detonation

[fyrman41]

Hey guys just join maybe an hour ago haha. So ive been searching through threads and various other places but can quite answer my problem. I have a 79 special with k&n oem style filters, pamco ingition with e advancer, and commando mufflers. The bike seems to be detonation under load between 2k and 3k rpms, it sounds like keys jingling. It's only heard when the bike is warmed up, and its less prevalent but sometimes still there on cool nights. I had the timing set very well with a timing light and it doesn't over advance, I even went from a #27.5 stock pilot jet to a #30, along with going from a #135 main jet up to a #142.5 and I havent lowered the needles. The spark plugs very light tan insulator nose and the left plug seems to have some small speckles on it, which I heard is a sign of detonation. Cam chain has been tighted and valve tappeds adjusted. I bought the pamco with e advancer figuring that might fix it, cleaned the carbs, check for air leakes ect. Im at wit's end. Bike runs great otber than that. Could I still be too lean?

Posted via Mobile

 

[TwoManyXS1Bs]

Welcome to the forum, fyrman41. Aside from detonation, 3 things that are mechanical problems can cause this symptom at that rpm.

Loose/worn crank and piston components.
Loose/worn camchain and tensioner components.
Pitted/cracked/worn valve tips and adjusters.

Those are best diagnosed with a mechanic's stethoscope, as in this thread:

http://www.xs650.com/forum/showthread.php?t=36068

Of course, if it is indeed a mechanical problem, a complete engine overhaul would be necessary...

 

[fyrman41]

The bike only has 15k on it. The pinging noise started after i did a cam tensioner, valve tappet, and timing adjustement one night. I had the old point ignition on it back the. I thought it was the centrifugal advance not working properly. I was having alot of trouble with it not advancing right. LOTS of trial and error with springs and advance rod servicing. It still does it with the electronic ignition, and ONLY under load below 3000 rpm and warmed up. Also super gasoline seems to reduce the noise if not cure it. I also retarded the timing a few degrees and havent heard the noise yet, but of course there's a bit of performance loss. I'm currently running mid grade 89 in the tank. The cam chain and guides do need replacing since when I changed the oil last there was plastic and metal bits all over in the oil, and this was after all the tighening and adjustments. I've done alot of studying of 91 reasearch octane that it calls for on the side cover back in the 70s, and most every answer says it's the same as regular grade 87 today. Its just what, and when this sound is that's got me worried. All I want is too keep the engine safe, I'm 21 and can't afford much of an engine rebuild lol

 

[fyrman41]

And engine stethoscope test does sou ds like a good idea, at least it should rule out possibilities.

 

[peanut]

if you have speckles of aluminium on the spark plug then yes you have detonation in that cylinder. jangling keys is a very good discription
Basically you have a hot spot forming in your cylinder head that is pre-igniting your fuel air mix before the spark from the spark plug

You should inspect the plug carefully with a magnifying glass but if you think you have evidence of detonation you should stop using the bike until you find the source and correct it or you are in danger of losing a piston .

The fact that it is happening only in one cylinder suggests that the timing is not the culpret so it would seem that your fuel mixture in that cylinder is too lean and you should notice a distinct difference in temperature between the exhausts with the detonating cylinder being much hotter.

Test that you have sufficient flow from the fuel tank and check the float very carefully in the effected carb looking for sticking float, filled float and sticking needle jet etc . Check the float height (see carb setting up in tech section )
Check that the carbs are in sync and the butterfly valves are opening in sync.

 

[Tomterrific]

Start using the highest octane you can get at the pump. Twenty cents could save your pistons.

Tom

 

[5twins]

I tried regular grade gas in every bike I ever owned. They all pinged with it. I've come to the realization and conclusion that any/all/every bike needs high test.

 

[fyrman41]

I can get 91 ethanol free near my house now that the general store just switched gas brands to Pit Stop. Cheap insurance for my bike regardless. Ill definitely check out the carb setup section, and narrow down as much as i can. The left plug does seem a little bit leaner than the right. It doesn't really have any gray or shiney particals on the insulator noses. They both have tiny brown specs on the noses, the left has a bit more particals and coarser than the right. Not sure if thats detonation or not.

 

[fyrman41]

Makes alot of sense 5twins, likely it'll ping somewhat anyway on low grades even when i work the kinks out. High test is definitely what I'll stick to. Alot friendlier to these little motors.

 

[peanut]

I can get 91 ethanol free near my house now that the general store just switched gas brands to Pit Stop. Cheap insurance for my bike regardless. Ill definitely check out the carb setup section, and narrow down as much as i can. The left plug does seem a little bit leaner than the right. It doesn't really have any gray or shiney particals on the insulator noses. They both have tiny brown specs on the noses, the left has a bit more particals and coarser than the right. Not sure if thats detonation or not.

yes it does sound like detonation from what you have described . Black specs are also common.
Why don't you google detonation in motorcycles and have a read up

Your problem is not fuel octane because combustion in the other cylinder is fine or so you say . Your problem sounds like it is confined to the one cylinder from what you have described

 

[jd750ace]

I agree with peanut. A single side detonation has zero to do with fuel at it's heart. I have 3 twin cylinders: a parallel, a V, and an L, and all of them run just fine in 100 degree weather on 87 octane. If I run the Road Star 2-up to the hills and it's 95 and above, I will go to 89. No reason to need high octane in a low compression motor other than it's exceptionally dirty in the top end, not tuned right, or it's under a very high load.
$0.02

 

[fyrman41]

The 2 plugs look the same to the naked eye both the same light tan color no obvious destruction going on. But its when you look at then close up. They look a little gritty with left being a tiny bit more than the right as stated before. I might need to tweak the left carb a tiny bit more, as it was dominating over the right carb a tad before i synced them. It still might be a hair dominant. . The floats work good and seem to be within specs. The carbs are clean the timing doesnt over advance. But after alot of reading on detonation and plug reading im thinking i might be a little lean in the mid to upper ranges? The ground straps are grey like they get a bit hotter than they should. Im already 3 sizes up from stick #135 mains, should I try one more size up? Or even try rasing the needle up a notch? You'd think 3 sizes up from stock mains would be plenty for only having K&N filters and commando mufflers with stock pipes.

Posted via Mobile

 

[XSLeo]

Have you read www.amckayltd.com/carbguide.pdf ? This is the carb guide, it has a section on tuning. It may help.
Leo

 

[fyrman41]

I attached a pic of the spark plugs. The right and left plug are in order. Hopfully its helpful. Leo thanks I read alot from the tuning guide it seems to point me in the direction that I'm kinda lean. I'm gunna try upping to a 145 main and see what that does and go from there.

Posted via Mobile

 

[peanut]

well there is no doubt about your engine running a bit lean ...it is

As regards detonation well I can see very little evidence but then the plugs are obviously clean and look relatively new so its hard to tell even though your images are excellent.

I don't think you should up your jets any more . if you need to increase your jets 3-4x then something is wrong somewhere else. You may be compensating for the problem without finding the source

Don't forget there are two parts to a fuel mixture and if you are getting too much air then that will cause a lean mixture despite your jetting and settings being spot on .

I don't mean to sound critical but you need to be utterley meticulous with this .

My suggestion would be to start from scratch and double check everything in sequence carefully . If you are certain that the timing is correct then check carefully around the carb stacks, whilst the engine is idling, for air leaks . If you remove the carbs then resurface the stub faces flat and apply some liquid gasket to both sides of the stub gaskets . Don't over-tighten them or they will distort and leak.

 

[peanut]

I agree with peanut. A single side detonation has zero to do with fuel at it's heart. I have 3 twin cylinders: a parallel, a V, and an L, and all of them run just fine in 100 degree weather on 87 octane. If I run the Road Star 2-up to the hills and it's 95 and above, I will go to 89. No reason to need high octane in a low compression motor other than it's exceptionally dirty in the top end, not tuned right, or it's under a very high load.
$0.02

JD I just noticed that you have the same bike and setup as fyrman .

Do you know what jets you are using off hand ?

 

[fyrman41]

well there is no doubt about your engine running a bit lean ...it is

As regards detonation well I can see very little evidence but then the plugs are obviously clean and look relatively new so its hard to tell even though your images are excellent.

I don't think you should up your jets any more . if you need to increase your jets 3-4x then something is wrong somewhere else. You may be compensating for the problem without finding the source

Don't forget there are two parts to a fuel mixture and if you are getting too much air then that will cause a lean mixture despite your jetting and settings being spot on .

I don't mean to sound critical but you need to be utterley meticulous with this .

My suggestion would be to start from scratch and double check everything in sequence carefully . If you are certain that the timing is correct then check carefully around the carb stacks, whilst the engine is idling, for air leaks . If you remove the carbs then resurface the stub faces flat and apply some liquid gasket to both sides of the stub gaskets . Don't over-tighten them or they will distort and leak.

Peanut- I thought the same thing that id already be jetted enough to compensate the filters and mufflers. The Pamco and mufflers are recent by a month. I had stock points ignition and stock mufflers. The stock mufflers were rotted and getting little holes in them, and the old points system would make the bike do the occasional fart and puke. But the bike still burns and pings the same now. The plugs have about 3000 miles on them i put them in this spring. I sprayed the boots and and other parts with carb cleaner and the ifle doesn't change one bit. The exhaust doesnt leak anwhere either.

Posted via Mobile