contact your lead - I think I'm going to move forward with the PTS build though. I ended up selling my Simons bench to a friend of mine for a little less than I paid for it. Simons did end up sending me a manual, but that was after I parted with the machine - I didn't read it much, I just called my buddy and let him know that I had the paperwork. Next time I get a little spare cash I'm going to go ahead and get that MDF and start working on the PTS build. :)

Quote:
Just a thought but for cams, you might want to talk to Megacycle. They do the best hard welds you'll find.

I know little about cams so far. Before a friend shared some work that he did with me, I never even thought about a camshaft profile. He made a graph of several different camshafts, and did all kinds of work to a 50cc Chinese scooter. The company he was with even won a trophy and set some records with that thing. :D Being a 2-stroke guy, I was never really much interested into the 4-strokes until then.

In the scooter world, the manufactures don't give you a cam card or any kind of explanation other than a "lobe height" measurement. A while back, I was building a 175cc (up from a 150 with longer stroke and larger bore) and I called the parts company in Florida that I get many of my parts from. They had a spec "A", "B", and "C" cam listed on the website, but with no specs. I offered to graph the profile of all 3 cams and provide dyno the results of each if they'd sell them to me at a discount. They didn't bite, but I did the profiles anyway - and damn, they were all three the same damned thing with a different letters stamped on the cam sprocket!

Here's the chart that I did:
Image
There are a couple of errors that I made on the "HF Intake" line (light blue). I later fixed those - it was just due to fat-fingering the keyboard.

Here's stock included:
Image

Now the awesome part. I got behind on the job, and didn't have time to do the extra dyno runs before the client needed the bike back, so I didn't have the data I wanted. Oh well... It was a fun build though:

Image
Image

Image
Image
Image

Details here: http://www.scooterinvasion.net/forum/vi ... php?t=3443

I suppose I've officially gone waaay off topic from John's original "carb comparator" heading. I apologize, but it was hard to resist. :)


Wed Jul 02, 2014 12:21 am
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Location: Pennsylvania
Saw a couple of those Honda's in the pits at the races this past weekend, looks like something that would be a good get around vehicle for the for the MH.

I'm thinking you need to start a thread so we can talk "Ruckus" :D

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Wed Jul 02, 2014 6:56 am
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Looking at the time slip it's pretty clear the NT291 win was all rider reaction time.

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Larry C

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Thu Jul 03, 2014 3:15 pm
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