Low Idle Misfire Goes away over 2200 RPM

[nvmike24]

I need some sage advice. I have a newly purchased 1990 FJ1200AC with 53000 miles. Previous owner was great at external cleanliness. Mechanicals were not his strong point IMO. Idle was hunting very badly, Misfiring from Idle to about 2200 rpm.  I was unable to get carbs synced and stay there for more then 10 miles, very loose carbs. Plugs were in poor condition and VERY lean! Caps were still covering the screws.

What has been done so far.
New NGK Spark plugs. Oil & Filter changed with a spin-on adaptor added. Reseal Valve cover, Replace Clutch 7 Wide 1 Narrow with new spring added to existing.
New Carbs from Randy @ RPM. Moved the washer to under the clip, 115 Mains, 40.0 Fuel Pilot, Screws 2.75 turns out. Uni-Pod filters installed, Air Box, Canisters and related California items stacked neatly in the corner of the shop never to be used again. Synced with no problems, Idle sounds ok but when load applied the engine feels like it is missing off idle, over 2200 rpm it seems fine. Does a first rate burnout!

Pulled back into the shop and checked exhaust temp with IR gun, #1-450f, #2-530f, #3-538f, #4-380f.
Pull tank again and check Compression, #1-160, #2-135, #3-140, #4-130. OK, so 20% diff from High to low. I did not oil the cylinders and retest, forgive me. Reassembled and sprayed Brake Cleaner on Carb Holders to see if there was any rpm change indicating an air intake leak. I did not notice any change in rpm.

Pulled the power connectors and Ohm tested the coils, 2.5 Ohm's both directions both coils.
Compression is an issue but why would the highest compression cylinder be 85 ish degrees colder the two that are 11% lower?. Plugs laying on the cover spinning the engine I see blue spark. Plugs in the engine cranks evenly enough that I do not hear the variation in compression.
Many years ago I was told all fuel problems start in the ignition and all ignition problems start in the carbs when running into the brick wall of WTF is going on.

I do not have another set of coils short of pulling the 84 1100 apart to try them.
Has anyone experienced similar problems?
Can the Plug Wires be removed or are they part of the coil?
How can the Plug Wires be tested?
Thanks in advance. Mike

[Arnie]

Disclaimer first - I'm not a "carb guru"

It sounds to me that you're still lean.  Are the manifolds tight to the head?  Is the O-ring btwn the manifold and the head sealing? Have you checked the float height?  You may need to raise the needles a bit more.  Does the needle have 5 grooves, or is it a US 1 groove needle?  If it has 5 grooves, move the E-clip to the next groove down and put the washer back on top.  If its a 1 groove needle, get another set of washers and use 2 washers under each.

Have you checked valve clearance?  This could be most of your problem.

Your inside cylinders will always read hotter than the outside pots.

Try making 1 (ONE) change at a time.  That way you'll know what is/was the problem.

Arnie

[56 CHEVY]

One question. When you say you "Moved the washer under the clip", was it the washer that the small spring sits on to hold the needle down or did you add a washer under the clip? This may be a stupid question but I know someone who did just that and his bike ran similar to yours until we figured it out.

[nvmike24]

No such thing as stupid questions IMO.

Per Randy's instructions I moved the washer from the top of the clip to the bottom if the clip. I do not recall being told to get another washer. Randy?

I would like to install new holders when available. Single groove needles. I've not touched the valves since they are soo quiet and lack of tool to remove shims. Stock exhaust on the bike.

This anomaly existed with the old carbs.

[yosemite]

 I know that it seems like a carb problem but you say your bike is very quiet and you have low compression on some cylinders try checking valve clearances these bikes tend to have clearances that close up with wear this could produce a misfire and loss of compression another place to look would be the ignition unit  the coils and ht leads do not separate (at least on European models) probably the easiest way to check these is by substitution
one other thought you say you changed the plugs, are the new ones chosen to match the old or did you get the grade from a catalogue/parts book I know someone who had a misfire on a z1300 kwak after the first service so he took it back they changed most of the electronics and fuel system under warranty but still had a misfire eventually he took it to another dealer who looked in a book and changed the plugs to the right grade and the misfire disappeared turned out the first dealer had an apprentice do the service he put wrong grade plugs in and when it went back they didn't check  just took the old ones out and put the same grade in so if the previous owner wasnt that hot on mechanicals....

[Dan Filetti]

I know that it seems like a carb problem but you say your bike is very quiet and you have low compression on some cylinders try checking valve clearances these bikes tend to have clearances that close up with wear this could produce a misfire and loss of compression another place to look would be the ignition unit  the coils and ht leads do not separate (at least on European models) probably the easiest way to check these is by substitution
one other thought you say you changed the plugs, are the new ones chosen to match the old or did you get the grade from a catalogue/parts book I know someone who had a misfire on a z1300 kwak after the first service so he took it back they changed most of the electronics and fuel system under warranty but still had a misfire eventually he took it to another dealer who looked in a book and changed the plugs to the right grade and the misfire disappeared turned out the first dealer had an apprentice do the service he put wrong grade plugs in and when it went back they didn't check  just took the old ones out and put the same grade in so if the previous owner wasnt that hot on mechanicals....

Nice First post Yosemite, just jumping in to help another, without a question of your own to start.  I'm frankly fairly jaded these days about new forum memberships, but you surprised me.  That does not happen often.    Welcome here.   

Dan

[racerrad8]

No such thing as stupid questions IMO.

Per Randy's instructions I moved the washer from the top of the clip to the bottom if the clip. I do not recall being told to get another washer. Randy?

I would like to install new holders when available. Single groove needles. I've not touched the valves since they are soo quiet and lack of tool to remove shims. Stock exhaust on the bike.

This anomaly existed with the old carbs.

You are good with just moving the washer as the white plastic needle holders are brand new and hold the needle tightly. Sometimes the plastic gets hard and loosens its grip on the needle allowing it to float up & down in the plastic. I move the washer under the clip on 99% of the carbs I build without any problem.

The valves on these bikes will never get noisy as the lash always tightens unlike a pushrod motor.

Since the problem was with both carbs there is something else going on. Did you sync at idle and 2000-2500 rpms?

Intakes are scheduled to be in my hands on the 31st.

Randy - RPM

[WestOzXJR]

Just reading through what you've written, you mentioned the primary side coil resistance check finding 2.5 ohm, what's it got on the secondary side?

Plus I can see no mention that you've actually tested the resistance of the spark plug lead end cap (the part that pushes on to the spark plug)... What are they supposed to be 5k to 8k ohm each max?

[andyb]

Highish mileage and a prior owner who didn't like mechanical stuff.

Valve lash is a great place to go.  While you're there, take a peek at the cam timing marks through the peepholes on the cam caps.  You may want to get a set of slotted gears, or slot your own, to bring things back to original timing.


Plug wires aren't really meant to be replaced, but it's doable.  But if they measured okay, why fool with it?  You're going to want to ensure the valve timing and lash are correct sooner or later, may as well get it out of the way before throwing money at it.

[nvmike24]

 I heve never checked sync above idle on a shaft linked carb setup. Used to do it on the old 4 cable Honda 750 setup. Always loosing Mercury during the process! Sticks are low on Hg as it is now. Looks like I will with checking lash after rechecking sync above idle. Anyone know where I can get my hands on some Mercury? Probably need to update to the new MP sticks.

[movenon]

Have the same problem. Done the same as you including adjusting the valves and balancing the carbs / new fuel filter etc, etc.  The bike has 32k with the original carbs. I have concluded that its the carbs that need to be cleaned and rebuilt. Only one carb responds to air adjustment. The needles are the original alum (?) units and are not the best shape. I ordered a SS screw replacement kit and complete (new jets, needles etc.) rebuild kits from RPM. I have about 30 -45 days of riding before it gets to cold for me so I just live with the "burbling" / slight miss up to 2300 rpm +- until I put the bike down for the winter. I don't know if any of this helps but thats my story.
Be thankful you don't have a new bike with fuel injection with 7 sensors involved and a cpu plus wiring. And when you go to the shop manual there is 90 plus pages just on the fuel system and most of it is tied to dealer test equipment. Wonder where a bike like that will end up in 21 plus years...... the test equipment will be out of date or broke and parts most likely the parts will be hard to get. I will stick with the basics. 

[nvmike24]

At Movenon, I know what you are saying about the 21 years. I bet there is going to be a market for EFI to carb swaps in the future.
So, back to the problem. #2 has one tight, (.076mm) Exhaust and #4 has 2, (.076 & .102mm), as well as some loose intakes, (.203mm). Shims and tool are on the way from Randy @ RPM.
Man, talk about one stop shopping and sound advice. I may need to take a ride to Northern California and buy him lunch. Good as any excuse for a nice run IMO.
What is the consensus on tight vs loose when splitting hairs on clearance?

[andyb]

Tighter will require more frequent checking and gain a pinch of power.
Mixed (one tight, one loose) will improve swirl and in theory improve combustion effiency, but you'll have to check because one's tight.
Looser will require less frequent checking.


Depends on what you want, really.

[movenon]

At Movenon, I know what you are saying about the 21 years. I bet there is going to be a market for EFI to carb swaps in the future.
So, back to the problem. #2 has one tight, (.076mm) Exhaust and #4 has 2, (.076 & .102mm), as well as some loose intakes, (.203mm). Shims and tool are on the way from Randy @ RPM.
Man, talk about one stop shopping and sound advice. I may need to take a ride to Northern California and buy him lunch. Good as any excuse for a nice run IMO.
What is the consensus on tight vs loose when splitting hairs on clearance?

My valves were on the tight side of the envelope I don't remember which ones off hand.  I set all my valves as close to the mid range as possable pushing to the loose side if I had to but within spec.. For me it has plenty of hp so I wasn't concerned with getting the last bit of fuel in it.  After that I balanced and adjusted the carbs.
Still has the "burbble". checked for air leaks etc. all was good. I can tell upon close inspection that the carbs have most likely never been off the bike. no "tracks". And the air adjustment only responds with one carb of the 4. Pretty sure they are gummed up beyond what Techron etc can deal with. Its good you are doing the valves because they probably need it and its a good time to do a good inspection. Take notice of the inside of the valve cover for heat related problems (cooked on oil) and surface condition (gives you an idea how the P.O. maintained oil etc). Are the phillips head screws on top of the carbs that hold the diaframs buggered up (if they are to P.O. has been in there). Check the intake manifolds for tightness. Be carefull there, don't reef on the screws to hard. The manifolds are a bit pricey. Consider replacing the fuel filter, its on the underside of the fuel tank I believe. Check the plug wires routing and condition.
On the valves if you have a dealer close by check with the SERVICE dept and see if they will exchange shims with you.  My dealer did so at no cost. In the valve adjustment: if one of the buckets pops off the tool, slide a quarter in place of the shim so you can reset the bucket. I have also used a penny. bends the hell out of them but thats the trick when it happens. Down load a copy of a service manual. In it there is a nice chart that is helpful in determining the replacement shim size. For this any year service manual will probably do. Drop a note after its back together with how it runs.
Ride safe. You only have a certain allotment for fun, don't use it all up at once

[Dan Filetti]

I can tell upon close inspection that the carbs have most likely never been off the bike. no "tracks". And the air adjustment only responds with one carb of the 4.

If the carbs truly have NEVER been off the bike, then I'm pretty sure the air-adjustment screws would have likely been capped-off.  The first time you screw with it, you must remove these caps/ covers (kind of like a hymen -just saying)

Dan