72CC Carb issues

[ratdude747]

I have a 50CC (bore kitted to 72CC) Gy6 that has a horrible lean pop during deceleration... i found that turning out the idle mix screw on the carb (new, Jetted to 80, 90 ran too rich) fixed that but KILLED my idle...Which leads me to think it's a coasting enricher issue?

Also, when the choke hasn't warmed up, it's impossible to start w/o giving it some gas... as soon as the choke warms up, the engine runs GREAT. Basically, the choke is over-riching the mix at cold start. Is this normal and would a manual choke conversion fix this? I'd rather not JB weld the passages as I want it to start on cooler mornings.

Suggestions?

PS- The scooter was a freebie but needed a new carb and a motor rebuild (hence the bore kit) among other things.

[mmsscooters]

is it a new barb? for a 72cc you should try an 85 jet. if its popping during de-accel you might need to rebuild the accelerator pump, scrappy dog has a rebuild kit now. check your pilot jet might be too small, 72cc will need a #34

[ratdude747]

I doubt it's the pump... that gives a boost when one first cracks the throttle... I acclerate fine and it cruises and (once the choke is off) idles fine... I don't see what that has to do with this.

I tried putting the Stock #70 (or 78, I couldn't read the last digit)... seems to be starting better cold... in the afternoon I'll see if it is doing better and if it's not running too lean. My suspicion is that both issues above are linked in that an oversized main jet is forcing the idle fuel mix screw to be set way to lean, which is causing more coasting leanness that the coast enricher can compensate for. At the same time, this excess fuel also is making the choke's fuel enrichement too much, causing a rich condition like observed.

I don't see why a bigger set of jets will fix this issue... if I'm having to set the idle mix screw as lean as possible (or just about) to maximise idle, then I doubt the pilot jet (or the main for that matter) is having an issue getting fuel.

I am running the stock air box w/new filter, btw, since I have EGR installed (and a plain filter wouldn't work in such case)? I also know, at least with the #80 jet (and the very rich running #90) that any vacuum leak would make it idle way out of control... fast enought to engage the clutch at even a minimal idle setting (or just about)... do bore kits require aftermarket air filters too?

Another strange observance on the bigger jets... When cold (but recently ridden) it would start and idle fine for 20 seconds or so, before getting in the usual way too rich routine. My petcock is fine (no fuel in the vacuum line; fuel s also feeding the carb just fine) and I didn't notice any obvious carb float issues (but I don't know how to check the float level on a CVK...)

[blueboy5000]

IN is lean

OUT is rich.

it's a FUEL MIXTURE screw on most 4 strokes and an AIR MIXTURE on 2-strokes

[blueboy5000]

since I have EGR installed

^^^ Yeah, eliminate that. When the PULSE AIR fails it creates a LEAN EXHAUST condition.

[blueboy5000]

I am running the stock air box w/new filter, btw

Also no good, run a 80 to 85 MAIN, #34 or #35 PILOT and an appropriate open-style air-filter.

[ratdude747]

What would I the do with the egr connection on the head? Or do I need to put in a new head on top of everything else? Could I fabricate a cover out of some spare sheet metal?

Also, where would my crankcase breather go?

[blueboy5000]

The crankcase breather ideally should go to a closed-circuit can. But some people juts let theirs stay open to the air, but if you do that, it will leak oil.

I use a catch can and I don't re-circulate the oil condensate, as the process of condesation of oil produces high amounts of h2so4, so I like to keep it separate. I made my can from an 8oz water bottle and an automotive oil breather filter.

[blueboy5000]

Yes make your own plate from thick sheet metal or steel. It's very easy. I went to NAPA and got a piece of exhaust gasket material, and I made a nice gasket. 4000 miles, and no leak.

[ratdude747]

Ok, I have a fresh gasket that with any luck won't fall to pieces when I remove the pipe. I'll figure something out with the breather.

Now, I'm having a hell of a time finding a #34 idle jet... I only saw one place that had it and their listing for the #85 main jet was broken (item not found)... do I have to get them from separate places or is there a seller (on ebay or independant) that has those (and the air filter too, since I want to save on shipping).

[ratdude747]

pulled the egr system and air box... fabricated a cover for the egr connection on the block (18g weldable sheet steel). getting closer...

[ratdude747]

Found the jets and filter... ordered. I'm sorta confused on how this breather can thing is setup... I'll figure it out. Or find some solution that works well. The body may be beat to pieces (sorta) but hell or high water I want it running right.

[ratdude747]

Been a while, some updates:

-added an external breather with filter. I ran the hose to a hanging hot-rod type breather filter which I hung from a strap attached to the petcock mount.
-put in an open element air filter and the suggested jets
-Still has issues:

-When idling, no matter what I do, it seems like I can't get it to run lean enough with the idle screw, both hot and cold. runs best with it bottomed out. This is with the #85 carb jet and #35 idle jet. Even does it with no filter at all. It's like it's dumping in WAY too much fuel. I tried adjusting the CV needle to no avail.
-sometimes misfires at high RPM or when I give it gas from a lower throttle position. the exhaust pulse noises seem to happen later and it's a lower tone with a drop in power (not a lean pop).
-when cold, idles OK for 45 seconds or so, then bogs down and is unstable (any load or a throttle crack too slow kills it). Once warm everything is better.
-I've been getting 65-60MPG if that means anything, top speed on flat land just over 40MPH

IDK if I just need yet another new carb or what... this one seems a bit odd (the construction was kinda weird compared to the corroded original if nothing else).

Other issues possibly related:

-BAD loud exhaust leak, probably due to the fact that the rubber cylindrical gasket doesn't mesh well with the pipe (large weld bead glob in the gasket area). IDK how I pulled it in the past as the suspension member seems to be in the way of one of the bolts hence why I haven't gotten a flat gasket to replace it with.

-Missing engine cover seal that goes around the head; it snapped when i reinstalled it as a result some of the fan air gets directed out of the gap, not out the air exhause at the bottom of the engine.

Suggestions?