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

[Anonymous]

Ive had the bike for about 6 months and has ran like a charm the whole time. I havent had to fix anything just a new set of tires. It ran fine before i parked it for about two months while i collected money for tires then it just went south. It started to just be really cold blooded. I would spray some starting fluid in the carbs and it would fire right up. When i can get it started it still runs great. That worked for about two weeks and now it just wont fire up. Ive taken the carbs off and cleaned the heck out of them. My mechanic told me to look at the valve train and check everything there. I am really just learning about motorcycle mechanics and dont know a whole lot yet. Im on a very low budget but i just love riding motorcycles, nothing gives me freedom like riding. Someone please help to get me back on the road before the winter comes.

 

[Anonymous]

First, do you have spark for sure? Pull a plug lead off and see if you have spark. If you have spark, then it's most likely a fuel problem. If you don't have spark, bingo, electrical problem.

Several possiblities. The fuel petcock on our bikes is vacuum operated. It tends to hang up, get leaky diphragms, etc. and the net result is that you get no fuel.

Take one of the float bowl drain screws loose, see if gas comes out of the float bowl. If not, you have a fuel delivery problem, usually the aforementioned petcock.

Try some of these diagnostics and post your results. We need a little more to go on.

I doubt it's valves or any other major engine problem. Spark and fuel, those two are needed to run.

 

[Anonymous]

First, do you have spark for sure? Pull a plug lead off and see if you have spark. If you have spark, then it's most likely a fuel problem. If you don't have spark, bingo, electrical problem.

Several possiblities. The fuel petcock on our bikes is vacuum operated. It tends to hang up, get leaky diphragms, etc. and the net result is that you get no fuel.

Take one of the float bowl drain screws loose, see if gas comes out of the float bowl. If not, you have a fuel delivery problem, usually the aforementioned petcock.

Try some of these diagnostics and post your results. We need a little more to go on.

I doubt it's valves or any other major engine problem. Spark and fuel, those two are needed to run.

Exactly what he wrote to the letter.
Always fuel or fire first.

 

[Anonymous]

Still wont start

Still wont start

I have taken the carberators completely off, gave them a very good cleaning. Checked all the jets and everything else except for what i think they call the choke valve or something like that. I know fuel is coming from the pitcock because when i take off the hoses fuel comes out. All of the bowls are full of gas and have been drained for the unteenth time. There is spark, i took one of the plugs out and hook the wire to it, grounded it and spark is there, i even felt it. I had the valve cover off today and everything seems to be in order not that i know how it is supposed to look. The thing that gets me is that when i do get it started it still is capable of out running my friends 02 Katana 600. Im not a mechanic on motorcycles by any means but im workin on it. Please Help!

 

[earlfor]

Is the gas that is in the tank, now two months old? If so, it may help to drain the tank and put a gallon of fresh gas in there.

Earl

 

[Anonymous]

I filled up about 4 days ago, the last time it was running and i always put premium in it. I have a fuel additive as well.

 

[earlfor]

Save your money. The 750's run better on regular gas. (I have one)

Earl

I filled up about 4 days ago, the last time it was running and i always put premium in it. I have a fuel additive as well.

 

[earlfor]

What exactly did you do when you "cleaned the heck out of the carbs"?

Have you checked your battery voltage and water level?

When you checked to see if the plugs were sparking, did you check them all or just one?

Earl

 

[Anonymous]

help

help

i checked just one plug to see if my coil was good. Cleaning the carbs entailed basically disassembling them as much as i felt comfortable and cleaning all the little parts. I looked at the needle and all the jets. Like I said, i did not clean the choke valves or whatever theire call. I dont have a book on my machine cause of low funding. And as far as the battery gos, i know mine is a little weak so I yanked the one out of the riding lawn mower. All it does is crank and crank and crank.

 

[Anonymous]

help

help

Spark is going to all cylinders, I just checked.

 

[earlfor]

Re: help

Re: help

You said, "I looked at the needle and all the jets". Do you mean you took them all out, looked at them and screwed them all back in? Or, do you mean you literally just looked at them and did nothing to them? Did you remove the pilot airscrew on the side of the carb? If so, did you count the turns so you could reset it to the correct position? Underneath the carb, protruding through the front of the cloat bowl, there is the pilot fuel screw. Did you remove that. If so, did you reset it to the original setting?

When you had the carbs off the bike and took the float bowls off....there is a 1.8? diameter brass tube about 1 inch long. That is your choke pick up tube. There should be a tiny hole in the end of that tube. Did you check to see if the hole in each of the four tubes was open? (you can clean them out with ONE bristle from a steel brush) Nothing larger.

After you have cranked and cranked, did you remove the drain plugs from your float bowls to verify that fuel actually is filling the bowls?

Is your choke cable hooked up to the carb choke linkage correctly? When you pull the choke, can you see the choke linkage and plungers on the carbs lift?

Are you twisting the throttle when you try to start the bike? You must not turn the throttle. The 750 starts with choke only. It will not start if you open the throttle.

Earl

i checked just one plug to see if my coil was good. Cleaning the carbs entailed basically disassembling them as much as i felt comfortable and cleaning all the little parts. I looked at the needle and all the jets. Like I said, i did not clean the choke valves or whatever theire call. I dont have a book on my machine cause of low funding. And as far as the battery gos, i know mine is a little weak so I yanked the one out of the riding lawn mower. All it does is crank and crank and crank.

 

[Anonymous]

help

help

i have done everything you just said. Im pretty sure that i got all the adjustments in the correct position from when i took the carbs apart. I will try starting it with choke only and see if that works. I have a fresh battery now too. Should I try the starting fluid anymore or not?

 

[Anonymous]

I've never had to use starting fluid on a bike. Under normal conditions, modern engines don't need it. Even my diesel truck doesn't need it.

Pull the spark plugs, are they wet with gas or fouled with oil?

The timing could have gotten waay off. Here's how to check with the bike not running: get an inductive timing light, the kind that clamps around the plug wire. Get a separate battery and use it to power the timing light. Then take the timing cover off and crank the bike, see if the timing marks line up. Do NOT try to power the timing light off the bike battery while you are cranking the bike (it may fry the light).

Oops, I just read you don't have a manual...You will need a manual. You can buy a manual for the price of a couple of cans of starting fluid, it'll save you money very quickly.

 

[earlfor]

Re: help

Re: help

Forget the starting fluid. You cant carry a can of it around with you for every time you want to start the bike. Thats absurd. LOL

OK, time to get serious.

The bike doesnt start. Obviously something is wrong. Continuing to press the starter button is not going to fix it.

Do exactly this. Take your time and be precise. Remove the carb stack.
Turn it upside down and remove the float bowl covers. In the corner of each float bowl, you will see a brass tube that is 1/8" in diameter and 1 inch long. In the bottom of that tube there is a small hole. The hole is about 1/4 the size of a straight pin. You will need a single bristle from a steel brush to ream that hole out. When it is clear, you will be able to clearly see the hole. You will be able to blow on the end of the brass tube and hear air going through. When you blow on the end, you will have to at the same time hold the choke plunger on the side of the carb in the up position to open the passageway so air can flow. Those tubes are the fuel pick up tubes for your choke circuit. They must be clear. There is no alternative. Do not try to remove the brass tubes from the carb body.

On the bottom (float bowl side) of the carb, the needle that is visable outside when the float bowl cover is in place is the fuel pilot screw. GENTLY ...with two fingers on a small screwdriver,....turn that screw all the way down until you just barely feel it stop. Then turn it out 1 1/4 turns. There is a slot in the top of the pilot screw. Note where the slot is when you turn it. Turn it out EXACTLY 1 1/4 turns. Do this on all four carbs.

On the side of each carb, just above the gasket surface of the float bowl, you will see another small screw with a slot in its head. That is the pilot air screw. Turn it in GENTLY until you feel it is all the way down. Turn it out exactly 2 turns. Do this on all four carbs.

Put the float bowl covers back on and reinstall the carbs. Hook up the choke linkage. Turn the barrel adjuster on the choke cable where it mounts to the carbs until with the handlebar choke lever closed there is only a slight amount of slack in the choke cable.

Hook up the throttle cable and adjust it for a slight amount of slack. You should be able to rotate the throttle grip about 1/8" before there is any movement of the throttle linkage on the carb. There is a barrel adjuster at the carb throttle cable end for this and a 2nd one underneath the throttle housing on the handlebars.

Once you have the airbox and airfilter in place and the airbox lids are on and the rubber connecting tubes for the carbs are clamped tight on both sides, install the tank. Connect the fuel line. Connect the vacuum line.
(the petcock vacuum line is connected to the #3 carb on your bike) the vacuum fitting on the #3 carb is on the left side of the carb above the float bowl gasket surface. Turn the petcock to prime, wait 15 seconds and turn the petcock to run. Pull out the choke lever. Do not touch the throttle. Ignition on, press starter button. Use the choke as you would a throttle until the bike has warmed up for a minute.

Let me know what happens when you have done the above.

Earl

i have done everything you just said. Im pretty sure that i got all the adjustments in the correct position from when i took the carbs apart. I will try starting it with choke only and see if that works. I have a fresh battery now too. Should I try the starting fluid anymore or not?

 

[earlfor]

Well Bill, I am always more challenged trying to help a new guy. I dont think he has had a chance yet to learn how to time an ignition or even where the marks are and which ones represent what. I considered ignition, but I figured if it ran two weeks ago and all he did was let it sit and if as he says, once running, it still would run fine, I suspect the ignition timing is at least close enough that it should fire or try to start. That bike has a points and condensor ignition, so even if the points are starting to wear, it should still fire the plugs.

Earl

The timing could have gotten waay off. Here's how to check with the bike not running: get an inductive timing light, the kind that clamps around the plug wire. Get a separate battery and use it to power the timing light. Then take the timing cover off and crank the bike, see if the timing marks line up. Do NOT try to power the timing light off the bike battery while you are cranking the bike (it may fry the light).

Oops, I just read you don't have a manual...You will need a manual. You can buy a manual for the price of a couple of cans of starting fluid, it'll save you money very quickly.

 

[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

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

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

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.