1980 750l

[Toedermarine]

Has spark, will turn over, timing set, fuel to cylinders....will not start. Any ideas?

Thanks

 

[Rich82GS750TZ]

First, welcome to the form.

Now, let’s back up. Get some background.
Are you new to bikes?
Bike new to you?
Did you ever have this bike running? If not, Carbs likely need a full clean. CV carb cleaning/rebuild Tutorial by Ed Ness is the Bible for this, found on BikeCliff’s Website. Link in Signature.
How many miles on this bike?
Have you adjusted valve clearance to spec?
These and other common things to consider are covered in the Top 10 Newbie mistakes thread.
If you need a service Manual (everyone does) you can download the GS 750 16valve FSM from BikeCliff’s Website. Link in my signature.

 

[tom203]

Maybe we overwhelmed him. But if he’s ok with his diagnosis so far…..might be “choke” use issue.
For cold start apply full “ choke”, but NO throttle ..and crank it

 

[Rich82GS750TZ]

So many come here, post a wide open, vague issue, get a laundry list of questions and things to check out, decide a 40+ year-old bike is maybe more than they bargained for, and just never come back. Did I come on too strong?

 

[Toedermarine]

Hmm, in response I bought the bike brand new off of the sales floor in 1980 from Stubbs Cycles in Houston. Typical maintenance over the years had the carboraters rebuilt in 2017, had the stater replaced in 2014, and have since replaced the usual electronic parts that wareout. Most recently replaced the head gasket do to an oil leak. Had to set the timing on the cams. Timing correct and compression good. Turns over but does not start. Asking for assistance not criticism. Thank you.

 

[Rich82GS750TZ]

No offense intended. People signing up, asking a vague question with no background info, then never coming back is a common enough occurrence. My only criticism, you have to admit, your opening statement left a lot of questions. That being your first post on the forum, we didn’t know anything about you or the bikes history or your history with it or any other bike. Now we know a bit more.
How long ago was this bike running well for you? You’ve mentioned having done typical maintenance since new. Does this include checking/adjusting valve clearance?
If you have proper fueling, compression, spark, and airflow, I don’t know what else could be keeping it from starting.

 

[pdqford]

So, are you getting any spark at the plugs?

 

[Toedermarine]

Many thanks, valve clearance is good and getting spark to the plugs. I'm a bit puzzled myself. Looks like I'll take her in.

 

[rphillips]

Just wondering, did you have any ign parts off under the ign cover? How did you find TDC when replacing the head and degreeing the cams?... Wondering if ou may be 360 degrees out of time.

 

[Jinks]

After a top end rebuild, I'm having the same problem on my gs850, got spark, petrol, valve clearence. How do I check for 360 deg out & how do I rectify?

 

[Toedermarine]

Many thanks, rphillips, i could be out 360 as well. Did not think about that

 

[Toedermarine]

Thanks everybody for the advice, she starts and runs, however there is a random high pitch popping forward of the #3 carb and light puff of smoke...possibly the carb boot? Any ideas?

 

[Nessism]

If the carbs have never been refreshed, that's a good place to start. There is a guy here with a rebuild tutorial that explains all, and he sells carb O-rings too.

 

[Toedermarine]

Many thanks for the advice.

 

[gustovh]

The ends of the cams are notched as you know, with notches either facing in or out, remove cam chain tensioner. One at a time rotate each cam 180 to face the other direction, ensure that timing mark has not changed and that there is 20 pins between the arrows, Reset tensioner. What I just wrote is from memory, consult your manual first. I bought a bike once that would not rev past 7000, stumped me for months until I counted the pins and had 21. Intake cam retarded, set cams proper and have ridden her for over 30,000 miles.

Good luck

V