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@vespigi avatar
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'62 TV175, '70 GP-RB250, '74 Rally 200. '03 PX200E
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@vespigi avatar
'62 TV175, '70 GP-RB250, '74 Rally 200. '03 PX200E
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Hi

My engine starts on the second kick when cold, but after about a 15 minute ride the engine won't start if I turn it off and try to restart. If I wait for the engine to cool it then starts again on the second kick. The clip below is trying to start the engine after about a 15 minute ride. The engine turns for a few seconds but does not respond to the throttle (even WOT) and then dies.

I initially suspected a faulty CDI. I checked for spark using two plugs in series and the spark looks fine. To be certain that the CDI was not faulty I swopped it out with a spare to no avail. I also used a new spark plug just in case.

The hot start problem has occurred as a result of me splitting the cases to change the clutch and fly side seals. When the barrel was off I sent it (together with piston and rings) to our local Vespa mechanic. He 'measured' everything up and he said all was within tolerance. He did hone the barrel as there was a small scuff mark below the exhaust port. The scuff has been there for a while as I remember seeing it the previous time I removed the barrel. After getting the barrel back from the mechanic I re-assembled everything and starting experiencing the hot start problem.

I noticed an oily leak on one side of the head and I subsequently pulled the barrel again to lap them. Before I put the barrel back I measured the following;
ring gap between 0.5 and 0,55mm.
squish clearance +- 2mm using the solder wire method
piston oversize 66.9mm.

I put the barrel and head back and no longer have the leak but still have the hot start probem. I measured compression at around 100 psi with a warm engine (I can't remember what my compression was before the hone but it has never been good)

I know that the measured figures are not great but the bike ran extremely well before I decided to do the preventative maintenance and change the seals. The bike now also bogs slightly for 1 or 2 seconds and about ΒΌ throttle but disappears as the revs build. I find this strange as I left the carb intact when splitting the cases.

Hoping someone can give me some direction on how to solve the hot start problem.
@olestra avatar
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2009 Piaggio mp3 500ie "Ephie"
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fuel line getting warm?
@ginch avatar
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Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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@ginch avatar
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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Mine does something similar. I suspect flooding even thogh it doesn't seem to leak normally. So my method when riding is to turn off the fuel as I stop or before I stop if I'm able to. Let it run for a little... 30 seconds maybe? Then it will start easily.

If it's doing what yours is in the video I'll turn the tap off, start it and wait for it to run out of fuel... you'll know because you'll be holding the throttle open and it will suddenly race. Fuel tap on. Ride off into the sunset!
OP
@vespigi avatar
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@vespigi avatar
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Thanks guys,

I will check the fuel line routing and will run the hot engine dry and see if it starts.

Will report back.
@ginch avatar
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Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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@ginch avatar
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Vespigi wrote:
Thanks guys,

I will check the fuel line routing and will run the hot engine dry and see if it starts.

Will report back.
Well it needs a little fuel of course!
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a lambretta or two
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Piston ring gap of 0.5-0.55? I'd swap in some fresh ones.

(Not that I'd expect this to impact your problem.)
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Mr. Clean
P,SUPER,V90, 50 Special
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SFvsr wrote:
Piston ring gap of 0.5-0.55? I'd swap in some fresh ones.

(Not that I'd expect this to impact your problem.)
I thought so too.. maybe the guy honed a little more than you thought.
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SFvsr wrote:
Piston ring gap of 0.5-0.55? I'd swap in some fresh ones.
isn't it supposed to be between .3mm to .5mm for the thicker rings...??


anyway...

this happened to me 3 years ago:
I was messing with my idle mix and set it too lean
was fine with a cold engine
but after it got hot the mix would get a bit more lean due to it being hot (350 F)
engine would die
once it cooled the idle mix was then just rich enough to allow starting

try adjusting the mixture screw a bit richer = 1/2 turn
OP
@vespigi avatar
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Olestra wrote:
fuel line getting warm?
Thanks Olestra, you were spot on.

I checked my fuel line and about 3 inches of the line between the carb and body was touching the plastic cylinder cowl. I pulled some slack out of the body and moved the line away from the cowl. Bike now starts again when engine is hot.

It is still bogging down at a 1/5 throttle which I find strange because I did not mess with the carb. Perhaps it is a combination of the hone and lap that has affected fuel air mix? I'm going to play with carb settings over the weekend and hope to sort out the bogging.

Thanks again.
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Ginch wrote:
Mine does something similar. I suspect flooding even thogh it doesn't seem to leak normally. So my method when riding is to turn off the fuel as I stop or before I stop if I'm able to. Let it run for a little... 30 seconds maybe? Then it will start easily.

If it's doing what yours is in the video I'll turn the tap off, start it and wait for it to run out of fuel... you'll know because you'll be holding the throttle open and it will suddenly race. Fuel tap on. Ride off into the sunset!
Ginch, I think you were right that the engine was flooding and closing the tap before killing the engine would have probably worked. Luckily Olestras recommendation solve the problem. I'm thinking that the hot fuel line was causing the engine to flood?
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SFvsr wrote:
Piston ring gap of 0.5-0.55? I'd swap in some fresh ones.

(Not that I'd expect this to impact your problem.)
I do realise that the gap is too big. Can I just swap out the rings or do I need to go to the next oversize piston?
@olestra avatar
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UTC quote
Vespigi wrote:
Olestra wrote:
fuel line getting warm?
Thanks Olestra, you were spot on.

I checked my fuel line and about 3 inches of the line between the carb and body was touching the plastic cylinder cowl. I pulled some slack out of the body and moved the line away from the cowl. Bike now starts again when engine is hot.
Glad I could help!

I had a hot fuel line problem with a 63 chevy quite a few years back -- I seem to remember using aluminum foil as a heat shield back then
@sdjohn avatar
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Johnny Two Tone
'15 GTS300, '86 PX125EFL, '66 VBB, '01 ET4
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With the marginal compression you can narrow your plug gap a bit and it will help with starting. Try 0.018"-0.020" or so. It can help.
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spiderwebb wrote:
SFvsr wrote:
Piston ring gap of 0.5-0.55? I'd swap in some fresh ones.
isn't it supposed to be between .3mm to .5mm for the thicker rings...??


anyway...

this happened to me 3 years ago:
I was messing with my idle mix and set it too lean
was fine with a cold engine
but after it got hot the mix would get a bit more lean due to it being hot (350 F)
engine would die
once it cooled the idle mix was then just rich enough to allow starting

try adjusting the mixture screw a bit richer = 1/2 turn
I was kind of leaning toward idle circuit. Would unscrewing the idle jet a bit, or maybe removing it while on the centerstand be worth while? Of course you wouldn't want to ride it that way. I had similar symptoms when my idle jet was clogged.
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Moving the fuel line away from the cowl has definitely helped the hot starting but has not solved the problem entirely as the problem occurred again (but not as frequent as before)

Spiderwebb & Panchoboots who suspected a lean idle circuit were also right. See thread below

Engine Bogs On Pull Off
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86' Vespa PX 200, 59' Lambretta LD 150
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Well I would say that the piston clearence to the cilinder could be more tight than normal, so that's why the engine stops when it gets warmer, but if you're saying that the fuel thing helped I have no idea Laughing emoticon
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Molto Verboso
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After experiencing vapor lock and no starts in hot weather, I install heat shrink tubing on the line beside the cylinder from where it exits the frame to the airbox.

http://www.ebay.com/sch/i.html?_trksid=p2054897.m570.l1313.TR2.TRC1.A0.H0.Xfuel+line+heat+shield&_nkw=fuel+line+heat+shield&_sacat=0&_from=R40
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The hot starting problem has re-appeared again. When the engine is hot I kill the engine and it will start if I immediately kick it again. If I leave it for a few minutes and then try to start it does what I show in the video clip in the beginning of this thread. While it's struggling to rev up you can open up the throttle and the engine does not react.

As Ginch recommended above switching off the tap before killing the engine definitely helps. Also, when the engine is struggling to rev up, closing the tap and waiting for the engine to responded to the throttle and rev up also works.

Why would the engine flood like this???????????????????

My long shot theory on why the engine floods is as follows;
I have a Polini venture installed on the carb. When you let the engine cool a little the hot air-fuel mix in the carb box cools and the some fuel runs down the venturi and sits at the bottom of the crank. When you then try to start, the engine floods while trying to get rid of the excess fuel. When I remove the carb cover, the inside of the cover and carb box is very wet.

Things that I have changed from when I first posted are as follows;
New rings (ring gap now 0.25mm)
Changed idle jet from 160/45 to 160/50
Swopped out the carb with another with the same jetting
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remove the fuel line from the carb and with the tap off does fuel flow...??
shouldn't flood an engine if the float needle tip is not deformed

float needle tip is the red type and is perfect ...??

float is not sticking open in the float bowl...??
you can sand the floats edges and the inside of the float bowl so that there is a bit more clearance. helps

I had a sticking float this year that made a engine bog way bad... I would have to turn off the tap and with engine just running waited till it used up the fuel in the float bowl. Then it would run great. Turn tap back on and ride.

If the float level in the float bowl is TOO HIGH then the idle and main jet suck too much fuel = bog
@ginch avatar
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Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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Location: Victoria, Australia
 
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@ginch avatar
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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Posts: 8896
Location: Victoria, Australia
UTC quote
spiderwebb wrote:
If the float level in the float bowl is TOO HIGH then the idle and main jet suck too much fuel = bog
There's no way to adjust that with an SI is there?

I feel your frustration Vespigi!
OP
@vespigi avatar
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UTC quote
To eliminate the carb as the problem I swapped out the carb with another one. I also used a brand new red tip needle on the second carb. The chances of the float sticking open on both carbs are slim.
When swapping out the carb the fuel line was obviously removed from the 1st carb with tap off, no fuel flow with tap off.
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Ginch wrote:
There's no way to adjust that with an SI is there?
nope

but he can make sure that the float is not rubbing on the float bowl
sanding the corners of the float and the inside of the float bowl helps eliminate issues...

after this a quick look at the float pin = they wear out too and become sloppy resulting in a float that can move about more side to side than it should.

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