Spark Plug question

Did a compression test yesterday and was looking at the plugs. I was wondering if these look OK or are they're running lean? Also noted the type of plug is a BP7ES but the manual states should be a BPR8ES would this be a problem?

Plugs are 1-2-3-4 left to right.

 

They look lean, for sure, how many clicks they been in there?

 

Only the previous owner and God know the answer to that question wizard but I re-gapped them recently and they were a similar colour then as well. I've done about 800km with them.

 

ya, that darkest of brown should be all over the plugs not certain spots

 

So I wonder if the plugs not being what the manual states is a big or little problem. Should I look at getting the correct plugs then see how they look after a run or maybe even a plug chop?

As all four plugs seem so similar maybe this is where I should start. Then if needed move on to adjusting the mixture screws and checking sync etc etc.

I'm sure that sometime soon I will have to go down the daunting road of "carb cleaning" but would like to avoid it a while longer if possible.

 

Plug #'s indicate heat range.

BP7ES runs "cooler" or rather removes less heat from
the cylinder then the "hotter" BP8ES.

The plugs actual firing temp is not much diffrent then the
other.

Race motors will run a plug according to the way the engine
is performing and I've heard of changes taking place during a
race.....but you should run the plug the manual calls for in
your bike.
Only under certain mods and conditions would you want
change the heat range of a plug

 

Apart from looking 'lean' they look near new, i'd say try the mixture screws to start 'n see what happens, right plugs later. ... if th carbs hav'nt been done since you don't know when, believe me it's worth doing. Daunting for th first time I admit............worth it, like your ride for th first time.

 

Start with the correct plugs.

 

With NGK the heat range gets hotter with the lower numbers. As far as that goes, if you have problems with oil burning, or are just riding in town, and not pushing it hard, then the 7 would be fine. If you are running long hours on the road, it is best to drop to the 8. Heat range just indicates how long the plug stays hot, thus with a hotter plug on a long ride you can get detonation. I have used NGK in everything i own including the lawn mower for 25 years. Great plu, you just have to make sure you match the plug to the type of driving, and condition of the engine. Proved that in lap time in the race car many times over.

 

They may be a little lean because they are not resister plugs. Make sure what wires you have as well. You could have resister plug caps. Maybe your sucking air around the box lid (some where common since they look the same) try pasting some caulk or modeling clay around the top though check the filter first to see if it has come apart. Maybe you can think of something else common ..I doubt all four box boots are split :roll: Good luck.

 

Now here's a strange thing. The Haynes manual for 80-84 XJ750's states a NGK BP7ES plug with suppressor style caps. Checked the caps and they're resistor types and all are within 10% of 5K ohms except number 2 cap which changes between infinite and 18K ohms.

It's the Yamaha XJ750RL supplement to the XJ900RK service manual that states use of the BPR8ES same as the XJ900.

With this in mind I think the plugs should be OK but may have to replace number 2 cap.

I'll check for leaks next and go from there.

I probably should have mentioned the bike as a Pipeline 4-1 exhaust which may make a difference.

 

If the Yamaha supplement says use 8's I'd use 8's but not "Rs" if you have resistor caps.

Run a set of non-R BP8ES for a while and see what happens (replace the #2 cap.)

 

What's your normal, cruising gas mileage? Should be around 46 MPG (US gallons) How does the bike feel seting off after waiting for a red light?

 

dont make it too hard, time, he's using km/liter

 

As long as it's not Litres per 100 KM- - that one makes Americans' heads explode !!

 

Well I'd hate to see brains splattered about the forum

On a recent country run I had 17.5 km/L which equates to about 41 mpg. Take off from lights is pretty smooth, my clutch control is a bit suspect at times , no power loss or spluttering.