Spark Plug Question

[SpecialK]

Hey everyone, I just picked up a 1983 Yamaha Maxim 400. The bike is in great shape for its age but unfortunately she doesn't want to start (I knew this prior to purchasing the bike). I plan on making a summer project out of it. Any ways, to cut to the chase I went to go pick up some new spark plugs today and according to the manual as well as the forum NGK BP7ES is the correct plug. I headed down to Canadian tire and realized that they did not have this plug which I expected because I believe its been replaced by the BPR7ES. I looked everywhere and finally came across a 3BPR7ES (I'm was hesitant about purchasing these as I was not sure what the 3 indicated). When I brought them home and attempted to put them in the engine they wouldn't even fit in the hole (to wide).

I guess the "3" has something to do with sizing.

What really puzzled me is when I went to go check what plugs were currently in the engine I noticed that they were "DR8EA" which Im pretty sure are incorrect. Can anyone confirm this?

Thank you!

 

[Specdog]

A DR8EA has a 12mm thread. A plug starting with the letter B has a 14mm thread. Also a plug with an R means it contains a resistor. Your plug caps, if they are like the SOHC will also have a resistor. You don't need two resistors.

 

[SpecialK]

Okay thank you, I must have a 12mm spark plug hole then. Is this normal for all xs400's or just the DOHC models? I haven't seen any mention of using "D" model or 12mm thread spark plug in any of my searches.

 

[Specdog]

The SOHC uses a 14mm plug. A non resistor BP6ES is standard for the later years.

 

[xschris]

D8EA is the stock plug for the bike. You may want to download the manual from the site to get all the correct specs for the bike Welcome to the forum. Post some pics of the bike, we love pics.

 

[SpecialK]

Okay great thank you, I will pick up a pair of the correct plugs and see what happens. I have a couple pictures of it nothing to flattering.
Over the weekend I plan on taking the carbs apart and giving them a good cleaning. I was able to get the bike to start by putting a bit of gas in the cylinder but other than that it doesn't want to fart on its own.

 

[xschris]

Looks like a good clean bike There are a lot of carb cleaning guides on here also.

 

[SpecialK]

Yeah its a great base to start with. I'll definitely have to check those over. What has got me rather puzzled is that when I crank the engine over with the electric start and remove the plugs after they are nice and moist with fuel but I guess its just not igniting. There is spark but the higher resistance plugs may not be allow for a strong enough spark to light the fuel.

 

[xschris]

Is the fuel fresh?

 

[SpecialK]

Yeah I put brand new fuel in the tank but I think a bit of old stuff was left over in the lines when I bought it.

 

[xschris]

It would be a good idea to start with clean carbs and new plugs.

 

[SpecialK]

That's the plan for this weekend, I'll pick up some new plugs and give the carbs a good cleaning. I'll probably check the valve clearance as well when I have the tank off

 

[willem]

welcome!

you should also consider a new battery, some spark plug caps and trimming the spark plug wire a little.

 

[DARKMIDKNIGHTWARRIOR]

Welcome to the forum!

 

[SpecialK]

Thank you for the suggestions! The battery was brand new last year and appears to be healthy but I will try a new one to see if that eliminates the problem. On the left cyclinder the spark is nice and bright blue but on the right it's thinner and much more orange.

 

[xschris]

You may want to test your coil.

 

[SpecialK]

I'm assuming that I should test for resistance right?

 

[xschris]

Yes, it should all be in the manual.

 

[SpecialK]

Okay great, thank you!