1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

Twice yesterday, I was on a six mile trek and the bike lost all power after about 4 miles/15 minutes. And it wouldn’t immediately restart.

I try and try again to start, it sounds like it’s going to, but it won’t catch. I check the gas flow and the tickler floods the carb, as it should. Fuel drips from the petcock when I pull the line off. The tail light is still working when I crank it.

I didn’t have tools to check the spark at the time, but after a few hours, I decide to crank it and it starts up just fine. I turn it off (cuz I’m at work and not yet ready to ride it home... I even start it up a few more times throughout my shift and all seems A-okay). After my shift, I try to drive it home and it dies again after about 15 minutes/4 miles of riding.

Any ideas? Thanks in advance.

Sachs and Vanagon.jpg

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

Ye olde BAD condenser. Replace with new.

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

I put in a new condenser back in September when I was trouble-shooting another problem (turns out the other prob was not the condenser, so my old condenser likely still works fine and I can stick it in there). Do you think the new condenser burned out? And, if so, what might cause this?

Is there a way to test the condenser? Thanks!(edited)

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

I would say condenser too, sweet Westy!

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

Thanks!

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

If it is, indeed, the condenser, what would make it quit working when hot and then start working again when cooled off?

I reckon I'll swap it out and find out the hard way, but am curious as to how that works and what's happening that cases it.

Thanks again!

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

A condenser is nothing more than an electrolytic capacitor in the ignition circuit that stores a charge. That stored energy is what allows the spark duration to last long enough to ignite the fuel. It also does smoothing so your points don't get eaten up from the sparky.

Malfunctioning when hot is a well known thing with capacitors..which is why they are rated for temperature when u buy em..

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

I appreciate you sharing your knowledge, Aaron. Maybe the condenser I put in there wasn't rated for the amount of heat the bike creates. I'll pop the older one back in and see if it takes care of the problem.

Trying to understand the cause: So condensers just can't function properly when overheated but aren't physically damaged in the process, allowing them to function again when cooled off?

Also, the bike ran fine for several months before having this issue. does that make sense with it being an overheated condenser? I hadn't ridden it in a few weeks, and since then, the outside temps have jumped up about 15 degrees here in Texas. Maybe that heat increase pushed the condenser past its threshold and accounts for why it hadn't happened previously.

Thanks for helping me wrap my head around the issue.(edited)

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

imo 4 miles seems like more than enough time to get to full temp

keep us posted, i had nearly the exact same issue with a 505d. changed condensor but no dice.

its a backburner project so i havent been messing with it in about a year but this post reminded me to try and figure it out.

keep us posted...

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

Condensers are made with a high temperature rating already, they live very close to hot burning things.lol ..if the condenser Is intermittent, it's just bad...it's a can filled with liquid and foil...lots can go wrong.

I was just telling you that caps in general CAN fail in high heat environments....

It's like a couple bucks to pick one up at an auto parts store, it's worth it to just spend the money...if it doesn't fix it...it only cost a couple bucks...

I just ask for a condenser for a 70 Chevy Nova...always works fine..has a mounting lug n a wire..

Just wire it in externally(edited)

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

I'll try to swap it out this week and get back to y'all.

@aaronb

Thanks again for helping me understand this. I've swapped it out before and it's a fairly simple job. I'll let you know what happens.

@bullsachs101

I'll post here what I learn. The thing is, I usually only ride the bike to work about once a week (if I'm running too late to bicycle), which is six miles. And it's always made the trek just fine. I do only ride it a few times a month, so it might be a spell before I can recount my results.

Re: 1979 Sachs Prima G3 dies when hot, won't restart until cool. Good condenser.

Doesn't seem to be the condenser.

I swapped it out, rode the bike for about three miles (ran fine) and shut it off. Went shopping. Tried to start the bike up about 15 min later and no dice. It turns over, the lights come on, it sounds good, but it won't run. I pushed/pedaled it home, stopping every so often to see f it was cooled down enough to restart.

I guess it cooled down enough by the time I finally got home to start back up (about 30 min of cooling down or so). I let it run, figuring that when it heated back up enough, it'd die. It died after about 30 seconds.

I'd read elsewhere that if the condenser is bad, you won't get a spark when it's hot. So I tested for spark. Got spark. Also, fuel is flowing. Compression is good.

What else could it be?

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

♣Slew Foot♣ /

Okay the light bulbs weren't replaced recently were they some of these older sax had 6 volt systems that were weak as hell and to compensate the bulbs were headlight 18 Watts tail running light 2 Watts and brake light 3 Watts their Oddball bulbs osram Sylvania anyways there is a return ground from the tail that works as a safety override so that if your bulbs are out the bike won't start you can either rewire the bike so that the return ground is grounded to the frame and likewise the tail and bypass the safety

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

Got spark. Also, fuel is flowing. Compression is good.

Still leaning towards the compression. I didn't read if you had ever got a gauge to measure it.

Re: 1979 Sachs Prima G3 rides for

I've had erratic spark issues that behaved like a bad condenser and I never managed to track down exactly - theyre the worst because theyre stochastic - you think you've fixed it because everything's working and then when you least expect it, jk - not working...

Personally I'd replace the ignition. you might be able to dig through and find an issue but I am pretty sure this is one of those ignition issues that will just torment you til you replace the whole thing.

Compression is a legit concern if you've still got your decomp, I always plug that - see the 505 performance wiki and there's a section on plugging the decomp.

Re: 1979 Sachs Prima G3 rides for

OG Crazy Wayne /

I would try removing the coil wire it turns Lefty Loosey to remove and righty tighty with a good push to reinstall I suggest you remove it and clip of quarter inch off the end make sure there is no rust or crap in there and reinstall with a dab of dielectric silicone in the connection try it out the spark plug boot also it is possible that the factory ceramic spark plug boot resistor has an internal crack.

If you need a new plug wire just find an old cathode tube TV and remove the HT high voltage wire that powers the tube it's the same as moped spark plug wire

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

find an old cathode tube TV

What is this? Is it worth robbing a museum of its display to get a spark plug wire?

0.89 a foot at Napa Auto part #734803

All your other suggestions are great but the TV thing your just reaching too hard.

Speaking of TV are you ever going to replace my LCD after the controller throwing tantrum?

Now I'm reaching to hard.

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

Museum? I still have tube TV's, they work great...stay off them...lol! ;)

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

Nobody threw fish in your cage S.Keller. If I want any response from you I'll head down to the telegraph office and tell them to type out a request on their Oliver typemachine then send it to you as a candy graham.

GAAACCCK

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

Forgot to ask if you still have a decomp and if so is it by any chance covered in black oil and gunk?

Cant hurt to swap it out with a m10 x 1.5-ish socket cap screw

Re: 1979 Sachs Prima G3 rides for

> OG Crazy Wayne Wrote:

> -------------------------------------------------------

> I would try removing the coil wire it turns Lefty Loosey to remove and

> righty tighty with a good push to reinstall I suggest you remove it and

> clip of quarter inch off the end make sure there is no rust or crap in

> there and reinstall with a dab of dielectric silicone in the connection

> try it out the spark plug boot also it is possible that the factory

> ceramic spark plug boot resistor has an internal crack.

>

> If you need a new plug wire just find an old cathode tube TV and remove

> the HT high voltage wire that powers the tube it's the same as moped

> spark plug wire

Good idea, first I just gotta top off my bike with petroleum distillate then revulcanize my tires before I go to the General Store.

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

Warm seal leak?

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

♣Slew Foot♣ /

Firstly never ever touch a cathode ray tube HT circuit they are live for up to 20 years and have enough voltage to kill you dead even unplugged for 20 years. And underneath your points Runza blue wire that blue wire sometimes gets bear by where and will mimic a bad condenser it will go until the amperage gets high enough and then it will Ark and kill the bike

Re: 1979 Sachs Prima G3 rides for

this got silly fast. set your point gap too. you can have "spark" and not run if the gap's too small

Re: 1979 Sachs Prima G3 rides for

Getting flooded? Try adjusting carb needle hieght. Maybe sucking in too much air? Faulty spark plug when hot?

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

I’m a little late to this party, but it seems that everyone has overlooked this in the initial post.

“Fuel drips from the petcock when I pull the line off.”

Sounds like the typical symptoms of restricted fuel flow. You should have a steady trickle of fuel. Not dripping.

If you have a steady trickle at first that slows to a drip, the cap vent may be blocked. If it’s a drip as soon as you open the petcock, you’ve got blockage in the petcock/screen.

You’re welcome.

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

♣Slew Foot♣ /

Yeah you left that it without really looking he said from the petcock so when he shuts it off he's saying it doesn't seal all the way

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

♣Slew Foot♣ /

I know that there's a weak spot behind the clutch Bell there is a seal and it has a thin metal washer and they tend to split and then when it gets hot that split the Gap gets wider and you'll lose compression or rather case pressure

Re: 1979 Sachs Prima G3 rides for 15 min then loses power, won’t restart right away

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

That’s not how i read it. He said nothing about drips “when turned to off position”.

However, I didn’t read this entire thread until now. “Not starting after 15 minutes in the General Store” throws a wrench in the fuel flow theory, but that may have been some other issue. Having two issues at once can make you chase your tail.

When working on 2 strokes, I’ve learned that whenever i’ve exhausted all other options, a brand new spark plug usually fixes it. I still don’t like the drip thing though.

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