More Jetting Notes

So...I was completely wrong in thinking I was running rich in the mid range. After adjusting the needle clip up two grooves (making it leaner), I went for a ride. It was terrible. It wouldn't take throttle at lower rpm, and would lose power at 3/4 throttle. I was able to clear it up by adding some choke, which adds fuel.

I rode home, and adjusted the needle clip to the lowest of the five groove positions, making it full rich. It responded instantly. It now runs great through the rpm range, even capable of pulling from a stop in 2nd gear. It is amazing how much of an effect such a small change can have.

As a reminder, here is the diagram of the needle clip arrangement:

The only issue I'm seeing now is I'm puking a bit of oil out both the main crankcase vent, and around the dipstick. Now I see why they made aftermarket breathers that screwed into the dip stick opening. I'll have to scan ebay for such a device.

C'

Mikuni Carb Adjustments

I've been tinkering with the jetting on Salty the past couple days, and have had a couple old Honda enthusiasts show interest in how this larger 24mm Mikuni will work on a small 50cc Honda. I'm curious too, and have only begun to start messing with things.

First, I wanted to link everyone to this page: http://www.iwt.com.au/mikunicarb.htm

This is a fantastic primer on how a typical Mikuni motorcycle carb functions.

The first two times I've run Salty, it was very boggy at lower rpm. This was compounded by the fact I have it geared very tall, using a 16-tooth front sprocket, a stock 40-tooth rear sprocket, and the taller 2.75"x17" rear tire. I'm also running a 1/4-turn throttle mechanism, which reacts much quicker than a typical slide throttle.

Pulling away from a stop wasn't easy. It would bog very badly unless I gave it a little Fred Flinstone action to get rolling. It also ran very poorly at low rpm in second gear, when trying to pull away from slower turns.

So I started by adjusting the pilot circuit, as this has the biggest effect on low speed, and low throttle opening running. Usually this screw is set at 1.5 to 2 turns out from all the way in. In my case, it was set at 1.5 turns out. After getting the bike warmed up, and with a decent idle, you simply turn the adjustment screw in or out, and you'll be able to hear/feel a change in idle speed. In my case, it was rather dramatic, as turning the screw out (making it leaner) raised the rpm quite a bit. If you go too far, the rpm will start to lower. So you get a feel for where to set it based on rpm. In my case, I settled on 2.5 turns out. I then adjusted the idle speed back to where I wanted it.

It immediately improved throttle response. Even with the bike just sitting in neutral at an idle, it was very boggy before. Now it just revs clean with no hesitation. I then went for a short ride. It was dramatically improved, especially pulling away from slow turns in 2nd gear at lower rpm.

I now need to turn my attention to full throttle use, as it isn't quite right. I have a feeling I'm quite rich overall, especially since I needed to lean it out so much even at small throttle openings. When I'm cruising at mid to upper rpm in second gear, it pulls very nicely as I open the throttle. But I notice the last 10-15% of the throttle opening makes zero difference to acceleration. If anything, it feels like it stumbles a bit. A check of the plug indicates it is running rich. Going from 3/4 to full throttle opening is right in the transition range between the needle and main jet circuits.

I don't have any spare main jets, so I'll need to order some. In the meantime, I thought I would play with the needle jet position (1/4 to 3/4 throttle mixture) by adjusting the needle clip position leaner. I'm currently set in the middle of 5 clip positions. so I'll move it up a clip and see what that feels like.

If it isn't too cold tomorrow, I might go for a short ride.

C'

Brake Light and Another Ride

I wanted to throw a brake light on Salty, so I could run him on the street. I never really thought about that when I made the seat/cowl though, so I needed a simple solution. Thanks to my previous experience doing a taillight for my rat bike project this spring, I decided to use a simple 9V battery as the power source. This way I don't have to tap into the lighting coil and worry about the rectifier with the stock wiring loom.

The end result is a 9V battery, a 9V battery holder, some wire, a stock rear brake light switch, and a pair of 1/2" push-in red lights. All the components are housed in the left side pod cover, and runs through the seat in plastic tubing to avoid and chaffing on the fiberglass. The lights simply push through a 1/2" hole I drilled in the bottom edge of the seat cowl, as shown below:



The lights are actually quite bright when viewed from behind.

After completing that task, I took another ride around the north part of town. I've learned a few things riding it:

-I need to move the pegs a couple inches lower, or a couple inches further back, or a combination of the two. I'm just too cramped.

-Having the bike geared so tall means that 2nd gear isn't that usable for putting around city streets. 1st is too short, 2nd is too long, especially for slower speed corners. I think I'm going to throw a smaller front sprocket on the bike, which luckily doesn't take much time.

-This bike is fun! It doesn't have the scoot of the rat bike, but being all hunched over and close to the ground makes it exciting, even at 40mph.



C'

Kickstand and Number

I finally got off my duff today around 1pm, and did a bit of work to Salty. Job one was to make up a kickstand, to replace the center stand. Centerstands are great for performing maintenance, but they are difficult to work around. Usually the exhaust, chain, and rear brake levers all have to be positioned just right to avoid interfering with the centerstand.

In my case, the only thing that interfered was the rear brake lever. I had built it with the centerstand down, not realizing it would swing up against the brake lever with the bike on its wheels. The easiest solution was to just take the damn thing off! I can still slide it under the bike if I want to use it for maintenance, but I built up a simple little kickstand for day-to-day use.

I had found a $7 kickstand made for a kiddy bicycle at Wally World a few week ago, which I installed on the Trials bike. As luck would have it, the K-Mart just down the street had the exact same unit. I bolted it right under the motor (where the stock footpegs normally bolt) and shortened it a tad to be the correct length. I topped it off by welding on a washer to give it a bit more contact area with the ground.



Job number two was to finally put some class letters/numbers on the number plates I had built many moons ago. In this case, M-PG 50. Modified chassis, Pushrod Gas, 50cc.






C'

Chain Cover

I spent a little time in the garage today working on Salty. It is about 45-degrees out, rainy and windy, but luckily the garage is warm! I raised the front ride height about 1/2", as I found the front shocks wanted to just barely bottom-out on small bumps. That wasn't difficult, just fiddly.

The other thing I did was take on old chain cover from the parts bin, clean it up, fit it, and paint it. These early Hondas had a fully enclosed chain cover to keep the oil from flinging off the chain and onto the bike, and keep dirt/grunge from getting onto the chain. Usually these covers are ditched the first time the chain is adjusted or replaced.



The cover is in two pieces, a top and bottom. Each piece bolts to the swingarm, and then they fit into each other for a tight fit.

C'

Riding Salty for the First Time!

After many months of little issues, combined with the fact I built up another complete bike (the Trials bike) I finally got back to Salty the past couple days. I had it running, but not very well many months ago. It was running very strangely, and sporadically. Sometimes it would kick over first try, other times I would wear my leg out trying to kick it over. If I got it running, I could never get it to hold an idle without needing the choke fueling circuit on, which of course raised the revs up high enough. So basically, I've been troubleshooting little issues and not having a lot of luck isolating the main problem. It wasn't fun dealing with the same problems everytime I turned my attention to it, so I moved on to other projects.

Yesterday I decided to take off the complete carb/manifold/fuel line and do a thorough cleaning. I drained the tank and didn't see any sediment. I built up a new fuel line with a small fuel filter, which it didn't have before. I also disassembled the carb and gave it a douche, even though it looked spotless inside. I put everything back on, and it fired up fairly easily. It still hunted a lot while trying to fast idle. Then, as I was glancing down at the ground, I hurt it sputter and I saw a little puff of moisture shoot out around the base of the intake manifold I had built. It kept sputtering, and shooting out. It was obvious there was a little crack in the intake manifold where I had welded it together. For a refresher, here is the manifold I built:



The "left" side of the manifold is where it bolts to the cylinder head. It is a very tight fit between the pipe and the nuts that secure it, so I had to file away a bit of meat. I also apparently didn't do a fantastic job welding it in that area, as the crack formed right there.

Guess what? I did a shitty job welding two intake manifolds. I had built a test manifold before this one, to get all my angles and dimensions correct. So I grabbed it out of the bin, and bolted everything back up. Salty fired on the first kick, and ran great for about 2 minutes, holding a perfect idle and taking throttle. Then I heard it stumble and saw a puff from the same exact location! What the hell. I think I'm just cracking what little weld is there as I tighten the nuts to secure it to the head. Two manifolds down. But at least I maybe found my mystery problem?

Instead of trying to fix both manifolds, or make a new one, I thought of some better solutions. One of which uses a stock C110 intake manifold, which I happen to now own three of. The two C110 parts bikes I grabbed from Ashland for $50 each had one. The problem is, this manifold is designed to use a small section of rubber hose that clamps to a round section of the stock C110 carb. The Mikuni I'm using has a bolt-on flange. So I have a few options. I can make up a new flange and have it welded to the stock C110 item. Which may be the best long term solution. I don't weld aluminum, however, so I'll need to find someone to do that for me though. I'll likely have two built.

The short term solution was to hack off the carb side of one of the manifolds I built. This side has a much wider hole spacing for the two mounting bolts, so I have a very good welded connection there. I then connected this piece to the stock c110 intake with a piece of 7/8" ID fuel hose I had. It is a very snug fit, and with a few ugly hose clamps it fits and feels secure.

It worked too, as the bike fired right up, held an idle, and even held a nice low rpm idle with no choke after it warmed up. It takes throttle well too. So of course, I grabbed my helmet and realized I was going to actually ride Salty for the first time. I was never able to get it running well enough to want to try.

So I did. I blasted up and down the road a few times, going through all the gears. It actually runs on the road now! I was very excited. It wants to bog a bit right off idle, but if I'm smooth with the throttle and give it a quick paddle or two to get it rolling, I can accelerate off. The engine in the bike is a 3-spd auto clutch, with a large front sprocket. So first gear is a bit tall, and I think the 1/4-turn throttle I have on it is a just a bit too quick reacting. I'm sure I'll get a bit smoother as I ride it more.

So there you have it, Salty not only seems to run, but it goes down the road. It isn't the most comfortable bike in the world, but it is actually doable on the road. I just fold up my long legs, hunch over, and go for it. I'm going to fiddle with a few more things this afternoon, and hopefully take him around the block more before the rain comes this weekend.



C'