Is it carb or ignition or could timing have jumped.

[Bud Wilkinson]

Apologies for the longish post but I wanted to include as much information as possible.
So I picked up a nice, unmolested looking 1987 FJ1200. K&N air filter and Yoshi pipes looks to be the only upgrades done. Had the 85 FJ1100 years ago, got this cause I love em so much.
She has a problem I'd like to run by the guy's that have been doing them the longest. Bike has run 50 - 100 miles in the last 2 years. When checking out the bike it ran but there was a definite miss. When ridding a short test it seemed to just fall on it's face when accelerating and hit a low 4000 RPM limit or plataue. Fuel tank looks great inside. I found cyls #3 and #4 header pipes noticeably cooler than #1 and #2 by applying moisture (spit) to each one. I knew it would need work and took the risk of bigger engine issues anyway. Here's what I've done so far.
Troubleshooting:
Cold dry compression test showed; 1 = 145, 2 = 145, 3 = 150, 4 = 142. Swapped the plugs 1,2,3,4 to 4,3,2,1 to eliminate a spark plug problem with no punning or performance change.
Spark is present at all 4 wires using a spark testing tool but visually is weaker than I'd have expected. Subjective opinion I know.
Some popping back on #3 and #4 with the air box off when running. All slides seem to move in unison.
Spray carb cleaner lightly at #3 and #4 and she seems to like it for a very short test time and got temp on #3 and #4 header pipes.
No RPM change when spraying carb insulator boots with carb cleaner.
Feeling lucky so far, thinking probably a carb issue. Something I have a lot of past experience with.
Repair Attempt:
Took carbs off and apart and, to my surprise, they look awesome clean inside. Evidence is definitely present that someone has been here before though and I'm not surprised. But then again the whole bike looks very clean as it should for a 28K mile unit. All the gaskets, diaphragms and o rings were all live and flexible. Only a little corrosion buildup below the screens on the float seat inlet side around the o rings. The needle sealing surface looked great too. All the equipment inside, without gauging every jet, is box stock by markings. The slide needles are the stock 1 slot units with no shimming washers under them. I did the whole cleaning job as I normally would and following the carb_cleaning.pdf found here along with the illustrated guide here.
The only obvious problem I found in the process was the float height was way more than 21.3 - 24.3mm spec. Like 27-28mm also leaving a very small float open droop of around 2 mm. In my experience this is not a good combination. The floats don't feel heavy, granted I haven't had them in my hand for over 25 years, or show any real damage. Thinking I may have found the problem with float height, I set the float height at 22.5mm to pick a number without compressing the needle spring and did my best to make sure they were even on both sides and had free movement without the bowl on. When I started the engine, it seemed to run better for a few seconds, until they all 4 started dripping from the choke air inlets once they got the bowls full. so I disconnected the vacuum line to the petcock to try to determine if it would be better than before. It never did run right and #3 -#4 were still noticeably cooler header pipes. I have, on the bench now, progressively adjusted the float height and filled the bowls till I'm back to 25.5mm and now only one drips at this point. I was also using the clear vinyl hose on the bowl drain to try and get a sense of where the fuel level actually was. Oddly enough the one dripping through the choke air inlet appears far below the bowl / body junction line while others are very close. It has never been my experience with any carb to be that far off of the specified float height and work well if at all. I have ordered floats and needle and seats to eliminate those components as well as the o rings.

The backfiring or popping, the cooler #3-#4 header pipes as well as the engine falling on it's face when test riding, has me a bit concerned though and questioning if there could be an ignition or cam timing problem. I didn't ride it far, under a mile, when I was checking it out and have limited it's running time when troubleshooting and when fuel started running out of the carbs. I am waiting for a good manual I ordered to show up to help outline procedures for cam timing check and ignition related troubleshooting too. Spark plugs, oil and filter and a proper 4 cyl carb sync tool are on the way too so I don't have to use my old Uni-Syn for this bike.
Any insight you guys can forward will be very valuable. I can't wait to ride her running properly.
TIA
Bud

[big r]

Have you talked to any one at RPM. They are the go to guys and although I haven't used them those that have are more than pleased with the results. I saw in another post that they charge $168 for a carb rebuild. Father Pat may chime with some ideas

[FJ_Hooligan]

Everything you describe screams dirty idle circuit to me.

Cold header pipes and spitting/popping.  Classic lean idle circuit symptom

[Flynt]

The backfiring or popping, the cooler #3-#4 header pipes...

As David said, you're probably running lean... carb issues or possibly a some vacuum leaks (although the spray test should have revealed a leak).  It's a well documented bitch to get your carbs free of the orifice shrinking "varnish" that evaporating fuel leaves behind.  I also had substantial carb experience before taking the carbs from my first FJ to RPM.  I cleaned them alongside Randy and realized how difficult it would have been for me to achieve the same results...  If I were you I'd go back to the carbs and make sure they are 100% clean, working as designed, and balanced properly before concluding it's not fuel.  I'd also recommend adjusting the valves before balancing the carbs...

As point of reference, my '89 was behaving very similar to what you describe although not as bad.  It was scariest when you went to roll on coming out af a tight corner and the engine hesitated.  After a couple hours at RPM, I needed to add a second clutch spring to keep the clutch from slipping badly at about 6K...  no more hesitation is an understatement!

Frank

[FJ_Hooligan]

Ignitions either work or they don't.  Nothing in between. Or, they work for a while then heat up and stop working.

Cams don't just "jump timing" unless something is drastically wrong with the cam chain.  It would have to be stretched enough that it would be slapping everything in the crank case.

Here's a long shot repair attempt that you can try with the carbs still installed.  Remove the idle mixture screw, spring, washer and o-ring.  Make sure you have ALL 4 components.  Next spray carb cleaner into the mixture screw hole.  Most of the spray will probably go directly into the intake.  Some of it might blow back through the idle circuit and wash out whatever obstruction you have.

Nothing guaranteed, just a long shot.  You did remove the idle mixture screws when you went through them before?

[Scottie1]

I had exactly the same problem with 2 pipes not getting hot. I was the carbs were full of crap and after RPM rebuilt and cleaned it runs perfectly now.

[Bud Wilkinson]

I get the feeling from the much appreciated comments, that the carbs are perhaps a bit more finicky than other multi Mikini setups I've dealt with. I never had this kind of trouble with my FJ1100. They just worked.

big r
I have not talked to RPM yet but will be ordering some stuff from their extensive list soon. Great opportunity to have a chat with them.

FJ_Hooligan
Ignitions work or not, or work and fail with heat - Copy that.
Jumped Cam Timing is unlikely, No real noise from the engine - Copy that.
Won't likely need the long shot repair in this case. It's getting completely torn down again.
Yes. I removed everything that would come out of the aluminum body without force. Including separating the assemblies and removing the choke plungers. I'll be doing it again and let the cleaner soak in the orifices a bit longer before blowing them out too. The only thing that didn't get removed aside from the machining block off balls was the one very small, press fit looking orifice on the right side of the air horn across from the pilot air jet. All 4 of those visually passed the same amount of carb spray cleaner and blown air as best as I could tell. I don't see them labeled in the "Illustrated Carburetor Guide" anywhere but I cleaned the heck out of them too.

Flynt
I will investigate a vacuum leaks again when I get the carbs done but initial indications were that the problem lies elsewhere.
Due to my compression test results, I'll do my best to get the carbs straightened out so she at least runs without a big 2 hole miss and balance them before I do the valves. I don't mind doing a re-balance if need be after a valve adjustment.
Mine isn't currently even running in a state that I want to ride it in down the block. Sounds like the carbs were the magic wand for you and many others. Hope my clutch will last the summer.

The confusing part and reason for asking about Cam timing and ignition system is with the carbs flooding at a height setting of up to 23.5mm and having "lean" popping. I only got them to 25.5mm on the bench and had one still dripping before I just ordered the floats, needles and seats. I won't know till they show up if the carbs will stop flooding at 22mm float height on the bench. In the meantime I'm going to do the complete disassemble and clean again paying particular attention to the suspect idle circuits in all carbs. I have the Motion Pro manometer and a remote tank setup and all the necessary skills for tuning and will be making sure the float bowls act properly on the bench before I even try to go any farther.
Thanks All for your input.

[Pat Conlon]

Pay particular attention to your float needle seat O rings.

[Bud Wilkinson]

Pay particular attention to your float needle seat O rings.

Well after looking those over again, it seems while they are live and flexible, there isn't much resistance if any on a couple between the o-ring and the carb body. Cleaning the carb well there too will help.

[Pat Conlon]

Pay particular attention to your float needle seat O rings.

Well after looking those over again, it seems while they are live and flexible, there isn't much resistance if any on a couple between the o-ring and the carb body. Cleaning the carb well there too will help.

If you have not changed them...go ahead and change them.
You should feel a tiny bit of resistance, a tiny bit, when you carefully slide float needle seats back on the carb body. The resistance comes from the new o ring sliding on the wall of the port.
If the float needle seats come off and go back on with no resistance, that would worry me.

[Bud Wilkinson]

Pay particular attention to your float needle seat O rings.

Well after looking those over again, it seems while they are live and flexible, there isn't much resistance if any on a couple between the o-ring and the carb body. Cleaning the carb well there too will help.

If you have not changed them...go ahead and change them.
You should feel a tiny bit of resistance, a tiny bit, when you carefully slide float needle seats back on the carb body. The resistance comes from the new o ring sliding on the wall of the port.
If the float needle seats come off and go back on with no resistance, that would worry me.

Ok, ordered the wrong seats. 1.5 not 2.3 for gravity feed. Used the new O-rings and needles.
Found the floats to be particularly finicky to stop them contacting the upper carb body protrusion when pushed slightly in one direction.
Sorted that all out, she fired right up and after syncing and setting the mixture screws, she just purrs till you twist on the throttle, then she screams.
Thanks for all the support here.

[Pat Conlon]

Success