Carb Noob

[MisterCinders]

So I have scoured the forums and BassCliff's site. I need to do the carbs and am a complete beginner at wrenching stuff.

I ordered the rebuild kits and new intake O-rings and fasteners.

I have new plugs, oil and filters (oil and air) ready to go onto the bike (1978 GS750).

While I wait for my packages, I offer the current symptoms and questions.

The Patient: 1978 GS750

Background - I am new rider and live in the city, so I have fewer opportunities to take the bike up to highway speeds. I have not really taken her over 40 mph. I bought the bike a couple of weeks ago and she was running pretty well (notwithstanding my meager riding/clutch skills).

I ran into a starting problem caused by a weak battery. Once I charged the battery, though, the electrical system seems OK. Haven't run the full Stator Papers yet, but after charging the battery and riding a few times, it maintains a solid 12.5-12.75v with the bike off.

Knowing that the carbs were in need of attention, but hoping to push that till winter, I did put some Sea Foam in the tank. I also added a bit of oil (3/4 qt.?) to get her to the full line.

Present State

This morning, I planned to ride the bike to work. She started up fine with a bit of choke and idled at about 1,000 RPM. After only a few blocks, however, the bike bogged down, was sluggish when moving from a stop, and stalled in neutral -- i.e., not because of my clutch skills. Even opening the choke (figuring it had not warmed up enough), the RPMs would not go over 2,000. Normally, the open choke idles at 3,000 - 4,000 RPM. I limped her back to the garage and sadly took the car to work. The short ride home had plenty of sputtering and some mild backfiring. In 1st gear, the engine struggled and felt like I was starting in a higher gear.

Other info, the plugs look black and oily.

Questions

Of course, I need and plan to go through all the checklist items folks point out here (carbs, airbox, intake rings, etc.). As I get ready for those tasks, here are some questions:

While the bike needs all the trimmings, do these symptoms indicate a particular need during the process (e.g., clean the carbs, but focus on ___ or look out for ___)?

I plan to check the valves. Do I need to pick up a full shim set ($100), or is it more sensible to figure out what shims are needed and just pick up those?

Since I have the plugs, oil, filters now, but won't have the carb kits until after the weekend, should I tackle the oil and plugs this weekend?

Is there any sense in changing them now and trying out an Italian Tune Up while I wait for the carb kits?

Or should that wait until after the carb work?

Soon after I got the bike, I went to fuel it up since I was not sure how much was in the tank. It only needed a gallon to fill. So, most of the fuel in the bike now may be a bit old (not years old, but could 6-8 weeks). Of course, I will drain the tank for the carb party. Would it help at all to drain the gas now and replace with fresh fuel?

Finally, the GS Map is not working, but I am in Chicago (north side). If any GSers in the area want to come by to offer advice in person, laugh at my ineptitude, etc., that would be cool.

Thanks in advance.

MisterCinders

 

[cowboyup3371]

MisterCinders, welcome. I experienced a little of the same thing except I already knew my bike wasn't running. I would thoroughly soak each carb for about 24 hours in the Berryman's fluid. As far as shims, do your measurements with a good metric feeler gauge and then shoot a PM to Ghostgs1 since he runs the shim club and you'll save yourself a ton of money. There's nothing wrong with doing the plugs and oil now and at least you'll be able to start wrenching on things and not wasting too much time. Make sure your air filter is new, oiled, and sealed up good with some weatherstripping tape in the air box (assuming you have a stock one and not pods). And yea, dump the fuel into your lawnmower or ant pile and start fresh. Your bike will love you for that. Plus, you'll have a chance to check out your tank and ensure there's no rust.

Basscliff will be along later but again...howdy.

 

[Big T]

Any work you do should be fine, but I'd start with the carbs and the gas tank.

I'd drain all the gas out and look inside your tank. You may have a sludge or rust build up in there -that could have gone down to your carbs and caused your problem. Get one of those little mirrors on a handle at the auto parts store and look around in there

Send the carb kits back - they're low quality and you don't need them. You don't actually "rebuild" the carbs, you just clean them and get them properly set. VM carbs are easy

You should measure your valve clearances now - get the shims you need from the Shim Club. You'll need the valves set to get your carbs set correctly

There's lots of GS people in your area, mostly in the suburbs. I'm sure you can get a helping hand if you get lost. You can find pictures of them in the Fennimore rally in the Meetingplace

North side? I've been known to hang around Halstead and Armitage (is that Near North side?)

 

[tom203]

"Knowing that the carbs were in need of attention, but hoping to push that till winter, I did put some Sea Foam in the tank. I also added a bit of oil (3/4 qt.?) to get her to the full line."

Was bike on centerstand when you thought it was low on oil? Also how much seafoam did you put in with about how much gas? After adding Seafoam, how long did you run before you decided to bailout? Too much Seafoam will cause strange behavior like you described till it disappears. Might take a good thirty minutes to work out. But this is in no way a substitute for a good carb cleaning. However, if it was running better before seafoam, I'd run it a bit longer and MAYBE you can put off the carb cleaning a bit.

 

[koolaid_kid]

You would be better served to use the VM Carb Rebuild Guide from Mr. BassCliff's site: http://members.dslextreme.com/users/bikecliff/
It is just to the right of the bike jpeg.
Follow the instructions closely and I suspect you will be quite pleased.

 

[MisterCinders]

Here is an update.

Changed the air filter.

Changed 3/4 of the plugs. One plug hole was bored out, so I need a helicoil (w/e that is ) to replace the other plug. Using the old one for now.

Changed the oil. That was a huge misadventure because of some dodgy threads on the filter cover bolts (which I have explored in another thread). For now, she is keeping the oil, but I am watching for leaks like a hawk. So far, so good.

I have not changed the fuel yet.

Started her up a few times to check the oil system. During those idle sessions (about a minute at a time), she behaves as follows:

With choke, she'll idle up to 3,00+, where I back down on the choke to idle at about 2,000 to warm up.

After idling steady for about 30 seconds, she starts to struggle. RPMs dwindle to 1,000 or less. More choke brings her back a bit. Throttle (1/8 - 1/4) also brings her back a bit.

She runs OK w/o choke once warmed (frpm,prior runs), but still sputters a bit.

Once the struggles begin, the exhaust smokes a bit - white smoke.

Any thoughts?

 

[BassCliff]

Hi,

Good work so far. Just keep going through the list; clean the carbs and install new carb o-rings (from http://cycleorings.com), adjust the valves, bench sync the carbs, install new intake boots and intake o-rings (maybe even new airbox to carb boots), vacuum sync the carbs. Then go from there.


Thank you for your indulgence,

BassCliff

 

[tom203]

She runs OK w/o choke once warmed (frpm,prior runs), but still sputters a bit.

Once the struggles begin, the exhaust smokes a bit - white smoke.

Any thoughts?

So how long has it run ( 5 minutes, 5 hours ?) since dose of Seafoam- and how much Seafoam did you add ( I asked this question before) ?
Sputtering and white smoke is classic seafoam behavior."runs ok w/o choke once warmed " sounds like improvement- but I'm only on my second beer!

 

[MisterCinders]

So how long has it run ( 5 minutes, 5 hours ?) since dose of Seafoam- and how much Seafoam did you add ( I asked this question before) ?
Sputtering and white smoke is classic seafoam behavior."runs ok w/o choke once warmed " sounds like improvement- but I'm only on my second beer!

I went with half a can of Sea Foam in basically a full tank of gas.

That was a week to ten days ago, and I have ridden it a few times since then. In the interim, I ran into an electrical hiccup (weak battery). Charged it up and rode again without incident for an hour or two. During that ride it seemed a little sluggish, but that could merely be my own squeamish newbie riding habits -- e.g., staying at lower RPMs/speeds because I am accustomed to car noises not bike noise, still getting used to the clutch interaction and stalling from time to time.

The last thing I did before the latest symptoms was to top up the oil because it looked pretty low in the sight glass. It is very hard to read the level. Fearing that I overdid it, I scrutinized the sight glass when I replenished the oil this morning. It is steady at the Full line.

I need to check the new plugs, but the old plugs showed black and dry. I suspect they are oily.

Comparing them to Clymers and other guides, I see this happy news:

Symptoms: Oily coating caused by poor oil control. Oil is leaking past worn valve guides or piston rings into the combustion chamber. Causes hard starting, misfiring and hesitation.

I will check the valves and clean carbs next. God help me if the problem goes deeper into pistion rings/seals. My baby wrenching skills probably won't take me that far down the rabbit hole.

One last question about draining the tank. How exactly do you drain the gas?

I picked up 2 5-gallon cans (one for old gas, one for fresh gas. Clymers helpfully tells me to "drain the fuel." I presume that you pull the fuel line, stick in can and set petcock to prime. Looking at the petcock, there seem to be two lines running out of it, but I can't figure out where the other ends are to pull them and run one or both into a gas can.

Removing the tank would reveal more, but don't I need to drain the gas first?

Or, if the vacuum operation prevents petrol from coming out of the tank, can you remove the tube from the petcock, leave it in On/Reserve and pull the tank with fuel to deal with it separately?

Thanks to everyone (especially BassCliff) for continuing to indulge me (see what I did there?).

MisterCinders

 

[Steve]

One last question about draining the tank. How exactly do you drain the gas?

I picked up 2 5-gallon cans (one for old gas, one for fresh gas. Clymers helpfully tells me to "drain the fuel." I presume that you pull the fuel line, stick in can and set petcock to prime. Looking at the petcock, there seem to be two lines running out of it, but I can't figure out where the other ends are to pull them and run one or both into a gas can.

Removing the tank would reveal more, but don't I need to drain the gas first?

Or, if the vacuum operation prevents petrol from coming out of the tank, can you remove the tube from the petcock, leave it in On/Reserve and pull the tank with fuel to deal with it separately?

To drain the tank, you remove both of the hoses from the petcock ONLY, do not remove them from the carbs. Get another length of hose to fit over the larger fitting on the petcock (ideally, it's 7mm, but 5/16" will work, with a clamp), put the other end of the hose in your collector, turn the petcock to PRIME.

Just so you know, you don't really need to drain the tank to remove it from the bike. If it's full, it will add about 30 pounds to what you have to lift off, but it should be fine, as long as the petcock is working properly.

If the vacuum hose happens to come off the carbs, you can put it back on easily enough, but if the fuel hose comes off, it is most often easier to pull the airbox and/or carbs to put it back in place.

.

 

[BassCliff]

Hi,

To familiarize yourself with normal maintenance tasks such as these, have a look at the guides and tips on my website. Removing the tank is pictured in the valve adjustment guide. There is a page called "Where Do These Hoses Go?" which explains connections to the petcock and carbs. Hopefully you'll find most of the information you need. If not, you know where to find us.

Thank you for your indulgence,

BassCliff

 

[tom203]

Yes, drain that seafoam contaminated gas and put some fresh stuff in; maybe drain fuel bowls also in case there's any sediment or water.
What's the mileage and when you bought it was it recently on the road?
As you're coping with this problem, don't lose sight of riding safety issues- new riders don't need any distractions!

 

[MisterCinders]

Yes, drain that seafoam contaminated gas and put some fresh stuff in; maybe drain fuel bowls also in case there's any sediment or water.
What's the mileage and when you bought it was it recently on the road?
As you're coping with this problem, don't lose sight of riding safety issues- new riders don't need any distractions!

Amen to the no distractions point. As I said, I am quite a cautious (i.e., wuss) rider. With these problems, I have even less confidence riding, especially at intersections, where responsiveness is hit-or-miss.

The mileage is/was about 17,300.

The bike was used regularly for the past year until about a month or two before I bought it, when the tags expired. The PO did not want to renew the tags since he was selling it.

Definitely going to purge the tank.

For a few new details, I started it up again this morning and idled it for a couple minutes to scope it out further in light forum comments. Here is what I noticed.

Cold start with a little choke (1/4 -1/3). Started right up and idled at about 1,000 RPM. Eased the choke a bit (1/3-1/2) and RPM went to 2,500. Let it run there for about 15 seconds, then dialed back the choke a bit. RPM went to 1,500 steady. Exhaust was clean throughout.

As I gradually closed the choke, the RPMs dwindled. Closed choke put the RPMs below 1,000 (maybe 800-900). With a little throttle (1/8 or so) she piped up, but then the exhaust got a little smoky, again white not black and not too thick. The post-throttle idle was much shakier, required more choke -- not a lot, maybe 1/4 - 1/3 to stay going. Closing the choke killed her.

Checked one of the new plugs, and it came out clean. Of course, I have only run the bike at idle a few times, so there may not be enough activity to show anything on the new plugs yet.

Thanks BassCliff, I have been studying those guides and the helpful posts ITT. Ready to tackle the tank now.

Stay tuned.

 

[MisterCinders]

Here is another question about the carbs/jets/valves.

From other threads about jets, I understand that an aftermarket exhaust system alters the jet settings (?). OTOH, I see other posts that say the jets on my bike are binary, they are screwed in or not, adjustments are made by installing different sized jets.

I note that my bike has Vance & Hines 4-1 pipes. How exactly does/should this affect my carb job and/or valve settings?

I ordered rebuild kits for the carbs and new o-rings Senor Barr. Despite an earlier post that suggested that I needn't use rebuild kits and should return them, I like the idea of having the back up pieces parts. Will the standard jets work with the VH exhaust?

Also, do the VH pipes change the valve clearances I should aim for?

Cripes, I am turning out to be more high-maintenance than the bike.

Thanks, nonetheless.

 

[MisterCinders]

So I drained the tank and pulled it.

Pulled the airbox, which looks pretty crappy.

Removed the carbs. Gonna break them down tomorrow.

Ready to change the intake rings and fasteners, when I see that 3 of the 4 have had the fasteners swapped to allen heads already. The fourth one has those AWESOME cheese tip screws that stripped to ****. Super.

The wiring underneath is pretty sexy too. After feasting on the cheese screw heads, those mice went to town on the wiring.

What have I done?

 

[cowboyup3371]

Honestly, you started the long process to bring this bike back to life. Pictures are encouraged please

 

[bwringer]

Yep, nothing unusual or insurmountable here.

It's well worth it to do a thorough job now -- you're trying to skip some steps.

You have 32 years of entropy to undo. Take your time, spend a little money when needed, and do it right. It'll be worth it.

 

[MisterCinders]

Yep, nothing unusual or insurmountable here.

It's well worth it to do a thorough job now -- you're trying to skip some steps.

You have 32 years of entropy to undo. Take your time, spend a little money when needed, and do it right. It'll be worth it.

I don't plan to skip any steps, but if I am missing something, let me know.

With tank, air box and carbs off, the plan is:

1. pull the intake boots and replace o-rings and fasteners;

2. check/adjust valve clearances;

3. clean/rebuild carbs;

4. remove and replace the oil filter cover bolts because they have dodgey threads;

5. obtain the thread expander/helicoil to change the No. 3 plug (which some PO bored out such that new plug won't fit.

Some other possible tasks are:

1. ditch my crappy airbox and go with pods;

2. tighten up the wiring situation -- everything works apart from the gear indicator, but I should replace and restore the insulation around the wiring harness; and

3. change out the jets.

1 and 2 are related, as I understand (barely) that changes to the air system will require changes to the jets.

What am I missing?

 

[Big T]

1 and 2 are related, as I understand (barely) that changes to the air system will require changes to the jets.

What am I missing?

You're over thinking this part

Changing the valve settings does not require new jets - you tweak the 2 adjustment screws

If you really feel you need new jets, get some from Z1 or jetsrus. Don't use the cheap junk in the K&L kits. Jets are precision devices, poorly made jets just cause you problems

Before you do any changes to the carbs, take them apart, clean them and note the main jet size, pilot jet size and needle position. This will let you know if your carbs have already been rejetted for the header

All the other steps look good. You are now on your way to curing the previous owner syndrome.

 

[MisterCinders]

Oh boy, this gets better and better.

Got the carbs off and separated.

Pulled the slide assemblies out to find that the slide on No. 2 is dented at the bottom edge. Here are some pics:

Checked Z1 and Bike Bandit, neither has that part. How the hell do I replace that?

Also the pilot screw on No. 1 had no spring.

The adventure continues.