1984 WR400 help

thanks for the info. ive ridden this many times. no runaways. no excess smoke. kill switch works.

i believe compression was much higher than 160 psi though. ill re-check when the head is back on. gasket arrives friday.

i was planning to try some aviation fuel: 100 octane low lead. a mate says i should upjet for that since its oxygenated. i may just mix a gallon of it with some 93 and see if i notice a difference.

would be better to find some leaded non oxygenated stuff to use..but that would boost octane. not much point unless you are going to cut out ethanol, and mix 91 e0 with your higher octane stuff. the oxygenated fuel will definitely alter your jetting, possibly by quite a but. you have to richen everything across the board if you run enough of it to make an octane difference.

I'm pretty sure that 100LL Avgas is not and never has been oxygenated?

im not sure. but after several reasons of why not to do it, i may grab some 110 from a local race track

vp 110 leaded is abundant around me. i mix it 50/50 with 91 e0. lead is definitely welcome to the longevity of a two stroke! jetting was richened but is very stable.

bad news my friends

after i put the head back on (new gasket and torqued), i ran it for a minute, then checked compression. mind you this is with a cheap gage, but it was only reading 110psi.

i did test a year or 2 ago and recall it being over 200 as i mentioned above, but its possible i was mistaken. but i usually remember things like this.

i dont understand why its so low if the cylinder looked so good (still had cross hatching).

would this low compression make sense to my lack of power? i did ride it this weekend for a day without issue (aside from the lack of power).
the ol girl climbed 2 mountains, navigated some rocky terrain, and was quite fun.

i did look in the transmission oil when i got back. the oil is atleast a year old, but it hasnt been ridden much since then. i believe it was red when put in. now it was pinkish and milky it was also a bit low

does that mean that crank seal is leaking?

it seems i needd atleast a hone and rings. if i put that amount of work in, i will also do crank seals. any how-to's on the seals? parts and info for anything/everything i will need? maybe do a new piston too? can the clutch side crank seal be done without pulling the motor?

The ignition side crank seal can be done in place, clutch side means splitting the cases unfortunately. Is it blowing heaps of smoke?
Tony.

These bikes aerate the gbox oil so it looks milky. Additionally, the alloy clutch plates also color the oil a milky grey...if there is a coolant leak, the gbox is full and spews out the breather ( dont ask how i know) if your gearbox side seal has failed, you will be leaving a smoke trail anyone could follow back to camp..and the smell will get you and burnt gbox oil burns your eyes. i havent read back thru the post but they are sensitive to timing. i went from 1.8 to 2.0 mm btdc and there was a noticeable lift in punch. Im still wondering what hit your piston. have you checked the reed block petal screws? if the po had left a loose screw in the housing, he might have been bodgying a fix in there. its a simple check to pull the reed block and inspect. Also, a blocked muffler can reduce power significantly. a mate had a 400 that just died up top when you expected it to go. it was too small a core diameter in the muffler. he had put a 250 muffler on by mistake. i would recheck the comp carefully and the timing and have a look at the reed block. also strip your carb and blow out all the jets. (if you have done any of this ignore my brain dump) They are a pretty simple affair and it shouldnt be to difficult to find a cause. keep hunting

by the amount of smoke you describe, i would say that it is definitely not leaking from that seal. im just figuring it would be best to do it while doing the top end. it could be 34 years old at this point.

keep looking for a cause? wouldnt you say the low compression is the culprit??

i have cleaned the carb a zillion times. including last week. and it was clean to begin with. the reed cage was also good with all 8 screws.
the muffler was swapped last year when this thread was going last time.

Before assuming low compression, can you use the same compression tester on another similar bike?
I've found that they vary wildly in some cases.
Before surprize rebuilt his 400, and it was very loose according to him, there was very little loss of power, it had plenty!
Tony.

interesting... i will verify the gauge when i can. i have used it on a few jet skis and it reads around the 150 mark which is where they should be usually

sounds like youve covered the basics pretty well. if you strip the motor you can measure the bore and get a real handle on its condition. i would strongly recommend stripping the engine down and replacing the seals, inspect the box and replace the needle roller bearings behind the kicker gears. i would send it to a husky engine man and it should be done to perfection unless your keen then there is plenty of help here on splitting the cases and what tools you will need. ( i will do a top end and clutches etc but i leave the cases to the magicians mainly so i can call them if summats wrong!) i am going to re read this post to see if there is anything we could have missed... good luck with the comp gauge. can you put it in gear and push it to give a good reading as the are awkward to kick hard.

ok well see. ive got a lot going on right now with winterizing all the watercrafts. so ill be updating on motor stuff in a bit

good luck, thats an art in itself...im preparing for the fire season here! i have reread the post and youve covered pretty much everything along the way so im a bit stumped as to your top end issue. the only thing standing out was the possibility of the ring being worn past serviceable limit as the mechanics of the piston and bore looked good. something to ponder a bit more on. clearly the engine seals are ok ATM as the vids dont show any signs of a dud seal. the bike did sound rich up top and the muffler issue was a good candidate but you went through that all right. My mates 400 was doing the no top end thing and he found he had too small a core muffler and a swap out fixed it. whats the airfilter status? new and lightly oiled? i will reread this again (23 pages) as its a great puzzle. hope you get all your water craft sorted for the freeze ..cheers