Engine knocking after carb job

[stilkus]

I am really frustrated, are carbs so difficult to deal with or am I having the I.Q of a house plant ???

Here's my story, my bike was never running as should and recently it backfired so I decided to take the carbs off for the zillionth time
I made sure that carb cleaner would go in every tube in the carb and verified idle screws were set to the right turns by counting the turns out when the pointed end of the screw would show on the inside of the carb.
done a bench sync and another one after the carbs were installed and everything was fine.
also checked the sparks and I am getting sparks on 4 cylinders, later done a long drive after I replaced the spark plugs, bike would not go past 190km/hr and seems to be loosing power at the high end/booster rpm badly.
after the trip I checked the plugs and they all looked normal with no deposits or anything.
I also added GUNK FUEL INJECTOR AND CARB MEDIC to a full gas tank ( the bottle is serves a 21 gallon gas tank, but I wanted an accelerated effect ) < img src=http://images.drillspot.com/pimages/7497/749770_300.jpg > because I live in Egypt and we don't have sea foam.

I also have an exhaust pipe leak on both sides, I don't know if this info would help identifying the cure, but I just thought I would let the experts know it as well.

the bike is a 1992 stock one.

now about the symptoms,
1- no backfires and carb coughing anymore.
2- engine vibrates so bad and I hear a knocking sound near the clutch ( it is different than the clutch basket sound )
3- when I remove spark plug wire from the rear right cylinder ( clutch side, back ) nothing happens and engine doesn't hesitate on idle, but if I do so while driving I feel that there's a great loss of power.

 

[mr.maxx]

3- when I remove spark plug wire from the rear right cylinder ( clutch side, back ) nothing happens and engine doesn't hesitate on idle, but if I do so while driving I feel that there's a great loss of power.

that makes me think you have either a bad plug wire...coil...or any any of the connections involed...may be fubar. check to make shure the plug wire has a good connection into the plug cap....maybe it came a lil loose when you changed out yer plugs....the wire actually scews into the cap. if the wires are old you can snip off 1/4 inch then re-screw it back.

 

[stilkus]

3- when I remove spark plug wire from the rear right cylinder ( clutch side, back ) nothing happens and engine doesn't hesitate on idle, but if I do so while driving I feel that there's a great loss of power.

that makes me think you have either a bad plug wire...coil...or any any of the connections involed...may be fubar. check to make shure the plug wire has a good connection into the plug cap....maybe it came a lil loose when you changed out yer plugs....the wire actually scews into the cap. if the wires are old you can snip off 1/4 inch then re-screw it back.

actually I switched both coils in the back cylinders and the same thing still happened which made rule out the coils. I might need to mention that both rear coils are in bad condition, but I tried them both on the left rear cylinder and they were both making a difference with the idle.

 

[stilkus]

I might need to mention that I took the rear cam cover off and checked for lifter clearances and found out that they were all fine. I don't have problems starting or idling the bike. it is all fine.

 

[one2dmax]

A simple carb sync out will make them knock and almost sound like a bad engine.

 

[stilkus]

A simple carb sync out will make them knock and almost sound like a bad engine.

I synced them on the bench and again on the bike and they were fine. that's what's driving me crazy. could it be something with the right rear carb ? and is it dangerous to drive when the cylinder power is uneven ? also when I flip the handle to full throttle the bike still runs uneven, is this a sign of a bad carb or is it still a carb balance problem ?

 

[[email protected]]

3- when I remove spark plug wire from the rear right cylinder ( clutch side, back ) nothing happens and engine doesn't hesitate on idle, but if I do so while driving I feel that there's a great loss of power.

You should notice some kind of difference in engine tone if the plug wire is removed. Sound like that cylinder is not firing. Based on what you said about switching coils around and it acting the same, it may be possible that there is no fuel getting in there at idle to ignite.

Have you ever checked the header temperature on that cylinder while at idle? If it is a lot cooler than the others, I would not hesitate to remove the carbs for the zillionth and 1 time and then tear into the jet block and check the pilot jets. Its possible to be plugged solid and not get enough fuel at idle but may pick up once the revs rise due to fuel coming thru different circuits in the carb.

 

[ZackDaniels]

When you've checked it all twice and thrice and nothing appears to be the problem start thinking elsewhere.

The bike idles fine but craps under load.
You've checked plugs and coils and spark appears fine.
You've sync'd the carbs and they're even both on and off the bench.

Spark : Looks perfect.
Gas : Looks perfect.

That leaves air.
You haven't mentioned the air filter, box, or lines. Dig into that and be sure a mouse hasn't taken residence or chewed a line. A line/hose leak might explain why it's fine at idle but craps under load because vibration is higher and a leaky hose just gets leakier.

Where is the exhaust leak? Further down the tubes shouldn't make a dramatic difference but right at the header would. If it's leaking out of the header you probably just need new exhaust gaskets which are cheap.

The only thing that doesn't have me convinced it's air at this point is:
Pulling a plug at idle should change the engine sound for sure. You may want to put a glass up to each jug and listen for differences, or if that's a bit inaccurate/low tech get one of these:
http://www.amazon.com/Lisle-52500-M...UTF8&colid=1LHI5CXRODZG&coliid=I1AA3CZD33ZXKQ

You may also wish to get one of these and be double sure your sparks are sparkin.
http://www.amazon.com/Lisle-20610-I...UTF8&colid=1LHI5CXRODZG&coliid=I1U20OZCCUFHYB

The gaps on the plugs are all set the same right? Double check that... in situations like this it almost always ends with a big forehead slap because it was something routine that you didn't think to check because you were hyper-focused on the complicated stuff. I know I've been there at least!

 

[dannymax]

You should notice some kind of difference in engine tone if the plug wire is removed. Sound like that cylinder is not firing. Based on what you said about switching coils around and it acting the same, it may be possible that there is no fuel getting in there at idle to ignite.

Have you ever checked the header temperature on that cylinder while at idle? If it is a lot cooler than the others, I would not hesitate to remove the carbs for the zillionth and 1 time and then tear into the jet block and check the pilot jets. Its possible to be plugged solid and not get enough fuel at idle but may pick up once the revs rise due to fuel coming thru different circuits in the carb.

Think Mike hit it on the head....blowing carb cleaner thru the ports helps but isn't enough....the carbs need to be completely dismantled for a proper cleaning.

 

[ZackDaniels]

Think Mike hit it on the head....blowing carb cleaner thru the ports helps but isn't enough....the carbs need to be completely dismantled for a proper cleaning.

I'm not 100% but if it was a flow problem wouldn't that cause the carbs to fail to sync or at least come quickly out of whack?

 

[stilkus]

I'm not 100% but if it was a flow problem wouldn't that cause the carbs to fail to sync or at least come quickly out of whack?

ZackDaniels, I will follow your advice and check for the pilot jet, I am not sure if there's any special areas which are known to block the pilot's jet stream or is it just the Jet screw ? I really think it has something to do with fuel because I checked the air and electricity and found out nothing to be damaged there . I need to ask you as well if the pilot Jet would affect the engine's power in the booster's zone ? because I can feel the loss of power there the most.

I am really grateful to all of the people helping me out as I use this bike as my daily commuter and I can't live without it for a single day, that explains why I was asking if it's harmful to drive the engine under this condition.

 

[mr.maxx]

unless you totally tore the carbs down....removed jet blocks....etc.....you cant be certain they are clean.

blowing carb cleaner thru the holes aint gonna cut it. usually :biglaugh:

 

[stilkus]

unless you totally tore the carbs down....removed jet blocks....etc.....you cant be certain they are clean.

blowing carb cleaner thru the holes aint gonna cut it. usually :biglaugh:

actually I removed the jet blocks last time I took them apart. I believe I am going to check this certain carb by opening the fuel bowls and taking the jet blocks out and check for the jets there.
I might also need to mention that I noticed one of the rubber plunges in the bottom of one of the jet blocks fit loose. I am not sure in which carb this thing was, but just asking if something like this could cause me a mess ??

I am also wondering about the power loss at high rpm ( booster zone ), could this be related to a lean condition ? I mean do I need to richen the floats ?

I adjust the float's semi circle area with the outer border of the circle marked in the middle of the jet block, isn't that right or do I need to move the floats anywhere else ? I am just asking because I am having a stock carb and is not rejetted whatsoever. Just wanting to double check everything

 

[PATMAX]

When I check out a Max to buy, I spit on my finger and touch each header right at cold start up and listen and feel for the tell tale sizzle. That tells me combustion is happening as it should. In a perfect world, Sean would have a loaner set of stock spec carbs on a "loaner"
program like he does for so many other parts but that is a huge risk/outlay for anyone to risk the carbs never coming back. Maybe longtime forum members could be trusted but I keep harping on people to have a spare rack of carbs on hand to eliminate carburation as their troubles. I understand not everyone can afford to have a spare set of carbs just in case. Maybe one of our carb Gurus can think of a way to make this program available. I feel for you Bro for needing your Max for transportation. Don't give up. It is always encouraging when your bike runs good at certain times but acts up. To me that means there is no catastrophic issues.

 

[mr.maxx]

the rubber plugs in the jet block need to fit tight. so yea that is an issue.

did you test the slide action to see if they all act the same when you press them in and release them? no holes in the carb diaphrams? when you put the carb lids back on did you make shure the springs were properly centered ?

 

[stilkus]

When I check out a Max to buy, I spit on my finger and touch each header right at cold start up and listen and feel for the tell tale sizzle. That tells me combustion is happening as it should. In a perfect world, Sean would have a loaner set of stock spec carbs on a "loaner"
program like he does for so many other parts but that is a huge risk/outlay for anyone to risk the carbs never coming back. Maybe longtime forum members could be trusted but I keep harping on people to have a spare rack of carbs on hand to eliminate carburation as their troubles. I understand not everyone can afford to have a spare set of carbs just in case. Maybe one of our carb Gurus can think of a way to make this program available. I feel for you Bro for needing your Max for transportation. Don't give up. It is always encouraging when your bike runs good at certain times but acts up. To me that means there is no catastrophic issues.

I am never giving up on my max, actually I sold my old kawasaki el250 because I was fed up with repairing the carbs there ( I have been haunted by carb problems all my life ) and then when I got the max, I do appreciate the effort that has been done to build this machine, that's why I never gave up on it till the day. Working with my hands teaches me a lot, but I also need to go to work relaxed to feed the family and the max

I will work on the carbs tomorrow morning and check for the header temp with the water on the finger method and will update the thread.

I am just a little bit worried that this cylinder would have low compression and that's why the motorcycle is behaving so ?? I don't need to undergo major repairs atm.

My engine has 26k miles, never had 2nd ge,lar issue and was ridden on regular basis.

I also need to mention that I always felt that the left side of the engine is doing most of the work as removing any of the spark plugs there would cause serious hesitation to the engine, compared to the right side, I would get slight hesitation with the front cylinder and no difference at all with the rear one.

 

[stilkus]

the rubber plugs in the jet block need to fit tight. so yea that is an issue.

did you test the slide action to see if they all act the same when you press them in and release them? no holes in the carb diaphrams? when you put the carb lids back on did you make shure the springs were properly centered ?

well, the diaphragms were replaced a year ago and they're looking and fitting good. I did the latest carb job in the house and I was really careful because I didn't want to repeat it again, but seems like it's a never ending job

I need to mention that I found some hard stuff stuck to the a/f screw tip but I cleaned it and spayed carb cleaner from the top jet and it sprayed out of the idle hole and the other jet under the diaphragm so I guess I don't have blocked pathways.

 

[dannymax]

Regarding float level....you can't depend on the little circles cast in the carb body, they aren't dependable. Use them as a rough setting but always do a wet level verification.

 

[m-cman]

I don't know what kind of carb cleaner you used or where you squirted it but some of them will dissolve rubber and other non metal parts in the carbs. (Diaphragm's, etc). I ruined one of those small enrichener diaphragms when carb cleaner was accidentally introduced by spraying the cleaner through some of the orifices. Some of the dissolved rubber blocked some of the small jets and passageways also. :bang head:

 

[stilkus]

People, Good News The bike is running even better than before, my Biggest complain right now the bike is a Disaster to control, with the tail swinging around every time I pull the throttle back

I wouldn't have done it without the help of the people in this great forum, I ride with confidence knowing that every problem has a solution here on this forum.


here is what I found, in the jet block of that cylinder there is a big needle with holes on it's sides and a small one with a tiny tiny hole at the end, well that tiny hole was blocked. I cleared it up and started, but nothing changed.

I suspected a weak spark and that's what was happening the whole time, the spark plug wire wasn't completely fit inside the coil end, it was 0.5 cm inside that's why I got a spark but it was weak, I pushed that wire fully inside and retained it so that it never goes off again and started the bike and felt the difference
The best part is that I don't hear engine knocking anymore, DAMN I was scared to death knowing it might have been a bad bearing or something.

Well, that was how I got it back running, I thought I would share the results also that was a stupid problem but I totally overlooked the spark strength before :S