Weak idle until hot

[chuck hahn]

I would look up what stock jets are per tge service manual. IFF you dont have STOCK pipes and airbox go up one size on jets. Also i asked what the plugs look like. Sooty is rich and TOO RICH makes it run like crap because it can burn alll the gas. Same with ashy white plugs. too lean and not enough gas to produce power. You need to check it all and guessing isnt gonna cut it

 

[DimitriT]

Here's a pic of the plugs numbered 1 - 4 from left to right.


https://immortalsunited.com/apps/memories/s/XAE2RaTds34TrkP

After looking at these I adjusted idle richness on #4 so that it is just barely firing when cold. We'll see if that fixes it.

 

[chuck hahn]

1 a little rich
2 and 3 a tad lean
4 way too rich

 

[DimitriT]

So the weak idle seems related to fouling and temperature. I think it can be explained this way: Cylinder #4 is way rich so it can run a bit stronger when cold and, while #2 and #3 are lean and run poorly when cold. As the bike warms up #4 starts to misfire as it is too rich but the bike isn't warm enough for #2 and #3 to fully contribute to the idle. When the bike is fully warmed up #2 and #3 finally contribute but #4 misfires and fouls up with soot. So there's an intermediate temp which can be a problem. Also I was noticing a tendency for weak idle after decel in gear. I think a rich cylinder will foul more easily when stopping at the bottom of a hill because the throttle has been shut and there's less air for it to burn the extra fuel.

So I adjusted the idle richness on #4 (very small increments needed on this one) just to the point where it is firing when cold. Did the same on #1. I will run it like this for a while and see if the intermediate temp cut outs get better. When I have a little more time I will adjust #2 and #3 a little richer. #3 may have some other problem (float level) as it doesn't contribute well to the idle. That will need to wait until winter when I will pull the carbs for a full service.

I used to own a Gunson colortune which may have helped here but I sold it as it wasn't too accurate. Too bad there's no oxygen sensor bung or any way to measure anything. Probably not practical with four carbs.

 

[DimitriT]

Thought I'd share my latest results. Here's the plugs after some tuning. Same plugs as before and #1 to #4 left to right.

https://immortalsunited.com/s/ya6wykm35DRzG3G

Bike rides much smoother. Hasn't stalled on me. It feels more confident around corners with better throttle. Feels safer. I thought it was pretty good before but now it feels like I can weave it around at low speed with confidence.

 

[chuck hahn]

Pretty close. "MAYBE" 1 and 2 could be ever so slightly richer based on how the electrodes looks a bit ashen. And the rims are a bit ashy as well. 3 looks right to me. Little tan on the porcelain electrode looks like it didnt get as hot as 1 and 2 did. 4 a tad rich but thats better than lean and overheating a cylinder and piston. If you can get them all as hood as 3 your money.

 

[DimitriT]

I'll add a little to #1 and #2 but it sure feels about right. #4 was all fouled up and is in the process of cleaning itself out. I'll look at them again in a week to see the difference.

One thing I notice is that as it is currently set, the bike idles at about 1100 rpm (indicated) most of the time but when I ride it at speed for say 30 minutes and come off on an exit it will idle all the way up to 1500 rpm until it cools off a bit. Is this normal?

 

[DimitriT]

Winter time means I get to do all the maintenance tasks I've been putting off.

High on the list is a float level check. Cylinder #3 was running rich and the idle circuit screw would bottom out without the cylinder cutting out. Also #3 was not contributing very well.

I put the carbs in my float level test jig and here's a pic:

From the image it is clear #3 is too high. Need to adjust float tab.

 

[chuck hahn]

Only one that looks relatively close to me is 4. spec is 2 to 4 mm below the seam of the carb body and bowl

 

[DimitriT]

Only one that looks relatively close to me is 4. spec is 2 to 4 mm below the seam of the carb body and bowl

I'm going to try better pics:

Carb #1:

Carb #2:

Carbs #3 and #4:

 

[chuck hahn]

Go in the middle of the range is what i shoot for. Same when setting float hts. What did the plugs look like to each corresponding carb?? Fuel to air ratio affects it too. Too rich and it needs to warm up a LOT to get sufficient heat in the cylinders to vaporize fuel easier. Picture putting water in a frying pan cold and it takes a while to boil. Heat the pan up real good and put water in and it instantly sizzles.. Same principle applies with the cylinders.
General forum wisdom says set the side air screws at 1 1/2 from seated as starting point.

 

[DimitriT]

I just shoot for the lower edge of the bowl lip or where the screw fasteners come up against the bowl. This is about 5mm from the edge of the carb body. The manual says to measure while the bike is running but I that's a pain so I do it with the carbs off the bike. I did manage to get them about right and the carbs are back on the bike. I ran it a few seconds to make sure nothing went wrong but I won't really be able to test until the March.