1983 GS1100E - Carb Fine Tuning

[Phaedrus]

1983 GS1100E
V&H 4 to 1
K&N Pods
Dynojet Kit

I've tuned a few bikes--not a master by any means, but very familiar with the process. Picked this bike up in NH, brought it back home to Cali. Overall fantastic condition (fully restored). It was running decently, kind of rough at 1/8 - 1/4, strong through redline. I went through the carbs for good measure when I got it home. The pods were dry, super gunky, and there was a lot of sediment in the bowls. Refurbed the filters, cleaned the carbs thoroughly, adjusted the float heights to factory spec.

Bike is much smoother 1/8 - 1/4 and pulls HARD through redline, but now I have tiny surges at 4-5k rpm in 4th/5th as well as crackling when closing the throttle from WoT. Slightly lean, right?... Well, after raising the needle by removing a washer, the surging is replaced by a nice flat spot @5k rpm in all gears and the bike doesn't want to pull through redline. Too rich...

Went back to the original needle height (3 notches down from top + 3 washers).

I then tried richening the idle circuit by a 1/2 turn out in order to smooth the surging, but it didn't seem to help. It did lessen the crackling after closing the throttle from WoT though...

Any pointers for trying to even this out? Should I try richening the idle circuit more until the surging is alleviated, maybe raise the float height by a millimeter? Or keep 1 washer out, lean out the idle circuit, and lower the float height a millimeter or two?

Any guidance would be appreciated.

Cheers

 

[niclpnut]

If it pulls even to red line at WOT and the needle setting seems good, adjust the float height a mm or 2 allowing for more fuel in the bowls. It will even transition from off idle and mid range. Will help with the popping as well.

 

[niclpnut]

Really good guide to follow as well:

http://www.factorypro.com/tech/carbtun.html

Nic

 

[Phaedrus]

If it pulls even to red line at WOT and the needle setting seems good, adjust the float height a mm or 2 allowing for more fuel in the bowls. It will even transition from off idle and mid range. Will help with the popping as well.

Right on. Yeah, that's what I figured. Got hasty and tried 2mm, had fuel pouring out my overflows :/ Will readjust to 1mm and test. This should be the ticket. Thanks for the reinforcement.

I've been going off of this guide: http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html which is just a more robust version of what you linked, from the same peeps.

Thanks again

 

[Guest]

Interest to know if this fixed the problem... keep us updated.

 

[Rob S.]

From the July, 1982 Cycle World:

Throttle response is good but there is a small amount of lean surge at steady-state cruising speeds and low throttle openings. It feels as though the carb pistons are undecided as to where, exactly, they want to position themselves. At higher road speeds, during hard riding, or in the fast-slow transitions of daily riding no carb problem is evident and the throttle is quick and responsive.

 

[Phaedrus]

After initial float adjustment to 21.4mm (stock is 22.4), cruising was much smoother. Though, there was still a mild surge noticeable enough to annoy me... Adjusted the float height again. I think I ended up setting them at 20.70mm. I'll test again later on today and see if that ironed the rest of it out. Will update.

From the July, 1982 Cycle World:

Throttle response is good but there is a small amount of lean surge at steady-state cruising speeds and low throttle openings. It feels as though the carb pistons are undecided as to where, exactly, they want to position themselves. At higher road speeds, during hard riding, or in the fast-slow transitions of daily riding no carb problem is evident and the throttle is quick and responsive.

Interesting... Factory float heights might have been too high? Strange that they'd let a bike hit the market with a cruising lean surge. Does anyone else experience this? When I first got the bike back from the east coast, there was no cruising surge. That was before I reset the float heights... :numbness:

 

[niclpnut]

If you haven't already, alot of us have gone up to a 47.5 pilot from the 45. Always seem a bit lean on the pilot circuit from the factory.

 

[Steve]

Just to be sure, ... where are you measuring your float height? :-k

Too many times, we find that it is measured from the top of the step, when it should be measured at the bottom.

The ultimate would be to use some tubing in the drain screw to see actual fuel height with the carbs in their proper orientation.

.

 

[Rob S.]

Interesting... Factory float heights might have been too high? Strange that they'd let a bike hit the market with a cruising lean surge. Does anyone else experience this? When I first got the bike back from the east coast, there was no cruising surge. That was before I reset the float heights... :numbness:

Some members have opined that it's so they could meet EPA restrictions.

 

[Guest]

Needle third notch up from bottom and do not use the DJ washer.
From bottom of needle (tip)/spring, washer, clip, spacer
47.5 pilot jets as mentioned
138 DJ main jet
3.5 turns out on the idle mixture screw

If you get surging at open throttle go up to a 130 Mikuni main jet

 

[Phaedrus]

Interesting re: EPA restrictions... Makes sense, though a bit surprising seeing as I've had to raise my float height ~2mm in order to get the bike to run smoothly.

Final setup is as follows:

Needle clip 3 notches down from top, +3 washers
47.5 Pilots
138 DJ Mains
20.35mm Float Height (22.4mm is stock)
3.5 turns out on idle screws

Way better (smoooooth) off-idle response, good power from 1/8 through WoT. No more surging at 4-5k rpms in 4th/5th. Though, I still have to test 5th gear at the current float heights. Last check was at 20.75mm and there was still a veryyy mild surge in 5th.

Basically my setup is identical to chef1366's. Sounds like a different needle height based on his description, but it isn't. Just different ways of arriving at the same height:

Needle third notch up from bottom and do not use the DJ washer.
From bottom of needle (tip)/spring, washer, clip, spacer
47.5 pilot jets as mentioned
138 DJ main jet
3.5 turns out on the idle mixture screw

If you get surging at open throttle go up to a 130 Mikuni main jet

Re: "surging at open throttle" -- are you talking about WoT or just any surging that occurs while the throttle is open i.e. cruising? You don't mention float heights in your setup. I'm assuming that instead of adjusting float heights you swap in the 130 Mikuni mains to allow a tiny bit more fuel overall. My WoT performance is perfect, so I'm gonna try to stick to the 138 DJ's and see if this final float adjustment did the trick.

Just to be sure, ... where are you measuring your float height? :-k

Too many times, we find that it is measured from the top of the step, when it should be measured at the bottom.

The ultimate would be to use some tubing in the drain screw to see actual fuel height with the carbs in their proper orientation.

Measuring from the bottom, following the shop manual. I'll definitely give the tubing a shot if I can't iron out this last bit of surge. I don't think I can raise the floats much higher... Will be good to see.

 

[Phaedrus]

Update:

Long ride on the twisties today. Smooth as butter in every gear except (5th @ 5k rpm, cruising around ~75mph)... As I said in the last post, don't think I can raise the floats any higher. I've got a set of 130 Mikunis lying around, so I'll pop them in and see if they help... or **** everything up...

Soooo close...