A little Vespa help
May 28, 2010 8:45 AM Subscribe
[Classic Vespa Filter] Calling all scooterists! Need some help. '64 VBB: I have gas in my carb box, a wet and black plug, and more smoke than typical.
The engine rebuild is fairly new. About three years ago, I put all new seals, new clutch plates, new piston and rings, new cruciform, new fuel tap, new brakes, etc. on the bike. Then it sat in storage for two years.
It's out of storage now. I cleaned the fuel tank, put new oil in the gearbox, checked the cables and electrics, generally cleaned everything, and rebuilt the carburetor.
Full rebuild on the carb, too -- new gaskets, new float and needle valve... took the whole thing apart and chem-dipped it.
So now, everything is basically starting on anywhere from the first to third kick. Problem is, it will run really well for a bit, and then it appears that I flood the carb. I get some dirty gas coming out of the back of the carb box, a light *pop* as the engine softly backfires once before dying. If I try to start again, I can't - I have to wait a little while for things to dry out. My spark plug (NGK B7HS, gapped to spec) at this point is black and basically fouled.
When the scoot is running, I seem like I am getting more smoke than I recall. My initial thought is that I am running too rich, and need to adjust the fuel mix screw on the carb... but that doesn't account for the flooding. The float doesn't *appear* to be sticking.
Any ideas?
The engine rebuild is fairly new. About three years ago, I put all new seals, new clutch plates, new piston and rings, new cruciform, new fuel tap, new brakes, etc. on the bike. Then it sat in storage for two years.
It's out of storage now. I cleaned the fuel tank, put new oil in the gearbox, checked the cables and electrics, generally cleaned everything, and rebuilt the carburetor.
Full rebuild on the carb, too -- new gaskets, new float and needle valve... took the whole thing apart and chem-dipped it.
So now, everything is basically starting on anywhere from the first to third kick. Problem is, it will run really well for a bit, and then it appears that I flood the carb. I get some dirty gas coming out of the back of the carb box, a light *pop* as the engine softly backfires once before dying. If I try to start again, I can't - I have to wait a little while for things to dry out. My spark plug (NGK B7HS, gapped to spec) at this point is black and basically fouled.
When the scoot is running, I seem like I am getting more smoke than I recall. My initial thought is that I am running too rich, and need to adjust the fuel mix screw on the carb... but that doesn't account for the flooding. The float doesn't *appear* to be sticking.
Any ideas?
The wet plug says one of two things to me (and I apologize for being basic here, I did read that you rebuilt the carb) a float that is at the wrong height or taking on fuel, or a float valve that is stuck or dirty.
My first move would be to pull the fuel line and blow some spray carb cleaner through the fuel bowl. There may have been crud in the fuel tank after sitting that settled into your nice clean carbs.
Maybe pull the float, hold it down in a bowl of hot water (if it's brass or plastic) and see if you see any bubbles escaping through a pin hole, or just make sure it floats (if it's foam). If you have a connection on the bottom of your carb, attach some clear fuel line and check the level that way.
Second would be to pull the plug, replace it in the cap with a brand new one and ground it against the engine block, while pressing the starter and make sure you've got a good strong bright blue spark. Maybe new plug wire or coil, if the spark seems weak.
As far as the mix screw: that's your fine tuning, don't mess with that until you have it running close to right.
Finally, check the cylinder compression, if you've got bad rings or oil blowby, that would also be causing the plug to foul and the fuel to overflow. Since you just redid these, it's a long shot, but sitting may have caused them to corrode to the walls, and then short of a complete teardown is to run the scoot until the walls hone back in.
Best of luck.
posted by 1f2frfbf at 9:07 AM on May 28, 2010
My first move would be to pull the fuel line and blow some spray carb cleaner through the fuel bowl. There may have been crud in the fuel tank after sitting that settled into your nice clean carbs.
Maybe pull the float, hold it down in a bowl of hot water (if it's brass or plastic) and see if you see any bubbles escaping through a pin hole, or just make sure it floats (if it's foam). If you have a connection on the bottom of your carb, attach some clear fuel line and check the level that way.
Second would be to pull the plug, replace it in the cap with a brand new one and ground it against the engine block, while pressing the starter and make sure you've got a good strong bright blue spark. Maybe new plug wire or coil, if the spark seems weak.
As far as the mix screw: that's your fine tuning, don't mess with that until you have it running close to right.
Finally, check the cylinder compression, if you've got bad rings or oil blowby, that would also be causing the plug to foul and the fuel to overflow. Since you just redid these, it's a long shot, but sitting may have caused them to corrode to the walls, and then short of a complete teardown is to run the scoot until the walls hone back in.
Best of luck.
posted by 1f2frfbf at 9:07 AM on May 28, 2010
If the answers you get here don't work for you, check out ModernVespa. Don't let the name fool you - they have a vintage forum also.
posted by o0dano0o at 9:26 AM on May 28, 2010 [2 favorites]
posted by o0dano0o at 9:26 AM on May 28, 2010 [2 favorites]
I asked Mr. Rabbit, who works on his own scooters, and here's his response:
Sounds like a combination of running too rich and vapor lock. First check to see if the fuel tank is venting properly,then adjust the mix on the carbeurator. The smoke is probaly due to sitting, once the engine heats up it should stop smoking so much. All this; of course, is speculation.
posted by rabbitrabbit at 9:58 AM on May 28, 2010
Sounds like a combination of running too rich and vapor lock. First check to see if the fuel tank is venting properly,then adjust the mix on the carbeurator. The smoke is probaly due to sitting, once the engine heats up it should stop smoking so much. All this; of course, is speculation.
posted by rabbitrabbit at 9:58 AM on May 28, 2010
Plus I hope you know about the fantastic Haynes manuals...
posted by aqsakal at 10:03 AM on May 28, 2010
posted by aqsakal at 10:03 AM on May 28, 2010
Response by poster: I can rule out vapor lock -- I had an issue with that before I put it into storage, and replaced the gas cap.
I'm gonna try leaning out my mix some and maybe moving to a slightly warmer spark plug, and see what that does.
In the meantime, keep suggestions coming! Thanks to everybody so far!
posted by kaseijin at 10:07 AM on May 28, 2010
I'm gonna try leaning out my mix some and maybe moving to a slightly warmer spark plug, and see what that does.
In the meantime, keep suggestions coming! Thanks to everybody so far!
posted by kaseijin at 10:07 AM on May 28, 2010
After another cup off coffee I'll also offer this: The big clue here is gas in the air box. That means the fuel level is too high and it's running out the back of the carb (and out the front into the cylinder fouling the plug). Dollars to donuts it's the float valve. Since you just rebuilt it, I'm pretty sure your float height is in spec and the float is solid and the valve itself is okay, these things shouldn't be harmed by a period of inactivity. Do check that the float valve will in fact turn off the gas flow by working the float manually with the bowl off. Also, are you turning off your petcocks when it's parked? Sometimes with a full tank, the float valve can be overwhelmed and flood the carb.
My Yammie does this constantly and there's nothing for it but drop the bowl and blast it with carb spray. Nine times out of ten, it's gunk that was in the gas, lines or tank clogging the float valve so it won't close all the way. Long term solutions include using POR-15 or another epoxy liner on the interior of the tank, and new fuel lines and inline fuel filters so now I only have to blast it two or three times a year (if my karma's running positive and the moon is in the right phase).
posted by 1f2frfbf at 11:25 AM on May 28, 2010
My Yammie does this constantly and there's nothing for it but drop the bowl and blast it with carb spray. Nine times out of ten, it's gunk that was in the gas, lines or tank clogging the float valve so it won't close all the way. Long term solutions include using POR-15 or another epoxy liner on the interior of the tank, and new fuel lines and inline fuel filters so now I only have to blast it two or three times a year (if my karma's running positive and the moon is in the right phase).
posted by 1f2frfbf at 11:25 AM on May 28, 2010
Response by poster: Warmer plug + leaner mix appears to have done the trick. Thanks, everybody for chiming in!
posted by kaseijin at 3:00 PM on May 28, 2010
posted by kaseijin at 3:00 PM on May 28, 2010
Just because you mention you're having problems with a VBB - you didn't get it from somewhere in Asia, right?
(Not entirely on-topic, I know, but Asian restorations are notorious for looking pretty and harboring undisclosed, serious defects to the point of making the scoot unsafe; VBBs or franken-VBBs are very common Asian restos, so if you do have one of these make sure you get it thoroughly checked out)
posted by AV at 4:28 PM on May 28, 2010
(Not entirely on-topic, I know, but Asian restorations are notorious for looking pretty and harboring undisclosed, serious defects to the point of making the scoot unsafe; VBBs or franken-VBBs are very common Asian restos, so if you do have one of these make sure you get it thoroughly checked out)
posted by AV at 4:28 PM on May 28, 2010
Response by poster: Haha no. I restored it myself, with the help of some other local scooter folks. It's all American. I've actually been in and out of every portion of the bike, save the wiring harness...but this carb issue was baffling me for some reason.
To elaborate on the thinning of the mix: The carb that I put on it (20/20, larger than the original) was a Spaco, not a Dell'Orto....so the threading is apparently different on the mix screw. Learn something new every day!
I have seen Asian restorations, though, that would make your brain hurt. I actually saw one where all of the case bolts were threaded, and somebody had jammed tinfoil down in the holes to get the bolts to grip. CASE BOLTS!!!
posted by kaseijin at 7:06 PM on May 28, 2010
To elaborate on the thinning of the mix: The carb that I put on it (20/20, larger than the original) was a Spaco, not a Dell'Orto....so the threading is apparently different on the mix screw. Learn something new every day!
I have seen Asian restorations, though, that would make your brain hurt. I actually saw one where all of the case bolts were threaded, and somebody had jammed tinfoil down in the holes to get the bolts to grip. CASE BOLTS!!!
posted by kaseijin at 7:06 PM on May 28, 2010
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posted by kaseijin at 8:49 AM on May 28, 2010