1977 gs750 Motor troubles

[Guest]

I recently bought a 77 gs750 ratted out bike love it to death needs a few things but the motor itself is probably shot the guy i got it from claims 2 of the 4 cylinders are stuck and if i could free them up the bike would run perfect something i am doubtful of he said he ran it and it bogs at 50mph and he checked the plugs two are clean the other two are black and burnt i haven't done a compression test yet would like to get some thoughts / advice before i toss money down the drain getting the test done then replacing the motor anyway

[bhm]

Dude, if it runs and you keep oil in there, it will keep running. To go out of trouble, go down the route recommended here for new members, you shouldn't be wasting money
I let mentors forward you to the welcome and homeworks papers.

[Byrdi]

I did check that site and the FAQ and nothing really in my problem area also it bogs so hard at 50mph i can't take it on the highway it sort of needs a fix lol

[tkent02]

Get a newer bike.

[Byrdi]

If i had no kids no wife and a **** ton of money i would

[Griffin]

I recently bought a 77 gs750 ratted out bike love it to death needs a few things but the motor itself is probably shot the guy i got it from claims 2 of the 4 cylinders are stuck and if i could free them up the bike would run perfect something i am doubtful of he said he ran it and it bogs at 50mph and he checked the plugs two are clean the other two are black and burnt i haven't done a compression test yet would like to get some thoughts / advice before i toss money down the drain getting the test done then replacing the motor anyway

So he's had this thing running on the highway, but two of the cylinders are stuck? Stuck on what? If he meant frozen in place, then you'd have big chunks of aluminum all over the floor as soon as it started up.

Have you done any maintenance to it at all? Did the previous owner? Go here:

http://members.dslextreme.com/users/bikecliff/

Download the service manual for your bike. Read the "routine maintenance" chapter (usually chapter two in the Suzuki manuals). Perform a valve adjustment.

You have picked up a bike that has been bobbed, chopped, or whatever the hell it's called now. The previous owner (or whoever did this) probably didn't do $hit to the bike to get it running correctly, and undoubtedly made things worse with his mods. I see it has pods and straight pipes, so the carburetor jetting is assuredly nowhere near to being correct. That bike is old enough to have a points ignition, I'm sure the points need adjusting as well.

The engine is the last thing I would suspect to be the root cause of your issues. Poorly executed modifications to the fuel and exhaust systems, coupled with poor maintenance on the ignition system are the first things I would look at correcting, as well as checking valve clearances.

At least your bobber runs, albeit poorly. Most of the "custom bobbers" I see for sale on Craigslist can't even be started.

[Byrdi]

that was the most concise and helpful forum post i have ever read dude thank you so much i will do all this and get back to you i have tomorrow off so i should have plenty of time

he did rejet the carbs although he admitted very poorly it does have straight pipes which i am going change as soon as i get some cash I'm putting in 50 hours at work this week so my new toy will be dressed up a little better

[Griffin]

that was the most concise and helpful forum post i have ever read dude thank you so much i will do all this and get back to you i have tomorrow off so i should have plenty of time

he did rejet the carbs although he admitted very poorly it does have straight pipes which i am going change as soon as i get some cash I'm putting in 50 hours at work this week so my new toy will be dressed up a little better

Fair enough.

By the way, the manual on Cliff's site is titled "GS750 8 valve".

You are starting deeper in the hole than if the bike was stock, but hopefully the customizer didn't hack up the wiring system too much. That's usually where these boobers go wrong off the get go.

[Byrdi]

got my first spin on it today thing got 6 miles to the gallon i think the valves are fine but he jetted it so badly its just pumping fuel through the motor so I'm gonna start with the carbs

[smooth_358]

Which two were clean and which two were working. Can check once started if all the pipes are getting hot or not

[Byrdi]

too late to dig into it tonight he said 2 and 3 so I'm guessing the center two

[hjfisk]

too late to dig into it tonight he said 2 and 3 so I'm guessing the center two

I'm guessing all 4

[Byrdi]

I'm guessing all 4

when he checked the carbs two came up clean the other two were burnt but yeah starting to think they are just really really off

[Griffin]

You need to pull the carbs and check out what jets are in them. You also need to dismantle them and clean them per this procedure:

http://www.thegsresources.com/gs_carbrebuild.htm