I love Carbs!

[CA]

I actually really do. they are like a puzzle. Anway here is my situation.

I got a new 79sf for my brother. (Other thread has larger explanation) Carbs needed work. So I just swapped my carbs over. I have yet to identify the exhaust on the new one, but I just pulled my pods over with it. Its amazing simple and fun to have the same bike.

Anyways. My bike was synched well. (Check stats in signature) I believe my idle mixture screws were a little lean as I had popping on decel and start-up. But I have found the kerker almost always does. I had a slight gurble up to 3k rpm. But other than that ran pretty hard and smooth. Although I felt maybe I was lacking a little power. And I was getting about 20 mpg, high 20's on the highway.

Plugs: 1- nearly white, little tinge of stuff. 2 - black 3- black 4- half black, half white.

My first thought was the pilot jet was dirty (probably not because they are clean) or not screwed in properly. I was about to check it between the swap, when I realized noting the difference between the two would help greatly.

Put them on, it fired right up. No popping ever. The bike ran much smoother, and I may venture to say a little more power if not just smoother throughout the rpm range. The gurble below 3k was gone.

Now I see the exhaust probably isnt kerker as it was running rich as the plugs will show. But it is a 4-1, which is curious.

Plug 1- very dark brown 2 - black 3-black 4 - black

My conclusions are as follows:
1. New bike needs smaller main jets, and maybe pilot jets?
2. Old bike needs new coils.
3. Old Bike needs idle screws turned out at least another turn

Now I have never messed with coils so I know nothing about them, and will use the tech tip to test them more extensively probably. But I am feeling Green coils coming my way.

Thoughts on this puzzle? Ways to diagnose more/better? I will be tearing into the old carbs and will probably order a series of main jets to swap out. I beieve I want 1 size smaller in my old bike and maybe 2 sizes smaller in the new one for better fuel economy. Do pilot jets affect fuel economy, I know the sure help it start in the morning.

THanks.

[dbeardslee]

I'd start with a trip to the fiche to verify what the stock jetting is. Then peruse the jetting recommendations tech tip, do the math, and figure out what size jets should be there. Then compare that with the jets that are actually installed. I've found the jetting recommendations to be pretty much right on the money, but I always confirm my jetting with colortune and plug color (after 1k miles). Don't worry to much about a black ring around the plug - it's the center of the plug that matters. Worn valve stem seals can give you a black ring, but you're not going to fix that at the carbs. IMHO you can't go wrong with the green monster coils - just make sure and open your plug gap a bit - .035-.040". Also, from my experience the float height has the maximum impact on that black ring. Raising them a mm or two (in the upside down orientation) can make a big difference. Whenever I measure my floats, I make sure I don't actually let the measuring device touch the float - they're way too easy to push down. I allow myself an extra mm, and then try to adjust so I've got that millimeter between my measuring device and the top of the float. And check both sides of the float - one side won't do. Also, don't assume that because the carbs were synced on one bike, they're still going to be in sync on another. You've got an entirely different set of pistons providing the draw, and that can be very different. And lastly, you've got brass floats in a '79, and every now and then you hear about one that's leaking. You can check them in water, and if you find a leak they can be repaired with solder.