Running Rich?

I have a 73-750 with single Mikuni. After a ride after sitting for about a year (waiting on a part) I took her out for about 75 miles. After one short, 20 minute stop, I had a hell of a time re-starting. Seemed to be flooded. After I got her going, she ran fine. Got home and pulled the plugs, they were a brown color.
From what I understand, this indicates she is running rich. Should I move to a step hotter plug? Currently running NGK plug in the 7 heat range. Same plugs I've been using since installing the single Mikuni.
As always, any and all comments and suggestions are welcome.

Thanks in advance, Steve

Light brown/tan is the perfect colour, don't whatever you do weaken the mixture.
Your hard to start suggest other issues .

steveyacht said:

I have a 73-750 with single Mikuni. After a ride after sitting for about a year (waiting on a part) I took her out for about 75 miles. After one short, 20 minute stop, I had a hell of a time re-starting. Seemed to be flooded. After I got her going, she ran fine. Got home and pulled the plugs, they were a brown color.
From what I understand, this indicates she is running rich. Should I move to a step hotter plug? Currently running NGK plug in the 7 heat range. Same plugs I've been using since installing the single Mikuni.
As always, any and all comments and suggestions are welcome.

Thanks in advance, Steve

Click to expand...

Interesting Steve, as my ‘74 850 has the same carb, set up by the po. R hand plug shows weaker than left, which itself indicates over rich, almost like he set the mixture up trying for a compromise between the two!
No issues with starting at all, cold or hot but there’s obviously an underlying cause. Difference in compression between cylinders?

As alway, any comments welcomed. Thanks.

Hope you get to the bottom of your starting issues. Carbs flooding when stopped? Try turning gas taps off when stopped then try starting.

Steve

Stevo said:

Interesting Steve, as my ‘74 850 has the same carb, set up by the po. R hand plug shows weaker than left, which itself indicates over rich, almost like he set the mixture up trying for a compromise between the two!

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Possibly caused by induction bias where both cylinders are fed by a single carb but one cylinder runs weaker than the other and can often be cured by fitting an anti-bias gasket that angles the carb slightly towards the weaker cylinder.

https://www.a7a10.net/forum/index.php?topic=7720.0

LAB thanks for that - never heard of bias. I was always taught to use a single carb and old exhaust pipes when running a fresh engine in, then swap to final configuration and retune.

The assumption is that before laying it up, it was not running rich (all jetting was spot on). Did you turn off the petcocks before laying it up? If not, the bowls could have overflown. Did you drain the bowls and put fuel stable in the tank? It may be old fuel vs rich. The fuel enricher (i.e choke) may be leaking. Is anything pushing down (even slightly) on the choke lever (if it's not cabled to the handlebar). If you have a choke lever on the handlebar, is it set up correctly so it's not pulling the enricher up when shut off?

Then there's the assumption that your jetting is correct. Is it?

Good luck

Bowls??? Am I missing something (probably!!)

The bike is single carb, no?

Comments apply to either single or dual carb setups

Stevo said:

Interesting Steve, as my ‘74 850 has the same carb, set up by the po. R hand plug shows weaker than left, which itself indicates over rich, almost like he set the mixture up trying for a compromise between the two!
No issues with starting at all, cold or hot but there’s obviously an underlying cause. Difference in compression between cylinders?

As alway, any comments welcomed. Thanks.

Hope you get to the bottom of your starting issues. Carbs flooding when stopped? Try turning gas taps off when stopped then try starting.

Steve

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For what it's worth, I always shut off the gas flow when I cut off the engine. I have a theory, it is a cold blooded SOB, I try to limit choke usage, but I'm thinking that even limited, the choke use fouled the plugs enough to make it hard to start. What do you think?

Float height too high or (something that happened to me on another bike) crustiness causing the float to catch on the spindle, or needle valve no longer completely shutting off fuel supply to the bowl?

steveyacht said:

After one short, 20 minute stop, I had a hell of a time re-starting. Seemed to be flooded.

Click to expand...

Generally, if flooded you open the throttle fully and kick. If flooded it will usually start in 1 or 2 kicks.

If you don't use the choke and the test above shows that it was flooded, I would suspect the seal on the end of the enricher since it was OK last year. It's also possible that the float is not working properly (dirty, sticky, etc.)

Bernhard said:

Light brown/tan is the perfect colour, don't whatever you do weaken the mixture.
Your hard to start suggest other issues .

Click to expand...

When you read a plug, it is not the coulour you should be looking at. Right down inside plug, on the porcelain where it meets the metal, there should be a black ring of carbon about 3mm wide around it. That indicates whether you have the correct size main jets. If you use colder plugs, the ring will be wider. The heat range of the plug determines how far the carbon burns off. When you ride a road bike, you do not usually doo 100 MPH, and then suddenlt cut the throttle and stop, so you ride a bit fiurther using part-throttle. When you do that the needle and needle jet mter the fuel and the appreance of the plug can be misleading. I think you will find your needle jet is one size too big, or the needle is one notch too high. Ether that, or your float bowl is flooding - vibration can cause that.
You should be able to ride normally and have the black trng on the prcelain, without doing plug chops. Plug chops are only for safety at high speeds, to stop from burning pistons. But on the road, you do not usually ride like that.
For a roadbike being used on high-speed freeways, I would always have the main jets a bit too rich.
When you adjust the needle and needle jet, you should make sure you never continue to ride the bike if the motor misses. It is the sign that the mixture is too weak, and you can do damage.