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Post by Karl on Aug 24, 2008 13:46:20 GMT -5
.....a modded one that runs bad.
I know, I know, that's obvious, but I've found out something about myself that I'm sure you all share.
I'd rather have a slower scoot that runs well than a faster one that has a bog issue.
I recently bought a 70cc top end for my scoot. Separately, I also bought a larger carb to match it that hasn't come in yet. Well, I put the top end on because the guy I bought it from said it would run with my stock carb. He was right to a degree. It starts fine and is peppier, but when warmed up there is a bog at about 1/4 to 1/2 throttle. It then catches and goes into the power band. With different jetting or needle placement I know I could fix that. But since I have this other carb coming in, I don't want to dial it in with the stock carb then have to undo what I did if ever I go back to the stock setup....like if/when I sell it.
Because it's a 2-stroke, it's only an hour's worth of work to change out top ends, now that I know this scoot.
Have any of you done this or something similar?
Am I that OCD? Yes, I am! ;D
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Post by 90GTVert on Aug 24, 2008 14:13:33 GMT -5
I did the opposite. I have a big carb doing nothing while my stock carb has the needle moved up and runs great.
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Post by Karl on Aug 24, 2008 14:42:18 GMT -5
I probably should have tried that, Brent.
I was getting a bit of a top end rattle that I think was from the wrist pin/bearing. Next time I install it I'm going to see how much play it had.
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Post by 90GTVert on Aug 24, 2008 14:51:26 GMT -5
I was getting a bit of a top end rattle that I think was from the wrist pin/bearing. Next time I install it I'm going to see how much play it had.  Ahh. In that case, you prob are better off stock. Going slow isn't gonna kill the engine, a bearing problem may. |
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Post by rallyrrr on Aug 24, 2008 18:24:26 GMT -5
If the top of the carb is easily accessed and removed, moving the needle is about a 5-10 minute job. The education gleened may be worth it. It is the same amount of time to move it back. If the flat spot goes away you would have also established a baseline to which to compare your larger carbs performance to.
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Post by 90GTVert on Aug 24, 2008 20:37:59 GMT -5
If the flat spot goes away you would have also established a baseline to which to compare your larger carbs performance to. That's a good point. In the name of science... kinda. ;D |
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Post by Karl on Aug 24, 2008 22:41:03 GMT -5
Oh yes, Reg, I'm very familiar with adjusting the needle. I actually did raise it a notch for my stock setup to richen it a bit. I should have played with it some more but I had that swap already in my head.
When things settle down after wifey-poo's surgery, I'll be able to tackle the scoot again. I'm just concerned about the top end rattle on that 70cc kit. It only seemed to rattle at idle, btw.
The wrist pin bearing for the 50cc piston is about 2mm narrower in width than the Wiseco one Brent recommended. They're both the same diameter, though and fit the 12mm wrist pin perfectly.
Under the crown of the 70cc piston where the wrist pin inserts into the two holes (what's the name of that?) is a little wider than the stock piston. The Wiseco wrist pin bearing wouldn't fit in the stock 50cc piston. The bearing was too wide.
Anyway, I'm wondering if I should get an even wider wrist pin bearing. There seemed to be a bit of play side to side with the connecting rod but I don't know if that was all in my head. I also heard that bit of rattle in there which I thought might diminish once it warmed up....and it seemed to. I did oil the bearing very well before install, too.
Hmmmm, what do yall think?
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Post by rallyrrr on Aug 24, 2008 23:06:06 GMT -5
Karl, I guess you're refering to the wrist or gudgeon pin bosses. From what I've read on other forums aftermarket aluminum cylinders naturally make the clattering sound. Mine did. I don't know about iron cylinders though. There needs to be some pretty good clearances for that bearing. This area gets pretty hot. My book says that the wrist pin should fall through the piston bosses with no catching or binding.
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Post by 90GTVert on Aug 24, 2008 23:07:14 GMT -5
Under the crown of the 70cc piston where the wrist pin inserts into the two holes (what's the name of that?) The wrist pin boss. There seemed to be a bit of play side to side with the connecting rod but I don't know if that was all in my head. You are allowed some play side to side, you just don't want play up and down on the connecting rod. I don't know if there is a spec for lateral movement or not for this engine. EDIT : rallyrrr beat me by 1 minute lol. |
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Post by Karl on Aug 25, 2008 9:09:56 GMT -5
OK, Gurus, that makes me feel a little better. I was more worried about it being too loose than too tight. The pin boss seems to fit fine, maybe almost a little snug but no play, that's for sure. Reg, the cylinder I have is iron, not the fancy aluminum!  Karl |
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Post by kevinx on Aug 26, 2008 20:35:23 GMT -5
I did the opposite. I have a big carb doing nothing while my stock carb has the needle moved up and runs great. what size is your stock carb? |
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Post by 90GTVert on Aug 26, 2008 20:49:49 GMT -5
I dunno anymore lol. By measurements someone had given me I thought it was 17.5. Having it off and checking it out recently, it appears to be more like 14mm or so (I don't have a mic that will get in there too really measure though). It also matches up to some specs of a 19mm. This is why people hate Chinese stuff. I've heard my scoot could have a 13-14mm carb, a 17.5mm carb, or a 19mm carb. God forbid they ever label something to make things simple.
It doesn't matter too much for this scoot, it runs well and is reliable so I don't care if I change it at the moment... but it would be nice to know.
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Post by Karl on Aug 26, 2008 20:54:22 GMT -5
Brent, if it helps, I was told that mine has an 18mm. So, since yours and mine are practically identical, I think that you could go with that. Stock, mine has a #70 main jet, too.
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Post by 90GTVert on Aug 26, 2008 22:03:55 GMT -5
My main jet has no number on it. It's quoted elsewhere as a 57.5 pilot and 80 main, but I dunno for sure. Here's a pic - the enrichener...  |
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Post by motomech on Aug 28, 2008 11:35:34 GMT -5
<<<<I'm just concerned about the top end rattle on that 70cc kit. It only seemed to rattle at idle, btw.>>>>
<<<Wiseco>>>
Although their pistons have gotten better, they didn't earn the moniker of Siseco for nothing.
What was the piston to cyl. clearance?
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Post by Karl on Aug 29, 2008 15:37:53 GMT -5
Moto, it was only the wrist pin bearing that was Wiseco. The rest of the kit was either Taiwanese or Chinese.
Tell me how to measure the piston to cyl clearance and I'll go measure it.
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Ahh. In that case, you prob are better off stock. Going slow isn't gonna kill the engine, a bearing problem may.
