Pretty Nervous...Top End Disassembly

[Aaron]

This story starts with a carb sync. The bike was running jsut fine, but i could tell it needed just a hair of syncing. I pulled the carbs and used the bench sync method as I have no sync tool. The job went easy without problems and I got the carbs back on. Started her up to hear a hage vacuum leak on the left. Removed the carbs, again. Found a giant tear in carb boot number one. Patched up the tear with high temp silicone and J.B. weld. Then i noticed that the spark plug wire for plug two was partially grounding out on the valve cover. Patched the hole in the wire with same high temp silicone for a temporary fix. Ran a compression test while I had the plugs out. Results were:
Cyl 1.- 145
Cyl 2.- 133
Cyl 3.- 125
Cyl 4.- 142
Put it all back together and started it up. Started with little effort and went into idle quickly. However... There was a prominent knocking on the left side of the engine, sounded like number one, but not 100% sure, could be number two. Stopped the engine, pulled the plugs to put a small amount of oil into the cylinders and checked for spark while i had the plugs out. No spark on 1, but fine on the rest. Let the oil soak overnight and tried to start it again. Still knocking. I have just pulled the valve cover to take a peek in there. No obvious damage of any kind, but now im nervous. To me the next logical step is to pull the head and look in the cylinder... but i've never gone that far into an engine that didnt belong on yard equipment. I am confident in my mechanical abilities, but I really dont wanna screw this thing up. I am also doing it in the parking lot of my apartment complex. It is in a covered parking spot, but still not the best environment. Is head removal complicated surgery or not? Any other ways I can troubleshoot the knocking? Am I being really stupid and overlooking something obvious and/or important? Please.....Help.

[motoman]

Ever considered maybe the vacuum advance is plugged on the wrong brass nipple? If plugged on nipple on intake manifold that vacuum can will hammer hard at idle.....JAT......before you tear it apart for no reason

[bikerphil]

You may hear a knock if the carbs aren't synced properly. BTDT. If it didn't knock before you did the bench sync, this may be your problem. Do check that vacuum advance is connected to #2 carb body and not carb boot as mentioned. You can build a vacuum sync tool for cheap, lots of info if you search the archives.

[Aaron]

Not the vacuum advance.

[Aaron]

I had planned on building a sync tool in the near future, just havent done it yet. How out of sync would the carbs have to be to cause a knocking? Especially a somewhat severe one like I heard. I used the Pre-Syncing Carbs method posted by Bill Kingson on my freshly cleaned carbs. I could only begin to guess at the previous settings of the carbs, but i would much rather it be carbs than engine knocking

[BA80]

I had planned on building a sync tool in the near future, just havent done it yet. How out of sync would the carbs have to be to cause a knocking? Especially a somewhat severe one like I heard. I used the Pre-Syncing Carbs method posted by Bill Kingson on my freshly cleaned carbs. I could only begin to guess at the previous settings of the carbs, but i would much rather it be carbs than engine knocking

Probably is. If it wasn't missing or knocking before, the logical assumption is it has SOMETHING to do with what you did.

Don't tear the top end off until you check your work.

[bikerphil]

I had planned on building a sync tool in the near future, just havent done it yet. How out of sync would the carbs have to be to cause a knocking? Especially a somewhat severe one like I heard. I used the Pre-Syncing Carbs method posted by Bill Kingson on my freshly cleaned carbs. I could only begin to guess at the previous settings of the carbs, but i would much rather it be carbs than engine knocking

They don't have to be out much. Sync it properly before thinking of tearing the motor down looking for bad bearings. I had this happen to me when I installed a used motor in my 79F. Once properly synced, the knock was gone. A bench sync's purpose is to get the carbs close enough so the motor will run and be properly vacuum synced. You will be suprised how little of a turn of the sync screw(s) will change things. Good luck!

[Aaron]

Alright... Never thought i'd be glad to have to tear into the carbs again. I much prefer this direction to going into the motor. I'm losing light tonight, but I will put together a shopping list for a homemade sync tool and get after it tommorow after work. Thanks for the suggestions fellas.

[11Rider]

I would think between the carbs not being synched and no spark to #1 cylinder you could get a knocking sound. Also, correct me if I'm wrong but usually a knock (if it's a mechanical problem) would come from the lower end. Top end could give a tick, but I don't think a knock is that common for a top end.

[TADracer]

Get your baseline back

I have said this before when reading a thread like this. Something you have done has caused you to lose your baseline tune up. It is most probable that your trouble is a combination of carb and ignition, not anything mechanical. These motors are fairly bullet proof.

If you had a plug shorting out to the head then you need to go through your ignition and check for condition of your wires and fix that problem. Since you had spark on all but #1 your coils are probably OK. Check your wires and that you have the correct plug heat range and check your timing after you get started up.

When you bench synced your carbs you threw away any tune up you had on them. Go back to all factory settings and then after you get her started, sync with a correct tool and adjust your idle mixtures and idle RPM per specs. If you have a split on one of your boots, replace it. The boots can run perfectly will with a bunch of cracks in them but a split in the wrong place (like at the carb spigot) is a problem waiting to happen and may throw all your tune up efforts off.

Get a manual, if you dont have one and you will find the correct procedures and correct factory settings for everything. I would not worry about those compression numbers since that was probably done with a cold motor. Needs to be operating temp for this and done with throttle open wide.

Thats where I would start and yes, this is from experience as I have gotten 'lost' on the tune up as I think most of us have at one time or another.

Good luck to you and have fun.

[James England]

There's no way a bearing will go suddenly like that. Your bike worked OK and, as said above, your baseline was OK. You do something and you get a knock. 99.9% it's something to do with what you just did. As a more obvious example, let's say your bike works fine, you pull all your HT caps off and forget to put one of the middle ones back on. You start the bike and it runs really rough and knocks. Is the next step then to say "Oh it must be the bearings. I'll take the engine out of the frame and check the mains". Obviously not. Just backtrack and triple-check what you just did and make sure you did it properly. Then you find you forgot to put the plug cap on. You replace it and....all is fine.

This has been mentioned before in a recent threadr re carbs. A shotgun approach to problems, or improvements and modifications, makes it very hard to know what it is that's gone wrong. If I were to replace my HT leads, HT caps and plugs, I'd probably put the plugs in first with the old HT stuff, fire up and make sure the plugs worked. Then the caps and leads. I'm always very wary of doing too much at once without verifying that the last thing done works OK. That way, you gradually move the bar up, as it were.

[DGXSER]

pulled the plugs to put a small amount of oil into the cylinders and checked for spark while i had the plugs out. No spark on 1, but fine on the rest.

If you have one cylinder not firing, it could easily sound like a knock. Figur eout why you have no spark on one cylinder, and you may solve the issue.

[Aaron]

Yeah, you guys are right and i knew it all along. I was going out there with a hammer instead of a microscope. I put it all back together in a better state of mind today to start the troubleshooting process over again. I do have faith that my problem lies in the carbs, but after checking for spark again, I found that 2 and 3 are fine, 1 and 4 are dead. I need to get spark back before I can get into the carbs again. No use tuning two cylinders. The fact that 1 and 4 are out leads me to think that ignition coil died on me, but I hear that these coils are pretty tough. Any other thoughts on that? I am completely green on motorcycle ignition systems, so please bear with my ignorance. Thanks again guys.

[motoman]

so please bear with my ignorance./ Good find there Aaron.......at times info given to diagnose can be confusing and seem a bit vague........so, by the same token bear with our knowledge of trying to diagnose.

[Aaron]

It's a two way street, thats for sure. Forgot to add, the compression test was done at operating temp with no carbs on, so should be pretty darn accurate. And I do have a manual, thanks to BUG. So far I have not made a blind move on this bike, I always read up on here before doing anything.