lovemysan wrote:I've never had in crankcase breathing issues. I always do a hard break in.
I was advised that if the bike starts to buck once speeds reach the 50-60 range, that it needs the decompression tube. The motor is doing exactly that. For $12 or so, I will give it a shot.
Am I completely nuts thinking that I need to be in the 130 range on the main jet? How about that the bike feels like it's starving for fuel across the board?
And for the needle jet, I am assuming that I would raise the needle height with some kind of spacer to richen the mixture in the middle portion of the throttle opening. Is this correct?
paracer wrote:And for the needle jet, I am assuming that I would raise the needle height with some kind of spacer to richen the mixture in the middle portion of the throttle opening. Is this correct?
This is correct. I used different thickness washers to raise my needle when I was experimenting. Ended up going back to stock needle jet position in the end.
I would be very surprised if your engine needed a 130 main jet. My engine is around 183cc and I'm only using a 118 main jet (with a 30mm carb). The spark plug indicates the mixture is just about spot on. When I was running my stock 24mm carb, I was using a 120 main jet and it was very close to spot on, maybe just a touch lean, but not by much.
As far as a decompression tube, the only thing I'm using at the moment is a vent tube on the valve cover that vents directly to atmosphere. I plan on installing a catch can to coalesce the oil vapor and allow it to run back to the engine case.
If you're interested in what I've done with my engine, you can read about it here: topic16629.html
Kind of a long read though...
BTW: I believe I'm running the same head as yours (Ruima), except I've "massaged" the ports and combustion chamber a bit.
I think we do have the same head. I also cleaned up the ports. I didn't know what to do in the combustion chamber, so I just rounded the edge around the squish band a bit.
The more I read about people's experiences with tuning and jets, the more I am finding that I might be anywhere across the spectrum. I saw notes indicating that I might be anywhere from the mid 110s up to well into the 130s. What I know is that I had to cover the inlet in my airbox significantly with duct tape to get the bike to operate well enough to get me back and forth to work.
What I did with the airbox is that I trimmed the filter panel. I removed the inlet tube and trimmed the surrounding material to be just outside of the lip that fits into the groove in the airbox. It does have a nice roar when I open the throttle.
I honestly feel that the mixture needs to be richened across the board based on what I had to do with the intake.
I'm also pretty confident that I installed the big bore kit correctly. The valves were gapped to .004" on intake and exhaust. There is no smoke other than the oil that likes to spurt from the dipstick. I drilled a hole in the dipstick to relieve pressure; this is a bad move. The timing should be correct as the bike starts nicely and runs well enough to commute to work.
I do have a question about the exhaust header gasket situation. The stock head did not seem to have a gasket attached, but there was a gasket pressed into the recess in the header flange. The new head appears to have a recess for a gasket. What's the deal with the head that we are using? Do in need to have a gasket in both the head and the header flange? I don't think I have an exhaust leak. I can't hear anything and it's been to rainy to crawl on the ground to feel.
My plan is to install a new spark plug and install a decompression tube this weekend. After that I will ride a bit, see what changes I find and check the plug. My local shop is ordering a few new jets so I will be able to play around a bit.
With a new spark plug, the bike pulled an extra few miles per hour. I was using the original plug up tp this point. By getting the tape correct on the airbox inlet, I can get the mixture fairly close. The bike pulls strong up past 60mph. I just need larger jets for the idle and main to be able to remove the tape completely.
I am really excited to get this thing running right. The bike feels really strong even with most of the air inlet covered.
paracer wrote:With a new spark plug, the bike pulled an extra few miles per hour. I was using the original plug up tp this point. By getting the tape correct on the airbox inlet, I can get the mixture fairly close. The bike pulls strong up past 60mph.
Are you measuring speed with a GPS unit or with the standard speedometer, which is about 10% optimistic? Getting past 60 MPH indicated is something any Buddy 125 should be able to do.
Some people are like slinkies. They're not very interesting, but they bring a smile to your face when you push them down the stairs.
If you're having that much blowby then a ring is either damaged or didn't seat at all. The 170i uses pretty much the same kit and doesn't have much blowby.
paracer wrote: The bike pulls strong up past 60mph.
Are you measuring speed with a GPS unit or with the standard speedometer, which is about 10% optimistic? Getting past 60 MPH indicated is something any Buddy 125 should be able to do.
No GPS. I know the speedometer is off. I don't mean to say that the bikes top speed is ~60mph. I am saying that my efforts are on the right track.
dasscooter wrote:If you're having that much blowby then a ring is either damaged or didn't seat at all. The 170i uses pretty much the same kit and doesn't have much blowby.
I think the issue is that I drilled a hole through the dipstick. And with less than 100 miles since I installed the big bore, I wouldn't be surprised if there was a bit of blowby at first. Now that I have installed a decompression tube, I am not seeing oil spurt up into the tube. I also don't feel pressure if I put my finger over the end of the tube. There is no smoke from the exhaust either.
I was able to pick up a couple jets today. With a 130 main, I was able to remove the tape from the intake. I need to do a plug chop to see how things are going, but I think I'm heading in the right direction.
Glad you're getting things sorted out. One thing for sure though, with the size mj you're using, the great MPG that the Buddy is known for is going to go down the drain. I'm already getting a relatively poor 57 MPG with my set-up. I have to fill-up every 65-70 miles or so. Luckily, San Francisco is a very compact city - hilly, but compact.
I'm pretty sure the reason you have to use such a large mj is because of the modifications you've done to your filter box. You're getting so much airflow through it now that the vacuum throttle slide (CV) system is not able to work correctly. The same thing happens when people use a sock/pod type filter in place of the airbox. On my airbox, I only removed the noise suppression rubber tube and opened up the air flow a small amount in order to minimize the affect on the CV function of the carb. If you plan on using a sock/pod filter, you might be better off using a flat slide carb instead of a CV type. It will be a lot easier to tune. There are some very reasonably priced Chinese made flat slides on eBay lately, but I don't know how good (or bad) they are since I've never played around with them. The one negative thing about flat slides is that you'll lose your automatic choke function, it'll be totally manual, if that matters to you. Kind of inconvenient since the carb is totally enclosed in the body work so you won't have access to the choke lever.
Take it easy on the engine for the first 500 miles or so. No high speed runs or long steep hills, otherwise, the rings may not bed-in properly.
What type of oil are you currently running? Not synthetic, I hope...
babblefish wrote:Glad you're getting things sorted out. One thing for sure though, with the size mj you're using, the great MPG that the Buddy is known for is going to go down the drain. I'm already getting a relatively poor 57 MPG with my set-up. I have to fill-up every 65-70 miles or so. Luckily, San Francisco is a very compact city - hilly, but compact.
I'm pretty sure the reason you have to use such a large mj is because of the modifications you've done to your filter box. You're getting so much airflow through it now that the vacuum throttle slide (CV) system is not able to work correctly. The same thing happens when people use a sock/pod type filter in place of the airbox. On my airbox, I only removed the noise suppression rubber tube and opened up the air flow a small amount in order to minimize the affect on the CV function of the carb. If you plan on using a sock/pod filter, you might be better off using a flat slide carb instead of a CV type. It will be a lot easier to tune. There are some very reasonably priced Chinese made flat slides on eBay lately, but I don't know how good (or bad) they are since I've never played around with them. The one negative thing about flat slides is that you'll lose your automatic choke function, it'll be totally manual, if that matters to you. Kind of inconvenient since the carb is totally enclosed in the body work so you won't have access to the choke lever.
Take it easy on the engine for the first 500 miles or so. No high speed runs or long steep hills, otherwise, the rings may not bed-in properly.
What type of oil are you currently running? Not synthetic, I hope...
I hear you on the mileage. I can already tell that it's gone to carp. Oh well.
I would love to switch to a more simple carb with a manual choke. I'm not a big fan of vacuum and electronic controls.
I have been going easy on the bike. And I'm using cheap dollar store oil for break in. I will switch to a better dino oil after 200 miles or so, then synthetic after 1000 miles.
So far so good. I'm running a 130 main jet and a 40 pilot. The bike idles a bit lumpy and has a stutter up to 1/4 throttle. I know it's lean because it runs great under choke. Mid range and up feels pretty good, but I'm not finished dialing it in. I feel like it's still a bit lean across the board. I think I need to up the pilot jet again and see where I stand.
I may change to a non-cv carb in the spring. I'm thinking that the reduction in vacuum and the changes to the air box are going to limit the effectiveness of the vacuum diaphragm. This would in turn hamper the mid-throttle performance of the engine. I also don't like the fact that I'm using jets at the large end of the spectrum.
Anyway, I'm digging the results of my efforts. Even with the tuning that remains, I can get the front wheel to lift pretty easily. It's funny; I pull from a stop, the bike stutters, then once enough fuel is present it really takes off. The bike pulls up to an indicated 65 much quicker than stock. I want springtime to get here so I can yank the windscreen off and really see what she can do.
Just an update. The bike is still running great. I ride almost every day to work and back, with other trips on the weekends.
I recently swapped out the stock carb and modified airbox for a generic 26mm CVK carb and a foam pod filter.
I went with a new carb because of the adjustable idle mix, and I didn't like that I was using the largest jet offered for the stock carb.
I'm still working on getting the right main jet in there. I started with a 125 main jet. Went up to a 130 just for kicks; power was nil. Now I know I need to downjet. I tried a 120 and the results were decent but not what I am looking to see/hear/feel. My next step down is a 115. I like that my jet size is coming down into a more normal range. I didn't expect that; I suppose that the new carb and filter are perhaps pulling a stronger vacuum on the fuel bowl which sucks more fuel through the main jet faster.
I was just reading about your issues with oil spewing out of your dipstick. I'd either plug up the hole you drilled or get a new dipstick. The reason oil is shooting out of the hole is not because of blow-by pass the rings, but because the dipstick is on the pressure return side of the oil pump. In other words, the oil that is being circulated through the engine via the oil pump is being pushed under pressure through the oil filter screen back into the crankcase, where the oil drain plug is. Your dipstick is right there.
I was pretty much on the same track as you. Though I don't have a thorough understanding of the gy6 engine's oiling system. I was pretty sure that I wasn't seeing excessive blowby. In fact, after 600 miles on the bbk, I don't find that I need to add oil. I have done an oil change and a filter/oil change since performing the work.
I'm waiting for warmer weather before I nail down the tuning. After that, I think I'm done nodding for a while. I need to make some of my work look more professional. I have a few loose ends to tie up.
