Carbs or valves? Just need opinions & input

[justme1100]

.......only if left under a 'shade tree'.

HA!

[Bonz]

Is it worth more of a look at the wet diaphragm tops? All of them are wet, correct?

[justme1100]

Is it worth more of a look at the wet diaphragm tops? All of them are wet, correct?

Yes they were. I tested compression and all cylinders were within 5psi of eash other, the inner 2 were lower than the outer cylinders. Spark seemed weak, need to test the coils but I think I will just replace them, 32 yrs old ya know. Getting new plugs too. If nothing else just to eliminate those as the issue.

[TopCatGr58]

Hey Just,

Okay, just doing a little brainstorming and wanting to recap things.

You had a little street drag beating a H-D, so I'm assuming that you were able to run the rpms up to 7K or so, but afterwards it wouldn't give you any power and would only run at idle up to 3K rpm max!

You had cleaned the carbs, but then the bike sat for some months. If you didn't have Sea Foam or such in the fuel, then like Brant/Motoman said, you can have some gum/varnish building up in the carbs. My 81SH acted that way, had cleaned them, ran the bike, but then forgot to put Sea Foam in before storing it. Next spring, would start/idle , but couldn't/wouldn't take any throttle...would die...because opening the butterflies would NOT let anymore fuel in because of clogged Emulsion tubes=engine died! Recleaned the carbs, and worked just fine again.

A street drag could stir up the slugde at the bottom of the tank, but you have stated that the carbs are still getting plenty of fuel, possibly too much.. wet vac. diaphragms!? However getting blow back into the carbs could also cause the fuel to get blown back into the carbs getting fuel on top of the diaphragms. The high rpm blast might have also allowed the cam chain to get/skip a tooth if the tensioner isn't tight....are you still running the OEM CCT or have a new ACCT installed? If it skipped a tooth, you could get severe blow back from the engine due to the valves not closing quick enough, the compression cycle pushing back into the intakes. You may need to take the valve cover off and verify that it's still in valve timing.

The XJ used the newer 3.0 ohm styled coils, they are stronger than the 78-80 1.5 ohm coils, but like you said, are 30+ years old. The TCI has both the cent. adv. and vac. adv. timing curves built/programmed into it. IF it's gone bad, then you may not be getting any timing adv, and the engine won't be able to increase in rpm very far!? You can test with a timing light against the timing plate just to see IF the timing mark moves any from IDLE up to the max rpm that you can get....if it attains only 3K and the timing marks don't move into the ADVANCED area, then the TCI may be damaged?? Also have you checked the exhaust pipes to ensure that you are hitting on all 4....all 4 sizzle with water spritzed after warmed up!?

Just a few thoughts of things to check!

T.C.

[justme1100]

Hey Just,

Okay, just doing a little brainstorming and wanting to recap things.

You had a little street drag beating a H-D, so I'm assuming that you were able to run the rpms up to 7K or so, but afterwards it wouldn't give you any power and would only run at idle up to 3K rpm max!

You had cleaned the carbs, but then the bike sat for some months. If you didn't have Sea Foam or such in the fuel, then like Brant/Motoman said, you can have some gum/varnish building up in the carbs. My 81SH acted that way, had cleaned them, ran the bike, but then forgot to put Sea Foam in before storing it. Next spring, would start/idle , but couldn't/wouldn't take any throttle...would die...because opening the butterflies would NOT let anymore fuel in because of clogged Emulsion tubes=engine died! Recleaned the carbs, and worked just fine again.

A street drag could stir up the slugde at the bottom of the tank, but you have stated that the carbs are still getting plenty of fuel, possibly too much.. wet vac. diaphragms!? However getting blow back into the carbs could also cause the fuel to get blown back into the carbs getting fuel on top of the diaphragms. The high rpm blast might have also allowed the cam chain to get/skip a tooth if the tensioner isn't tight....are you still running the OEM CCT or have a new ACCT installed? If it skipped a tooth, you could get severe blow back from the engine due to the valves not closing quick enough, the compression cycle pushing back into the intakes. You may need to take the valve cover off and verify that it's still in valve timing.

The XJ used the newer 3.0 ohm styled coils, they are stronger than the 78-80 1.5 ohm coils, but like you said, are 30+ years old. The TCI has both the cent. adv. and vac. adv. timing curves built/programmed into it. IF it's gone bad, then you may not be getting any timing adv, and the engine won't be able to increase in rpm very far!? You can test with a timing light against the timing plate just to see IF the timing mark moves any from IDLE up to the max rpm that you can get....if it attains only 3K and the timing marks don't move into the ADVANCED area, then the TCI may be damaged?? Also have you checked the exhaust pipes to ensure that you are hitting on all 4....all 4 sizzle with water spritzed after warmed up!?

Just a few thoughts of things to check!

T.C.

Well I found out that the wet diaphragms are rather common so wiped off and not worried about that. My step-brother related a story to me that is very similar so I swapped out the ignition unit with one I had on my donor. I have the auto-adjuster up grade and no this issue occurred just 2 weeks ago. All four are hitting, fuel flow is a-ok, clean filters. I will be road testing tomorrow (Friday) once I pull the carbs to adjust for a slightly lean condition. I am only afforded a couple hours each day but I have all day on Friday, more if it rains. Thanks for the input. I will keep updating as I go along. If nothing else I have had a chance to go thru the connections as it had been 2 years since I checked and cleaned the connections under the tank. I am praying it wasn't a cam chain skip, I guess I will know soon enough. I haven't been able to pull the cam cover as the PO did something to shift the whole engine forward enough that the center bolt hits the cross member. I will have to cut something to get it off. I just might as I do have a 2nd titled frame I would swap to. And thats the beginning of another story

[TopCatGr58]

Hey again,

Okay, the ACCT, that's good so I also doubt any cam chain skip now!! The engine mounts can wear down, compress. Mine is also difficult to get to on the front center valve cover bolt. You can try putting a floor jack and a block of wood, and jack up the front of the engine to see if it moves it far enough to clear the frame cross brace.

Cleaning the connectors is a good thing....try the ones that plug into the TCI as well. Nice that you have a loaner TCI to try out...what model is your donor?? It will need to be an XJ, or at least an 81 4RO type, not the 2H7 type. The 4RO also has the cent. adv. timing curves programmed, it just doesn't have the vac. adv. curve.....but that's mostly for fuel economy under cruising. The Cent. Adv. curves are the ones that provide all of the POWER timing advance. A fellow on here has installed and is using a 4RO TCI on his XJ just fine. The XJ is less likely to have the PU coil wire problems, and you said you are sure it's hitting on all 4, so that would indicate that they are working and not shorting.

Good luck, keep us posted on what you find, and if you fix it!

T.C.

[justme1100]

Hey again,

Okay, the ACCT, that's good so I also doubt any cam chain skip now!! The engine mounts can wear down, compress. Mine is also difficult to get to on the front center valve cover bolt. You can try putting a floor jack and a block of wood, and jack up the front of the engine to see if it moves it far enough to clear the frame cross brace.

Cleaning the connectors is a good thing....try the ones that plug into the TCI as well. Nice that you have a loaner TCI to try out...what model is your donor?? It will need to be an XJ, or at least an 81 4RO type, not the 2H7 type. The 4RO also has the cent. adv. timing curves programmed, it just doesn't have the vac. adv. curve.....but that's mostly for fuel economy under cruising. The Cent. Adv. curves are the ones that provide all of the POWER timing advance. A fellow on here has installed and is using a 4RO TCI on his XJ just fine. The XJ is less likely to have the PU coil wire problems, and you said you are sure it's hitting on all 4, so that would indicate that they are working and not shorting.

Good luck, keep us posted on what you find, and if you fix it!

T.C.

4 yrs ago I came across another 82 XJ, non-running, with a clear title and only $50. I needed the fork clamp and wiring harness after a critter jumped out in front of me on a curve and a tree stopped me. I have spares of stuff and in some cases 3's of things I have picked up over the last 6 yrs. I know how difficult it is to find XJ stuff. Thanks and we shall know in a few hours if the new box corrects my issue. I would have my fingers crossed but it makes it difficult to wrench that way

[justme1100]

On the road again!

Talk about chasing your tail. Turns out I had a bad connection on one coil, something gummed up my carbs but not sure what. I think it might have been something to do with my old fuel filters. Getting on the throttle must have sucked some of the crap up from the bottom of the float bowls. I still need to work on a slightly lean condition and at least I had a chance to clean the electrical connections under the tank. Thanks to all that replied and for your input. The Beast owes her life to this forum. Happy Riding!

[Diskman01]

I was gonna chime in on this also. I too ran my 78 up to "plaid" last Friday while playing with a newish Camaro at a light.. Totally lost my top-end power. Felt like fuel starvation on the top end of the RPMs.

Looked into it yesterday and one of the coil power wires was very loose. It just popped out while poking around there. It was the wire that connects to the other coil wire into that double plug (red/white). I did the Honda VF1100 coil update 2 years ago.

Have since tightened everything and gave her a quick carb sync. Ran like a scalded cat, but more electrical gremlins cropped up last evening. sigh.

Glad you got yours figured out! Might want to take an hour sometime and pull all the power connectors apart, clean with contact cleaner or WD40 and re-attach. Corrosion gets in those and causes weird problems over time..