Another carb thread!!

[baylensman]

Okay so I have synched the carbs and understand the process and it worked well in making the bike much more responsive.

 

However, when syncing we are just bring the 4 units in line with each other at some arbitrary point. I'm wondering how I would go about leaning out all 4 carbs?

While the bike runs well when idling its a bit rich, others have commented on the raw gas smell, its not like a dead hole or even eye watering you can just smell that slightly sweet note of unburned gas.

The flip side is at a cold start even at 70" I need to either use the choke or jockey the throttle for 30 seconds or so to keep it running, after that it won't stall at all.

Also my MPG is still on the low side of acceptable (30-32) around town.

 

So the bike has KN filters and I switch back and forth between stock mufflers and Harley Pipes depending on how many canadians are in residence in the park, no other mods yet. Bike has 22K miles.

[cowpuc]

I'll just make this comment to serve as an opinionated (and probably not a very good one cause I have never owned or worked on a 2nd Gen) answer to both this post and that other one you made looking for pre season prep advice.

1st,,, and this goes double if you have been using Seafoam as I have found the use of Seafoam to put a coating on my plugs ceramic insulator, because of the sensitivity to over choking because of the smaller plugs we use - I would swap in a new set of standard NGK's and gap em at the low side so when they heat up over time and open up like plugs tend to do, they have the whole tolerance range to open into.

Because your scoot is not cold starting without the choke,, IMHO - your running fat problem is probably not related to the floats being set to high.. Knowing this, I would probably drop the metering rods 1 1/2mm and see if that didnt clean it up.. On my 1st Gens it was necessary to shim em down using little nylon washers I got for a couple cents each from Ace Hardware but yourr bike may be more of the traditional bike with the "C" clip on the metering rods to adjust em.. I would check the diaphrams when I set the metering rods and of course, resync after wards.

 

Also,, IMHO,, if your using KnN filters and especially if you are oiling them,,, its fairly easy to restrict airflow and fatten up the mixture that way too.. I love my stock paper filters that allow just the right amount of air box restriction BUT - lots of folks go oil treated KnN's..

[BlueSky]

How many turns out are the idle mix screws? You might try turning them in a little as you watch how the engine runs. They are harder to adjust on these engines than on the old carbed autos, but they should be turned in until the engine speed starts decreasing and then unscrew them slightly. The carbs will need to be synced after adjusting the mixture screws. These carbs also have enrichment circuits that may not be working correctly.

[bongobobny]

When you are syncing the carbs, all you are doing is adjusting the throttle plates so that they are all pulling the same amount of air through each of them at the same time. This does absolutely nothing as far as the air/fuel mixture! What you need to balance the air/fuel mixture to the proper ratio is to either use a CO "sniffer" or use a colortune plug. The CO analyzer is more precise and easier to read but costs a lot more. There are removable threaded metal caps on each exhaust pipe to insert the analyzer probe into and you adjust your mixture screws for a reading of 5.1 on each carb. If you use the less expensive special colortune plug, it screws into where the spark plug goes for each cylinder and you adjust the mixture screw for the "perfect" shade of blue on each one. You need to literally place yourself under a black hood to properly see the color, what you are looking at is the actual explosion of fuel through a tiny window!

 

You can try turning in all of the screws and backing them out 2 1/4 turns as a starting point, but that is only a rough setting and not completely accurate. Fine tuning each one will get the bike running at the optimum amount and bring fuel efficiency back to the 40MPG range...

 

Also, what the Pucster said about float adjustment is also very important!!!

[BlueSky]

This Yamaha video covers carb adjustment on the Gen1 and should be the same for the Gen2. In the video, it is stated that the idle mixture adjustment and the carbs sync should do done concurrently.

 

Edited May 10, 2018 by BlueSky