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78 1000 C pilots

chuck hahn

chuck hahn

Forum LongTimer
Past Site Supporter
Ok this may be a dumb question, but i was wondering if ..in theory..that turning the pilots out another half turn would make much of a difference on top end speed. With them set as they are i am topping out around 115 MPH. my 750s do better than that. The pilots are now out 1 5/8 turns from lightly seated ( VM 26 carbs). I was thinking turn them out to an even 2 turns. Probably run a bit rich at that point and just fine tune down with the air screws..does this seem logical? I should also state the obvious before you ask..yes i have replaced the intake boot orings and the boots are in excellent shape with no wear. Just looking for the optimum setup here. As for jets, i didnt look inside, so i am gonna have to say at this point i believe they are stock carbs all the way around.
 
Chuck,

The pilot circuit is for low speed, not wide open. You need to mess with the main jets if you feel top end performance is not what it should.
 
Chuck aren't you Pilot's supposed to be around 5/8 out? and your air mixture around 1 1/2.
 
I dont know!! I took the bike down and did the frame off restore and was curious to see what they were set at and bottomed them out just to see where they were set. I did all 4 and that what they were at. I was thinking go to a full 2 out to allow more gas flow..then fine tune with the air screws..I am not all that well veresed on carb setup but understand the basics here. And the air screws were out 1 1/2 turns.
 
Ok ED.. I will have to check whats in there now then..i am assuming stock mains. What is the stock size, and what would you suggest to get a bit more top end???
 
chuck hahn said:
Ok ED.. I will have to check whats in there now then..i am assuming stock mains. What is the stock size, and what would you suggest to get a bit more top end???
Click to expand...

Chuck,

The fuel screws are typically set in the .75 open range, air screws about double that. A stock bike shouldn't need more than 1 turn open on the fuel.

If the bike is stock I'd use the stock mains and then perform some plug chops to get a read on the plugs. I'm not a fan of changing the jets without knowledge of what's going on with the system first.
 
Well it idles just fine and very smooth..it jumps like a scalded dog at the first flinch of the throttle and pulls strong and no hesitations at any RPM range. I just think its a bit doggish on top end speed since both of my 750s are matching what a 1000 is doing!! Seems i should easily get 130 out of the 1000..or at least i wish!! So you guys are saying that i should reset the pilot screws to only a max of 1 turn out then..no need for the 1 5/8 that they are at? And keep screws at the 1 1/2 out that they are now?
 
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I thought the GS1000's came out with VM28's, 0.95 mains, it sounds as if your throat size and maybe even your main jets are too small... something to think about.
 
rsck said:
I thought the GS1000's came out with VM28's, 0.95 mains, it sounds as if your throat size and maybe even your main jets are too small... something to think about.
Click to expand...

US market 750/850/1000 bikes built prior to the 1980 model year received VM26 carbs. I've heard that certain market 1000S bikes had larger VM carbs, but haven't heard much else. Which bikes received VM28's?
 
here are the 1978 vm26SS carb specs for the 1000 c straight from my Suzuki service manual

78%201000%20carb%20specs.jpg
 
Chuck

A few notes on the posts so far

1. If your fuel screws are 1 5/8 out and you bike idles nicely, you probably have some air leaks because that's double the fuel flow it needs. Turn them back to under 7/8 and see what happens
2. The fuel screws do nothing for the top end, as Ed noted
3. Your main jets stock are #95, per Spyderman
4. If you're making a top speed run, the bike should run right to redline in gears 1,2,3, then take longer in 4th. You should be able to reach 115 mph in 4th
The main factor in top speed is wind resistance, which rises as the cube of the velocity. You may not be able to go faster than 115 due to wind resistance.

Before you start tearing into the jets, do some plug chops at WOT. See if you're lean there before you change anything

I've run my 78 down the long straightaway at the race track and I haven't gotten it up to 120 mph. That's because I'm a huge wind block. The bikes goes right up to 100 in 3rd, then creeps up from there in 4th. I never get to 5th.

Also, as Dan says, use something accurate to determine how fast you're really going.
 
Yeah i am a big sail too..at 255 LBS. I have had her twisted to the max and got between 115 and 120 on a dead calm day at 80 degrees outside. I read that the 750s top speed according to factory specs is 123 MPH and have tested both the 77 and the 78 and both run right at that mark according to the speedos..maybe im dreaming of a 130 plus pig!!
 
well accoridng to the Suzuki published spped for the 750s is 123 MPH and they both seem to performe within a mile or two on the speedos up to that spec i think the speedos are close enopugh to tell whats going on..Maybe its me thats dreaming and EXPECTing more out of the extra 250ccs here.
 
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Chuck, Don't forget your bike has an aftermarket exhaust system on it (4 into 1 ). the pilot settings are going to be greater than standard because of it.

what is the tooth count on the front and rear sprockets? someone may have changed them along the way and that would account for your loss of top end speed.
 
I hadnt thought to count the teeth And remember that per our phone chat today, I got that stock exhaust coming..so that will change everything yet again!! probably best to get that on, figure out this wiring issue with the starter button, check the size of the mains currnely in there( which i can do this week and report back ) THEN see whats up..Oh and yes i know it needs the valves done as well.Lots of issues going on that i just need to get sorted out i guess!! Maybe i should just put the whole thing on the trailer and bring it down to your place instead of you coming here..that way i can bring my spare shims and see if anything i wont need will swap to some of the ones that you need for the 850!!
 
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chuck hahn said:
Maybe i should just put the whole thing on the trailer and bring it down to your place instead of you coming here..that way i can bring my spare shims and see if anything i wont need will swap to some of the ones that you need for the 850!!
Click to expand...
That sounds good. I have a shim tool and a cam cover gasket you can use until it gets replaced. the only problem I see, you will have two bikes to trailer home after we pick up the Cooley.

what say yea?
 
Thats the least of the problems..how big of a moving truck will i need to get 5 bikes and all my house hold furnishings to TEXAS!! Guess i could bring down the 1000 C and then shuttle it back home . THEN turn around and combine your Indiana run with my picking up the Cooley. I mean we dont need to go to Indiana and Kentucky the same week we work on the C either!!
 
Get the stock exhaust back on, set the screws as mentioned ( mine are fuel 3/4 and air 1 1/2 - 1 3/4) The bike runs pretty strong and with a GPS will pull close to but not quite 130 mph (200+ kph) on a good day. Tach and speedo are a little wonky as normal but looks pretty close to redline. Only non stock items are Dyna ignition and K&N replacement filter and I weight in at about 210. I also run with supersport bars.
 
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