PE400 self igniting

[pmc57]

What can cause a PE400 or any two stroke for that matter to self-ignition? The bike was runnine very erratic when it started to rev very high and not cut off or shut down even when the plug lead was removed. I seem to recall something similar on the forum a few months back.
Any tips or advise on where to start re fixing the problem appreciated.

[shortshift]

On the PE400 if you lift the cylinder off there is a small decompression notch machined at the top right hand corner of the exhaust port.
This made the 400's easier to kick over, or so it was purported to.

One issue back in their days was that this notch would fill up with carbon, due to cheap mineral oils being used with high Bright Stock content, and cause a hot spot leading to pre-ignition and running on when the kill button was pressed on.

It also led to many seizures on the 400 and this was reported by many of the Suzuki dealers back then like Geoff Udy Suzuki, Mick Hone Suzuki and BTX Motorcycles, ..........in fact one QLD dealer had 13 x 400's seized in the shop at the one time.

In my own 400 I have cleaned the notch of carbon and run 100% synthetic oils at 20:1 ratio with no issues.

So I would inspect the notch, clean it with a sharp object (and any carbon in the combustion chamber and piston top) and run a quality oil in the fuel of at least a 98 octane.

[lukeb1961]

dieseling is usually caused by carbon buildup and timing problems. In effect, the thing no longer NEEDS a spark plug. I would pull the head off and look at the state of the piston crown and head. Next, confirm the timing on the thing is fairly close to factory. Another thing to look for is excessive compression - did someone forget to reinstall the head gasket?

[pmc57]

Thanks guys for your input. I was also thinking, before it started to do it's own thing, I had to keep using the chock to keep it running, this tells me it was running very lean.
Could a leaky main seal be causing it? If it sucking air past the seal it would be running so lean and getting so hot that the plug starts acting as a glow plug.
More thoughts please.

[LWC82PE]

lean or just a blockage or restriction in the carby. Could probably benefit from a clean and blow out with compressed air. I had that problem on a ATV once. Owner said it wont run with out the choke and has to leave the choke on all the time. I striped the caby, blew it all out then put it back on and then it was good as gold and would run with out the choke.


how old is the motor, how much work has it done? sounds like it could need a full overhaul with new crank seals and a top end de-coke.

take off the flywheel and check the left crank seal for signs of leaking oil and check to see if the seal is hard.

is the bike hard to start?

[lc4]

A quick way to verify if it is a carbon biuld up is if it still runs after shuting off try giving it  full throttle. The fresh charge of fuel will cool the "hot spot".

[lc4]

Thanks guys for your input. I was also thinking, before it started to do it's own thing, I had to keep using the chock to keep it running, this tells me it was running very lean.
Could a leaky main seal be causing it? If it sucking air past the seal it would be running so lean and getting so hot that the plug starts acting as a glow plug.
More thoughts please.

A leak down test will answer that.

[shortshift]

On the 400 (This wont solve your immediate issue) try lifting the jet needle in the carb by lowering the clip position.
I guess it is in the stock 2nd notch from the top, go straight to 4th from the top (2nd from bottom), check for improvement in acceleration, no running on when shutting the throttle, and smooth rise in revs. If this improves things then go to the bottom clip setting to raise the needle to its highest position in the carb. This is done easily by just rotating the carb in the lossened rubber boots while still on the bike and unscrewing the top cap off first.

Like others have said you may have dieseling when the engine runs on its own oil whether it comes from transmission oil leaking past the seals, excess 2T oil sitting in the bottom of the crankcase, or air leaks causing leaness due to hot spots (This tells me you have carbon build-up and a carboned up notch).

PE's came out with fairly sharp edges on the ports and it is recommended when you lift the head off to grab a small fine rat-tail file and round off the exhaust port edges with piston at BDC. I have seen these edges shear off aluminium from the piston in this region that later affects performance (Blowby causing the carbon in the notch to overheat).

So you have a few hours of enjoyable work tonight!!

[Hardex]

I had a PE400 back in the 80's and it back fired and ripped a Hugh hole in my foot (I lived in Townsville and I was young and stupid and tried to start it with thongs on) ended up in hospital with 10 stiches and blood poisoning.After getting home from hospital I tried to pull the flywheel of (because I new the main seal was blown)
and broke some magnets of the inside of the flywheel .Found the seal was leaking and then found that the motor had seized some time earlier.Because back in those days you couldn't get wiseco O/S pistons for it,(Ithink they only went to .50 oversize) I had to buy a new barrel and flywheel .First ride back on the near new motor and found doing wheelies better than ever ,got caught by the local cops and they threw me into the back of the cop car and I spent 8 hours in JAIL (can you believe that???) went to court following Monday and was fined $500.00 bucks and lost a heap of points on my licence.
Sold the bike to pay for fine and purchased an xr350 rd.Lived happily ever after.
Moral to the story Check the main seal and watch the flywheel when you pull it off and don't pull wheelies in Townsville.

[shortshift]

Yep magnets coming off the inside of the flywheels was a common problem on the PE. It pays to look at them when you remove the flywheel.
I heard it pays to examine them for security if not to fix them before reassembly. I will check mine again soon.

[I had an XR350RE too and gave me some 10 years of happiness and trouble free running. These bikes (and esp the 250RE) started the death of the 2 stroke dirtbike.]

[LWC82PE]

make sure you use the correct puller as well. some people try all sorts of things like bashing it with a mallet, which does it no good.

you can by the pullers from various ebay shops and i thin www.repairmanual.com has them. Your local bike shop who sells MCS stuff can also sell you one. Or just get some think plate steel and drill 3 holes to line up with the 6mm threads on the flywheel and then drill and tap a center hole for a large bolt that will press on the end of the crank

[mposs]

Check for cracks/leaks in the rubber fuel inlet manifold between the carb and the barrell.

[Bamford#69]

Hi
if you have a 2 stroke that runs erratic , usually just after you kickstart it , when it is both hot and worn not only is it "dieseling" I'll bet it is also running backwards as well , it doesn't require throttle , spark or ignition  it is actually using the oilly exhaust system for fuel , and the hot cylinder and the hot carbon deposits in the combustion chamber to cause a "glow plug" effect to make it run, ( backwards or frontwards) the motor will stop if you select a gear and stall it , hard to do as the motor wont respond to  the throttle, , or by putting your hand over the exhaust to stop the oxygen being sucked in through the muffler/exhaust.
If you understand an ignition combustion engine , that is one that uses an ignition system that provides a spark to ignite the  flamable fuel /air mixture , and then the compression combustion motor that uses heat via high compression ie; a diesel engine, to combust the combustable fuel/ air mixture,it will make diagnosis easier.

[frostype400]

if you have problems with a pe400 im always after them they are my favourite bike i have two of them definetley can be hard to kick over so if anyone ever wants to get rid of one in project or complete runner form let me know very fun to ride if they arent doing silly things my 400t has sat me up vertical thats the only not fun part about them brakes are pretty much useless sometimes have heard of about alot of them seizing etc etc but never happened to mine anyway except i havent had them from new so it might have happened thanks Michael.

[frostype400]

never heard of that before but dont doubt it being true when youve got a big bore 2 stroke you dont want it behaving erracticly in any way and the logic is there for that to be quite possible i hope it doesnt happen to mine has any one got a good pe400 pipe and muffler i need one to fire one in the shed to see if it does anything out of the ordinary thanks Michael.