[Richie95F0]

Hey guys! Im new to the site, but not to the mini scene. I've got a few of those chinese x15's on hand, but thats not why im here.

Recently i acquired a 1989 Yamaha YSR50 w/ a derbi swap. The Derbi is direct from Team calamari, with the BBK on it. Has a 24mm flat slide mikuni in it as well. Should be pretty sweet, but thats honestly where the coolness ends.

The bike runs, and starts fine. However itll cold start with NO choke on. Now i also know 2 stroke somewhat, and i know that that is very uncommon, so the pilot hjet must be too rich. Ive cleaned and cleaned the carb again and again, with the same result. Thats not my biggest issue. The issue im having the most trouble with, and im almost certain its not carb related (maybe the cdi/coil unit) is that when the bike is on, and i twist the throttle, the bike will only rev up til about 6000rpm. It wont go past that. I was thinking that it could be a clogged pipe, but im seriously doubting that. I was also thinking the reeds, but my intake manifold has 2 bolts on the bottom, and 2 rivet looking things on the top. Ill take a picture to illustrate.



Anywho, heres some basic pictures of the bike it self, then ill post a picture of the intake, along with a video of the 6000 rpm issue.

Reason why im making this thread is because 1) im new here, and 2) i didnt see a ysr / gpr ssub forum. If a mod could kindly move this thread to the appropriate section, thats be huge!

Thanks guys!













Thanks for reading!

Heres the youtube Videos of the starting and Reving issues.

 

[Luckystar64]

I have some experience with those Derbi engines, as I raced some Metrakit racers for years. It kinda seems like the crank bearings could be bad. Seems like something is binding. I used to have a problem with the damn jetting changing in the heat of the afternoon, and it would bog on the top end. What exact MK motor setup are you running on it? There are alot of configurations. You might as well go back to stock or whatever, because you can't get parts for the MK engine kits anymore. If they did a major top end upgrade w/o using the "speed" bearings-- the stock crank bearings may be junked. I think Derbi just went out of biz too-- no? Switch to an Aprilia motor... hahaha! --L*64

 

[Richie95F0]

Im not sure as I purchased this entire setup for 800$. Thats the first advice ive gotten in about a week though. Heres the original craigslist ad.



apparently the engine is brand new with roughly 3 hours on it. Im not familiar with the 2 stroke side of the mini scene, mostly 4strokes, but ive owned a cr80 in a past, and ive had to troubleshoot that plenty of times.

MK meaning metrakit? Im not very sure what was used.

Could it really be the bearings already?!

Thank you Luckystar

Keep the advice coming, and if worse comes to worse, ill throw in a cr85 or a yz85 engine, as i actually know about those. Derbi and Aprilla are a completely new world to me.

 

[Jarret53]

Did some research and Derbi was bought by Piaggio in 2001 and they closed the Derbi factory in Spain in 2013 and relocated it to Italy and the Far East but I think they are still around.

 

[Richie95F0]

Thats definitely good to know! So a friend is thinking that i have crazy reed fluttering and/or bad rings. Ill do a compression test tonight and then chexk the reeds

 

[PocketBikeRacingTsmmr]

Do check the reeds....dealt with loose reed block last year on a bike,drove me crazy trying to figure it out.

I'd say try to play with jetting and needle settings...since they could not get it right...it's prob all screwed up..

 

[Richie95F0]

Do check the reeds....dealt with loose reed block last year on a bike,drove me crazy trying to figure it out.I'd say try to play with jetting and needle settings...since they could not get it right...it's prob all screwed up..

Thank you for the response. Im really leaning away from bad crank bearings. Only way i can see this happening on this new of an engine is if it was run with no water in the radiator. Theres definitely water in there, but im going to do a flush later. One quick question though, where is the drain plug? Or do i just take off the lowest hose in the system? Also, the radiator doesnt have a traditional cap, its got a weird nipple thing, which i can hook up a hose to a funnel, then fill it, but i was wondering if thats the proper way. I know youve gotta squeeze the hoses as it is filling too.Tonight ill pull the intake off and get to the reed block. What exactly am i looking for? Never had to mess with reeds beforw this bike.As for the jetting, i will definitely mess with that, as the main jet is missing the washer that team calamari speaks about on their website. Is the mikuni 24mm flat slide the best carb for this, or can anyone suggest a better one.Also, what type of tubing can i use as an intake? I have to reroute the carb because where i try to put it, it doesnt sit flat and that will obviously cause issues.Thanks for the help guys!UPDATE:: 9:15am Florida timeRan a cold compression test on the derbi motor and got 70psi.Put the plug in and let it cool up for about 7 or 8 minutes and got 60psi.Gotta be the ring!Pulled the head and this is what i found so far. Cant get the entire head off with the engine installed.Update:: got the cylinder off and measured with a tape (dont have the other tool..caliper or something) and it measures an inch and 7/8 which is 47.625mm which must be 48mm? Ive been looking but can someone help me find a piston ring for that size? Cylinder walls look great. Only thing that concerns me is how the coolant turned into like a calcium like substance.Thanks guys! Ill be washing and getting all of this crud off.

 

[Luckystar64]

I'm interested in knowing if Derbi is still around myself. As far as that particular engine is concerned, those are Metrakit parts. Metrakit is for sure out of biz. I have no idea which configuration you have, but as far as I know, ya can't get parts for any of them. If you could get the OEM Derbi stuff, that motor runs pretty well, and it's as bullet proof as the day is long. --L*64

 

[Richie95F0]

I'm interested in knowing if Derbi is still around myself. As far as that particular engine is concerned, those are Metrakit parts. Metrakit is for sure out of biz. I have no idea which configuration you have, but as far as I know, ya can't get parts for any of them. If you could get the OEM Derbi stuff, that motor runs pretty well, and it's as bullet proof as the day is long. --L*64

Thank you for that. Definitely reassuring. Have had a bunch of stuff go down the past few days. Nothing major, getting bike to rev to 9k+ but its struggling to. Got a couple different jet sizes coming, along with a couple carb to intake mounting ideas/parts. Will post pics as the stuff comes in.Thanks for reading!

 

[Pierce]

You have a metra kit prorace set up. Metra kit is out of business but I think you can still get stuff for that top end through Treats in San Fran. Look them up. The coolant is all messed up because they didn't use the right kind. Make sure to clean it all out. Water with water wetter works best for that engine if you are never going to leave it in freezing weather. Make sure you clean out the water pump real well with that kind of mess.

 

[Richie95F0]

You have a metra kit prorace set up. Metra kit is out of business but I think you can still get stuff for that top end through Treats in San Fran. Look them up. The coolant is all messed up because they didn't use the right kind. Make sure to clean it all out. Water with water wetter works best for that engine if you are never going to leave it in freezing weather. Make sure you clean out the water pump real well with that kind of mess.

Thank you Pierce. Ive already taken the top end apart and went at it with a wire brush. Got most of the calcium build up off. Then i reassembled and ran a 50/50 vinegar distilled water set up for 20 minutes or so. After that i made a mixture of water wetter based on the directions on the back. Im in south florida and the coldest it gets here is like 45, and thats on extremely rare cases.Ive seen treatland.tv and i actually like their site. Im unsure as to if i have a 47mm or a 46mm as my piston measures 46.7 mm and i havent measured with a caliper yet.Thanks for reading!

 

[Luckystar64]

How do you know it's the Pro Race? The gold head? I had a Pro race 76cc,and a 50cc setup before, as well as a 72cc SP. I never had any idea what the damn difference was when I was getting parts from Oz. I'm not even sure he knew. Maybe the Pro Race had a stroker crank? The MK parts made the bike run strong, but the OEM motor was a bit stronger than an NSR50, and you could get 10K miles out of it. As far as parts availability the Aprilia is the best 50cc Euro motor IMO.

I used to get parts from Spi-Parts in Cali. They told me awhile ago that they couldn't get Metra stuff anymore, which is why I sold my bikes. --L*64

 

[Richie95F0]

How do you know it's the Pro Race? The gold head? I had a Pro race 76cc,and a 50cc setup before, as well as a 72cc SP. I never had any idea what the damn difference was when I was getting parts from Oz. I'm not even sure he knew. Maybe the Pro Race had a stroker crank? The MK parts made the bike run strong, but the OEM motor was a bit stronger than an NSR50, and you could get 10K miles out of it. As far as parts availability the Aprilia is the best 50cc Euro motor IMO. I used to get parts from Spi-Parts in Cali. They told me awhile ago that they couldn't get Metra stuff anymore, which is why I sold my bikes. --L*64

The gold head is one way of telling. The ports inside also match the pro race ive seen online. Just countless hours of comparing what i have to the different combos online tells me that its a pro race. The fins on the inside of the cylinder, outside of the cylinder wall (where water flows) matches the pro race as well. The port mapping is identical to the pro race. Im learning more and more as the days go on. I can still get entire cylinder kits for these engines, along with piston rings and pistons. Im sure theyre getting harder and harder to come by, but as of now a top end rebuild shouldnt be too hard to accomplish. Id like to get my hands on a watercooled yz85 engine or a blaster engine, even if they are the 2 most popular swaps. The engine i feel is still fresh with only a couple hours on it, but i wanna be prepared for the future.Thanks for reading!

 

[Richie95F0]

Just another small update. Broke down and installed the main jet along with another thorough carb clean with it all apart again. Put it all back on the engine, installed the spark plug and she fired right up. Let it idle for about 10 minutes and then took it for a quick run. WOW. it revs out to 13000 rpms now but hits a slight wall before it reaches it. Thinking the needle jet but im not sure.Anyways, i ran the gas out of the carb and parked it. Got a couple parts in yesterday so i went back to the garage to tinker with it. Noticed the oil spot again. So im wiping and looking, wiping and looking, wiping and looking, and then BAM! I found where the oil is weeping from i think.It appears as if the guy tried to pry on the right side of the engine case, stator side, and ended up causing a small crack. So i yanked the engine out, cleaned it up with a dremel, to rough it up and create a little more usable surface area, then JB welded it.I know I probably should have taken a welder to it, but I havent entered that market yet, and i figured if jb weld doesnt hold, ill grind it off and weld that sucker. Supposedly its good up to 2300+ PSI, and 550F. Preparation of the surface is key, and i think i nailed that.Anyways, I figured now would be a good time to strip it and start sending stuff out to powder coat. So thats what im doing.. Time to start the official rebuild!Got a works shock, that needs some restoration.Any one got any idea what type of dry nitrogen they used to fill these? Like the type that costco fills customer tires with? If not, ill contact Works themselves, and send it in for a rebuild. Shock has like 0 room for compression.. its weird. Maybe when they fill it, itll make the ride height an inch or so higher in the rear. Thatd be nice.Swing arm and brake stay were chrome dipped by the previous owner, and its in pretty good shape.. So i took some marvel mystery oil for starters and gave it a thorough wipe down. Then i proceeded to go over the slight blemishes with tin foil on the shiny side. Works great. Tonight after work ill pick up some chrome polish.So heres what im thinking..Neon green frame and wheels, with white plastics. - OR -Neon yellow frame and wheels, with blue plastics (yamaha-ish style) with maybe some white thrown in, and or black.- OR - Neon Green frame and wheels, and some other color combo that goes..Opinions? Im hoping to have it all done by christmas, if not right after the first of the year. Ill be pricing powdercoating more seriously once i get the forks and tree clamps off.I need ideas on paint scheme.What color should i do the pipe and the accessories? Like the rear sets, etc etc.Thanks guys!

 

[billythekid]

R any of the parts your gonna powder coat polished I would like to trade them out for stock parts I texted u in the beginning and told u I had derbi parts and I'm in Florida also if the cracked spot doesn't jb weld I have a bottom end for u

 

[Richie95F0]

Nah the swing arm is chrome dipped, and i was contemplating stretching it. The chrome is actually in decent shape, with the exception of a few spots. Not sure if youd want that, and the bushings need to be replaced i think. The swingarm bolt is very tight through thereThanks on the bottom end. Id have to make the decision of another bottom end, or pricing out a swap. Although this engine is going to hauullllll i can tell.Ill update as i get things done. Saturday im off so ill probably take the frame and wheels to the powder coater and get an estimate on things.Thanks for reading!