1983 XJ650 Won't rev past 4k

I recently did a bit of an overhaul on my old xj. Rebuilt starter, new 4-1 Mac Exhaust, changed to K&N pod filters, new plugs, oil, after all this I was told to rejet the bike as well. I bought the Dynojet 1&3 stage kit, followed all instructions, and used the .118 jets and rebuilt carbs with new gaskets, floats, and float seats as well. Floats are all reset to 17.5mm

The bike revs in neutral great, no issues revving to redline. However as soon as I actually ride the bike, it has lots of lower end power, but as soon as I get to around 4k rpm the bike just sputters and no longer accelerates. Ive tried 1,2,3 and 4th, all with the same result. Thinking that Id overjetted, I removed carbs and replaced the original .112's that were in the bike before, with the same results. It seems worth noting that the plugs are black, I have tried leaning the bike out, I currently have the mixture screws at only 1.5 turns out, and I dont want to risk hurting the bike by leaning those out anymore until I get a second opinion.

Sorry for the wall of text, any help is greatly appreciated. Thanks,

Justin

 

Read "what about pods" in the "Information Overload Hour" forum.

Gary H.

 

Did you clean the carbs first?
IN THE CHURCH OF CLEAN
Did you get the air jets back in the right places, and not the places that the manual shows?

 

I am aware that pods can be finicky and I appreciate the concern. But I also know they are more than possible to work, and the symptoms I'm having do not seem to point towards having pods over an air box issue. I have fully cleaned the carbs, and reset the air jets in the same spots that I removed them from. Is there a different set up that I should be aware of for them?

 

HOW thoroughly did you clean the carbs?

After you set the floats, did you do a wet-setting ? 17.5mm is the baseline. You may need to adjust----

In neutral, there's no/minimal load even to redline. Get on the bike and you now have a couple hundred more pounds to move, more torque needed, which means more fuel needed, and wider throttle...... Which means more fuel getting sucked out of the bowl. If your fuel level is too low, then the bike is "running out of fuel"

 

Sorry no fan of pods... your carbs did you replace all the butterfly jets? How are your intake boots.? Are your carbs all synched?

 

"More than possible" is a huge stretch. The bike can be made to run OK with them, but that's it. It will never run as well as a bike with the factory airbox. CV carbs are not designed to run without a specifically designed intake air volume and velocity.

 

Your symptoms kind of DO sound like the notorious pod puzzle. It is a path you have chosen, their finicky nature will be a challenge - but as you already know, they can be made to work.

That being said, the majority of advice is coming from people who run stock machines. You have modified the intake and exhaust of a balanced system.

Did the bike run proper BEFORE you modified the intake and exhaust?

 

The bike ran, but was always kind of off, it ran funny at different times, and never seemed to pull very well, it had some jet changes and a homemade 4-1 on it when I bought the bike. My intake boots are all good, no leaks, although I did not replace any butterfly valves while I had it apart. I did wet set it, and all seems well in that department. I appreciate all the responses, I only went with the air pods due to the fact that the bike had already had someones hands over the system and messed it up, and I had no way to get an unchanged airbox for it. The original had been cuts and was not in good shape. It seems to me the issue is lack of air, should I try to lean it out more with the mixture screws? It does still foul the plugs at an idle. Or should I put the original airbox back on to see if that fixes my issue?

 

go original air box get it running right , the and only then think pods

you need to sync the carbs and color tune the mixture pilot jets

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

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


dod you clean the the "power valve" or "emulsion tube"???

 

Okay, so put factory air box back on, same issue. I cleaned the emulsion tube very thoroughly. Should I take apart and check if there is any build up from elsewhere that got into there?

 

Not sure if its worth noting, but I forgot to mention that the original reason I started working on the bike is because my starter went. I rebuilt my factory one and it starts great now,is it possible that the issue may be electrical rather than a fuel/air issue?

 

Have you checked valve clearance.. very important when it comes to synching carbs..

 

Just to not follow the pics in the manuals, as they are mislabeled.
This is the correct placement.

 

Yes, that is how my air jets are placed. thanks for the suggestion though. I have not checked valve clearances, however due to the fact is revs to red line perfectly in neutral, I believe (correct me if Im wrong) they should be fine. It is only under a load where I have this issue. I never touched the actual motor, other than an oil change, during this work

 

How it revs in neutral won't tell you a thing about valve clearances. Pull the cover. Check them.

 

If your spark isn't advancing you would get that symptom. That has electronic advance unlike mechanical weights that can stick. Has anyone had an ignition module go bad by not advancing? You could check it with a timing light.

 

The behavior you are describing pretty accurately describes carb trouble. I think the slides/diaphragms may be a good place to focus some extra attention on- do they move freely (people around here like to ask if they "pass the clunk test"), are you sure the diaphragms have no pinholes and are sealed perfectly around the edge with the carb caps? With the engine under a load, the vacuum changes, which directly effects how the slides operate (via the diaphragms). Are you certain there are no vacuum/air leaks in the intact tract (throttle shaft seals, intake manifold boots)? Are all the vacuum port caps on, and the vacuum line going to the petcock secured and not leaking? Test with carb spray or an unlit propane torch.

 

check the wet set fuel level as suggested it is quick and does not require removing the carbs

link
Setting the fuel levels

 

If the plugs are black, take the pods off and try it . Could be the type of pods .
Do you have the tubes that went from the airbox to the carbs, mount the pods to those.

 

Don't neglect the valves as suggested, it is a requirement for a well tuned engine and could be the issue.

A weak spark will give similar symptoms - idle and revving OK until placed under a load where larger fuel quantities are not ignited because of the weak spark.

What have you done electrically to the bike? Has the fuse box been inspected / upgraded? Have you done any continuity checks on the coils and caps to be sure they are OK? Inspected connectors for corrosion, etc.?

 

On my Xj550 getting it to get close to redline under load was cumulative maintenance:
Bad spark plug cap causing weak spark (cap read open - not sure how it fired at all)
Valves out of adjustment
Sealing cracked intake boots
rebuilding petcock for better flow

All these cumulatively worked toward increasing power and revs under load.

 

And ^^^ That^^^ sums it all up.

An internal combustion engine is a system of systems, all of which must work correctly in order to function.
If it seems like we are all-over the place with our suggestions, that's simply because there are a number of issues that can cause what you are experiencing.

 

Appreciate all the help everyone. So I did some more tinkering with the bike today. I took all the carbs off, and thoroughly cleaned everything again. I reset the floats again, with a different set of calipers ( the old ones were a little off). It did seem to improve the situation a bit, and give me a bit more insight on the problem. The bike will rev all the way up, the issue seems to be once the throttle is turned past the 1/2 way point. Once I hit this point, either the fuel isnt being detonated as Rooster said, or for some reason it isnt gets enough air/vacuum. I didnt have time to do much other checking, was getting dark out. Will maybe try some electrical things tomorrow. Does anyone have a link for valve clearances?

 

Agree with kmoe plus others.... your coils could be breaking down or tci could be failing , valves out of adjustment,dirty carbs, out of adjustment. Or could be as simple as bad spark plugs or plug caps . Everyone is trying to help sometimes we may get technical just realize some of us had similiar problems . One other thing you state you put a jet kit in are the jets in proper position IE pilot and main jet in correct position and are they tight?( I had one the main jet fall out and bike idled fine would not rev past 4500 rpm sound familiar?)

 

AIRHEAD VALVE ADJUSTMENT with Pics

AIRHEAD VALVE ADJUSTMENT Part 2: The Tool vs. ZipTie -w/pics

 

start with valves.
check fuses next

you need to wet set the carbs caliper setting it just a referance point