Carb Problem?

[Donvito]

I am a new member and would like to thank everyone for all the great information provided.

I have an 87 with about 47k miles that I purchased new. Although, I am not a mechanic, I have always done all maintenance on the bike except for a valve adjustment done at 30k. The only repair it ever needed was a starter gear train replacement that I did myself.

A couple of months ago, after sitting for a couple of months, the bike would only run with the choke on. Relying on info from the forums, I tried the Seafoam treatment with no luck so I removed and cleaned the carbs. After this, the bike runs without the choke but cylinder #4 won’t run. So far I have synced the carbs, changed the air and fuel filters, changed the spark plugs and switched cylinder 2 and 4 plugs, measured the carb fuel level, checked for vacuum leaks as best I could, tried adjusting the idle mixture screw and removed the carb vent hose. I have also switched the diaphragm and slide assembly between #3 and 4 carbs with no change. (I don’t know if this is recommended but I wanted to try it before buying a diaphragm)

The cylinder will run if carb cleaner is sprayed directly into the carburetor.

I am not completely sure this problem didn’t exist prior to working on the carbs. So, I am looking for other tests or possible fixes I can try. If I have to remove and disassemble the carbs again, where should I focus my attention?

The bike has been trouble free for 22 years so I don’t have much experience in these matters. Thanks for any help provided.

[GeorgeS]

How long since you replaced " All " the plugs ?

 

I would suspect the Plug wire itself, remove from Plug Cap, and Ing Coil, trim the wire ends and re-install, ( this is easy to do ) ( after you remove the air cleaner box ) .

 

The idle mix, adjust screws, should all be set to 2 1/4 turns open, then minor adjustments from that point.

 

Possibley the " Throttle Plate " of the #4 Carb, is Sticking, Lubricate the rod that the plate rotates on. ( use a WD-40, then a light lubricant )

 

Has the Fuel Filter, ever been changed ???

 

Has the Gas Tank ever been completly Drained ??? If not, highly reccomended !!

Simply drain at petcock, and start with all new gas. ( might be water in bottom of tank !! )

 

Possibly a bad Spark Plug Cap. Remove, all 4 and measure the Resistance across all of them. should all be about the same.

 

Then, its possible that the Ignition Coil is going bad !! Check the Small 2 wire plug going to the Ing Coil, Clean it, and measure the resistance thru the Primary winding, it should be "" 3.8 Ohms " thru the winding. I reccomend, comparing this Resistance reading on all 4 coils.

But even if that is good, the coil could be failing. However the Coils on the 1st Gens, rarley fail.

You might try Swapping Coils between Cylinders, to see if the problem follows.

 

If you still don't have success, I guess I would do a compression check, next. Make sure good compression in that cylinder.

 

 

Another item: PickUp Coils, Loacted under the Stator, The 5 wire cable from pick up coils, going to the 6 pin plug of the TCI. About half way, enroute, located under your left knee as you sit on the bike, Find the plug, open it, and Clean it. checl for loose wires on both sides of that Plug. The signal from pickup coil to fire each cylinder, go thru that plug. ( This is a Very Common Trouble Spot !! )

 

Pull Both Plugs out of the TCI UNIT, and Clean the PINS!!! Apply Dialectric Greese to the Pins !! Or If nothing else, clean pins, with WD-40 .

 

Another item: The Run Stop Switch, has caused a lot of Ignition problems, I don't think this is your problem, BUT CLEAN THAT SWITCH ANYWAY !!

 

??? I guess your on a Witch Hunt, hope some of these suggestions help, good luck

[wes0778]

This may be a totally off the wall thought, but somewhere on here I think:confused24: I have read these V4s won't run right with the air box off. If you are able to spray cleaner in the #4 carb you must have the box off. Try putting it on and see how it runs.

[Squeeze]

Well, George covered pretty much everything which can be a Culprit.

 

I'd check the Jets on the "missing" Carb. PAJ#1( in the Carb Throat) and PAJ#1 (behind the Diaphragm) are the same Dimension and it's easy to interchange them. No need to ask how i think of that first. The smaller Number(75 to 95) should go into the Carb Throat and the bigger Number (170 or 180) should be located behind the Diaphragm.

 

When this checks out, i'd concentrate in the Idle Circuits of the Carb as a next Step. http://www.vmaxoutlaw.com/tech/cleaning_pilot_jets.htm

[Donvito]

Thanks for the advice. I have changed all the plugs and the fuel filter. When I remove the spark plug wire from #4, insert another plug and run the bike I do get a spark (and a shock) Should I try switching the spark plug wires between #2 and 4? As far as measuring resistance I'm not sure what that means but will try the other suggestions.

 

The air box is back on the bike with the filter installed.

 

Thanks.

[Squeeze]

Since the missing Cylinders fries with the Help of something flammable, i'd concentrate on the Fuel/Mixture Side. If the Ignition would be the main Culprit, spraying Carb Cleaner into the Carb wouldn't help firing the Cylinder.

Edited June 28, 2009 by Squeeze
Lots of Typos

[steve crossley]

if you are spraying in to cylnder and it runs while you do that means it has spark . that says your not getting fuel . check drain screw on carb to see if it has fuel . if not you most likley have a stuck float on that carb . chances are good if others are running that is the first place to start.even if you cleaned carbs.

[Donvito]

Thanks. Checked the fuel level and compared to #3 carb and levels are the same.

 

Just to eliminate the ignition system, is there a way to test the voltage at the spark plug? Could it be a weak spark? What is the proper voltage?

 

Before removing the carbs, is there anything else I should check? Should I do a compression test or is it unnecessary because the cylinder fires with carb cleaner?

 

Thanks for your help.

[steve crossley]

still sounds like no fuel. if it was no spark the cyl. would not fire at all . if you are getting fuel to carb and is not fireing you have a fuel jet pluged . to find out if you are getting fuel to carb open drain screw to dead cyl . turn key to run and kill switch to run. you should have fuelpumping out out drain hose and hear the fuel pump pulsing. if nothing start engine and watch for flow. its good to hook a clear fuel line to drain hose and to a container to keep fuel off bike. if you take carbs off use a small wire to clean all jet holes with compresed air and carb body also . check fuel output on feed hose to that carb. check needle float assy. make shure not stuck. check inlet on carb (where feed hose goes. dont give up . let me know what happens.

[GeorgeS]

Back up to the TCI. Pull the Two Large Plugs from TCI, and Clean the Pins.

 

Find the plug enroute between PickUp Coils, and Clean the Pins.

 

Also, You might have to " remove " the TCI, and then remove its cover, put the Unit into an Oven set at about 110 Deg. F, for about 2 hours, to DRY OUT the

" Moisture inside the Unit " ( I know that sounds crazy, but this is a very common problem on these TCI units. They collect Moisture, and this causes them to fail )

 

NOTE: These units have 4 seperate circuits on the ONE Circuit board inside the unit. Any one of these 4 can fail, and the other three still continue to function normally. ( thus takeing out one cylinder )

 

Almost everybody who is still running a 1st gen bike has done this proceedure.

 

Too remove the TCI you almost have to remove the Air cleaner box, and the Battery box to get access. The 4 #3 Allen Head Screws are NOT easy to remove. Be sure to use a #3 APEX TIP in a 1/4 Socket, mounted on a 1/4 ratchet to be able to get enough TORQUE to break those screws loose. ( they are usually very tight. )

 

 

To take resistance readings, you need to buy a " Digital Volt/Ohm meter " Go to radio shack, cost about $50.00 for a decent one. ( forget the $15.00 units they are junk !! )

[mbrood]

The first thing that hit me was the idea... "it ran ok before I..."

 

There's a few things in a carb overhaul that can cause problems. Did you make sure the fuel jets in the jet body got their respective rubber plugs? (three holes, two plugs...) Did you insure the small o-ring was in place between the diaphragm cover and carb body? Did you insure the idle mixture screw below that cover was basically set to 2 1/4 turns out from a "soft" bottoming?.

 

If the float bowl fuel levels are right and spraying something down the throat gets her to fire... something is halting or resricting gas flow. On a running engine, you can usually put your palm over the carb opening, creating a vacuum, and get your hand "gas wet" from the suction... but first I would simply pull that spark plug. If it's dry, it's back to checking INSIDE that carb. If it's wet, it may be simply (?) flooded... leave the plug out for a couple hours to dry out the cylinder and give her a second try.

 

Things to look for on disassembly, is the gasket under the jet block cracked and leaking, are the jets in their "respective" holes, are the rubber plugs correctly seated.

[Donvito]

I attached a hose to the carb drain hose, opened the drain screw and started the bike and I have good fuel flow. Also checked the fuel level again and it is good.

 

Adjusted all idle mixture screws to 2 1/4 turns out.

 

Removed the air box, started the bike and placed my hand over #4 carb opening which caused the cylinder to run. It will continue to run as long as I keep my hand over the opening and restrict the air flow. What would cause that?

 

Getting ready to remove the TCI if you still think I should.

[mbrood]

You were restricting airflow, causing more vacuum that sucked fuel in... my first guess would be it's getting too much air... look for an air leak... probably a bad seat above or below the carb on the rubber intake manifold. spray some carb cleaner at the rubber joints while she's running... if the rpm changes, you found the problem.

 

You can hook up a "spare TCI" on the cables and let it "dangle" on the side... but if you are getting spark, I wouldn't bother. You know it fires if you change the air/fuel mix... (resticted intake).

[Venturous Randy]

Worked on a friend's 89 looking for a problem with dead cylinder and it ended up being a corroded resistor in the spark plug cap. It would fire some thru a hand held plug, but not under pressure.

Take that cap apart and look at the resistor. Go up inside where the plug connects and you can unscrew the inside and the resistor will come out.

RandyA

[steve crossley]

sounds like an air leak . yep ! if you cant find one you still might have to check carb. pull manifold off and eye ball it good.

[Squeeze]

You were restricting airflow, causing more vacuum that sucked fuel in... my first guess would be it's getting too much air... look for an air leak... probably a bad seat above or below the carb on the rubber intake manifold. spray some carb cleaner at the rubber joints while she's running... if the rpm changes, you found the problem.

 

You can hook up a "spare TCI" on the cables and let it "dangle" on the side... but if you are getting spark, I wouldn't bother. You know it fires if you change the air/fuel mix... (resticted intake).

 

What Mike said !!

 

Either Air/Vacuum Leak somewhere, or the Fuel Jets are mostly clogged.

[Donvito]

Thanks. Couldn't find an air leak and vacuum on 3 and 4 are the same so I assumed the problem is in the carb so I pulled them off. Rubber intake boot looks real good. Posting pics of the boot and top and bottom of carb #4.

 

Gonna try to separate the left and right banks. Couldn't loosen the screws last time so if you have any suggestions I would appreciate it.

 

Should I replace the upper and lower clamps while I have them off and where can I find them? Checked auto parts and hardware stores last time but they only carried hose clamps.

 

Will post again when I have something to report and let me know what pictures to post. Thanks for all you help.