Priority of carb crap

[roost]

So I've been working on my 1980 gs 750 this summer and haven't been able to get the bike running well, actually its getting worse.

There are common threads about carb cleaning, carb synchonizing, air/fuel adjustment, and valve adjustment. The order of these tasks seems to depend on ensuring the carb cleaning worked?

SO here's my problem. After cleaning my carbs, the bike would idle with the choke 1/2 out until warm, then would slowly die. I've tried to adjust the idle screw without any help. Tried to adjust the air/fuel screw, which probably made things worse.


How do I know I cleaned the carbs well enough? Should the bike idle without the choke?

[Nessism]

A carb rebuild tutorial is linked in my signature. Unless you want though them to the extent in the tutorial, you didn't do them well enough.

Also, check my signature again for the Top Newbie problems and read though that too.

Good luck.

[Steve]

How do I know I cleaned the carbs well enough? Should the bike idle without the choke?

When you have cleaned the carbs "well enough", the bike is well on its way to running properly.

As you mentioned elsewhere in your post, you also need to check valve adjustment and carb sync.

As far as specific order, you should do the valve adjustment first, to ensure that each cylinder is drawing the proper amount of mixture with each stroke. You can do that while waiting for your carbs in the dip.

Starting with a slightly rich mixture on the screws will help your engine run while synchronizing the carbs.

When the carbs have been synchronized, it will be easier to fine-tune the mixture.

Should the bike idle without "choke"?

Definitely.

Yeah, it might take some "choke" to start it and warm it up, but then it should idle just fine without any help.

.

[Dave8338]

My 850 even starts, without the choke...

[1_v8_merc]

The choke really isn't a choke on these bikes, it just enriches it.

So if you're running with the choke on, then stalling when it goes off....you either have a dirty Pilot Jet(idle jet), have dirty/old fuel, or possibly have a mixture problem.

Also, check your Idle knob.

And goto basscliffs website, grab a copy of the manual, and get your Mixture settings to factory settings FIRST.
(You will know when the settings are incorrect, because the bike won't start, or runs very badly)

Even 1/8's of a turn can affect the bike dramatically.....depending on the Carb.

[Steve]

The choke really isn't a choke on these bikes, it just enriches it. ...

Exactly why I always put "choke" in quote marks.

[dueller]

Also, check your Idle knob.

And goto basscliffs website, grab a copy of the manual, and get your Mixture settings to factory settings FIRST.
(You will know when the settings are incorrect, because the bike won't start, or runs very badly)

Even 1/8's of a turn can affect the bike dramatically.....depending on the Carb.

Yeah, your idle knob may be too low...

Should the bike idle without "choke"?

Definitely.

Yup, just may not run well but should run!

[roost]

Could someone explain the physiology of checking valve clearence? How does it affect the engine running/tuning?

I'm guessing I'll need to go through the carbs again. Is it important to buy new o-rings, or just clean the carb jets?

I've tried adjusting the idle screw, but I'm not close enough.

[Steve]

Could someone explain the physiology of checking valve clearence? How does it affect the engine running/tuning?

Changing the clearance on the valves will affect when the cam actually moves the valves.
Loose clearances will mean that the valves open later and close earlier.
Tight clearances mean that the valves open earlier and close later (if at all ).

Yeah, the clearance specifications are rather small, so it's possible that the valves are so tight, they won't be spending much time on their seats, possibly burning the edges (especially in the case of exhaust valves).

On the intake side, if the valves are tight, some of the intake mixture can actually be pushed back toward the carbs by the time the valve closes. The jets in the carbs don't really care which way the air is moving, they will just add some more fuel. When the valve opens again, air heads back to the cylinder, picking up even more mixture. This makes it REALLY difficult to start an engine with tight intake valves.

Because of the difference in the way each cylinder will breathe, based on valve adjustment/timing, you should do the valves first, then adjust your carbs.

I just did an adjustment on my bike a couple of weeks ago. It was starting just fine, running just fine, giving good gas mileage, so why check them? I had put about 5,000 miles on it since I got the bike, that's why.

Three of the four intake valves were still well within spec, which is why it was starting so easily. However, ALL of the exhaust valves were tight, two of them had to be changed two shim sizes. Fortunately, because they all were changed, the difference from one cylinder to another was not changed much. I checked the carb sync, it was close enough that I did not mess with it (I had checked it a couple weeks earlier, and it was fine).

.

[Gonzo]

I'm guessing I'll need to go through the carbs again. Is it important to buy new o-rings, or just clean the carb jets?

Get new o-rings. They loose elasticity as they age and don't work right anymore. Plus they are dirt cheap anyway. Might as well do it right while you're doing it. http://www.cycleorings.com/ Mr. Barr can hook you up right.

[SqDancerLynn1]

As others have said there are things that need to be done / checked. We have all been thru it. Any shortcuts usually ends up with doing the work a 2th time

[BassCliff]

Hi Mr. roost,

If you go through the maintenance lists in your "mega-welcome" and address every task, you will have a safe, reliable, fine running machine. If you skip any steps or take any shortcuts then you will be left stranded on the side of the road at best, injured or severely dead at worst. You have a 30 year old machine that needs 20 years of maintenance. Take your time, do it all properly. Then you and your bike will be insanely happy.


Thank you for your indulgence,

BassCliff

[TheCafeKid]

There are no shortcuts. Trying to use shortcuts just means doing them more than once. And that's not much of a shortcut then is it?

Replacing the Orings is just one of the many equally crucial steps in cleaning/rebuilding your carbs. The tolerances here are so fine that even the slightest of air leaks will make life more difficult.

Follow the tutorial. Clean/rebuild them properly.
Assure your airbox is sealed, the air filter clean and oiled (if required)
Assure there are no leaks around your intake boots (this requires replacement of the Orings behind the boots)
Adjust your valves

Otherwise you're just spinning your wheels. In the garage. Making vroom vroom sounds.

[roost]

Is there a good link/tuturial for adjusting the valve clearance? The carb cleaning link was really helpful with pictures, etc.

[Gonzo]

Cliff's post contains a link to your mega-welcome that has nearly every single thing you'll need. Take the time to click them, ingest what you can, get familiar with it, then dive into the bike.