Raise From the Grave 2: Carb Boogaloo

[bamarama]

Well after some off time due to holidays, heavy work load, and other general crappiness, I am ready to try and get my bike running again. As it stood, I had gotten everything back together and had synced the carbs (the merc levels would be equal at idle, a little throttle unbalanced them, is this a problem?). I went for a ride but it was real laggy. I spit on the exhaust and found that 1 and 3 were hot, but 2 and 4 were cold (each pair had one hot one cold). And that's where I left it. So........

Is it possible to seemingly sync the carbs without getting combustion on all 4? Maybe this is why throttling sent the mercury levels haywire...

I know I've got a spark on all 4 as I checked all the plugs and wires individually.

Mainly I'm trying to determine if I wasn't firing from the very beginning and just thought I was when I falsly synced the carbs or if even though I'm getting a spark it's too weak or something else.

Any ideas why I might not be firing on opposite pairs? Some sort of common cause failure instead of stuck carbs or something? I'm guessing I need to go ahead and order the carb rebuild pieces like I was about to back in October and get to work huh?

Thanks for the advice yall....I'm nearing my 1 year anniversary of the pizza guy incident, so I'd like to get this thing running by then.

bama

[md86]

You checked out that coil wiring diagram thingy a while back , right ? I THOUGHT that was you anyway ...... simplest explanation I got for the odd non-firing thing you got going on .

[bamarama]

Yeah, I'm pretty sure I checked it and made sure I had the right wires goint to the right plugs. I'll double check this weekend though, maybe even see if sitting there for 2 months magically made things work again (please Jeebus please!)

[steves]

Bad coils? Compression check?

[bamarama]

Well I plugged a spark plug into each coil wire one at a time and saw a spark on all 4 coils. How do I test for bad compression?

[steves]

http://www.katriders.com/forums/viewtopic.php?t=24172&highlight=compression+test

[bamarama]

Thanks steves, I think I'll try and check out every possible thing before I even attempt that.

Is there a way to test for a sticking carb valves or a plugged carb before rebuilding them (I tore them down and cleaned them before throwing them back on the bike)?

Also, is there some quantitative way to test for spark strength to see if my spark is too weak?

[steves]

Thanks steves, I think I'll try and check out every possible thing before I even attempt that.

Is there a way to test for a sticking carb valves or a plugged carb before rebuilding them (I tore them down and cleaned them before throwing them back on the bike)?

Also, is there some quantitative way to test for spark strength to see if my spark is too weak?

Found this http://www.dansmc.com/electricaltesting.htm

Do you have a service manual? It should have the correct numbers in there, and maybe a way to test.

[bamarama]

Ok, well i did some work today and this is what I found:

1. I had the two wires from the right coil mixed up, so I got that corrected....however:

2. I couldn't get the bike to start feeding gas down into the carbs.

3. I pulled the plugs and all except number 3 were wet (prob have to pull the carbs and break 3 down to see what the deal with that is), but I still figured with one not getting gas the engine would still fire up.

4. I started testing for spark. I had a weak spark at 1 and no perceivable spark at 2,3, and 4. This could have been because my battery was low (~12V with bike on, couldn't check while I was cranking).

5. I'm going to let the batter charge up completely and see if I can get it to fire up without 3. If that works I'll pull the carbs and deal with 3.


So....If it's not a weak battery issue, it must be the coils themselves, but since I could see a spark at 1 I figured i'd be able to see one at 2 as well. Any thoughts?

bama

[StevieB]

Well I plugged a spark plug into each coil wire one at a time and saw a spark on all 4 coils. How do I test for bad compression?

First, plugs will fire much more easily at atmospheric pressure (outside of the engine) than at combustion chamber pressure (screwed into plug hole.) Therefore, a simple check of plugging a spark plug into the cable and watching for spark really only tells you that spark EXIST, not the quality of it. Spark plug testers, basically a dummy spark plug with a clamp on it, are calibrated to compensate for that. Also, a normal spark plug test at 1 bar (1 atmosphere, or about 14.7 psi) can damage electronic ignition components- doesn't happen often, but much cheaper to buy the proper tester, and saves you loads of head-scratching diagnostic time, that ONE time it does some damage.

Compression test is a bit involved, and anyway, usually a tester includes the basics. Be sure you get a compression tester that has the right adapter for motorcycle plugs, or you will be making a run back to the auto parts house, or worse.

And yes, coil voltage will be low if battery voltage is low. All a coil can do is increase the existing voltage a certain multiplier. If you start with 14 volts, you may end up with 20,000, but if you start with 1 volt, you may only get 20,000 / 14, or about 1400 volts. Extreme example, but it illustrates the point.

You need, at the very least, a fairly sophisticated volt meter (or a occilliscope) to quantatively test coil voltage, but it can be done, and the meter come in handy many other times, too. About $50 or more, as I recall.

[md86]

The tester I got from JC Whitney has several adapters , and one fit the Katana . But , even if compression is low , as long as it ain't REALLY freakin low , it'll still run . Mine was at about 110 , which is QUITE low , but still ran ok .

[bamarama]

Okay, well I was running (good compression?) 2 months ago, I just had the 2 wires switched up apparently. So I'm gonna let my battery charge back up and try it again tomorrow morning. If it doesn't crank I guess I'll invest in a spark plug and a compression tester to try and figure out what's going on. I'm bout ready to part this goddamn bike out, eat my losses, and buy a new bike.

[md86]

Well , the wiring I'd BET is the major part of the problem . Yeah , charge the battery and try again . With the one carb running cold apparently , I'd assume there's some gunk in the pilot circuit most likely .

[marky522]

To test your coil any decent volt meter will work, you need to make sure you have a fully charged battery and when you crank the bike your voltage doesnt drop below 10.5V (car spec, unsure if applicable to bike) then you need to find your resistance specs from the manual and check your primary and secondary resistances in your coil. To check coil output you would use this http://us.st11.yimg.com/us.st.yimg.c...1931_229181790 find out what your coil output should be, and use 3/4 of that setting on the tool and see if you have a good spark, if you have proper voltage and ground to the coil, and you arent producing enough voltage the coil is bad...

Mark