Tuning with an air/fuel meter.

[Don R]

I'm a novice at the Suzuki GS1100e so some of this might be assumptions just based on my limited knowledge.
. My 81 came from a drag racer that bought it to replace the one that he used to race and lost in a divorce. He realized that he wasn't riding it enough, tried cleaning the carbs but it needed more work as the gas had gone bad. It sat for a considerable time.
It has a set of 29 smoothbore Mikunis that have the 1.5 slides. Even an 8 valve 1 liter Suzuki wants 2.0 slides. I've been tuning it with an Autometer wide band O2 meter. It clearly doesn't like the 29's even with pro drag racer jet recommendations. The high vacuum generated pulls a lot of fuel.
I had contingency money from auto meter from our drag car wins so I cashed it in on an air-fuel meter. I built an exhaust probe from some moly tubing left over from a funny car repair. It inserts into the muffler and samples the exhaust from near the collector. The meter plugs into the battery charger plug so it's portable from bike to bike. A foil wrapped bungee cord holds it into the pipe.
Anyway I bought a set of mikuni 36 flatslides, K&N filters and a push pull throttle. I'll post my testing of the new carbs when I get them installed. 20240315_182703 (1) o2 meter low res.jpg

[Don R]

Here is the unfinished probe on my goldwing but you get the idea.

[slayer61]

You're not really gonna stuff in in the tail pipe are you? Is that what the Goldwing picture is showing us?

[Don R]

Absolutely. There is a good exhaust flow through the probe, it's similar to the ones I've seen used at chassis dyno's. There is no danger of blocking flow in the Kerker on the GS. I've used it on cb750 4-4's with a drilled baffle, RC engineering 4-1, and the GL1000.

[Don R]

The 36's should be here today, the filters tomorrow and the push-pull throttle on monday. I'm helping a friend put a hood on a blown 41 Willys today.

[Don R]

I got the Mikuni 36 mm radial flatslides on today, it now has the flatslide rattle. Installation was easy, it started easily, no leaks and idled right immediately. I didn't get the push pull throttle, it's due on monday so a real test will need to wait. I'm excited to compare the air/fuel ratios to the 29's.

Edit: I got a couple laps around the neighborhood, I saw it as lean as 13/1 but it is mostly in the 12's. I'll know more when I get some time behind the handlebars.

[grcamna2]

I got the Mikuni 36 mm radial flatslides on today, it now has the flatslide rattle. Installation was easy, it started easily, no leaks and idled right immediately. I didn't get the push pull throttle, it's due on monday so a real test will need to wait. I'm excited to compare the air/fuel ratios to the 29's.

Edit: I got a couple laps around the neighborhood, I saw it as lean as 13/1 but it is mostly in the 12's. I'll know more when I get some time behind the handlebars.

A good set of performance carbs Don.
How's your replacement fuel valve/petcock flowing;is there room to clear the top of the new carbs ?

[Don R]

It clears well now. The frame had pipe insulation and KZ tank cushions on it to keep the tank up off of the #1 carb top. It still rubbed a little, the 36's clear beautifully. I haven't gotten after it yet, but it clearly takes less throttle to get the same acceleration that it had with the 29's. I flowed the petcock fully into the tank and it drained nicely. I used my brake bleeder to provide the vacuum. Reserve actually seemed to work correctly so I'm still wondering what the false reserve business was. Maybe a pickup or coil getting hot? Both times were about 45 miles into a ride. But I did one 50 mile ride between them with no issues.

[grcamna2]

It clears well now. The frame had pipe insulation and KZ tank cushions on it to keep the tank up off of the #1 carb top. It still rubbed a little, the 36's clear beautifully. I haven't gotten after it yet, but it clearly takes less throttle to get the same acceleration that it had with the 29's. I flowed the petcock fully into the tank and it drained nicely. I used my brake bleeder to provide the vacuum. Reserve actually seemed to work correctly so I'm still wondering what the false reserve business was. Maybe a pickup or coil getting hot? Both times were about 45 miles into a ride. But I did one 50 mile ride between them with no issues.

Could the Reserve problem be because of the tank rubber lifting/tilting the back of the tank up?

[Don R]

I wouldn't think so, it was only lifted slightly. If it's an electrical issue or something still in play, I will find out soon enough.

[Don R]

I drained the tank two times through the petcock now and it worked fine both times with the gas cap on too. I got the push/pull throttle and new grips on, but didn't get a test ride tonight.

[Don R]

I rode it today, the air/fuel was rich with low 10-1 range on the lower rpms and at mid to higher throttle openings it settled in the high 12's to low 13-1's. I had not touched the carbs out of the box. I read up on the pilot screws and it said 1/8 turn to 1/2 turn, they were a full turn and setting them to 1/2 leaned out the off idle and low rpm range a lot.

[Don R]

I have the pilot screws set to 3/8ths, the lower rpm's are leaner, I'm still surprised how much time it spends at barely open throttle, the 34mm carbs may have opened a little more. At half throttle it's in the 12-1 range but at wide open throttle the air/fuel goes all the way to 9.8's I may drop the main jet a couple sizes when I do it. It's supposed to have 130's in it now. I have 125's for sure but only three 127.5's dangit.

It still only goes 85mph. Hmmm.

[Spiff]

I have the pilot screws set to 3/8ths, the lower rpm's are leaner, I'm still surprised how much time it spends at barely open throttle, the 34mm carbs may have opened a little more. At half throttle it's in the 12-1 range but at wide open throttle the air/fuel goes all the way to 9.8's I may drop the main jet a couple sizes when I do it. It's supposed to have 130's in it now. I have 125's for sure but only three 127.5's dangit.

It still only goes 85mph. Hmmm.

9.8 on a NA motor is to rich! Should be in the 12.5 to 13's for best power.
Interestingly I had the same idea and made a probe and all that. Unfortunately readings was all over the place but I later found out that my cam timing was off by a couple of teeth which wildly impacted the running of the engine and probably made the AFR readings interesting... I might revisit this again now that it's actually running decent

[Don R]

I agree on the WOT A/F ratio, I was going to re-jet it and dropped out a bowl plug today but the jet came with the emulsion tube and it wouldn't come out of the bowl hole. I tried to unscrew the jet while holding the tube with an 8mm wrench but it appeared that I was just messing up the jet so I put it back together.
Since the carbs have to come off, I'll drop the needles a notch also.