Where to start? 3 Cylinder Bike...

[ChiefCass]

1989 XVZ13 63K Miles. Purchased 2 years ago and finally got suspension and other troubles sorted.

I've been getting a few weekend close-to-home miles over last 2 months. 2-4 hour rides max. (I don't trust her yet).

Bike has developed (or I just began to notice?) a low RPM miss.

 

Under low throttle acceleration at about 3600RPM I hear popping from exhaust then, as RPM increases to around 4000, a 4th cylinder appears to engage and bike smooths out.

Closing throttle from high RPM results in a backfiring fit as it slows through about 4500RPM - very predictable.

At constant cruise any RPM bike vibrates and sounds like a 3 cylinder machine.

At Wide Open Throttle, bike is "notchy" with moderate acceleration up to about 4000RPM then Oh My Dear God! It appears to discover the 4th cylinder and earns its reputation.

It's producing 37MPG over the last 8 tanks of gas. Not right.

 

Mucho Seafoam thru unit: ~10% of every 2nd tank has been miracle juice. Figure 8 tanks is enough to fix the "bad gas" scenario & do all the chemistry cleaning possible on the bike with Seafoam. Another solvent recommendation before fiddling with her guts?

 

What should I be looking for, do, check, buy, etc.?

 

A reference to a thread covering my problem is probably all you need to post - I simply can't whittle down my search enough to find the right / best one.

 

I'd love to hear any advice that anyone has to give me - lord knows I'm not much of a mechanic: witness installing 3 used mono shocks all resulting in too high a ride height only to find the linkages that came with the replacement shocks were ALL different than the original. Pull original linkage off of blown shock, install new shock into old linkage and install onto bike and, Presto! FIXED! Arrrgh!

Edited September 4, 2015 by ChiefCass
Title Addition

[taz112]

I had the same problem cleaned all jets, new plugs getting spark and still had problem. Got some heat shrink as last resort and put on plug wire caps. Solved the problem. Plug wire was

arching when in place. It was an easy fix. If you have tried everything else I would look at plug wires.

 

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[ChiefCass]

I had the same problem cleaned all jets, new plugs getting spark and still had problem. Got some heat shrink as last resort and put on plug wire caps. Solved the problem. Plug wire was

arching when in place. It was an easy fix. If you have tried everything else I would look at plug wires.

 

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Thanks. Will post follow ups as I can.

 

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[frankd]

Whereas your gas mileage isn't great, it's not too bad.

 

Check for spark in all 4 cylinders. Take a good spark plug and test each cylinder. Make sure you ground your test plug. When you test for spark, it'll become obvious which cylinders are running at idle.

 

If you have spark to all 4 corners, maybe one your intake port rubber plugs has a hole in it That would kill low speed operation of a cylnder.

 

If you don't find anything wrong, you'll have to pull the carbs and see what's plugged.

[Patmac6075]

What do your plugs look like?

how is your sync?

I'm thinking perhaps a vacuum leak? Maybe a clogged jet?

If it were me, I'd yank the plugs first...just to see if they're all "brown paper bag" colored. Maybe you have one that's really white (lean), or one that's sooty (rich). That should get you enough information to begin narrowing your search. If you can narrow it down to one cylinder you can start eliminating what's NOT causing the problem. At least that's the way I'd go about troubleshooting the problem.

[Great White]

Start with plugs, then check and meter caps (should be 5K ohms), then spark wires and insulation. Check electrical plugs in the ignition circuit and TCI for corrosion. Meter coils if you want, but in my experience they rarely are the problem. Last in the ign system is the TCI, but I'd move on to carbs before replacing that (IE: it's $$$)

 

Once you've verified the ignition system is good, head over to the carbs.

 

Verify settings IAW service manual. Then do carb synch. Valve clearances should be checked prior to carb adjustments.

 

If none of that works, the carbs need to come off for a proper disassembly, inspection and cleaning. "Proper" cleaning involves soaking in a special cleaner or time in an ultrasonic bath.

 

 

I chased and odd miss for what felt like forever. Found it in a spark plug cap that had infinite resistance on a meter check due to corrosion inside the assembly. When running, the spark would jump the corrosion in the cap but the spark would be very weak at the plug. I cleaned mine, but the best fix for the average backyard wrench is just to replace them. Brand new NGK caps are cheap and easy to replace..

Edited September 6, 2015 by Great White

[Karaboo]

You might want to check the diaphragms before pulling the carbs. Check for pinholes and replace or patch (carefully and temporarily) as required. You may have a slider that is sticking in the bore, until you get enough oomph at higher rpm to move it into a smoother operating zone.

[ChiefCass]

Thanks for the many leads. My progress so far (very little due to commitments) is I pulled air filter and shot combustible carb cleaner down each throat - same change on all 4 cylinders: RPM dropped. So I'm seriously considering my next move is to pull plugs and look at them, cap resistance and spark intensity. Eliminate or fix then tackle carbs...

Again, thanks. Familiarity with these machines and opinion to save me time, effort and expense is exactly what I was looking for.

 

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[ChiefCass]

I pulled the side cover this morning in preparation to pulling plugs for diagnosis and found the choke linkage for the right bank disconnected (picture>)

(Doncha love learning about stuff the previous owner did?)

I reconnected and then bent it very slightly so it'd stay where I put it.

 

Then I took Blu out for test ride and... MUCH BETTER but still not the complete fix:

- Low RPM still runs on mostly 3 cylinders and hesitates in idling parking lot maneuvers.

- "Kicks in" much more smoothly without the popcorn noises in the exhaust at about 3200RPM

- Still backfires under deceleration right at 4500RPM: Set your watch by it!

 

I do NOT understand why not having choke on the right bank would make a difference in the way the bike runs WITH THE CHOKE OFF.

The linkage "engages" the choke forcing a richer starting and warmup mix. With the linkage disconnected, the choke fails in the open or "disengaged" position and no vacuum or throttle condition should be able to pull it closed. What the Heck? Is there an idle enrichment circuit that's actuated by choke position? Yes, I'm a newbie. Yes, I need to read more about these bikes. Yes, I haven't dealt with carbs since Throttle Body Injection came out and not much even before that.

 

I invite comments and I still plan to get into those plugs and see what's up with them... after I take a little ride... Too nice a day to twist wrenches. I've got all Winter (in Michigan) to do that nasty tear-down and repair stuff.

 

Thanks!

[greg_in_london]

This may be more use further into the diagnostic cycle, but I'd chip in with two points.

 

The first is that if you have an intermittent spark it can be hard to diagnose, as you may see it when you test for it and also the exhaust will still feel hot (ouch !). I bought a cheap temperature sensor from Ebay (and then a much better one from Lidl) - check out http://www.ebay.co.uk/itm/LCD-Non-Contact-Infrared-Digital-IR-Laser-Thermometer-Probe-Temperature-Sensor-/271517740132?hash=item3f37b7ec64 With one of these you can see if one exhaust is cooler than the others without burning yourself. It's cheap and easy.

 

The second is that sometimes there is a break in the wires in the pick-ups, though maybe all the duff ones failed 15-20 years ago.

 

My money would be on an HT lead or a blocked jet. Or maybe a naff spark plug.

[ChiefCass]

Ok. Reattached right bank choke linkage, pulled all plugs and inspected spark and condition of each. Golden gray all 4, none black and strong spark as well. Multimeter battery dead so didn't check cap resistance. Bike still has vibration / 3 cylinder "feel" and hesitates badly at low RPM parking maneuvers often nearly dumping us in the dirt. Choke link has eliminated (?) the popcorn exhaust noises under low acceleration at high RPM. No more "Oh My God" PowerBar behaviour when accelerating through 3500 RPM. Still get 1-3 backfires when deceleration rolls through 4500 RPM.

Question: I have no idea if bike has ever had valve clearance adjusted... 63k miles. Would concensus be to have dealership adjust valves before ripping my carbs off and diddling with them? Manual tells to adjust valves before synching carbs...

Your thoughts?

Thanks!

 

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[VerntureVet]

You can check the valve clearance yourself follow the directions in the manual. I got my "88 not running with 60k+ and would put a good bill that it was never done on my 88. Yet the valves were in tolerance and did not need re shimmed

 

I would shim the valves myself if needed and you feel comfortable doing it. The most pain in the rear part is not knowing what shims you need ahead of time and some of the shims run $30-40 from the dealer.

 

Check fuel float level

 

Then sync. your carbs and check for vacuum leaks. check that the crank vent hoses under the air intake are still connected. Believe it or not sometimes even a 1/2 hole in the air-box can make the 1300 have fits.

 

Set your Pilot by turning it all the way in till it gently snugs and back it out 2 turns to start.

 

Your popping noise on deceleration and load change could be from running lean. UnBurnt air/fuel in the exhaust is being ignited in the muffler due to high exhaust temps from a lean burn.

 

Slow diaphragm movement can also give you them acceleration fits. While your in the outer carb checking the Diaphragm. Clean up the piston and make sure your springs are all the same length. This may also be a good time to install a washer on the Jet needle.

 

You can use carb cleaner and open the carb drain as you spray threw the jets and other accessible orifices.

 

If none of that helps then think about breaking the carbs down for a good detailed cleaning and adjustment.

Edited September 13, 2015 by VerntureVet

[BlueSky]

When you had the air cleaner off, did you observe the sliders operating in unison?

[ChiefCass]

Nope. Next weekend...

 

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