Hard starting hot and cold

[znen13]

Hello,

I am experiencing difficulty starting my scooter under all circumstances. The scooter runs great, good power, no other problems—but it never fires up quickly, requiring several seconds of cranking and repeated attempts. When it finally does start, it usually is somewhat weak or unstable for the first second or two before stabilizing.

-Compression recently checked at 170psi. Cylinder, piston, rings are new with maybe a couple hundred miles.
-I have tried setting the valves looser than spec (0.005”) and also within specs with no affect on the symptoms.
-every time I have checked for spark, it is there. Coil and CDI recently replaced.
-carburetor is new, all passages and orifices checked and in good condition. Mixture screw needs to be 2.5 turns minimum for stable running, or it tends to stall when the clutch releases after coasting to a stop. Have tried enriching and leaning the mixture screw with no affect on starting.
-enricher seems to work properly with a clear drop in idle rpms after a few minutes of running from cold start.
-I just replaced the float because I found that one of the two pontoons had taken on some gas. New float didn’t affect symptoms.

One other observation is that it seems sometimes almost like the timing is over-advanced during cranking, especially if I open the throttle up during cranking, like part of the combustion is working against the piston reaching TDC. If this is the case, I haven’t been able to find a way to alter the timing.

I welcome any suggestions.

[geoffh]

Welcome to forum,never hurts to change the spark plug,does the scoot start off starter motor or kick start, what make and model and year is it.

Geoff

[znen13]

Thank you! It’s a 2013 Znen Glide. It will start with kick or starter. Sometimes kick seems to work a bit better but it never starts on the first kick.

I do have a new plug that I haven’t tried. I’ll give it a go tomorrow morning.

[dayang]

When starting g it cold twist the throttle 5-6 times fully, then make sure no twist when pressing start button. The accelerator pump will prime the intake. Then feather it to a smooth idle

[GrumpyUnk]

What dayang said. The twist grip opening the throttle will make the accelerator pump squirt in a few shots of fuel, making the initial mixture for startup a bit richer. Rather than cranking to get fuel:air from the byvalve(choke/enrichment) you have given the engine a blot of rich mix from the initial turning of the crank and the first stroke of the piston.
Given the 2.5 turns for the idle mixture screw, it may be you have a leak in the intake and are getting extra air that is not coming through the carb. The richer idle mix will then allow for that extra air and make the mix palatable to the engine. If you have the idle hard stop(throttle plate) set a bit too high, you will have an unstable idle speed as you are running on a combination of the idle circuit and the intermediate circuit. You can perhaps check by turning the idle stop on the linkage side of the carburetor back a quarter turn. You may have a more stable idle and perhaps easier starting. The hard stop setting does not need to open the throttle plate very much given the small displacement of the engine, so being a bit too open is an easy thing to do.
Some of the newer carburetors do not have an 'accelerator pump' that shoots a jot of fuel into the venturi when the throttle is opened. These will lack the brass-colored shaft that is pushed down by the throttle linkage when the throttle is opened manually or by cable. The pump is built into the body of the carburetor, and is on the rear of the carburetor, assembled with three screws(hoping to identify to those looking for it). The assembly is missing on newer carburetors. I have not investigated to see how they work.
tom

added.  Opening the throttle will make the engine crank over differently.  It allows more air into the cylinder, and that should add to compression work, but it seems to allow the starter to crank easier due to lowered vacuum.  A puzzlement, I note.
 Given it is a HOT and COLD situation, I would check more for leaks.  A loose clamp on the intake elbow, or a bad gasket where the elbow clamps to the cylinder head, or a split vacuum line, or a loose fitting where a vacuum line is pushed onto a vacuum petcock or emissions gizmo could cause hard starting.  The elbow has an O-ring to seal to the cylinder head, which could be flattened and not springy enough to form a good seal.  The vacuum ports could have a crack where they blend into the elbow.  Get out your smoke machine and flood the intake with baby oil smoke, checking for smoke appearing where it should not.
 The 'weak or unstable' idle may indicate you have the hard stop set a bit too open, so you are not 'in the idle circuit at idle' or are just on the edge.  Because it is present both hot and cold, and the idle is unstable, it points more and more to an air leak.
tom

[pinkscoot]

I had a Zen 150 with the same problems. I put a 38 pilot jet in and raised the needle 1 washer (no adjustment on it so I stuck a washer under it). My Scarabeo 150 had the same problem but there is wealth of information out there on Scarabeos. Bigger pilot and raised the needle. It takes a little persuading under 30 deg F but starts everytime.

[znen13]

Thank you for your detailed responses! Regarding vacuum leaks, I have replaced the inlet o-ring and inspected the manifold for leaks. With such a tiny displacement a very small leak could be impactful, but I haven’t been able to find one.

If 2.5 turns is excessive for the mixture screw, what is the typical value that works well for most people?

As for throttle stop setting, I don’t have a tach so I picked a speed that gives a stable and fairly slow hot idle. Currently, when the engine is running at fast idle on the enricher, the clutch just starts to engage and pull at the rear wheel a little. Not enough to move the scooter with me on it, but enough to spin the wheel on the center stand. There is no clutch engagement at hot idle though.

My carburetor does have the accelerator pump and it does work. Sometimes priming it to start (cold) seems to help, while other times it almost seems like it’s TOO rich when primed. I guess I will have to experiment with a certain number of priming strokes and be consistent.

I have had some success lately by topping off the battery charge. Starting is definitely helped by the fastest possible cranking speed. I have had some pretty easy cold starts. Hot starting usually requires cracking the throttle slightly just when the engine starts to catch. If I don’t do it right on the first or second attempt, it doesn’t take very long before I can tell cranking speed starts to diminish.

[znen13]

Just wanted to follow up on this post, because I think I just now found out the root of the problem thanks to a video from this site.

I had installed a new orange CDI when I first got the scooter because it came with the coil and wire and I figured it would be good to have all new parts. Turns out the orange CDI doesn't really have an advance curve to speak of; it just holds the timing at maximum all the time. This excess advance at cranking and idling speeds is why I was having trouble starting.

I believe it was also related to the stalling that would sometimes occur when the clutch releases after high speed operation. The reduced timing at idle with the stock CDI means that I had to turn my throttle stop screw in a bit to achieve the same idle speed as I had with the orange CDI ( I have a tachometer now). I think this extra throttle opening stabilizes the mixture better when transitioning from coast to idle.

Since swapping back to the stock CDI, starting is a breeze, and I have not had any stalling, with no apparent penalty in performance.

[GrumpyUnk]

Personal opinion, the orange parts set is not a wortwhile investment. The CDI is set as above, advanced, and the little box is full of sand. The plugs are nothing to write home about as is the coil.
Generally stock items will work as well or better, and cost less.
YMMV, but I don't think I have it wrong.
tom