Need help with lack of power problem xj700

Hi im looking for some advise for my 85 xj700, its having a lack of power problem, and at lower rpms almost feels like a miss higher rpms just doesnt want to go it runs good intermittently. Some days it runs better and then it sits overnight and runs poorly again. I have recently replaced the ignition coils wires and plugs with yamaha coils wires and ngk plugs the coils and wires had infinate resistance. Today i took the carb apart, pull it apart cleaned the jets, bowl and set the float height, little to no improvement, turned the mixure screws all the way in and backed them out 2 1/2 turns with little to no improvement. I know it needs to be colortuned and carbs syncronized but dont know if that could make that drastic of an improvement. Dont know if there are anymore adjustments or where to go next any suggestions would be greatly appriciated..

 

Is the bike stock? Are the valves in spec? Do you have the stock spark plug caps--2 have resistors and two don't. Are the new coils the proper ones for the XJ700? Did you do a bench sync when you had the carbs off? Have you thoroughly cleaned the carbs, including enrichment and pilot systems? What do your plugs look like? I have the same bike, stock, and I had to get all the above done before it ran well.

 

I fixed it, i swaped the ic ignitor and it is running excellent. I think the excess resistance in the old ignition system may have comprimised the old one. The bike is pretty much stock except for pod filters which i learned were bad after i cut the airbox out of the bike. I have them covered 90% with electrical tape to make them work better. But i plan on putting it back to stock. The spark plug caps are stock i measued the resistance of all four and were around 5000 ohms. The coils and wires are oem yamaha. I noticed two caps were longer than the other two, i have them on cylinders 2 and 3. All i did with the carbs is take the bowl, float, main and pilot jets, pintle and seat, out from the bottom, removed the rubber diaphragm and needle from top, cleaned everything, set float height, adjusted 4 screws on top next to choke plungers 2 1/2 turns out from lightly seated and put back on bike. The plugs on 1 and 2 looked great, 3 looked black rich, and 4 was covered in gas. I dont think that 4 was barely firing. I will pull the plugs again and check now that it is running good. Also is it true that the engine has to be removed to get the airbox in and out?

 

Jordan, glad you found your problem. From your explanation, it does not seem that you have split the carbs and completed a thorough carb rebuild. Maybe you indeed did so and just didn't include that in the description of your current problem. The fact is that a vacuum leak somewhere as well as a clogged enrichment circuit (either partially or completely as well as more than one circuit being clogged) could cause the schitzo symptoms your engine is presenting to you.

I know this because I had one.

Hopefully you're good to ride off into the sunset. Things to think about:

Problem related to air to consider...
An intake manifold can have a crack allowing air in where it should not be. They can be small and hard to spot and of course behave differently as the engine warms up. Additionally your throttle shaft seals (if never previously replaced) are more than likely "crispy." Crispy shaft seals do not do their job well and of course allow air in where it should not be. The carb set needs to be split in order to access them. Change them as well as your fuel o-rings while you are in there.

Problem related to fuel to consider...
If your enrichment circuit is blocked (partially or completely) you will get mixed results when you swing the choke lever to the right. Consider that you have 4 carbs and perhaps some circuits are clear and some are not. Now your carbs are not getting what they equally need, and what's worse... They are fighting with each other! You've got to make sure that ALL circuits are COMPLETELY clear. This is a pain in the rear to get done if you have a blockage. Patience and determination will prevail though. Dip, soak, prob, pick, etc... just don't ENLARGE the passage with all of your cleaning efforts. I found that a single strand from a bicycle break cable was thin enough to do the job, yet strong enough to get down in there. When you have it clear, placing the red straw from your carb cleaner spray can (down the passage on the bowl rim) and squirting it in should produce a geyser stream from the bottom of the bowl. Watch your eyes... you don't want to get carb cleaner in there.

So, first you need to make sure your valves are in spec. All you do with the carbs won't matter if your valves are not right. Luckily, everything you need to know about this is here:
http://xjbikes.com/forums/threads/airhead-valve-adjustment-with-pics.14827/

Then you should pull your carbs again. Inspect your intake manifolds for cracks. They could be tiny (mine was and it was only one crack on #2), if they exist make no mistake, they are letting air in. Use RTF sealant to cover cracks or a combination of a rubber bicycle tube and RTF (if they are larger) to get the job done.

Then pull your carbs apart all the way. Zestfully clean everything again. Dip the bodies in Berryman cleaner (1 gallon can you'll find at the auto parts store). Rinse as directed on the can. Replace the throttle shaft seals, o-rings, and it wouldn't hurt to replace the butterfly hardware (2 screws per... go with allen head) while you're there. Lock Tight on the threads so they stay put. I found this very helpful and was a great step by step pictorial of the process. Click here:
Replacing your Hitachi throttle shaft seals - It was done by Len @ xj4ever.com (http://xj4ever.com) and by the way, he sells EVERYTHING you need.

Syncing and color tuning as you suggest is all good, but a valve adjustment, good cleaning/rebuild and bench sync of carbs will get you MOST of the way to where you want to be.

To answer your question, I do believe you have to remove the engine to remove/install the air box (can someone confirm here?). Honestly, your problems related to air could lie here as well as you have pods. For my bike, I even replaced the brand new foam "high performance" air filter that the bike came with, with a stock paper air filter. The correct amount of air/flow is so important to these carbs. Alot goes on under their little hats!

Good Luck.

 

Thank you I appreciate your input. I did not break the carbs apart and I do believe the throttle shaft seals are leaking. I was spraying the intake boots with carb cleaner while it was running looking for vacuum leaks and spraying around the shaft seals did make the engine bog down. The bike is running the best I have seen it since I have had it but I believe it's still not 100%. It has 37000 miles and does not seem to be cared for too we'll I had to change the oil several times to get it to come out clean though the engine sounds healthy. When I had the bowls off I did spray threw the passage in the bowl with no problem. I'm not exactly sure what the enrichment circuit is. Again thank you for your advise

 

Hello again,

If you've successfully sprayed through the passage from bowl rim, down and back out from the floor of the bowl, you've cleared the most difficult part of the enrichment circuit. The enrichment or "choke" on your bike includes the plunger that is actuated by the u-shaped fingers (there's four) that rotate on the chrome rod that spans your carb set. That plunger sits in a bore in the carb body that is ultimately connected to the brass tube that sticks down and fits into the passage that your sprayed through (in the rim of the bowl).

Take a look at this: Inside your Carbs - On page 25 you'll see a dissected carb which shows it clear as day. The picture is of a Mikuni carb. You have a Hitachi, but for the purpose of this discussion, it is the same. Thank you again to Len @ xj4ever.com for the write up.