Puch Magnum

Just picked up a Magnum on Craigslist. It starts up and runs at low rpm but dies as soon as you try to accelerate. The previous owner said it did 60 mph before he disassembled/reassembled the top end one day. I guess he abandoned the hobby because he bought new bottom and head gaskets but never installed them.

I just disassembled the head/cylinder/intake/exhaust. The bottom and head gaskets look alright (I'm gonna replace them anyways), but the intake gaskets look kinda homemade and incorrectly sized.

My question... could gaskets cause this problem? The engine starting up but dying when I accelerate?

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Re: Puch Magnum

I probably should have checked for air leaks while it was still assembled. I'm probably just gonna go ahead and buy the intake/exhaust gaskets so it will have all fresh gaskets.

Re: Puch Magnum

Overpriced Parts /

Shame you bought a custom bike with sooo much jury rigged and aftermarket stuff .

Post what cylinder kit, type of za50 bottom( needle crank or stock crank, oil injected or not, gearing, intake , carb pipe, etc.

Re: Puch Magnum

Athena AJH 70cc

20mm Dellorto carb

It's reeded, not sure which brand though. Plastic reeds.

Not sure what needle crank vs stock crank means. I haven't opened up the crank case yet, just the top end.

If this thing WAS oil injected, it's not anymore.

I'll check the gearing tomorrow in the sunlight, my garage has poor lighting right now. Also, I think the wheels are from a Tomos.

Carb/Intake Pipe/Filter picture is attached.

ON A POSITIVE NOTE:

I just reassembled the top end and was able to start it up and ride a couple laps around the block. Only hit 15ish mph though, but I'm still excited. I'll check for air leaks tomorrow in the sunlight.

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Re: Puch Magnum

Overpriced Parts /

Looks like 19-20x36 gears

About 48-low 50 mph gearing , head is on wrong by 1/4 turn

You have a non oil injected engine which is good

Timing before jetting : set timing around 14-14.5 degrees before top dead center to start to start whatever it takes to keep below 400° F on head temp gauge. I would tear down top end and inspect for seize damage since there was no head temp gauge on the bike and the person may not of known he seized (fix the head position too).

Do not run bike until timed correctly and protected with a head temp gauge

Re: Puch Magnum

Haha damn I probably never would have noticed the head being on wrong. That's how I bought it so that's how I put it back on when I disassembled/reassembled today. I'll fix it tomorrow.

I'm buying new gaskets. I'll have to look into purchasing a temperature gauge and do a little research on timing.

Thanks for the advice.

Re: Puch Magnum

One more question:

When I disassembled the head/cylinder from the block I noticed that one stud bolt wasn't very tight. When I reassembled it I noticed the stud was backing out of the block as I was lightly tightening it.

I cleaned out the threads and it seemed to tighten (wasn't trying to push it, because the block is obviously somewhat stripped). Would it be advisable to drill/tap the block hole one size higher (7mm instead of 6mm)? There seems to be enough space in the head/cylinder hole to accommodate a larger diameter stud. Not sure if I can get adequate torque with the current hole.

Re: Puch Magnum

Overpriced Parts /

See if you can just retap same size first

Your not supposed to use much torque only 8-9 ft lb

Otherwise tap for 7 mm stud

Re: Puch Magnum

Alright, I'll obtain a torque wrench and 6mm tap asap and see how it goes.

It must have been a previous owner who stripped it because I barely tightened it yesterday when it backed out. I bet the ass who sold it to me knew it was stripped.

Thanks again.

Also, can you recommend an appropriate temperature sensor?

Re: Puch Magnum

Trailtech makes one you can but on treatland.tv

Re: Puch Magnum

Something seems off between the intake manifold and carb...

Re: Puch Magnum

My guess was that the intake wasn't designed for that carb, so he welded a short piece of pipe between them.

Re: Puch Magnum

Hey Ken, you say my head is off by a quarter turn? How do I know which way is correct? The compression chamber lines up with the cylinder regardless of the orientation. And the pattern of fins on the head don't match the ones on the cylinder in any orientation.

Thanks for the answers, this is my first moped and I'm learning as I go.

Re: Puch Magnum

Overpriced Parts /

Yours is a sideways offset cylinder so your head needs to be 1/4 turn different I believe but ya you can leave it for now.

I Always put a new (1.53) head gasket every time I take off the head, new base gasket every time I remove the cylinder and new intake gasket when I remove intake for no leaks ever. Base gasket and intake gaskets I cut from my own material many times so they're very cheap to replace

Re: Puch Magnum

Problems.

I had to drill/tap one of four za50 studs to 7mm... no problem. New base/head/intake/exhaust gaskets, torqued the head down to about 8 ftlb. Cleaned the carb. Tried starting it and it dies out as soon as I release the clutch lever (no kick start, I'm sprinting to start it). This is with the suggested Dellorto tuning from the wiki. The needle is in the slot third from the top which I guess is one notch lower than suggested, but I've tried accounting for it with the mixture screw and... nothing. Idle jet is a 50.

I had the thing doing 10-15 mph a week ago, so I don't think it would be a timing issue. I can't see why I'd have LESS compression after torquing everything down. It was barely sealed before with that stripped stud hole. Piston rings looked pretty good.

Any ideas?

Re: Puch Magnum

That seems like an awfully big idle jet....is your plug soaked after you try to start it?

I run mikuni but my pilot(idle jet) range from 10-15....might be worth a look

Re: Puch Magnum

According to the wiki entry for tuning Dellorto PHBG carbs "Most (kitted) bikes like an idle jet somewhere between 40 and 50."

50 is what came with the carb so I figured it would at least start up (it DID idle a week ago). This thing isn't even trying to idle now. I stop running and so does the bike (the headlight does come on when I'm running).

Another question... how do I drill start the bike when the flywheel nut is righthand threaded and the motor spins counterclockwise? Do I need to apply a bunch of locktight so the drill doesn't undo the nut?

Re: Puch Magnum

sounds like you tightened everything up so now you might be drowning....if you have a filter on there now...pull it...and try again..and get that idle up high...adjust it down if you get it running

Headlight has nothing to do with ignition..stator(magnets) take care of that

Re: Puch Magnum

jeeeeebus 50 is high for a PHBG idle jet unless you have some massive air leak.

try something lower than 45.

probably the PO had a gigantor air leak and instead of finding it and fixing it just up-jetted until the bike was rideable?

I think I have a 42 in mine with a similar set up

try that and if it runs for any reasonable length of time try riding it and checking plug but yeah a temp gauge is your friend.

they are relatively cheap for the investment

good luck

Re: Puch Magnum

Overpriced Parts /

Miss Tammiecat~ Wrote:

-------------------------------------------------------

> jeeeeebus 50 is high for a PHBG idle jet unless

> you have some massive air leak.

> try something lower than 45.

>

> probably the PO had a gigantor air leak and

> instead of finding it and fixing it just up-jetted

> until the bike was rideable?

>

> I think I have a 42 in mine with a similar set up

> try that and if it runs for any reasonable length

> of time try riding it and checking plug but yeah a

> temp gauge is your friend.

> they are relatively cheap for the investment

>

> good luck

I got two bikes that have 50 idle jet in them that work fine

They worked fine with a 42 and a 45# idle but I just used the 50 because I used the 42 and #45 jets in other bikes and had a pile of #50 idle jets.

Re: Puch Magnum

Get a re threading kit instead of a tap and die. It will fix your stripped threads instead of making all new threads. Cost about 120$ on amazon.

Re: Puch Magnum

Well 3 of the 4 stud holes were fine, only one was stripped. The 7mm bolt cleared the holes in the cylinder/head gaskets just fine, so I didn't see the problem with stepping the one stud up a size.

Tammiecat, you think the oversized idle jet would cause it to not start at all? You are right about the previous owner's airleaks. With that stripped head stud I doubt they were getting adequate compression. But they also claimed to have had the bike going 50+ mph with the current setup. Maybe all thanks to their airleak...

Re: Puch Magnum

i don't know you may be a t a way higher altitude than I am.

If you have compression, spark and fuel you should at least start. unless your timing is waaay off

is your plug fouled? check for spark while trying to kick it over. If it is weak it may not start without alot of effort.

changing an idle jet is easy enough, give it a shot with a fresh plug knowing you have spark.

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