'78 GS750 - HELP - Wont start and I am bike retarded

[Anonymous]

ok so i bought a 1978 gs750 that looks to be in good condition. but i cant get it to start. it pops and backfires and thats it. i.....

replaced spark plugs
new air filter
cleaned carbs
new battery

there is a weak spark on all four plugs. could this be the problem? what would cause this? i heard someone say the words, "bad ignition module".

what is an ignition module, what can i search for on ebay in other to replace one (is it always called an ignition module???) and could this be the solution to all my gs750 woes?

your help is deeply appreciated because i am a poor student.

[Anonymous]

I dont believe that the 78 750 has an ignition module. I think it is points ignition and that would be the next place to look for trouble. Do you have a book? It will save you lots of agro and educate at the same time. If all four plugs give a weak spark, one could assume that it something that they have in common, the source of 12v from the battery. You could have a bad connection between the battery and the points like the kill switch ect. Keep up the dialog and others more familiar with your particular bike will advise.

[Anonymous]

yeah i have the haynes manual but i dont know much of anything about bikes so things like points and ignition module and coils mean little to me.

[Hotblack]

Well you should check as many simple things as you can first. Are you sure you didn't mix any of the plug wires up? I don't think weak spark would cause popping and backfiring, but spark at the wrong time sure could.

If you're sure the plug wires are okay you should make sure the ignition timing is within reason. This is described in your shop manual. If you don't have one you really really REALLY should get one. I'm not very happy with my Clymer, it's next to useless. I hear good things about the Haynes manuals.

Your '78 won't have an ignition module unless it's been monkied with, it should have two sets of points on the right end of the crankshaft. Also check there's no oil or anything on the point backing playe, you don't want anything interfering with the ground. Bad point gap settings can also account for weak spark, and are more likely than bad coils.

I'm sure there are other possible causes of popping, but these are simple things you need to make sure are right before getting in deeper.

There's also no guarantee you're getting enough gas to each cylinder, but i'd recommend seeing if you can get it to where it doesn't pop anymore when you crank it. Then if it still won't start you can delve into fuel matters.

Don't worry about being 'bike retarded', it's a lifelong learning process. Bikes are both simpler and more mysterious than (most) four wheel transportaition. If you want to talk about, say, Fiats, well that's different.

[Hotblack]

I just saw these two replies which came up while I was typing mine. It's good you have a manual, read as much as you can from it, try to tell what you can from pictures. A good book that can help is Motorcycle Maintenance by Mark Zimmerman. Lots and lots of picures. Try to find someone who can coach you in person too, that's a bif help. 3phase has good suggestions too, and as you get into it if it's a really sticky problem we've got some really smart people here who absolutely can help you through it.

[mark]

You've got a motorcyle that's almost 30 years old! If you want to enjoy it, you'll have to get to know a lot about the bike. You'll need to buy some basic equipment if you don't want to spend mucho dollars at a bike shop, especially a voltmeter. Get a manual like everybody else said, and go through the "tune up" procedures.

Also when you ask for help, let everyone know if your bike has any modifications or is completely stock. If you've got a 4 into 1 exhaust for example that takes additional tuning and carb work usually.

I agree with the above posts, you don't have an igntiion module you have points ignition. You have to set your own point gap and timing and make sure that you're condensors are O.K. unless its been modified. Read the stator papers "on the home page" as well as the section on how to clean carburetors. You have valves to adjust, compression testing, etc. etc. etc.

You say that points etc. don't mean that much to you right now. If you're going to have that bike, they soon will!


Lots of people on this site are willing to help and know 100 times more than I do. Keep after it!

[braindead0]

Make sure you've got good gas!

The Haynes manual should have a pretty good ignition system troubleshooting section. Follow it along, read everything (one thing you have to do with the Haynes, don't just read the first paragraph ;-)... When it gets to a tool that you don't have (say a feeler guage for adjusting the points gap) write down the numbers it needs, and feeler guage... Stop at an auto parts store and ask for a feeler guage that'll read those numbers.... (make sure to note that it's in mm not inches..

Keep your eyes out for other motorcyclist in your area, odds are there's someone with good mechanical experience.. and often people are willing to help.

Oh yeah: update your profile here with at least your city/state... maybe someone is nearby would be willing to help out.

[jonr]

How many miles on your 750? I had about 35,000 when I replaced my coils with Dyna coils. Also, one of the first things I did after I bought the bike was put on electronic ignition. Messing with points sucks in my opinion. It's an ongoing hassle and if you feel like blowing the $125 for electronic ignition (Dyna-S), it will at least keep you trouble free in that department....

J