Sachs Suburban Stalls at Stops

Haden Asay /

Jun 21, 2020 11:11PM

Hello everyone,

I have a completely stock 1980 Sachs Suburban with 800 miles that's in great shape, but stalls at stops. I know this is a common problem and I know it can usually be sourced to the clutch. I have had the clutch apart dozens of times with different shims and different parts from two sets of clutches and here's what I've found out:

- With a 0.80mm shim, the bike goes 30 mph as it should, but stalls when I stop. With this setup, I have around 0.2mm of preload. Play at the starter lever is within spec at 1mm and the screw on the clutch arm is turned 1/4 out from touching.

- With a 0.60mm shim, the bike goes 28 mph and stills stalls at stops. Preload is within spec.

- With a 0.40mm shim, the bikes goes 28 mph and stills stalls. Preload is still within spec.

All of this leads me to believe that the clutch isn't my problem, but rather that the bike isn't idling low enough. The bike runs great, although the idle does sound a little off to me and also a little choppy. Any attempt to lower the idle anymore kills the bike. The plug is a nice brown color, plug gap is fine, timing is fine, air filter is new, gas is fresh, carb is stock square bing with the stock jet, no air leaks that I can find with carb cleaner, and the bike behaves the same with an ebay carburetor. The carb does appear to leak gas from the bowl or elsewhere, but I can't find an air leak around there. Maybe the float level is too high? Would that not allow the bike to idle lower? Here's a video of it idling and stalling with the 0.60mm shim. Does the idle sound right to you? I don't have experience with how a two-stroke should sound and idle.

https://drive.google.com/file/d/19ckgo1KvGU1VhtaF65_xnbLMn-ONTfzR/view?usp=sharing

I've run out of ideas and need some different perspectives on this, so if you have any input it would be greatly appreciated, thanks.

Re: Sachs Suburban Stalls at Stops

pat splat /

ggspeed

Jun 21, 2020 11:16PM

I didn't know sachs had "coaster breaks".

Re: Sachs Suburban Stalls at Stops

Michael Branscombe /

film495

Jun 22, 2020 02:27AM

if it is stalling, why not just try to run the idle a little higher?

Re: Sachs Suburban Stalls at Stops

Haden Asay /

haden2342 OP

Jun 22, 2020 03:13PM

It's stalling because the clutch is slightly engaged at idle because I believe the idle is too high. That's why when I got the brake in the that video the rpms slowed until it died.

Re: Sachs Suburban Stalls at Stops

Richard Eberline /

rockettman

Jun 22, 2020 08:51PM

electrical issue

Re: Sachs Suburban Stalls at Stops

Born to be WillD /

Go to branch

willd

Jun 23, 2020 01:45AM

what's up with your decomp? theyre often troublesome and could very likely be why your bike wont hold an idle without the idle being too high

Re: Sachs Suburban Stalls at Stops

Aaron Blair /

aaronb

Jun 23, 2020 01:58AM

I would think decomp in this situation, Sachs are pretty strong idler's and I've had stock Sachs bikes that would overheat the clutch at idle but never stalled the engine.

That's just my bad clutch tuning but still, they can grab alot at idle and still not stall.

What trans fluid are you running?

That thing is idling perfectly, if anything a little slow. Have you tried increasing the idle?

Might also be a problem with your donut. (edited)

Re: Sachs Suburban Stalls at Stops

Haden Asay /

haden2342 OP

Jun 23, 2020 03:07AM

The decomp is stock, I haven't plugged it. Is there a way to tell if it is leaking or should I not even bother and just plug the thing?

I am running type F ATF for the transmission fluid and the level is good.

I have not tried increasing the idle, but the way you put it makes sense so I'll give that a shot.

I also have two other donuts, one that I bought when I thought that was the problem and another that was in a junk engine I bought when I thought the rest of the clutch was the problem. Both look worse, but I'll try one of them since I don't remember ever doing that.

Re: Sachs Suburban Stalls at Stops

Born to be WillD /

Go to branch

willd

Jun 23, 2020 06:53AM

you can kindof tell if it's leaking. one semi-reliable telltale is the symptoms you describe, though there are plenty of other causes too like too rich jetting. There's no reason for jetting to change but if all else is stock this can still come about from buildup plugging up the exhaust or debris restricting flow in the air filter.

The other good tell is that the decomp exhausts out a little hole on the bottom side of the cylinder, if that has a lot of oily buildup under and around it that can be a sign of a leaky decomp, however some blows out any time you're using the decomp as intended also, so it can get messy over time without being caused by a problematic decomp, while it's also possible that the hole stays relatively clean despite leaking... so it too can be misleading

Re: Sachs Suburban Stalls at Stops

Haden Asay /

haden2342 OP

Jun 23, 2020 03:44PM

So a leaky decomp has little effect on top-end performance? The bike hits 30 no problem. I'll probably plug it if none of this other stuff works.

I've had a look at the exhaust before and it seems fine which makes sense to me with the mileage on the bike. The decomp exhaust has always been oily, but I've never cleaned it and the bike hasn't seen much action. I have seen a few drops come out of it in the past after a day of messing with the bike so I'll keep that in mind.

Re: Sachs Suburban Stalls at Stops

P D /

pdcomm

Jun 23, 2020 04:26PM

You are assuming . That usually gets folks in deep doodoo .

For a dollar and a little time you can be sure that the exhaust is clear .

Dollar store oven cleaner or drain opener and a garden hose .

Re: Sachs Suburban Stalls at Stops

Haden Asay /

haden2342 OP

Jun 23, 2020 06:41PM

Seems easy enough, I'll have to give that a shot as well.

Re: Sachs Suburban Stalls at Stops

Richard Eberline /

rockettman

Jun 23, 2020 08:41PM

compression test for the decomp.

Re: Sachs Suburban Stalls at Stops

Haden Asay /

haden2342 OP

Jun 23, 2020 09:20PM

So I tried turning the idle up and that seemed to do it. It will now idle just fine with the wheel on the ground. I will still take a look at the exhaust and decomp though. Thanks everyone!

MOPED ARMY

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