electrical or carb problem... time to vent

[Milktown]

ok so i have a 78 gs750 that has given me nothing but problems since i bought it this winter. its a 1978 gs 750E. i bought it with 28000 miles and drove it about 150mi to get it home getting about 37mpgs but it ran descent enough but i knew i could do better. took the carbs appart gave them a good cleaning, replaced the points and started getting about 39 mpgs. idle is a bit jumpy but nothing too bad tho i dont know how smooth its supposed to be. after a while on long rides it would start bogging and backfireing and eventually started doing it all the time so i replaced the coils and problem solved. at one point i was getting 45mpgs but usually around 41-42. a couple weeks ago the petcock went bad so i put in a manual one. then i started leaking gas so i replaced the needle and seat valves and once again problem solved. ran good for about a week and now im getting the same bogging/backfireing through the carbs like the coils have gone bad again after having less then 1000miles on em. can this happen these are the coils i put in: http://www.motorcycle-superstore.com...T.ac=SLIsearch

[OldVet66]

Unless you soaked the carbs in carb cleaner and replaced the O-rings, the carbs were never cleaned properly from the beginning. The boots from the motor that hold the carbs on often need replacement as well as the O-ring that goes between the motor and boots. Did you sync the carbs after cleaning? Sometimes the air box needs to be resealed so no extra air leaks in except for the factory holes. The air box boots need to be soft and pliable enough to seal well. I get 44MPG on my GS1000E with stage 3 jet kit pods and four into one pipes, if I drive normally, so you should be doing better than that. Plug caps can break down with age. I had all sorts of ignition problems until I changed to a Dyna-S ignition system, but the stock systems work nicely. At this point there are two many variables until you cover all bases. I would guess that you have a vacuum leak at the boots, but there are many things that could cause those symptoms. The float needles will not hold if you leave your manual petcock on all the time. I take it you did cap off the vacuum port for the old petcock. I almost forgot one of the most important, have you checked and adjusted your valves?

[tkent02]

I would guess that you have a vacuum leak at the boots, but there are many things that could cause those symptoms.

No, there's only one: lack of maintenance.

[mike_of_bbg]

Have you checked your voltage at the coils? Often "bad coils" are really an issue with resistance in the electrical system leading up to them. Fresh coils might mask the problem for a while - until it progresses. Also, what are the primary impedances of the new coils? 3 ohm coils might make your points wear out more quickly. If you like the bike and plan to keep it for a while, in the end an investment in a Dyna S ignition and a coil relay mod might pay out huge dividends. Cleaning the electrical bits of the ignition switch might also help out.

Those needle valves are not meant to hold back the pressure of a full tank of fuel for hours on end. Yes, even new ones. If you park your bike with the manual petcock left on, eventually the leaking will come back.

If your model has intake boot o-rings those should be replaced, the boots should be replaced if they're cracked, and the entire intake system should be looked over for potential leaks.

[MisterCinders]

What are your valve clearances? In that long list, I didn't see a valve adjustment.

[1_v8_merc]

You really shouldn't be spending a dime until your 100% sure what the problem is.

Your gambling with your money basically, and it usually won't pay off.


99% of the time, these bikes just have an extremely Simple problem, or lack of maintenance.
This lack of maintenance can cause all kinds of things to go haywire, and mimic other symptoms/ problems.


Ex: your lights get vastly brighter when you Rev up the throttle.
Instead of dumping $70 on a battery or new charging system, all you needed to do was clean the wiring harness! Which can be done for free.

[BassCliff]

Greetings and Salutations!!

Hi Mr. Milktown,

I must apologize for being remiss in my duties. It seems you have eight posts in the forums and I have yet to give you a shout out. Your "mega-welcome" will contain a couple of maintenance lists, tasks you must perform in order to have a happy GS motorcycle. Take no shortcuts, do all the required maintenance, and your GS will love you for it.

Anyway, let me dump a TON if information on you and share some GS lovin'.

I just stopped by to welcome you to the forum in my own, special way.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. Now let me roll out the welcome mat for you...



Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[Milktown]

Thanks for the input from everyone looks like I got some work to do...

[Big T]

Since you have points, I have to ask

Did you replace the condensors also???

What you are describing sounds like "worn out" condensors to me

[straycat]

I've just been going through the pain barrier with mine . I started with intake o rings,then carb strip with new o rings. Rebuilt with careful attention to float heights , then messing with jets, needle positions to no avail. Discovered that I had less than 10 volts at the coils. Upgraded wiring ,grounding,cleaned up fuse box and did relay mod on coils. I then discovered that the battery was been fried by a faulty reg/rec which I've now replaced. I am buying a new battery tomorrow. Fingers crossed !
It's not always obvious what the problem is,you have to keep going,else it's just another ebay bike that "needs the carbs cleaning" !!!!!!

sc
sc

[koolaid_kid]

Correct, straycat. Usually you are peeling away the layers of the onion. You solve one issue, only to find out that it uncovers another one. Solve that one, look for the next. Once you are down to the core, then you can breathe a sigh of relief. I never expect it to be only one thing; that would be futile and exasperating.

[mike_of_bbg]

Usually you are peeling away the layers of the onion. You solve one issue, only to find out that it uncovers another one. Solve that one, look for the next.

Yeah. Two years of peeling (plus a little bit of riding) here. I hope I've finally gotten to the bottom of my last issue Of the top ten issues on BassCliff's list I've had to address nine of them, plus a few that weren't on there.

Hang in there, we're all here to help you.

[Milktown]

i really appreciate all the gs love from everyone, but unfortunately i am moving to the other side of the world in a few months and i have not the time nor the finances to find my gs zen. therefore i am going to sell my 78 gs 750... and cry while im doing so.