'81 GS1000G Hesitation at 1/2-3/4 Throttle. Running Lean?

[Phaedrus]

So, this 81 GS1000G has been a rat project for awhile. I'm back to trying to tune the carbs.

Here's a quick run down of what I'm working with:

- Freshly Rebuilt Carbs
- Dynajet Stage 3 Kit (170 Main Jet)
- K&N Highflow Pods
- 4 to 1 Exhaust (Dented)

Ever since I rebirthed him, he's had hesitation issues. At first I thought it was the jet needle height, so I raised 'em to the second to last notch. Not much better. Installed the K&N's hoping it was a lack of air issue. No better.

A few months have passed since the original shake down and I took her for a test ride today.

Here's the updated symptoms:

- #4 carb spits back into it's pod pretty frequently, particularly on deceleration.
- Acceleration is smooth, steady until about 1/2 throttle.
- At 1/2-3/4 throttle he lurches, intermittently losing power.
- If I try to open from half to full, power plummets. Seems to be starved of either air or fuel.

I checked the plugs yesterday and they were pretty white. This, and he's hotter that he should be makes me think that he's running lean. I also mentioned above that the 4 to 1 has a pretty good sized dent from the PO bottoming out. I'm wondering if it's causing intake/exhaust issues...

What do my symptoms point towards? I'm thinking that tomorrow I'll raise the jet needle up to the last notch and do a dynamic sync of the carbs (currently only bench synced). With the pipes as they are, I can imagine that the syncing is pretty far off.

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I should note that I'm waiting on a tach cable currently, so I don't have any way to read RPMs.

Thanks for any insight.

 

[Guest]

If your plugs are showing that white, yeah a lean condition. Check your rubber boots and orings to the intake side of the head. Might need a valve adjustment as well, when was the last time one was done? The dent in the exhaust I wouldn't think cause the leanness, if anything would cause some back pressure and make it a bit rich, though it would have be a really nasty dent. Check the fuel flow from the petcock as well. Could be the carbs aren't tuned right yet either, process of elimination.

 

[GSX1000E]

Is there NO MUFFLER at all on this bike??? A Dynajet 170 is equal to a 160 Mikuni jet. I have the same bike with no jet kit and it runs fine with 127.5 Mikuni main jets, K & N pods and a stock-type exhaust.
Either you have NO muffler and/or NO O-rings in the intake manifolds or large cracks in your intake manifolds. Something is WAY WRONG with your set up.

 

[Guest]

Lean on the idle mixture screws
lean on the needle
rich on the main

 

[Phaedrus]

Lean on the idle mixture screws
lean on the needle
rich on the main

Thanks for the response.

I attempted to address these issues by:

- Readjusted the idle mix screw on #4, turning the screw while the bike idled to see where it wanted to be.
- Raised the jet needle 1 notch (final notch).
- Swapped the main jet to the dynojet 118s.

When I opened the carbs, I found that the main jets had fallen out of their seats in #3 and #4 and were just chilling at the bottom of the bowls... No wonder he gave out at full throttle on the test ride yesterday...

Once I finished the adjustments, I warmed the bike up with open intakes (no pods).

- I'm still getting a lot of spit back into carb #4, no matter where the screw rests (except when fully seated).
- Playing with the throttle now, at 1/2-3/4 I get tons of backfiring.
- Full throttle and the bike seems to hesitate, but it's hard to tell with all of the backfiring.

She's not even test ride worthy at the moment... Have to sort out what the heck is going on.

- I think that the popping/spitting in #4 is a timing issue. I replaced the signal generator/governor recently and the adjustment is quite possibly off.
- I assume the jet needle is too high now and that I'm getting too much unburnt fuel being pushed into the exhaust headers, causing backfiring?
- Not sure if the 118s are helping or hurting at this point.

The next plan of attack is to adjust the timing so #4 stops spitting. Then, lower the jet needle 1 notch and see if it stops the backfiring. If I can clear up those 2 symptoms, I'll be able to hone in on the main jet more accurately.

Let me know if ya'll have any insight!

 

[Phaedrus]

Update:

Figured it out with the help of a local dyno tune shop--JLK Precision Motors out here in the Bay Area.

Turns out the Stage 1 & 3 dynojet kit comes with untapered jet needles. This was ****ing my **** up. Replaced the untapered needles with the stock needles and adjusted to the 4th notch down, popped back in the 170 main jets, and turned my fuel filter around after doing a blow test (blew air threw it to see which direction was more restrictive)--bike runs like a champ!

Still need to sync the carbs properly so I can get rid of the hideous pops and crackles, might adjust the pilot jet slightly as per JLK's recommendation, but for now the bike is actually rideable so I'm stoked! Gonna take it out for real test tomorrow. Probably needs new plugs after all of that haphazard tuning...

Not that this was a hot thread, but thanks for the tips.