Need Help with Puch engine...

James Foster /

Ok, I'll get straight to the point. My 1978 Puch maxi Free Spirit moped is being a real pain lately, and I'm having trouble getting it to run. Here's what it has installed on and around the E50 engine;

70cc Airsal kit.

Tecno Estoril exhaust.

14mm intake manifold with 15mm bing carb(70 size jet currently installed, and needle jet is at second to top notch.)

Low restriction air cleaner.

Slightly modified transfer ports on the crankcase to match up evenly with the transfers on the 70cc bore.

New contact breaker points set at near stock position.

Brand new NGK BP4HS spark plug.

And a new high tension ignition coil, along with a new spark plug cap and wire.

Now that you know what's installed, here is what the specs are;

Compression is right at 100 psi, the spark plug has a nice consistent bluish/white spark, timing has been set correctly, and the carb gets fuel to the engine. I have tried every jet from 70-82, every needle position, a couple of different carburator's, and a range of new spark plugs. But, even after all of that, I still can't find out what the problem is. It just won't start. So I ask of everyone here, if you have any suggestions, let me know ASAP...

Thank you,

JF

Re: Need Help with Puch engine...

you got compression.. fuel and spark .. it should fire up ..

try a squirt of Starter Fluid. If it starts there's some sort of fuel problem.. it could be polluted fuel .. could be anything..

put an in-line neon

spark-tester between the plug and the coil.. you might think you're getting spark but are not.

Re: Need Help with Puch engine...

Jason Luther /

right. i had a bad ht coil on my motobecane. it would even spark (must have jumped a minut gap inside the coil, since i didnt get continuity) but it wasnt a good enough spark. since its a new coil and everything check your grounds and kill switch. maybe its shorting out enough to give intermitant spark or something. you got all of that fancy stuff, are you using your choke when trying to start?

Re: Need Help with Puch engine...

James Foster /

Well, I tried the choke, but it didn't seem to do much. I'm thinking that it's getting flooded by too large of a jet, because every time I take out the spark plug, it's wet with gas. Starting fluid made it run for a few seconds, but that was it. And I even tried starting it with no air cleaner, but it still floods. So, I might want to try getting some smaller jets, like in the 62-68 size range(like I don't have enough already). If that solves it, then that'll be a relief. But if it doesn't, I might try testing the coil and the timing again, just in case...

Well thanks for the advice guys, and hopefully I'll be updating on this within a week or so. :)

JF

Re: Need Help with Puch engine...

Check the wires at the buss bar make sure the screws are tight mine came loose giving inconsistant starts stalling Ect. I thought the kill switch was bad but screws came loose.HTH.Jim

Re: Need Help with Puch engine...

If it starts with Starter Fluid the ignition components are ok.

A main jet's size has no influence on starting or idling or low speed .. and it only begins to have an effect near mid-throttle.

The bike should start and run fine below mid throttle with the main jet completely removed.

It's possible that the carb's float level is too high. Float level is critical to metering the proper air:fuel mix ratio at all throttle openings (including starting and idling).

Aside from an improper float level adjustment, the cause of a high float level could be a leaking float needle. The cause of a leaking needle could be a lot of things..

a needle's nose or a needle seat that's damaged or dirty..

a float that's hung up and doesn't move freely for some reason..

a float that is partially or completely "waterlogged". (Some floats have a number stamped on them .. it's their dry weight in grains or grams .. weigh it.)

The engine is flooding.. unless there's some hidden air-restriction that you've overlooked, the carb's got a problem metering fuel.

Re: Need Help with Puch engine...

you a fan of bump starting or are you just pedaling it? I find that once I clean and reassemble my moped it is a little finicky to restart again- and I'm running stock. It usually turns over easier if I bump start and am careful not to pull the throttle out much to flood the engine.

Re: Need Help with Puch engine...

Jason Luther /

i still say its getting too much air to start. especially since you have a hi-perf air cleaner and 15mm carb. a wet plug doesnt mean its flooded. put the choke on and dont give it any throttle.

Re: Need Help with Puch engine...

Hate to bring this up, but it sounds like you are low on compression.. 100 is an absolute bare minimum for a 2-cycle engine. Many 2-cycle engines will not run at all, below 100psi.

Are you sure that all is well with that Airsal top end? Typical compression on a good-running ped should be in the 150+ range. New top-ends will not reach full compression until they are fully broken-in, but you should be starting with something better than 100psi.

Worth looking into.

Re: Need Help with Puch engine...

James Foster /

Hmm, interesting observations guys. Well, first of all, Joew might have a point with the flooding issue. I shall check that before I do anything else. Secondly, I actually got too lazy to use the pedals, so for now I use a 19.2 volt cordless drill to turn over the engine. It's actually very effective, kinda like the electric start on my spree. And lastly, I thought It was getting too much air for starting at first, so I put the choke on at many different positions while turning it over with no throttle. It made it run at idle for about 1-2 seconds, but when you opened the throttle, even the slightest amount, "whhaaaa..." and it dies instantly.

Oh and another thing to mention; The carburator that's on there is a 15mm bing, but it's a model from a different bike. Sorta like the one in the attachment above, except there's a metal shroud that surrounds the filter. And because of that shroud, I had to raise up the intake manifold by about an inch. It still seals very well, and the carb now fits nicely on there.

If any of you have comments on this, or more suggestions, keep them coming. I really appreciate the advice on this guys, and who knows, I might actually get it running good for once... :)

Thanks,

JF

1123342785_ah5286.jpg

Re: Need Help with Puch engine...

James Foster /

Actually Legend, I have looked into that, and I'm worried that it could be a problem. If anything, it's probably not helping the engine start any. Could be a leaky head gasket, or a leaking piston ring(single ring setup). I'm sure tempted to just go all out and get a Polini and a new carb for it. If only I had the money...

Thanks anyway,

JF

Re: Need Help with Puch engine...

Jason Luther /

everything is still pointing to too much air

Re: Need Help with Puch engine...

You said that you had to raise the intake so the carb would fit!

It sounds to me to be an air problem.

You have to much air coming in around the intake or carb.

I bet it's the spacer you put in-between the original manifold and head.

Have some one spray starting fluid around the intake wile you start it if it starts then look for the leek.

Buy the way I have the same carb and I made a intake out of the original Puch that swung the carb out to the side.

Good Luck!

Mike

Re: Need Help with Puch engine...

jf,

My approach works like this: If you know that 100psi is not right for a good top-end, then fix it. You have way too many varaibles right now, so eliminate the ones that you know about. Like I say, 100psi is right at the ragged edge of runnable - 2-cycles are not like 4-cycles, most of which will still bang along with 60 or 70psi.

Even if the bike was running, you'd still have low compression.. and you'd still have to fix it. See my logic?

Maybe pull of that cylinder.. check that the piston is intalled the right direction, that the ring is not on upside-down. Check the ring and bore for any scoring. Check the cylinder and head surfaces for warpage, and the gasket for damage.

Re: Need Help with Puch engine...

James Foster /

I see you're point, but the problem is, I've already checked all that. My conclusion was that the ring is leaking not due to scoring, but by a bad break-in period. Back when I broke the kit in, I had virtually no idea what I was doing, and the kit had no instructions whatsoever. On top of that, I was using semi-synthetic oil, which probably didn't help the ring break-in properly.

After messing with the puch for about an hour earlier today, I noticed that the spark coming from the spark plug was ok, but inconsistent. And to top it all off, the piston was hitting the tips of the new spark plugs while it was being turned over, making the gap too small; even though they were the exact same model number that's recommended. So now I've gotta use a slightly older plug and I've got to find out where the electrical problem is on the bike. Looks like I've got a lot of work to do...

JF

Re: Need Help with Puch engine...

Jason Luther /

the bp4hs is kinda long, though i r an one afor a while in my stock puch. get a b5hs.

Re: Need Help with Puch engine...

James Foster /

Alright I'll look into it. Thanks Jason! :)

JF

Re: Need Help with Puch engine...

Oh yeah, the 'P' in BP5HS stands for 'protruded tip'. Go to a non-P type, and your interference problems should be solved. Sounds like you found at least one very major issue, here.

Plug gaps that are too small reduce the voltage (and hence power) of the spark. Below a certain gap (based on the type of ignition) the spark cannot introduce enough heat energy into the cylinder to get a good burn going.

About the bad break-in.. take the cylinder to a small engine shop, and have them put a pattern on the bore with a ball hone. Assemble the engine with a new ring and try again. That should get your compression back.

Re: Need Help with Puch engine...

Also, just in case: make sure that the rings don't have the gaps all in a row. Rotate them so they are either 180 degrees apart (2 ring piston) or 120 degrees (3 ring piston), or else you will lose lots of compression.

Re: Need Help with Puch engine...

James Foster /

Good note to consider Shawn, although my Airsal kit is set up for only one piston ring. Too bad the compression loss problem isn't that simple on my bike, but thanks for the thought anyway. :)

JF

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