Need help with carbs

[harmon44e]

I'm working on a bike (1980 GS850) for a neighbor that has a sparatic popping sound from the carbs. The story of the bike goes as follows: he took it to a shop becuase it wouldn't idle, they said the problem was the intake boots, then said the packing was bad in his mufflers. Instead of repacking the mufflers they rejetted his carbs and put on aftermarket air filters. $800 later the idle problem is fixed but now has a popping sound.

The bike runs fairly good, a little sluggish outside the powerband but smooth and no problems in higher rpm range. The popping can't be duplicated but happens most often at cracked throttle (cruising and decel) and no specifc RPM, and in all gears and is sparitic between carbs. It will also do it at idle and doesn't seam to care if its cold or warm. I have a 550 and campaired to mine his takes a long time to warm up and needs to be chocked. We are in the 200-300 sea level range.

I took the carbs off and cleaned them and recorded the folling jets sizes (I'm usure of what the correct jets names are but hope someone can tell by the #'s) 180/40/146 (only 3 had 146 one was a 136 ). The idle screws are all at different levels with one even being completely closed. He does not have the orignal air box and I have been unable to find out what the orignal jet sizes should be (in the event he goes back to stock).

The current air filters are K&N RC-2382 and the paper work says to increase jet size by 10% but like I said I have no idea what stock is. I'm under the assumtion that it didn't have the probelm before the "rejetting" and it does after then it must be a carb issue. I'm very mech inclined but bikes are still new to me and I need help in knowing which way to go. Ideally the cheapest way possible. He paid $100 for the filters and in my opinion I think the best option is to get the carbs matched to it. So I'm all ears (well in this case eyes) for advise.

[BassCliff]

Greetings and Salutations!

Hi Mr. harmon44ee,

Your friend has just experienced why we encourage each other to do our own work. In my humble opinion, you have done the GS850G a great disservice by installing pod air filters. Now it could take many days/weeks of performing plug chops, trying different main/pilot jet sizes, adjusting mixture screws, shimming needle jets, etc. After adding pods and pipes, one of the simplest things to do is to install a Dynajet Stage 3 kit. That gets the carb tuning pretty close. Now, before you start thinking that I know what I'm talking about, I'll shut up, invite you to visit my website for lots of 850G lovin', and give you your mega-welcome!

Let it be known that on this day you are cordially and formally welcomed to the GSR Forum as a Junior Member in good standing with all the rights and privileges thereof. Further let it be known that your good standing can be improved with pictures (not you, your bike)!

Perhaps you've already seen these, but I like to remind all the new members. In addition to the carb rebuild series, I recommend visiting the In The Garage section via the GSR Homepage and check out the Stator Papers. There's also a lot of great information in the Old Q&A section. I have some documentation on my little BikeCliff website to help get you familiar with doing routine maintenance tasks (note that it is 850G-specific but many tasks are common to all GS bikes). Other "user contributed" informational sites include those of Mr. bwringer, Mr. tfb and Mr. robertbarr. And if your bike uses shims for valve adjustments, send an email to Mr. Steve requesting a copy of his Excel spreadsheet that helps you keep track of clearances, shim sizes and other service work.

These are some edited quotes from one of our dear beloved gurus, Mr. bwringer, with ideas on basic needs (depending on initial condition), parts, and accessories.

***********Quoted from Mr. bwringer************
Every GS850 [and most other models] has (or had) a set of well-known issues that MUST be addressed before you have a solid baseline for further troubleshooting. It's a vintage bike, and it's quite common (as in, every single GS850 I have had contact with) that there are multiple problems that have crept up and slowly gotten worse over the years. It's not like a newer vehicle, where there's generally one problem at a time.

These common issues are:

1. Intake O-rings (install NEW OEM or Viton only - common nitrile O-rings will quickly deteriorate from heat)
2. Intake Boots (install NEW -- these cannot be repaired)
3. Valve clearances (more important than most people think)
4. Carb/airbox boots
5. Airbox sealing
6. Air filter sealing
7. Petcock (install a NEW one)
8. On '79 models, install new points or Dyna electronic ignition (or at least verify that the old points are working correctly)
9. On all models, it's fairly common to have problems with the spark plug caps. These are $3 or $4 each, and often worth replacing if you're keeping the stock coils/wires.
10. Stock exhaust with NO leaks or holes -- good seals at the head and at the junctions underneath.

Carburetor maintenance:

Replace the intake boot o-rings, and possibly the intake boots. Here's the procedure:

http://bwringer.com/gs/intakeorings.html

Here's an overview of what happens with this particular problem:

http://cycleorings.com/intake.html

You'll also want to examine the boots between the carbs and the airbox. There's a good chance these are OK, but check them over.
And finally, if things still aren't exactly right, you'll want to order a set of o-rings for BS carbs from the GS owner's best friend, Robert Barr:

http://cycleorings.com

Once you receive these rare rings of delight, then you'll want to thoroughly clean and rebuild your carburetors. Here are step-by-step instructions that make this simple:

http://thegsresources.com/gs_carbrebuild.htm

OEM Parts/Online Fiches:

I would definitely double and triple the recommendations to use Cycle Recycle II and Z1 Enterprises as much as possible. These guys are priceless resources. Z1 tends to have slightly better prices, CRC2 has a wider range of goodies available. If you're near Indy and can bring in an old part to match, CRC2 has a vast inventory of used parts.
http://denniskirk.com - Put in your bike model and see what they have.
http://oldbikebarn.com - seems to be slowly regaining a decent reputation, but it's still caveat emptor. They don't have anything you can't get elsewhere at a better price anyway.
http://www.babbittsonline.com/ - Decent parts prices. Spendy shipping. Don't give you part numbers at all. Useful cross-reference if you obtain a part number elsewhere. Efficient service.
http://bikebandit.com - Fastest. Middlin' prices. Uses their own parts numbering system to obfuscate price comparisons -- can be very confusing for large orders. Cheapest shipping, so total cost usually isn't too bad.
http://flatoutmotorcycles.com - Slow. Cheapest parts prices, crazy shipping costs. Don't expect progress updates or much communication. Real Suzuki part numbers.
http://alpha-sports.com - Exorbitant parts prices. Different type of fiche interface that's quite useful at times, especially with superceded part numbers. Real parts numbers. Shipping cost and speed unknown due to insane, unholy pricing.

Stainless Bolts, Viton o-rings, metric taps, dies, assorted hard-to-find supplies and materials, etc:

http://mcmaster.com - Fast, cheap shipping, good prices. No order minimum, but many items like bolts come in packs of 25 or 50. Excellent resource.
http://motorcycleseatcovers.com - Great quality, perfect fit (on original seat foam), and available for pretty much every bike ever made. Avoid the textured vinyl -- it's perforated.
http://newenough.com - You DO have riding gear, don't you? Great clearances, always outstanding prices and impeccable service.
***************End Quote**********************

Additional parts/info links:

GSR Forum member Mr. duaneage has great used upgraded Honda regulator/rectifiers for our bikes. Send him a PM.
New electrical parts:
http://stores.ebay.com/RMSTATOR or http://www.rmstator.com/

http://www.ricksmotorsportelectrics.com/index.php

http://www.electrosport.com/

For valve cover and breather gaskets, I recommend Real Gaskets (reusable silicon):

http://www.realgaskets.com

Carolina Cycle

http://www.carolinacycle.com

Ron Ayers Motorsports

http://www.ronayers.com

MR Cycles

http://www.mrcycles.com

Moto Grid

http://www.motogrid.com

Salvage/Used

http://www.ricepaddymotorcycles.com

http://www.ozpowersports.com/

If all else fails, try this:

http://www.used-motorcycle-parts.org/

Used bike buying checklists:

http://www.amadirectlink.com/roadride/Riderresc/checklist.asp

http://www.clarity.net/~adam/buying-bike.html

Lots of good info/pictures here:

http://www.suzukicycles.org

http://www.cyclechaos.com/wiki/Motorcycle_Wiki

http://www.bikepics.com
Basic motorcycle maintenance/repair:
http://www.dansmc.com/mc_repaircourse.htm
Online Clymer manuals:
http://search.ebscohost.com/ Click on "Small Engine Repair" then "Motorcycles". User=library, password=library. Note: This link may not work if you are on a school campus.


Thanks for joining us. Keep us informed of your progress. There's lots of good folk with good experience here.


Thank you for your indulgence,

BassCliff
(The unofficial GSR greeter)

Click here to visit BikeCliff's website.

[psyguy]

i would put the original jets back in and use the original airbox for a start
only after you have a decent running engine in a stock configuration it is worth playing with the carbs

you may just get lucky and sort his problem by doing something simple, but what exactly that "simple" thing might be could cost a lot money and time...

if the engine compression is in spec as are the valves and if there are no intake leaks, the carbs are thoroughly clean and the rubber orings in them are good, then (and only then) i would go for 42.5-45 on the pilot jets and 117.5-120 on the main jets (while using the pods)

the sizes of the main jets you mention might be a different sizing/measurements, not mikuni parts


for the stock jet sizes look up the sticky thread in this forum

[Steve]

Stock main jets in an 850 are 115.
With a stock pipe and pods, you might need 120 or 122.5 mains.
Pilot jet should remain stock.
You might need to shim the needles.

I agree that modifications are best done after good running in stock configuration is acheived, but without a stock airbox, you are going to have to take your chance.

.

[rustybronco]

The story of the bike goes as follows: he took it to a shop becuase it wouldn't idle, they said the problem was the intake boots, then said the packing was bad in his mufflers. Instead of repacking the mufflers they rejetted his carbs and put on aftermarket air filters. $800 later the idle problem is fixed but now has a popping sound.


I took the carbs off and cleaned them and recorded the folling jets sizes (I'm usure of what the correct jets names are but hope someone can tell by the #'s) 180/40/146 (only 3 had He paid $100 for the filters and in my opinion I think the best option is to get the carbs matched to it.
So I'm all ears (well in this case eyes) for advise.

http://www.thegsresources.com/_forum...ad.php?t=73723
dig through it and you will find the jet sizes.

spent $800 + $100 and the problem is fixed? I don't think so....
I'll give them the carb boots may have been bad, but does the exhaust sound loud?
my opinion...
find a air filter assembly on e-bay, put it back on, put the correct jets in it and go from there. and lest I forget, don't have him go back to that place of repair, EVER!

[dtkid]

I didn't read the entire post...however, if the popping is pretty much the only problem...you may stop the popping by installing new exhaust gaskets.

When the exhaust is not "sealed" to the motor block cold air can get sucked into the breach. The fact that the popping occurs upon deceleration indicates that new exhaust seals are needed.

[harmon44e]

Thank you for the welcome and like most people I wish I'd found this site months ago. I don't object going back to stock and working our way out from there, Acording to the info I have gather from this site the stock jet sizes should be

GS850
starter jet #32.5
pilot air jet #200
pilot jet #42.5
main jet #115

Yet every rebuild kit that I have located the jets do not match these specs. does anyone know of a kit that has a variety of jets? Or a place that you can get specific sizes? Or does anyone have some laying around that they want to let go? Or am I looking for the wrong sizes?

I'm going to run through all the other possible causes but know for sure that one of the carbs is not jetted the same as the others and the air mixture screw was completely closed on a different one; that makes no sense to me at all. Since all the carbs pop I don't think that is the cause but needs to be adressed so that it doesn't result in being a problem later.

[psyguy]

http://www.carbkitscapital.com/

http://www.wgcarbs.com/

http://www.motorcyclecarbs.com/

[Big T]

For jets, try jetsrus.com for cheaper prices. They're genuine Mikuni jets, fast shipping.