78 GS 750. Engine wont start not sure what to do.

[SqDancerLynn1]

It could be the spark is their but weak?? If it has the original coils they could be suspect. I had problems with my 79/850 It looked like it had spark?? put new points,condenser, cleaned the carbs No luck Replaced the coils (used) it fired right up. It could also have a low voltage at the coils, get the volt meter outand start checking, BLOCK the points open when checking the voltage

[Anonymous]

Still need help

Ok, just something i am thinking. While I had the bike in my Garage awaiting funds for new tires, i had to remove the exhaust and the whole nine yards. Well, me being the brainiac that I am, Decided to fire up the bike with no muflers just the pipes from the exhause ports. Theres about 2 feet of pipe per cylinder and the weather was not really cold at all. I know on a car that running open headers can cas a warping of the valves but i dont know with a motorcycle. As I stated, all of the valve train appears to be in normal specs. But the bike ran fine and started fine before I took off the muflers and started it up about three times. It only fired up three times without even sputtering then one day it just decided that it wasnt going to start anymore. A waited for tires, got them, then shot some starting fluid in the air cleaner and it fired right up. I figured problem fixed but apparently not. I did have the bike running just four days ago with the normal starting problems and it ran just fine. This problem is beyound my expertise. Im sure glad I found this site so other people can help me get back on the road.

[KEITH KRAUSE]

I think he said the bike ran fine until he parked it for two months.
Either the starter/pilot circuits gummed up or the electrical connections deteriorated from moisture.
I would clean the contact surfaces of the points first. If that didn't help, I'd clean the carbs as Earl said. Since he's new to carb work, I wonder if he's doing a good enough job on the starter/pilot curcuits? We all know how small some of the holes are and how easy it would be to miss something.
If the pilot screws have been moved, they can be fun getting them re-set. If the throttle bar was taken out, the carbs will need a synch.

[Anonymous]

help

I did take off the cover where the points and all that are and cleaned those things that are on the round thing. (Please excuse the non technical language.) I tried moving the whole thing to adjust the timing and nothing has worked so far. I put back to the original position because i marked where it was before i moved it.

[Anonymous]

still need help

I did all the carb stuff that was was mentioned in complete detail. The damn thing just wont start. While i was trying to start it i pulled off all of the plug wires to see if it sounded different and it sounded the same as I crank on it with all the wires off. I know im getting spark because they are all arching about one inch when the boot is off. I am completely out of ideas.

[earlfor]

Re: still need help

OK, assuming you have spark and assuming you have set the fuel pilot screws and the airscrews correctly and you have verified there is gas in the float bowls by removing a bowl drain plug, then the only thing left is ignition timing. This is in the tips and tricks section of the site, but I figured its easier for you if I just copy it here.

Setting the ignition timing.


The round 6" plate that both sets of points are mounted on (breaker
plate) is held in place by three screws located at 12, 4 and 8 oclock.
Loosen the 3 screws on the breaker plate. Note that the screw at 12
oclock is in a slot. Rotate the breaker plate until the 12 oclock screw
is centered in the slot. Tighten the three screws.

We will replace the left side set of points first (located at 9 oclock
position) These are the points for cylinders 1 and 4.

Take a 19 mm wrench and rotate crankshaft until points are at widest
gap. Unscrew hold down screw on pointset and remove points. Note the
white wire that goes to the pointset and the placement of the insulator.
The insulator must be correct or the points will be grounded out and
will not work. Put the new points onto the breaker plate, set the gap to
14 thousandths, and lightly tighten the hold down screw. Install white wire.
Rotate crankshaft once again with 19mm wrench until points are at widest
gap. Check that widest gap remains at 14 thousandths. Adjust and
retighten holddown screw if needed.

Rotate crankshaft until rightside points are at widest gap (for
cylinders 2 and 3) Remove old points and install new points and set gap
at 14 thousandths. Note insulators on black wire installation. Rotate
crankshaft with 19 mm wrench again stopping at widest gap. Recheck gap
as you did with the left pointset. Adjust and retighten hold down screw
on points if needed.

THE ABOVE COVERS SETTING THE POINTS GAPS




Next is the timing:

Timing for cylinders 1 and 4 (the left set of points)....................
With 19 mm wrench, rotate crankshaft while looking through the timing
window and align the mark that looks like F1| with the timing mark on
the engine case.
(the line following F1 is the mark (|)

note: some bikes will have a stationary timing mark on the engine case
and some will have a mark on a stationary timing plate that can be seen
through the timing window)

Connect a continuity lights wire lead/clip to the white wire clip on the
left pointset. Clamp continuity light probe tip to ground on the bike or
battery negative terminal.

Turn ignition switch to on (do not attempt to start bike, just switch
ignition to on)

The continuity light should be on.

Loosen the three screws on the breaker plate located at 12, 4 and 8
oclock. Rotate breaker plate until continuity light just flickers out.
Retighten the 12, 4, and 8 oclock screws on the breaker plate.

Unclip continuity lead from left pointset.



For the Right pointset
Rotate crankshaft with wrench until you see the timing mark F2| become
aligned with the stationary timing mark on the engine case.
Connect continuity light lead to black wire on right pointset.
The ignition should be switched on and the continuity light should be on.

The right pointset is mounted to a breaker half plate.
You will see that you can loosen the mounting screws on this breaker
half plate and this will allow you to move the right pointset. This will
adjust the timing without changing the points gap. When you rotated the
complete breaker plate for the left pointset to get the continuity light
to flicker out, thats what you did. You adjusted the timing on cylinders
1 and 4 without changing the gap on their pointset.
Unfortunately, the whole breaker plate being rotated moves BOTH sets of
points, so that is why you must set the left side first and that is why
the right side is mounted on its own independent half breaker plate.
SOoooooo.... Smile Loosen the breaker half plate on the right side and
rotate as needed to cause the continuity light to just flicker out.
Tighten the half plate back down when satisfied with the adjustment. Smile

Remove continuity light and HOPEFULLY, start bike..


Earl

I did all the carb stuff that was was mentioned in complete detail. The damn thing just wont start. While i was trying to start it i pulled off all of the plug wires to see if it sounded different and it sounded the same as I crank on it with all the wires off. I know im getting spark because they are all arching about one inch when the boot is off. I am completely out of ideas.

[Anonymous]

This is crazy

Ok, I rode the bike today. Don't get your hopes up. My friend and I pulled it behind my van until it finally started. Once we got it going and warmed up it ran great. This is exactly what I dont understand. I can even shut off the bike for about 30 minutes and it will fire right up with no hesitation. It has been sitting now for about 4 hours and Im back to the same old wont start problem. What are your thoughts on this. It has to be getting fuel or else it wouldnt run. The timing is apparently set right or else it would run like crap. I just dont know.

[earlfor]

Re: This is crazy

I think you need to take the carbs off and have a mechanic clean them.

Earl

Ok, I rode the bike today. Don't get your hopes up. My friend and I pulled it behind my van until it finally started. Once we got it going and warmed up it ran great. This is exactly what I dont understand. I can even shut off the bike for about 30 minutes and it will fire right up with no hesitation. It has been sitting now for about 4 hours and Im back to the same old wont start problem. What are your thoughts on this. It has to be getting fuel or else it wouldnt run. The timing is apparently set right or else it would run like crap. I just dont know.

[KEITH KRAUSE]

By now it's obvious that it's carburetion. The bike starts and runs fine once warmed up, but won't start without a jump when cold.
The only sure difference here is when it's warmed up, it's a richer condition, and when it's cold, it's a leaner condition.
The bike's mixture is too lean to start the bike with the starter. The things that could cause this are:
A poor carb synch,
Choke plungers not operating correctly,
Choke circuit clogged/gummed up,
Pilot circuit in 1 or more carbs not completely clean,
Manifolds or manifold o-rings leaking.
Anything else wrong with the carbs/intake such as, low float level/fuel flow problems/incorrect jets, would also noticably effect the engine when warmed up also.
The first four problems I list, fit your described symptoms exactly. The last problem I list , leaking o-rings or manifolds, would create a start up problem but would normally include an "idle" rpm that rises several hundred rpm's more as the engine reaches operating temperature. Does your bike do this? One version of the "leaking intake" scenario goes like this.
At cold start up, you have to turn up the idle adjuster knob to get the bike to start. Once the bike warms up, the rpm's start rising higher and higher. You turn down the idle adjuster and the bike seems OK. You park the bike until it's cold and you find the bike won't start up again until you turn up the idle adjuster again...an endless cycle.

[Anonymous]

maybe

Well, when the bike used to start fine I have always had to adjust the idle until i rode it around for a while then i could adjust it and it would stay. So if i turn the idle up high the bike will start with the starter? I just want to spend the least amount of money and do as much of the work myself to get the bike running. But your sure its the carburators? Nothing else could be the problem?

[KEITH KRAUSE]

Re: maybe

Well, when the bike used to start fine I have always had to adjust the idle until i rode it around for a while then i could adjust it and it would stay. So if i turn the idle up high the bike will start with the starter? I just want to spend the least amount of money and do as much of the work myself to get the bike running. But your sure its the carburators? Nothing else could be the problem?

Turning up the idle may help it start but that's not the fix from what I've read about your problem.
Without actually seeing/testing the bike, I can't swear it's the carbs but from what you've said I would do the things I said above. They are all typical maintenance and must be done from time to time for the bike to run well.

[nastyjones]

Try removing the points cover & look at the condition of the points. There are 2 sets in there. Maybe one set is rusted. They can be cleaned w/an emery board.
Don't use your wife's & don't ask me how I know. LOL

Paul

[Anonymous]

help

Basically, I dont think its the points because it runs fine after i get it started. Carburation is a possibility but i really dont know how. I am kind of also thinking that the spark may be there and in time but just a little weak. This still doesnt explain how or why the bike runs fine when i actually get it started.

[KEITH KRAUSE]

Re: help

Basically, I dont think its the points because it runs fine after i get it started. Carburation is a possibility but i really dont know how. I am kind of also thinking that the spark may be there and in time but just a little weak. This still doesnt explain how or why the bike runs fine when i actually get it started.

I gave an explanation for your problem in my earlier post.
I'll say it again, a little differently.
With a decent spark and timing which you say it has, the reason your bike starts OK hot but not cold, is because the engine is subject to a lean condition when cold. The choke should allow it to start, if the carbs are operating correctly. If it won't start when cold, then you have an excessively lean condition and the problem is one or more of the following:
A poor carb synch, (synch carbs)
Choke plungers not operating correctly, (look to see them going up and down)
Choke circuit clogged/gummed up, (clean)
Pilot circuit in 1 or more carbs not completely clean, (clean)
Manifolds and/or manifold o-rings leaking. (replace, most often the o-rings are what's bad)
Your problem is one or more of the above. Take care of them all and your bike will start the same way cold as it does when hot.