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?