Not Starting

[Topman]

So, I acquired my 750 with a known charging issue, and which ran decently with the help of some starter fluid, clearly needing some work. After some debate I took the advice of many and cleaned the carbs. Dipped everything, replaced O-rings with help from Mr. Barr, rebuilt piece by piece, adjusted float heights, loosened mixture screws 3 turns out to start. Replaced intake boots, didn't have to worry about intake O-rings on the '81, replaced boot between air boxes. Adjusted valve clearances, and put new spark plugs in. Replaced stator and R/R which were both fried. Cleaned all electrical connections. Replaced clutch cable and clutch springs, rebuilt rear M/C, and replaced chain and sprockets, also put in new K&N Air and Oil filters. Some of that I am aware is not necessary to get the bike running, but I wanted to catch everyone up on what I've done thus far.

Just got the carbs and boots all put on today, set up the gas tank on an elevated platform to hopefully get to synching the carbs, but couldn't even get her started. With a clear fuel line installed, fuel was pretty obviously getting to the carbs. Pulled the plugs and saw there was still a good spark. Noticed a little of what appeared to be oil (?) on the ends of the spark plugs if that helps in diagnosis. Where should I turn next?

Thanks for any help.

[cowboyup3371]

What happens when you try to start it? Is the battery fully charged? Are the fuses good? How high up is the tank? I've heard if it's too high it will die out so it needs to be about the same height as normal. If you are using the normal tank, is the vacuum port connected as well or are you just running it on prime?

[BassCliff]

Hi,

What is the voltage at the coils? Is it near battery voltage?


Thank you for your indulgence,

BassCliff

[azr]

Are you sure gas is getting into the carbs? crack the drain plugs a bit to make sure fuel is in the float bowls. What did you do with your timing? double check your wires are all in the right spots. When you're doing as much work as you have it's very easy to put something back together in the wrong spot ie; carb body, plug wire, ect...believe me I know.

[spyug]

A couple of times after rebuilds, I have found bikes hard to start and often you have to crank away for awhile. Problem is that with a bike battery it will run down very quickly and even witha battery showing 12+ volts it may not have enough "oomph" to turn over and fire the coils. You can check for spark and it has some but it may be weak and intermittent at low voltage. It will crank merrily until down at 8 or 9 volts but there won't be enough juice for both.

When first starting I always find that hooking on a bigger automotive battery with lots of cranking amps helps tremendously. Just make sure its not in a running vehicle as that can over power and possibly wipe out your electronics.

Another issue I've seen is if the carb bench synch is not done and the butterflies slightly open at rest(i.e. are closed tight). It will be the devil to start.

Keep at it, you'll get it soon.

Good luck,
spyug

[Topman]

Thank you for the quick responses.

Cowboy: When I try to start, it turns over like it wants to start, just doesn't.. Battery is fully charged, after the night of sitting it was over 13, but after running some tests and cranking a few times it around 12.7. When I had the tank up, it was maybe half a foot up with the vacuum port plugged, being fed via the prime position. Although after failing that way I also tried mounting the tank and starting it with the standard setup.

Basscliff: I've been reading on how to specifically test the voltage at the coils, and have ended up running several tests on the coils, what I've found: The primary resistance is in spec at 4.5 Ohms, the secondary however, took me a minute to get, but landed on one side just above 25, and on the other a hair below 30. I realized that's not in spec but wasn't sure what that meant, so I kept doing some of the tests on your odd and ends page. The voltage I got from the orange/white wire to the negative battery terminal for both was about 11.75, that leads me to believe there may be a short in the wiring somewhere, but as hard as it is for me not to just begin removing the wiring harness to clean and inspect, I felt as though I should put a post up on my current progress and wait for any feedback first, so I'll continue with any other tests I can dig up for now.

Azr: Gas is definitely getting to the carbs, I pulled a drain plug and it came flowing out. Didn't mess with the timing at all, figured even with the timing off slightly I could at least get it to start for now. After all it did run before, with the help of starter fluid unfortunately , but I refuse to touch the stuff after reading what people have to say about it on these forums. And as for installing something incorrectly, I suppose it's possible, but I did my very best (slightly compulsive) to put everything back where it was, took pictures before removing each piece just to know that it went back on in the right spot and in the correct fashion.

Spyug: I appreciate you sharing your experience, but with the evidence of other possible electrical issues, I'll hold off on cranking with an external battery for a few days. Also made sure I bench synced as per the instructions I found on this site, used a guitar string and none of them were closed tight at rest.

Once again thank you everyone for your help, I've got the next 3 days off work so I'm hoping to make some real headway on this baby.

[tom203]

Are you using the "choke" and does it appear to work at carbs when you use it? My 650 won't show any interest in starting from cold start unless I fully deploy it.

[dueller]

Have you tried different choke positions? Tried with throttle at different positions? Are you sure that was oil on the plugs and it wasn't gas (i.e. flooded)? I think someone has said as long as you have over 10V you SHOULD be okay on the coils but don't quote me on that. Does it try and catch but just never fully does? Sounds like maybe you might be flooding it our if the plugs are wet. Try leaving them out for a couple hours to make sure there isn't a buildup of fuel in the cylinder maybe. Just spitballin

[Topman]

I've tried it with, and without the choke. Same thing either way.
The choke is working properly at the carbs, although it slips a little, can't ever seem to hold itself entirely open, but that's not new, it couldn't do it prior to the cleaning/rebuild either. When I use it I usually have to hold it open all the way myself or stick something between two of the posts at the carbs to hold it open completely.

EDIT:

Dueller, I noticed it yesterday and it was black so I assumed oil, but after reading I learned it will almost always be black whether oil or fuel, unfortunately I never did put my nose to it so I'm not sure which it was, and I of course cleaned them after I noticed it. Went to check just now but even after all the cranking I've done since cleaning, it has not reappeared.

I did have a bit of a development. Tom's question made me want to go back and crank it with an assuredly full open choke, so I propped it full open with a screw driver bit (photo) and gave her the first crank in over an hour (good charge in battery) and by god did she get close, believe I even got a quick puff of exhaust out the tailpipe, but still only so close.

[Topman]

Managed a few more tests. As per steps 11 and 12 in Mr. Matchless' addition to the Electrical Odds and Ends page, I tested the resistance across the Blue and Green wires coming from the Signal Generator, with my multimeter on the 200k Ohm setting, I'm getting a reading of 500 Ohms, well above the desired 250-360 range. Also tested for a 12V DC between the orange/white and black/white wires coming from the Signal Generator, and only came up with 11.8.

Both numbers appear to be off, so I'm, well not quite sure what that means, too much resistance and not enough voltage, Signal Generator's bad? Perhaps it's malfunctioning but not completely toasted and that's why I still get a spark from all the plugs? Just not enough to start the engine..?

Thanks again everyone.

Also thought to note that I tried Mr. Almarconi's igniter test. When attaching the negative multimeter lead to the green wire, I got neither a #4 spark on contact, or a #3 spark on disconnect. That is another thing I don't understand because according to that my igniter is faulty, but how then would I be getting a spark when the plugs are grounded to the cylinder and I turn the engine over?

[dueller]

Thinking you have a problem of too much fuel in the cylinders from all the attempts to crank. I would pull all the plugs and put cotton ball or something like that on the spark plug hole so that nothing will fall in there but still have some venting of the cylinder and leave it till morning. That may help get any unburnt fuel out of the cylinder. Just a thought. Especially if it is attempting to fire with WOT. That means you are probably rich IMHO.

[azr]

The readings you have for your coils sound fine. Have you looked at the colour of the spark on all four plugs yet. You want a nice strong, blue spark and as well to know for sure spark is getting to all the plugs. Really it shouldn't be this hard to start the bike. All you need is gas, spark and air. If fuel is getting to the plugs they should be wet with fuel after trying to start but not firing. Pulling the plugs and checking for a good spark will tell you about the spark and it sounds like you have taken care of the air with new filters, checking for leaks at the head with new boots and such. Try kicking it real hard.

[Topman]

Just checked in the pitch black. The sparks are all a good blue, but I'm not quite sure what a "strong" spark is versus a "weak" one. I've got the plugs out as Dueller suggested, to let any residual fuel dry up, guess we'll see in the morning.

Thanks for sticking with me guys, I'm very stumped by this one, and would absolutely love to be able to get some rides in before it gets too cold here in the northern midwest.

[tom203]

The readings you have for your coils sound fine. Have you looked at the colour of the spark on all four plugs yet. You want a nice strong, blue spark and as well to know for sure spark is getting to all the plugs. Really it shouldn't be this hard to start the bike. All you need is gas, spark and air.

I agree- the readings sound good to me. Dry plugs off if they are wet and then restrict air filter element somehow ( wrap oily shop rag around it), use full choke - no throttle input- give it a go.

Added; did you see those fuel bowl gasket pics from Basscliff- pointing out that some replacement gaskets need you to punch out for the choke vent? I'm useless at searching, but someone else will find them if you don't.

[Steve]

Have you tried different choke positions? Tried with throttle at different positions?

Although it is common to use different "choke" positions, there should only be ONE throttle position used when starting an engine, especially if you are using the "choke", too.

DO NOT TOUCH THE THROTTLE.

The "choke" (actually an "enrichener" system) uses the high vacuum caused by the closed throttle to draw fuel and air through different jets to provide the richer mixture for cold starting. Opening the throttle AT ALL will defeat that system.

.