engine trouble

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Lately a friend has been having lots of top end engine problems and I cant seem to figure out why. His stock zenoh 26 on mb was running fine suddenly it locked up we removed plug , was clean maybe slightly lean but far from extreme top of piston showed no signs of detonation little bit of carbon starting to build up, but ring stuck . After asking around we determined that our 32:1 mixture maybe the issue so we went to 25:1 . We pulled head on his stadium truck to change head and piston to 28.5 specs and use top end on mb. After removing head we noticed that this ring was on its way out, looking at this plug its clean ( no white or tan coloration no black carbon buildup) we replaced the 2nd head with reed ported head ,thinking that its still the same fuel problem. Both of these engines have only had approx 3-4 tanks run thru. After break in he ran engine hard and behold another seized piston ring after pulling this plug this plug shows sign of being rich(slightly oily black carbon ) anyone else having this type problems? The really weird thing is during this time I've been running my race runner and rally car with no problems using fuel from same can I don't run as hard or as long but this appears unusual.
 
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re engine trouble

The oil mixture was changed from 32:1 to 20:1 and the oil was changed to Klotz synthetic racing oil
 

Timmahh

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#3
plenty are running from 25:1 to 40:1 without big worries.
it only takes a short run too lean to lean-sieze these motors.

they will not take a lean run like a nitro will. needle adjustments must be in Small incriments. 1/18th to 1/12th turn MAX. checking plug color as you move up thru the RPM Rage making sure your rich as you move up the rpm range and fine tune from there.

once porperly tuned you hsould be ok. but beign just a bit too lean is a killer.

i run my Baja at 25:1 and will be moving to Klotz STP at 32:1, which i currently run in my Bergonzonis without issus. the BOSS motor is actually stated to be run at 50:1 via the manufacturer.
 
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Shouldn't you be able to read plug after and realize that was the problem? I know that by then its too late but then you would have an answer .When I rode dirt bikes you could look at a plug and if you ran lean and did not notice the plug would tell how rich or lean you were at a glance .At this point the engine did not appear to have run lean from what ive seen.
 

Timmahh

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#8
Dman, i hear what your saying. I think the biggest Differance, between these motors and say the dirtbike motor is Cylinder Plating. These don't use Naskil as a plating from what i understand. plus its no where near as thick as a bike cylinder. so it tends to "give up" easier.

the trick on reading the plug, checking plug color for those wondering what "reading the Plug" means, it as soon as you change the RPM range, your plug will change colors with the different RPM. so you could of been ok at idle and great at the top rpm range with the tuning, but the mids may of been in the "lean" area, and you wouldnt know if you never checked the plug color at the midrange RPM.

say the motor Lean Siezed at wot and you were on a long wot run when it siezed, then the plug should be light tan/grey in color as you would expect.

but say the sieze happened at the beggining of the middle RPM Range, and you were running below that rpm range for 15 or 20 seconds. and then wotted it, and it went lean and siezed with in a couple seconds.
in a situation like this the plug may look a nice medium brown color, as you just come off a long low rpm run, where the tuning was fine. when you wotted it, it siezed up the beggining of the rpm rise, but the runtime at that higher RPM was so short there wasnt enough time to make the plug LOOk lean.

it only takes a few seconds say 5, or start to change the plug colors. if you siezed before that, the plug color could be off. see what im saying?
 

Timmahh

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#10
damn it was running so good
That is Useally a Tell Tale sign.


THE MOTOR WAS RUNNING BETTER THAN IT EVER DID BEFORE!!!! I don't KNOW WHY IT SIEZED!!! lol

Famous last words.

something to think about. if it was nice and warm out, say in the 70s when you last ran, and the day it siezed it was say 40 out, that 30* temp change would of made the air cold enough to get very dense, comparted to 70*, and would of made a 70* tune turn lean at 40*

T
 
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