Ready to throw in the towel

82 xj650rj with 50,000km on it. Bought it non running, not sure what the PO had done to it. Can't get the thing to run on all 4 cylinders.#1 and 4 are hot but #2 and #3 the exhaust pipes are only warm. So coil issue right? Nope. Just installed 2 new coils, and I'm getting spark on all four plugs. Carbs have been in and out 4 times, can't be them. Could it be the TCI unit? I opened it up and there was a bit of corrosion on one connector spade but otherwise looks ok. Compression is 150-120-120-150 valve clearances are ok. This thing should run but it just doesn't.

 

Have you swapped plugs to see if the problem follows?

 

Yes, all new plugs moved around several times. Just now I took out plugs 1 and 2 and ran the engine with just #2 and #3 in. The engine would run with the choke on but just barely and died when throttle was opened.

 

Did you check each cylinder with a "Colortune"?

 

No I don't have a colortune. But I imagine # 2 and 3 aren't burning right since they barely run. I'm thinking it can't be carburetion since I cleaned them out multiple times but maybe....?

 

Not sure I'd be happy withe teh compression difference on those two middle cylinders - ever had the top end off?

 

No I was trying to avoid an engine rebuild. 120 is low but the engine should still run with that compression.

 

What exactly did you do to the carbs when they were out?
"It can't be the carbs" is the most common carb issue that we deal with here.

 

Took everything apart without splitting the rack. All the jets are clean, all the passageways are clear. I just took the carbs off again and sprayed starting fluid into each intake one at a time while turning the engine over. #1 and 4 seemed to fire much stronger than #2 and 3.
Can the head be removed without taking the engine out on these bikes?

 

Get the "Colortune" plug. We need to be sure the air/fuel is like the rest. It is interesting that the offending cylinders have the lowest compression, but I'd really like to see the Colortune on them. Could explain a lot. Never assume that the carbs are not the problem because they were "cleaned". "Clean" carbs cause the most problems if cleaning just broke up old varnish and dirt but was not removed completely.

P.S Throwing in the towel is not an option.

 

Being the middle 2 are low, and run hottest. id wonder if the head gasket is blown between those cylinders.

 

Ha ha, OK I won't throw in the towel just yet. But I might put it on the back burner. I have a GT750 that needs a bunch of work.

Since it doesn't fire properly while shooting starting fluid in , is it possible to get it to fire properly even if the carbs are perfect?

 

Maybe, but I did a leakdown check and didn't notice anything leaking between the cylinders. Compression went up when I put some oil in those 2.

 

head can be removed with motor in bike.
ohm out the pickup coils.
do you have the correct tci for a non yics motor TID14-08 5v210

 

Are you sure the #2 and #3 spark plug wires are on the correct plugs?

 

low compression will cause cylinders to fire very weak. if pressure went up with oil you could have bad rings and/or cylinders or rings are frozen
a 50/50 mix of acetone and atf can unfreeze rings when soaked. about a tablespoon will start the process let soak a day then add another to soak
did 1 and 4 increase pressure with oil?

 

2 and 3 plug wires are inter changeable because of the wasted spark ignition. both cylinders fire at top dead center with 1 cylinder in top of compression stroke and the other cylinder at the top of the exhaust stroke

same deal with 1 and 4

 

have you ohmed out the spark plug caps and trimed back the wire a little bit. wire ends can corrode. cap resistor can fail.

you will find ignition specs in this thread
The Ultimate Relay, Switch, Sensor, and Diodes Guide


did you remove the mixture screws and replace the tiny o ring under the washer?

have you synced the carbs? bench or running sync?

 

Yes, yes and yes. New coils, wires and caps. Mixture screws removed and washers, O rings re-installed.
Haven't checked the pickup coils, will do that next. What do you think is the minimum compression for this engine to run correctly?

 

I checked the pickup coils 630 ohms so they're good. Found another connector that was fairly corroded. I notice that one connector on the TCI box has 5 spades but the connector on the wiring harness only has 4 wires?

 

Check the float level on #2 and #3, may be too high, are the plugs in those cylinders dark and wet?

 

Nobody else finds fault with "cleaned" carbs but the rack wasnt broken therefore throttle shaft seals were likely not replaced, etc? Unless I read something wrong? If the ignition system checks out, the compression is within 5-10% of each other, my logic says it has to be with the carbs/fuel delivery. Having the carbs done right is a very important step one, having a colortune and vacuum sync gauge is a very close second. Not trying to be an a hole but that is my thoughts on the subject.

 

I hear what you're saying, I've overhauled a lot of carbs and on several occasions found I'd missed something small that made a big difference. These carbs seem pretty simple though. But I'll check them again.

 

specs on compression

XJ650 and XJ750 air-cooled engines:
Minimum: 128 psi
Standard: 156 psi
Maximum: 171 psi
Max. variance between lowest and highest: 14 psi

only 4 wires is normal

what are you using for new ignition coils?


pick up coils
1982 XJ650RJ Seca (non-yics engines): 700 ohms +/- 20% = 560 ohms to 840 ohms acceptable range

 

Thanks for all the info, looks like I'm at minimum compression on those 2 cylinders. I found another connector with corroded terminals, so cleaned it up. Probably hasn't been disconnected in at least 25 years. Removed the mixture screws on the carbs and made sure they were clear. Put everything back together and success! It's now running on all cylinders! Now time for carb sync and maybe I'll try and find a colour tune. Thanks for your help!

 

so was it the ignition or the carbs - will we ever know? Would be good to re-test compression after it's run for a while - I'm curious about this.

 

"Carbs just gone through" is one of the scariest phrases when I am looking a old bikes...it translates to "500 bucks less on the offer" to me. LOL GLad you had success!!!