As many have stated, the rear cylinder is always hotter than the front. I've never actually measured the differences... so I have no experience to draw from on what is, or is not, a normal difference.

Your delta between front & rear seems excessive for 1 minute of running, on the kick stand.... but that is just my gut feeling...

It has been awhile since I have owned and worked on an EVO, and I never worked on the MM FI system....

The popping may be related to the heat issue or maybe not... decel popping can be tune, exhaust leak, intake leak, etc... a hot running cylinder can be tune, intake leak, bad injector, etc...

Since it runs good, it may not be the tune or a dirty injector...

You can do some checks yourself for cracked/loose/leaking exhaust, or intake.

If you don't feel comfortable checking yourself, or can't find anything wrong, I suggest you try to find an independent shop that knows the MM FI, or at least has EVO experience, and have them take a look...

It may well be normal, but I don't remember thinking my '89 Heritage (EVO Engine) was a hot running engine at anytime during the years/miles I owned it....

 

Poppin on decal can be caused by a crack in the Y part of the muffler at the weld, an intake or exhaust leak at the head, and also a leak at the header/muffler joint. If you take the mufflers off you can see how they cut a funky notch in the end to allow the metal to tighten up over the header pipe. That funky notch isn't always cut away enough to allow the mufflers to tighten properly. They are easy enough to get off, you'll see what I'm talking about when you do it. Take a small file and add some clearance to that notch. Tighten them up really well and that will help, if not cure your problem. You can verify the other possible leaks by visual inspection, running a small amount of water in the areas while the bike is running to see if it kills the engine, or even using propane to see if the motor speeds up. Having fixed and/or verified all those issues, there is one other culprit: The throttle position sensor (TPS). There is a video out on the internet on how to set an EVO Mac Minerelli TPS. It isn't hard, just takes awhile. The real hard part is digging the epoxy out of the adjustment screws. The MoCo didn't want us to fix them. They also didn't tell us that they set the TPS lean so the bikes would all pass emissions testing. Watch the video then i'll give you one helpful tip: when you dig out the epoxy, loosen the screw, then tighten it back up tight. Now dig out the other, loosen and retighten to snug. Loosen the first one and retighten to snug. When you make the adjustment, use a real small hammer and gently tap on the housing (where it rotates) while you watch the voltage change on the voltmeter. Then CAREFULLY tighten up both screws and recheck. If you go twisting that housing around it's gonna be a real pain to get the voltage to where it needs to be.

Now, you've done all the above. Before you start your motor, pull the plugs and have a look. Probably both ashen gray from running too hot (lean). Replace them. I like Autolite 4265s. Run whatever flavor blows your skirt up but for the love of God, don't run Champions or those crazy weird two prong things. Big twins like to run on the fat side (rich). Your bike will run better, you will lose that amount of hesitation you feel when trying to accelerate a little hard, and it will run cooler. Oh yeah, no more popping either. I did all this on my 98 RKC, made a huge difference.

Carl

 

I agree