Top end rebuild "running in problems"

Hi guys let me start of by identifying my bike and my problem
I have a 1981 xj650 maxim non yiccs
Running Pods and a 4-2 custom exhaust

I brought the bike with a slipping start clutch so we all know what that means
Split cases!!
So while in there i did the top end,which lead to further things like stripping the cases to get blasted.
With the top end done and rebuilt carbs

The bike starts very well even in these cold New Zealand winters (choke for 10sec max)
Bike idles great BUT headers 1 & 2 get hot very quickly while 3 & 4 stay cold for quite some time 3-4min
3&4 exhaust spits a flame at around 3k rpm

Work that has been done

Engine split and reassembled with
new top end
New pistons
New rings
New valves
Shimmed vlaves

Carburettors blasted,stripped,cleaned,rebuilt with new
Diaphragms
Shaft seals & O rings
Jets 45 pilots 120 mains
Float level set
Bench synced and then vacuum gauge set

New dyna tek coils and leads (non resistance type)

I will upload a running video in the morning

Your help would be greatly appreciated

 

Photo 1

 

Try a colortune plug. You can order them from Xj4ever

 

What did you set the idle mixture screws to?
More importantly, are they coarse-thread, or fine-thread.

 

No particular method just set to 3turns out and fine thread

 

Those are huge jets for a 650cc engine!

Nice looking engine.

What do the spark plugs look like on #3/4?

You should perform and compression test on all the cylinders.

 

I will do that this afternoon .
45 is what the bike had in it when it was in its factory form and 120 is what SIGMA racing jet kit gave me as well as a 130..

 

Unsure why it’s such poor quality but gives you the idea

 

also one shim added to needle jet

 

Regardless of what it had in it, stock is a 40 pilot, with 110 mains (even in NZ).

3 turns out on a stock bike is a tad on the rich side, and with your jetting you might be rich at idle (even with the pods). Pull the plugs and give us some good pics of the rings and ground straps.

 

^^^+1 know is correct the other item did you wet set your floats? Just a thought uneven filling of the float bowls to find out get a container with markings drain one float bowl at a time see how many ounces drain out as long as close your ok . Cheers

 

Okay these photos wore taken after about 3min of idling
Headers 1&2 wore very hot by then.burn to touch.
3&4 wore cold
Plug 1

 

Cylinder 2

 

Cylinder 3

 

And finally 4

 

Will give this a go to thanks mate

 

Okay another question have you taken it for a high speed ride of say 15 to 25 miles and then checked plug , note if you are only checking at idle this is what plugs can do on occasion.

 

Bike back fires very loudly on low revs (pilot jet)
But pulls well when opened up.
Got upto about 30-40km down my street and killed the engine and checked the plugs and they all pretty much looked like this.. 3rd cylinder was more of a wet black.
It has only started backfiring from been rich since I took it for its first ride down the street last week.
It just concerns me how hot 1&2 headers get from idle when 3&4 stay cold.
Thanks for the reply’s guys
Guess I need to get some smaller jets say 42-116

 

1-4 are all very rich. 3 and 4 are both wet. Did you smell gas on them, or is that oil?

The coldness on 3&4 is the result of the plugs being wet. Those plugs aren't firing well until they get hot, and even then they probably aren't firing well.

 

3 is still wet even when checking this morning without having the bike running.
4 is definitely the cleanest plug.
3 does smell like gass but does look to have oil deposits over it
Or could that be a build up of fuel from not firing? It does leave a black oily stain when I clean it with a rag.
Sorry this is my first engine rebuild so it’s all new to me..
Could I have possibly damaged a oil ring when slidding the cylinder over the pistons?
What would you suggest my next steps are?
Thanks again

 

Also the bike has only ever been idled with a few short low rpm revs since the rebuild and it’s first start 2months ago.
As I havnt finished the build yet so I couldn’t ride it. Last weeknd was the first time I have ever moved the bike under its own power and I guess the plugs wore well and truely fouled by that point. Hence the fouled wet plug on 3. So maybe I should get smaller jets with some new plugs and take it for a decent ride to bed in the rings??

 

Before tackling the oily deposit you need to get the jetting right.
Rings take time to bed in and seal properly, so that oil may end up going away altogether. With the jettung right the plugs will get hot enough to burn the oil, and you should get a much better looking plug.
Did you replace the valve stem seals?

 

Okay that sounds like a great plan I will order those and see how I get on.
Yes to new valve stem seals.
Thanks heaps for help guys!

 

Have you done a compression test since it went back together?

 

I did one not long after it’s first start and it was 120 even across all 4
And I was told that will go up once the rings bed in.
Much better than the 75-90 I was originally getting when I first got the bike.

 

Okay guys we have a update!
New jets 42/116. (was 45/120)
New plugs and a colourtune

This all took awhile to get to little old New Zealand.

Fired the bike up no problem rode it around the block to warm it up.
Already a huge difference in acceleration! And bike was also sounding nicer.

Got in the shed plugged the colour tune in
Cylinders 1&2 wore lean so I set them to a nice blue spark.

Plug 3 was very rich so I adjusted that also

Now plug 4 was not igniting at all unless I opened the throttle.. just sparking.
So I obviously have a blocked idle circuit because I can fully unscrew the mixture screw and nothing will change in the way of combustion.

Is it normal for say 1&2 to need such big difference in idle mixture Turns to 3&4?

What a awesome wee tool!!
So I guess I need to find that blockage and then go from there as well re sync the carbs too...

Will try upload a video

 

Until you get cylinder #4 firing the results on the other 3 cylinders will be somewhat meaningless.............

 

Sorry it’s probably not the best video
But do you think it could also be the idle circuit if I can wind the mixture screw right out and nothing happens?
But if I give it a rev/ change over to main jet it’s fine ?

Once firing properly it’s sync then colour tune then repeat is that correct?

Thanks

 

Try going all the way in and back it out 2 turns and start these what happens ...or have you already tried that?

 

I have not tried that no. When I started the bike with the colourtune on #4 I had no combustion like in the video so I just adjusted the mixture screw out. But nothing changed.
I’m pretty sure this idle circuit has been blocked the whole time that’s why the plug has looked so clean.
I will try this though before pulling the carbs for a clean.

 

If you are patient, and have a magnetic tipped screwdriver with a 90º bend, you can remove the float bowl from #4 without pulling the rack.
I do agree that the idle circuit on #4 is probably clogged since you can see that there is no fire on 4 until the main jet is in play, and the colortune plug is working with the other cylinders.
It could also be that the pilot jet backed out and is sitting in the bottom of the float bowl.

 

I will definitely see if I can try do that moe
The less I’m pulling on those old intake boots the better.
And try unblock the circuit on the bike.

 

Ok so I pulled the carbs today to try clean out that pilot circuit.

When eyeing up my butterflies
#4 has light shining through no mater what adjustments I make to the syncing screws.
The other 3 close nice and snug to the carb body ( idle screw backed right off)
I pulled the butterfly and noticed this notch is that ment to be there? I feel like it’s stopping the plate from sitting how it should ?

 

The throttle plate should all be round(ish) with no notches. Set it on the shaft with the screws loose and see if you can file it to make it fit correctly. You'll have to take it easy and make sure that you don't overdo the material removal process. File a little, check for fit, repeat.

 

O

Okay so I cleaned the throttle plate up
Cleaned the carb out, double checked everything
Bench synced.
Fitted and ran the bike vacuum synced the carbs
#4 was out so adjusted that which brought the revs right up and now it idles quite high with the idle screw backed right off.
And still no combustion from #4 below 1/4 throttle.
All needles on the guage looked like this and that says vacuum leak.

Took it for a spin around the block
Runs very well quite surprised how well
As I had never ridden a XJ before.
All plugs has white tips. Lean.
So guess I do have a major vacuum leak?

 

don't look at what's printed on the face of the gauge, that's generic stuff written for every engine ever made. all your looking for is they all read the same numbers.
i don't think there is even a spec given in the factory book about vacuum

 

I thought that might be the case...given that it’s a cheap kit.

 

how high is the idle now?
try this, set the mixture screws at 2 3/4 out, hook up your sync gauges, start it and turn the idle knob in until the rpm goes up a little, now check your sync and readjust as necessary, use the idle knob to bring the idle down, check the sync, if at any time the idle knob won't bring the idle down and the sync is still right, then you have a vacuum leak.
if your idle is 3k, that's good enough to start with. if you keep the sync right the idle knob should stop the engine.
i think #4 butterfly is holding the rest of them open

 

When I ran it from bench sync it idled nice around 900
Once I adjusted 4# to suit the vacuum gauge it rose upto 2-2.5k
Given all this it still wasn’t firing on 4

I will try this though.

 

When you filed the #4 throttle plate to fit, were you able to get it to sit in the bore without any gaps of light showing (throttle fully closed, but not set to the baseline for idle)?
If not, then I think you should source a throttle plate that was cut properly from the beginning. That gap is critical to metering fuel at idle and off-idle.

 

I

I could not get it to close/seal perfectly like the others. I thought it would still allow the pilot circuit to still let fuel get sucked through enough to fire.

I will get searching for one though.
Do any other bikes use the hitachi 32 carburettor?


I will also get new intake boots.

 

Oh it'll let fuel in, but it'll also let too much air in and that's the problem you're running up against.

All of the air cooled, non-turbo XJ650 and XJ750 models use the HSC 32 carbs.

 

Should I try swap in #1 throttle plate into #4 carb body too rule out that the throttle plate is causing the fault ?

 

I don't see how you could do that without it just moving the problem to #1. If you want to do that extra work go ahead, but I'd just wait on getting a replacement throttle plate.

The other issue is that even though all of the throttle plates are supposed to be identical there is some minor fitting that sometimes needs to be done, since the bores aren't always perfectly machined, and the plates have to be a very close fit or they can't do the job properly. Swapping throttle plates often requires a bit of sanding, and if you do that, then #1 wont fit into #1 correctly anymore.

If the carbs are out could you give a good pic of the #4 throttle plate in the carb, throttle closed, with some light behind it (preferably with the slide lifted as well)?

 

Carb 1

 

#4 out of interest

2&3 have little to no light shine through

 

I think, your carbs have been rebuilt incorrectly in the past - the wear pattern on no4 butterfly looks like its from rubbing on one side of the bore, no1 doesn't look good. The disc has to sit perfectly cental, and not rub on one side before you tighten the screws - a light tap to seat everything works for me.

 

I think the shaft seals had become so worn that the shaft had a lot of side play and unfortunately wore the plates out
The shaft still does have some play.
Do you think #4 needs replacing too?