Plugs

[lancelot455]

I have had a problem with #1 cylinder running cold at idle(i can grab the pipe)Even after a ride it is running about 100 degree's cooler than the others..
Here is a pic of the plugs pulled from it. they have about 200 km on them. I replaced them yesterday.How do you think the carbs need to be adjusted.I'd like to get it running right
I also noticed when riding at a constant speed that the tach will fluctuate about 3-400 rpm. Any help is appreciated.

1-4 left to right


1 and 2


3 and 4

[James England]

It looks to me as if #3 and #4 are running much to weak. The plug insulators are white and this is a sign of there being too much air in the fuel/air mixture. This means that they will run much hotter. Looking at all the plugs, I'd say that your 'problem' cylinder (#1) is actually running correctly. #2 is slightly rich.... they should be a tan brown colour, ideally. It's 3 and 4 that are running too hot and, when you feel the header pipes, you can tell that. You need to richen the mixture on your 3 and 4 carbs. How to do this depends on what model bike/carbs you have. Are your mixture screws in front of the carbs, nearer to the engine?

The tacho fluctuation has been regularly mentioned on the forum. It's either a charging problem from the alternator or, more likely, just a dicky tacho. MIne used to do it until I changed my ignition coils. You'll find loads of posts on how to diagnose and fix this. I never bothered fixing mine. To test your alternator, just start your engine, put the headlamp on and rev the engine. It should brighten up as you rev. Like I say, it's more likely to be the tacho itself.....

[natemoen]

If your pipes (at the flange) are around the 270-300ish degree range that seems to be around the norm after warmed up. I would agree that 3,4 look maybe a little lean but then you have barely used the plugs. 2 looks wet so that is probably a bit rich and maybe 1 is a hair rich as well. But I aint no expert so dont take my word on it.

[lancelot455]

It looks to me as if #3 and #4 are running much to weak. The plug insulators are white and this is a sign of there being too much air in the fuel/air mixture. This means that they will run much hotter. Looking at all the plugs, I'd say that your 'problem' cylinder (#1) is actually running correctly. #2 is slightly rich.... they should be a tan brown colour, ideally. It's 3 and 4 that are running too hot and, when you feel the header pipes, you can tell that. You need to richen the mixture on your 3 and 4 carbs. How to do this depends on what model bike/carbs you have. Are your mixture screws in front of the carbs, nearer to the engine?

The tacho fluctuation has been regularly mentioned on the forum. It's either a charging problem from the alternator or, more likely, just a dicky tacho. MIne used to do it until I changed my ignition coils. You'll find loads of posts on how to diagnose and fix this. I never bothered fixing mine. To test your alternator, just start your engine, put the headlamp on and rev the engine. It should brighten up as you rev. Like I say, it's more likely to be the tacho itself.....

Mixture screws are at the front of the carbs by the head... with 115 mains and 47.5 pilots which is factory.

[James England]

Mixture screws are at the front of the carbs by the head... with 115 mains and 47.5 pilots which is factory.

In that case, you unscrew the mixture screws to make the mixture richer. I'd unscrew the screws on carbs 3 and 4 by say 1/4 turn. Go for a burn for 10 miles or so, then check the colour. If still on the light side, try another 1/4 turn and so on. You might want to turn carb 2's screw IN an 1/8th turn and check the colour.... it does look rich. Once you get the mixtures right, you should find the header pipe temperatures similar.

By the way, my plugs are all tan brown on about 2/3rds of the insulator but still have a white patch for the other third. They've never been uniformly tan coloured all over.

I think the fact that you have hardly used the plugs doesn't matter. 1 and 2 went brown in the same time/mileage as 3 and 4 didn't. You've used them enough for a drastic difference in combustion colour to become apparent. You chaned all four plugs at the same time, didn't you?

[SFerinTEXAS]

#1 cylinder running cold at idle

First thing I would suspect is clogged pilot jet

[James England]

First thing I would suspect is clogged pilot jet

Yes, could be. If it were my bike, I'd remove all the carbs and rebuild them with Georgefix kits. I know it sounds extreme, but it's the only way to do it IMO. They're not expensive kits (especially if you're in the US) and it's the only way to be sure. If one's blocked, they could all be, to some degree. If you're going to strip one carb, you still have to remove the whole bank of 4, and if you get that far, you may as well do the job right, I'd say, whilst they are all off.

I did the above to my carbs, just as routine, and I was surprised by the gunge and filth in all the carbs. The long jet that the needle goes into, the one with all the little holes in it.....many of the holes were blocked completely. It's not a hard job to do, especially if you do it one carb at a time..... don't strip them all at once and have bits everywhere. It's worth replacing the crosshead screws with allen bolts on the float bowls and the diaphragm caps too.....

Once you've done a proper carb clean and rebuild, you won;t have to do it again for years and at least you know it's been done. I also put good quality in-line filters on my fuel pipes.

[SFerinTEXAS]

Quick test is to swap wires on 1 and 4. If the problem moves to 4 then its electrical, if it stays on 1 then its carb.

I totally agree with James last post. Except I never buy parts unless needed which is very seldom.

[James England]

I never buy parts unless needed which is very seldom.

I know what you mean but sometimes you need parts from a preventative point of view, don't you think? Like... if you have the head off for some reason and your camchain has 10% life left, it makes sense to replace it, even though it's not strictly 'needed'. I recently rebuilt my clutch and put a new release bearing in, even though the old one hadn't failed.... since I was in there and it cost only $4 or so. In the case of these carbs, it's going to be a bit of a job taking off the bank of carbs etc and the rebuild kits really don't cost much. It's possible that the other carbs will do the same thing, one by one........if the fault is caused by dirt/blockage.

I'm not advocating 'fault diagnosis by replacing parts' ... that really is replacing parts unnecessarily unless you get lucky first time... Switching the leads on 1 and 4, then feeling the pipes is a good idea. I don't know whether I'd hope the fault moves though! A one carb rebuild would cost less than a new ignition coil........

[SFerinTEXAS]

Again I am agreeing with you James. In that all the carbs should be gone thru on any of these bikes when you first get them. And I would never put suspect parts back in so kits would be a good idea for the uninitiated.

When I scored my XJ i had no room for it here and had to store it until I was ready to do the hump(restore). Pulled the carbs, tank and brakes off to come home to be completely gone thru before the restore began.Those are a given MUST.

[lancelot455]

I know what you mean but sometimes you need parts from a preventative point of view, don't you think? Like... if you have the head off for some reason and your camchain has 10% life left, it makes sense to replace it, even though it's not strictly 'needed'. I recently rebuilt my clutch and put a new release bearing in, even though the old one hadn't failed.... since I was in there and it cost only $4 or so. In the case of these carbs, it's going to be a bit of a job taking off the bank of carbs etc and the rebuild kits really don't cost much. It's possible that the other carbs will do the same thing, one by one........if the fault is caused by dirt/blockage.

I'm not advocating 'fault diagnosis by replacing parts' ... that really is replacing parts unnecessarily unless you get lucky first time... Switching the leads on 1 and 4, then feeling the pipes is a good idea. I don't know whether I'd hope the fault moves though! A one carb rebuild would cost less than a new ignition coil........

I had the carbs cleaned and rebuilt last Sept when i bought the bike. Stored it in oct took it out a month ago.I do not think that they tuned the carbs properly though. I had them off a couple days ago to repair a couple of vacuum leaks. Only took me like 5 min to remove the bank of carbs.I will try to switch 1 and 4 plug wires and see if that moves it.

[James England]

I had the carbs cleaned and rebuilt last Sept when i bought the bike. Stored it in oct took it out a month ago.I do not think that they tuned the carbs properly though. I had them off a couple days ago to repair a couple of vacuum leaks. Only took me like 5 min to remove the bank of carbs.I will try to switch 1 and 4 plug wires and see if that moves it.

It depends on what sort of job they did on the rebuild. I posted here a while ago after buying a set of 'cleaned and rebuilt' carbs from the US. They were absolutely atrocious and completely unuseable. I ended up sending them back to the 'expert' for a refund and that's why I cleaned and rebuilt my carbs myself. I may sound cynical but I don't really trust anyone to do a proper job. Another XSive had the same problem with his carbs. There are a couple of people on eBay who advertise their services but I would recommend doing it yourself. I was slightly daunted by the prospect of doing it myself but it really is simple enough if you do one carb at a time, use the correct tools and do it methodically. If you read some of the threads here, you'll see that many 'professionals' are completely useless, especially on bikes as old as ours.

Since you can take the carbs off quickly, I would seriously recommend stripping and cleaning them one at a time yourself. The fact you had them done by someone else means that you don't know what's been done to them or not done to them. New jets? New float needle and valve? New diaphragms? Or not? Thorough clean, especially the float valve hemispherical filters? etc etc. At least if you do it yourself, you know exactly what's been done/ I did mine several months ago and it runs perfectly.

[3Phase]

Lancelot, you really should do your own carburetor cleaning.

I'm in the middle of cleaning the carburetors for my '79 Special and they were in pretty bad shape when I took them off the bike. I didn't have to replace any parts except the pilot jets, which basically disintegrated when I removed them. Here are the carburetors before cleaning:-



Floats and needle jets afer cleaning and polishing:-

Click for slideshow with more images

[natemoen]

Dang! Them some shiny clean floats!

[3Phase]

Dang! Them some shiny clean floats!

A little time, carb dip, Simichrome, cotton pads, Q-tips and toothpicks, Nate.

The top left float has a small leak where the solder seam is corroded so of course I had to clean all of them after cleaning the leaky float or the bike would never run correctly! After cleaning and polishing it looks like the leaky float has different solder than the rest of the floats so someone did a bad repair job or used the wrong solder but it's easy enough to fix.

Seriously though, the parts have to be clean and smooth or they won't work correctly and they'll plug up again when the new dirt and gunk in the lousy fuel we get today sticks to any oxidized metal or old dirt and gunk.