1979 GS1000E - K&N Filter, Re-Jetting?

[mkaczmarek]

Hi,

First off I'd like to say this webpage is great. There is so much knowledge here I don't know where to start.

I recently got a 1979 GS1000E with about 38,000KM. The bike had been sitting for about 3-4 years. I wasn't able to start it at first as the choke cable was completely stuck (ceased). Once that was replaced it fired up on the first try, (wouldn't run without choke though), after a slight adjustment of the air screws on the carbs it started to run without choke. Regardless it does still have an intermittent backfire even at low revs.

Work which has been done on the bike so far includes:

-Oil and Oil filter change

-Fuel tank had rust (previous owner only had about 1/5 of tank filled, and no fuel stabilizer). Tank was removed, and repaired with POR-15 fuel tank repair kit. I highly recommend the product to anyone that wants to fix up their tank, its an amazing product.

I have picked up a K&N air filter (direct replacement for the stock), but haven't yet put it into the bike. If I do end up putting it in do I have to do rejetting in the carbs? If so what size jets would be recommended for this application. Mind you I have not done any other mods and it does all look stock (including the original Suzuki 4 into 2 exhaust).

There are many posts that somewhat touch on this topic but nothing specific with regards to my situation. I have been using K&N products in all my cars that i've owned up till now and it was the first thing that came to mind when thinking of "mods".

I have the bike running on a fresh tank of Sunoco Ultra94 gas (is that a good octane rating or should it be lower?)

Any help would be greatly appreciated. Also, any suggestions as to what could be causing backfiring?

 

[robinjo]

Completely dissasemble and clean your carbs and put new rubbers in them.:-D

 

[mkaczmarek]

K&N & Rejetting...

K&N & Rejetting...

Thanks, I kinda figured that carb cleaning would be required regardless, but I wanted to know what parts to get before I go ahead and remove it for cleaning, this way I have it all ready to be done in one shot.

In my case what size jets should I get if I end up switching to the K&N air filter, I will still be using the airbox, this is just a filter replacement, not air pods or anything of the sort.

 

[Sandy]

I'm running the K&N stock replacement filter in my '79 GS1000 and stock exhaust. I found the stock jetting to be spot on when running with or without the air box lid in place. I was getting some back firing on high speed over run but after rebuilding and syncing the carbs that went away. You've probably got one carb running a little lean do to either dirty carbs or bad syncing or both. Clean them up, change all the o-rings and give them a good sync. The hard parts, needles, jets, etc. usually don't need replacing but soft parts, gaskets, o-rings etc. should all be replaced. There's lots of info elsewhere on this sight about setting for your carbs. Just do a search for VM carbs. Good Luck. Oh yeah, make sure the valve clearance, spark plugs and ignition are in good order before doing the carb sync.

 

[SqDancerLynn1]

For the carbs the main thing you need is the O rings http://www.cycleorings.com

 

[KEITH KRAUSE]

Sandy...very unusual that removing the stock air box lid hasn't effected your jetting. It has on a couple of 1,000's I've jetted, including my own at one time. It leaned out my jet needle circuit the most. The main and pilot circuits too, but to a lesser degree.

 

[Sandy]

Sandy...very unusual that removing the stock air box lid hasn't effected your jetting. It has on a couple of 1,000's I've jetted, including my own at one time. It leaned out my jet needle circuit the most. The main and pilot circuits too, but to a lesser degree.

The key here is probably that I'm running stock exhaust and most of my riding is at 3,000 feet or over. I've done plug checks with and without the lid on and there really isn't a whole lot of difference, a slight difference yes but well within range. If you've got the better air flow of an aftermarket pipe there could a greater difference due to a less restrictive pipe. With the K&N filter and lid removed I did notice better throttle response through the mid range and slightly better power at full throttle, maybe 200 to 300 higher rpm in top gear. Probably due to a slighty leaner burn but as I said well within range according to the plug checks.

 

[mkaczmarek]

"To rejet or not to rejet...", synching tools

"To rejet or not to rejet...", synching tools

Ok, from the responses I've been seeing posted so far i'm guessing that a thorough carb cleaning should solve my backfiring problems? I have ordered those O-Rings today, I feel more comfortable ordering from a source that specialized solely in the GS's. When I was speaking with the parts guy at my local dealership he said there are various options for "Carb rebuild kits" but mostly I would still have to get various parts ie. certain O-Rings and jets seperately, they simply don't carry an All-in-one kit for it.

I guess what I'll do is remove the carb, clean all parts thoroughly (soak the jets for a day or so in carb cleaner? and put in the new O-Rings.

As to the "synching", I must admit I have never done it, but have looked over the guide that is on the website. Would you all say that guide is accurate in terms of the steps I should follow when working on my carbs? Any additions/alterations/suggestions anyone could add from past experiance? If not I'll just follow the guide and post an update once the work is done.

In terms of a carb synching tool, is the Carbtune II and the Carbtool (screwdriver/socket combo) pretty much the best tools to get for the job?

http://www.carbtune.com

 

[Sandy]

The VM Carb rebuild article is a great resource. The only other things you may need to check is the choke reservoir in the float bowl if you've had any rust in the tank and if your fuel tees leak after reassembly there is a quick fix here http://www.thegsresources.com/_forum/showthread.php?t=84789
Most of us use the mercury stick gauges similiar to those you mentioned with good results, they seem to be the industry standard. As for the adjustment tool, it would be a nice luxury to have, but a box end wrench with a long flat blade screwdriver works fine for me. Also make sure you don't rev the motor more than necessary and chop the throttle with the carb sticks attached or you'll be wondering where all the mercury in your gauges went. Let us know how it goes.

 

[KEITH KRAUSE]

Since the bike sat so long, the carb cleaning/o-ring rebuild is a must.
As for your backfiring, it could be a rich mixture due to clogged air passages in the carbs, but much more likely is electrical related.
Don't know if you have a newer ignition system or the stock points set up. If points, there's a good chance they need to be filed/cleaned and their dwell and the ignition timing re-set. Check the points and look for pitting (failing condensor?) and uneven contact. If not cleanable, replace and get a new set and condensors too. Can't tune the bikes carburetion without doing the electrical check first.
Also, as basic maintenance, inspect/clean the sparkplug cap connections and clean and gap or install fresh plugs. Should be NGK B8ES.
As for your carb work, just to add, set the floats at .94" to .95".
Always adjust the side air screws using the highest rpm method. They'll end up somewhere between 1 1/2 to 2 turns out normally.
You'll probably have to tinker with the pilot fuel screws (underneath) too. On a stock bike, try 1 turn out initially, test, and go from there.

 

[wiredgeorge]

You asked a bunch of things so I will try and respond to them...

-Fuel tank had rust (previous owner only had about 1/5 of tank filled, and no fuel stabilizer). Tank was removed, and repaired with POR-15 fuel tank repair kit. I highly recommend the product to anyone that wants to fix up their tank, its an amazing product.

------ I highly recommend and inline fuel filter for any older motorcycle. While you have treated the tank, residual rust will stay in the system plus you pick up stuff from the fill ups at the service station...

I have picked up a K&N air filter (direct replacement for the stock), but haven't yet put it into the bike. If I do end up putting it in do I have to do rejetting in the carbs? If so what size jets would be recommended for this application. Mind you I have not done any other mods and it does all look stock (including the original Suzuki 4 into 2 exhaust).

------- No rejet is needed but I like to swap the OEM #15 pilot jets for #17.5 pilot jets as they make starting and warm up easier and I feel tuning the idle circuit a bit easier. I would do this even with the stock air filter.


I have the bike running on a fresh tank of Sunoco Ultra94 gas (is that a good octane rating or should it be lower?)

-------- Poor idea to use 94 octane in your GS. The higher octane is needed by SOME engines that have higher compression in order to retard combustion. The higher compression engines will suffer pinging unless they use higher compression gas and/or retard ignition advance. The effect of higher octane gas in your bike will be incomplete combustion which will eventually soot up your combustion chamber and will build up on your valves. In time the soot will harden; especially on your exhaust valves and any pinging will detonate the carbon soot and cause the valves to pit. Lower (87 octane) gas will burn much cleaner and leave your combustion chambers including your spark plugs cleaner.

Any help would be greatly appreciated. Also, any suggestions as to what could be causing backfiring?

The backfiring can be either electrical or due to dirty carburetors. The electrical issue is just oxidation on contacts in the path the power takes to power your coils. You can check this by measuring power at your coils when you turn the key on and the bike not running. If you have less than 12 VDC, you will get backfiring due to poor spark. This is VERY VERY common on older bikes. If you have that problem, drop me a note and I will direct you to the already prepared info you need to fix the problem. The power goes from your fuse area, to and through your ignition switch via at least one connector, then to your kill switch through another connector and back out of the kill switch to yet another connector and then to your coils... the old switchs and connectors are the place where the oxidation occurs and cleaning may or may not make voltage issues better. The second reason for backfiring is generally air leaks in the pilot or choke circuits. Leaky choke plunger pads (the rubber gets hard and doesn't seal), the vacuum caps on your vacuum fitting being cracked, poor sealing of our intake manifolds or being cracked and the orings around your pilot fuel mixture screws are the most likely air leak places. Also, lean condition caused by obstruction in the pilot circuit where gas flows... that would be in the pilot jets themselves and in the passageways going through the circuit all the way to where gas atomized in the little hole in front of your needle jet are also very possible sources of the problem. Cleaning of the pilot circuit is needed if this is the case. If you have carb related questions, you can stop by my web site and there is a carb related message forum where I can probably help answer questions as I don't look in on this board every day.

 

[mkaczmarek]

Great Info

Great Info

That is a lot of good info.

I'll try your suggestions and since I will be taking the carb apart anyways I will change those jets from #15 to #17.5 as per your suggestion. I have noticed the bike takes a while to warm up and if this helps I will definitely do it. Btw, some say that original suzuki parts are best (quality), while others say aftermarket is just as good, what do you think I should buy?

==========================================================

I had an aside question and having looked at your website I figured I'd ask you since you seem to specialize in this area.

I was thinking about getting myself a spare set of carbs for this bike, I realize that my '79gs1000e has the Mikuni VM26mm. I basically wanted to do a little project in my spare time and at a relative low-mid cost, while not rendering the bike inoperable for the duration of the project.

What I had in mind was getting either another set of Mikuni VM 26mm, 28mm, 29mm etc. which I understand would be the simplest replacement for the VM26mm I have currently? By this I mean, not having to worry about throttle cable replacements etc.

However the other option that is mentioned on your website is the newer BS33 or 34 (I forget exactly). These require the throttle cable replacement right? among other parts that connect the carbs to airbox/engine...

I was wondering what pros and cons there exist between going for the VM style carbs (especially the bigger 28mm, 29mm etc.) versus the newer BS34mm?

What would you suggest.

What I want from my bike first and foremost is reliability. Since I won't ever be racing it I think it has ample power to begin with (although some may say you can never have enough). I think a good combination of reliability, easy of use/maintenance, efficiency/economy. Not sure what else to mention.

I guess in the near future I might have to replace the exhaust but I'm not convinced that I want to go to a 4-to-1 for the added performance. I think it takes away some of the character of the bike when the rest is stock and looks out of place...but I digress.

Looking forward to your reply and anyone else's for that matter.

 

[humhead]

In order to use BS 34 Carbs, You'll need a cylinder head from an 80 or newer 1000/1100 2 valve motor. You'll also need the valve cover (different bolt pattern) Airbox assembly (if you're keeping it stock) A 1980 1000e throttle & choke cable wouldn't hurt

Terry

 

[mkaczmarek]

In order to use BS 34 Carbs, You'll need a cylinder head from an 80 or newer 1000/1100 2 valve motor. You'll also need the valve cover (different bolt pattern) Airbox assembly (if you're keeping it stock) A 1980 1000e throttle & choke cable wouldn't hurt

Terry

I didn't realize the BS carbs would require so much stuff to be replaced. in other words, I think I'll stay away from the BS34 carbs...

In the case of the various VM 26mm, 28mm, 29mm etc. I take it its less "complicated" and less parts need changing?

Basically the purpose of this would be to do some thorough quality work on carbs, basically learn some things while not rendering my motorcycle inoperable for the duration of the project. and in the end having a spare set of carbs, hopefully tuned and working

 

[Dink]

The main cause of "back-firing" is air leaks into the exhaust system. The unburnt fuel and "fresh oxygen" in a hot exhaust is the cause.

Dink

 

[humhead]

Mikuni VM series carbs from 750 or larger GS Suzukis & KZ 900 - 1000 Kawasakis
will fit with little or no mods. One thing to watch for is the choke actuation.
Is it cable (what you should have) or lever (78 or older). If you find a set from another bike, you'll have to change the jets & cutaway to Stock 1000 specs.
This could be done while cleaning. I strongly recommend changing your intake pipes & o-rings. 26 year old rubber sometimes loses it's ability to seal, making carb tuning difficult.
What size VM's you use depends on what other mods you make to the motor & how you're gonna ride it.

Terry

 

[BadBillyB]

In order to use BS 34 Carbs, You'll need a cylinder head from an 80 or newer 1000/1100 2 valve motor. You'll also need the valve cover (different bolt pattern) Airbox assembly (if you're keeping it stock) A 1980 1000e throttle & choke cable wouldn't hurt

Terry

You can use a Kaw intake boot part #16065-1036 on the small port 2V head and it will accept a set of 33 or 34 carbs...I would recommend new ones though as they dont use an "O" ring to seal. The boot face is rubber.....BadBillyB

 

[humhead]

You can use a Kaw intake boot part #16065-1036 on the small port 2V head and it will accept a set of 33 or 34 carbs...I would recommend new ones though as they dont use an "O" ring to seal. The boot face is rubber.....BadBillyB

Once again, I've learned something. Thanks, Billy Is there any problem with carb to port size mismatch? An 8mm difference in diameter could leave an awfully big lip.

Terry

 

[mkaczmarek]

Changed Fuel and backfiring is all gone.

Changed Fuel and backfiring is all gone.

Well, after the suggestion to use regular 87 Octane fuel versus the 94 Octane I used previously the backfiring which was previously evident and at times extremely loud is now completely gone.

Now I still haven't gotten a chance to take out the carbs to clean/synch them, since I'm still waiting for the parts to arrive. But I guess in my case the backfiring was mainly fuel octane related.

I don't know where I'd be without this website/forum and the wealth of knowledge and input I get from all the users here.

My cheque will be in the mail this week.

 

[BadBillyB]

Once again, I've learned something. Thanks, Billy Is there any problem with carb to port size mismatch? An 8mm difference in diameter could leave an awfully big lip.

Terry

I dont remember, honestly, but these are the boots I used when I had 33 smoothies on my 1175 street motor. If theres a slight lip, it would need to be radiused though..........BadBillyB