poor fuel flow, air leak, ethanol gas, or.... ?
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Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8129
Location: Atlanta, GA
Thu May 16, 2013 7:11 pm quote
Been keeping my eyes on these symptoms for a bit, but they seem to be worse recently so I thought I would bounce it past you:

The scooter:
1980 P200E, stock 24/24E, stock exhaust and air filter.
116 mj with BE3 mixer

The symptom:
bogs when opening the throttle, feels apathetic at WOT, stumbles slightly at 1/4-1/3 throttle. Plug color (b8es) is pretty light

The jets have been cleaned - putting a 118 main in doesn't really change the behavior much. But it idles well, doesn't change rpms erratically or race, starts 1st kick warm, 2-3 when cold. 135 psi compression...

I guess in the absence of any wild air leak behavior, I'm trying to think of other causes - is there a way to test whether gas flow is insufficient to the carb (thinking partially obstructed tap or fuel line?). I noticed this stuff more prominently "after a fuel-up" recently, so part of me is wondering about shitty gas/ethanol playing in somehow, but it seems kind of a stretch.

Last edited by xantufrog on Mon Jun 17, 2013 8:55 pm; edited 1 time in total
Ossessionato
a lambretta or two
Joined: 31 Mar 2012
Posts: 3726
Location: San Francisco
Thu May 16, 2013 8:17 pm quote
Screw out the fuel mix screw at back of carburetor 1 full turn. Then blip the throttle to see effect.

Of course, if your exhaust is clogged or your timing is too retarded this won't matter much.
nothing at all
Joined: 14 Nov 2008
Posts: 9657
Location: westla
Thu May 16, 2013 8:37 pm quote
Quote:
too retarded.
I get that a lot.
Addicted
1961 vbb and 1981 p125x
Joined: 25 Mar 2013
Posts: 579
Location: iowa
Fri May 17, 2013 6:49 am quote
Fuel flow is pretty unlikely, but you can check it by pulling the fuel line off the carb and opening the tap. Any hesitation when you blip the throdle should be correctable with the air bleed, screw at the back of the carb. As for fuel I shy away from ethenal myself I've heard everything from it can cause air bubbles on jets, vapor lock, to it wipes the oil off of bearings in a 2 cycle. I do know from running old cars that a carb cannot adjust for diff for fuels. So you need to pick something and run with it. Here's the theory, the caloric value or amount of energy in ethanal is less than petro so it takes more to equal the same amount of energy, note on a flex fuel car the mpg goes down as you add ethanal. With fuel injection the car meters the exshausts and adjusts the injecters, with a carb you'd need to rejet for each mixture. Bottom line adjust the air bleed and chances are your problem will go away.
Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8129
Location: Atlanta, GA
Fri May 17, 2013 7:08 am quote
Thanks folks - I know that the mixture adjustment should tackle the stumbling while riding at 1/4 throttle, but am most concerned about the mediocre behavior at upper throttle range and bogging when opening the throttle. If it's really lean, I gotta find out why - based on the light plug color I hadn't considered the opposite of a plugged up pipe, but it has been a while since my rusty-ass pipe was decoked and I know plug color isn't everything.

I'll play with the mixture screw as suggested and report back on the general effect. Realistically any serious repairs will have to wait until I finish my move to SF in the coming couple of weeks, but I couldn't just ignore the issue entirely that long
Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8129
Location: Atlanta, GA
Fri May 17, 2013 7:09 am quote
318ti wrote:
Fuel flow is pretty unlikely, but you can check it by pulling the fuel line off the carb and opening the tap.
The fuel definitely flows, I was wondering if there was any way to measure the proper rate of flow - get a sense for if it's sub-optimal in some way? Like, enough to cause some odd behavior but not enough to stop the beast from running.
Hooked
Stella
Joined: 24 Aug 2012
Posts: 272
Location: Tampa, FL
Fri May 17, 2013 7:48 am quote
You can check what is adequate fuel flow. It takes simple math.

Find your MPG. My Stella is 75-80mpg.

I drive 20 miles a day and fill up 2 gals every 7 days. (my ODO is broken)

Now I can see that dividing

2 gal/7dayss=.2857gals per day

*128=36.5oz per day.

36.5oz/20miles = 1.828 oz of gas per mile

With a top speed of 55mph (most fuel consumption)

55mph/60mins= 1.1 min/mile

1.828oz/mile*1.1min/mile= I average 2.01 oz/min

And this isn't close to exact because of how the throttle at WOT and accelerating will consume much greater amounts than at idle.


This was a stupid long way to do this. I was bored at work.

That was the long, this is the short:
So measuring into a cup, I would turn on my tap, and I would need to see at least 3-4oz/min for high consumption. I hope to see closer to 8oz/min.


I'll estimate for a P200

2gal/4days=.5gals per day

*128=64oz per day.

64oz/20miles = 3.2 oz of gas per mile

With a top speed of 65mph (most fuel consumption)

65mph/60mins= .92 min/mile

3.2 oz/mile*.92min/mile= A P200 average 2.94 oz/min
Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8129
Location: Atlanta, GA
Mon Jun 17, 2013 8:53 pm quote
So following Chris's advice, I gave the mixture a turn out. The closed to open bog is pretty much gone, so that did help. Overall, scoot runs like a dream. California suits it. However, it still has kind of a 1/3 throttle hesitation - kind of a 35mph in 4th situation where you can feel the power pulsing. Below that throttle position it's fine now, and it clears up again if you open the throttle a wee bit more.

I'm pretty sure turning the screw out further isn't a great option as it's pretty damn sooty at the current setting. Change out the BE3 mixture stack? Drop the main back to a 116 and see whether that clears up the transitional mixture?
Molto Verboso
79' P210 GickSpeed Special
Joined: 23 Sep 2012
Posts: 1407
Location: Limbo
Mon Jun 17, 2013 10:09 pm quote
What condition is your fuel line in? Is it all twisted inside the frame? The cheap clear plastic line sucks IMO. I had an issue with stalling at higher revs due to my fuel line recently. I replaced mine with some black rubber fuel line with a 5/16" ID. Made sure the line was just a little longer to get from the fuel tap to the banjo inside the carb. That solved my delima. It could very well be many other things too though as others suggested, but what I have said above about the fuel line might be easily overlooked.
Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8129
Location: Atlanta, GA
Tue Jun 18, 2013 7:41 am quote
Hey WP2,
My fuel line's in good shape - black rubber kind replaced about 1.5 years ago at about 24" in length. Thanks!
Ossessionato
Joined: 22 Oct 2011
Posts: 4401
Location: Tega Cay, SC
Tue Jun 18, 2013 4:22 pm quote
I think most of the folks on here know way more than I know about vespas, but I would check the timing first before any carb work.
Hooked
1981 Vespa P200E
Joined: 29 Apr 2013
Posts: 462
Location: Tierra Azul, NM
Tue Jun 18, 2013 9:01 pm quote
What octane fuel are you using?
Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8129
Location: Atlanta, GA
Tue Jun 18, 2013 9:16 pm quote
93 octane
Hooked
1981 Vespa P200E
Joined: 29 Apr 2013
Posts: 462
Location: Tierra Azul, NM
Tue Jun 18, 2013 9:26 pm quote
Try running the cheap stuff I noticed a definite difference between the high and lower octanes. Mine seems to like the low grade. Won't hurt for certain.
Hooked
Vespa PX200
Joined: 27 Jun 2010
Posts: 429
Location: Belgrade
Thu Jun 20, 2013 12:36 am quote
@xantufrog -- out of curiosity, what % ethanol is the gas in your neck of the woods? My old PX ran OK on American / Canadian 10%. However I did run into big problems in Brazil: the bike simply was way too lean on the min. 28% ethanol garbage they sell down there. So I took some advice from locals there and upjetted from 116 to 122 and got running again, after a fashion.

Anyway I don't know what the biofuels situation is in North America right now but I do hope the minimum requirements don't start creeping upwards as they have in some other places. It's terrible for two-strokers.
Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8129
Location: Atlanta, GA
Thu Jun 20, 2013 9:27 am quote
Thanks for the thoughts! It's 10% ethanol in most locations here - I think the maximum for normal gas stations is 15%, and it must come with a warning at that? I've never actually seen 15% sold but I know it is in some areas.
Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8129
Location: Atlanta, GA
Wed Nov 06, 2013 7:24 pm quote
hell
I'm finally back on two wheels - went for my first ride on Saturday after months of recovery following my broken shoulder and accident. Yay!

Bad news is, these hesitation issues persist, and are worse than ever...

Same behavior as before, sort of a stumbling at 1/4-1/3 throttle. Generally speaking, it's still mild and you don't notice unless riding along for a stretch holding steady at that throttle position. But the issue has gotten worse in that there are some stumbling episodes where the scooter will almost die without careful feathering of the throttle.

It revs out nicely and you can't feel the hesitation at high RPMs and WOT - it feels specific to that low range. One observation I'd like to add: this dying event seems to come after stints riding at high rpms. For example, coming home from work this evening, when accelerating hard from a light and running along a ways at 1/2+ throttle in third (so the RPMs were held pretty high for a bit), and then I shifted up into 4th, this severe stumbling/bog happened.

It doesn't seem to happen regularly, though... if I let it settle down, keep riding, and deliberately rip up to high rpms, hold there for a ways, and then shift to 4th it isn't reliably reproduced...

Here is what I have done:
Cleaned the carb several times (today I did a REAL thorough total teardown clean every part, blow out every channel, checked float needle condition and action...)
Sprayed carb cleaner around base of carb, base of carb airbox, and around seams of cylinder head and cylinder base.
Brand new spark plug, fresh gas
Fuel flows nicely from the gas hose.
Checked gear oil for gas.
Finally, deciding this might be an electrical issue, I disconnected the kill switch wire. But riding home with that off, I still ran into this issue as described above

At this point I am leaning towards one of two possibilities:
1) CDI (I believe it is the 33y/o original) may be failing, such that the spark is failing in certain conditions (like after high-rpm stints - I know they can "overheat" when they start to go)
2) there's some kind of obstruction in the fuel tap so that yes, the gas flows nicely, but it's not enough

neither of these seems overly compatible with the stumbling being most obvious at 1/4-1/3 throttle, but maybe that's just a sweet spot for the problem to be felt by the operator. I just don't see any evidence of air leaks, no weird revving or anything, idle is rich and chug-chuggy, spark plug isn't coming up ghost white, and I know that carb is clean.

I don't know - it's a big disappointment after all that time in recovery and rebuilding the front end and everything (though I don't know why I thought the issue would magically fix itself)

Any additional thoughts?
Molto Verboso
px200
Joined: 13 Apr 2010
Posts: 1267
Location: london
Wed Nov 06, 2013 8:31 pm quote
Hello

Wonder if running a hotter plug might help, the standard recommended in the UK is B6, i also wonder about the hygroscopic properties of ethanol fuels and i am not thinking here about absorbing water while it is in your tank, more absorbing water while it is the petrol station tanks, do US stations top off their tanks (keep them full) UK practice is now just to hold enough fuel for a few days sales.
So the petrol is fairly fresh.
One last thought is do you need to adjust timing to account for the lower volatility of modern petrols.

Grumpy

PS glad you are recovering.
Mr. Clean
P,SUPER,V90, 50 Special
Joined: 27 Jul 2010
Posts: 10207
Location: This is't my locker!
Wed Nov 06, 2013 8:46 pm quote
Grumpy wrote:
do US stations top off their tanks (keep them full) UK practice is now just to hold enough fuel for a few days sales.
Hello back Grumpy!

I can't speak for everywhere in the US, but here in Los Angleeez, there's not going to be any gas going stale.. it's a wonder they can keep up with refilling for all 8 zillion of us gas guzzlers! I follow what you're saying though... interesting thought.
Ossessionato
2015 GTS300, 1974 Primavera, 04 Ninja 250
Joined: 04 Apr 2013
Posts: 4605
Location: San Diego, CA
Wed Nov 06, 2013 9:42 pm quote
I had a bog like this. I got a new fuel tap, new fuel line, rerouted what was incorrect, and opened up the holes on my fuel cap to breathe better. I don't know for sure which of those did it but it was sorted by that combo, which is all pretty cheap stuff.
Addicted
Joined: 01 Jan 2012
Posts: 629

Wed Nov 06, 2013 10:59 pm quote
replace the spark plug cap
cheap
easy

might be the fix
issue could be vibration at a certain rpm

http://jet200.com/catalog/product_info.php?products_id=352
Molto Verboso
px200
Joined: 13 Apr 2010
Posts: 1267
Location: london
Thu Nov 07, 2013 3:47 am quote
Another quick thought would if you have a resistor cap on already with a resistor plug, that gives some interesting running problems.

Grumpy
Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8129
Location: Atlanta, GA
Thu Nov 07, 2013 8:12 am quote
Thanks folks for all the ideas!
Actually I neglected to mention it's a new non-resistive NGK plug cap installed a couple of months ago (and using a non-resistive B8ES), so I doubt the cap is at fault

I am hesitant to point my finger at the timing since I haven't touched the stator in years (and have had to deal with E10 gas for years too) - why would it get worse? My inclination is towards something failing, but maybe I need to find someone with a timing light in the area.

The pipe hasn't been cleaned in maybe 4 years... may be getting coked up, but I would think that would cause the opposite of the "lean-like" symptoms.
Member
1980 P200E
Joined: 28 Jul 2012
Posts: 10
Location: USAF
Thu Nov 07, 2013 1:11 pm quote
I have had this problem periodically w/mine as well. Since the octane was fairly low, I added octane booster. I also use an ethanol treatment. I'm not sure if it's one or both of them. but when i only use the octane, it doesn't get any better. I think we were going to change out the spark plug too, just haven't gotten around to it since we moved to the UK.
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