Thanks for the link. What I find most interesting (besides the step-by-step guide) is that a problem that gets worse as the engine warms is a rich condition, which makes sense now that I read it. So even with the 102 jet, that is clearly the problem I am having with the 89 carb rack. I would guess a needle position problem or perhaps a float level issue. This is consistent with what I just observed where turning the mixture screw OUT (increasing richness) makes the problem worse.

 

It takes a lot of trail and error to get them perfect. When I was racing mine I went through about 20 iterations of jet combos, needle heights, and others for the first decade until I dialed it. Total tuning time was at least a day for each iteration, but mine was stupid modified. If you get the dyno jet stage 2 kit it comes with a ton of different main and idle jets, 2 types of needles with 6 heights each, shims, and other tuning goodies, but no good tuning instructions.

 

I am going for reliable, smooth and consistent. The bike is owned by a relative beginner who I certainly hope won't race it. Can I still get the dyno jet kit if I want to tune it? Assuming I can ever get it to just run decent. I currently have a carb rack and makes the bike run good cold and idle good when cold and warm and a carb rack that idles terrible but seems to cruise better after it is warmed up.

 

Have you thought about returning the muffler back to as close to stock as possible? That would help you even things out more than anything.
I understand that due to the age it might be tough to find an OEM one, but there should be something close to it available.

 

So you are thinking go with stock exhaust and stock jets and then MOD from there? It is a good point about getting a baseline since every part I have has some unknown history. But even if I go to the stock exhaust, it is unclear which needles I should use since it seems like between the two carbs I have 4 completely different needle sizes. Also have discovered a number of mistakes in carb re-assemply; such as the pinched diaphragm in one of the needle assemblies I just found in the 89 carb rack. Not sure how this problem would result in cruising problems only after the bike warms up; but it is definitely not a good thing. I will consider this option and see if I can find a cheap stock muffler.

 

That is what I would do. I say this for a couple reasons. One, getting the stock sized parts, needles and such are much easier. Two, the documentation to help you get everything right for a stock bike is much better. Three, and this is the biggest one in my book. Your son is starting out on a bike. Having things smooth and consistent while he's twisting the throttle will help him as he gains experience and confidence as a rider. Also having a loud bike might gain him some unwanted attention as he learns the ropes of being on two wheels in a four wheeled world. I've had these discussions with my son also as he wants to get on a bike. It's a different world on the road for folks just starting out than it was when we started. Because of cell phones and similar things, a new rider really needs things stacked in their favor as they learn situational awareness on a bike, IMO.

 

It makes sense. He does have an 06 CBR 600 also that he is learning on; so he is getting experience on a bike that is very easy to ride. I use the 87 to ride with him or more often my Harley so I don't get distracted with 'what the heck is going on now' vs. focusing on him. I just ran some tests on the original carbs that show signs of a vacuum leak (low idle, idle stays up after hard acceleration, then drops) spraying areas with WD40. No question that spraying the throttle shafts makes the idle speed up. Spraying the mounting rubber seems to have no effect; which is what I would expect since they are new. So it looks like I will focus on the 89 carb rack and try to disassemble the throttle shafts on the original carbs and see where those orings go that I got in the rebuild kit. I will post some pictures of disassembly if I can figure it out.