Maxim-X Break down at high rpm and vacuum lines popping off

Two years ago this Maxim X was tuned to perfection and the compression was excellent. I put star Tron and seafoam in the gas and The next spring it ran just like it did when I put it away. I had a minor slide in April 2014 and only used the bike for maybe 300 miles of driving over all of last year. Last fall I put in the same additives and ran the bike on occasion throughout the winter to keep the engine going.

When I took it out this year it started right up, idled well but I found it broke down with WOT at 8K, If I just gave it gas instead of WOT, it goes right straight to the red line with no problem. I used the carb tune to see if the sync was out of adjustment And when the bike was warmed, the readings looked perfect; all four slides were within 1/2 marker of each other. Even though a color tune adjustment won't matter at the upper RPMs, I checked that and all the cylinders were burning right at idle with the existing settings. Thinking it may be the TCI or electrical, I checked all the connections and used Deoxit on all of them, exchanged the TCI with my spare, Checked that the air filter and air box were good, Drained all of the gas and filled with fresh and headed out on a long ride.

It acted lively but not quite as powerful as I remember it and after 40 miles of driving, WOT At 8K still caused it to break down and not even be able to reach the redline of 10K, the bike would slow down like it was Starved for air. But again, slightly less than full throttle and it would go to the red line with no problem whatsoever. But when I got off the interstate it was now idling not clean but fairly rough and by the time I got home it was almost stopping while idling. I put the carbtune back on And when I started it up the roughness was gone and the carbtune settings were Ideal. The roughness started up again after idling for a while and I tried ever so slightly adjusting the air adjustment screws And it started starving while idling and then the vacuum lines to the Carbtune kept on popping off of cylinder four and two, even though I replaced all the settings to what they were before I started.

There is only around 10,000 miles on the bike, The compression was excellent less than 500 miles ago So I don't think there's any issues with the valves and I ran the bike every month during the winter, the bike has been garaged and the gasoline well cared for during the winter. My only original concern was the breakdown at the high rpm but now it is popping off those lines almost as fast as I can put them back on and stalling out. I've already replaced the throttle shaft seals in the carburetor 18 months ago and was running perfectly after that rebuild. And again, there's maybe 600 miles on it since that rebuild.

What might I now need to look at because there's obviously something going on I've either forgotten or don't know?

Thanks,

Gary

 

Even though you don't think there are any issues with the valves, you need to check the clearances.
Clearances should be checked every 5,000 miles (at least on an XJ650) .
http://xjbikes.com/forums/threads/airhead-valve-adjustment-with-pics.14827/

 

if your intake valves are open during the compression stroke your vac. ports are under pressure.
do your compression test again and compare your new to old readings.
if you have never adjusted your valves, you are wasting your time trying to sync it and tune it.

 

Thanks for the reply!

If my memory is correct, valve recheck is at 25K for the Maxim-X series; a much longer interval but much more of a PITA to accomplish with the 5 valves and their miniscule shims. I have a 2nd engine with valves done and ready to ready to drop in when I need to do my valves, it'll be easier that way & do the shims over the winter with that engine out of the bike.

But of course things can go wrong early so valves could be the issue but I feel that is a lower chance of causing these problems than something else, because the mileage has been so little between the engine running fantastically and now the problems I'm seeing are large and there are two cylinders with kickback issues. I've literally put on less than 500-600 miles over the last two years. I'm thinking carburetion or electrical but do need all the suggestions I can get.

 

what damage ocured in your slide?

 

As minor as can be, I scraped the end of the L muffler, just at the outer bell, no denting, cracked the aftermarket wind screen, scratched the left front & rear taillight, cracked the left mirror, ground down a bolt on the aftermarket foot peg that is attached to the outer edge of the 3 point engine guards, no damage to the engine, body or frame.

 

Battery voltage?

Gary H.

 

While the service schedule does say you can wait quite a while longer before checking the valve clearances; you are not the original owner, so you can only assume that they are in spec and were never monkeyed with by a previous owner. Assumptions rarely turn our the way that we want them to.

The clearance check won't take but an hour or so, and will make it easier to diagnose the problem that you are having. You can also have a look to see if the cam chain tensioner hasn't maybe gone a bit slack and allowed the cam timing to jump.

 

Because it was suggested, I ran a cold compression test and was surprised:

1 - 150 pounds
2 - 30 pounds
3 - 120 pounds
4 - 150 pounds

One suggestion I was given was to squirt oil in to check for a broken ring and see if the compression raises . I put in a Tbs of Rotella diesel and it did, #2 went immediately up to 70 pounds.

So that makes me wonder if maybe the ring might be stuck to the piston instead of snapped. There's no smoke when it's running and all the plugs look equally colored & identical to the eyes, no carboning but they're only 600 miles old.

If it is a stuck ring, how does one unstick a ring in a bike other than run it? I could squirt Kroil in there & see if that does it but don't like the idea of Kroil affecting the wet or starter clutch.

Thanks!

 

A tablespoon or two of equal parts Automatic Transmission Fluid and acetone, or the same amount of kerosene. Pour it down the plug hole and let it sit overnight, then run the bike (it will smoke).

 

Won't that trash the oil? I'd think I'd need to change oil before running it. I remember messing up the clutch in a 650 Maxim when I put Amsol in it but, I'd been using the same oil in an XJ11 for a long time with no issues but within a few miles the 650 clutch was slipping. Flushed with dino oil and all returned to normal.

But back to your suggestion; just run it at idle, take it out & open it up? Kerosene I don't have but Acetone and ATF I do have. I'm willing to give it a try if there's no clutch damage likely.

& thanks for the suggestion.

 

The small amount will not harm the oil in the slightest, and will definately not make the clutch slip. If you are really worried then just use Seafoam (which is mainly Naptha).

Let it sit, run it at idle until it is warm, then take it for a ride. Let it cool overnight and rerun you compression check.

 

Will do. & thanks.

 

K-moe, The compression I was having issues with was
1 - 150 pounds
2 - 30 pounds
3 - 120 pounds
4 - 150 pounds

I followed your suggestion and used the 50/50 acetone and ATF, I let it sit overnight in the cylinder and the next day I rode it and when hot
1 - 165 pounds
2 - 145 pounds
3 - 130 pounds
4 - 160 pounds

When allowed to cool
1 - 145 pounds
2 - 135 pounds
3 - 125 pounds
4 - 140 pounds

So that was a massive change in #2. Thanks for the idea & that low compression is now resolved! It did not resolve my issues with bogging down bad at 8K & up with WOT however, so something still is amiss. I just bought a leakdown tester and am going to see if I have valve or ring issues. Hoping to not have to do shims, it will keep the bike off the road for a long time between IDing the needed shims and getting them in there & all the rechecks to be sure it's all to specs.

I have a spare engine with freshly done shims which I bought a couple years ago & it's just sitting waiting to be put in, can't lift & maneuver it myself any more, not this year anyway so I suppose I do need to deal with the shims while the engine is in the bike, I figured it would be easier to simply exchange engines (using the break-away frame on the X to make that quick & easy) and then do the shim job on this engine during the winter, in the basement.

The carbs were just gone over 600-700 miles ago and they were perfect. 44MPG and full acceleration across the band. Used Star Tron with seafoam in the tank over the winter and ran the engine to temp monthly. Have gone through a few tanks of fuel since last year so it's not bad gas/gum deposits.

Curious.

 

Resolution to the problem

I ended up replacing the shims in the Maxim-X and other than being a Royal pain on this kind of engine, it went without incident all but two of the valves were needing re-shimmed and those two were almost too thin so I replaced them with thinner shims as well. I did a leakdown test and all cylinders are well into the green. Tested compression and it's 150, 150, 140, 150.

However, when I started the engine and began to carbtune, all the problems I originally had were still there, nothing had improved by getting the valves in spec. At first all was seemingly fixed but as the engine warmed up it began to misfire and #2 cylinder started popping the vacuum line off to the carbtune as quickly as I put it back on. Discouraged, I took it for a test ride and sure enough, I had the exact same bogging issue I wrote about earlier starting around 8K. If I WOT at 8K, it would not go past that RPM and was bogging heavily.

My guess now was the carb needed rehab but I'd done a complete rebuild including shaft seals less than 1000 miles ago. The other guess was maybe the pickup was getting an irregular signal at higher rpm. I already tried a different TCI and that didn't help.

So I contacted Dave (Hogfiddles) and ran it by him & he suggested I check the plugs. The plugs are really new NGK Iridium and with less tan 1000 miles on them, are surely too new to fail. But I took his suggestion and pulled the ones from the spare engine and went for a test run and... there was my old bike once again! Zero issues, redline under full power and assertive full power throughout the power band.

The problem was the Iridium spark plugs were failing at high RPM under load.

Now to decide what plugs to use, I have no resistor in the plug cap, was relying on the internal plug resistor for that 5K of resistance. Maybe it's not really an issue and I can just use copper core plugs and not worry about the resistor in the cap.

But I wanted to offer the resolution to this problem and give props to Dave for thinking of the right solution.

Gary

 

Glad to help, Gary!!! Ooooh, I'm getting those warm fuzzies. Oh wait--- must be all these freakin' deer flies

 

I got some extra Deer flies down here I can send ya, if you're running short.

 

Stupid summer. When is winter here?

 

Good call Dave! I'm glad you helped him track down the trouble with the misfire. When Gary and I talked a week or so ago, my gut feeling was it had to be ignition related.

Also, just to be sure now that you've proven that all the "base engine" specs are good, verify that all the connections between the pickups and wiring leading to the TCI are good. And don't forget the ones for the charging system and battery ground at the rear of the engine. These 30 year old bikes need some tlc you know.

Tony

 

Yes, all the old connections are likely to be a mess on any bike this old so... One of the first things I did to resolve the bogging issue was to deoxit every connection in the bike. The only ones I missed are the ones to the engine, I need to find where the plugs for them live and those two plugs will make it 100% deoxited!

What a relief that this X is running properly, especially with new shims, recent carb rebuild and a good ignition system. I shouldn't have to break into the engine for a long time now.

Shouldn't...

 

Order the resistor version of the stock NGK plugs, or another set of the iridium plugs. What you found was a maufactoring fault in the plugs, which can happen with any plug as they are all batch tested since the manufacturing volume is too high for individual testing prior to delivery.

 

K-Moe, I just read a lot of spark plug info regarding resistors and apparently the resistor while cutting down on the intensity of the spark, also lengthens the duration of the spark. Apparently the lesser spark of greater duration is a good thing for combustion so I decided to go with another set of the same; NGK DR8EIX. Supposedly this is the right one for the Maxim-X and since they get good press, as you suggest, it must of been a glitch in the Mfg process. Advance Auto had them in stock in a neighboring town for $7.09 and that was a good price so I picked them up.

The engine kicked over on the first rotation and as I suspected, the carbtune was pretty well off the mark. Adjusting the X this time was different, it was steady when I'd make an adjustment, no unexpected swings. Got all the bars lined up and I didn't check the colortune, it's tough on the X with the narrow channels the plugs go into, arcing is an issue for me between the extender and the walls. I may colortune tomorrow but when I took the test ride, it was with full power again, no hesitation and it reminded me of my XJ11 in pulling ability; a different power curve but both bikes are well matched in many ways. The heavier XJ11 is a better interstate cruiser.

Looks like the Gremlins are out of the bike now and all is well. Draining the antifreeze tonight and refilling tomorrow. Nasty green brown colored antifreeze, probably 30 years old...

Now to strip the tank, bondo a small dent, primer, paint & clear coat.