Carb Rebuild Results

I finally found time to get my carbs back on my bike after a full rebuild. I flipped the petcock to prime to fill the bowls and then flipped it back to on. The bike started right up with a little bit of choke. It sounded fine but died after a few minutes of idling and wouldn't start back. I thought I might have some bubbles in the fuel filter so I turned it back to prime and saw gas flow. It started right back up but when I tried to blip the throttle, it would die. It was at that point that I remembered that I forgot to plug the vacuum line back into the petcock. That's why it died and didn't like when I blipped the throttle. After plugging that back in, it idled great and sounded awesome. I can't express how happy I am that things worked out so good. My setup of the carbs must be really close cause it starts right up and runs good. Now, to do the colortune and running synch to get things exact.

 

Congratulations. Sounds like you did it right. As far as using the colortune plug I suggest that you close each pilot screw until you get the white flame--lean setting-- and then open it until you get the blue flame. Then install new plugs and ride for 15-20 miles and read the plugs. As needed open the pilot screw about the width of a dime or less and ride and check again. Repeat until you get a nice tan color on the plugs. Starting from an almost lean setting with new plugs makes it real easy to read the plugs. I have a XJ700N and my pilot screws are open between 1 1/2 and 2 and the plugs look great, the bike starts easily, runs well, and the mpg is about 43 on the highway.

 

Will do...thanks.

 

Ok, I'm officially frustrated...sorry for the long post. For the past 3 days I've been trying to get my bike dialed in after a complete carb rebuild. I went to Church and replaced everything using a complete deluxe rebuild kit from Chacal. I am 100% certain things were spotless and all holes were probed and carb cleaner sprayed through them and that was after soaking overnight in Berryman's. After getting the carbs put back in and with the mixture screws at 2.5 turns out, the bike started and seemed to run good. I got my colortune plug out and tried to use it. It didn't really work good. I never get a white flame or at least I can't tell the difference from a blue flame and white. When I screw the mixture screw in all the way, I get no flame, just the spark from the colortune plug. When I start backing it out, the first flame I see is blue. When I keep going, it becomes a stronger flame but doesn't seem to change colors till it turns orange. I guessed with the colortune by adjusting the screws till the flame looked the brightest and still in the blue color. That put me at about 3.5 turns out for #1, and about 2.75 turns out on the others. I did my running synch and got that right. My first ride after doing all of that was great. It pulls strong, scary strong from 6000 rpms all the way up to 9500 rpms which is as high as I took it. It never did that before rebuilding the carbs. Anyway, I rode about 25 miles and then checked the plugs. #1 was white with almost no color at all, #2 was totally black, #3 and #4 were just a little darker than tan. So, I adjusted the #1 mixture screw out 1/2 turn, #2 in 1/2 turn, #3 and #4 in 1/8 turn. I cleaned the plugs with carb cleaner and a brush, let them dry and put them back in(yes, they all went back in the same hole they came out of). Another run of about 25 miles and I checked the plugs. They all looked about the same so I made the same adjustments that I did the day before, cleaned the plugs again and put them back in. Another run and checked the plugs. They looked about the same so same adjustments and cleaned the plugs and put them back in. Next run and checked the plugs. #1 and #2 still looked the same but now #3 and #4 were black. WTH! I've been making #3 and #4 leaner by screwing in the mixture screw slightly and now they flip to rich! And, #1 is still white and clean at 5 turns out and #2 is still black at only 1.25 turns out! I decided to start over at 2.5 turns but to make sure that things were ok, I took the #1 and #2 mixture screw out(I left the spring, washer and o-ring in there) and sprayed carb cleaner down the hole using the straw. I forced it to all go through the pilot mixture hole. I then replaced the mixture screws and screwed them all the way down and back out to 2.5 turns. I did a running synch again after doing that. After several more runs and adjustments, #1 is looking better but I think it's about 3.25 turns out. #2 is still black on the ground strap but half the insulator is a dark tan and the other half is black. I would guess that I'm about at 1.75 or 2 turns on that one. #3 is looking really good now. #4 is still a little dark but it's getting better. Anyway, I know the carbs are clean and all passages are open and everything is put back together correctly. I'm running an inline filter from Chacal and even ran my gas through that filter when doing my wet set of the fuel levels (which I double checked after moving the carbs and re-leveling them just to make sure). Why are my mixture screws not acting like they should? Why would #1 still be lean looking even at 3.25 turns out? Why would #2 be so rich looking at only 1.75 or 2 turns out and have half of the insulator tan and the other half black? Why did #3 and #4 flip from being close to right to black when I was slightly screwing the mixture screw in which should be making it lean?

 

mixture screw then spring then flat washer o ring last?
the mixture screw only adjusts the idle circuit .
plug chops should be done on the road to test at rpms for each circuit.

do a sync then color tune then sync then color tune....untill you are happy with the results
when you find blue and orange you turn screw 1/2 way back to orange from blue

what are you running for an air filter?

 

Yes, I took particular note of that order when doing my reading from the church of clean.

I'm not happy with the color tune process at all. I never get a white flame. I have a blue flame from probably 1 turn out all the way to 3.5 or 4 turns when it turns orange. That's a huge range and seems useless to me. Maybe I don't understand the procedure exactly.

Can you clarify what you mean by this...maybe word it a different way? I'm not sure I follow what you mean.

Stock airbox and stock filter which appears to be pretty clean (can easily see light through it when held up to any light source).
Thanks for the response.

 

your color tune manual states to set mixture screw 1/2 way back to orange from blue.
find orange turn back untill blue then set half way back to orange.

 

My color tune didn't come with a manual. Maybe that was something important that I should have had. If I follow that though, I'll end up with my mixture screws around 3 or 4 turns out. That doesn't seem right when the factory recommended starting point is 2.5. My carbs have all stock jets and everything was in clean working order when I finished the carbs. Why would it take so many turns of the mixture screws to get it where it needs to be?

 

you must turn very slowly let it balance out then adjust again , as suggested above a dimes width you have to let the motor catch up to the turning

you can also us it to check main jets , I will photo mine and post it up tomorrow for you

 

Thanks, that would be interesting to see.

 

Ok, after reading the color tune instructions that I downloaded from their site, I decided to try it again. I wish I could say that it went better but it didn't. I still feel the same as I did before...color tuning just doesn't work...at least not for me and not on my bike. I warmed the bike up and put my YICS tool in. I then did a running sych since the color tune instructions say to do the synch first. That worked great just like it's supposed to. Then, I started with cylinder #4 with the color tune. Started the bike up and I could see the spark of the color tune plug but no flame unless I rev the engine. So I started screwing out the mixture screw...no change. I can't get any flame in that cylinder unless I rev the engine. So, I switched to the #3 cylinder. With the color tune plug in the #3 cylinder, the bike wouldn't even idle. I had to turn the idle screw way up just so it wouldn't die. I could see flame though so I tried adjusting the mixture screw. I screwed the mixture screw in all the way and the flame was still blue. I unscrewed it and the flame didn't change till about 5 or 6 turns out and then turned more orange. That just can't be right. I pulled the YICS tool out and the mixture screws don't seem to affect the color of the flame at all. I can screw them all the way in or all the way out and the color of the flame doesn't really change much. I'm so sick of this thing now. I just spent over $400 on parts and tools to rebuild the carbs and followed the guides to the letter and now I have a bike that the mixture screws don't seem to really do anything or work like they're supposed to. It's obviously not tuned right and doesn't seem to follow how things are supposed to work. The gas mileage is the same as it was before doing the carbs, about 30 to 35 mpg. Sure there's much more power above 6000 rpm but that sure isn't worth $400 to me. I don't know what else to do to it. Color tuning don't work and trying to tune it by the plug colors seems to be hit or miss, especially when the mixture screws don't seem to have much effect. Does anybody do exorcisms on carbs? I think that's the only thing that will help. I'm going to take a break from it and try to come back although I have no idea what to try next. Any suggestions?

 

What tool are you using to do your synch? I use a 4 vacuum gauge set up with restrictors .My carbs on 750 all read 5hg . You should have about even if the carbs are not truly synched it will be hard to get right with the color tune. I have to ask have you adjusted valves?

 

Good question from Jetfixer on the valves. They must be right before attempting to adjust the carbs.

I had a lot of issues trying to use the color tune also. My symptoms were different though, in that I had trouble achieving a rich condition. Most notably was the poor idle when installing the color tune after running just a minute or two. I had two issues that were causing problems.

The main one was the external tank that I was using just wasn't flowing gas correctly (not sure why), but I had to keep tapping on the carbs (brand new float needle valves from Len), and wiggling the fuel hose to keep the carb bowl fuel levels at the proper height. Try checking the wet set on the bike to make sure gas is flowing and keeping the fuel level where it should be. The bike should be reasonably level on the center stand from side to side to do this, and as for leveling front to back just make sure you place the clear hose in the center of the carb bowl drain, this should match the 3mm mark from your bench setup.

Make sure the base of the head is very clean where the spark plugs mount. The color tune is just hand tightened using the supplied copper washer, so any crud could potentially allow air to be sucked in through the plug hole.

Doing the color tune near dusk helped also. My old eyes are not what they used to be, and the color was much easier to see in the darker environment.

#2 could be rich from the choke circuit. Make sure the tang on the choke rod has moved far enough to let the choke plunger totally seat. Try pushing down on the plunger just to be sure it is fully seated. Corrosion can also be a factor where the choke brass plunger seats in the aluminum carb. You may need to inspect the plungers for dings and the carb body for pitting at the seat.

 

I adjusted the valves about 1500 or 2000 miles ago (just checked my notebook it was only 1000 miles ago) and did a random check of a couple while I was replacing the rubber donuts on the valve cover bolts about a month or so ago. They were still the same according to my notes. To do my running synch, I use a digital 2-port tool called the Harmonizer. My carbs all read right at 8 inHg.

 

Valves were adjusted 1000 miles ago.

I had all sorts of issues with the color tune. It seems to work somewhat on some cylinders and not at all on others. I always see a spark from the color tune plug but sometimes see no flame from the cylinder unless I rev the engine. Sometimes there's always a little bit of orange with the blue flame and sometimes I can't get any orange at all. I'm using the fuel tank from the bike just with a little longer fuel hose and set to prime. The longer hose I'm using is clear and it seems to flow fine. The base of the head where the spark plug mounts appears to be pretty clean. I was doing this last attempt last night at 1am in my garage. The only light I had on was a flashlight in my hand so I could see the mixture screw as I adjusted it. I will check the wet set with the carbs on the bike although, like you mentioned, with the carbs as angled as they are front to back, I'm not sure how accurate it would be. Where along the side of the carb would the 3mm measurement be right when the carbs are leaning so far forward? Who knows...but I guess it should be somewhere in the ballpark and show me if I have a major problem.

I did a full break of the rack and cleaned the choke plungers when I did my carb rebuild. They all looked great and the seats appeared fine to me. I've also pushed down on the plungers and the choke fingers to make sure it's totally seated and off. That doesn't necessarily mean the plungers are seating properly but I'm not sure there's a 100% way to verify that. That's what's so frustrating about this. Everything appears to be clean, in good condition, and setup right but certainly acts like it's not. By the way, the rubber boots on the engine side are basically brand new and looked great inside and out when I had the carbs off. The PO told me that they were replaced and the carbs gone through shortly before I bought it from him. When I did the carb rebuild, I could tell somebody had been through them not only because jets were installed wrong and fuel levels were wrong but also because the carbs were really clean...no stains, gunk, or anything. Of course they still got totally disassembled, soaked in carb cleaner, all openings probed with wires, and then carb spray shot through each opening to make sure they were clear. And, of course, I put the jets back where they go with the help of people and information on this forum.

 

I re-checked the fuel levels with the carbs on the bike. On centerstand and level side to side but of course not front to back...that would require removing the rear wheel and jacking up the front quite a ways. I checked the level right about the Hitachi symbol on the side of the carb, actually just slightly in front of it. All three were dead on 3mm.

 

So, just to reference one of your earlier threads where you found jets swapped. Hopefully some carb guru's can get you sorted out.

http://www.xjbikes.com/forums/threads/main-air-jet-question.91618/#post-517536

From that thread it seems you would have all the jets properly placed.

So, with the color tune indicating mostly blue, and unable to obtain white that should indicate a rich mixture. However, it sounds like the plug color for number 1 is contradicting that, which may be because the plug chop method is a bit of a science in itself - certain RPM, cut throttle, and then read plug.

Maybe you are the victim of the PO, and even though the jets are numbered correctly there is always the possibility a drill has been used either to clean or purposely enlarge. Either way if the stock 40 pilot fuel jet has been enlarged then you may not ever get to the white (lean) flame or notice much change in color during adjustment.

Also, if number one is as lean as you described that should cause some popping on deceleration. Did you have any of that? A picture of the plugs might help.

 

I agree that anything is possible. I did have to buy one new #40 pilot fuel jet from Chacal because one was really gouged up and I had to use vice-grips to get it out. I used cleaning wires I got from Chacal to gently probe the jets and holes in the carbs. It seemed that the jets were similar sized between carbs just judging from the size wire I used to probe them. As far as the color tune, sometimes I'm able to make the blue flame go away by screwing in the mixture screw and sometimes I'm not. Things seem to change every time I try the color tune. The first time I did it, I couldn't get any flame at all until I opened the mixture screw to 5 or 6 turns out but the others worked fine except not getting a white color, only blue and orange. Last night when I tried it, I couldn't get a flame from #4 unless I revved the throttle. That doesn't make any sense to me at all. As far as reading the plug color, last year or was it the year before even with the wrong jets in the carbs, I was able to tune them using the mixture screws and watching the plug color. I got them looking really nice. I realize that doing plug chops at various rpms is the exact way to do it but I think I should be able to use the plug color just to get an overall tuning like I did before. Right now I'm getting one plug white, one plug black, one plug good, and one plug good but probably a little rich. Just all over the place. Maybe I should just put them all at 2.5 turns, do a synch and leave them that way. Concerning popping, I was getting some popping when trying to do the color tune the first time when working with #1. It doesn't pop when riding though.

 

Any more suggestions? I don't really know what to do next. Right now carb #1 mixture screw is at 3.5 turns out and the plug still looks lean and #2 is at 1.5 turns out and still looks rich. It seemed to start easier when I first put the carbs back on with all at 2.5 turns. Now when cold, if I use more than a tiny amount of choke, it won't start. It starts best with no choke and a little throttle. I know that's not right. Is it worth buying all new jets to make sure nobody drilled them out larger (both air and fuel or just one or the other) ? What could cause not getting a flame with the color tune on some cylinders sometimes? Should I try to tune each carb to the highest vacuum reading instead of using the color tune? Should I pull the carbs and spray carb cleaner through the pilot mixture openings and other openings again? What's my next logical or most likely next step? Thanks for all the help so far but I still need more.

 

This. It sounds as if some of the pilot fuel circuits are still plugged (partially or fully). You can try using the Colortune again on the problem cylinders, and bump the choke lever just a bit, see if you get a flame color.....the choke draws fuel from a different circuit than the pilots, so if the choke give you flame and w/o choke = no flame.......well, then you know for sure that the problem is the pilot fuel circuit. Check and make sure that the mixture screw o-ring in that carb isn't puckered, or got pinched/damaged during install.......make sure the AIR JETS 9under the vac piston diaphragm) are not reversed on any of the carbs.

Besides the obvious problems (black plugs), tuning-by-plug-color isn't the best or most reliable way to do things:

http://www.motorcycleproject.com/text/reading_plugs.html

"The proper plug color found in Japanese overhead valve engines doesn't at all resemble the pictures found in virtually all books and on online, whose images come from 1950s cast iron V8s."


Also, gotta ask: are your valve clearances in spec?


Remember, black sooty plug tips are an indication of INCOMPLETE COMBUSTION, not necessarily a "rich" mixture:

Why are my plugs carbon-fouled (dry, sooty black deposits)?:

- Carbon fouling is the result of incomplete combustion----for any reason. It is most often associated with an overly rich fuel mixture (whatever the cause), but can also be caused by an overly lean fuel mixture (or poor spark, etc.) In a lean-mixture condition, most of the un-burnt mixture gets pumped out the tailpipe, but some fuel droplets remain in the cylinder and add themselves to the next intake charge. That's not a very precise way of metering the mixture, so when it's finally rich enough for a spark to ignite, that particular charge may be too rich, resulting in incomplete combustion and plug fouling. So carbon-fouled plugs can be due to rich or lean conditions.......your Colortune spark plug will tell you for sure. If you have a light blue or white-ish flame, intermittent flame, and/or intermittent flashes of yellow within an otherwise white-ish flame, then your fuel mixture is too lean.

And by the way.........if the spark that happens to ignite this overly-rich mixture is the "wasted spark" (which occurs in each cylinder at the top of the exhaust stroke, it will occur JUST AS THE INTAKE VALVE IS OPENING ---- so the backfire pressure wave may be directed back up the intake tract!