detonation?

[brentR]

how can one tell if they are experiencing deto.
ive been recently having a problem with my plug tops loosening. just yesterday i found one of my plugs to have backed out
and on idle i can hear almost a 'ping' that varies with throttle
plugs read fine

setup;
83mm ported
35cc domes 185psi (run 91 oct minimum)
single 46mm 145H 117.5L, 2.5/95G, 1.5L 1.25H

 

[Mouthfulloflake]

pull the head and look at the tops of the pistons.

Ive read more than once where plugs working loose was a symptom that eventually became peppered pistons.

 

[brentR]

what would be the cause of deto ?

 

[Mouthfulloflake]

heat.

either from exhuast restriction, lack of cooling, lean mixture,or advanced timing, or any combination of those things.

185 is the brink of 91 octane right?

 

[Mouthfulloflake]

I run a 120 lo, 145 high 44mm carb at 185lbs per hole, with advanced timing, stock ports, and 81mm bore.

im flowing less air than you, with more fuel, and more timing, just for comparison.

 

[brentR]

im running dual cooling and ive been watching my water temps I think the pipe is running a tad cold IMO. I do have advanced timing, max 3mm CCW. the jetting was recommended by LPW so i have faith in it.
i was starting to think 91 might be the culprit im going to try a tank of 94 and see what happens.

 

[Mouthfulloflake]

I would run a larger pilot, and stick the timing to stock if I had any symptoms like that going on to be honest.

and I like to be on the brink too.

I ran a 120 pilot with a 53mm carb....

Or of course, run 93/94 and dont hold it WOT

 

[brentR]

Ive only done a few WOT runs for short periods but not all that often. Would that still cause problems off idle?

Ill try a tank of 94 before I start tearing into it.

When I pull the head what signs am I looking for?

 

[Mouthfulloflake]

if you have a domed - edit meant to say O ringed -head, its no problem to yank it and inspect.
I would before I ran it again.

and seriously, my junk is apt to blow too!
rattling the plugs out woudl scare me though.

look at the piston wash AND for pitting or erosion of the piston itself

 

[brentR]

it was only one plug tho if that makes a difference.
yeah its a riva girdled

if theres deto, what does the wash look like?

 

[#ZERO]

Replace the spark plugs and torque them to 22 ft lbs and see if they come loose.

The OEM spec of 14 ft lbs is for the short reach plugs.

 

[brentR]

pulled the head
front jug is wet from a little oil I put in when i did compression test
front jug also looks like some deto, could that be from the plug backing out?
domes look good to me, no pitting
rear jug looks like its burning well?

 

[Mouthfulloflake]

I cant tell from those pics..

#0 is far more qualified than I to help you diagnose it!

 

[#ZERO]

It looks fine from your pictures, just wipe your parts off with some carb clean and through it back together with a new zinc anode.

 

[Watcon]

Spark Plugs

It's difficult to make a 100% evaluation, but spark plugs loosening are generally caused by detonation in the mid range.. If you have the timing advanced 3mm with an OEM cdi, you might be on the edge already. This depends upon the impeller pitch, stinger diameter, etc.. If you have an aftermarket CDI such as MSD, most have even more timing in the middle of the curve.. You could test a few things by blending some higher octane fuel to reach approx 98 Octane, and/or you might try a larger nozzle / or smaller impeller to lighten the load??

Randy

 

[brentR]

im running a 13/16 3mm cutback with stock dia nozzle. i was lookin to having it bored over
its a stock CDI, planning to goto MSD

 

[dajnglst]

Do the canadians have to use ethanol blended fuels also ?

I question jetting with new pump gas. Have seen some weird stuff floating around in carsb I have rebuilt recently.

There is water and what looks to be silicone ? does not bond together when moved around.

Three parts density in some cases.

What the hell blends the ethanol to bond with gasoline?

I would just suspect the ethanol fuels are absorbing more moisture and forcing leaner jetting to make throttle response better.

Any opinions?

Is there anyone selling det counters for PWC's ?

 

[dajnglst]

Anyone selling det counters for PWC's ?

Could probably just rig one up from GP bike, but wondered if someone had water resistant model available.

?????

 

[Superjet3]

I was having issues with deto loosening my plugs but I was running 225psi on pump gas (93) and an enhancer. Over the winter I had Chuck from team scream machine me a new set of domes and my compression is at 200psi(Front) and 195psi rear. I have not had a problem since. I would back your timing down a bit. The stock CDI does not retard the timing at higher rpms.