MAC 4-1 jetting for GS1100E?

[gspaul]

My bike will do nearly 200kph( Speedo reading), that's in theory of course.I allway's observe the speed limit.( Well I can see it, but it's a blur)
So I can not see a reason you won't be faster!

[KEITH KRAUSE]

What's redline on your bike Steve?
I don't know about top speeds, but I'm just saying that some models won't redline in 5th gear. And yes, a lot of top speeds you see/hear is bragging.

[mark m]

It was my impression that these bikes could go 240 km/hr stock which is 9000 RPM in 5th gear.

That works out to 149mph, Steve. Which is significantly higher than the 135mph or so that I have seen in magazine tests from that era. My 1100 will easily pull an indicated 9500 in 5th and that is showing a bit over 210kmh at that point. It was still pulling hard and would have easily made 10,000rpm if I hadn't backed off. I believe my tach is reading a bit high, though, and a disassembly and clean up is in order, but I just haven't got to it yet. When I get that done, hopefully I will have some more accurate info on this.


Mark

[KEITH KRAUSE]

Just another quick though Steve...when you bench synched the carbs, did you adjust the throttle plates for the fully open position correctly? You can adjust them "too open" and possibly cause your top end complaint.

[Anonymous]

I should be able to run the bike on Saturday. I told my boss to work me like a government mule until the GSR Convention and she took me seriously.

Cheers, Steve

[Anonymous]

Keith: I finally got it done!

Minimal Throttle gives me two flat black plugs and two slightly blacker plugs. (2.5 turns out on pilot)

1/3 Throttle gave me 4 flat black plugs indicating rich but not really really rich were you'd see they are fluffy and thickly covered. (lowest notch on needles)

Full Throttle gave me 4 white plugs. I dyno'd my bike yesterday and got a reading of 83.67 HP so I'm short on power as you'd expect from the plugs. (Edit 115, not 117.5 Mikuni small round main jets)

The bike hasn't been sync'd after the last pilot or needle clip adjustments so I believe that's why my idle colours are a little different.

What do you think I should do next? Move the clip back up a notch and get bigger mains? I think I'd prefer to try different mains before trying another petcock.

Thanks, Steve

[KEITH KRAUSE]

Keith: I finally got it done!

Minimal Throttle gives me two flat black plugs and two slightly blacker plugs. (2.5 turns out on pilot)

1/3 Throttle gave me 4 flat black plugs indicating rich but not really really rich were you'd see they are fluffy and thickly covered. (lowest notch on needles)

Full Throttle gave me 4 white plugs. I dyno'd my bike yesterday and got a reading of 83.67 HP so I'm short on power as you'd expect from the plugs. (117.5 Mikuni small round main jets)

The bike hasn't been sync'd after the last pilot or needle clip adjustments so I believe that's why my idle colours are a little different.

What do you think I should do next? Move the clip back up a notch and get bigger mains? I think I'd prefer to try different mains before trying another petcock.

Thanks, Steve

Hi Steve. Looking back at previous posts, the jet needles were too lean at position 4. Though you didn't do a 1/3 throttle test at that time, I think your performance description suggested the needles were lean then. Now your tests show on the rich side with the needle at position 5. So it's obvious, if the stock needle is to work, you need to try position 4 1/2. That means adding a jetting spacer directly on top of the e-clip, leaving the clip in the 5th position. Spacers are about .022" thick.
For the main, you're getting pretty good flow increase for just a pipe. If 117.5 is as lean as you say (white), then I'd try a full size up, 122.5.
For the lower throttle/pilot circuit tests, I believe by lowering the needle 1/2 position, you'll see some needle overlap effect and that will lighten the plug reads some. Leave the mixture screws where they are and wait to see what the needle adjustment does for the minimal throttle position reads. Remember, a vacuum synch is critical for accurate reads for the needle/pilot circuits. It must be done. Besides uneven reads, how can you really know which levels to go by? The "higher ones" or the "lower ones"? They must all be uniform.
Hope the main jet suggestion works. I don't want you wasting your money on my suggestions only. It's trial and error. Some shops will swap the jets if you didn't damage them at all. Another reason I like jet kits.
PS: I sure hope that fuel valve isn't causing the lack of top end. We'll see what the larger mains do. Good luck!

[Anonymous]

Oh so close, I went from 115 (thought they were 117.5 in the last post but I corrected it) to 120 mains and the bike wouldn't redline in any gear. It would bog down. I removed the airbox cover and it was running just like the 115s with the cover on. I may have picked up 250 RPM in 5th gear but perhaps I'm just getting bolder and braking later. :twisted: I didn't get any plug reads tonight because I was passing cars before every run and there was also an airport cop watching me. I didn't feel too safe stopping.

I'll have to decide what to do now...if I can get a partial refund on my 115s or 107.5s I'll swap them from 117.5 If I can't do that I'll try to swap with a member here and run without the airbox cover (assuming it shows better WOT plugs) until then.

I won't have another day off for atleast a week so testing is going to be at a standstill again...I do plan on putting in half thickness washers.

Steve

[wayne cooper]

Quick thought

All the talk about max speed leads me to one thought-Wheel bearings. I know they will not effect your MPH but a speed wobble can seriously effect your future. 8O My one front was shot with only 32k on it. About $15 per side at bearing supplier. Seems a lot of people overlook the little devils. If nothing else this little note might be read by someone who hasn't checked theirs. Ok a little question- can the non-adj. needles be swapped out for adjustable needles or would I have to get the complete unit?

[Anonymous]

Hi Wayne,
If your bike was origionally sold in Canada it will have adjustable needles. I hear that the jet kit needles have a different taper. Keith has also told me you can shim non-adjsutable needles. Thanks for the tip about the wheel bearings too. I check that stuff once in a while but not on a daily basis. My bike is getting ready to roll 86K and it had OEM bearings when I put on the tires last year.

I'm starting to think that the engine is worn out. It has good compression but it sure is burning a lot of oil. I think I've been topping it up after every second tank this year! I missed a shift while going down hill today and pegged the tach at 12 grand so the engine seems to be mechanically sound even if it's a little loose.

Steve

[KEITH KRAUSE]

I'm not sure what's going on with your bike Steve. You say that 115 mains give poor top end and white plug reads, but 120 mains create a bog? You didn't take a plug read with the 120's but I'm assuming the bog was at full throttle? The bog would be a rich condition and the plugs would be dark. One full size up, (115 to 120) would not cause such a drastic change, in my opinion.
You have just mentioned that you suspect the motor is tired and is using a lot of oil? This could cause your problem of course. Oil in the mixture will compromise combustion. Less than optimum combustion will lower the top end performance for sure.
I have to say again I find it odd that you've had to raise the jet needle 2 positions for just a pipe mod, and in my opinion, the Mac's don't flow that well. Even if it was a Kerker or V&H pipe, 2 positions richer is odd.

[Jethro]

Plug reads are too hard for me. How do you test the main jet circuit? A couple of miles? I don't know if I can bring myself to ride at WOT for a few miles- guess I could use the highway at 3:00 in the morning and hope I don't get arrested! That's at least 130mph for me.

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.

Just for reference Steve, my 81 1100E would pull at about 125mph max when I was neck and neck with my buddy who actually had a speedo that went over 85mph. That was when the bike was in excellent running condition and stock gearing and jetting.

[Hoomgar]

Plug reads are too hard for me. How do you test the main jet circuit? A couple of miles? I don't know if I can bring myself to ride at WOT for a few miles- guess I could use the highway at 3:00 in the morning and hope I don't get arrested! That's at least 130mph for me.

You really need a Dyno if you can find one. That's the ticket.

[KEITH KRAUSE]

Plug reads are too hard for me. How do you test the main jet circuit? A couple of miles? I don't know if I can bring myself to ride at WOT for a few miles- guess I could use the highway at 3:00 in the morning and hope I don't get arrested! That's at least 130mph for me.

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.

Just for reference Steve, my 81 1100E would pull at about 125mph max when I was neck and neck with my buddy who actually had a speedo that went over 85mph. That was when the bike was in excellent running condition and stock gearing and jetting.

At least your speeds are more believable and I'm sure, truthful.
There is a lot of exaggeration here me thinks. I've ridden a few of the models and they were good running bikes that simply couldn't go as fast as some here say, at least not on level ground. Maybe down a steep grade. The only thing wrong with this bragging is it makes others think something's wrong with their bike. A few mph is nothing. We all know there's some difference between bikes, even good running ones. But saying your bike will go 138 or whatever when it's probably good for only 125 is just BS.
I won't brag up my lightly modified '79 1000's top speed, but I will say for its mod's, (1085/pipe/pods) in its class, I have one of the best running 1000's on this planet. Over 26 years, I've gotten into a lot of little "trophy dashes" and done well. It runs strong and I fool a lot of people on our rides. But I can only go about 125 on level ground, if you believe the speedo, which seems about as accurate as the guys next to me. I can't get to redline in 5th gear either, but I seriously doubt there's something wrong with my bike. But to read some of the claimed top speeds here, you would think there's something wrong.

[Anonymous]

This is helping me out here guys. I have the same kind of issue with my 81 GS1100E. Although the motor has only 17k of baby ridden miles, V&H pipe and pods on stock carbs, it has some running issues I'm dealing with. I'm learning about the jets and needle info pretty fast just with this topic. Make this topic sticky or archive it