I can't take it anymore!!!

[Mahalaleel]

So, I have been testing various theories and fixing random things for two months now on my '78 GS750.

I started by cleaning the carbs. Installed them and had problems getting it to start. Recleaned them. Now it starts up fine with one or two kicks.

Then the idle was SUPER high. Like 3000 RPM. When i pushed down physically they would return to about 1400. Anything below 1400 and it stalls out.

So I switched some of the slides around in the carbs and re-synched them.

I found an intake leak between the boots and the engine, fixed that. Replaced the o-rings.

Now it starts, and will idle at 1300-1400. Anything lower and it will stall out. When I give it very little amounts of throttle the RPM climb normally.

If I give it more than 1/8 throttle it starts to cut out, fart and pop.

What did I do now!?!?!? Is there anyone in Utah that could make a trip to help me out? I've gotten to the point where I may just abandon the thing or sell it.

Please save me!

[almarconi]

Its a 32 year old bike, what did you expect?

Trying to fix an old bike willy nilly is just an exercise in futility. Get a service manual, read it and then go through each system on the bike and fix what is needed.

On a bike that old, pretty much everything that is rubber will need to be replaced. How did you clean the carbs? Strip, dip and replace all the o-rings?
You could have electrical and/or fuel delivery issues. Until you formulate a game plan to get the basic maintenance done, I'm afraid your not going to have much success.

Don't get discouraged, you can get it running. It will just take some time, money and lots of patience.

[indyjoel]

Dont give up, someone will come up with an idea.

[Mahalaleel]

On a bike that old, pretty much everything that is rubber will need to be replaced. How did you clean the carbs? Strip, dip and replace all the o-rings?

Yes

You could have electrical and/or fuel delivery issues. Until you formulate a game plan to get the basic maintenance done, I'm afraid your not going to have much success.

I haven't looked into electrical other than confirming that all four cylinders are getting spark, which they are.

I think it's a fuel problem. My biggest fear is that the carbs still need something.

I have the air and fuel pilot screws out one turn and two turns as instructed. Could adjusting those resolve anything?

The fact that the throttle problems happen with 1/4 throttle and up suggest to me that it's one of the jet/screws in the carbs. They should all be clean.

Could it be the float bowls?

Sorry to seem so dramatic, I just got really frustrated tonight.

[almarconi]

I have the air and fuel pilot screws out one turn and two turns as instructed. Could adjusting those resolve anything?

Your air screw should be about 1.5 turns from lightly seated, the fuel screw about 5/8-3/4 of a turn from lightly seated if your bike has Mikuni VM carbs. Who instructed you to use your settings?

Your float height and fuel level in the bowls should also be set according to the manual. You do have a manual for the bike right? Float height you can set with a calipers, fuel level is set with a clear tube. Do a search for the procedure or look in your repair manual (you do have the repair manual?) Did I mention that you really should have a repair manual.

Before messing with the carbs you should check the valve clearances. If they are not within spec they should be adjusted.

[boingk]

1] Are you running stock intake and exhaust?
2] Are you running stock carb settings and jets?
3] Is your choke connected and functional?

- boingk

[Mahalaleel]

1] Are you running stock intake and exhaust?
2] Are you running stock carb settings and jets?
3] Is your choke connected and functional?

- boingk

1. Stock exhaust. Pod air filters (PO installed)
2. Carbs and jets unknown (PO may or may not have adjusted for the pods)
3. choke is connected and functional, just hella hard to move

[hampshirehog]

If it's running pods you'll need to check the mains and needle position. It's almost certainly running weak from your description.

[tkent02]

If he's in Utah, he's likely at a fairly high elevation, the fuel and air screw settings need to account for this. Pipe and pods of course will effect things too.

There's really no way top go about it but to get everything else in the entire engine perfect and start doing plug chops to get the carburetion right.

It takes a lot of time.

[Mahalaleel]

So, you're in Colorado? I'm from Fort Collins. Yeah, Provo is pretty high. I don't know exactly.

I have no history on the bike. Is there a guide to tuning with plug chops?

There's a certain jet or screw that provides fuel at different amounts of throttle, right? The problem with it at 1/4 throttle could be a specific jet or screw?

[tkent02]

At 1/4 throttle is mostly the jet needle in charge, but is it too rich or too lean at the time? You need to know. Look at Cliff's site, there is a page on there about plug chops.

[Nessism]

Its a 32 year old bike, what did you expect?

Trying to fix an old bike willy nilly is just an exercise in futility. Get a service manual, read it and then go through each system on the bike and fix what is needed.

On a bike that old, pretty much everything that is rubber will need to be replaced. How did you clean the carbs? Strip, dip and replace all the o-rings?
You could have electrical and/or fuel delivery issues. Until you formulate a game plan to get the basic maintenance done, I'm afraid your not going to have much success.

Don't get discouraged, you can get it running. It will just take some time, money and lots of patience.

Listen up to this advice! All true!

If you want the bike to be reliable you need to do all the maintenance. Have you adjusted the valves? Does the bike still have the rubber brake lines installed? Replaced the points lately?

As others have already said, the bike won't run for crap with those pods unless the carbs have been rejetted. Running it that way will also damage the engine due to a lean mixture condition will cause the engine to run hot. Elevation is working in your favor regarding the rejetting but still, you need to put in the time or the bike will crap out and eventually destroy itself.

[Mahalaleel]

Good news! I think

Yesterday I put it all together, pumped up the front tire, and went for a little ride around the neighborhood.

The RPM still hang when I pull the clutch in, decreasing very slowly. It sounds like air is getting sucked rather loudly from somewhere. I'm not sure if it's just the sound the pods make, but it's hard to tell.

I want to do plug chops. I read the guide on basscliff's website. Any other tips?


Also, I will eventually do everything needed for the bike (check valve clearances, etc.) I'm just focusing on correcting the major problems first, because if it's going to cost too much or I can't fix it I will probably sell the bike instead of replacing every single part.

[Big T]

Good news! I think

Yesterday I put it all together, pumped up the front tire, and went for a little ride around the neighborhood.

The RPM still hang when I pull the clutch in, decreasing very slowly. It sounds like air is getting sucked rather loudly from somewhere. I'm not sure if it's just the sound the pods make, but it's hard to tell.

I want to do plug chops. I read the guide on basscliff's website. Any other tips?


Also, I will eventually do everything needed for the bike (check valve clearances, etc.) I'm just focusing on correcting the major problems first, because if it's going to cost too much or I can't fix it I will probably sell the bike instead of replacing every single part.

1. Proper valve clearances are critical to proper tuning - it may never run correctly without this
2. Get a second set of spark plugs for the plug chops - that way you can have a set that's not burning hot (Install carefully in hot motor)


Frankly, I'd try to source an airbox. Pods with a stock exhaust are just a PITA with no discernable upside

[boingk]

Pods with a stock exhaust are just a PITA with no discernable upside

I can think of a few:

1} Throttle response much improved
2} Reusable, servicable filter media
3} Increased performance (if you get the jetting right)

- boingk