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6K views 22 replies 5 participants last post by  Sue Davis 
#1 · (Edited)
83 VT750 will not start

We are having a issue with a1983 VT750 bike starting, we started a post in the newbie area about this, and we are checking into the battery's condition. The bike is new to us so we are in the processes of giving it a complete check out.
Carbs were overhauled not long ago and a new complete engine piston and cylinder was installed due to crack in the old one.
The clutch handle is broken off half way and the master cylinder needs overhaul, we noticed that the small switch is missing for the clutch master, will this missing switch effect the starting of the bike? Dash light show it in N.
Thanks
 
#2 ·
We are having a issue with a1983 VT750 bike starting, we started a post in the newbie area about this, and we are checking into the battery's condition. The bike is new to us so we are in the processes of giving it a complete check out.
Carbs were overhauled not long ago and a new complete engine piston and cylinder was installed due to crack in the old one.
The clutch handle is broken off half way and the master cylinder needs overhaul, we noticed that the small switch is missing for the clutch master, will this missing switch effect the starting of the bike? Dash light show it in N.
Thanks
That switch should only affect starting in gear, should not cause an issue for starting in neutral.
 
#3 ·
I agree ! As long as the neutral switch works it should still crank without that lever switch. The neutral switch grounds the coil for the starter solenoid to complete it's circuit.
On these old bikes if the kill switch is off, the power to the coils is cut off, so it won't fire up, but it will still crank the engine with the start switch.
 
#4 ·
Okay so the switch on the clutch is only to start the bike if you are not in neutral or keeps it from starting if not in N as long as the lever on the master is pulled in?
I believe swifty2014 that we will have to take a look at that problem address on the other post first on the resistance on the neg side of the battery we had. Also take a look at the kill switch to make sure it is not corroded on the inside or broken.
On the neutral dash light can it be possible that it shows N but could be a wire bad or loose giving a false indication?
After we check that battery out we will jump it with an 12v auto battery to see if it will start with a bit more crank power, if it does the battery is at fault and will check into the AGM battery's.
Thanks
 
#7 ·
Okay so the switch on the clutch is only to start the bike if you are not in neutral or keeps it from starting if not in N as long as the lever on the master is pulled in?
Be aware, if the PO for some reason jumped the clutch switch wires your bike could try to start while in gear.

You should be able to find Master Cylinder with lever on ebay.
 
#5 ·
Hi guys we checked the kill switch today with a tester and it shows the switch is good.
Pulled the battery and it has two low cells with less than ten hours on the battery.
Drained the carb float bowls to see and smell the fuel and both looked and smelled fine and had plenty of fuel
Hooked up the car battery with the jumpers directly to the bikes battery cables and pulled a spark plug wire (lest side #1) and used a nail to ground and had no spark when cranking.
We found a coil wire was off one of the terminals on the left side coil after moving the fuel tank up out of the way to view.
Tried the spark test again and now have spark, yellow blue.
Reinstalled the plug wire and tried to start but still would not fire up.
Fuel is on, and has good fuel, fuel pump is working, lights are on and working, checked the fuse in the headlight and its good, not sure were the other fuse's are and if they would effect starting. I will download the manual for this today. If anyone has any suggestions I will be more than happy to give them a try. Cheers
 
#6 ·
As long as it will crank that means the circuit for the neutral switch must be OK. Maybe just a bulb out. If you are getting spark, the coils are being powered by the kill switch circuit. So check the plugs and see if they have gotten flooded. This dual fire set up fires both plugs as in a waste spark system but it is a closed loop with 2 plugs in 1 cylinder. So one fires forward and the other in reverse direction. Weird system but it usually works.

Since each are gaped at .035 " that means the spark has to jump a total of .070 gap. That's a lot. As a wild experiment I was going to ground one plug on each cylinder once when it wasn't starting but flooding, but I got it started so I never tried it.
You might give it try so all the spark energy goes through 1 plug just like on a car. See if it fires up easily. No harm done.
 

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#8 ·
Wow that is interesting on the spark set up on this VT750, it is kind of weird. Yes we should pull all the spark plugs and check the condition and gap. Hopefully we will have a battery today time permitting. The PO did remove the three yellow wire connector that most refer to as a problem and they replaced with spade connectors with heat shrink covering. So that was done. I guess we should also check the air-box and filter also.
Did not see any tampering of the original clutch switch wires other than the two hanging from master cylinder due to the switch missing. When we were turning it over with the jumper battery yesterday it sounded more like the starter was spinning and not catching the to crank the engine or engaging. Can the starter be a question for not starting? I saw were a gent posted a video on this site to show what his engine sounded like while turning over, ours kind of sounded like that. I think swifty2014 made a reply telling him to tap on the starter to possibly release the pinon to engage. In time we will fined the reason why it will not start, just need to stay at it by the numbers.
Thanks guys.
 
#9 ·
The recommendation to tap on the starter is to free up stuck brushes inside when it won't do anything at all. No sound from starter.
If the starter is making a funny noise and not reliably turning the engine that is a different story.
That points to the starter clutch unit on the flywheel that is a one way "sprag" clutch to crank in the forward direction and freewheel when the engine fires up.

With the kill switch OFF try to crank it for 5 to10 seconds to see if it has a constant rhythm of the engine turning.
 

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#10 ·
I see so no real need to tap on the starter since it is turning.
We should have a battery today so we can try that with the kill off.
Going to pull all the plugs today to see what they look like. Sorry for the slowness, work gets into the way of this project. Thank you.
 
#11 ·
Well I see this is going to be a long posting as of today I had the chance to check a few items but still need a battery, no one locally has one. Checked all the open to view wiring and see nothing that stands out. Pulled the spark plug wires from the coil and the solid copper wire was in need of a bit cut off as they were pretty spread and deep possibly not making good contact so I cut less than a 1/4" off the ends with a razor blade and reinserted in the coils so now they have a bit better contact at that end. Pulled the two L/R rear spark plugs but I do not have a socket to get into the front ones to remove the spark plugs so that's a tool I need, mine is a 18mm but to wide. The two plugs I pulled were black and wet more carbon with fuel but cleaned off very easy, and they were gaped at 0.021 and 0.028 instead of the 0.035 in. :surprise: So who knows what the two front ones look like. The plugs are NGK D8EA and the book calls for NGK DPR8EA-9 for normal running. Not sure of the differences in the two but it may be a lot.
The air filter is dirty but can still see light. Not sure were the fuse box is but did check that one in the headlight 10A and checked the 30A, but not sure if I missed any that would be part of the staring system. Shocks mount bolts were loose and some bolts missing to hold a few items to the frame like thermostat housing bolt, rear fuel tank bolt and such. This is going to be a fine long inspection but until I can get it to start I will check everything else latter. Wow!
 
#12 ·
I looked up those D8EA plugs and they are gapped smaller. = .028"
The correct ones with -9 on the end are the correct ones gapped to .035".
When I used to work for Nissan we used plugs with a -1.1 on the end signifying a .044" inch gap.
The .9 means .9 of a MM, and the 1.1 means 1.1 MM.
A MM is about .040".
Spark plugs school for the day.

Get the correct ones to start with. NGK DPR8EA-9

I got a spark plus socket from Home Depot and it works fine for our engine. I put a small piece of fuel hose in it to hold the plug from falling out on the ground.
 
#13 ·
I appreciate your help and information, clearly you know more about these Shadows than I do.
Well someone gaped them a bit smaller as I found a socket at Harbor Freight and removed the other two plugs, .020 and .025. Someone was looking for more heat on a plug when replacing them or they hit the floor a few times due to heavy drinking, heck one was not even fully seated in the hole, I could of removed that one with my fingers. As soon as I get the battery and new plugs I will post the findings with those items installed. Is there a bracket for the right side muffler, I notice it had a black hangar on it but not connected to anything. More stuff.

thank you
 
#14 ·
#15 · (Edited)
Well still no T battery in the local area so I hooked the car battery to the old gal to check a few things. One was to check spark to the plugs.
Come to find out I am not getting fire from the left side coil to both spark plugs (front left and right rear cly).
I checked the manual for the test of the coils and this is what I have from our test.

Continuity Test

Primary Coil resistance should be 2.0 ohms, we get 2.1 ohms from both the spade connectors on the coil.

Secondary Coil check should be 29-40 ohms were the plug wires should be in place:
First tested direct to the coil spikes (no wires) and got 23.71, then with the plug wires in place we get 53.6 to 54.8

I thinking this is the staring problem. Now I have to ask are the spark packs that are on the rear fender a possible cause also.
 
#16 ·
Many of us here went to these type AGM batteries.
They are less expensive for the quality and have better crank amps. Mine works great after over a year.
SigmasTek STZ14S battery

When testing the coils the 2 ohms is fine. But the secondary is 1000s of ohms ( usually about 25000 ) so you have to get on a scale to measure up to 40 to 50,000 ohms. If that is what you mean, then take the wires out of the coil terminals and measure each component separately. Maybe a corroded connection at the coil. Others have found that. And each spark plug end cap will be around 5000 ohms each. The wires are copper with no resistance built into them if still the factory wires.

The ignition units may be bad but they are hard to find. One way to see if they are signalling the coil is to have a 12 volt test light and touch the probe tip to the coil - (negative terminal),And when you crank the engine the light should flash on and off each time the ignition unit grounds the coil. So you can compare the good side coil to the other side for the grounding signal.
 
#17 · (Edited)
Thanks swifty2014 for the information. As for the testing the Pri-Coil the 2.1 reading was what I got from both terminal posts and not sure if that 2.1 was over the limit for that test. The tester is set to auto for the reading so I just wrote down what I saw. I guess the secondary coil reading would be 53,600 - 54,800 ohms if correct. Since it say 29-40 would this be in the red for the coil?
Also I see no + or - signs on the coil posts to tell me what is poss/neg, is there suppose to be symbols on the coils?
I was thinking that one the spark box for that side (left) was bad so being that they are the same I switched the spark unit boxes to left to right to see if I would get spark to the ones not sparking, when I cranked it over the left coil did not change, still had no spark and the ones that were sparking were still sparking so I assumed that the spark boxes are good and the coil is bad.
We tested the Pulse gen wires were it says Resistance : 480 ohms +/_ 10% . On # 1 cyl we get .866 and #2 cly we get .850 ohms.
Hope you guys can make sense of this, I guessing a bit here that the coil is the problem. What are the grounds on the coil, it it were they mount to the coil holding brace on the frame? Are there any other tests on the coil to confirm? Are the plug wire caps with a resistor inside like the type. I read that if a cap is failing at spark plug it will shorten the life of the coil that fires it.
I can test it again if you folks need more information.
Thanks much
 
#18 ·
You said you tested the plug wires out of the coil and test the 2 ends of the secondary by itself. Should be around 25,00 ohms. The wires are stranded copper so the should be 0 ohms unless they are broken. Unscrew the end caps from the wires and look for 5000 ohms in each one. You must have high resistance in there somewhere.

The pulse gens are too high however, if they should be in the 480 range. I think there is a 4 pin plug at the air filter cover to test them there, disconnected.

No + or - marks on the coils they can be connected either way to work.
If you switched the ignition boxes and the problem stayed the same, I would take the coils off and look for cracks, etc. Then swap them and see if the problem follows the one coil. Then you know for sure. There are no ground connections for the coils they are a simple transformer type.
 
#19 ·
I am going to do the tests again and switch coils from left to right side. Yeah the PG readings seem high, would this be a concern for not starting or not firing a coil, I did find it at the air filter, with four pins. I will check it again. I will add that the tachometer stopped working and maybe the yellow wire going to the coil should be removed just in-case the tach was shored out internally grounding out the coil. That is a shot in the dark. Will post the new test in a bit.
Big thanks.
 
#20 ·
Good point about the tach shorting the coil negative signal !
I saw a You Tube video of the tach being repaired for a LOOSE solder connection inside, but you have to cut the housing and re-solder the terminal board and the guy said it worked.

 
#21 ·
Okay here are the new results and always there is good and bad. We will start with the good - the PG test was wrong, tested at the wrong end of the plug, new readings are 418 and 416.
The other is strange but now the left coil the one that was not working is producing spark at the rear cylinder, so now all cylinders are sparking. Not sure what changed but it is working yet it still will not fire up.
I checked the starter motor connection and taped the body lightly to see if it loosens up anything inside and checked the starter relay and both are working. I checked power to the 30 amp main fuse, and it is pushing power.
I put a test light on the coils while cranking it over and the light would pulsate on each coil. Both side of the coil have power.
Due to the clutch safety switch is missing I put a jumper wire between the to connectors just in case it made a difference.
The bad, from cranking the bike it has drained my car battery. Want to ask is the fuel pump suppose to click every time the key is turned on, if so this one will click one out of ten times.
I did not remove the yellow tac wire from the coil (not sure if I can to start it up) as it is part of the coil loop into the tac and out, is there a connector that can remove the tac from the system or if the tac failed (not working) it has to be repaired to complete the system?
I am at a loss on were to check next, not sure if it is a carburetor problem or what. :neutral:
 
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