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Post by gatormoto on Apr 10, 2009 14:41:44 GMT -5
Hey guys... I have a really slow batch of 49cc Shenke scooters. All of the ones we've gotten in the past go 35-40mph, but this batch is only pushing a solid 30mph. We have changed out the mufflers, cdi, and carburetors and still no change in speed. They have the 139qmb engines on them, just like all our past shipments. They seem to be running very lean, very little brown, if any on the spark plugs. The carbs originally came with a size 79 jet and we switched to a size 85. Also, raised the needle position higher.
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Post by Enviromoto on Apr 10, 2009 15:49:30 GMT -5
So are they still slow?
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Post by gatormoto on Apr 10, 2009 20:09:38 GMT -5
Yes, sorry... after doing everything mentioned, still no change. 30mph top speed and running very lean. Anyone else have any suggestions? We are running out of ideas.
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Post by Troll on Apr 10, 2009 20:42:29 GMT -5
Does the variator have a washer on it or could the pistons be smaller then a true 50?
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Post by cruiser66 on Apr 10, 2009 21:10:28 GMT -5
So you still are running lean with the larger jets and carb adjustments? Usually means extra air getting into the intake. Did you check out the intake manifolds and the airboxes? Might be a defective run. Also, what are the rpm's when you are at max speed? If the engine is maxed out at 30 mph, maybe somebody at the factory slipped in the wrong gears in the tranny. Maybe they slipped in a transmission intended for 16" wheels? Very unusual in that it is a consistent problem on more than one scoot.
66
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Post by Enviromoto on Apr 10, 2009 21:57:59 GMT -5
I have heard that the new Tank's are snails as well....
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Post by gatormoto on Apr 10, 2009 22:02:36 GMT -5
I will check on these suggestions tomorrow at the shop and will report back. I'm not going to stop until I find the issue, because it has to be something. All of our orders last year for these same models easily went 5-9mph faster than these are going, with the same engine, same tire size, etc.
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Post by Enviromoto on Apr 10, 2009 22:06:28 GMT -5
66 had mentioned something about variations on the heads. Something about the intake ports being different sizes.. Maybe they have started to restrict these down a bit?
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Post by cruiser66 on Apr 10, 2009 22:30:36 GMT -5
There is a variety of heads out there. I have three 1P39QMB heads all with different size ports. The head with the smallest ports is 15.4 mm intake and 15.75 mm exhaust. The stock head on my scoot is 19 mm intake and 19 mm exhaust. This could certainly be a way of restricting the speed. My scoot has no problems with 42 mph (GPS) carrying 225 pounds.
66
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Post by gatormoto on Apr 11, 2009 13:08:07 GMT -5
OK... here's what we found so far this morning:
Our order last year had 20.17mm intake ports on the cylinder head and our new inventory has 18.20mm ports. Thoughts?
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Post by gatormoto on Apr 11, 2009 16:33:07 GMT -5
OK, another update. We put the 20.17mm head on the new scooter and actually saw a decrease in performance... dropped to less than 30mph. We're going to check the gearing on Monday... this thing is driving us nuts. Have about 8 hours into it and haven't been able to figure out a thing.
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Post by medman1952 on Apr 11, 2009 17:02:44 GMT -5
I know you said you changed the carb, but did you see any difference in the intake, air cleaner, manifold, air box?
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Post by gatormoto on Apr 11, 2009 19:11:53 GMT -5
Didn't see any glaring differences... but will check further on Monday. When we found the ports were smaller we were excited and thought we finally solved the puzzle, man were we bummed when it actually slowed the scooter down w/ bigger ports. I'm no mechanic, but with that happening I'm thinking it's still got a limiter in there or the wrong size gears. I'm not too happy we have to wait until Monday to try more!
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Post by cruiser66 on Apr 11, 2009 20:19:38 GMT -5
How do the exhaust ports compare? I don't think that you would realize any performance gains from the 18 to the 20mm head. You are limited by the size of the intake manifold and spacer to less than 18mm. Did you use the same cam for each head? The 20mm head might have a lower compression ratio than the 18mm.
66
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Post by Skoot on Apr 12, 2009 9:40:09 GMT -5
Take a look at the flywheel and see if they have retarded the timing trigger, or if the stator is in a different position from a previous model. Might be trying to get california carb certified or something. Leaning the mixture and retarding the timing will lower HC and NOx
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Post by harrywr2 on Apr 12, 2009 11:28:15 GMT -5
The QMB139-003's are restricted in the variators. The stock variator with stock weights ends up being in top gear at 4,500 RPM.
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Post by Enviromoto on Apr 12, 2009 20:36:00 GMT -5
Did you use a different variator or just weights on yours?
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Post by gatormoto on Apr 13, 2009 11:52:40 GMT -5
Striking out left and right. Just swapped out variators... no change. Then opened up the tranny and checked gear sizes. old and new has the exact same gears. At this point we've swapped carbs, spark plugs, cdis, variators, weights, gears, cylinder heads... still no change. Last shipment still does 35-39, new shipment still does 30.
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Post by medman1952 on Apr 13, 2009 11:58:46 GMT -5
And the head swap was with the old cam? you also did check the timing advance? Skoot has a valid point there.
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Post by gatormoto on Apr 13, 2009 12:02:59 GMT -5
Yes, head swap was with the old cam and we checked the timing advance.
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Post by harrywr2 on Apr 13, 2009 12:12:22 GMT -5
Slightly heavier torque/contra spring perhaps?
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Post by gatormoto on Apr 13, 2009 12:16:59 GMT -5
swapped clutches, so even if that was the case, we changed it. we even measured the lift of the intake and exhaust lobe on the camshaft.
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Post by medman1952 on Apr 13, 2009 12:31:31 GMT -5
Seems the only logical remaining cause could be a Voodoo witch doctor cast a spell on the scooters.
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Post by gatormoto on Apr 13, 2009 12:39:15 GMT -5
ya, tell me about it. makes no sense at all.
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Post by harrywr2 on Apr 13, 2009 12:47:11 GMT -5
Any difference in compression....could they have used a slightly shorter crankshaft?
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Post by tortoise on Apr 13, 2009 13:02:31 GMT -5
They seem to be running very lean, very little brown, if any on the spark plugs. As mentioned by cruiser66, has the intake manifold vacuum port been temporarily plugged during testing to rule out an emissions plumbing vacuum leak (causing a lean air-fuel mixture)? |
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Post by Enviromoto on Apr 13, 2009 13:41:20 GMT -5
Measure the belt length.
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Post by gatormoto on Apr 13, 2009 13:41:50 GMT -5
Looks like we figured it out. Unbelievable. We had a few techs working on it, and when they put their heads together, they didn't realize to check the oil. The oil that was used was slowing the scooter down. Drained it out, put fresh oil in the motor, now it's going 36. Unreal
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Post by Enviromoto on Apr 13, 2009 13:44:58 GMT -5
The oil was slowing it down? Why because it was overfilled?
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Post by scosgt on Apr 13, 2009 14:31:38 GMT -5
Wrong viscosity?
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