#3 not firing

[dfwthompson]

Well I've exhausted the extent of my knowledge on this one. During the sync I noticed a lack of throttle response. In checking #3 was considerably cooler than the others. I swapped plug and cap from working #1 to #3....no change, #1 still HOT, #3 much cooler. Checked fuel in #3 by drain screw...ok, fuel drains. Checked primary at 2.9 ohms and secondary at 12.10 ohms per cap test doc.

 

What have I missed? If the plug wire was bad the Secondary test would not have checked out at 12.10 ohms. If the plug or cap were bad, #1 would have shown signs of not firing after swap. TCI connectors clean. I'm missing something. Where do I go from here?

[Peder_y2k]

Did you confirm that there is NO actual spark at #3? If there is a spark, then the carb is not functioning properly to provide the proper fuel mix. If the mix is too rich or too lean, combustion will not occur making the cylinder cooler than the others.

Likewise, a hot cylinder is also an indicator of carb malfuntion, as the mix is on the lean side, but enough for combustion. The proper mix will carry enough heat away to bring cylinder temps to normal.

I suspect the carbs to be either dirty, or out of adjustment, or both, or even a vacuum leak if there is definately NO spark at the plug.

-Pete, in Tacoma WA USA

[dfwthompson]

Thanks Pete...No I did not confirm there was no fire. Not sure I know how unless grounding the plug and watching for spark is the test. I'll confirm and drain #3 again.

 

Vacuum checked with starter fluid...no increase in RPMs, 43k miles-carbs have never been off. Fuel tank very clean and recently treated fuel with staybil and berrymans. Soaked and drained carbs several times prior to syncing. Will advise....Thanks again Pete for your response.

[frankd]

That's basically how you check for spark. Seeing that you swapped the plugs with a good cylinder, you're relatively certain that spark plug is good. Pull the plug wire off the plug, put a spare (or a good used plug) in the plug wire, and ground the base of the spark plug. Start the bike, and look for a repeating spark. This will tell you which way to go.

[GeorgeS]

I would try replaceing the plug with a new one, before ripping and tearing anything else.

 

I just put a new one in a CX-500 last week, it failed two days later, replaced again, runs fine !!

[dfwthompson]

Pete, I confirmed I have fire....checked air/fuel mix screws, all are 2.5 out. Guess it's fuel related. Never pulled the carbs on this one. Is there something I should do prior to cleaning the carbs? I think I'll pull the airbox and introduce #3 to a lil chemtool. Can you recommend a place for the carb kits? Thank you for all your help. I'll advise when problem is found and resolved.

[dfwthompson]

Tried that already George...no change.

[dfwthompson]

I'm wondering if I have covered all basis before removing carbs for cleaning.

What I've done so far: verified there is fire at #3, verified fuel in bowl and soaked and drained bowl several times with berryman's and staybil, removed air/fuel mix screw/spring/washer/o-ring, cleaned passage through PA1 and and that of PA2 with carb cleaner and re-set I/M screw at 2.5 turns out, all diaphragms replaced earlier this year, inspected tank to be very clean, fuel filter previously changed.

 

I still have a sluggish throttle, does not maintain higher rpms on repeated revs and #3 still has a much cooler exhaust temp at cyl. compared to the other 3 cylinders (very hot 2 touch). Is there anything else I can do prior to pulling carbs for cleaning?

 

Below is a list of parts replaced on a rebuild by mbrood. Is there anything else I should add? Thanks guys for all your HELP and advice!!

 

’86 VR carb parts list by mbrood

 

I know there are more parts that some might find needed... but here's the parts that went into mine.

 

4 22U-14147-00-00 O-ring (goes on the post under the jet block)

4 22U-14968-00-00 Cap, rubber, large (goes into the base of the jet block)

4 22V-14968-00-00 Cap, rubber, small (goes into the base of the jet block)

4 3JB-14199-00-00 Gasket (jet block gasket)

4 4G0-14142-37-A0 Pilot Jet, 37.5 (tiny idle gas jet inside jet block, MKI used a different size)

 

4 3LD-1490H-00-00 diaphragm set 5 (coasting enrighment valve, I suspect ethanol may have caused this to deteriorate)

[Peder_y2k]

At first blush, did you try enriching the idle mix by turning the pilot screw out some? On my machine that runs great, the pilot screws can all be turned in to the point the engine slows down due to the mix being lean, then turned out until it slows down again from being too rich. The 2-1/2 turns out is just a starting point.

-Pete, in Tacoma WA USA

[dfwthompson]

Thanks again Pete...#2 and #4 plugs at 2.5 out looked picture perfect where #1 and #3 looked a bit on the rich side. I'll adjust per advisement and let you know the outcome.

 

Thanks

john

[GeorgeS]

Maby I missed something, but are you sure that your Carb Linkage is " Synced" properly ??? Also, Does your " Pull " throttle cable, have some " Slack " before the mechanical linkage starts to move, ???

((( IF not, you need to do a RE-Sync !! )))

 

Have you carefully inspected, the Intake Manifold Rubber section for cracks, and leaks !! ( Intake leaks )

 

Have you done a " resistance check " of the Plug caps ??

 

Have you removed the plug wire from that cylinder, and nipped off 1/4 inch, then Re-Installed the 7MM

plug wire, At the Coil, and at the Plug cap ??

 

Possible a " sticking " float valve -- ??

 

Intake Air Leaks ??? Have you checked the intake manifold mounting bolts, ??? or

possible a Leaking O-Ring where the manifolds are bolted to the heads.

There have been reports, that even after replacing the O-Rings, still leaking, and adding a sealant to the O-Rings was required to stop the " Intake Leak " !!

 

Have you checked the Intake stacks on top of carbs, to make sure the Alignment , Marks, are in the proper position. ???

 

Are your sure the Clamps, Above, and Below the carbs, are makeing a tight Intake seal ??

 

Have you done a " compression Check " ???? If you find nothing else, well, maby you have a badly leaking valve , or stuck ring. Not likley, but a possibility .

 

Even if you are sure the Sync is OK, I would try, RE-Setting the Pull cable to 1/8 inch of free play.

Reset, the Master Idle to " Just makeing contact "

 

Reset all three Sync screws, to " Just makeing contact "

 

NOW, Re-Do the SYNC proceedure with your --- Morgan Carb Tune ---- tool ( you do have one don't you ??? )

 

Do a resistance check of All 4 plug caps, make sure they all are the Same, I think its 5000 ohms, main thing is that they are all Same !!

You can screw out the Copper fitting that the plug fits into, and Remove the Resistor, Spacer, and Spring. If you think you have a bad CAP. ( ie: you can dissasemble the plug caps, and inspect all the internal parts )

Also, after removeing the INERDS, Stick a rod up to the top, and do a resistance check thru the top of the plug cap. On a CX - 500 plug Cap, I found that the Wire in Top of the Cap, was OPEN CIRCUIT. !!

This is not repairable, and plug cap went into the trash can.

 

-- Note: the 5000 ohm caps, can be modified to make them " Non - Resistor " Caps. Simply remove the Resistor, and replace with a section of 1/8 diam. brass rod. --- (( you still have 5000 ohms inside of the spark plugs. ))

Edited November 5, 2013 by GeorgeS

[dfwthompson]

Thanks George...let me answer all your question as they appear in your response.

 

but are you sure that your Carb Linkage is " Synced" properly ???

carb linkage synced properly.....not sure of procedure or understand the verbiage "linkage synced" If referring to the slide adjuster...yes, it's properly adjusted

 

Does your " Pull " throttle cable, have some " Slack " before the mechanical linkage starts to move, ???

Yes, Pull throttle cable = 1/8" play

 

Have you carefully inspected, the Intake Manifold Rubber section for cracks, and leaks !! ( Intake leaks )

Yes, also sprayed starting fluid with no increase in rpm

 

Have you done a " resistance check " of the Plug caps ??

Yes, also swapped plug and cap with known working #1 cyl

 

Have you removed the plug wire from that cylinder, and nipped off 1/4 inch, then Re-Installed the 7MM

plug wire, At the Coil, and at the Plug cap ??

Yes, wire looked good and I left just a tab of wire protruding from the plug wire ensuring a better connection at coil and cap.

 

Possible a " sticking " float valve -- ??

Carb not flooding and fuel bowl is filling with fuel

 

Intake Air Leaks ??? Have you checked the intake manifold mounting bolts, ??? or

possible a Leaking O-Ring where the manifolds are bolted to the heads.

There have been reports, that even after replacing the O-Rings, still leaking, and adding a sealant to the O-Rings was required to stop the " Intake Leak " !!

Checked that with starter fluid with no increase in rpm...

 

Have you checked the Intake stacks on top of carbs, to make sure the Alignment , Marks, are in the proper position. ???

No...was not aware there were alignment marks. Please explain.

 

Are your sure the Clamps, Above, and Below the carbs, are makeing a tight Intake seal ??

Not sure now after just learning there are adjustment marks on the carb stack.

 

Have you done a " compression Check " ???? If you find nothing else, well, maby you have a badly leaking valve , or stuck ring. Not likley, but a possibility.

No compression check done yet.

 

Even if you are sure the Sync is OK, I would try, RE-Setting the Pull cable to 1/8 inch of free play.

Cable is good

 

Reset, the Master Idle to " Just makeing contact "

Reset all three Sync screws, to " Just makeing contact "

NOW, Re-Do the SYNC proceedure with your --- Morgan Carb Tune ---- tool ( you do have one don't you ??? )

No Morgan...just a SyncPro and will re-set master idle and 3 sync screws to just making contact.

 

Do a resistance check of All 4 plug caps, make sure they all are the Same, I think its 5000 ohms, main thing is that they are all Same !!

I swapped cap and plug from working #1 to #3. No change...

 

I played with the air/fuel mix settings per Pete last night and greatly improved the throttle response. I still don't understand why #3 is not getting as hot as the other cylinders. Thanks George...I'll re-set and re-sync and advise of outcome.

[dfwthompson]

George, In response to your question below....

 

Have you checked the Intake stacks on top of carbs, to make sure the Alignment , Marks, are in the proper position. ???

 

Yes, after careful inspection of the air box I visually verified the intake stacks to be properly aligned. Never noticed these marks before. Thanks for the heads-up!!

 

I'll re-set and re-sync tomorrow and advise. Thanks again for your help!