Some carb questions to get the beast running!

[650cafe]

Hello all,
I'm sure I can find the answers to my questions by doing a search and sifting through dozens of similar threads, but I find asking the basic questions usually results in a quicker solution.
Background: Purchased a 1983GS650GL from a bike shop owner. He claimed to have rebuild the carbs. According to him all the bike needed was some minor reassembley of some parts, but to run he said it just needed a battery and a clean fuel tank mounted up and hooked up to the carbs.

Yeah....I've been down this road before too....

Anyway, I got a new AGM type battery. Check the first item, and the bike turns over good.

I have a spare Sportster tank on hand, so I used it as a fuel supply until I can get a good tank for this project. Hooked up the Sporty tank to the fuel line, dumped some gas into the tank, fuel is flowing down into the see-through filter. For a second some gas dribbled out of the overflows, but a couple taps on the bowls stopped it. Cracked the bowl drain bolts, got gasoline there.

Tried starting it, nothing. Pulled the plugs. All 4 are used, but looked OK. Cleaned them up, regapped them, checked them for spark, all sparked. The plugs were dry.

Tried cranking it again, still nothing. Pulled plugs again. Still dry. Shot a little starting fluid into each carb. She fires and runs for a second then dies. Pulled plugs; still dry.

Despite pumping and pumping the throttle and playing with the choke the bike still isnt getting fuel. Fuel is making it to the carbs, as evidenced by the gas in the bowls, but that seems to be as far as it's going. Twisting the throttle opens the butterflies on the engine side of the carbs, but I cant see that any fuel mist is being shot into the carbs, and the slides arent going up and down. These are CVs, which i have very little experience with...do the slides move with airlflow/vaccuum? The choke assembly seems to be operating normally from what I can surmise.

I gues my question is, me being unfamiliar with CV carbs, where would be the most likely place to start looking for a carb issue? I dont want to tear them off, but it's clear they need cleaned again. The bowl drain screws were gummy, and the slides were sticky at first. I can now push them up by and and they come back down, albiet slowly.
If I take them off will I need to re-sync them? Or can I do a simple clean up job, noting adjusting screw postions, etc, and give it a go? Any advice here is very welcome.

[slayer61]

He claimed to have rebuild the carbs... He lied to you

The bowl drain screws were gummy, and the slides were sticky at first. I can now push them up by and and they come back down, albiet slowly.


These are sure signs that you need to strip and dip your carburetors. Also look for deteriorated diaphragms on the top of the slide. CV carbs aren't any tougher to clean than slide carbs. Take lots of pictures and notes. Hell, take one apart at a time leaving the others for example if that helps, Paul

[Agemax]

try blanking off the vacuum port on the carbs that would normally join to the fuel tap.
top front of No.2 carb i believe. if that is left open without running a vacuum tap then that will cause starting difficulties

[tom203]

Follow the carb cleaning mantra on this site; your gummed up carbs likely have gummed up passages- The "choke" system has its own pickup in bottom of each fuel bowl which climbs up little passage to carb throat and helps to get things going- no fuel here means no run . Once you clean carbs, do NOT apply throttle or you defeat the purpose of the "choke" (actually a fuel enricher).
When cleaned properly, these carbs perform wonderfully. Read thru this long link and give it a go

http://www.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

[650cafe]

wow..great responses right away! Thanks guys. I was wondering about the vaccuum line. My main question was answered today...the bike will run. It turns over well, has spark, and given a shot of something flammable into the intake and it makes sound.
I think he did clean the carbs, but the bike has been sitting since then and obviously the carbs have re-gummed-up. I was really hoping to not have to mess with them, but it looks like I'll have to.
At any rate I can move forward with the project knowing the bike will run...I can sort out that stuff later. Thanks guys!

[BigD_83]

What Agemax said and then start looking into the valves...

Clearance and Compression numbers?

[JTGS850GL]

Carbs need to come off and rebuilt correctly. Here's a link to give you a step by step:

How to rebuild your CV carbs

and

Mikuni BS CV Carb Rebuild Tutorial

Not as hard as it may seem. The only area that I've had any issues with were getting those stuborn air screws out. Follow the rebuild guide to the letter and you shouldn't have any problems. Pic up a set of Orings from here:

CycleOrings.com

And while your at it, here's a great site for more information:

BikeCliff's Website

[JTGS850GL]

Man you guys are fast!!!

PS, pumping the throttle will do nothing on a CV carb. They don't have any type of accelerator pump.

+1 on doing the valve adjustments first. Tight valves will mess up your carb adjustments.

[BigD_83]

Man you guys are fast!!!

PS, pumping the throttle will do nothing on a CV carb. They don't have any type of accelerator pump.

+1 on doing the valve adjustments first. Tight valves will mess up your carb adjustments.

While it is true that turning the throttle will not help with the GS650,

This ^^^^^ isn't exactly true. The Mikuni carbs that were stock on this series do not, but other CV carbs (like some Keihin carbs on Hondas) do have accelerator pumps.

[Steve]

He claimed to have rebuild the carbs. According to him all the bike needed was some minor reassembley of some parts, but to run he said it just needed a battery and a clean fuel tank mounted up and hooked up to the carbs.

You know how to tell when a previous owner is lying?

Yeah, his lips are moving.

Anyway, I got a new AGM type battery. Check the first item, and the bike turns over good.

Good choice.

I have a spare Sportster tank on hand, so I used it as a fuel supply until I can get a good tank for this project. Hooked up the Sporty tank to the fuel line, dumped some gas into the tank, fuel is flowing down into the see-through filter. For a second some gas dribbled out of the overflows, but a couple taps on the bowls stopped it. Cracked the bowl drain bolts, got gasoline there.

The in-line filter might be OK for testing, but not usually recommended for use while riding. Most fuel filters purchased at an auto supply house are designed for cars with pressurized fuel delivery systems. Our bikes do not have fuel pumps, so those filters are too restrictive to allow enough flow.

Tried starting it, nothing. Pulled the plugs. All 4 are used, but looked OK. Cleaned them up, regapped them, checked them for spark, all sparked. The plugs were dry.

Tried cranking it again, still nothing. Pulled plugs again. Still dry. Shot a little starting fluid into each carb. She fires and runs for a second then dies. Pulled plugs; still dry.

As you are seeing, just because you have gas in the float bowls does not mean that it's getting into the cylinders. The only thing between the two is all the small passages inside the carb bodies.

Despite pumping and pumping the throttle and playing with the choke the bike still isnt getting fuel. Fuel is making it to the carbs, as evidenced by the gas in the bowls, but that seems to be as far as it's going.

See, you are coming to the same conclusion, too.

Twisting the throttle opens the butterflies on the engine side of the carbs, but I cant see that any fuel mist is being shot into the carbs, and the slides arent going up and down.

There is only one model GS that I know of that came with accelerator pumps, and your bike is not it.

The slides will not be going up until the bike is running and you have enough air flow going under them to generate sufficient vacuum to lift them. At this point, that is not a problem.

These are CVs, which i have very little experience with...do the slides move with airlflow/vaccuum?

As air moves faster through a tube, pressure decreases, this is the Bernoulli principle and the reason for the venturi (the narrowed-down area) in the carb. As the throttle butterflies are opened, air has to really speed up in the narrow area under the slides. The pressure of the air under the slide gets lower, and that is channeled up, through a hole in the slide, to the chamber above the diaphragm at the top of the carb. THAT is the vacuum that lifts the slides, not the engine vacuum between the throttle butterflies and the intake valves.

The choke assembly seems to be operating normally from what I can surmise.

I beg to differ with you on this one. If the engine did not start and idle, the "choke" is not working properly.

I gues my question is, me being unfamiliar with CV carbs, where would be the most likely place to start looking for a carb issue? I dont want to tear them off, but it's clear they need cleaned again.

Well, you answered your own question. Sorry, but you HAVE to take them off and clean them. By now, it should be clear that using the word "again" is not proper, as they probably were not cleaned properly the first time.

The bowl drain screws were gummy, and the slides were sticky at first. I can now push them up by and and they come back down, albiet slowly.

That might be acceptable if the bike has sat in the corner of a barn for the last 20 years or so, but not for a bike whose carbs have been recently "cleaned".

If I take them off will I need to re-sync them? Or can I do a simple clean up job, noting adjusting screw postions, etc, and give it a go?

Simply removing the carbs and putting them back on will not require a re-sync, but to properly clean the carbs, you will need to strip them down COMPLETELY.

You will need to go from this:


to this:


and back to this:


When you put them back together after that, you will need to re-sync them.

Man you guys are fast!!!

Funny, I am usually accused of being half-fast. (please say that carefully )

PS, pumping the throttle will do nothing on a CV carb. They don't have any type of accelerator pump.

Sorry, can't make a blanket statement like that. MOST of the GS CV-type carbs did not have pumps, but the 450GA did.

As BigD mentioned, there were other manufacturers of CV-type carbs that offered pumps on them, but none of them were used on Suzukis.


.

[JTGS850GL]

Sorry, I meant the CV's that were used on his bike. Thanks for the clarification.

[650cafe]

Thanks Steve. That was a very succinct post. You answered all my questions, recognizing that I might actually have some mechanical ability and a modicum of knowledge, just no expericence with this subject.

Your answers were pretty much all the ones I didnt want, but that I already knew. I've never had a problem with a CV carb. My wife's Sportster has one and I've never once had a problem with it, and it does have an accelerator pump.

If I remember the PO's story, he rebuilt the gang about 2 years ago. It doesnt seem evident that the bike has been a runner since then. He also claimed new head and valve cover gaskets, which is true...I can see the clean edges of new gaskets poking out of those surfaces. I dont doubt that he did something to the carbs, but as you say, I'm not convinced it was done properly.

Well as I said, my main question was answered today....the bike will run. It may need the carbs cleaned and the valves adjusted, on and on, but I feel confidant I moving forward with my customization of it. I trust this forum will be here to help me through the process of rebuilding this bike. It's impressed me so far. Thanks to all.

[650cafe]

Ok...ordered the whole she-bang from cycleorings.com....o-ring kit, intake seal kit, even the new SS intake mounting screw kit, and some bowl gaskets from cycle-recycle. I think I'm gonna hold off doing this job till I have a good couple days to devote to it. i have a weeks vacation coming up in November...think I'll slate this project for that.
Until then I need to work on cleaning up the electrical system and eliminating systems I dont want/need. I built a new battery holder today, and I need to fabricate a framwork in the area under the seat where the airbox used to reside for the remaining electrical stuff to go. I'll be posting questions about the electrical system in that section soon. I keep this thread for when I start building the carbs, if I have questions.

[850 Combat]

Get it running right first. Good plan.

[Steve]

Plan on more than a couple of days.

Each carb needs to spend about 24 hours in the dip.
Assuming that you start this on Friday evening, you will remove the carbs from the bike, separate the rack, disassemble the carbs and get the first one in the dip on Friday.
Saturday evening, you will take out the first carb, put in the second one.
Sunday, you will take out the second and put in the third.
Monday, you will take out the third and put in the fourth.
Tuesday, you will finally take out the fourth carb.

Even though you will have rinsed each carb in HOT water, shot some spray through all the passages and followed that with some compressed air, you probably will not get the carbs together, let alone on the bike, before Thursday.

By the way, all that down time is a perfect time to check valve clearances, if you haven't done that already.

.