SB50P Hard to Start

[az_slynch]

A friend of mine had acquired an '89 Elite E for his mom and asked me to help him get it running. Here's where it stands:

I've completely dismantled the carb per instructions in the Wiki pictoral guide, even pulled/cleaned the emulsion tube. If you blast carb cleaner up the pilot pickup tube, it comes out the little port just downstream of the needle in a healthy stream. Tank has been dumped, flushed and filled with fresh gas. Bike has a new vaccum petcock and strainer screen. The carb bowl fills up nicely. The carb was set to with the mixture screw 1 1/2 turns out and the needle was set to the middle position. The air box was cleaned thoroughly and a new filter was oiled with UNI filter oil (per instructions on the can) and installed. Clamp and airbox boot were checked for good sealing.

When the bike is kicked or the starter is engaged, the bike starts to an idle, then sputters out after 3-5 seconds of runtime. Cranking the throttle will prevent it from starting at all. When it dies, if the screw is taken out of the carb bowl, the bowl drains out a at least a half-shotglass of fuel. Fiddling with the idle stop or the mixture nets no remarkable changes. This makes me suspicious of the pilot, but the pilot seems to flow fine when hit with carb cleaner.

I pulled the throttle slide and moved the needle to the top notch. The bike would not start at all. I pulled it again and moved it to the bottom notch. The bike starts and can be revved with the throttle, as long as the throttle isn't actuated too briskly. It can be ridden, but has a bad flat spot between 5-10mph. Once the engine starts winding up, it pulls to 31mph (seems quick for a stock SB50P).

My gut instinct says that the pilot is still not working right, but I can't believe carb cleaner would shoot through it so briskly if it was still clogged. I'm wondering if an air leak or leaky reeds could cause an issue with vaccum draw from the pilot. The carb's coming out for an overnight stay in a chem dip tonight; does this sound like the issue or should I be looking elsewhere?

EDIT: Two other things of note. Tested the bystarter, it's working. No throttle when the needle is in the bottom notch and it's cold, or it dies. Extends when powered with 12V for several minutes. No idea on the measurement, though. The stick I was using wasn't calibrated. The other item is the carb bowl gasket. Bought a new one, it didn't seem to help. Is there a seal for the mixture screw?

[Bear45-70]

Giving scooters throttle when cold almost ALWAYS results in a dead engine. Cold blooded beasts, wait until warm before trying the throttle.

If it was reeds you would have even more trouble starting it. Vacuum leak is a good possibility. The needle moved up makes no sense, in that it has nothing to do with starting. Moving the needle down and having it run says the float level could be set too low.

[az_slynch]

The needle moved up makes no sense, in that it has nothing to do with starting. Moving the needle down and having it run says the float level could be set too low.

Honestly Bear, I was grasping at straws. I moved the needle down to see if it was running off fuel from the main or the pilot. Since I wasn't having much luck with making noticable changes with the mixture screw, I figured that if I moved the needle down, it would restrict the main more than it was in the middle position and would reduce any impact the main was having on idle. Since the bike wouldn't start at all after that test, I figured the pilot was doing little-to-nothing and that moving the needle up might give it enough fuel early in the throttle range to try throttling up. It sorta worked, as the bike could (barely) be ridden. I'll go over the setup again with an eye for vaccuum leaks. I didn't look at the O-rings in the spacer or manifold junctions, and the manifold-to-crankcase bolts haven't been checked.

[Bear45-70]

The needle moved up makes no sense, in that it has nothing to do with starting. Moving the needle down and having it run says the float level could be set too low.

Honestly Bear, I was grasping at straws. I moved the needle down to see if it was running off fuel from the main or the pilot. Since I wasn't having much luck with making noticable changes with the mixture screw, I figured that if I moved the needle down, it would restrict the main more than it was in the middle position and would reduce any impact the main was having on idle. Since the bike wouldn't start at all after that test, I figured the pilot was doing little-to-nothing and that moving the needle up might give it enough fuel early in the throttle range to try throttling up. It sorta worked, as the bike could (barely) be ridden. I'll go over the setup again with an eye for vaccuum leaks. I didn't look at the O-rings in the spacer or manifold junctions, and the manifold-to-crankcase bolts haven't been checked.

The main circuit flows no fuel at idle. If it does you have one of two things wrong, float level way to high or the idle speed way to high. It takes quite a bit of air flow ro activate the main fuel circuit.

The moving the needle down says your engine's dying problem is fuel related and whether it is to much or too little I'm not sure yet.

On the carb spacer, make sure it is right side up and facing the right way, "o" ring to the manifold.

[bradthreee]

If you blast carb cleaner up the pilot pickup tube, it comes out the little port just downstream of the needle in a healthy stream.

I dont know if this is insignificant, but whenever I clean the carb and shoot carb cleaner in that little hole it never shoots out like that. Its tiny enough to only allow a drip or so to flow through. Maybe the PO went a little crazy with the wire cleaning it?

[az_slynch]

Brad, it's possible. The PO hadn't run the bike in years and didn't know much about it mechanically. He may have let a friend bang on it; as far as I can tell, it was painted by someone other than Honda. After checking the seals on the current setup out, I may just try the carb I bought from backinblack on it and see if it works better. Of course, if it works better, dude's gonna have to find his own carb. I bought this one for FailSpree!

[bradthreee]

Please post results of what you've found. I'm pretty sure it'll be a weekend affair...

[az_slynch]

Posting my findings, as promised:

The bike now runs properly. Starts immediately, revs up with no issue. The problem was in the carb. Funny thing is, I looked that four carburetors (three of mine, plus the bikes carb), two from Sprees and two from SB50Ps, and three of them had the same issue.

The bystarter sleeve was pinched in the carb body by an overextended mounting screw. I'd bet that each of those carbs was put back on a bike without the spacer once before.

I didn't recognize the issue at first, as the needle on the bike's bystarter was stuck into the mount on the bystarter. I thought it looked odd, but I knew the bystarter was different that what was fitted to the CH80 Elites. I wasn't until I pulled apart the SB50P carb that I'd gotten from backinblack that I found a small spring. I figured I'd need it, as the first bystarter was missing a spring. The mount on the bystarter still looked funny to me until I looked at the Spree carb I'd gotten with the motor I'd bought off d3m0nk1d. I had swapped it off with FailSpree's original carb because I didn't like the fact that the float bowl was puttied together. Still, it had parts missing and a brass sleeve installed in the housing. Something didn't look right and I wasn't sure until I found CaptDan's post reply which mentioned the housings getting dented by a screw being run down too far. So I started checking carb bodies. Sure enough, all three had a screw dent in them. The fourth, on FailSpree, was fine. I pulled a complete bystarter out and realized my issue.

Took the SB50 carb and removed the bystarter sleeve. Used the best spring, needle and sleeve from the three screwed-up carbs. Straightened out the carb body with a Dremel, a chainsaw sharpening stone and a steady hand. Cleaned the carb body out extensively, put it together and reinstalled it. Got a fresh set of intake O-rings from Checker/O'Reilly's, the HELP! branded O-ring kit has a good sized O-ring, get two kits.

I took pictures with my camera and I'll upload them. I see it's a documented issue, but I didn't find visuals. Considering that three of the four carbs I had were affected by this, it should have a visual aid. No telling how many other PA carbs out there have this problem.

BTW, Brad...pull the mixture screw when cleaning the pilot circuit and spray from the intake pipe, you will get a good spray out through the port in the venturi.

[az_slynch]

Here's the short pictoral on the issue.

[bradthreee]

BTW, Brad...pull the mixture screw when cleaning the pilot circuit and spray from the intake pipe, you will get a good spray out through the port in the venturi.

Sorry ,

I thought you meant the thin brass tube that runs parallel with the main tube that holds the main jet.

[az_slynch]

Sorry ,

I thought you meant the thin brass tube that runs parallel with the main tube that holds the main jet.

Brad, you did think correctly. If you pull the adjuster screw and blow cleaner through the brass tube, it will come out the venturi port in a decent stream.