New (hopefully) observation on weak HT 80cc motor - anyone seen this ?

[chrisnbush]

Huh, thanks. I have the clip as high up on the carb needle as it will go which I understand to be as lean as possible. I have noted that the gap was a little wet, not white and brown as desired I think. Again was thinking to go to 66/80 cc grubee carb, but wouldn't it be even richer ? I think ive seen threads on making the jet smaller somehow, is this easy ?

Thanks again

 

[Ghost0]

Adjusting the needle has the most effect at low throttle settings and does next to nothing at WOT. The jet size controls fuel flow at WOT. You can get different size jets from Dellorto, they are 5mm and the stock hole size is .7 mm and I would recommend a .65 mm. You can rejet yourself if you have a soldering iron and the correct set of bits.

 

[khillr48]

Carb fog

The fuel fog in front of the carb is usually caused from the lack of scavenging of the exhaust. I've even seen it on 4-strokes. An expansion chamber will help both power and scavenging. But it's a fine line between torque and top end. The header pipe from the engine to the chamber will tune the power. A long header pipe makes torque and a short pipe makes top end. But the exhaust is where it's at.
Good luck, let us know how the tuning goes.

 

[andynogo]

I've got a 66/80 motor and that was 4 stroking constantly so I've had to make the jet smaller- down to slightly less than .5mm! That's with a proper air filter, expansion chamber exhaust, slight porting- mostly cleanup.

Runs beautifully now and can fine tune it with the needle. It cruises at 50-55km/h and I've seen 61- with standard sproket on the back. I don't top speed it very often though as it is pulling some revs!

Yours certainly sounds like it's running very rich. Get some jet drills off ebay or use fine wires if you have it. Solder up the jet and re-drill it smaller. You can also use mig welder tip cleaners to change the size of the jet orifice.

 

[AussieSteve]

Dellorto 5mm jets fit these carbs. I think you can buy direct from them. I'm not sure of the exact range, but I think that a #50, #65 and #76 are available. (0.5, 0.65 and 0.76 mm)

 

[andynogo]

Buy jets? Went round four or five shops of different types and all I got was blank looks! Typical Perth response. Usually followed by "Yeah, well, I spose I could ask someone over East...but it'll take a couple of weeks..."

Took me three minutes with a soldering iron and some solder...

 

[AussieSteve]

That's what the internet is for. For a range of sizes - again not sure of the range, try:-
http://www.rocksolidengines.com.au/
(You'll need to contact Tony, they're not listed on the site, but he says that he has them.)

Also, if you want a larger jet, 0.76mm:-
http://www.zbox.com.au/
(These are listed on the spares page)

As mentioned, I think that Dellorto sell them directly from their website, too.

The problem with soldering and drilling is that you can't swap back to the old one or a different size without re-soldering and drilling. Also, not everyone has a range of drill bits in these sizes. They're harder to get than Dellorto jets. If you have a couple of ready-made jets, no dramas, especially if mods are ongoing and more re-jetting will be needed.
(Jets cost about $5 each, no big deal.)

... Steve

 

[chrisnbush]

The Dellorto guy got back to me - the part number for the jet is 1486 (5mm), the orifice size range from .3 mm on up, by 0.01 so they have every thing. 3.28 pounds, which is about 5 bucks, but I would want to get a range of sizes I think. Wonder what shipping is.

I am going to get some jet drills, but want to look at the jet first - take it out of the carb. My experience with soldering is electrical, and I don't think my iron is going to get that piece hot enough to melt the solder on it. I can drip solder into it, but that won't stick.

Wondering if I should use pipe solder and if so if I need rosin core - I have some. Seems like not a problem to solder them, could just reheat and clean them out, right ?

 

[chrisnbush]

BUT you know as much as I like to mess around with these things, wondering if this "CNS" (whatever that means) carb that spookytooth isn't maybe a better answer in the big picture.

You can "tune" your fuel + air mix with these, right ? Anyone have experience with a racing carburetor, which I assume as a group allow you to do this ?

I have been using my centermount for basic transportation for 2 years now. I swap out motors when they go (got 2500 on one), maintain my rear wheel (spookytooth) but will swap it out when it goes. Tank and carbs are pretty stable, along with sprocket and my light setup. My frame is old schwinn cruiser, close to solid heavy steel - this is the base.

If I get a tunable carb, then I can swap in pretty much any motor - 49, 66, 80 whatever and tune it appropriately. I have a couple of rebuilt motors in the wings I can drop in this way, and don't want to limit myself to any particular displacement. I am working to have them all setup with mounting studs, clamps, and carb input tube.

I figure I could get the SBP tuned exhaust, and this would work pretty much for any motor, although I might have to have a supply of the header tubes as I understand the lenght of these has an effect on the tuning related to the RPM of the engine.

I also want to get a supply of these slant heads with higher compression, both 49 and 80 cc so I can just swap this in for whatever I purchase. I like DAX as a engine supplier, he stands behind what he sells, but he doesn't have slant heads.

Using these things for basic transportation I am trying to minimize my down time. If I come home broken, I want to be riding to work the next day.

I guess I am kind of crazy about this ****. I have a lot of ideas - was thinking about rigging a tube extension for the exhaust so I can run it under my coat to keep me warm (it is cold in NH this time of year). And maybe some screws + bolts in the tires...

addict

 

[mauicruzer]

Thanks for all the info.

Good to reading!!