high altitude timing adjustments

[raceman]

l`m at 7000 feet here in Santa Fe.That`s higher then a mile,higher then Denver and in fact the highest capital city in the nation.Less o2 means less power and advancing the timing for altitude is common practice with older vehicles and absolutely needed for some of them.Anyone at high altitude on the forum that has some good experience to share? l have a 78 GS1000 with Dyna/Andrews and it is an absolute DOG compared to how l think it should run.l`m still shaking the bugs out and the carbs need jetting before l mess with the timing but any help is appreciated........:-D

[salty_monk]

RenoBruce is high up (home is 5500ft) & has a 78 1000 with Pods & V&H 4:1. Maybe his settings can give you an idea...

Dan

[raceman]

l did a little research and l`ll pull out the timing light but one problem is that l don`t have a manual...

[Ghostgs1]

Hey raceman, I'm near Denver and I am using the factory timing marks, but I too have been thinking about increasing the timing. The manual doesn't address high altitude timing changes, don't know if it is a good idea or not.

[Dan Ruddock]

Gas sold in high altitude areas will typically be lower octane rated gas. They know you don't need the higher rating stuff so it's in their best interest to sell the low grade stuff. If you are at altitude you can use a lower rating gas or you can bump up the timing but just 2 degrees at a time and then test it to see if there is any ping problems. I would not try anything more than 4 degrees. The best way to compensate for altitude is to add more C.R. but that can be a problem at lower altitudes. It is best to get the jetting right first as this can kill your power if it is too far off. Dan

[salty_monk]

Interesting... When I was in NV with Bruce my bike seems to run better on the gas we bought across the border in CA. I thought it was me or the ethanol additives here in CA or something!

Dan

[KEITH KRAUSE]

You need to set the timing correctly BEFORE any re-jetting. This also assumes the bike is ready to re-jet. Valve clearances, clean carbs, etc...
I'd first try the factory recommended timing. Verify good blue spark. Then install jetting that makes sense.
What mods on the 1000? Give brand names of mod parts too.

[raceman]

Thanks keith,you really seem to know your stuff about these bikes. Okay here`s the rundown: 12-k mile motor
yna/andrews coils
:29mm smoothbores (l`ll pull the carbs this afternoon and post the jetts for you)
:new gen Supertrap(specifically for the GS1000,isn`t the type with tunable plates)
:crap pod filters(temporary until l get the good oval K&N`s) .

l don`t have a manual so for timing l left the PO`s settings.l do have a shim tool and tons of shims so l suppose l need to get on the valves before l go further,that and record the carb settings and jets. The bike felt like it had too much timing so l backed it off a bit and it seems to run better and start better.l noticed when l was starting it before that the timing might be off,it had that "wants to run backwards" catch on ignition. this is gone now. There is also the possibility that two cylinders are out of whack and two are okay..

[raceman]

l went out and set the timing with a light and added three degrees advance.l haven`t checked the jets on the carbs yet because l have to ride the bike still today.l noticed that when parked in neutral and l rev the bike it pops quite a bit as the revs come back down or on decel

[KEITH KRAUSE]

29 smoothies!? Not those again. Just kidding...a little.
The 29's are perfect for your 1000 but because they are basically an aftermarket race carb, they can come to you with who knows what jetting, and the jetting is commonly off, not to mention worn parts can factor in. Instead of the basic main jet/jet needle/pilot jet questions, there's the cut-away question that brings up different opinions as to which gives best results. The slides are expensive too if they need changing. Many times the needle jets are changed too so it can be quite a challenge. Add in your richer elevation and it may take some trial and error.
I don't have a lot of tried and true 29 experience but I do understand how they operate and have some basic jetting knowledge for them. There are some members here with those carbs and it would be nice if they see this and participate. Several 29 owners have asked questions here and we've tried to work on the jetting, but, most of them just disappear and very little confirmed good final jetting specs are shared. "Rock" has shared some info here, as has "Firstimer" (I think firstimer has 29's).
I'll be off on vacation starting this Friday too, so I can only give a little help. I'll be back in about 12 days if help is still needed.
It seems you're bent on having the advance changed from factory. OK.
The valve clearance check is important and needs to be done before any vacuum tool synch. Be sure to follow the EXACT factory method when checking the valves. I just posted the factory method at another thread if interested. I'll try to get that threads name so you can look at it.
The decel' pop after revving is typically a lean symptom. A little is acceptable in my opinion, just not too much. Trying to completely eliminate all decel' pop can results in worse problems. Be sure the decel' pop isn't in part caused by re-used header gaskets.
Like I've said, be sure the bike is ready for the re-jet. All other tuning must be done first so you know any problems are jetting related. Carbs must be clean and fresh inner o-rings are suggested. Fresh manifold o-rings are usually needed too.
If you really are going to pick up some K&N pods, it's probably best to do that now, or you'll be going through the jetting again in my opinion.
Regarding the cut-away, many here say the 2.0 is the correct one for Suzuki's, but many say the 1.5 is correct. It can depend on mods and conditions of course. Your high elevation may tend to favor the leaner 2.0 slides.
If I have time tomorrow night, I'll check in and help if I can, but I'll be busy. Good luck with it.

[KEITH KRAUSE]

Look up "GS1000 valve clearance problem" in the tech section if you need exact factory valve clearance checking/adjustment method.

[raceman]

thanks a LOT Keith. As for the timing l typically do advance at this altitude since they really respond to it.Keep in mind there`s 20% LESS oxygen at the 7400 feet elevation where l am compared to see level. l wouldn`t bother at see level. Today l will pull the carbs and document the jets comparing to the other posters.l will get this tuned.My friend blew me off the bike a few nights ago on his 1200 Sportster,that`s just wrong