Plug gap??

[ZeroShadez]

So i have a 1978 xs650 special. Ive got ngk plugs with 40mm gap. Is that to much? I don't think it misfires. A little bit hard to start cold 4 kicks or so. It also idles high sometimes. Could that be due to the plugs?

 

[Bushyeyed1]

I found that mine likes 0.032” gap. The tolerance is 0.028”-0.032”, but some will open the gap larger if they have a upgraded ignition coil. I do have an upgraded Andrews ignition coil myself and still came back to the stock specs.

 

[ZeroShadez]

I found that mine likes 0.032” gap. The tolerance is 0.028”-0.032”, but some will open the gap larger if they have a upgraded ignition coil. I do have an upgraded Andrews ignition coil myself and still came back to the stock specs.

Intresting so if my bike is running good with 40 i can go down to 32 without issues? And could what im doing now cause high idle

 

[Bushyeyed1]

I was giving you a gap in inches not mm just so your tracking. Wider gaps burn more fuel and yes it’s safe to go down to a minimum of 0.028 inches. Too close of a gap and it won’t start so maybe shoot for the middle at 0.030 inches. Plugs are not the causes of high idle.

 

[hovel]

1mm=.040" so there's NF way your plugs are gapped at 40mm. Part B: Plug gap has nothing to do with idle speed unless, of course, it won't idle at all.

 

[ZeroShadez]

1mm=.040" so there's NF way your plugs are gapped at 40mm. Part B: Plug gap has nothing to do with idle speed unless, of course, it won't idle at all.

Yes i know lol. And thank you if it has nothing to do with my idle ill leave them alone.

 

[5twins]

But, that large gap may be responsible for your harder starting. I run .032" as well, and that's with better aftermarket coils too. I used to use the .028" spec when I still had points and wimpy stock coils.

 

[ZeroShadez]

But, that large gap may be responsible for your harder starting. I run .032" as well, and that's with better aftermarket coils too. I used to use the .028" spec when I still had points and wimpy stock coils.

Ok so as for my idle i have bs38 carbs. The idle adjuster is on the left side what is the other adjustment screw in between the 2 carbs

 

[5twins]

That is the sync screw. It matches the speed of one carb to the other. Actually, it adjusts the speed of the right carb only, but that's all you need to match them. The idle speed screw on the left carb sets it's speed then you use the sync screw to match the right carb to it.

 

[ZeroShadez]

That is the sync screw. It matches the speed of one carb to the other. Actually, it adjusts the speed of the right carb only, but that's all you need to match them. The idle speed screw on the left carb sets it's speed then you use the sync screw to match the right carb to it.

Oh okay good to know. How do you know they are synced

 

[5twins]

Well, the best way is to hook vacuum gauges or a manometer to them and read their vacuum signals at idle. Sync them at idle and they will also be synced at all the higher RPM speeds as well.

 

[Bushyeyed1]

Check out the Tech section there you will find lots of good answers for the carbs.

 

[5twins]

Here are instructions for building a cheap manometer .....

http://www.powerchutes.com/manometer.asp

I have an ancient store-bought "Carb Stix" manometer with mercury in it. It has always served me well. But, If I didn't have it, I'd build one of these.