83 Royale rear cylinders twice as hot as front

[daveblaster3]

Rear plugs look totally clean. No tan, no black, just like brand new. Front plugs have dark tan to black and look rich to me. Spits black specs out of both sides of the exhaust. Bike stumbles a bit when accelerating from a stop, kind of smooths out if i stay light on the throttle. If i grab a handful it really stumbles then takes off like a raped ape. Front cylinder temp is a round 200 the rear is almost twice that. 380-385.

Im pulling out whats left of my hair on this sucker. Preignition maybe? Could the advance be bad? Have the hose hooked up to #1 venturi port. Carbs are synced. Sea foamed the crap out of it and replaced all diaphrams.

Stuck an aftermarket fuel filter and changed the long hose out. Maybe clogged petcock? Weak pump? Maybe im overthinking it... Can someone give me a shove in the right direction or at least a place to start? Check timing?  Carb disassemble? Thanks in advance...

[BlueSky]

Based on my experience tinkering with my Kawa ZN700, the exhaust temps close to the head should run in the 270 degree range when running right.  Higher than that would indicate a lean condition and lower might indicate those cylinders aren't firing properly for some reason, ignition or fuel.  

I would unscrew the plug caps and check the copper core wire on the end for green stuff indicating corrosion.  If so, snip a bit of wire off and reinstall.  Harder to do would be to check the other end of the wires.

I also would check the fuel level in the carbs.  If it is like my 89, it was easy to do by slipping a tygon tube over the drain tube while running, opening the drain valve and holding the tube up to see the level. 

 

There is also a method of carb cleaning without removing them that might be worth trying.  We call it the shotgun method.  Search and ye shall find.

Edited August 24, 2021 by BlueSky

[daveblaster3]

Thanks for the help...I did unscrew the plug caps and gave the resistors a little brush with sandpaper. I understand some folks replace them with old jets. I was wondering if welding rod would serve the same purpose. I might try that upon reassembly. I was also wondering about the choke circuit. Maybe one of those little guys is passing fuel thru. I will eyeball that as well. Then again it seems like its getting plenty of air and starving for fuel...I just cant seem to nail it down.

 

[saddlebum]

In the 2nd picture the two top plugs are running rich the bottom two are about right, though a tad more tan would not hurt. I doubt timing is an issue otherwise all four cylinders would be effected the same, since timing is controlled electronically and timing  advance is based on the signal sent to the ign unit by a vacuum sensor connected to the vacuum port on #1 cylinder ( though you may sometimes find it connected to #2 cylinder ). I would start by checking the fuel enrichment valves. They are small plungers which are on the outside of the carbs and controlled by  a forked lever which are manipulated by the choke lever. Make sure they are not stuck in the enrichment position they should move freely when you manipulate the choke lever.  Next I would check the diaphragms. Very simple task just remove the side covers from the carbs. 4 screws each. Carefully slide out diaphragm and barrel assembly. closely inspect the diaphragms for holes or tears and note if the barrels slide out smoothly or if they are sticky coming out. ( This is also a good time to give the carb and any accessible passages a good flush with carb cleaner )If the diaphragms  look fine carefully put them back in. On the needle end of the barrel there is a small hole make sure it is in the 6 o'clock position when you reinstall. If holes are found replace the diaphragms. Some have had luck patching tiny pin holes with silicone or E6000 glue.

( Last year I made a batch of homemade water proofing for my tents and camping gear consisting of a 50/50 mix of 100% pure clear silicone and mineral spirits as I was brushing it on my tent floor full of pin holes I began to wonder how it would work on diaphragms. Thought someday I May try it on an old set put it in the bike and see how well it works ) 

Moving on. I would also check the fuel levels as mentioned earlier, though unless a float has gone bad or someone has tampered with it I am inclined to think you may not find an issue here. If it is a sticky needle valve not seating properly you generally get fuel coming out of the overflow tubes at idle. If you do find the float levels out of adjustment  you will have to remove the carbs to adjust them.

While you have them off you could overhaul them or at the very least remove inspect and clean the enrichment valves, making sure they move freely. You will need new mounting gaskets and seals for these. Remove and replace the needles and seats. While you have these parts off flush all accessible passage with carb cleaner, let soak and then blow out with air. As you reassemble everything, don forget to bench set your float levels. I like to bench set them wet this allows me to ensure there are no leaks before putting them on the bike. ( I will attach a PDF of the set up I rigged up though there are other ways of doing it ) ( i believe there is a dry set up method shown in the tech section as well). Either way you will want to recheck once it is back on the bike and running.

Cleaning First Gen Carbs On The Bike.pdf Home made set up for wet setting floats on the bench.pdf

Edited August 25, 2021 by saddlebum

[daveblaster3]

Thank you for your priceless wisdom. I did remove the carbs and completely disassemble them. The rebuild kit i got did not have enricher block gaskets and i think 1 or 2 may be creating a giant vacuum leak. So I will order 4 in the near future. The kit had idle jets and mix screws so i replaced all that with new but it did not come with emulsion tubes or a small enough main jet. 150 I believe was the smallest so I reused  the 117.5.  The diaphragms were relatively new but Im considering installing the ones that came with the kit. The needle was also of a different design so I stuck with the old one. I did replace its seat so im wondering if thats part of my new crappy running bike. Pops, sputters and God forbid i forget to open the garage door fully or my eyes start burning and my Carbon Monoxide detector starts screaming. Obviously first rebuild attempt was a fail. I bent a float bowl tang so that was exciting watching fuel spew out of the carb the wrong direction. I will get some clear tubing to test the actual levels. I did replace all boots and wires and it seems to be firing like its supposed to. Resistance measures low though, could that be a potential issue? I cleaned the plugs and reused them as they are a couple weeks old.

Again I appreciate your input. 

David J

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