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Post by pinkscoot on May 28, 2018 18:23:06 GMT -5
I tried my theory about not enough air to the carb and put a generic open filter on it. I still ended up with the 50 slide and the needle as lean as it would go. I stopped the MJ at 82 and decided that the 77 with the air box was probably a good tune. Maybe it was the wet rainy day but it still had some stutter to it. I'll see how it is when its drier. It did sound great with the open filter so maybe I go back to it.
I then started tuning the CVT. I put the Delta Clutch on with white springs set as tight as possible and a white contra spring. I also put the Dayco belt on to see how it did. The Dayco belt is smaller and longer, it used a little more of the variator. I changed the weights to 5.5gram as well. I then tried the Malossi belt and it felt the same but not as much variator. I called it a day on tuning because the bike race in town was going full tilt and roads were blocked and there were to many lost cagers that got in my way. Tomorrow might be better and I can give it another go.
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Post by pinkscoot on Jun 7, 2018 19:58:18 GMT -5
I've spent the last week tuning and this is what I've found. I started with the engine running okay and a few gurgles with the 5.5 and white springs on the softest settings. I tried 4gr weights and it sputtered so bad it was undrivable but I got to 10,000 rpm. This was new to me, I never knew that lighter weights could affect the tune. Lesson learned. I started working my way up and found 5.5gr was acceptable but that it was best with 6 grams but 9000 rpm was the top and I didn't get full belt travel. The gurgling was from 1/4-1/2 throttle, I'm already as lean as I could go there. I have a 60 slide and a w10 and w11 needle on order. Then I reread my whole thread again and stopped on the BBK install. My pistin at BDC wasn't clearing the floor on the transfers. At the time I just wanted to get it together and not deal with it. Now I think its why I'm not getting what I want out of it. I think if put spacers under the cylinder to get the transfers up to the piston and then shaved the top of the cylinder so that I got the squish I wanted I would be seeing better gains. So you don't have to go to the post here it is: I finally had a day off and was able to get to the Derbi yesterday. I decided that at 110psi compression I should put the kit on. While pulling the engine I discovered I never connected the ground up, that might have been the problem with how it was running but I still wanted the hire compression and I had the kit already to go on so why not go for the extra power. I also got the Durations while I was at it. The exhaust was 180 degrees and the Transfer was 126 degrees. Here is the port map I did of the cylinder: I don't know enough to know how this compares to other kits. one thing that concerned me was that at BDC the piston didn't completely clear the ports: Here it is at TDC: The squish was .94, not what I would like but pulling the base gasket would make it worse for the transfer ports. The solution would be to take a little off the cylinder to get the better squish. Maybe in the future I'll do some work on it. I put a 19mm Dellorto Clone that I have because I don't have a good mix of Weber jets and I wanted to go to a Dellorto carb to see if they are as easy to tune as everyone says. I also put the carbon fiber reeds that came with the kit in. The engine started and ran well. I tried the plug Malossi specced and it ran okay, it was maybe a little rough. I put the B9ES plug it and it ran much smoother. The engine ran a bit cooler than it did with the old aluminum Cylinder. Today I'll start tuning it in. I have a new belt for it, the old one is 16 years old and I'm not sure I want to trust it. I look forward to comments on the durations and port map. I know that shaving the top of the cylinder with glass and sand paper would take forever. Does anyone have any suggestions. It would also raise my 180 exhaust and lower my 126 transfers. Would this be a bad thing. Any help would be appreciated. I may go looking for another kit that would maybe be a better fit.
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Post by 190mech on Jun 8, 2018 3:23:57 GMT -5
I reread your port map write up.Looks like a thicker base gasket or a thin spacer would get your transfers even at BDC,that will raise your port durations also,Then the head/combustion chamber needs to be adjusted.Would be good to post a pic of the head..
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Post by pinkscoot on Jun 8, 2018 10:54:55 GMT -5
Here is a picture of the kit:
I would love to keep it simple and mill the head dow but being liquid cooled I'd need to re-cut the gasket grooves. The cylinder looks to be a better candidate for it. I think we are talking 1-2mm though and that will take a while hand sanding it. Do you have any suggestions on the best way to get it done?
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Post by 190mech on Jun 8, 2018 11:55:52 GMT -5
I used to lathe cut cylinders to bring the deck down till one jumped out of the chuck and was destroyed. Now I'm doing them on a vertical milling machine with a rotary table,kinda tricky to set up sometimes,but safer than the lathe!
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Post by pinkscoot on Jun 8, 2018 12:09:11 GMT -5
Let me see if I can find someone around here thats interested in doing it. Machining is not something that I have any experience with.
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Post by pinkscoot on Jun 8, 2018 14:37:44 GMT -5
I called around and no one is interested. Let me see how much I'm really looking at and I get a piece of glass and sand paper and just do it while I sit at work. Its better than eating popcorn all night.
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Post by 190mech on Jun 8, 2018 16:19:13 GMT -5
Yep!Cast iron cuts easy,,start with 80 grit to get it close,then finer for a good seal..Good luck,keep us posted...
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Post by pinkscoot on Jul 6, 2018 11:12:55 GMT -5
So I got the engine out and started looking at everything and took this to another thread to get specific answers. The thread is here: 49ccscoot.proboards.com/thread/23004/bbk-right-on-derbi-predator . 190mech helped me decide that milling of the Cylinder wouldn't get me where I need because I can't take the full 2mm off but only some of it. I decided to go back to the 50cc stock cylinder and do some work on it to get it better. I'll do a port map and durations so I can better see what I have. I also think I had the reed block in backwards. Its a single reed and looking in the manual they showed it facing the cylinder and I had it the other way. Any thoughts on this will help. I'll get pictures today or tomorrow when I get off work.
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Post by pinkscoot on Jul 7, 2018 7:57:13 GMT -5
I was able to get pictures of the reeds and the intake.
Any suggestions on which way they should face? They were facing toward the back but I would think they would want to face toward the cylinder so that the mixture would go right into the cylinder and not bounce around the case. It may not really matter because they face straight down.
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Post by 190mech on Jul 7, 2018 9:21:34 GMT -5
Right,the mixture should be directed toward the cylinder base and transfer ducts..The way it is now it will be crashing into the spinning crank!
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Post by pinkscoot on Jul 7, 2018 10:55:34 GMT -5
That could be why this scoot was so hard to tune. I have found several pictures of these intakes and they all show it the other way. Hopefully Monday I'll have it running again.
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Post by pinkscoot on Jul 7, 2018 17:33:42 GMT -5
While sitting around work babysitting a show I was able to do a port map on the stock 50cc cylinder:
Next to it is the Malossi port map. As I studied it I came to the conclusion that Malossi just uses the Minarelli cylinder casting and bores it differently. The distances on the ports would work well with the almost 2mm difference in stroke. I may go back to this kit on my naked build but for now I just want to get the scoot tuned and running.
A question I have is the stock cylinder has a tiny boost port cut in it and the piston has no boost port. Here is the cylinder:
Should I open this up and cut one in the piston or just leave it alone?
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Post by 190mech on Jul 7, 2018 18:39:00 GMT -5
No wonder your Malossi jug doesnt match up,41.5mm from the deck to the base of the transfers and you have a stock 38mm stroke!!Holes in the piston arent needed in a case reed engine,those are some rough looking port ducts in that stock cylinder...
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Post by pinkscoot on Jul 8, 2018 14:55:52 GMT -5
Do you think I should clan the ports up as well as that crappy transfer that looks burned into the aluminum?
I was able to get the stock jug back on before work. I tried it with out the gasket and found that at BDC the transfer ports were still covered by just a nettle bit. I know before with the gasket they were fine:
I then checked the squish and it was .97 not the best but the gasket will make it worse. The Exhaust duration is 186 and transfers are 120. I'm thinking I'll go with a gasket to get the transfer floors right and sand some off the cylinder to make it right and get the squish down.
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