Running Rich?

I have cleaned the carbs, put in new float needls, synced the carbs, and have the air fuel screw adjusted. But I am still running rich. The bike has a 4-1 exhaust on it w/ the stock jets on them. Is there anything that I can try?

 

You didn't say if you adjusted and checked the float levels. New float needles can change the level. Also, you need to specify at what speed it's rich before anyone can help you, is it at idle, just off idle, midrange or WOT?

 

Okay, I've got a similar issue (maybe)?

1982 XJ650J (Maxim). When I got it, it ran on 2-1/2 cylinders at low speeds, okay at mid-range and above. #1 plug was sooty black.

Cleaned and rebuilt the carbs, set float levels, new float needles, installed in-line fuel filter. Ran better, but still a low-speed miss and hesitation off-idle up until about 2000+ rpm's, when it came alive. Synced and colortuned it. Now the #1 plug looked better but the #4 plug was sooty black.

Discovered the 1/4 coil was bad (120 ohms on primary lead) and replaced with Dyna coils, new wires, caps, boots, and plugs. Cranks right up, runs much much better, but still has that off-idle hesitation (up until 2000+) rpms and then runs like a screaming ape. #2, 3, & 4 plugs look great (a bit lean if anything), but the #1 plug now looks fine on the "bottom" half (closest to the piston) end of the insulator and electrode, but the rest of the insulator/electrode/etc. is still thick, sooty black.

Also, after the bike warms up.....I mean really warms up, 20+ minutes of riding.....then the idle speed increases from 1100 rpms up to 1500+ rpms at idle. Yes, choke is off!

I've tried running propane around the intake boots/carbs to see if there's a vacuum leak, and that makes no difference in rpms. When we had the carbs off we checked the intake boots really well and found no signs of cracking. The airbox boots are new, the air filter looks fine, the fuel levels in the bowls (by opening the drain screw with a clear hose connected to the bowl) seem to be okay, maybe not perfect, but definetly not too high.

Any ideas?

Thanks!

 

chacal, it sounds like you have some cylinders that are too lean but one that's too rich. If the plug has black soot on it then it's certainly too rich.
You might also still have air leaks. Probably still need to clean the carbs several more times and replace the intake boots if they have cracks whether you can find leaks or not. Or at least cover and seal the outside with RTV and a piece of rubber innertube or something.

 

I couldn't agree with Steve more. But should that check out and float levels are set correctly then it may be the jets. A 4-1 header with stock jets should not run properly. The header should reguire a change on the stock jets. Some guys instead of buying the right jets drill out the stock ones. So they may say 110 but are actually 117.5. When a 116 is what is needed. Only way I know of to check is with the drill bits used to drill out carb jets. The non-cutting end of the drill bit can be carefully inserted into the jet to check size. But I still think Steve has hit the right and most likely problem. I only consider the drilled jet because of the 4-1 header.

 

Have you checked the air filter - could be running rich due to blocked filter.

I had 4-1 Exhaust with 95 main jets and that was running lean.
Changed jets to 112 and running very rich.
Cleaned out the air filter - now running (almost) perfect.

 

AdeXJ, how could you have any size besides 110 or 112?

 

When I got it, It had Mikuni carbs from an unknown bike (possibly Suzuki).
The Main jets were 92.5's (not 95's, sorry).
Managed to get some 112's from a local breaker - these jets came from a XJ600 (unfortunately, he only had the jets, not the complete carbs).

The main problem I've had with the 750 has nearly always been carb related (rich, lean, no power, no start, etc), but it appears to be pretty much ok now (several carb cleans, numerous stripdowns, replace jets, boots, more cleans, etc).
At least now I can pull out the carbs, strip down, clean, replace into bike, and have it running again in about an hour.

 

Steve, I tend to agree with Ade that due to the need to pull my carbs several times, I can have them out and back in a very short time.

Sounds like you have air leaks but that they may only appear when the bike starts to get up to full operating temps.
Those boots that looked like they werent leaking may indeed be the culprits!? There is also another thing to look at, the boots between the filter housing and the carbs.
If you get a boot that leaks or has a fold under the clamp it can cause the carb to not perform right.

You might get that baby good and warmed up (20 min+) and then check for leaking boots, on both sides of the carbs.

Let us know what you find out.

Good Luck