Erm.. wont start!

[class1c]

Hi
This is the first time I have ever posted to the gs resources forum, though I have looked at the site a few times in the past. Good site.
I have a 1977 gs750 which I am working on at the moment. It was running, but not very well - so I pulled the carbs off and cleaned them up a bit. There was some gunk in the float bowls but in general it did not seem that bad.
Now, having replaced the carbs I can't get any life out of the engine - it wont start at all. I actually suspect that somehow the type of petrol I am using might be wrong - before when I started the bike I used optimax, which is a higher octane fuel, now I just filled it with ordinary unleaded.
I cant work it out, so was hoping for some suggestion from informed members on here.
Please note - I have checked the electrics and it is sparking ok...
Thank you for any ideas
Peter

[Billy Ricks]

Have you checked valve clearances and compression numbers?

[rgierer]

I run unleaded in my 77 750 all the time. I don't think it is the gas. Are you getting fuel to the carbs/plugs?

You , of course, have the air box back on.

It is my excpereince that when you put the carbs back on, you attach airbox, put petcock on prime for 30 secs or so, push down the choke, hit the start button and stuff happens.

[Billy Ricks]

I run unleaded in my 77 750 all the time. I don't think it is the gas. Are you getting fuel to the carbs/plugs?

You , of course, have the air box back on.

It is my excpereince that when you put the carbs back on, you attach airbox, put petcock on prime for 30 secs or so, push down the choke, hit the start button and stuff happens.

Not priming the carbs may be part of the problem.

[class1c]

Thank you for the feedback.
Just finished watching the brazil v croatia game - (soccer)
Thanks for the input about the unleaded. I'll assume the fuel is ok. I left it on prime for a while and fuel is definitely making it to the float chamber. If you undo the drain screw at the bottom of the float chamber, it comes rushing out.
I am suspecting this now may be a mixture issue (too rich/lean) or perhaps a balancing issue. The thing is, most of the time I don't even seem to get a 'pop' - the sound of even one cylinder firing. Just virtually nothing. I will try a bit more tomorrow.
Kind regards
Peter

[Billy_Oliver880]

You have established that you have compression and you got spark? Did you go through and dip the carbs and clean them thouroughly?

[class1c]

hi billy_oliver
Im not all that technical with bikes. Is there any easy way to get an idea if there is a correct mix going to the cylinder, if there is compression etc.
I was planning on getting a can of easy-start tomorrow to see if that would do any good, but I don;t know. I sprayed some carb cleaner through the airbox but it didn't change anything.
Regarding the carbs, I didn't take them completely to bits and dip them, but I did take the float bowls off and also removed the main jet and pilot jet which I squirted with carb cleaner. They appeared clean. I sprayed some carb cleaner down the fuel line and watched it seep out through the fuel inlet valve, so assuming the valves are ok. It was working short while ago - cleaning was supposed to improve this! But seemed to have the opposite effect.
One thing I didn't try was cleaning the air inlet jets. Is it possible there is not enough air getting through or the air flow is blocked somehow?
Regards Peter

[rgierer]

If you removeed the jets on the side aand bottom of the carbs and did not replace o-rings you may or may not have created a bit of a problem.

0-rings are available for 16.00 from Robert Barr on this forum.

You can do a search and get the basic settings on these two jets as well.

I suspect you are more challenged by air than fuel.

Do you feel like the carbs are on the boots solidly?

When you get it running I would suggest you check the o-rings connecting the boots to the head by sraying WD-40 or some other like product and seeing if your performance changes.

For what it is worth I and many others have been in this spot more often than we like to admit.

Hang in there. The 77 750 is a beast with no downside.

[class1c]

hi
an update. After trying various things, it appears there is no spark.
I had thought there was one because connecting a strobe light between the plug cap and negative illuminates the light, as it should. I even got the odd electric shock from playing about with this.
However, when removing the plug and resting it on the side of the engine (after rubbing the engine block to make a shiny surface-better contact) for some reason I can see no spark. Is this the fault of the spark plug or is ther not enough current going in to create a spark. I don't know
I am more convinced now that it is some kind of electrical fault, rather than carburation.
Thanks for any advice
Peter

[class1c]

quick question.
Are the coils in the gs750 prone to fail occasionally? Anybody have similar problems?

And is it possible to replace them fairly cheaply, as I am thinking of replacing the coils, checking the ht leads and somehow checking the points. Should there be a spark at the points?

Questions, questions, eh!
Kind regards
Peter

[rgierer]

I would not be quick to change the coils. On this bike I would first go to the points.

This is tough as there are three things that need to happen for a bike to start. Fuel, air and spark.

I always like to make changes to one at a time and know the last is good before I go to the next.

Fist confirm everything is solid on the carb replacement. Plenty of fuel and plugs are wet.

Then pull off the point cover and just take a look.

Do a search on how to set the points on this forum. Earlfor has a very clear and detailed process.

I would take care to mess with things as little as possible to confirm power to the points. This bike has dual points. 1 for each coil.

The truth is that if one coil is bad the bike will run just poorly. I road ne of my bikes 300 miles with one coil.

Because you are not getting any action I would stand back and assess, fuses connections etc before I go too far. If you have the stock air box it is easy to have pulled wires free from connectyors pulling that out and putting it in again. I have done it more than once.

[class1c]

I see, rgeirer, and thanks for the info. IT sort of suggests that it is unlikely both coils could blow at the same time, therefore perhaps thats not the prob.

I've had a look at the points and sort of set them to what it says in the book (Haynes manual) though the book was a bit vague but in truth I don't think its actually a timing fault. I'm going to get the voltmeter out tomorrow and see if I can determine for certain if there is something stopping the spark from being created.

Was just looking through some of the pictures on this site of other people's bikes. Nice. The GS series seem to be one of the most popular 70s bikes still around: they apparently make good customs too. Perhaps that is a good advert for Suzuki reliability. Mine is basically stock and has the single front disc. Was thinking of finding a larger disk perhaps from a Katana and substituting it. Don't know if I would be able to get a substitute (dual-pot?) caliper on there though.
Kind regards
Peter

[rgierer]

A wire or connection loose has high probability if the problem is electrical. Those airboxes can be nothing short of a wresting match

[class1c]

condensers

Hi

I wonder if someone could help me.

After doing a bit of testing I can get a small, weak, erratic spark on some of the plugs. But I suspect the condensers may be shot (as they are 30 years old). The reason I am saying this is I got a weak spark on two of the plugs but no visible spark on the other two. I then tried swapping the condensers around and the situation seemed to be reversed. Its inconclusive but I need to try new condensers and see if it could solve my ignition problem.

I have seen the web page listing the Dyna ignition kits and would love to get one but its not feasible from a money perspective.

My question is do I have to have the exact correct condenser. as in

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=8052791656

(its same as gs750) or can I just use any condenser. Needless to say, my local spares shop sells condensers but not for 1977 Suzukis (only for cars).
kind regards
Peter