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GS1000 Mid throttle hesitation

  • Thread starter Thread starter allenbrown
  • Start date Start date
A

allenbrown

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My '78 GS1000 runs with pods and a 4 into 1 exhaust with no baffle. It has a really responsive low end and solid high rpm range. Lately when I'm cruising about midthrottle it cuts down to what sounds like a cylinder or two dropping out. If I goose it, it shoots off no problem once I let off a little it's back to sounding like theres something wrong. I don't know if it's too much gas, too much air, float setting? Anyone have the same problem before? Carbs are clean and have been cleaned recently again when I started noticing this. Clean (red koted) tank, no inline filter, gets good clean fuel flow. Any ideas?
 
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I can predict the responses...
Cleaned carbs? as in disassembled, dipped replaced orings? Are they Jetted properly?
no baffles=loss of torque at normal driving. No baffles are a benefit at W.O.T. pretty much only. no fuel filter? yikes, I did that once.... once.... tiny spec of rubber tubing, stuck in the carb and ran like poo... from what I hear Pods r tough to tune proper anyway. Cafe Kid had a response on the difficulty of pods on his GS. Have you read the carb info on Basscliffs site? Good Luck!
 
have you rejetted it for the filters and the exhaust yourself or are you using a dynojet kit?
try raising the needles a notch, see if it makes any difference
 
How do you raise the needle? Do I have to take the tops off the carbs? I've heard of some people raising the needle. I haven't put a kit or new jets in it yet. I've been debating on what size to get. It has no baffle because the baffle broke, I'd like to run it with one just need to order a new one.
 
The needle controls the mixture at mid throttle. Do a plug chop at about 1/2 - 2/3 throttle and check the plugs for rich or lean.

Based on that result, adjust the needle clip up (if rich) or down (if lean). You might also want to check and set the float levels.
 
if its running with standard jets, and pods and no baffles, expect to fork out for an engine rebuild real soon
 
allenbrown said:
How do you raise the needle? Do I have to take the tops off the carbs? I've heard of some people raising the needle. I haven't put a kit or new jets in it yet. I've been debating on what size to get. It has no baffle because the baffle broke, I'd like to run it with one just need to order a new one.
Click to expand...

On the VM carbs, you'll need to pull the slides out, which requires removing the throttle bar, but you can otherwise leave the carbs on the rack.

Then remove the brass slide to pull the needle. The needle has a spring, a circlip and two plastic spacers a thick one and a thin one. You can adjust the needle two different ways.

First, you can move the circlip up or down the five notches in the needle - 1 -5 from top to bottom. Up = leaner and down = richer. With pods and pipes, you should probably be in the 4th slot.

Second, you can shim the needle for a finer adjustment. The spacer on top of the circlip controls the height of the needle. You can swap the two spacers to put the thick one below and the thin one above the clip. You can also replace the thick spacer with a stack of thin washers and remove one or two to raise the needle less than a full slot.

Once you set the needle and return the slides to the carbs, you'll need to bench sych and then vacuum synch the throttle slides.
 
What should my main jet size be? I don't really want to buy a whole kit if I can buy a set of mains a slow jets for a decent price.
 
allenbrown said:
What should my main jet size be? I don't really want to buy a whole kit if I can buy a set of mains a slow jets for a decent price.
Click to expand...

You might need a DynoJet kit for the better taper on the needle. That said, Dyno doesn't make a kit for my bike which has very similar carbs to yours. I think there is a Dyno kit for your bike, but not sure why your VMs and not mine.

If your stock needle is adjustable (i.e., has the clip and slots) and doesn't suffer from some taper issue, then you may be able to dial in your jetting with some changes to the needle slot, main jet size and possibly a larger pilot jet. That's what I have to do.

Yes, it's cheaper than a kit, but beware, it's pretty aggravating going in and out of the carbs repeatedly to adjust the jets.

Dunno your bike, but the 1979 GS1000 stock main jet is 95 and stock pilot jet is 15. Check and see what jets you have in place now. If you are only hitting a flat spot mid-throttle, the PO might have re-jetted for the pods and pipes. That would be lucky and unusual for a PO.

Otherwise, you might start out with mains at about 115 and maybe a 17.5 pilot. Pick up main jets in a few sizes though (maybe 115, 117.5 120?), as you probably will need to test WOT a few times before settling in on a good main jet.

Others that have switched to pods/pipe on a GS1000 could give you better guidance though.
 
unless you have a whole bucket of jets "guessing" your jet size can prove to be a lot more expensive in the long run than buying a dynojet kit.
my 78 1085 runs a harris race pipe with vm26's fitted with bellmouths and a dynojet kit.
however, i ditched the dynojet main jets as it was running far to rich at WOT. i am now running on 112.5 mikuni mains and it runs fine
 
Alright I just ordered the dynajet stage III kit. I'll keep you updated on how it works out.
 
And consider putting the baffle back in the exhaust. While it may sound powerful without it, you're throwing away a ton of bottom end torque for a tiny bit of top end power (that you only experience in a very narrow powerband). I replaced the 2.5" diameter "competition" baffle in my Kerker for the standard 1.5" dia. baffle. The improvement in rideability is huge and she still makes a hearty growl above 6,000 rpm. She will also go well past redline without dropping off the power band compared to stock mufflers.
 
My baffle fell apart from some poor welds by the PO. I'm trying to find a good replacement. Mine is the megaphone 4-1 Mac. I've found the replacement online but I'm not sold one which one I should get. How did you go down in diameter? My inlet is 2.5 the outlet is 3.something.
 
allenbrown said:
My baffle fell apart from some poor welds by the PO. I'm trying to find a good replacement. Mine is the megaphone 4-1 Mac. I've found the replacement online but I'm not sold one which one I should get. How did you go down in diameter? My inlet is 2.5 the outlet is 3.something.
Click to expand...
Those must be the dimensions of the megaphone, not the baffle itself.

Here's the place I found with the best prices on replacement baffles.
http://www.newmotorcycleparts.com/exhaust_parts/baffles.html

As for the baffles, the Mac uses an offset dual-tube baffle as opposed to the straight thru Kerker. The Kerker can be had with a 1.5, 2.0, and 2.5" tube. I posted some pictures in this thread: http://www.thegsresources.com/_forum/showthread.php?t=189567
I think there is only one size baffle for the Mac.
 
UPDATE:

i ordered the new baffle too. I took the carbs apart and readjusted the float height. HUGE difference, they were they same height but all too high or low depending on which way you look at it, so it wasn't getting enough fuel I think. Running good again now but I'm waiting on the dynojet kit and new baffle to get here before I ride it too much more.
 
Ok so I installed the new dynojet kit, it started right up but at about half throttle it starts bogging. The plugs look rich/black. I'm guessing this means the needle clip needs moved which direction for a leaned mixtures? Or any other suggestions?
 
lower the needle, which means raising the clip will lean it out. its a pain but try one notch at a time
 
You should take stock of where the clips are obviously and compare that to the DJ kit instructions. Many times, moreso with CV carbs, people attempt to jet for pods and pipe by hand rather than shelling out cash for the quick and effective jet kit (whatever the brand) and go about it all cock handed. You'd be amazed at the ridiculous sizes of mains I've found in carbs. 1100Es with MIC 150 mains (stock was like 112.5 or 115) in an effort to compensate for the stock needle's lack of taper. This is usually where people have problems (the needle circuit). The attempt is made to overcome by sticking a stupid large main in there to feed the needle circuit, but then the bike falls on its face drowning up top, and won't idle for crap.

See what the PO has done first (pilots, mains, fuel and air screw setting and clip position). Sometimes it's easier to put it back close to stock settings and then start as if you're the first person to re-jet.
 
Update-Sorry for the delay.
To get my bike running PERFECTLY, I used the needles on the lowest setting, plus a the supplied washer on top of the needle. I used the smaller of the jets that came in the dyno kit. I installed my new baffle before getting it right, and used bellmouths. I couldn't get it lean enough with the baffle in without using the bellmouths, the pods wanted to make it bog at wto. With the bellmouts/ velocity stacks it got it right on track. Now it's all working properly.
 
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