MAC 4-1 jetting for GS1100E?

[Anonymous]

I went ahead and tightened the exhaust the other day. While some of the bolts were a little loose there wasn't any change in the noise BUT the next day the exhaust baffle broke loose and got sucked 1/2 inch deeper into the cannister. Today I pulled the baffle out and drilled another hole in it so I could bolt it back on and the result? The bike is running kinda bad...hopefully when I check the plugs I will find that it's running rich.


Steve

[Anonymous]

Hehe, 5000 km later and I'm still riding around with the bike running lean. Atleast I understand the problem a bit better now. One issue is that the slip-on is leaking a bit so I will have to cut off the cheezy MAC clamp and get a band clamp to cover up the slots. I'll fix that up on Monday. Since posting last year I've changed the manifold gaskets and shimmed the air filter to fit better in the box. My petcock is messed up so I've started running it on prime and I've blocked off the vacuum lines. The vent lines are not on the carbs but the T fittings are still in place.

Now back to the jetting. When I'm cruising down the highway at 4000 RPM in 5th (roughly 110 km/hr with stock gearing I think) the bike is running well. All it takes to maintain this speed is the lightest of pressure on the throttle. If I actually turn the throttle I will speed up. I can burry the tach in the first 4 gears but I haven't got enough power to burry 5th.

Do you guys still think jumping from 107.5 up to 120ish Mikunis is the way to go? I was at the dealer today and they said they had lots of Mikuni jets for snowmobiles. Will these be the same as for our bikes?

Thanks, Steve

[Dink]

Mikuni jets are even easier than that, there are two types one is the nut type, the other is flat, our bikes with CV carbs take the flat ones.
BTW I believe 115 would be worth a try before 120.
Dink

[Anonymous]

Thanks Dink. I went to Mikuni school today searching for some mains. There are only two more places in the city to check but nobody seems to have enough of each size or the correct type. Turns out there are big and small round jets and hex jets. Supposedly the small jets will replace the big jets but I'm not sure if they'd be able to hold the washer in place on our bikes. The best thing is that jets are cheap. 3 to 5 bucks a piece from what I've seen.

Steve

[Anonymous]

The small ones do fit! Now if only I had a chain on my bike to test them out. :x

Steve

[Anonymous]

The 115s aren't scary enough, I'll have to go bigger. 5th gear roll-ons are actually pretty weak. Atleast I've got one black plug now, I've never had that before. Does anybody remember which way you turn the pilots to get them to richen up? I've got them at 3.5 turns as per the manual but #2,3,4 are white. I synched the carbs at 3000 RPM with the middle ones a bit lower.

Thanks, Steve

[Anonymous]

I went for another ride so there's a bit of an update.

First, When I'm WOT in 3rd at 8-9 grand the bike surges. I tried looking up the term "surging" but it's used too often. It's like the bike doesn't want to go into the red area anymore. What do you guys think this is indicating?

Second, I turned the pilots back in one turn. The popping when I snap the throttle closed has come back. Does this mean I need different pilots?

Thanks, Steve

[Anonymous]

The saga continues... I dropped the clips down to the bottom (1 notch) and I'm getting better midrange. I turned the screws in 1/2 to 3 turns out and I'm getting a better start but now I'm getting a quick sputter when I'm open the throttle for a roll on. Once that passes I'm running better than before. Still can't do much better than 7000 RPM in 5th, I had it up to 7500 for a touch tonight. The 115 mains seem to be better but I've got 120s on the way. Ah well, the engine should be cool enough to get in there and check the plugs as well as turn the screws in another half turn.

Steve

[KEITH KRAUSE]

Are you re-jetting for a pipe only? Stock airbox with the lid still on?
As a general rule with your carbs, you can go to about 4 turns out on the mixture screws. If the results are still too lean, you go up a step on the pilot jets.
I test and get plug reads for the jet needle at 1/3 throttle. Get some tape and mark the grip and housing to be sure. Chop the bike off for the most accurate reads. Take a piece of hose and a rag with you to help you remove/install the hot plugs. After the needle circuit looks good, I then install the largest main jet I can that doesn't create any bogging during a full throttle roll on in 5th gear at 60 mph or close. The bike should pull strong. Some bikes won't redline in top gear on level ground.
I'm assuming all other work has been done correctly, carbs clean, floats adjusted, synch, ignition timing, good spark at all 4 plugs, valve clearances...

[Anonymous]

Hi Keith,
My bike is running the stock airbox with an OEM style EMGO paper air filter. The cover is still in place as I do not have the desire to do a complete rejet of the bike. The 4 into 1 still has the baffle in it too. My goal is to get the most fuel possible through this setup.

I have synched the carbs a couple days ago but I need to do that again since I've changed a lot of different things. The valves are within spec as I checked that when I had to inspect the cams last week. The floats should be okay, you explained to me how to check them last year. The advance has not been checked, I don't have a strobe. It looks like my cam chain is stretching though as my cams notches are out of alignment just a touch. Plugs and caps are about 5K km old.

I think my problem is the mains at this point. I get the impression that I am not burning enough fuel to get past 9000 RPM in 4th or 7500 RPM in 5th. Yep, I can't accelerate in 5th when I upshift so I suspect I need more fuel. Does this make sense?

Cheers, Steve

[KEITH KRAUSE]

I don't know what you mean by "I can't accelerate in 5th when I upshift so I suspect I need more fuel".
I wonder if you've got good fuel flow? 5/16" fuel line? New vacuum line? Clean petcock?
I find it unusual you have had to raise the jet needle 2 positions just for a baffled Mac pipe. This too could be a sign of poor fuel flow. I'd like to know what the plugs say at 1/3 throttle now.
The mixture screws at 3-4 turns out could be considered normal.
I would guess 2 full sizes up on the mains (117.5) or close.
I wonder why #4 is running rich if it's been subject to the same maintenance/tuning procedures? Good spark and solid/clean connections? Same vacuum as the other cylinders?
Some 1/3, full throttle and minimum throttle plug reads would be nice.

[Detman101]

For a MAC 4-into-1 pipe with the standard baffle you will be running 115s or 117.5s for the mains.

The 115s will be a tad on the leaner side if you are using the EMGO pods.
The only way to compensate for it would be to have your needles in the highest position.

The 117.5s will be perfect if you're running EMGO pods and have stock needles. For adjustable needles you would have them 2 notches from being raised to the highest position.

But that is just my experience. I'm running 115s in my cv carbs and the bike goes perfectly at WOT with them. However, using the 115s I'm at the highest adjustable notch on my needles.
I believe that if I went to 117.5s and lowered my needles two notches it would give me more adjustability should I ever want to swap exhaust cans on the MAC header.


For a MAC 4-into-1 pipe with the RACING baffle you will be running 120s or 122.5s for the mains.

Good luck.

[Anonymous]

Hi Keith,
I'll get back to you on the plug readings some time during the weekend. I'm going to be working a few evening shifts so I won't be able to ride during daylight. How far should I travel at each throttle position before killing the engine? The last two plug reads after normal shutdowns showed that all of the plugs were black. The one black plug previously may have been airbox related, I found that the two outer carb tubes going into the airbox were not sealing properly.

As for fuel flow, I put in a new petcock with smaller pick-up tubes (that you advised against). You can see a photo of it in the Tips and Tricks section. The bike has not shown any difference in performance and the petcock is meant for Harleys up to about 1300 CCs.

What I was trying to say before about upshifting is that my maximum roadspeed is the same in 4th and 5th gear.

Current carb settings:
Mains - 115 Mikuni
Adjustable needle - raised all the way, stock was middle
Float level - stock
Vent tubes - gone, tees still in place
Pilot screws - 2.5
Float needles - new
Other jets - stock

Cheers, Steve

[KEITH KRAUSE]

I usually go a couple miles for each circuit read, though the pilot circuit can be difficult and the reads fluctuate some.
Back on the 23rd you had 1 black plug at #1 and 3 white plugs. That could have been a poor carb synch, maybe. But since then you said you raised the needles one more position, which is as rich as the stock needle can go. Though you say the performance seems OK, all the plugs are now black. Regarding the needles, I still need to know what the 1/3 throttle position reads will say and the carbs MUST be synched to get accurate reads. I think your black plugs will probably not improve much at 1/3 position. As I said before, I think 2 positions richer on the needle is too much for just a pipe. Just my opinion. Do the 1/3 test and we'll know. Mark your throttle and housing to be sure. As I tell everyone, I can do these tests where I live. It may not be as safe for you. Be careful.
I like to get the needle right first, then I simply install the largest mains I can without creating any bogging at 5th gear/60 mph roll ons. Works for me. If we lower the needles 1 position and the plugs look acceptable, and then the mains are determined as I said, the bike should run well at higher speeds.
I'm not sure if your model with stock gearing will redline in 5th gear/level ground. Some bikes won't. My bike runs well but won't redline in 5th. It'll go about 7,700 rpm's according to my tach and may possibly hit 8,000 but I don't want to push it (8,500 is redline). Maybe your model does, but I'm just mentioning it in case you're expecting too much. I do know your bike will go faster in 5th than in 4th though. I still don't trust the "aftermarket" fuel valve you're using. I hope it's not causing a problem. Re jetting can be difficult enough without trouble shooting being mixed in.

[Anonymous]

It was my impression that these bikes could go 240 km/hr stock which is 9000 RPM in 5th gear. It would be a real dissapointment to find out otherwise. Up until now I have not been giving roadspeed numbers because my speedo is far less accurate than my tach. Anyway, I just did some number crunching with GearCalc and it's showing my top speed to date has been 119 MPH (191.7 km/hr). I think that's pretty slow considering the speeds some members have been bragging about achieving.

Steve