Cam Timing on 16v GS1100

[Tom R]

I checked the lobe centers and lift on my '80 GS1100 yesterday and came up with 97.5 degrees and 0.295" (7.5mm) on the intake side, and 107.5 and 0.276" (7.0mm) on the exhaust side. This jibes pretty well with the service manual specs for '83 cams, which are 97/109.
From perusing the forum a bit, it seems a lot of people will time their cams somewhere around 105/107 for street use. My question is: Being that I have a set of adjustable cam sprockets sitting on my work bench, would I see an "improvement" by retarding the intake cam to 105 (I could probably just leave the exhaust as is) - Or some other numbers? I put improvement in quotes because I realize it'll really just change the torque curve. As is, The bike is used for street riding, though I have run it at a couple of vintage track days in the past - maybe again in the future.
Some pertinent information: The bike has k&n pods, Factory Pro stage 3 needles, and a V&H 4-1 super sport pipe.

Just looking at the specs for previous years, from the factory the the 16v 1100 had 110/109 lobe centers for the '80 through '82 E models and 105/109 for the GS1000sz. The '83 picked up an additional 0.5mm of lift on both cams and an additional 12 degrees of duration on the exhaust side. So it wouldn't be a very radical change to make, but is it worth while?

[Tom R]

Hopefully gonna button this up over the weekend... planning on setting to 105/107.5
Does overlap and LSA play much of a role in engine performance? For example 97/102 would have much more overlap than say the stock 110/109 timing, but peak power would come in earlier...

[mmattockx]

Hopefully gonna button this up over the weekend... planning on setting to 105/107.5
Does overlap and LSA play much of a role in engine performance? For example 97/102 would have much more overlap than say the stock 110/109 timing, but peak power would come in earlier...

http://www.webcamshafts.com/pages/degreeing.html

Down towards the bottom of this page there are good explanations of what does what and how changes affect things. I am setting my 1100E to 106I/108E this spring on the advice of a tuner I trust. You won't be far off that with your numbers and it is supposed to produce a mid range monster that is superb for street use.


Mark

[Tom R]

My earlier question should have been... how does the gs1100 engine respond to overlap and lsa? Even with an lsa of 103, my bike had no problems starting or idling, problems I'd associate with such so much overlap. I was more wondering how far you can push it before it's a problem
So I set my intake and exhaust timing to 105.5 and 107.5 after a few mishaps of initially setting it up one tooth off and pulling the threads out of a cam cap bolt hole - probably over torqued it a dozen or so years ago when I put the '83 cams in it... I used to do stuff like that - luckily I had a helicoil kit on hand.
i didn't get to test it on the streets because of rain, but initial start up had a few hiccups. Notably, I needed way more choke and had to increase the idle throttle screw than before the change, and even heard a few pops through the carburetor... something else I haven't heard in a long time.
I would think less overlap would give a better carb signal and make the idle smoother, but so far not the case - seem like lean symptoms to me. Anyone come across this before? Carbs are freshly clean this year and bike ran and idled fine last week.

[mmattockx]

I would think less overlap would give a better carb signal and make the idle smoother, but so far not the case - seem like lean symptoms to me though. Anyone come across this before?

The tuner I spoke to said that he had to go richer on the pilots, sometimes a touch leaner on the mains when going to 106/108 from stock. I am going to do it this spring but haven't got that far yet.


Mark

[Tom R]

I have 47.5 pilot jets right now with mixture screws out 3.5 turns, but I do have some 50's on hand. I'd think any more than 3.5 turns it's time to go to a bigger pilot jet.

[mmattockx]

I have 47.5 pilot jets right now with mixture screws out 3.5 turns, but I do have some 50's on hand. I'd think any more than 3.5 turns it's time to go to a bigger pilot jet.

47.5's were stock in Canada so going to 50's with pods and a pipe on doesn't seem crazy to me. I would agree that 3.5 turns out on the mixture screws is getting towards the end of the adjustment range. Just for reference, my Canadian model '82 1100E has 47.5 pilots with APE pod filters and a Kerker 4-1 system. I am at 3.25 turns out on the mixture screws at the moment, so not much different than you.


Mark

[Tom R]

I finally had a chance to test it out yesterday. I backed the idle screws out another half turn and took it for a quick ride. Traffic was kinda heavy, so limited opportunities to open it up, but it felt pretty good, still popping on decel though and a rising idle as it heated up... so I brought it back in and pulled the carbs. I installed the 50 pilot jets and reset the screws to 2 turns out. Then, against my own advice of one change at a time, I raised the needles one clip position. I only had time for a 20 minute ride after putting it back together, but it ran decent... still had to adjust the idle speed screw at stop lights as the idle rose about 400 rpms as it got up to temp, a little popping on decel still. I had a couple of short second gear wot throttle runs... it pulled pretty good, but at around 7500 rpm it felt like I had a set of secondaries - it really pulled. I'm guessing I should have left the needles in the center groove. Doh! Might get some time for a ride today, I'm going to back the screws out another 1/2 turn and see how it goes, prob won't have time for the needles.

[gustovh]

7500 is the beginning of the power on those engines.

V

[Tom R]

Was a very abrupt transition though. According to the factory pro tuning guide, that's also about the point where its all main jet... makes me think the needle might not be right ... it didn't feel that way before I moved the needle up a notch.

[Tom R]

Before I retarded the intake cam 8 degrees, it used start to really pull hard around 6k - The front wheel would always start to lift at that point during 1st gear wot runs. I was hoping to broaden the power band out a bit when I started playing with it.