Modern Vespa

Just when you think everything's going great...

I did a couple hours of serious riding around the area today, city traffic, 50mph backroads, up steep hills and down, and for the second time in a couple of weeks, the engine dies going down a steep hill, but not down a moderate hill. It doesn't seem to matter if I'd just climbed the hill or it I'd been on a level plateau for a while, it seems to just not like steep declines, and it won't start again unless I level it out and kick it or use the electric start several times. The TT CHT doesn't indicate overheating, the tank is near full, the fuel line is 24" and is routed normally (as far as I know). My gut feeling is that the bowl is empty, but can't figure out how that could be.

Anyone else ever have this problem?

the carbs float must not like that angle of use

either the float bowl is filling up with extra fuel or air is getting into it via the overflow vents and causing the engine to die.

too rich or too lean

are you coasting down this steep road in neutral or in gear...??

try it in gear so that as you get to the bottom you can pop start the engine before you come to a full stop.

Hmmm... good thought... that would mean a steep downhill is holding the needle open and flooding the engine. Should've thought of that. I've had the carb top off not long ago and the float and valve are not hanging up at all.

Going down hills like that I pull the clutch and let it idle. On the next steep hill I did try goosing the throttle with the clutch pulled and it <i>seemed</i> to help on that one. I'll try that more often.

It didn't used to do this, but the engine didn't used to be ported, have an ultra-efficient rotary induction valve, and require a tweaked carb, either. All sorts of things are different.

Edit:
BTW, this particular instance was a 16% downhill grade.
Edit2:
The other incidence last week was a different street but a similar grade ~17% (thx to Google Earth!)

Does it die just idling for the same amount of time you coast down the hill?
While at the same temperature as on top of hill before going down.
How big are these hills? Mile or 500 foot?

Jim-

Did some serious downhill in the Dolomiti without probs, but since my PX is autolube, I did not fall prey to the "no engine braking" Old Wives Tale.

Sounds like a fuel problem, either bowl overflowing or running dry. Dry makes more sense, as the float is hinged in a manner where a "nose down attitude" would have the gravity effect on the fuel in the bowl of "lifting" the float in relation to the hinged end.

You could jack up the rear of the scooter, see if it dies at idle. turn off the fuel valve and pull the float chamber cover, if you want to do an "experiment".

Another possibility is that there is some contamination in the fuel tank ( water?) which only gets picked up when pointing downhill. You might see some sign of that if you can examine the contents of the float bowl.

When it happens, you could pull the spark plug and look for wet/dry. If dry, put the plug back in, pull the choke and spin it a while. Remove plug, if still dry, fuel delivery problem.

I've had fuel line vapor lock on three different P Series in hot weather, while idling. It has not happened again since installing heat sleeves on the line from the air box to the frame. It gets hot down there, and fuel boiling can begin as low as 100 degrees depending on the formulation. A vaporized bubble in the line can be an effective shut-off valve against the very low gravity feed pressure.

Great responses. Thank you. After posting this above, the more I thought about it I realized that I couldn't determine whether nose-down was going to hold the float up or down. If I still had my shop set up and the spare time, I <i>could</i> set up the spare carb on an inclinometer, attach a metered line to the banjo, and measure the fall in the line at various angles, but I don't see myself being able to get around to that anytime soon.

Yesterday's hill was about 300' ground distance and I had been descending lesser grades without issue just before. Last week was about 1000' ground distance but I had been level for several miles before descending.

Since it is still autolube, I'll see what happens if I go back to more compression braking since that's something I used to do more of before the engine work and didn't notice this. If not for this little annoyance, it's running great and flies up the same hills without bogging, even much longer ones that are a mile or more in length.

I don't think there's water in the tank. I've gotten so fed up with that issue that now I'm religiously keeping the tank full after every use and using Kolor Kut to keep an eye on the dissoved water content in purchased and stored fuel, but next time it happens, if in a safe place I'll try pulling over and check the plug for that tell-tale oil and vinegar glisten.

I wouldn't be surprised if someone on GSF or Vesparesources has already figured this out, but it's difficult to search forums when I'm not fluent in either German or Italian.

This is probably not related, but just in case, I've always wondered about this...

http://www.sip-scootershop.com/en/products/washer+oil+tank+outlet+_24545100

This is the later-model washer at the bottom of the oil tank that has a hook on it just the right size for the fuel line to pass through and be held there. When I got this bike new the 60cm fuel line was routed through it and every time I've replaced the line I've routed it back through there. In other words, the fuel line exits the fuel tap on the left side, runs down the side of the oil tank and underneath through this holder over to the right side where it runs back up to exit the body through the rubber grommet.

Is this the normal line routing? I have nothing else to compare.

Crazy thing did it again today going down the same very bumpy, very steep hill (Portland is becoming infamous for crap street paving). It wouldn't start when I got to the bottom. Pulled the plug and it was totally fouled. Replaced the plug and it took a lot of kicking and a lot of smoke to get it going. I think the whole cylinder must've been flooded.

I'm really puzzled about this, but after last week's near-tipover resulting in very similar symptoms, I'm wondering if the float is getting stuck open when just at the right angle. I'll guess I'll have to a) pull the carb and check it out on the bench and/or b) do a finger-on-the-clutch-breather test to make sure the seal isn't leaking (it had better not be - I purposely had someone else install this one).

I'll post my findings when I find them.

Very bumpy may be the key. I've had the flooding problem on slow, bumpy downhill runs. It seems the float gets "jiggled" and floods like a defective needle/seat. It can also happen when hauling in a stiff suspension trailer. A puddle of fuel can result if you don't turn off the fuel tap.

For SI carbs:

If you lean the scoot far enough on the engine side, fuel will begin to drip out of the venturi spray nozzle as the fuel rises with the lean. Improvised enrichner for cold starts.

Leaning it the other way, with the fuel shut off, will help start a flooded engine due to a lowered jet well fuel level.

Ah, I wonder if this be where a spring loaded needle valve might help? I'll see if I can get hold of one for the SI 20. That's the easiest thing to try first.

So today I popped in a spring-loaded needle valve from Dellorto and gave the same hill another go. I went up the bumpy hills a good couple of miles, turned round and came back down and the new needle valve didn't help at all. Just like last time I had pulled the clutch to let it idle while I used both brakes to navigate the twisty steep downward grades of 100 year old badly cracked and sunken basalt/concrete macadam and after about a half mile the same thing happened as before, the engine just quit, except this time I pulled immediately over and checked the plug and found it dry and brown, which implies it was actually fuel starved. It took about a dozen kicks and nursing the throttle to get it going again. After that, I kept it going with some difficulty down the remaining mile and a half by using only the rear brake and blipping the throttle.

(Last time it did this the plug appeared very fouled, however I may have caused that by repeatedly trying to bump start it while coasting down the hills. On the other hand, if it was starved for fuel why would it be flooding? I don't get it.)

After this I rode over to another hill that's peculiar in that it consists of 2 streets running parallel to each other in a straight line for 1/2 mile or so at about 16 deg downgrade. The difference between the 2 is one is the same as above, old very bumpy basalt macadam, practically cobblestones, while the parallell street is smooth asphalt. It's died before on me on the bumpy side so this time I chose the asphalt side, pulled over near the bottom, put it in neutral and sat there for a couple minutes and sure enough, it kept happily idling away. This implies that it's the bumpiness combined with the angle that's the problem, not just the angle.

I've ridden on these hills several times before without a problem, so I'm very puzzled why this wants to be an issue just in the past year. I wonder if it's the fuel line? Suppose it's partially blocked? The steep angle and bumpy road probably causes fuel to spill out the overflow on the front of the carb and the float should refill it, but what if the fuel flow is low and it can't refill fast enough? I'm making this up.

Fuel line? Tap?

Any thoughts are welcome. I'm not anxious to go pulling the tank for the umpteenth time, but will if I have to.

either the float is sticking open or closed
either way the mix is not correct

either the float is rubbing on the float bowl and staying open too long(overfilled float bowl) or the float needle tip is ridged causing it to "stick" (under filled float bowl).

90 % of the time this happens to people it is due to the float needle remaining open too long = flooding

if you have not sanded the float itself a little you might want to. The middle of the floats have those "lips." A little there and also the inside of the float bowl where you might think the float could rub might help...??

good luck

jim-

you do not need to pull the clutch on downhill runs with an autolube engine. That's strictly pre-mix issue. Did I don't now how many consecutive km in the Dolomiti letting engine braking assist me.

If letting off throttle I would definitel pull in clutch, even with oil injector engines. You'd still need gas to cool top end since if engine breaking the piston is going at higher RPMs.

Seems like it is either the slope or the road conditions/bouncing that are causing you problems. Why not figure out which it is... get you scoot pointed down the hill, pull over and hold the bike in place with your brakes and see if that triggers your issue.

I had a few hours today so I took it over to the 2 parallel steep streets to check it out. I went up the bumpy cobbled one and started back down the non-bumpy one, pulled the clutch and it idled all the way down. I went up a second time and halfway down the non-bumpy side the engine started idling slower and slower. I tried to keep it going with the throttle but it eventually just died anyways. This didn't feel like a bowl running dry. In the past, whenever I've run the carb dry either by accident (taking off with tap closed) or on purpose to work on it, the engine always raced for a few seconds before quiting. This was different. It just slowed down until it stopped.

I coasted to the bottom and parked it on level ground. I pulled the plug and it was dry and brown like before. I shined a flashlight in the hole and the piston crown looked dry and brownish/blackish. I kicked it a few times just to see what happened and it kicked easy and nothing seemed to come out of the hole. By now it's been about 5 mins since it stopped so I tried kicking it and it took about 15 attempts to get it going. It required a fair amount of throttle to keep going for about a minute but eventually started idling normally.

Just because I'm getting paranoid, I had already had a hose fitted to the clutch breather under the cowl, so while it idled I put my finger tip on it and felt a slight vacuum. I turned up the idle and it was still there. I put the cowl back on and got it home. Wanting to double check what I'd felt, I started it up in the garage while it was still hot and I could not detect a vacuum any longer I even tried attaching a vacuum gauge to the hose and the needle didnt' even quiver.

Just to add to the weirdness, I am using the same compression gauge I've had for years, the same gauge that read 145 when this bike was new, the same gauge that read 110 just before it blew up a few years ago, and the same gauge that read 155 last year when I put the HRS repaired parts all back together. Now I'm getting cold readings of 180 and hot readings of 165. Either the compression has shot way up or my gauge has gone bonkers.

I honestly don't even know what to think anymore. I'm considering ordering a complete stock top end and ditching the 'stock plus' one, and probably pulling the crank while I'm at it to check on the clutch seal.

I have no idea what could be wrong.

What jetting do you have in your carb?

Jim

Is the float on your bike hollow and partially filled with fuel, clutching at straws here, or is the bumping causing the spark to disappear via intermittent disconnect of the low or high tension side.

Good luck

Grumpy

oliver, that data is in my signature, but it did the same thing when I had it jetted leaner. I've been having to richen it to improve running. I'm starting to think there's got be an air and/or gear oil leak somewhere.

Grumpy, no, the float is a new Dellorto, white, empty, and no sharp edges.

This bike is going to make me crazy. I'm already preparing to tear it down to try and see what's going on.

Stock Sito 125/150 exhaust
Undrilled filter
160/BE3/106, 55/160, #7 uncut slide, SI20/20D
Repaired rotary pad by HRS
Stock+ top end by HRS
BR7HS, 0Ω NGK cap
14K miles

Jim, you've got 14k miles on it... is there One thing you can pinpoint that you changed right before you started having troubles?

What have you changed between running fine and trouble?

Any difference in fuel line? and different length or routing?
Change in electronics? CDI etc? New tap? New or changed jets?

Just trying to look at anything in particular or combination of things you may have done differently between when the bike was runninf well and now?

Unfortunately, that's an impossible question to answer. It hasn't run right since multiple clutch side crank seals started popping out one after another almost 5 years ago at about the 8500 mile mark. That problem was finally fixed by using the steel shelled PX/Stella seals, then I lost a ring or bearing which chewed up the crankcase and ate the rotary pad, then I put it back together after HRS repaired the pad and I've been struggling with running issues since. The only thing that's different between now and before that catastrophe is the top end. It's not quite stock but what HRA calls 'stock plus' with corrected port timing. That's why I'm tempted to tear it apart to look for issues, then revert back to pure stock top end. If that doesn't fix it I think I'll push it off a cliff. (More likely it'll wind up on CL which would be sad because I hate to give up on machines. Any machine should be repairable as long as parts are available.)

Aaah shit.. I see.. so it's not easy to backtrack and maybe find the issue..

I hope you don't give up on it. There's an answer to all these things.. it may not be as simple as we'd hoped, but it's out there and can be done..

Maybe going back to stock is a good option.. Al does the best work around, but maybe going back to a stock top end will help shed some light...

Whatever you do, don't push it off a cliff!

Unless you've got 5 or 6 good cameras set up and some serious pyro set to blow when it hits the bottom!

Kidding aside, I hope you stay with it.. and can get it running right again... there're good minds here and where there's a will..

Grasping at straws... but you mentioned bumpy road.. once I had a problem.. the bike would run, then stall out then run, then stall.. and I was on the side of the road, and just decided to start with the simple things... I checked the plug wire and it was not completely secure on my CDI.. I screwed it on and that was that.. no more trouble.. as soon as I got home, I clipped it and re-attached it and the problem was history..

I know you've been looking at carb stuff, and sorry if you've been over this, but have you checked your connections like the plug wire.. at both ends?

have you tried to swap & test with a few different floats & needles?
I had similar symptoms to yours not so long ago, kept dying when idling at stop signs at the bottom of two steep inclines on way to work. I swapped out the brand new white float and red tipped needle, with an old dellorto brown float and black tipped needle, and that very specific issue dissapeared.

May be a stupid suggestion... but can you jack up the back end of the scooter to simulate going downhill? Maybe you can recreate the problem while not moving.

I'd like to recap all the various symptoms, some of which may be nothing, some may be related to a problem.

1. When first put back together, the cold and hot compression measured 155. Kicking it took some effort and firmness or it would occasionally try to kick back. Now cold compression reads 180 and hot compression comes down to 165. Kicking it is easy now. Why it goes down after warm is weird. Both readings are too high.

2. The minor mods done by HRS were such that with a stock exhaust, stock jetting should've been sufficient, but it wasn't. Over time I've had to increase the pilot jet to improve cold starting and idling, and the main to keep temps down at 1/2+ throttle when climbing even a moderate incline.

3. I often get an embarrassing amount of white smoke when starting from cold that seems to burn off once it's fully warmed up.

4. This weird dying thing when going down steep inclines.

5. I have a hose on the clutch breather and I've detected a vacuum there, but not always. This makes me think the seal is leaking (again!) and downhill drowns the engine.

Edit:
5a. I recently drained the gear oil to give it the sniff test and there was ZERO hint of gasoline. I also measured what drained out and it was about 70cc's less than what it took to fill it. N.B. I've been using RedLine MT-85 GL-4 fully synthentic gear oil and it shifts great but I wonder if it's impervious to picking up fuel odors.

6. Otherwise, it seems to run strong, but I don't know what to compare the mods too. That's why I'm considering reverting to a stock top-end for awhile.

It's been suggested that perhaps the autolube is over oiling or dripping while sitting. That might explain #3 but I don't see the relation with the others.

Right now I've marked the flywheel to indicate the range that the valve is closed so I can make sure it is closed when parked. I want to see if any excess oil appears to pool on top.

oliver, your suggestion is interesting and sounds like flooding. I have extra carb parts I can try, but aside from a few Dellorto jets, most are newer SPACO parts since I only have a SPACO carb. However, taking all the above into consideration, I'm skeptical it's that simple and am preparing to drop the engine and tear it open soon.

also grasping at straws here (and forgive me if already asked and answered; i skimmed a bit of the post) but, what is the level of fuel tank when dying out?

is it possible that the incline is such that it's causing the fuel to block the breather on the tap?

something i'd try here would be using an additional external fuel tank to eliminate that possibility.

-g

Fuel tank has been at least half full. The question of the breather is a good one. What would happen if it were permanently blocked? I don't quite understand what it's even for, unless it's to vent the tap for better drainage, much like a sink or tub vent/overflow.

But if it merely ran out of fuel at some funky angle, why wouldn't it just correct itself when righted again and not be so hard to restart for several minutes afterwards? It's like it's flooded, but I've not seen enough to confirm that. The other thing is in the past, whenever it's run out of fuel it runs a little choppy for a few seconds, starts to speed up, then quits. Whenever it does this thing though, it just starts slowing down and defies any attempt to keep it going with the throttle.

I'm just throwing out ideas here too, but if the clutch seal were leaking slightly, wouldn't it run lean and force me to upjet (which I've had to do), and is it possible that when tipped forward at a steep angle the gear oil might reach the slight leak and choke the engine not with fuel, but gear oil? I have been using RedLine synthetic MT-85 gear oil and I wonder if I'd been using dino oil the symptoms might be more obvious. And if this oil is getting into the top, how is it combusting? Is this why my compression seems to be going up?

I don't know, I still think I'm just going to have to see what's going on inside. Right now though, I'm testing the autolube to see if the check valve drips.

Edit: What I really need is a leak down tester.

Hello

It really sounds like the effect you get when vent hole in the tank is blocked, so it may be breather problem.

Regards

Grumpy

This does sound exactly like the issue i had. On my ride to / from work, the scooter would die at exactly the same spots (at 2 stop signs at foot of steep downhills), and it was very difficult to then get the scooter running again, but once it ran, then it would run fine until it idled at the same spot the next day I never totally understood the issue, but it did disappear as as soon as i swapped out float & needle.

This engine looked factory new clean when I installed it 1K miles ago and still did several hundred miles ago. Now there's black chunks of crap falling off of everything, and the exhaust was partially blocked with it. I don't know if the exhaust is even still usable.

I ran out of paper shop towels and gloves, so this is as far as I get for today. Sometime later this week I'll dig deeper and post pics of what I find. I suspect the combustion chamber is totally crapped up, which would explain the climbing compression readings.

Thanks for following.

leaky leaky = dirty dirty

that is a lot of coke buildup

No kidding. I've never had this problem before. Too much fuel? Too much oil? Too much of both?

Seriously though, most of my riding has been on paved and recently rained on streets and roads, so I don't think it's a lot of road dirt. I haven't started digging into it yet, but the inside of the carb box is dry and shows no signs of leaking anything from in there. No where on the engine is there any sign of wet seepage from anything, and the 2T oil hose is clamped and also dry on the inlet. I know the tires do wear down and throw out a lot of black rubber dust, but they haven't worn down that fast. Can it be from the exhaust? I'm expecting the head to be pretty badly coked up.

I haven't had to deal with this kind of symptom before.

If your exhaust is as choked up as it could be, judging by the pics i think you may have found a large piece of the puzzle for your original issue.

After reading all of this I think it may be a combination of things rather than just one. Start with what you know - the piston is pretty coked up. clean that up and try again. I looked at your stats and I may be wrong, but the 105 main jet seems a little rich. Stock is 100. Maybe try that. Make sure you have a good base carb box and carb gasket and torque to specs. My p200 carb used to loosen up every few weeks until I used a little blue locktite. When I think of more things, I'll post again. Hang in there.

Oil all over - maybe like the 2T oil check valve isn't seating and oozing all over the engine inside & outside & fouling your cylinder plug & exhaust ? Doesn't that piston crud looks like oil rather then rich fuel? Oil crud on the plug can explain the poor running.

Hello

Where does that clutch breather pipe go?

Grumpy

That's a smashed clutch breather I was given years ago that I had dremeled the bell off of and made into a hose nipple for testing. The hose went to the real breather which was tie-wrapped to the underside of the cowl support bracket. That way, I could pull over, disconnect the hose and see if I felt vacuum, which I did.