Thoughts on what to do.

Hello,
I've just recently purchased a 82 xj650 maxim. When I picked it up previous owner told me everything that he did to it(cleaned carbs, tune up) and that these bikes are cold natured. I figured it was a carb/fuel issue. After getting it home and digging into it I found this bike has had a hard 34,000. She only has 60psi of compression on all cylinder, wet is about 90. I've tried soaking rings with different brands of (snake oil). Also notices that it has a weak spark. Coils ohm good on both sides. They are getting 12 volts while cranking. I checked valves and they are within spec (intakes .005 exhaust .007) If its above 50 degrees outside she starts right up with choke and runs if the fuel petcock is on PRIME. if its cold she cranks and cranks or if I turn fuel petcock to on. Looking online its real easy to sink 100's of $$ in these obsolete parts if I were to rebuild. What do you suppose would happen if I just ran it like this? Also what I think is weird is despite low compression I get no crankcase pressure at vent tube? Thanks

 

Start here:
http://www.xjbikes.com/forums/threads/the-information-overload-hour.27544/

Realize that the previous owner may or may not have refurbished the carbs when he 'cleaned' them. After you read the Information Overload reconsider if you want to invest the time and money to bring this great bike back to a safe and reliable condition.
If you answer yes, then know that all you 'obsolete' parts are available here from XJ4Ever plus all the advice/ help you need lies here within this great community of XJ enthusiast.

 

TCI ignition systems throw a spark that looks weak compared to a CDI ignition system. It's not weak, just different. Make sure that the plug caps themselves are within spec (you migh even take the resistors out and check for corrosion), and that the ends of the plug wires are corrosion free (they can be cut back a bit until you get to clean wire).

Read that link up above me.

Are you checking the compression with the engine warm, and the throttle wide open? If not then do that and you'll see the numbers come up.
If so, then try a different compression gauge. We've had more than a few people find that their gauge is faulty.

Just cleaning 30 year old carbs won't do. The throttle shaft seals and other rubber parts (aside from the diaphragms) dry up and start leaking. I'll wager two things:
1. The previous owner didn't do a thorough job of cleaning the carbs (he likely missed the enrichment jets in the float bowls).
2. If the throttle shaft seals aren't leaking vacuum now, they will be soon.

IN THE CHURCH OF CLEAN

Read ^^that one^^ as well.

As for the parts costs: In the end you'll still spend less than you will buying a motorcycle that needs no work at all (and they all need work, even new ones).

 

Thanks fellas, I will look at the pages you sited. I kinda suspected the ignition wouldn't be as strong as modern ignition. Can I pull the head and cylinder assembly with engine in bike? I wanna fix her right if it makes sense but I'm eager to ride her also.

 

Check your valve clearances first---- if they're out of spec, get them in spec then recheck the compression.

Also, if your compression tester is a Harbor Freight variety ( or of similar ilk), get a real one and test again.

 

I missed this on my first read through. You didn't specify the units for your measurement.
If you used metric, either you put in an extra 0, or the clearances are a lot too tight.
If you used inches, you're good, but both will need to be checked again fairly soon (I'd say 2,500 miles instead of the usual 5,000).

 

AND...... if you used the wrong manual, you may have used the wrong measurements to begin with.....

 

Ok I need some more guidance. After removing and disassembling my engine I found cylinder is worn out/ pitted. Several bolts broken in head and it's also unusable. Ruined it trying to extract intake/ exhaust bolts that broke. I'm thinking it will be more costly to repair than to just replace. This is a 1982 650 YICS. I've found several 80-81 non YICS good engines. Will this engine fit in my frame. Also will my carbs run this engine properly without any mods. Are there any advantages to YICS vs non. Thanks

 

I'm in central ny, I have a few extra engines.....

 

A non-YICS engine will fit.
YICS has a fuel economy advantage, and a slight power advantage. Given the small tank that the 650 max has, you want the YICS engine in order to get as much range as you can.

 

There are intake boot differences, and some minor carb differences.... there are internal engine/transmission differences,etc--

 

And wiring differences, and ignition system differences....

Point is, you want a YICS engine for the ease of swapping it.

 

Ok you've convinced me that I need a YICS. Are these rare engines I'm not finding my parts on eBay.

 

Not at all… There's a gazillion of them around

 

I guess I just don't know were to look.
Can you point me in that direction. Tried eBay.Starting to feel depressed I got a $900 piece of scrap at this point. Doesn't help that I can't leave well enough alone. I should have just changed oil and rode it as is. The inside of this engine tells me for certain she had a hard life. Intake cam is scared from low oil. I'm afraid to take pan off and look at main/rods. Pistons have enough carbon on them to make a bag of charcoal. It's sad that it's been neglected. I really like the bike so i don't want to part and frankly in too deep to stop.

 

Ebay:

370220212167

Not mine, not related......

 

Does it have to be a engine from a Maxim or will engine from a seca work.
Hogfiddles,
Do you have a good YICS 650 that you would part with.
I guess I'm gun shy now with my situation. In the bike world what is considered high miles for a used engine.

 

You could use a 750 engine and rejet carbs

 

A Seca engine will fit, but it's solidly mounted, and it will need to have the shift mechanism swapped.

High miles for a used XJ engine? Well over 100K.

 

Thanks for info guys, I'm going to stick with what Yamaha gave her and perhaps *upgrade her later. Thanks to hogfiddles for turning me onto a possible new engine. I've got a inquiry out with questions too seller.

 

You might be really happy just doing the top end? If you can find a good price on the rings and other parts it would mostly only cost time. I think a lot of the bikes that have 30K or above that were not maintained have lots of carbon. Once you pull the jugs you would be able to see how the inside of the engine looks and make a call from there. Good luck either way and just keep wrenching on her.

 

I wanted to keep her stock but guys I found alot more 750 yics than 650. They are a cheaper price too. I know there is probably a thread on what I need to modify from 650 to 750. Can someone direct me please. Or give some first-hand insight.

 

Engine swap info, and much more, here: http://www.xjbikes.com/forums/threads/the-information-overload-hour.27544/

 

Wonderful thank you k-moe.

 

Update, I'm picking up yics750 this weekend end. If I rebuild my 650 carbs with this kit they should run my 750 right?
Fit Hitachi HSC32 Carbs

Float bowl gasket
2.0 Float needle and seat
Y403S Slide needle
#112, #122 and #43 jets
Mixture screw, spring, washer and o-ring

 

I found these specs from church of clean thread.
Years & Models: 1981-3 XJ750 Maxim, Midnight Maxim, and Seca USA models
Carb Manufacturer: Hitachi
Carb Series: HSC32
Main FUEL Jet Size: #120
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #80
Pilot AIR Jet Size: #225
AIR COMPENSATOR Jet Size: #36
Main jet NEEDLE ID: #Y-13
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
going off this the kit on Ebay it will be too rich, right.

 

US models run a little leaner than Canadian models and if you have pods or 4-1 exhaust that will change things.
Canadian bikes had 42 pilot and 122 mains in some years

 

The only thing that needs to be changed are the jet needle and the main fuel jet. Everything else is the same. If you can get those seperately for less than the kits cost, do it.

 

I sent a email to xj4ever. To help me get correct parts to do a total overhaul on carbs.

 

Update:
I went and picked up used engine over the weekend. Turns out to be a 700(696cc). Never the less it was in my price range and had better compression and less miles. It's out of a 1985 so wiring is different so I will have to re pin or get creative. Not too concerned, I'm pretty good with electronics so should be simple.

 

carb jet specs

http://xjbikes.wikidot.com/carb-specs

 

You'll also find the 700 engine is a bit snappier, too

 

Nice thanks for info. I wish I could have rode her as a 650 to compare.

 

U.S. Government to Yamaha: "No more engines over 700cc or you pay us a big tax."

Yamaha management to Yamaha engineering: "Can you make a 700 that's more powerful than the 750?"

Yamaha engineering: "Easy peasy."

Yamaha to U.S. Government: "OK."

 

can someone describe proper operation of fuel petcock. It has res at 9 o'clock and works off vacuum. On at 6 o'clock and it doesn't flow fuel at all. Prime at 3 o'clock and it flows constantly. I understand Prime fills carbs but what about on,res. There is no reserve tank?

 

Does yours look like this? (this was when I had mine taken apart last summer)

Res and On are both vacuum operated whereas Pri is not and used to prime the float bowls before starting the engine. I've used Pri if the bike's been sitting a while. On is where mine sits the majority of the time.

 

reserve and on work off of vac line prime is free flowing.
there is no seperate reserve tank.
the petcock has two intakes inside of the tank. when full and in on position it takes fuel ffrom the upper portion of the tank.
when fuel gets low you motor will stumble you then switch to reserve and fuel flows from the lower intake.

sounds like your petcock may be clogged or in need of rebuild if fuel does not flow in on position.
there is a screen in the oem petcock that covers both intakes if it is an after market petcock there may be 2 screen filters.

see this thread
Rebuilding the Yamaha Vacuum Fuel Valve w/pics
there is a screen in the oem petcock that covers both intakes if it is an after market petcock there may be 2 screen filters.

 

Looks just like that,
Ok so if tank is low it will only flow from reserve. The tank is pretty much empty so I will need to fill it and check it again. I removed it and cleaned up stuck vacuum plunger. with vacuum it flows WD-40 when it's ON. I wasn't aware there was a baffle/res compartment in tank. Once I get new engine running I will fill it up and see what happens.

 

yes not enough gas will keep it from flowing when set to ON
ther is no reserve/baffle compartment in the tank. just on top of the petcock there is a filter baffle

SEE this thread for full details of the petcock
Rebuilding the Yamaha Vacuum Fuel Valve w/pics

 

There isn't a seperate reserve compartment or baffle in the tank. The main (ON) fuel draws from a taller intake tube than the reserve does.

In this drawing the ON is the taller tube, and the RES is the shorter tube. The yellow stuff is the fuel.

 

I see, I removed mine from the tank to see it first hand. Now I understand. Working on rebuilding my carbs now. Hope to have them back together and on bike before weekend.

 

SHE runs, got alot to do yet but got her to the point to start. Pretty blue flame out exhaust side of head.didnt run her more than a minute but yeah it was awesome.

 

running without exhaust? you should light it up at night for a real show

 

Vids or it didn't happen.

 

lol I'll see what I can do. Still got something going on with carbs. She won't start unless I put hand over carb and crank to suck gas in. I'm certain those carbs are spotless. I haven't done is check float levels yet.

 

... think I found your problem....

 

I hope your right. Getting some clear PVC line tonight.

 

I couldn't figure out how to post a video. So I posted it to my YouTube channel.
.
Try the link. I setbfloat levels. I had to turn pilot mix screw out 4-5 turns to get it idling right. Color tuned her and she seems to be running/ riding good. That color tune plug is a life saver. I could see it running lean. At WOT it runs a bit rich. May have to change main jet or needle.

 

It's an xj700 from 1985-1986... It will run a bit rich at wot. The 'slightly too rich' also helps to keep it 'slightly cool'......which keeps it from 'slightly burning up' due to running 'slightly too lean' for 'slightly too long". You Colortune at idle. That's why it's called an "Idle Mixture"

 

You did figure out how to post a video. They have to be linked.

You will need to redo the idle mixture once you have the exhaust in place.
4-5 turns out is a lot.