Stops accelerating at 5000 rpm ???

Hi all. Another carb query (or maybe ignition?).

My bike starts without probs, idles (though in a slightly lumpy way), picks up beautifully under acceleration all the way to... 5000 rpm, then just doesn't seem to want to rev any further. If uphill or on the flat then I have to short-shift to get a move on.

It will struggle past this if going downhill, but not particularly cleanly, or happily.

BTW, will red-line all day when not under load - and smoothly

Carbs have been stripped and cleaned properly and float levels checked too - all according to the first rule of this forum. Plugs are more or less the right colour and shims were done 1000 miles ago

Any ideas please,

Nige

 

5000 isn't very much! If it was a two stroke, I'd say air filter - but I know it isn't!
I would suggest fuel flow first. It sounds exactly like the OPPOSITE of my 600 which coughed and spluttered to 5000, then was ok. That was blocked pilot jets.

Mark

 

Doubtful ignition.

What's happening is once you're on the mains it's not pulling the right mixture. If your emulsion tubes are clear, and the carbs are truly religiously clean, go "clunk" and all that, no holes in the diaphragms...

I hate to say it...

Throttle shaft seals. Get somewhere you can safely do a couple of "plug chops" from the RPM where it's falling flat, and I'll bet you anything they look lean.

Did you examine the outer shaft seals when you had the carbs off?

 

Hi Fitz,

Didn't really bother with those shaft seals...

Will do the plug chop and see what's what.

Nige

 

You might want to pop the clips and nylon washers off the outside ends of the throttle shafts and inspect the only two seals you can get to. If they're toast, then that's your problem, as you can be reasonably sure the inner ones you can't see are equally bad, if not worse.

Unfortunately, if the outers look OK it's no guarantee that the other six are good; but if they're shot you can stop looking.

 

Outer shaft-seals look OK to me. Have also lifted the lids on carbs 1 and 4 to re-check my "clunk" test - all seems good.

I know it's not right to assume from these cursory checks that all is OK with the other carbs. However, they have all been recently stripped/checked/cleaned so I don't want to go through all that again at the moment.

PS - will pull higher revs if I down-shift a couple of gears to get past this flat spot. I know this was a recognised requirement when they were new too (though I think the flat spot was a little higher up at 6000 rpm). It just seems a bit cruel to a 30 year old engine.

Nige

 

Nigel,

I know what you mean about feeling guilty when you rev the pi** out of an old engine....kinda makes me feel as I imagine I would if I commited child abuse.

Do that plug chop. That last bit of info was new and very helpful...."will pull higher revs if I down-shift a couple of gears to get past this flat spot" as I doubt Fitz would have suspected shaft seals had he seen that earlier.

I think that if A-- you can get somewhere as was suggested and ride it in the bad spot for a couple or few miles, then turn it off and coast to a stop. Do NOT slow down normally and pull off the road then shut it off..no, no ,no. Just turn it off while holding the throttle steady after riding as far as you can in the bad rpm then take a peek and see what the engine is telling you.

or B- find someone local to you that knows how to tune engines...he will probably be able to pinpoint it rather quickly.

Last suggestion....99.99999% of the time when I hear about a bike needing "the carbs looked at"...the problem turns out to be ignition related. I'm not telling you that I think that is where your problem is as I don't have near enough information to pin it down for you and don't want to send you to check this, then check that..... just telling you what has been true in most cases in the past.


jeff

 

Thanks Jeff (and, of course, Fitz).

Yes, I aim to do the plug-chop before too long.

I have also found (forgotten I'd hung onto it) a spare Ignition Module which I can swap out if it points in that direction. (same model number as the one on the bike, though 06 suffix as opposed to 14).

Nige

 

Hi all - Happy Easter.

Bike seems to be improving a little with use. Did the plug-chop this morning, ran about half a mile at 5500rpm then clutch in and hit the kill switch.

All plugs looked OK to me - nice and light. I've put some pics of the plugs here, so your opinions would be very helpful.

If you think all ok there, then here's the next question...

I tried revving it to around 8500 in first, which it did, but when I changed up and got back on the gas it felt like it was not getting enough fuel and lost power for a while. Do you think my in-line filter could be starving it at higher revs?

 

Take the inline filter out to try it - it has been the culprit before.

Perhaps its the camera angle, but the plug gaps look small to me.

 

I agree..plug gaps look dodgy to me, especially #4 and #4 is rich compared to th others. By th book plug gap..0.7-0.8mm / 0.023-0.032 in, may not be all of th problem but it will help. Maybe new plugs as well..even better.

 

I agree as well. #1 looks a tad lean, #4 is a bit rich, and the gaps on all look way too tight.

What type of inline filter are you running? It's a possibility as well.

 

Thanks for the responses guys.

Plug gaps are set according to my Haynes Manual - maybe it's wrong. What should gap be?

Filter is just a cheap little throw-away item - maybe I should throw it away (I put it on after the tank re-paint, as there was some overspray residue in the tank - which I think has all gone now).

How would I address Fitz's comments about #1 being a bit lean and #4 a bit rich - at these revs, would the mixture screw fix it, or something else.

Thanks again guys, look forward to your further comments.

Nige

 

Spark Plug Gap per factory book: 0.7mm~0.8mm (.027"~.032") I usually go with ~.028".

The plugs don't give you strictly results from the RPM you did the plug chop from, so yes the mixture screws can affect the color even at 5000rpm, because you have to run up through the pilots to get on the mains.

From the results of your latest test, it does sound like you might be suffering a fuel-flow issue. Try running on "PRI" at highway speeds; maybe the vacuum system isn't keeping up. And definitely change the fuel filter.

 

lean, rich? Dont even start messin with the carbs till you get the right plugs with the proper gap. How did your plugs get so closed up?

 

Have you checked th filter in th tank..since you mention overspray in th tank, might be some left. Plug gaps ..see above^^ gotta say #4 doesn't look like it's got a gap. Keep following th logic, it wins most times.

 

Thanks Fitz - , and you too Waldo - and everyone else.

I've just checked those gaps - I screwed up when I gapped them (thought they looked a bit tight). I gapped at .008", not .8mm - got my Imperial and Metric mixed up.

Now rectified and will try the bike again tomorrow.

PS. Nevertheless, plugs all look reasonably light tan now, and that's with a further 25 miles of town and country riding since the plug-chop.

I will also screw #1 mixture screw out a quarter turn, and #4 in by the same amount.

I will do another plug-chop at 5500-6000rpm and try and post some closer-up pics of results. Just these few little issues to sort before a good bike becomes a great one.

Keep the XJ faith, and thank goodness for this site.

Nige

 

I think your very lucky for the quick eye's on the forum.
I saw those gaps as well and wondered how you kept from
welding them together lol.
Of course I hope that solves the prob-but check the fuel tower
as Bushy suggests, a small piece of stuck crud can do it.

 

Fit a NEW set of properly-gapped plugs and I'll bet it runs like a sexually-violated large primate.

Having your plugs gapped tight like that it would have been running like it had fouled plugs. Which exactly fits your symptoms, come to think of it.

 

I'll try it with the same plugs first (now gapped correctly) as they're virtually new.

Will take a look at the fuel tap (in-tank) filter if it still shows signs of fuel starvation.

Thanks for now fellas - hope it's this simple. Will report how it goes.

Nige

 

I guess you have direct knowledge of these? LOL

 

Bill have you ever seen a pic of Bigfitz?

 

Guys, have you never heard the term "runs like a raped ape?"

Nige, let us know. I guarantee it'll be better to some degree.

 

You guys.... LOL!

 

Seems to run better now - with plugs gapped correctly (well, it would, wouldn't it?). Certainly better lower down too, with a steady idle when warmed up. Also seems to re-start easier when hot.

I'm just going to ride it for a while now instead of messing with it, as it seems better with each mile put on. Just done a 25 mile run this afternoon and it's been good.

Thing is, maybe I should just adjust my riding style, considering it's a 30 year old bike, and maybe lower my expectations a little - I tend to ride my bikes for all their worth. Ridden at 80% it's a really nice ride; nice to ride quick, rather than balls out... - and it's still the best bike I've owned for handling and comfort combined, sooo good in the bends (and that's out of around 17 bikes)

Thanks for your help guys, as always,

Nige

 

Hi Nige - just a thought. I remember that one of the complaints about the 650 was it was a bit flat in mid range when it was brand new - perhaps it rides as it did 30 years ago. (Am I really that old?)

Looks good to me and I certainly wouldnt say no!!!

Mark

 

I think that's probably true - I have some contemporary road tests and they all say the same. I'm really (though of course some 25 years after the event) comparing it with a CBX550 which I had at that time which seemed faster but, of course, that was when it was virtually a new bike.

I think I'll just enjoy the XJ for what it can do...

Nige

 

Spin the motor a little bit...

After we had this discussion and a couple of others, I paid actual attention to my shift points on the 550 while out this past weekend:

1st-2nd: normal: 5K-6K, brisk, 7K, romping: 7K.
2nd-3rd: normal: 7K, brisk, 8K, romping 9K-redline.
3rd-4th; normal: 7K, brisk, 8K, romping: 9K-redline
4th and above: anything above about 7K in 4th is illegal everywhere...
so we don't discuss 5th except that the bike will pull redline in 5th no sweat...
and I take the 5th when it comes to 6th...

But you get my point. These motors really come alive above 6K so I like to let them stretch their "legs" a bit...

If you're worried about longevity, hold it to 8K or 8500; but don't "short-shift" the poor thing to death either.

 

Everywhere except the autobahn...lucky Germans

 

For Massachusetts, New Hampshire and New York, ... you need the Bike to be able to run wide open.
Last time I rode over the Mass Pike to go visit my sister; traffic was cruising-along at 80, and I think there was a play going-on to be in the lead.

The Tach was on 6000 ~ 6300 for most of the day.

I was angry that 5th Gear was so close.
I kept shifting; looking for another gear.

 

The 550s have a six-speed...

Detroit freeways roll at 80mph too; when they're rolling.

These motors will cruise at 7200rpm all day if you want; to the point where you can feather nearly onto trailing throttle and just howl along getting great fuel economy. There seems to be a "sweet spot" just over 7K.

(This assumes properly functioning carbs and a properly tuned bike.)

 

I think my problem is now resolved on this one guys, thanks to your input.

Interestingly, I've just re-read a December 1980 road test ("Bike" magazine) and it would appear my bike runs exactly (allowing for 30 years ageing, of course) like they did when new...

Apparently they found that it would rev up to 5k nice and quick, then just about sit there unless you dropped down one or two cogs to get it above the 6k where things started to happen.

They also noticed that there wasn't much power available between idle and around 3k - meaning either a faltering, or screaming get-away from standstill - another behaviour that I recognise.

Anyway, the upshot is that as it's now apparently performing very much as it did when new then the carburation can't be that far off now.

All the best

Nige

 

I run a 750 Max.
I took-out the hesitation by:
1.) Clean Tunin
2.) Fine Tuning.

Clean Tuning:
Perfectly Cleaned Carbs
Polished Diaphragm Piston Bores
Clean Air Filter (New or Blown Clean with Compressed Air.)

Fine Tuning:
Plug Chopping until the Mixture is slightly above Critically LEAN.

The Plugs are Tweaked to be Light Brown. Very Light.
There's no problem with Hesitation.

The Problem is at Top End.
5th Gear isn't an Overdrive.
It's a range higher than 4th; not by much, though.

 

Thanks Rick, just about got all the above covered now...

Took it for a ride today (around 115 miles) and it just seems to get better the more it's run.

I found a nice stretch of straight road and pulled just below red line (about 9000rpm) from a standing start, in the first three gears - backed off a bit once in fourth, but just wanted to see if it would do it without any signs of fuel starvation. Seemed OK to me.

Here's a pic of it on it's travels today.

Nige

 

By George, I do believe 'e's got it! Congrats, man, seriously.

Sho 'nuf is purty. (I'm planning on the red scheme with fully blacked out wheels as well.)

Also sounds like it's running correctly now, it ran right up to 9K without hesitation, right?

Go ahead and spin the motor upward of 6K more often; that's where the powerband just gets going. Run it to 7500 or 8K when riding briskly; you're not going to hurt it, honest. Nine grand's not abuse either; even the occasional accidental excursion a few hundred RPM past redline won't cause anything to go "bang" trust me.

 

Hi Fitz,

Yes, from a standing start it revs quite freely (tiniest hint of a misfire somewhere in the middle - maybe coils?) through the gears under load - also OK if you change down a couple of cogs for an overtake. Seems to pull harder if you're into 7000 +. Very much like a two-stroke power band really. It will certainly do for now - if I get an opportunity to try some different coils then I may do that at some stage.

As I say, it seems happier the more miles I put on it - last week I seemed to have some fuel starvation "symptoms" when accelerating hard from standstill, yet today it was much better.

I really enjoyed the bike today to be honest - long may it continue.

Ref: the wheels - I had them blasted then powder-coated black because it was the easiest (and cheaper) option - also it was done about a mile away from home. To get them done black, but with polished alloy spoke-edges and rims would have meant sending them away and a lot more money. I actually prefer the all-black finish anyway now it's done.

Nige

 

When you have "Holes in Performance" and trouble getting the Bike to respond to Wide Open Throttle, ... check:

Correct MAIN FUEL Jets
Clogged Ports on Emulsion Tube.
Diaphragm Rubber's conditions.

Diaphragm Pistons Bores Clean / Polished and allowing FREE Movement to Piston.

Clunk Test.

 

Hi Rick.

Correct Jets - Yes
Emulsion tube ports clear - Yes
Diaphragms good condition - Yes
Clunk test - Pass

Thanks,

Nige

 

Some impediment preventing the Throttles from Tilting to Wide Open.

?) Cable length.
?) Bent Cable End Securing Bracket
?) Throttle Grip Control position.
?) Wrong, Wrongly Positioned or Inverted Clamp stopping Sync Screw Travel.

Will it Rev-up beyond 5K "No Load"?

 

It really does seem to be there or there abouts now - yesterday's ride was good. It will red-line up through the gears now, as proven by my standing start test yesterday (see my post above). Cold start and idle are improved too.

Nige