TOPIC:

Okay, got some W20ESU's sourced, they're the Nippon Denso equivalent. Are they as good as the NGK's? Looks like NGK's would take a couple of days to get here & im impatient , if they're much better i'll order them too.

Here is a Wiki write up on Heat Range from this link, en.wikipedia.org/wiki/Spark_plug#Sealing_to_the_cylinder_head





Those Denso plugs are good, NGK is also good. Once you get it running, take it out and build some heat. Then check the plugs.

Thanks Motor Head, that has helped my lack of spark plug knowledge.

I paid particular attention to the 2nd last paragraph where it states that the plug hotness or coldness will not affect the cylinder temp. Maybe my excessively sooty deposits are making things run badly.

I'll be going home with the new plugs & im going to change the high octane unleaded fuel to ordinary stuff incase it is burning too fast or per igniting. There in only 2 RON between the 2 types of fuel we have here, super UL at 97 & ordinary UL at 95, i think i also have the option of no ethanol in some places.

I'll change the fuel & plugs to see how that goes & report back later

Higher Octane fuel burns slower than a lower octane. If it burns to fast, then you have problems. These engines need a higher octane at sea level, but with altitude can handle less octane as cylinder pressures decline. You service manual, and the sticker under your seat will suggest a minimum octane rating. 87 I think, but can't remember which rating type that is

Motor Head wrote: Higher Octane fuel burns slower than a lower octane. If it burns to fast, then you have problems. These engines need a higher octane at sea level, but with altitude can handle less octane as cylinder pressures decline. You service manual, and the sticker under your seat will suggest a minimum octane rating. 87 I think, but can't remember which rating type that is

Yeah sorry i did get that ass about face! Flamin eck i knew high octane burned more slowly!!

Anyway it wont hurt to try changing the fuel & the plugs to see if that makes a difference for all it'll cost

where i live the atmospheric pressure is about 1000 - 1010mb & about 200ft above sea level.

Guys i gotta thank you so so much, i'd honestly never have thought that 2 seemingly small differences would have such a big effect on things!

I replaced the plugs & fuel & she seems to run pretty good now. Settles back down to idle nicely, infact nearly too nicely, & revs clean with both cylinders at about the same temperature. There is no unburnt fuel stinging my eyes in the garage either now.

I dunno if you can hear it in the video but she gargles a bit when setteling down in RPM. Im just putting that down to the small baffled cans, i can live with it & somehow i find it pleasing as its a bit 'raw'



Plug after running this time

After 1.5 year a big thank from me!
I have a z750 1984 completely rebuilt.
For weeks trying to solve the problem, the engine is not started without choke.
idle only when the engine was hot
Check again valves, camshaft, cylinder compression, pulled the carburetor is controlled again, check out the air intake boots, everything was okay., The plugs ( NGK BR9ES ) are new only few hours working.

Finally read this Post and try the same solution.
Change petrol and new spark plugs.
And there was miracle!
Now works perfectly, I'm getting ahead easily and without choke.
So simple was the solution!
The last time buys plugs ngk, short-circuit very easily already spoiled 3 sets.
Will try next time DENSO W24ESR-U

Did anyone notice that the first Iridium plusg he was running were "R" BR8EIX resistor plugs, instead of the "non-R" B6ES? That would cause excessive resistance if the wires he has, have the built in resistors in them also, no?

750steve wrote: Hopefully these are simple fixes;

1/ Backfires when coming down the revs on the right cylinder

4/ Takes a while to return to idle (1000RPM), when i rev itthe RPM comes down quickly enough to 1300 RPM but then takes about 20 secs to return to idle speed


Does this sound like i need to check the timing?

Based on those two, my guess would also be a vacuum leak somewhere.