Checking coils OFF of the bike

[bighamms]

Bike: 1981 gs450s
Issue: bike turns over easily, but doesn't fire up... Almost has if there's no spark to create combustion.

Ok, so my bike has yet to run. I was pretty sure that I had some bad coils (i deduced this by hitting the start button while have 1 of the plugs out of the plug hole, and grounded on the engine .....no spark to either plug when I tested). so I bought a new set of coils off or ebay. the ad said that they were working and came off of an '89 gs500. The coils have the exact same setup as my original (single tower, 3 ohms output).

So how do I test the coils outside of the bike to eliminate faulty coils. I have tested the plugs on my power washer, and they get plenty of spark. I'm starting to think that the issues is occurring before the coils, but not sure where to check.

Help.

[chuckycheese]

Coils

Right off hand, I'd guess you've got an extra set of coils. First of all, take a look at the recent post authored by jpmanguy.

[bighamms]

@chucky....Yes, I now own two sets of coils. I have the set that is original to the bike, and a newer set that came off a gs500.

After submitting my post, I went back to the garage, pulled each plug, grounded it on the motor and cranked it again. this time, both plugs got plenty of spark. I reinstalled them in the bike and hit start... Still would NOT fire up. it turns over all day long, but won't actually fire up.

[chuckycheese]

Compression

Have you ever checked the compression? If not, you really should. My first guess would be that it's a fuel issue since you've got a good, robust spark. You can check it a couple of different ways. You can remove the gas line at the petcock, connect an auxiliary hose and run it out away from the engine (so you don't get gas all over the place) and crank your starter.

Since it will create a vacuum on the petcock, gas should flow from the hose. Also, you can do the same thing except just put it on 'prime' position and gas should flow out of it without cranking it over. I'd suggest you do both....and see what you get. Petcock problems are really common on these bikes.

[bighamms]

@ chucky... i don't have any sophisticated compression tools, but another member told me to take out one of the plugs and place my finger over the plug hole when starting the bike. I've never done this before and was a bit unprepared as the bike damn near sucked my finger down the hole. I reported this back to the forum and the consensus was that I have really good compression.

should the plugs be wet/moist when I pull them out? currently, they are dry. It's possible that I'm just not getting fuel into the motor hence the spark from the plug is mute... I rebuilt the petcock about a month ago.

I'm just not sure how to proceed at this point.

[chuckycheese]

Ok

OK...it sounds like your compression is probably just fine. Do you know, for sure, that your petcock is working properly? If you've got compression, spark and gas....it should fire.

Also, you've never seen the bike run. If you haven't been through the carbs, thoroughly, you have no idea what it's like in there. Believe me, it can be astonishing!!

[bighamms]

@chucky... i don't know for sure... to test the petcock, I have done the following:
1. tried starting the bike several times and then pulled float bowl screw and there is always fuel in the bowl
2. have taken tank off several times and there's always fuel in the fuel line
3. with tank off of bike, and vacuum line still attached to the petcock, I've given several quick sucks on the vacuum line and fuel has shot out of the petcock
4. my petcock doesn't have a PRIME position, but I've tried to start the bike in ON, RES position with & without full and partial choke.

It seems as if I am missing something so simple, yet I just don't see it. Unfortunately, I have yet to find anybody in the st. louis area to take a look at it. I have called a few bike shops, but I get the sense that when I tell them its and '81, the conversation becomes increasing more costly...

[chuckycheese]

Ok

OK....#3 would lead me to believe gas is flowing. (The others aren't nearly as compelling).

So, what about the condition of the carbs? Have you taken a look in there? "Just because you've got carburetors doesn't mean they're "carburetin"!!!!!"
--Chuckycheese--

[bighamms]

completely rebuilt the carbs about two weeks again. Tore them down, soaked all parts/pieces in chem-dip for 24 hrs, order new o-rings from Robert Barr, new mains/pilot from Jetsrus.com and new gasket from ebay. I think the carbs are solid. I had read that these bikes really prefer the airbox on the bike (which it is). So i also used weather stripping where possible to seal up any leaky spots. The only thing I haven't done to the airbox is mess with the filter (ie. oiling it). Actually, I'm not really sure it's even the correct filter. Looks a lot like the filter in my shopvac (black and somewhat porous) . but haven't been able to find a pic of the original filter online, so this could very well be the correct setup. I did give the interior of the airbox a good cleaning.

[chuckycheese]

Darn it

Well, I'm really sorry but I'm about stumped. It sounds as though you did a nice job on the carbs, you've got gas flowing, you've got compression and decent plugs.....I don't know what to suggest.

The only other things I can think of are:

1. Catastrophic problem in carb reassembly where they were put back together incorrectly.
2. Electrical problem such as the signal generator, transistor unit, or coils.

If you have a multimeter and a shop manual, the tests for the above mentioned possibilities aren't hard. I hope you can figure it out and that someone with better ideas will offer you some assistance. Let us know what you find...it will be helpful to others. (I hope you get it figured out soon!)

[bighamms]

@chucky...thanks man. I will definitely keep the forum posted. I am pretty confident that it is something simple that I'm overlooking. Just need to get a fresh set of eyes and ears on this thing.

[chuckycheese]

Yeah!!

@chucky...thanks man. I will definitely keep the forum posted. I am pretty confident that it is something simple that I'm overlooking. Just need to get a fresh set of eyes and ears on this thing.

I feel badly for you because I can totally understand your frustration. I feel sure your problem will be fairly easily solved and that you'll soon be flying down the road with a smile on your face.

I'm still hopeful that someone will come along with some better ideas. (By the way, over the years I've had some problems that turned out to be incredibly simple.)

[tas850g]

Are the wires from the harness attached to the correct lead on the primary side? I attached the (+) and (-) wires in reverse when i reinstalled my coils. I still had spark and fuel but it obviously would not run b/c of timing.

[bighamms]

@ tas850... that I do not know. i took care to label the old coils and connections prior to unhooking them with the assuming that they were hooked up correctly. I suspect that they were as the original coils had the original wires with one end soldered to the coil and covered with some sort of hardened material and the other end crimped into a terminal coupler. It looks like its all original.

Something that i didn't mention before is that on occasion is will turn over and then fire briefly, but not long enough to gas it or keep it going. But since owning the bike, that has only happened a hand full of times in the last 2+ months.

I asked earlier if the plugs should be moist when I pull them out. Mine are dry. It just seems like the fuel and spark are not playing well together and therefore no combustion. What if I tried the following:
1. pour a bit of gas into the spark plug hole or
2. pour a bit of seafoam into the spark plug hole or
3. get full coverage insurance on the bike, drop it off down by the river, collect on the insurance and buy something that runs

Just throwing out options....

[superdave]

I asked earlier if the plugs should be moist when I pull them out. Mine are dry. It just seems like the fuel and spark are not playing well together and therefore no combustion. What if I tried the following:
1. pour a bit of gas into the spark plug hole or
2. pour a bit of seafoam into the spark plug hole or
3. get full coverage insurance on the bike, drop it off down by the river, collect on the insurance and buy something that runs

Just throwing out options....

I like number 3 personally...

But failing that, have you tried running it off starting fluid? Obviously you don't want to use it as a rule, but if it starts with a few squirts then that is a very strong sign that you have compression and spark. Then, of course, the focus is on gas.