1982 GS750E Jetting / Jet needle question:

[MK3Brent]

Greetings,

I have a 1982 GS 750E.

Modifications are:
Pod filters
Open exhaust manifold (4 into 1) design.

I'm trying to properly jet the carburetors.

They have been cleaned thoroughly and have some mystery jets from the previous owner. (no clear numbers are legible.)

I am waiting for my fuel level gauge to arrive so that I can accurately determine the bowl fuel level, but until then I would like to ask some simple questions.

1. In my searches, I notice many advising to adjust the jet needle height. I have CV carbs, and have disassembled my jet needles, and see no such grooves or areas for adjustment. (Are these a Canadian only feature?)
   
   
   
2. The service manual from 1982 says the stock main jet is #117.5 while the pilot jet is #37.5.
   I haven't seen people post these numbers as their 1980+ main and pilot jets; (Are my numbers from the manual accurate?)
   
   
   
3. For my modifications, I determined that a #120 main, and #45 pilot might be in the ball park. (Can anyone else suggest other jet sizes based on their experience? Altitude = sea level)
   

I appreciate your reading.

I have enjoyed the amount of information posted by Bikecliff, and might even find some of my answers in my next session of reading.

 

[Steve]

No, your jet sizes will NOT be 120 and 45.

If anything, they will be closer to 135 and 40.

However, you have to ask yourself a quick question: Do you want to sit there and fiddle around and GUESS what jets or do you want to just spend the money and get a DynoJet Stage 3 jet kit?

You can get all the jets in approximately the right sizes, but the DJ kit has differrent needles, and THEY are what really makes the difference.

.

 

[Hoosier Daddy]

... and you are correct. The factory needles did not have the selection of grooves on the CV carbs. Again, you ought to just buy the Dynojet kit. I'm saving up for their kit myself
Are you really going to run an open header?

 

[MK3Brent]

I was going to purchase the stage 3 kit from Dyno-Jet, but didn't know who to trust.

I like quantifying things, and no one could give me numbers about their "kit."
Looks like I'll just get the kit, and give it a shot.

And done. Bought a DJ stage 3. Thanks for the suggestion.

 

[MK3Brent]

Installed DynoJet stage 3 kit.
Bike runs fairly similarly.

I made a fuel level gauge for the carburetor bowls.
With the bike on the side stand, each bowl read around the right level.*

*(Bowl #1 which is the lowest, seemed a little high which may be due to the bike being on the kick stand.)

I have removed the carburetors and am going to re-measure the fuel heights while on the bench with a fuel source.

If the bowl fuel heights are correct, I'm going to assume the ignition is the next culprit.

What the bike is doing:
Under cruise conditions with throttle held constant the bike sputters and jerks.
Problem seems to be more noticeable when the tank is full.

The vent hole is clear, though I am uncertain about the cap. (Maybe I'll try a make-shift cap that cannot hermetically seal the tank for a trial run.)

Battery voltage is 12.8V, however I have not stripped back the + conductor to the coils to test voltage.

How likely do signal generators go bad or get dirty enough to interrupt ignition?
I noticed the bolts are <8mm so I'll have to get some smaller tools to inspect.
I've read that a fellow forum member here alleviated a sputter by running w/o the ignition cover over the signal generator. (Something about the heat.)

Any thoughts or comments are welcome.

 

[MK3Brent]

Looks like cylinder 2 & 3 were not firing.
In my experience with ignition coils, they either fired or didn't.

I measured resistance across the wires of my "good" coil and then the "bad" coil.
The good coil measured .4Mohm, while the bad measured 4-5Mohm.

I'm wondering if the wires are just bad, but without removing them I cannot be certain.

I'll replace the coils with a good after market set so I can replace wires in the future.

Is dynatek the name of the coils folks here recommend?

 

[koolaid_kid]

The quick and dirty way is to switch the coils. If the firing follows the coil, you have a bad coil. If it does not, you need to work backwards, igniter or signal generator.
The Dynatek green coils are what you want.

 

[MK3Brent]

Good plan.
I think I'll test the resistance of the signal generator first, then try that idea.
We finally have power back at the house after Irene passed over head. (Very lucky the house wasn't destroyed compared to some of the others in this state.)

If the firing issue sticks with cyl 2 & 3, then I know I have either a wiring issue, or the ignitor/signal generator issue.

Thanks for posting.

 

[MK3Brent]

Problem is following my black/yellow trigger wire.
Both coils work.

I traced down to the ignitor and found some loose connections.
Re-soldered and bike ran well again.

When cool, the bike starts and rides great.
I can ride for about 10mins before I lose my black/yellow triggered coil.

Could this be an internal issue with the ignitor?

My signal generator's resistance reads: 360Ω
This might be high, and when the temperature increases it might be just too much. Thoughts on that one too?

 

[Hoosier Daddy]

Where in the hell did you find a keyboard with an ohm symbol ?!?
LOL

 

[MK3Brent]

Where in the hell did you find a keyboard with an ohm symbol ?!?
LOL

I'm an engineer.
They give them to you when you graduate.

 

[koolaid_kid]

There are transistors inside the igniter. They can overheat and cause exactly what you are reporting (and what happened to my GS also). An esteemed member here (Nessism, Matchless?) has discussed replacing them. I merely purchased and installed a Dyna S. My problems were solved. BTW, it replaces both the igniter and the signal generator.

 

[koolaid_kid]

I'm an engineer.
They give them to you when you graduate.

Dang, I'd better get in touch with UT, I missed the ceremony.

 

[MK3Brent]

There are transistors inside the igniter. They can overheat and cause exactly what you are reporting (and what happened to my GS also). An esteemed member here (Nessism, Matchless?) has discussed replacing them. I merely purchased and installed a Dyna S. My problems were solved. BTW, it replaces both the igniter and the signal generator.

Yes, this is what I did too.
Replaced with Dyna-S. Should arrive tomorrow and I'll button it up.


To help tie up the first questions I had at the beginning of this thread, here are some pics of the DynoJet stage 3 kit. (in case anyone searching this topic finds this.) :-D

Jet needles on the 4th notch from the end.