78 GS1K Carb Rejet? Bad Fuel Economy - KEITH KRAUSE!

[duaneage]

Dude,

If you move the spark plug wires from 1-4 to 2-3 and vice versa,

You have to also move the wires on the coil so that the points will fire the correct plugs. you can't just move the spark plug wires alone. Move the primary connections on the coils as well.

Do I have to come up there and open up a can of whoopass?

[Hoomgar]

Dude,

If you move the spark plug wires from 1-4 to 2-3 and vice versa,

You have to also move the wires on the coil so that the points will fire the correct plugs. you can't just move the spark plug wires alone. Move the primary connections on the coils as well.

Do I have to come up there and open up a can of whoopass?

I'm am going to sit back and watch you and Keith go at it about that one.
Then when the winner is sufficiantly whooped I'll step in and finish him

How sure of that are you Duane? The coil leads that is?

[KEITH KRAUSE]

Duane, no argument here. Obviously the ol' coil swap idea I suggested was not complete info. Sorry for the confusion Mark.
It's been awhile since I've had to trouble shoot for a possible spark problem and I simply relayed the info to Mark that others suggest to use at this site. "Swap the leads" is always mentioned, but not the need to swap the wires too. This re-jetting/trouble shooting over the web is wearing me out.
So Mark can go ahead with the swap test; if we suspect the coil feeding 1/4 to have a weaker spark, we will swap its plug leads to 2/3 plugs and swap the white wire (for coil 1/4) with the black wire for coil 2/3. Correct?
We're trying to see if the darker plug colors at 1/4 move around with a possible weak coil, before blaming carburetion.
Can I use my "get out of a whoopass free" card on this one?
Mark, hope you didn't already change the coil tonight. If you did, it's probably OK anyway.

[Hoomgar]

Can I use my "get out of a whoopass free" card on this one?
Mark, hope you didn't already change the coil tonight. If you did, it's probably OK anyway.

No whoopass on this one buddy
Buy that man a beer!

Yeah I swapped out the coils last night before the above posts were made.
I am going to just test with these coils as I know they are good.

Then pending the results it may be back to the bench for the carbs.

No worries. I am having fun with it at this point

Thx you guys.

[Hoomgar]

OK Keith, here is the plug read I promised. As always, it is way lighter looking in the picture than it is in person but it is on the lean side for sure.

But you should be able to see how much more uniform the read is compared to all previous reads. It is way better.

Now, lay that setup wisdom on me buddy

[img]http://groups.msn.com/_Secure/0SwCFAt4VRy*JRdMUQy38vQlxCcbNERDtJOck12T3otdiwoZfN hkHi2yfcx0hrHgXPvokeGTwYOzlfWwGYVy96MWfpkaKRfmvJhC R1ExI4bHLt4gIfwLNog/DCP_7471.jpg[/img]

[KEITH KRAUSE]

Sorry for the delay Mark. Had to help my father in law again.
I'm gonna say to put the e-clip in the bottom position (5).
When they were at 4 with the weaker coil, you did get some surging, most likely from 2/3, so I'm gonna go with what I said from the beginning. Needles at 5.
Put the pilots fuel screws at 1 1/4 for now.
Highest rpm for the air screws. If they still don't respond as you'd like, just set them to 1 3/4 for now.
Re-synch and set idle to about 1,000/1,100.

[KEITH KRAUSE]

Just to add Mark.
Pay close attention to throttle position. I want to get the jet needle circuit performance good and the plug colors should fall in line. I'm most concerned with throttle openings at about 1/5 to just under 3/4. I want the least overlap effect from the pilot and main circuits.
The bike should feel strong anywhere between those two positions. For example, say you're in 3rd, 4th, or 5th gear running strong and steady at 1/4, you should be able to open it up to just under 3/4 and get strong acceleration. The throttle response should be good under any throttle opening combinations, as long as you keep it between 1/5 and just under 3/4. If it feels good between these points, do some steady 70 mph cruising and see what it feels like. If you like the results, go do your plug chop test at 1/3 for a couple miles. If you liked the performance, the plug colors should be acceptable for the needle circuit.
If the needle circuit is good and you have any problems at smaller throttle openings, we should be able to adjust them out with the pilot fuel and air screws without compromising the needle circuit.
If you do try any 5th gear/60 mph full throttle roll ons, or any full throttle test and you have a problem such as bogging, we should be able to change the main jets and not compromise the needle circuit.

[Hoomgar]

OK I have the carbs back in the bike. It was almost 1:00 AM so I went to bed. No time for a ride plus it was drizzling and I wasn't in the mood for that.

I have the needles in the fifth position down. (highest needle setting)

The pilot screws all 1 1/4 turns out each.

The air mixture screws are all 1 1/2 turns out each.

Plugs gap rechecked. (all good)

Cable slacks adjusted and 1/3 throttle position marked on throttle tube.

I am ready.

Tonight (weather permitting) I am going to a different area to get the chop test reads. I need a better straight away for this than what I have been using. To many country grandpa and grandma's on the roads here and I feel rude passing people seeing as how they are my neighbors.

I will take sockets and camera with me so I can record plug reads on location.

I'll post results then. Not sure what time though?

[KEITH KRAUSE]

Ok Mark. Just be careful. A 1/3 throttle test is really the only way to tell how the needle circuit is burning/performing. The test for main is even more fun.
Don't forget the vacuum synch. Can't get accurate reads or evaluate performance without a good synch. If you feel rushed, remember the levels don't have to be PERFECT as you did before, but they should be within that 1/2" zone. You can always fine tune the synch later if you're too rushed.

[Hoomgar]

Keith, at 1/3 throttle this bike wants just over 90 mph :?

Anyway, it's done. Sync is perfect. Idle mixture for max idle is close as I could get it.

It is running really good. I cannot tell what the smoke level is because I have no one here to see it but it is still daylight so I got to do a perfect 1/3 throttle chop test.

Here is the results.
Needles all as I said they were except air screws adjusted for max idle:
[img]http://groups.msn.com/_Secure/0SwAAAN8ViS*JRdMUQy38vQQ21U2VgobLzM6QLaJ1!7hC83L!B 4Dw0wJCScrpGRD1DflBtH6lX1BmJQoneHrJABL9pkh0WWa1EUx gmQPOrTjlDNKDYJvSwQ/DCP_7472.jpg[/img]

Still lean on 2 & 3 and just about perfect on 1 & 4.

But notice how even they are now. 2 & 3 are very close. Same with 1 & 4.

[skip]

My ZRX had larger jets in the middle from the factory. the center cylinders always run hotter and n leaner. the ZRX had 92's on the outside and 95's in the middle to keep those cylinders cooler and not as lean this was from the factory

[Hoomgar]

My ZRX had larger jets in the middle from the factory. the center cylinders always run hotter and n leaner. the ZRX had 92's on the outside and 95's in the middle to keep those cylinders cooler and not as lean this was from the factory

interesting


So I have 125 mikuni mains in right now. Maybe I should go up a notch in the center two? What is the next size up I wonder? That is a good idea skip. It's unconventional, I love it

[duaneage]

I think that one possible variable could be the pods. I am not a fan of pods because they do not perform a few key functions that the airbox assembly does ( Keith, don't yell at me!)

1. With the airbox the carb has a velocity stack to straighten airflow. The rubber airbox tube allows the air to enter straight into the carb and reduces turbulence. It is difficult for air to bend 90 degrees without turbulence that varies with rpm. Look at the area surrounding the filters, is there a uniform amount of free space to draw air from, especially at 90 MPH ( you really should get a radar detector)

2. As each carb draws air there is a pressure drop at the mouth of the carb. This causes noise and also affects air intakes on adjacent carbs. It can be quite severe at certain speeds, resonances can develop that affect airflow, especially on the middle carbs because they are surrounded by bike parts and the other two filters.

3. Velocity stacks move intake pulses higher in the throat, reducing the likely hood of reverse air flow. Fuel will flow in either direction through a carb, causing fuel stand off clouds in the air filter. The velocity stack presents a column of air that dampens the pulses.

4. Air has mass and the stupid air box we all hate provides an air reserve that further smoothes airflow into the engine. The airbox is a capacitive component in this regard, the velocity stacks are inductive and work on the Helholtz principle of open tube resonance. By raising the resonance of the tubes higher than the engine rpm you get good airflow without pulsing.


This is a street bike, not a racer. If all you cared about was WOT in the top three gears then pods are the way to go. But most engines are driven at half to 1/3 the top engine speed so it makes sense to optimize for that range.


Try this, if you want. Put four rubber tubes on the carbs about 2-3 inches long and see if it behaves differently. Of course with all the other tuning changes it may not work right. But it is easy enough to try.

OK Keith, you can yell at me now :roll:

[Hoomgar]

I found an air box that was offered to me. But they want 50.00 dollars for it! 8O

I think that is way steep but maybe I am wrong? What is a good price for a used GS1000 air box? I'd rather put one back on at this point.

[duaneage]

I found an air box that was offered to me. But they want 50.00 dollars for it! 8O

I think that is way steep but maybe I am wrong? What is a good price for a used GS1000 air box? I'd rather put one back on at this point.

For a 30 year old bike???? I would take it. You can always eBay it again.

Seriously, headers are easy to rejet for and a good bang for the buck, i loved the 4-1 on my 76 cb550 I had, but on the intake side I cringe when I see pods, the intake on these bikes is so tricky.