Opinions on my acceleration issues.

Well, if everything is as you say... Can we entertain the possibility that at some point you may have had some passage enlarged? I would imagine that would cause a symptom like this.

 

It's not outside the realm of possibilities. Do we have any methods for checking clearances to see if that's the case? I have a set of welding tip cleaners, so if someone has a list of orifice sizes I can check against...

How much wear are we talking about with the emulsion tube and needle? Visually everything seems even and polished, perfectly round, etc.

Is there something that could be keeping it lean down low, causing me to richen the mixture screw, then off idle go rich at that mixture setting causing the bog? Or would a rich mixture screw not be able to cause that?

 

I don't know how a 4-port manometer is use to check FUEL LEVEL?

but for wet set you should (optimally: carbs off the bike and in a device to hold them level) used a single clear flexible tube to check each float level in turn

I am guessing you have two issues working at cross effects:

1. lean bottom due to fuel level or air leak or other issue

2. worn or improperly seated needles -- or -- worn or poorly seated emulsion tubes

 

Those were two separate statements lol. I was answering two of someone's questions.

Let me do a quick recap:

Carbs have been boiled in lemon juice, 24hr carb dip, air/carb cleaner blasted.
Jets/passages/emulsion tube probed and checked
Valves in spec.
No air leaks, confirmed with propane and starter fluid.
Replaced intake manifolds, throttle seals, fuel o-rings, mixture o-rings. Polished float needle valve.
Rebuilt petcock, good flow.
Floats wet set.
All jets in correct location and correct (stamped size)
Bench sync'd using small holes as reference.
Running sync with YICS port blocker and custom ATF manometer.
Colortune used to check mixture, end up needing to richen it up to get proper idle.

 

what oblong looks like -- hard to see w/the naked eye

http://www.factorypro.com/products/Miku ... t_buy.html

FWIW with as many miles as you have -- Aside from the obvious seals -- I'd replace as many carb parts as you can afford to starting with main/pilot jets and the emmulsion tubes and the needles unless they look flawless

consider new pilot screw orings and washers

I wouldn't polish float needles -- they have rubber tips -- may degrade them -- I'd replace them

consider new diaphrams

this guy at jbmindustries.com has good value on diaphrams

 

We're starting to get into ridiculous amounts of money here for things that might not solve my problem.

$50 to replace fuel jets. $62 to replace air jets. Needles I can't even find for sale, and your emulsion tube link would be $144 to replace them all. My diaphragms are supple, I don't see why I'd replace them. My float needles aren't leaking, and my levels are set fine, so until they leak I don't see why I'd replace them yet. Now, if you guy's are telling me that all these things are 40k mile consumables... well that's sucks, but fine I'll roll over.

We're starting to get into buy used carbs or find a new bike territory here. I would rather spec what I have to make SURE before I just replace it willy-nilly. I'm not opposed to replacing parts that have been identified as faulty, but not as a troubleshooting technique. I've already spent way more on this bike than I should have for it's condition, and it STILL isn't roadworthy.


Now then, what I want is some troubleshooting ideas and tips I can do with the carbs still on the bike first, such as the tape-the-intake trick which I will try... after which I'm sure i'll have to pull them off AGAIN to do more in depth troubleshooting, such as checking the emulsion tubes for being oblong, rolling the main needles on glass to see if they're straight or worn, checking actual ID on the jets to make sure they're not gouged, etc.

 

I understand -- I am sorry -- I don't know why folks think old (particularly high mileage bikes are cheap -- well, the initial check may be cheap)

Run tests as suggested by me others -- but the evidence so far is:

>> 1. lean idle -- see if you can cheaply figure out why -- do tape test although this will likely confirm what we know -- so what is cause for too lean? too much air in a circuit? pilot screw seals new, washers in right place, etc.

>> 2. rich middle throttle -- likely culprit is emulsion or needles (assuming air is OK)

Now assuming TOP end is OK?? Then we atleast don't have to worry over Man Fuel Jets although oblong emulsion richens top end too

but unfortunately if your float needles are inconsistent, and your fuel and/or air jets are all inconsistent, and your emulsion tubes are inconsistent, or your float needles are worn... etc. etc. (or your valve specs are off)

you're going to chase your tail

carbs are expensive

try to test and Prioritze if you can

 

Expensive doesn't bother me... so long as the results are positive. So far I've been spending money and getting 0 return. If I need to buy a new motor, fine. If I need to buy new carbs, fine. But I'm not going to replace every part in the carbs just to still have the problem and have to buy ANOTHER set and start over, you know?

I appreciate the suggestions. The concept that my surge is RICH not LEAN is a new lead. I'll see what I can do to track it down.

 

Just to be clear -- sloppy, sloppy -- GO! (when opening throttle is rich)

Sudden death when hitting throttle -- or excessive off-throttle backfire is lean

(or wide apply open throttle -- sudden let go of throttle -- sudden momentary surge -- this is another sign for lean)


also, maybe -- unless your head is about to explode -- Do a few 5k plug chops

 

Got it. Thanks for the clarification. I'll check it out tonight. No power at any throttle, then popping and surging then normal DOES sound like rich according to that. I'll do some plug chops too.

Quick question, i've done some looking around and haven't come to a steady conclusion... are the enrichment plungers supposed to be metal on metal? Because mine are. There is no rubber in there to seal them when they close, is that how it's supposed to work in the Hitachi's?

 

Yes, no rubber parts.

 

Gotcha. Good news there then lol.

Ok so I set my mixture screws back to 2.75 turns across the board, and re-sync'd. Didn't bother checking with a colortune, I know they would all read lean lean lean. What I did do was a plug chop at just under 5k, right before it was going to surge.

1: Normal
2: Lean
3: Lean
4: Rich

Interdasting. Sounds like the worn out needle/tube theory might be right for my surge issue. As far as the idle mixture goes, well... still in the dark. I'm going to pull them back off and give them another looking over, maybe take some pictures for you guys that have been following along.

 

I took apart my number 4 carb that was reading rich, and here is the orifice tube:



I had a spare so I cleaned it up and replaced it. The rest looked fine, couldn't see that they were out of round, the needles looked great. Could a little ding like that cause these issues, or at least the surge one I guess?

 

next time you have it running, check for vacuum leaks where the YICS passage goes from the head to the cylinders. there's o-rings in there that might leak, doubtful, but it could happen.
your air cleaner is seated right...?
the little fingers that lift the choke plungers aren't holding any of them up

 

Hmm, first i've heard of that. I thought the passage was molded INTO the head, not attached with orings. Seems like something in a 40k motor that might have deteriorated? I'll check, though my previous propane and fluid checks haven't surfaced anything.

It should be, but i'll double check.

They're certainly not being held up with the fingers, but since it's metal on metal it's always been in the back of my head that they could be marred or not completely sealing... but not sure how I could check on that since they're enclosed.

 

take the plunger out and mark the cone with magic marker, put it back in, spin it a few times, take it out and see what you have

 

Th yics is moulded into both th head and th cylinders, th head gasket and 4 O rings seal th join.

 

That will effect it... I'd replace that

 

Replaced it, no change. Plungers seemed fine.

I think I'm going to start looking around for a shop to take a look at this thing. My hopes are not high, since at this point I feel like I know more about them than someone who hasn't messed with XJs would... but I'm not sure what else to do. Yall have run out of ideas, and I haven't found another set of carbs for sale.

 

First, double check the diaphragms. Make sure there are no pin holes. Do the light test in a dark room. Then, check to see if there are any abnormal holes drilled in the slide pistons. That is a popular mod to richen the mixture. If you have a set of parts carbs, using welding tip cleaning wires, measure the holes in the emulsion tubes against those in your carbs, and to verify they have not been drilled out.

The main jet needles do wear, they are soft. It really sounds to me that they are worn on the tips, and just as they begin to lift, they are letting more fuel in than they ere speced for. Once they open (or lift higher, they pass the worn area and the stumble smooths out.

Also, you mentioned early in this thread, that you did a yics block sync, and it changed when unblocked. Do not waste time with an unblocked sync result, it is futile. The yics port connects all 4 carbs and you will not get the same results unblocked. Your goal with the sync is to sync the vacuum (at idle) to the lowest cylinder result equally across all cylinders. That means tune each individual carbs to the lowest performing cylinder. (I don't feel the sync is the issue.

What is the history of the bike? Any info from po? Was the bike modded and you are restoring to stock?

My suspicions are either worn main jet needles, or po mods to increase fuel.

 

My diaphragms look great. I've light tested them, and no pinholes show. No abnormal holes drilled, i'd checked for that. My emulsion tube holes matched the spares I picked up, so they should be good too.

I don't know much as far as PO history. Basically, I was stupid and got screwed. The carbs had overflowed into the crankcase, so he wouldn't let me hear it run. He said his "mechanic friend" had rebuilt the carbs recently, and that the bike was in great riding shape. At the least that last part was a lie, if not all of it. I've tripled my money into it trying to get it to run right and operate safely. The only upside is that the bike doesn't seem to have ever been modded. Everything on it was stock.

I guess I'll see about replacing the needles then. I just haven't found anyone selling them. XJ4Ever doesn't have any listed.

 

Send Len a PM and ask him, he just might have some.

 

There are several carb assemblies for sale on ebay. Check this link I think they are the right ones. Considering the rarity of carbs for these bikes and the need for them I don't think you'd have a problem if you needed to recoup your $. It would be great to see a resolution to your long running issue.

http://www.ebay.com/sch/i.html?_trksid= ... b&_sacat=0

 

This would be a good start. From the looks of the dent in the emulsion tube, if that had been there a little while, it would have worn the needle. So just using the same needle and replacing the jet would not solve the issue. If you happen to have the needle that accompanied the jet that you used as a replacement, that might help before buying new.

 

Visually inspect needles and roll them on glass to ensure straightness.

IMHO I'd replace all jets, and emulsion tubes 1st, then retest for run -- then if still issues -- needles...

Len has these things, and this guy www.jbmindustries.com
has good diaphrams -- I'd replace them too

 

Screw it. I just bought that set of Canadian carbs off ebay. I probably would've spent twice that replacing needles and jets.

Guess we'll find out pretty quick if it was the carbs, or something in the motor. I'll let yall know what happens!

 

This will be interesting to see if the CN carb jetting difference solves some of your lean issue knowing that the US jetting was lean for EPA. Good luck with it and let us know how it works out.

 

I hope all goes well -- someone else's old carbs may be no better -- IMHO, it is just MUCH easier to spend the money and replace ALL critical items - emulsions, jets, diaphrams, all seals, new pilot o-rings and washers and springs, new gaskets, needles (if ANY hint of wear).

The frustration and repetition involved with "rebuild a bit" and "find-more-issues" and to not really be sure what they are is maddening and can kill your drive to finish.

I know this is expensive... but doing so gives you another 30 year mortgage, otherwise, year after year you may have iissues

 

Well, I'd be spending twice on parts what I'm getting a whole bank of carbs for. They LOOK to be in really good shape, and all my new rubber bits will swap over. I'd say this is a better gamble than throwing more money on new parts when these carbs could still have blockages I'm just not capable of removing, or have been modified in a way I can't tell.

My fingers are crossed.

 

So, got the new carbs, stripped and gave them a thorough cleaning, popped them on and.......

They do the EXACT same thing as the last set. 5 turns out on the mixture screws to get a proper mixture at idle, bog until 5k then surge. Anybody still want to tell me it was my carbs?

At this point I have to figure on a 49k mile motor that either the low compression is causing issues, or someone has burnt/bent a few valves. From here it's either going to the junkyard, where for my money i'll at least get the satisfaction of watching as it gets crushed, or try to source a new motor and cry myself to sleep.

But seriously, I guess i'll just pull the motor and and yank the jugs, maybe i'll find something glaringly obvious that is causing this. *shrug*

 

Time for refurbished head, valve job etc.?

Before you scrap it (never get decent cash for that) part it out if you can't keep fighting the good fight. But I give you props for all your effort so far. Since this thread is a novel, quick question what were your compression numbers and did the wet test indicate rings or valves? Forgive my laziness/ignorance.

 

This sounds remarkably similar to my '83 750 Seca. It seems to be running rich, and I have a horrible "flat spot" at 2500-2800 RPM. Makes it a challenge to get going at stoplights, especially on a hot day. Once you pass the 3000 mark, it surges and takes off and runs fine. My mileage also seems a lot lower than it should be - mostly in the 40-43MPG range, dipping all the way down to 35 once.

I checked the valves (all within spec, but a couple at the close end) and the carbs. I noticed that the screws were set at 5-5.5 across the board except for one at 3.5. (and it seemed to have an occasional miss at idle before, so that was probably the 3.5)

Figuring somebody had been fooling around with them and messed up the adjustments, I took them all back to 2.5 to see what it would do. End result was it wouldn't idle worth a darn. By the time I got it idling reasonably smooth again, I was back up to 4.5-5 turns. The hesitation isn't quite as bad as it was, but now I get a little popping on closed throttle.

I definitely haven't tried nearly as much as you have yet, so this thread has been very interesting, although not very encouraging. Hope my problems turn out to be easier to solve. I plan to try some of the suggestions given here.

I am in Colorado and do 99% of my riding at 6000'+. Jets are all stock, so I'm assuming dropping down a size on the mains would probably be in order. My first thought was to drop the needle down a notch, but of course the needles in these Hitachi's are non-asjustable. Grr. Maybe I'll get lucky and smaller mains will clean it up for me.

I'll be watching closely to see if anything else develops here, and it I run across anything, I'll post too.

 

Well, the Saga of the Seca has ended. I sold it.


Just kidding! It was the TCI module the whole time. At the advice of a non-XJ bike friend I threw a hail mary and ebay'd a new one. The bike immediately started running correctly after a re-tune. I still have some tuning quirks to work on, it still wants the mixture screws on the rich side, and it seems a little down on power in the top end, but at least now I have motivation to start spending money and fixing stuff.

Thanks to those that stuck through all of this with me! See yall on the road.

 

I've been reading through this and am glad you found the solution. Way to stick with it!!

 

Thanks for posting a follow-up. Too often I'll get something fixed and forget to come back on here and thank those who helped.

And this one's another case where the cure doesn't seem to fit the symptoms. But glad it worked! I've had a few of these head-scratchers myself. I would have thought that the TCI either works or doesn't -- but what do I know?